WO2025163913A1 - Heater element and vehicle interior cleaning system - Google Patents

Abstract

A heater element 100 comprises: a honeycomb structure 10 having an outer peripheral wall 11 and a partition wall 14 that is disposed inside the outer peripheral wall 11 and demarcates a plurality of cells 13 serving as flow paths extending from a first end surface 12a to a second end surface 12b; a pair of electrodes 20a, 20b provided to the first end surface 12a and the second end surface 12b; and terminals 30 provided to at least a part of the pair of electrodes 20a, 20b. In the heater element 100, the ratio of the thermal expansion coefficient of the terminals 30 to the thermal expansion coefficient of the honeycomb structure 10 is 1.00-1.38, and the ratio of the thickness T of the terminals 30 to the length from the first end surface 12a to the second end surface 12b of the honeycomb structure 10 is 0.03-0.20.

Description

Heating elements and cabin purification systems

The present invention relates to a heater element and a vehicle interior purification system.

There is a growing demand for improved cabin environments in various vehicles, including automobiles. Specific demands include reducing _CO2 emissions in the cabin to suppress driver drowsiness, controlling humidity in the cabin, and removing harmful volatile components, such as odorous components and allergy-inducing components, from the cabin. Ventilation is an effective measure to meet these demands, but ventilation can significantly reduce heating energy in winter, resulting in reduced energy efficiency. This energy loss, particularly in battery electric vehicles (BEVs), poses a problem of significantly reduced driving range.

As a method for solving the above problems, Patent Documents 1 and 2 disclose a vehicle interior purification system that captures target components, such as water vapor and _CO2 , in the vehicle interior air using a functional material such as an adsorbent, and then heats the target components to react or desorb and release them outside the vehicle, thereby regenerating the functional material. Such vehicle interior purification systems require as much contact between the air and the functional material as possible to ensure the target components' capture performance, and also require the functional material to be heated to a predetermined temperature to promote regeneration. Regeneration can be achieved, for example, by removing substances adsorbed on the functional material through an oxidation reaction, or by desorbing and discharging substances adsorbed on the functional material. In either case, the functional material must be heated to an appropriate temperature depending on the adsorbed substances.

In Patent Document 3, the applicant proposed a heater element comprising a honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall that define a plurality of cells forming flow paths extending from one end face to the other, with at least the partition walls being made of a material with PTC (Positive Temperature Coefficient) properties; and a pair of electrodes consisting of a first electrode and a second electrode, the first electrode and second electrode satisfying specified conditions. This heater element can widen the area in the direction in which the flow paths extend that can effectively heat the functional material.

Japanese Patent Application Laid-Open No. 2020-104774 Japanese Patent Application Laid-Open No. 2020-111282 International Publication No. 2023/074202

In some heater elements such as those described in Patent Document 3, terminals are provided on the pair of electrodes to facilitate electrical connection with an external power source when heating by current flow. In this case, it is necessary to ensure water resistance by firmly joining the pair of electrodes and the terminals to prevent water from entering between them. This is because moisture such as rainwater may flow into the area where the heater element is located in the vehicle interior purification system, and if water enters between the pair of electrodes and the terminals, it may cause a short circuit. Furthermore, the presence of moisture between the pair of electrodes and the terminals may easily cause corrosion of the pair of electrodes, ultimately resulting in poor current flow and reduced heating performance.
However, when a pair of electrodes and a terminal are firmly joined, the honeycomb structure, which has a lower strength than the terminal, may be damaged because the thermal expansion coefficient of the honeycomb structure differs from that of the terminal.

The present invention has been made to solve the above-mentioned problems, and its object is to provide a heater element that can improve the bonding between a pair of electrodes and a terminal, thereby improving water resistance, while suppressing damage to the honeycomb structure.
Another object of the present invention is to provide a vehicle interior purification system equipped with such a heater element.

As a result of extensive research into heater elements in which terminals are provided on at least some of the pair of electrodes, the inventors discovered that the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure, and the ratio of the thickness of the terminal to the length from the first end face to the second end face of the honeycomb structure, are closely related to the above-mentioned problems. Based on this knowledge, they discovered that the above-mentioned problems can be solved by controlling these ratios within specific ranges, leading to the completion of the present invention. Specifically, the present invention is exemplified as follows:

(1) A honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that serve as flow paths extending from a first end face to a second end face;
a pair of electrodes provided on the first end surface and the second end surface;
a terminal provided on at least a part of the pair of electrodes,
a ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure is 1.00 to 1.38;
A heater element in which the ratio of the thickness of the terminal to the length from the first end face to the second end face of the honeycomb structure is 0.03 to 0.20.

(2) A heater element according to (1), in which the ratio of the area of the terminal in contact with the electrode to the area of the first end face or the second end face of the honeycomb structure is 0.051 to 0.243.

(3) A heater element according to (1) or (2), in which the ratio of the Young's modulus of the terminal to the Young's modulus of the honeycomb structure is 0.99 to 2.83.

(4) A heater element described in any one of (1) to (3), in which the terminal is provided on at least one of the electrodes on the outer peripheral wall, among the electrodes provided on the first end surface and the second end surface.

(5) A heater element according to (4), in which the terminals have a width of 1.0 to 5.0 mm.

(6) A heater element according to (4) or (5), in which the terminal has a thickness of 0.3 to 3.0 mm.

(7) A heater element described in any one of (4) to (6), wherein the thickness of the outer wall is 0.2 to 1.5 mm.

(8) A heater element described in any one of (1) to (7), wherein at least the partition walls of the honeycomb structure are made of a material having PTC properties.

(9) A heater element as described in (8), in which the material having PTC properties is composed primarily of barium titanate and is substantially free of lead.

(10) A heater element according to (8) or (9), wherein the material having PTC properties has a volume resistivity at 25°C of 0.5 Ω·cm or more and 3000 Ω·cm or less.

(11) A heater element described in any one of (1) to (10), comprising an adsorption layer on the surface of the partition wall.

(12) A heater element according to (11), wherein the adsorption layer contains an adsorbent capable of adsorbing one or more selected from moisture, carbon dioxide, and volatile components.

(13) A heater element according to (11) or (12), wherein the adsorption layer contains a catalyst.

(14) At least one heater element according to any one of (1) to (13),
a power source for applying a voltage to the heater element;
an inlet pipe communicating between a passenger compartment and the first end surface of the heater element;
an outflow pipe having a first passage communicating the second end surface of the heater element with the passenger compartment;
a fan for directing air from the passenger compartment through the inlet pipe into the first end face of the heater element.

(15) The outlet pipe has, in addition to the first path, a second path that connects the second end surface of the heater element to the outside of the vehicle,
the outflow pipe has a valve capable of switching the flow of air passing through the outflow pipe between the first path and the second path,
a first mode in which the applied voltage from the power supply is turned off, the valve is switched so that the air flowing through the outflow pipe passes through the first path, and the ventilator is turned on;
a second mode in which the applied voltage from the power supply is turned on, the valve is switched so that the air flowing through the outflow pipe passes through the second path, and the ventilator is turned on;
The vehicle interior purification system according to (14), further comprising a control unit capable of switching between the above.

