TECHNICAL FIELD

The present invention relates to a method for producing a honeycomb structure.

BACKGROUND ART

A ceramic honeycomb structure has improved characteristics such as heat resistance and corrosion resistance, and has a structure including partition walls that define a plurality of cells extending from one end face serving as a fluid flow path to the other end face. Therefore, the ceramic honeycomb structure is used as a support for catalyst devices utilized for environmental measures, recovery of specific materials, and the like, and as a filter for purifying exhaust gases, in various fields such as chemistry, electric power, and steel industries, and the like.

As a method for producing such a honeycomb structure, for example, a method for producing a honeycomb structure is disclosed, which includes extruding a green body obtained by kneading a forming raw material containing a cordierite forming material, water, an organic binder and the like to produce a honeycomb formed body, and then drying and firing the honeycomb formed body (see, for example, Patent Document 1). In the producing method, the organic binder used for the forming raw material is a component that provides plasticity and shape retention to improve formability of the green body into the honeycomb formed body. Therefore, an increasing amount of the organic binder added improves the formability of the green body. In order to form a large honeycomb structure or a honeycomb structure having a complex cell structure which has increased the demand in recent years, a green body having better formability than in the case of producing a small or simple honeycomb structure is required. As a result, an increased amount of the organic binder may have to be blended into the forming raw material.

The organic binder in the honeycomb formed body gelates (i.e., separates water) when it is deprived of water during drying. By this gelation, the honeycomb formed body is cured so that its strength is improved.

However, the organic binder is burned out during firing, which causes a decrease in mechanical strength of a honeycomb structure. In particular, since spaces occupied by the organic binder tend to be defective, the mechanical strength of the honeycomb structure is deteriorated when an amount of the organic binder added is increased. Further, in the large honeycomb structure, the inside of the structure tends to have a higher temperature due to heat of combustion when the organic binder is burned out during firing. Therefore, thermal stress due to a temperature difference between the inside and outside of the honeycomb structure tends to generate defects such as cracks, thereby reducing the mechanical strength of the honeycomb structure as well as significantly decreasing a yield.

Furthermore, the combustion of the organic binder during firing generates CO2and harmful gases to be released to the atmosphere, which causes environmental problems such as air pollution and global warming.

To solve the above problems, prior art discloses a technique for producing a honeycomb structure which suppresses the generation of defects such as cracks to maintain high strength and low thermal expansion by blending an inorganic binder or a forming aid into a forming raw material (see, for example, Patent Documents 2 and 3). Prior art also discloses a technique for producing a honeycomb structure which has improved strength without containing large amounts of an organic binder and an inorganic binder, by applying a predetermined aqueous electrolyte solution to at least a part of a surface of a ceramic formed body (see, for example, Patent Documents 4 and 5).

CITATION LIST

Patent Literatures

Patent Document 1: Japanese Patent Application Publication No. 2002-292616 A1Patent Document 2: Japanese Patent No. 4745963 BPatent Document 3: Japanese Patent No. 5001892 BPatent Document 4: Japanese Patent No. 5647051 BPatent Document 5: Japanese Patent No. 5658067 B

SUMMARY OF INVENTION

Although the producing methods described in Patent Documents 2 and 3 provide an effect of suppressing the generation of defects such as cracks, they have problems that an effect of sufficiently suppress the generation of defects such as breakage due to the temperature difference or shrinkage difference between the surface and the inside of the honeycomb formed body in a temperature range during firing. In particular, the producing method disclosed in Patent Document 2 employs a forming material containing, in addition to the cordierite forming material and the organic binder, a dispersion obtained by previously dispersing smectite such as montmorillonite in water. When montmorillonite is added to the forming raw material, a thermal expansion coefficient of the honeycomb structure tends to increase, so that thermal shock resistance is decreased only by addition of montmorillonite. Further, in the producing method disclosed in Patent Document 3, the generation of defects such as breakage can be somewhat suppressed such as by decreasing a temperature rising rate during firing. However, such a method causes another problem that a production time and production cost of the honeycomb structure are increased.

Moreover, the producing methods disclosed in Patent Documents 4 and 5 include the step of applying the aqueous electrolyte solution containing predetermined cations to the surface of the honeycomb formed body, which causes a problem that the producing method is complicated.

The present invention has been made to solve the above problems. An object of the present invention is to provide a method for producing a honeycomb structure that can suppress generation of defects such as breakage due to a temperature difference or a shrinkage difference between a surface and the inside of a honeycomb formed body in a temperature range during firing and can have improved thermal shock resistance.

As a result of intensive studies focusing on an inorganic binder used in production of a honeycomb structure, the present inventors have found that a magnesium silicate mineral having a 2:1 ribbon type structure, which is generally used as a thickener, an adsorbent or the like, has properties suitable as the inorganic binder, and completed the present invention.

Thus, the present invention relates to a method for producing a honeycomb structure, the method comprising the steps of: kneading a forming raw material containing a cordierite forming material and then forming it to produce a honeycomb formed body; and firing the honeycomb formed body to provide a honeycomb structure, wherein from 0.1 to 6.0 parts by mass of a magnesium silicate mineral having a 2:1 ribbon type structure per 100 parts by mass of the cordierite forming material is added to the forming raw material.

According to the present invention, it is possible to provide a method for producing a honeycomb structure that can effectively suppress the generation of defects such as breakage due to a temperature difference or a shrinkage difference between a surface and the inside of a honeycomb formed body in a temperature range during firing, and can have improved thermal shock resistance.