According to the present invention, it is possible to provide a heater element that can improve the bonding between a pair of electrodes and a terminal, thereby improving water resistance, while suppressing damage to the honeycomb structure.
Furthermore, the present invention can provide a vehicle interior purification system equipped with such a heater element.

1 is a schematic diagram of a cross section parallel to the extension direction of cells (flow paths) of a heater element according to an embodiment of the present invention. FIG. FIG. 1B is a schematic diagram of an end view of the heater element of FIG. 1A. FIG. 10 is a schematic diagram of a cross section parallel to the direction in which the cells (flow paths) of a heater element according to another embodiment of the present invention extend. FIG. 2B is a schematic diagram of an end view of the heater element of FIG. 2A. 1 is a schematic diagram showing the configuration of a vehicle interior purification system according to an embodiment of the present invention.

A heater element according to an embodiment of the present invention comprises a honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall that define a plurality of cells that serve as flow paths extending from the first end face to the second end face; a pair of electrodes provided on the first end face and the second end face; and terminals provided on at least a portion of the pair of electrodes, wherein the ratio of the thermal expansion coefficient of the terminals to the thermal expansion coefficient of the honeycomb structure is 1.00 to 1.38, and the ratio of the thickness of the terminals to the length from the first end face to the second end face of the honeycomb structure is 0.03 to 0.20. This configuration can improve the bond between the pair of electrodes and the terminals and enhance water resistance while suppressing damage to the honeycomb structure.

Embodiments of the present invention will now be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments, based on the common knowledge of those skilled in the art, as long as they do not deviate from the spirit of the present invention, also fall within the scope of the present invention.

(1. Heater element)
The heater element according to the embodiment of the present invention can be suitably used as a heater element for a passenger compartment purification system in various vehicles such as automobiles. Examples of the vehicle include, but are not limited to, automobiles and trains. Examples of the vehicle include, but are not limited to, gasoline-powered vehicles, diesel-powered vehicles, gas-fueled vehicles using CNG (compressed natural gas) or LNG (liquefied natural gas), fuel cell vehicles, electric vehicles, and plug-in hybrid vehicles. The heater element according to the embodiment of the present invention can be suitably used in vehicles without internal combustion engines, such as electric vehicles and trains.

Fig. 1A is a schematic diagram of a cross section parallel to the direction in which the cells (flow passages) of a heater element according to an embodiment of the present invention extend, and Fig. 1B is a schematic diagram of an end face of the heater element of Fig. 1A.
As shown in Figures 1A and 1B, the heater element 100 includes a honeycomb structure 10 having an outer peripheral wall 11 and partition walls 14 disposed inside the outer peripheral wall 11 to define a plurality of cells 13 that serve as flow paths extending from a first end face 12a to a second end face 12b, a pair of electrodes 20a, 20b provided on the first end face 12a and the second end face 12b, and terminals 30 provided on at least a portion of the pair of electrodes 20a, 20b.

The heater element 100 can be used as a support (carrier) for forming an adsorption layer. Fig. 2A shows a schematic cross-section of the heater element with an adsorption layer formed thereon, parallel to the direction of extension of the cells (flow paths), and Fig. 2B shows a schematic end view of the heater element in Fig. 2A. Note that Figs. 2A and 2B have the same configuration as Figs. 1A and 1B, except that an adsorption layer is formed.
2A and 2B, the heater element 100 includes an adsorption layer 40 on the surface of the partition wall 14. The adsorption layer 40 may be provided on the inner surface side of the outer peripheral wall 11 that constitutes the cell 13.

In the heater element 100, the ratio of the thermal expansion coefficient of the terminals 30 to the thermal expansion coefficient of the honeycomb structure 10 is 1.00 to 1.38, preferably 1.11 to 1.38. By controlling the ratio of the thermal expansion coefficients within this range, the difference between the thermal expansion coefficients of the honeycomb structure 10 and the terminals 30 becomes small, thereby making it possible to suppress damage to the honeycomb structure 10 when the terminals 30 are joined.
The thermal expansion coefficient of the honeycomb structure 10 is measured in accordance with JIS R1618:2002, and the thermal expansion coefficient of the terminal 30 is measured in accordance with JIS Z2285:2003.

In the heater element 100, the ratio (T/L) of the thickness T of the terminal 30 to the length L from the first end face 12a to the second end face 12b of the honeycomb structure 10 is 0.03 to 0.20. By controlling the ratio (T/L) within this range, damage to the honeycomb structure 10 when joining the terminal 30 can be suppressed.

In the heater element 100, the ratio (S2/S1) of the area S2 of the terminal 30 in contact with the electrode 20a or electrode 20b to the area S1 of the first end face 12a or second end face 12b of the honeycomb structure 10 is preferably 0.051 to 0.243. By controlling the ratio (S2/S1) within this range, damage to the honeycomb structure 10 when the terminal 30 is joined can be reliably suppressed.

In the heater element 100, the ratio (Y2/Y1) of the Young's modulus Y2 of the terminal 30 to the Young's modulus Y1 of the honeycomb structure 10 is preferably 0.99 to 2.83. By controlling the ratio (Y2/Y1) within this range, damage to the honeycomb structure 10 when the terminal 30 is joined can be stably suppressed.
Here, the Young's modulus Y1 of the honeycomb structure 10 is calculated as follows. First, the bending strength of the honeycomb structure 10 is measured in accordance with the four-point bending strength test method specified in JIS R1601:2008, and a "stress-strain curve" is created from the measurement results. The slope of the "stress-strain curve" thus obtained is calculated, and the slope of this "stress-strain curve" is defined as the Young's modulus.
The Young's modulus Y2 of the terminal 30 is measured by the strain gauge method in accordance with JIS Z2280:1993.
Each component of the heater element 100 will now be described in detail.

(1-1. Honeycomb structure)
The shape of the honeycomb structure 10 is not particularly limited. For example, the outer shape of a cross section perpendicular to the flow path direction (the direction in which the cells 13 extend) of the honeycomb structure 10 can be a polygon such as a quadrangle (rectangle, square), pentagon, hexagon, heptagon, or octagon, a circle, or an oval shape (egg, ellipse, oval, rounded rectangle, etc.). The end faces (first end face 12a and second end face 12b) have the same shape as the cross section. Furthermore, when the cross section and the end faces are polygonal, the corners may be chamfered.

The shape of the cells 13 is not particularly limited, but can be a polygon such as a square, pentagon, hexagon, heptagon, or octagon, or a circle or an oval in a cross section perpendicular to the flow path direction of the honeycomb structure 10. These shapes may be a single shape or a combination of two or more shapes. Among these shapes, a square or hexagon is preferable. By providing cells 13 of such a shape, it is possible to reduce pressure loss when air flows through. Note that Figures 1A, 1B, 2A, and 2B show, as an example, a honeycomb structure 10 in which the cross-sectional outer shape and the shape of the cells 13 are square in a cross section perpendicular to the flow path direction.

The honeycomb structure 10 may be a honeycomb joined body having a plurality of honeycomb segments and a joining layer joining the outer peripheral side surfaces of the plurality of honeycomb segments. By using the honeycomb joined body, it is possible to increase the total cross-sectional area of the cells 13, which is important for ensuring the air flow rate, while suppressing the occurrence of cracks.
The bonding layer can be formed using a bonding material. The bonding material is not particularly limited, but a ceramic material with a solvent such as water added to form a paste can be used. The bonding material may contain a material having PTC properties, or may contain the same material as the outer peripheral wall 11 and the partition walls 14. In addition to the role of bonding the honeycomb segments together, the bonding material can also be used as an outer peripheral coating material after bonding the honeycomb segments.

The thickness of the outer peripheral wall 11 is not particularly limited, but is preferably 0.2 to 1.5 mm, more preferably 0.2 to 1.2 mm, even more preferably 0.2 to 1.0 mm, and particularly preferably 0.2 to 0.8 mm. By making the thickness of the outer peripheral wall 11 0.2 mm or more, it is possible to ensure the bondability with the terminal 30 and the strength of the honeycomb structure 10. Furthermore, by making the thickness of the outer peripheral wall 11 1.5 mm or less, it is possible to increase the electrical resistance to suppress the initial current and reduce the pressure loss during air flow.
Here, in this specification, the thickness of the outer wall 11 refers to the length in the normal direction of the side surface from the boundary between the outer wall 11 and the outermost cell 13 or partition wall 14 to the side surface of the honeycomb structure 10 in a cross section perpendicular to the flow path direction.

The thickness of the partition walls 14 is not particularly limited, but is preferably 0.01 to 0.30 mm, more preferably 0.02 to 0.20 mm, and even more preferably 0.03 to 0.18 mm. By controlling the thickness of the partition walls 14 within such a range, the strength of the honeycomb structure 10 can be ensured.
Here, in this specification, the thickness of the partition walls 14 refers to the length of a line segment that connects the centers of gravity of adjacent cells 13 in a cross section perpendicular to the flow path direction and that crosses the partition walls 14. The thickness of the partition walls 14 refers to the average value of the thicknesses of all the partition walls 14.

The cell density is not particularly limited, but is preferably 30 to 120 cells/cm ² , more preferably 35 to 110 cells/cm ² , and even more preferably 40 to 100 cells/cm ^2. By controlling the cell density within such a range, a sufficient amount of the adsorption layer 40 can be supported while ensuring the strength of the honeycomb structure 10.
Here, in this specification, cell density is a value obtained by dividing the number of cells by the area of one end face (first end face 12a or second end face 12b) of the honeycomb structure 10 (the total area of the partition walls 14 and cells 13 excluding the outer wall 11).

The cell pitch is not particularly limited, but is preferably 0.90 to 2.00 mm, more preferably 0.95 to 1.70 mm, and even more preferably 1.00 to 1.60 mm. By controlling the cell pitch within such a range, a sufficient amount of the adsorption layer 40 can be supported while ensuring the strength of the honeycomb structure 10.
Here, in this specification, the cell pitch refers to a value obtained by the following calculation: First, the area per cell is calculated by dividing the area of one end face (first end face 12a or second end face 12b) of the honeycomb structure 10 (the total area of the partition walls 14 and the cells 13 excluding the outer peripheral wall 11) by the number of cells. Next, the square root of the area per cell is calculated, and this is defined as the cell pitch.

The length of the honeycomb structure 10 in the flow path direction and the cross-sectional area perpendicular to the flow path direction are not particularly limited, and may be adjusted according to the required size of the heater element 100. For example, when used in a compact heater element 100 while ensuring a predetermined function, the honeycomb structure 10 can have a length in the flow path direction of 2 to 20 mm and a cross-sectional area perpendicular to the flow path direction of 10 ^cm2 or more. The upper limit of the cross-sectional area perpendicular to the flow path direction is not particularly limited, but is, for example, 300 ^cm2 .

The partition walls 14 that make up the honeycomb structure 10 are made of a material that can generate heat when electricity is passed through them; specifically, they are made of a material with PTC properties. If necessary, the outer peripheral wall 11 may also be made of a material with PTC properties, just like the partition walls 14. This configuration makes it possible to heat the adsorption layer 40 by heat transfer from the heat-generating partition walls 14 (and the outer peripheral wall 11, if necessary). Furthermore, materials with PTC properties have the property that, when their temperature rises and exceeds the Curie point, their resistance rises sharply, making it difficult for electricity to flow. Therefore, when the heater element 100 becomes hot, the partition walls 14 (and the outer peripheral wall 11, if necessary) limit the current flowing through them, thereby suppressing excessive heat generation by the heater element 100. This also makes it possible to suppress thermal deterioration of the adsorption layer 40 caused by excessive heat generation.

The volume resistivity of the material having PTC characteristics at 25° C. is not particularly limited, but is preferably 0.5 to 3000 Ω cm, more preferably 1 to 2000 Ω cm, and even more preferably 5 to 1000 Ω cm. A volume resistivity within this range can ensure appropriate heat generation with the driving voltage used in various applications.
In this specification, the volume resistivity at 25° C. of a material having PTC characteristics is measured in accordance with JIS K6271:2008.

From the viewpoint of being able to generate heat when electrically connected and having PTC characteristics, the outer peripheral wall 11 and the partition walls 14 are preferably made of a material whose main component is barium titanate ( _BaTiO3 ). Furthermore, this material is more preferably a ceramic made of a material whose main component is barium titanate ( _BaTiO3 )-based crystal particles in which a portion of the Ba is substituted with a rare earth element. In this specification, the term "main component" refers to a component that accounts for more than 50 mass% of the total components. The content of _BaTiO3 -based crystal particles can be determined by fluorescent X-ray analysis. Other crystal particles can also be measured in a similar manner.

The composition formula of _BaTiO3 -based crystal particles in which a portion of Ba is substituted with a rare earth element can be expressed as (Ba1 _{-xAx ) TiO3} , where A represents one or more rare earth elements and 0.0001≦x≦0.010.
A is not particularly limited as long as it is a rare earth element, but is preferably one or more selected from the group consisting of La, Ce, Pr, Nd, Eu, Gd, Dy, Ho, Er, Y, and Yb, and more preferably La. x is preferably 0.001 or more, more preferably 0.0015 or more, from the viewpoint of preventing the electrical resistance at room temperature from becoming too high. On the other hand, x is preferably 0.009 or less, from the viewpoint of preventing the electrical resistance at room temperature from becoming too high due to insufficient sintering.
The content of _BaTiO3 -based crystal particles in the ceramic, in which part of the Ba has been substituted with a rare earth element, is not particularly limited as long as it is an amount that constitutes the main component, but is preferably 90 mass% or more, more preferably 92 mass% or more, and even more preferably 94 mass% or more. The upper limit of the content of _BaTiO3 -based crystal particles is not particularly limited, but is generally 99 mass%, preferably 98 mass%.
The content of BaTiO ₃ -based crystal particles can be measured by fluorescent X-ray analysis. The content of other crystal particles can also be measured in the same manner.

From the perspective of reducing environmental impact, it is desirable that the materials used for the outer wall 11 and the partition wall 14 contain substantially no lead (Pb). Specifically, the Pb content of the outer wall 11 and the partition wall 14 is preferably 0.01% by mass or less, more preferably 0.001% by mass or less, and even more preferably 0% by mass. A low Pb content allows, for example, heated air to be safely applied to living organisms such as humans by contacting it with the partition wall 14 during heat generation. Furthermore, the Pb content of the outer wall 11 and the partition wall 14, converted to PbO, is preferably less than 0.03% by mass, more preferably less than 0.01% by mass, and even more preferably 0% by mass. The lead content can be determined using ICP-MS (inductively coupled plasma mass spectrometry).

The lower limit of the Curie point of the material constituting the outer wall 11 and the partition wall 14 is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 125°C or higher, from the viewpoint of efficient heating of air. Furthermore, the upper limit of the Curie point is preferably 250°C or lower, more preferably 225°C or lower, even more preferably 200°C or lower, and even more preferably 150°C or lower, from the viewpoint of safety as a component placed in or near the vehicle interior.

The Curie point of the material forming the outer peripheral wall 11 and the partition walls 14 can be adjusted by the type and amount of the shifter added. For example, the Curie point of barium titanate ( _BaTiO3 ) is approximately 120°C, but by substituting part of the Ba and Ti with one or more of Sr, Sn, and Zr, the Curie point can be shifted to a lower temperature.

In this specification, the Curie point is measured using the following method. A sample is attached to a sample holder for measurement and placed in a measurement tank (e.g., MINI-SUBZERO MC-810P, manufactured by Espec Corporation). The change in the sample's electrical resistance relative to temperature change as the temperature rises from 10°C is measured using a DC resistance meter (e.g., multimeter 3478A, manufactured by YOKOGAWA HEWLETT PACKARD, LTD.). The Curie point is determined as the temperature at which the resistance value, based on the electrical resistance-temperature plot obtained from the measurement, is twice the resistance value at room temperature (20°C).

(1-2. Pair of electrodes)
A pair of electrodes 20a, 20b are provided on the first end face 12a and the second end face 12b of the honeycomb structure 10. By applying a voltage between the pair of electrodes 20a, 20b, it becomes possible to cause the honeycomb structure 10 to generate heat by Joule heat.

The pair of electrodes 20a, 20b is not particularly limited, but may be, for example, a metal or alloy containing at least one selected from Cu, Ag, Al, Ni, and Si. It is also possible to use an ohmic electrode that can make ohmic contact with the outer peripheral wall 11 and/or partition wall 14 that have PTC characteristics. The ohmic electrode may contain, for example, at least one selected from Al, Au, Ag, and In as a base metal and at least one selected from Ni, Si, Zn, Ge, Sn, Se, and Te as a dopant for n-type semiconductors. The pair of electrodes 20a, 20b may have a single-layer structure or a laminated structure of two or more layers. When the pair of electrodes 20a, 20b have a laminated structure of two or more layers, the materials of the layers may be the same or different.

The thickness of the pair of electrodes 20a, 20b is not particularly limited and can be set appropriately depending on the method for forming the pair of electrodes 20a, 20b. Methods for forming the pair of electrodes 20a, 20b include metal deposition methods such as sputtering, vapor deposition, electrolytic deposition, and chemical deposition. The pair of electrodes 20a, 20b can also be formed by applying an electrode paste and then baking it, or by thermal spraying. Furthermore, the pair of electrodes 20a, 20b may also be formed by joining metal or alloy plates.

The thickness of the pair of electrodes 20a, 20b is not particularly limited, but is preferably approximately 5 to 150 μm when baking an electrode paste, approximately 100 to 1000 nm when using dry plating such as sputtering and vapor deposition, approximately 10 to 100 μm when using thermal spraying, and approximately 5 to 30 μm when using wet plating such as electrolytic deposition and chemical deposition. Furthermore, when joining metal or alloy plates, the thickness is preferably approximately 5 to 100 μm.

(1-3. Terminal 30)
The terminal 30 is connected to the pair of electrodes 20 a, 20 b and is provided on at least a portion of the pair of electrodes 20 a, 20 b. The provision of the terminal 30 facilitates connection to an external power source. The terminal 30 is connected to a conductor connected to the external power source.

The material of the terminal 30 is not particularly limited, but can be, for example, a metal. While elemental metals and alloys can be used as the metal, from the standpoint of corrosion resistance, electrical resistivity, and linear expansion coefficient, it is preferable to use an alloy containing at least one element selected from the group consisting of Cr, Fe, Co, Ni, Cu, Al, and Ti.

The position at which the terminal 30 is provided is not particularly limited, but it is preferable that the terminal 30 be provided on at least the pair of electrodes 20a, 20b on the outer peripheral wall 11, out of the pair of electrodes 20a, 20b provided on the first end face 12a and the second end face 12b. The terminal 30 may also be provided on part or all of the pair of electrodes 20a, 20b on the outer peripheral wall 11, or may be provided so as to extend outward beyond the outer edge of the pair of electrodes 20a, 20b on the outer peripheral wall 11. The terminal 30 may also be provided on part of the pair of electrodes 20a, 20b on the partition wall 14, or may be provided so as to block some of the cells 13.

The width W of the terminal 30 is not particularly limited, but is preferably 1.0 to 5.0 mm, more preferably 1.5 to 4.5 mm, and even more preferably 2.0 to 4.0 mm. Furthermore, the thickness T of the terminal 30 is not particularly limited, but is preferably 0.3 to 3.0 mm, more preferably 0.4 to 2.5 mm, and even more preferably 0.5 to 2.0 mm. By controlling the width W and thickness T of the terminal 30 within the above ranges, damage to the honeycomb structure 10 can be reliably suppressed when the terminal 30 is joined.

The method of connecting the terminal 30 and the pair of electrodes 20a, 20b is not particularly limited as long as they are electrically connected; for example, they can be connected by diffusion bonding, a mechanical pressure mechanism, welding, etc.

(1-4. Adsorption layer)
The adsorption layer 40 is provided on the surface of the partition wall 14. Alternatively, the adsorption layer 40 may be provided on the inner surface side of the outer peripheral wall 11 that constitutes the cell 13. By providing the adsorption layer 40 in this manner, the adsorption layer 40 can be easily heated, allowing the adsorption layer 40 to exhibit its desired function.

The adsorbent contained in the adsorption layer 40 is not particularly limited, but is preferably capable of adsorbing the components to be removed (one or more selected from moisture, carbon dioxide, and volatile components). The adsorption layer 40 may also contain a catalyst. The use of a catalyst can enhance the purification of the components to be removed and the ability of the adsorbent to capture the components to be removed.

The adsorbent preferably has the ability to adsorb the components to be removed at temperatures between -20 and 40°C and desorb them at high temperatures of 60°C or higher. Examples of adsorbents with this ability include zeolite, silica gel, activated carbon, alumina, silica, low-crystalline clay, and amorphous aluminum silicate complexes. The type of adsorbent can be selected appropriately depending on the type of component to be removed. One type of adsorbent may be used alone, or two or more types may be used in combination.

The catalyst preferably has a function capable of promoting the oxidation-reduction reaction. Examples of catalysts having such a function include metal catalysts such as Pt, Pd, and Ag, and oxide catalysts such as _CeO2 and _ZrO2 . One type of catalyst may be used alone, or two or more types may be used in combination.

Volatile components contained in the air inside a vehicle cabin include, for example, volatile organic compounds (VOCs) and odorous components other than VOCs. Specific examples of volatile components include ammonia, acetic acid, isovaleric acid, nonenal, formaldehyde, toluene, xylene, paradichlorobenzene, ethylbenzene, styrene, chlorpyrifos, di-n-butyl phthalate, tetradecane, di-2-ethylhexyl phthalate, diazinon, acetaldehyde, and N-methylcarbamate-2-(1-methylpropyl)phenyl.

The thickness of the adsorption layer 40 may be determined according to the size of the cell 13 and is not particularly limited. For example, from the viewpoint of ensuring sufficient contact with air, the thickness of the adsorption layer 40 is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more. On the other hand, from the viewpoint of preventing the adsorption layer 40 from peeling off from the partition wall 14 or the outer peripheral wall 11, the thickness of the adsorption layer 40 is preferably 400 μm or less, more preferably 380 μm or less, and even more preferably 350 μm or less.

The thickness of the adsorption layer 40 is measured using the following procedure. First, an arbitrary cross section parallel to the flow path direction of the honeycomb structure 10 is cut out, and a cross-sectional image at approximately 50x magnification is obtained using a scanning electron microscope or the like. This cross section is also aligned to pass through the center of gravity of the cross section perpendicular to the flow path of the honeycomb structure 10. For each adsorption layer 40 visible in the cross-sectional image, the thickness is calculated by dividing the cross-sectional area by the length of the cell 13 in the flow path direction. This calculation is performed for all adsorption layers 40 visible in the cross-sectional image, and the overall average value is taken as the thickness of the adsorption layer 40.

From the viewpoint of ensuring that the adsorbent material performs the desired function within the heater element 100, the amount of the adsorbent layer 40 is preferably 50 to 500 g/L relative to the volume of the honeycomb structure 10, more preferably 100 to 400 g/L, and even more preferably 150 to 350 g/L. The volume of the honeycomb structure 10 is a value determined by the external dimensions of the honeycomb structure 10.

(2. Heater Element Manufacturing Method)
The method for manufacturing the heater element 100 according to the embodiment of the present invention is not particularly limited as long as it has the above-mentioned characteristics, and can be carried out in accordance with a known method. Hereinafter, an exemplary method for manufacturing the heater element 100 according to the embodiment of the present invention will be described.
The method for manufacturing the honeycomb structure 10 that constitutes the heater element 100 includes a molding step and a firing step.
In the molding step, a clay containing ceramic raw materials including _BaCO3 powder, _TiO2 powder, and powder of a rare earth nitrate or hydroxide is molded to produce a honeycomb molded body with a relative density of 60% or more.
The ceramic raw material can be obtained by dry mixing each powder to obtain a desired composition.
The clay can be obtained by adding a dispersion medium, a binder, a plasticizer, and a dispersant to a ceramic raw material and kneading the mixture. The clay may contain additives such as a sifter, a metal oxide, a property improver, and a conductive powder, as needed.
The blending amount of components other than the ceramic raw materials is not particularly limited as long as it is an amount that allows the relative density of the honeycomb formed body to be 60% or more.

Here, in this specification, the "relative density of the honeycomb formed body" means the ratio of the density of the honeycomb formed body to the true density of the entire ceramic raw material. Specifically, it can be calculated by the following formula.
Relative density (%) of honeycomb formed body=density (g/cm ³ ) of honeycomb formed body/true density (g/cm ³ ) of entire ceramic raw material×100
The density of the honeycomb formed body can be measured by the Archimedes method using pure water as a medium. The true density of the entire ceramic raw material can be calculated by dividing the total mass (g) of each raw material by the total actual volume ( ^cm3 ) of each raw material.

The dispersion medium can be water or a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. It is particularly preferable to use a combination of methyl cellulose and hydroxypropoxyl cellulose. One type of binder may be used alone, or two or more types may be used in combination, but it is preferable that the binder does not contain alkali metal elements.

Examples of plasticizers include polyoxyalkylene alkyl ethers, polycarboxylic acid polymers, and alkyl phosphate esters.

Dispersants that can be used include surfactants such as polyoxyalkylene alkyl ethers, ethylene glycol, dextrin, fatty acid soaps, and polyalcohols. Dispersants may be used singly or in combination of two or more.

Honeycomb molded bodies can be produced by extruding clay. During extrusion molding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

The relative density of the honeycomb formed body obtained by extrusion molding is 60% or more, preferably 65% or more. By controlling the relative density of the honeycomb formed body within this range, it is possible to densify the honeycomb formed body and reduce its electrical resistance at room temperature. There are no particular restrictions on the upper limit of the relative density of the honeycomb formed body, but it is generally 80%, preferably 75%.

The honeycomb molded body can be dried before the firing process. There are no particular limitations on the drying method, but conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying can be used. Among these, a drying method that combines hot air drying with microwave drying or dielectric drying is preferred, as it allows the entire molded body to be dried quickly and uniformly.

The firing step involves holding at 1150-1250° C., then increasing the temperature to a maximum temperature of 1360-1430° C. at a rate of 20-600° C./hour, and holding for 0.5-10 hours.
By holding the honeycomb formed body at a maximum temperature of 1360 to 1430°C for 0.5 to 10 hours, it is possible to obtain a honeycomb structure 10 whose main component is BaTiO ₃ -based crystal grains in which part of the Ba has been substituted with a rare earth element.
Furthermore, by maintaining the temperature at 1150 to 1250° C., Ba ₂ TiO ₄ crystal particles generated during the firing process are easily removed, and the honeycomb structure 10 can be made dense.
Furthermore, by setting the temperature rising rate from 1150 to 1250° C. to the maximum temperature of 1360 to 1430° C. at 20 to 600° C./hour, it is possible to generate 1.0 to 10.0 mass % of Ba ₆ Ti ₁₇ O ₄₀ crystal particles in the honeycomb structure 10 .

The holding time at 1150 to 1250°C is not particularly limited, but is preferably 0.5 to ₁₀ hours. By setting the holding time to such a value, _Ba2TiO4 crystal particles generated during the firing process can be stably removed.

The firing step preferably includes holding the mixture at 900 to 950°C for 0.5 to 5 hours during temperature increase. By holding the mixture at 900 to 950°C for 0.5 to 5 hours, _BaCO3 is efficiently decomposed, and it becomes easier to obtain a honeycomb structure 10 having a predetermined composition.

Before the firing step, a degreasing step may be carried out to remove the binder. The degreasing step is preferably carried out in an air atmosphere to completely decompose the organic components.
Furthermore, the firing step is preferably carried out in an air atmosphere from the viewpoint of controlling electrical properties and reducing manufacturing costs.
The firing furnace used in the firing step and degreasing step is not particularly limited, but an electric furnace, a gas furnace, or the like can be used.

A pair of electrodes 20a, 20b are formed on the honeycomb structure 10 obtained in this manner. The pair of electrodes 20a, 20b can be formed by a metal deposition method such as sputtering, vapor deposition, electrolytic deposition, or chemical deposition. The pair of electrodes 20a, 20b can also be formed by applying an electrode paste and then baking it. Furthermore, the pair of electrodes 20a, 20b can also be formed by thermal spraying. The pair of electrodes 20a, 20b may be composed of a single layer, or may be composed of multiple electrode layers with different compositions. Below, a typical method for forming the pair of electrodes 20a, 20b is described.

First, an electrode slurry containing an electrode material, an organic binder, and a dispersion medium is prepared and applied to the first end face 12a or the second end face 12b of the honeycomb structure 10. The dispersion medium can be water, an organic solvent (e.g., toluene, xylene, ethanol, n-butanol, ethyl acetate, butyl acetate, terpineol, dihydroterpineol, Texanol, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether), or a mixture thereof. Excess slurry on the periphery of the honeycomb structure 10 is removed by blowing and wiping. The slurry is then dried to form a pair of electrodes 20a, 20b on the first end face 12a or the second end face 12b of the honeycomb structure 10. Drying can be performed while heating the honeycomb structure 10 to a temperature of, for example, approximately 120 to 600°C. The series of steps of application, slurry removal, and drying may be performed only once, but by repeating this process multiple times, a pair of electrodes 20a, 20b of the desired thickness can be provided.

Next, terminals 30 are placed at predetermined positions of the pair of electrodes 20a, 20b, and the pair of electrodes 20a, 20b are connected to the terminals 30. The method for connecting the pair of electrodes 20a, 20b to the terminals 30 can be the method described above.
The terminal 30 may be provided after the adsorption layer 40 described below is formed.

Next, the adsorption layer 40 is formed on the surfaces of the partition walls 14 and the like of the honeycomb structure 10 .
The method for forming the adsorption layer 40 is not particularly limited, but can be, for example, the following process. The honeycomb structure 10 is immersed in a slurry containing an adsorbent, an organic binder, and a dispersion medium for a predetermined period of time, and excess slurry is removed from the end faces and outer periphery of the honeycomb structure 10 by blowing and wiping. The dispersion medium can be water, an organic solvent (e.g., toluene, xylene, ethanol, n-butanol, ethyl acetate, butyl acetate, terpineol, dihydroterpineol, Texanol, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether), or a mixture thereof. The slurry is then dried to form the adsorption layer 40 on the surface of the partition walls 14. Drying can be performed while heating the honeycomb structure 10 to a temperature of, for example, about 120 to 600°C. The series of steps of immersion, slurry removal, and drying may be carried out only once, but by repeating the steps multiple times, an adsorption layer 40 of a desired thickness can be provided on the surface of the partition wall 14 or the like.

(3. Vehicle cabin purification system)
According to an embodiment of the present invention, there is provided a vehicle interior purification system including the above-described heater element 100. The vehicle interior purification system can be suitably used in various vehicles such as automobiles.

FIG. 3 is a schematic diagram showing the configuration of a vehicle interior purification system according to an embodiment of the present invention.
As shown in FIG. 3 , the vehicle interior purification system 1000 includes at least one heater element 100, a power source 200 such as a battery for applying voltage to the heater element 100, an inlet pipe 400 connecting the vehicle interior with the first end surface 12 a of the heater element 100, an outlet pipe 500 having a first path 500 a connecting the second end surface 12 b of the heater element 100 with the vehicle interior, and a fan 600 for introducing air from the vehicle interior into the first end surface 12 a of the heater element 100 via the inlet pipe 400.

In addition to the first path 500a, the outlet pipe 500 may have a second path 500b that connects the second end surface 12b of the heater element 100 to the outside of the vehicle. The outlet pipe 500 may also have a valve 300 that can switch the flow of air through the outlet pipe 500 between the first path 500a and the second path 500b.

The vehicle cabin purification system 1000 can have two operating modes: a first mode in which the applied voltage from the power source 200 is turned off, the valve 300 is switched so that the air flowing through the outlet pipe 500 passes through the first path 500a, and the ventilator 600 is turned on; and a second mode in which the applied voltage from the power source 200 is turned on, the valve 300 is switched so that the air flowing through the outlet pipe 500 passes through the second path 500b, and the ventilator 600 is turned on.

The vehicle interior purification system 1000 may be equipped with a control unit 900 that can switch between the first mode and the second mode. The control unit 900 may be configured, for example, to be able to alternate between the first mode and the second mode. By repeatedly switching between the first mode and the second mode in a fixed cycle, it becomes possible to stably discharge the components to be removed from within the vehicle interior to the outside of the vehicle.

In the first mode, the air in the vehicle cabin is purified. Specifically, air from the vehicle cabin flows into the first end surface 12a of the heater element 100 through the inlet pipe 400, passes through the heater element 100, and then flows out from the second end surface 12b of the heater element 100. Components to be removed from the air from the vehicle cabin are removed by being adsorbed by the adsorbent as they pass through the heater element 100. The clean air that flows out from the second end surface 12b of the heater element 100 is returned to the vehicle cabin through the first path 500a of the outlet pipe 500.

In the second mode, the adsorbent (adsorption layer 40) is regenerated. Specifically, air from the vehicle cabin flows into the first end surface 12a of the heater element 100 through the inlet pipe 400, passes through the heater element 100, and then flows out from the second end surface 12b of the heater element 100. The heater element 100 generates heat when energized, which heats the adsorbent supported on the heater element 100, causing the components to be removed that have been captured by the adsorbent to desorb from or react with the functional material.

In order to promote the desorption of the components to be removed that have been adsorbed onto the adsorbent, it is preferable to heat the adsorbent to a temperature above the desorption temperature depending on the type of adsorbent. For example, it is preferable to heat at least a portion of the adsorbent, and preferably all of it, to 70-150°C, more preferably to 80-140°C, and even more preferably to 90-130°C. Furthermore, it is preferable to carry out the second mode for a period of time until the adsorbent is sufficiently regenerated. Although this depends on the type of adsorbent, in the second mode, for example, it is preferable to heat the adsorbent to the above temperature range for 1-10 minutes, more preferably for 2-8 minutes, and even more preferably for 3-6 minutes.

Air from the vehicle compartment flows out from the second end surface 12b of the heater element 100, carrying with it the components to be removed that have been released from the adsorbent while passing through the heater element 100. The air containing the components to be removed that flows out from the second end surface 12b of the heater element 100 is discharged outside the vehicle through the second path 500b of the outlet pipe 500.

The voltage applied to the heater element 100 can be switched on and off, for example, by electrically connecting the power source 200 and the pair of electrodes 20a, 20b of the heater element 100 with an electric wire 810 and operating a power switch 910 provided along the line. The power switch 910 can be operated by the control unit 900.

The ventilator 600 can be switched on and off by, for example, electrically connecting the control unit 900 and the ventilator 600 via an electric wire 820 or wirelessly, and operating a switch (not shown) on the ventilator 600 using the control unit 900. The ventilator 600 can also be configured so that the ventilation volume can be changed by the control unit 900.

The valve 300 can be switched, for example, by electrically connecting the control unit 900 and the valve 300 via an electric wire 830 or wirelessly, and operating a switch (not shown) on the valve 300 using the control unit 900.

The valve 300 is not particularly limited as long as it is electrically driven and has the function of switching flow paths, but examples include a solenoid valve and an electric valve. In one embodiment, the valve 300 includes an opening/closing door 312 supported on a rotating shaft 310, and an actuator 314 such as a motor that rotates the rotating shaft 310. The actuator 314 is configured to be controllable by the control unit 900.

In order to stably ensure the above-mentioned functions, it is desirable for the vehicle interior purification system 1000 to have the heater element 100 positioned close to the vehicle interior. Therefore, from the perspective of preventing electric shock, it is preferable that the driving voltage be 60V or less. The honeycomb structure 10 used in the heater element 100 has low electrical resistance at room temperature, so it is possible to heat the honeycomb structure 10 at this low driving voltage. There is no particular limit on the lower limit of the driving voltage, but it is preferable that it be 10V or more. If the driving voltage is less than 10V, the current when heating the honeycomb structure 10 will be large, so the electric wire 810 will need to be thicker.

In the embodiment shown in Figure 3, the ventilator 600 is installed upstream of the heater element 100. More specifically, the ventilator 600 is installed midway through the inlet pipe 400 that connects the heater element 100 to the vehicle interior, and air that has passed through the ventilator 600 flows into the heater element 100 by being forced into it. Alternatively, the ventilator 600 may be installed downstream of the heater element 100. In this case, the ventilator 600 can be installed, for example, midway through the outlet pipe 500, and air that has passed through the inlet pipe 400 flows into the heater element 100 by being sucked into it.

The present invention will be explained in detail below using examples, but the present invention should not be construed as being limited to these examples.

_BaCO3 powder, _TiO2 powder, and La( _NH3 ) _3.6H2O powder were prepared as ceramic raw materials. These powders were weighed to achieve the desired composition after firing and dry-mixed to obtain a mixed _powder . Dry mixing was carried out for 30 minutes. Next, water, binder, plasticizer, and dispersant were added in appropriate amounts in the range of 3 to 30 parts by mass total to 100 parts by mass of the obtained mixed powder, and kneaded to obtain a clay body with a relative density of 64.8% after extrusion molding. Methylcellulose was used as the binder. Polyoxyalkylene alkyl ether was used as the plasticizer and dispersant.

Next, the obtained clay was put into an extrusion molding machine and extrusion molded using a predetermined die so as to obtain a honeycomb structure having the shape shown below after firing.
Shape of cross section and end face of honeycomb structure perpendicular to the flow channel direction: square Shape of cross section of cell perpendicular to the flow channel direction: square Thickness of partition wall: 0.13 mm
Outer wall thickness: 0.5 mm
Cell density: 83 cells/cm ²
Cell pitch: 1.00 mm
Cross-sectional area of honeycomb structure perpendicular to the direction in which the flow channels extend: 6052 mm ²
Length L from the first end face to the second end face 12 of the honeycomb structure: 10 mm
Thermal expansion coefficient of honeycomb structure: 7.6×10 ⁻⁶ /K
Volume resistivity at 25°C of the material constituting the outer wall and the partition wall: 15 Ω cm
Curie point of material constituting the outer wall and partition wall: 120°C

The resulting honeycomb molded body was then dielectrically dried and hot-air dried, then degreased in an air atmosphere in a firing furnace (450°C x 4 hours), and then fired in an air atmosphere to obtain a honeycomb structure. Firing was carried out by holding the body at 950°C for 1 hour, then heating it to 1200°C and holding it at 1200°C for 1 hour, then heating it to 1400°C (maximum temperature) at a heating rate of 200°C/hour, and holding it at 1400°C for 2 hours.

Next, a pair of electrodes was formed on both end faces (first end face and second end face) of the obtained honeycomb structure. The pair of electrodes was formed as follows: First, an electrode slurry containing aluminum (electrode material), ethyl cellulose, and diethylene glycol monobutyl ether (organic binder) was prepared, and the honeycomb structure was immersed in the electrode slurry from the first end face to the desired depth in the flow path direction of the honeycomb structure. Next, excess electrode slurry on the outer periphery of the honeycomb structure was removed by blowing and wiping, and the electrode slurry was then dried to form the pair of electrodes.

Next, terminals having a predetermined width W and thickness T and made of the following materials were prepared.
Terminal A: Ti (Young's modulus 106 GPa, thermal expansion coefficient 8.4×10 ⁻⁶ /K)
Terminal B: SUS430 (Young's modulus 200 GPa, thermal expansion coefficient 10.5×10 ⁻⁶ /K)
Terminal C: SUS304 (Young's modulus 193 GPa, thermal expansion coefficient 17.3×10 ⁻⁶ /K)
Terminal D: SUS316 (Young's modulus 193 GPa, thermal expansion coefficient 16×10 ⁻⁶ /K)
Terminal E: Cu (Young's modulus 130 GPa, thermal expansion coefficient 17.7×10 ⁻⁶ /K)
Terminal F: Al (Young's modulus 70 GPa, thermal expansion coefficient 23.8×10 ⁻⁶ /K)

Next, the above terminals were connected to a pair of electrodes on the outer peripheral wall so as to satisfy the conditions shown in the following tables. The terminals and the pair of electrodes were joined by soldering.
In the tables below, the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure is represented as the "CTE ratio," the ratio of the thickness T of the terminal to the length L from the first end face to the second end face of the honeycomb structure is represented as "T/L," the ratio of the area S2 of the terminal in contact with a pair of electrodes to the area S1 of the first end face or second end face of the honeycomb structure is represented as "S2/S1," and the ratio of the Young's modulus Y2 of the terminal to the Young's modulus Y1 of the honeycomb structure is represented as "Y2/Y1."

Each sample of the heater element obtained as described above was visually evaluated for the presence or absence of cracks (particularly cracks occurring on the outer peripheral wall). In this evaluation, a sample in which no cracks occurred was indicated by ○, and a sample in which cracks occurred was indicated by ×.
The results are shown in the tables below.

As shown in Tables 1-1 and 1-2, in Test Nos. A-1 to A-81, the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure (CTE ratio) and the ratio of the thickness T of the terminal to the length L from the first end face to the second end face of the honeycomb structure (T/L) were within the predetermined ranges, so no cracks occurred.
In contrast, in Test Nos. A-82 to A-90, although the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure (CTE ratio) was within the predetermined range, the ratio (T/L) of the thickness T of the terminal to the length L from the first end face to the second end face of the honeycomb structure was outside the predetermined range, and therefore cracks occurred.

As shown in Tables 2-1 and 2-2, in Test Nos. B-1 to B-81, the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure (CTE ratio) and the ratio of the thickness T of the terminal to the length L from the first end face to the second end face of the honeycomb structure (T/L) were within the predetermined ranges, and therefore no cracks occurred.
In contrast, in Test Nos. B-82 to B-90, although the ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure (CTE ratio) was within the predetermined range, the ratio (T/L) of the thickness T of the terminal to the length L from the first end face to the second end face of the honeycomb structure was outside the predetermined range, and therefore cracks occurred.

As shown in Tables 3-1 and 3-2, in Test Nos. C-1 to C-70, the ratio (T/L) of the terminal's thickness T to the honeycomb structure's length L from the first end face to the second end face was within the specified range, but the ratio (CTE ratio) of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient was outside the specified range, resulting in cracks. Furthermore, in Test Nos. C-71 to C-79, the ratio (CTE ratio) of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient and the ratio (T/L) of the terminal's thickness T to the honeycomb structure's length L from the first end face to the second end face were outside the specified ranges, resulting in cracks.

As shown in Tables 4-1 and 4-2, in Test Nos. D-1 to D-60, the ratio (T/L) of the terminal's thickness T to the length L from the first end face to the second end face of the honeycomb structure was within the specified range, but the ratio of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient (CTE ratio) was outside the specified range, resulting in cracks. Furthermore, in Test Nos. D-61 to D-69, the ratio (CTE ratio) of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient and the ratio (T/L) of the terminal's thickness T to the length L from the first end face to the second end face of the honeycomb structure were outside the specified ranges, resulting in cracks.

As shown in Tables 5-1 and 5-2, in Test Nos. E-1 to E-50, the ratio (T/L) of the terminal's thickness T to the length L from the first end face to the second end face of the honeycomb structure was within the specified range, but the ratio of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient (CTE ratio) was outside the specified range, resulting in cracks. Furthermore, in Test Nos. E-51 to E-59, the ratio (CTE ratio) of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient and the ratio (T/L) of the terminal's thickness T to the length L from the first end face to the second end face of the honeycomb structure were outside the specified ranges, resulting in cracks.

As shown in Tables 6-1 and 6-2, in Test Nos. F-1 to F-62, the ratio (T/L) of the terminal's thickness T to the honeycomb structure's length L from the first end face to the second end face was within the specified range, but the ratio of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient (CTE ratio) was outside the specified range, resulting in cracks. Furthermore, in Test Nos. F-63 to F-71, the ratio (CTE ratio) of the terminal's thermal expansion coefficient to the honeycomb structure's thermal expansion coefficient and the ratio (T/L) of the terminal's thickness T to the honeycomb structure's length L from the first end face to the second end face were outside the specified ranges, resulting in cracks.

As can be seen from the above results, the present invention can provide a heater element that can improve the bond between a pair of electrodes and a terminal, thereby improving water resistance, while suppressing damage to the honeycomb structure. The present invention also can provide a vehicle interior purification system equipped with such a heater element.

DESCRIPTION OF SYMBOLS 10 honeycomb structure 11 outer peripheral wall 12a first end face 12b second end face 13 cell 14 partition wall 20a, 20b electrode 30 terminal 40 adsorption layer 100 heater element 200 power supply 300 valve 310 rotating shaft 312 opening/closing door 314 actuator 400 inlet pipe 500 outlet pipe 500a first path 500b second path 600 ventilator 810, 820, 830 electric wire 900 control unit 910 power switch 1000 vehicle cabin purification system

Claims (15)

a honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that serve as flow paths extending from a first end face to a second end face;
a pair of electrodes provided on the first end surface and the second end surface;
a terminal provided on at least a part of the pair of electrodes,
a ratio of the thermal expansion coefficient of the terminal to the thermal expansion coefficient of the honeycomb structure is 1.00 to 1.38;
A heater element in which the ratio of the thickness of the terminal to the length from the first end face to the second end face of the honeycomb structure is 0.03 to 0.20. The heater element described in claim 1, wherein the ratio of the area of the terminal in contact with the electrode to the area of the first end face or the second end face of the honeycomb structure is 0.051 to 0.243. A heater element as described in claim 1 or 2, wherein the ratio of the Young's modulus of the terminal to the Young's modulus of the honeycomb structure is 0.99 to 2.83. A heater element as described in claim 1 or 2, wherein the terminal is provided on at least one of the electrodes on the outer peripheral wall, among the electrodes provided on the first end surface and the second end surface. The heater element of claim 4, wherein the terminals have a width of 1.0 to 5.0 mm. The heater element of claim 4, wherein the terminal has a thickness of 0.3 to 3.0 mm. The heater element of claim 4, wherein the thickness of the outer wall is 0.2 to 1.5 mm. A heater element as described in claim 1 or 2, wherein at least the partition walls of the honeycomb structure are made of a material having PTC properties. The heater element described in claim 8, wherein the material having PTC properties is composed primarily of barium titanate and is substantially free of lead. The heater element described in claim 8, wherein the material having PTC properties has a volume resistivity of 0.5 Ω·cm or more and 3000 Ω·cm or less at 25°C. A heater element as described in claim 1 or 2, comprising an adsorption layer on the surface of the partition wall. The heater element of claim 11, wherein the adsorption layer contains an adsorbent capable of adsorbing one or more selected from moisture, carbon dioxide, and volatile components. The heating element of claim 11, wherein the adsorption layer contains a catalyst. At least one heating element according to claim 1 or 2;
a power source for applying a voltage to the heater element;
an inlet pipe communicating between a passenger compartment and the first end surface of the heater element;
an outflow pipe having a first passage communicating the second end surface of the heater element with the passenger compartment;
a fan for directing air from the passenger compartment through the inlet pipe into the first end face of the heater element. the outflow pipe has, in addition to the first path, a second path that connects the second end surface of the heater element to the outside of the vehicle,
the outflow pipe has a valve capable of switching the flow of air passing through the outflow pipe between the first path and the second path,
a first mode in which the applied voltage from the power supply is turned off, the valve is switched so that the air flowing through the outflow pipe passes through the first path, and the ventilator is turned on;
a second mode in which the applied voltage from the power supply is turned on, the valve is switched so that the air flowing through the outflow pipe passes through the second path, and the ventilator is turned on;
The vehicle interior purification system of claim 14, further comprising a control unit capable of switching between: