Patent Application
20240208300
The present invention claims the benefit of priority to Japanese Patent Application No 2022-208619 filed on Dec. 26, 2022 with the Japanese Patent Office, the entire contents of which are incorporated herein by reference in its entirety.
The present invention relates to a heater element for vehicle air conditioning.
In various types of vehicles such as automobiles, there are increasing requirements for improvement of vehicle interior environment. Specific requirements include reduction of an amount of CO2 in the vehicle interior to suppress driver's drowsiness, control of humidity in the vehicle interior, and removal of harmful volatile components such as odor components and allergy-causing components in the vehicle interior. The effective measure for such requirements includes ventilation, but the ventilation causes a large loss of heater energy in winter, leading to a decreased energy efficiency in winter. In particular, a battery electric vehicle (BEV) has a problem that its cruising range is significantly reduced due to its energy loss.
As a method for solving the above problems, Patent Literatures 1 and 2 disclose a vehicle air conditioning system in which components to be removed such as CO2 and water vapor in the air in the vehicle interior are trapped by a functional material such as an adsorbent, and the components to be removed are then allowed to react or desorbed by heating to discharge them to the outside of the vehicle and regenerate the functional material. Such a vehicle air conditioning system requires more contact between the air and the functional material in order to ensure the performance of trapping the components to be removed, and the ability of the functional material to be heated to a predetermined temperature in order to facilitate the regeneration of the functional material. The regeneration can be carried out, for example, by removing substances adsorbed on the functional material through an oxidation reaction, and by desorbing and releasing the substances adsorbed on the functional material, but both cases require the heating of the functional material at an appropriate temperature depending on the adsorbed substances.
On the other hand, Patent Literature 3 discloses a heater element, including: a pillar shaped honeycomb structure having an outer peripheral wall and partition walls disposed on an inner side of the outer peripheral wall and defining a plurality of cells forming flow paths from a first end face to a second end face, wherein the partition walls have a PTC property, the partition walls have a thickness of 0.13 mm or less, and the first end face and the second end face have an opening ratio of 0.81 or more. This heater element is used for heating a vehicle interior, and is an efficient heating means. Therefore, the use of such a heater element as a support for the functional material can contribute to the shortening of the regeneration time of the functional material. In particular, it is believed that since this heater element can be heated by electric conduction and has a PTC property, it can easily heat the functional material, while suppressing excessive heat generation and thermal deterioration of the functional material.
In the heater element described in Patent Literature 3, the temperature increase time (regeneration time of the functional material) could be shortened because the thickness of the partition walls of the honeycomb structure is 0.13 mm or less so that the heating area is increased.
However, if the thickness of the partition walls of the honeycomb structure is smaller, cracks may be generated in the partition walls due to the influence of temperature differences within the honeycomb structure. The cracks generated in the partition walls can be suppressed by increasing the thickness of the partition walls. Further, if the thickness of the partition walls is increased, the current conduction resistance is reduced, so that the heating time can be shortened. On the other hand, if the thickness of the partition walls is increased, the pressure loss will be increased. Therefore, it will require a higher rotation speed of each of blowers installed before and after the heater element, resulting in a decrease in an energy efficiency.
The present invention was made to solve the problems as described above. An object of the present invention is to provide a heater element for vehicle air conditioning, which can suppress the cracks generated in the partition walls even if the thickness of the partition walls of the honeycomb structure is small, and which can also shorten the temperature increase time and reduce the pressure loss.
As a result of extensive studies for honeycomb structures used in heater elements for vehicle air conditioning, the present inventors have found that the above problems can be solved by controlling a relationship between a time until a temperature reaches 80° C. when a voltage of 10 to 13.5 V is applied to a heater element for vehicle air conditioning and a heating characteristic factor represented by a volume resistivity, an opening ratio, a specific heat, and a density of the honeycomb structure, and they have completed the present invention. That is, the present invention is illustrated as follows:
[1]
A heater element for vehicle air conditioning, comprising:
heating characteristic factor=a volume resistivity [Ω·cm] of the honeycomb structure/an opening ratio [%] of the honeycomb structure×a specific heat [J/kg·K] of the honeycomb structure×a density [g/m3] of the honeycomb structure. (3)
[2]
The heater element for vehicle air conditioning according to [1], wherein the opening ratio of the honeycomb structure is 71.7 to 80.3%.
[3]
The heater element for vehicle air conditioning according to [1] or [2], wherein the volume resistivity of the honeycomb structure is 10 to 20 Ω·cm.
[4]
The heater element for vehicle air conditioning according to any one of [1] to [3], wherein the specific heat of the honeycomb structure is 400 to 500 J/kg·K.
[5]
The heater element for vehicle air conditioning according to any one of [1] to [4], wherein the density of the honeycomb structure is 5.6 to 5.8 g/m3.
[6]
The heater element for vehicle air conditioning according to any one of [1] to [5], wherein the partition walls are made of a material having a PTC property.
[7]
The heater element for vehicle air conditioning according to any one of [1] to [6], further comprising a functional material-containing layer provided on surfaces of the partition walls parallel to an extending direction of the cells.
[8]
The heater element for vehicle air conditioning according to [7], wherein the functional material-containing layer comprises a functional material having a function of adsorbing one or more selected from water vapor, carbon dioxide, and volatile components.
[9]
The heater element for vehicle air conditioning according to [7] or [8], wherein the functional material-containing layer comprises a catalyst.
A heater element for vehicle air conditioning according to an embodiment of the present invention (which is, hereinafter, abbreviated as a “heater element”) includes: a honeycomb structure having an outer peripheral wall and partition walls disposed on an inner side of the outer peripheral wall, the partition walls defining a plurality of cells, each of the cells extending from a first end face to a second end face to form a flow path; and a pair of electrodes provided on the first end face and the second end face; wherein the partition walls have a thickness of 0.14 mm or less, and wherein the heater element satisfies the following equations (1) and (2):
in which y is a time [seconds] until a temperature reaches 80° C. when a voltage of 10 to 13.5 V is applied to the heater element for vehicle air conditioning, and x is a heating characteristic factor represented by the following equation (3):
heating characteristic factor=a volume resistivity [Ω·cm] of the honeycomb structure/an opening ratio [%] of the honeycomb structure×a specific heat [J/kg·K] of the honeycomb structure×a density [g/m3] of the honeycomb structure. (3)
By having the above configuration, the heater element according to the embodiment of the present invention can suppress cracks generated in the partition walls even if the thickness of the partition walls is lower, i.e., 0.14 mm or less, and also shorten the temperature increase time and reduce the pressure loss.
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. It is to understand that the present invention is not limited to the following embodiments, and those which have appropriately added changes, improvements and the like to the following embodiments based on knowledge of a person skilled in the art without departing from the spirit of the present invention fall within the scope of the present invention.
The heater element according to an embodiment of the present invention can be suitably utilized as a heater element for use in a vehicle air conditioning system for various vehicles such as automobiles. The vehicle includes, but not limited to, automobiles and trains. Non-limiting examples of the automobile include a gasoline vehicle, a diesel vehicle, a gas fuel vehicle using CNG (a compressed natural gas) or LNG (a liquefied natural gas), a fuel cell vehicle, an electric vehicle, and a plug-in hybrid vehicle. The heater element according to the embodiment of the present invention can be particularly suitably used for a vehicle having no internal combustion engine such as electric vehicles and electric railcars.
As shown in
The heater element 100 can be used as a support (carrier) for forming a functional material-containing layer 30.
As shown in
Each member forming the heater element 100 will be described below in detail.
The shape of the honeycomb structure 10 is not particularly limited. For example, an outer shape of a cross section of the honeycomb structure 10 orthogonal to the flow path direction (the extending direction of the cells 13) can be polygonal such as quadrangular (rectangular, square), pentagonal, hexagonal, heptagonal, and octagonal, circular, oval (egg-shaped, elliptical, elliptic, rounded rectangular, etc.), or the like. The end faces (first end face 12a and second end face 12b) have the same shape as the cross section. Also, when the cross section and the end faces are polygonal, the corners may be chamfered.
The shape of each cell 13 is not particularly limited, but it may be polygonal such as quadrangular, pentagonal, hexagonal, heptagonal, and octagonal, circular, or oval in the cross section of the honeycomb structure 10 orthogonal to the flow path direction. These shapes may be alone or in combination of two or more. Moreover, among these shapes, the quadrangle or the hexagon is preferable. By providing the cells 13 having such a shape, it is possible to reduce the pressure loss when the air flows.
The honeycomb structure 10 may be a honeycomb joined body having a plurality of honeycomb segments and joining layers that join outer peripheral side surfaces of the plurality of honeycomb segments together. The use of the honeycomb joined body can increase the total cross-sectional area of the cells 13, which is important for ensuring the flow rate of air, while suppressing cracking.
It should be noted that the joining layer can be formed by using a joining material. The joining material is not particularly limited, but a ceramic material obtained by adding a solvent such as water to form a paste can be used. The joining material may contain a material having a PTC (Positive Temperature Coefficient) property, or may contain the same material as the outer peripheral wall 11 and the partition walls 14. In addition to the role of joining the honeycomb segments to each other, the joining material can also be used as an outer peripheral coating material after joining the honeycomb segments.
The thickness of the partition walls 14 is 0.14 mm or less, and preferably 0.10 to 0.14 mm, and more preferably 0.11 to 0.13 mm. By controlling the thickness of the partition walls 14 within such a range, a heating area (a contact area with an air flowing through the cells 13) is increased, so that a temperature increase time (a regeneration time of the functional material) can be shortened. Furthermore, an amount of the functional material supported can also be increased.
As used herein, the thickness of the partition wall 14 refers to a length of a line segment that is across the partition wall 14 when connecting the centers of gravity of adjacent cells 13 with the line segment in the cross section orthogonal to the flow path direction. The thickness of the partition wall 14 refers to an average thickness of all the partition walls 14.
Although the thickness of the outer peripheral wall 11 is not particularly limited, it is preferably determined based on the following viewpoints. First, from the viewpoint of reinforcing the honeycomb structure 10, the thickness of the outer peripheral wall 11 is preferably 0.05 mm or more, and more preferably 0.06 mm or more, and even more preferably 0.08 mm or more. On the other hand, the thickness of the outer peripheral wall 11 is preferably 1.0 mm or less, and more preferably 0.5 mm, and more preferably 0.4 mm or less, and still more preferably 0.3 mm or less, from the viewpoint of suppressing the initial current by increasing the electrical resistance and from the viewpoint of reducing pressure loss when the air flows through the cells 13.
As used herein, the thickness of the outer peripheral wall 11 refers to a length from a boundary between the outer peripheral wall 11 and the outermost cell 13 or the partition wall 14 to a side surface of the honeycomb structure 10 in a normal line direction of the side surface in the cross section orthogonal to the flow path direction.
The cell density is not particularly limited, but it is preferably 2.54 to 140 cells/cm2, and more preferably 15 to 100 cells/cm2, or 20 to 90 cells/cm2. By controlling the cell density within such a range, the pressure loss when the air flows through the cells 13 can be easily reduced while ensuring the strength of the honeycomb structure 10.
As used herein, the cell density refers a value obtained by dividing a number of cells by an 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).
The cell pitch is not particularly limited, but it is preferably 1.0 to 2.0 mm, and more preferably 1.1 to 1.8 mm, and still more preferably 1.2 to 1.6 mm. By controlling the cell pitch within such a range, the pressure loss when the air flows through the cells 13 can be easily reduced while ensuring the strength of the honeycomb structure 10.
As used herein, the cell pitch refers to a value obtained by the following calculation. First, 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) is divided by the number of the cells to calculate an area per a cell. A square root of the area per a cell is then calculated, and this is determined to be the cell pitch.
The opening ratio of the honeycomb structure 10 (the opening ratio of the cells 13) is not particularly limited, but it is preferably 71.7 to 80.3%, and more preferably 72.6 to 76.0%. By controlling the opening ratio within such a range, the pressure loss when the air flows through the cells 13 can be easily reduced while ensuring the strength of the honeycomb structure 10.
As used herein, the opening ratio of the honeycomb structure 10 refers a value obtained by dividing the total area of the cells 13 defined by the partition walls 14 by the area of one end face 12b (first end face 12a or second end face 12b) (the total area of the partition walls 14 and the cells 13 excluding the outer peripheral wall 11) in the cross section orthogonal to the flow path direction of the honeycomb structure 10, and multiplying it by 100. It should be noted that when calculating the opening ratio of the honeycomb structure 10, the pair of electrodes 20a, 20b, and the functional material-containing layer 30 are not taken into account.
The length of the honeycomb structure 10 in the flow path direction and the cross-sectional area orthogonal to the flow path direction may be adjusted according to the required size of the heater element 100, and are not particularly limited. For example, when used in a compact heater element 100 while ensuring a predetermined function, the honeycomb structure 10 can have a length of 2 to 20 mm in the flow path direction and a cross-sectional area of 10 cm2 or more orthogonal to the flow path direction. Although the upper limit of the cross-sectional area orthogonal to the flow path direction is not particularly limited, it is, for example, 300 cm2.
The volume resistivity of the honeycomb structure 10 is not particularly limited, but it is preferably 10 to 20 Ω·cm, and more preferably 13 to 18 Ω·cm. By controlling the volume resistivity within such a range, it becomes easier to shorten the heating time while suppressing the cracks generated in the partition walls 14. Furthermore, heat can be generated with a low driving voltage.
As used herein, the volume resistivity of the honeycomb structure 10 means a volume resistivity at 25° C. Further, the volume resistivity of the honeycomb structure 10 is measured according to JIS K 6271:2008.
The specific heat of the honeycomb structure 10 is not particularly limited, but it is preferably 400 to 500 J/kg·K, and more preferably 430 to 480 J/kg·K. By controlling the specific heat within such a range, it becomes easier to shorten the heating time while suppressing the cracks generated in the partition walls 14.
As used herein, the specific heat of the honeycomb structure 10 is measured by a differential scanning calorimeter (DSC).
The density of the honeycomb structure 10 is not particularly limited, but it is preferably 5.6 to 5.8 g/m3, and more preferably 5.65 to 5.75 g/m3. By controlling the density within such a range, it becomes easier to shorten the heating time while suppressing the cracks generated in the partition walls 14.
The partition walls 14 forming the honeycomb structure 10 are preferably made of a material that can be heated by electric conduction, specifically made of a material having the PTC property. Further, the outer peripheral wall 11 is also preferably made of the material having the PTC property, as with the partition walls 14, as needed. By such a configuration, the functional material-containing layer 30 can be heated by heat transfer from the heat-generating partition walls 14 (and optionally the outer peripheral wall 11). Further, the material having the PTC property has characteristics such that when the temperature increases to exceed the Curie point, the resistance value is sharply increased, resulting in a difficult for electricity to flow. Therefore, when the temperature of the heater element 100 becomes high, the partition walls 14 (and the outer peripheral wall 11 if necessary) limit the current flowing through them, thereby suppressing excessive heat generation of the heater element 100. Therefore, it is possible to suppress thermal deterioration of the functional material-containing layer 30 due to excessive heat generation.
From the viewpoints that can be heated by electric conduction and has the PTC property, the outer peripheral wall 11 and the partition walls 14 are preferably made of a material containing barium titanate (BaTiO3) as a main component. Also, this material is more preferably ceramics made of a material containing barium titanate (BaTiO3)-based crystals as a main component in which a part of Ba is substituted with a rare earth element. As used herein, the term “main component” means a component in which a proportion of the component is more than 50% by mass of the total component. The content of BaTiO3— based crystalline particles can be determined by fluorescent X-ray analysis. Other crystalline particles can also be measured by the same method.
The compositional formula of BaTiO3-based crystalline particles, in which a part of Ba is substituted with the rare earth element, can be expressed as (Ba1-xAx) TiO3. In the compositional formula, the symbol A represents at least one rare earth element, and 0.001≤x≤0.010.
The symbol A is not particularly limited as long as it is the rare earth element, but it may preferably be 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. The x value is preferably 0.001 or more, and more preferably 0.0015 or more, in terms of suppressing excessively high electrical resistance at room temperature. On the other hand, x is preferably 0.009 or less, in terms of preventing the electrical resistance at room temperature from becoming too high due to insufficient sintering.
The content of the BaTiO3-based crystalline particles in which a part of Ba is substituted with the rare earth element in the ceramics is not particularly limited as long as it is determined to be the main component, but it may preferably be 90% by mass or more, and more preferably 92% by mass or more, and even more preferably 94% by mass or more. The upper limit of the content of the BaTiO3-based crystalline particles is not particularly limited, but it may generally be 99% by mass, and preferably 98% by mass.
The content of the BaTiO3-based crystalline particles can be measured by fluorescent X-ray analysis. Other crystalline particles can be measured in the same manner as this method.
In terms of reduction of the environmental load, it is desirable that the materials used for the outer peripheral wall 11 and the partition walls 14 are substantially free of lead (Pb). More particularly, the outer peripheral wall 11 and the partition walls 14 preferably have a Pb content of 0.01% by mass or less, and more preferably 0.001% by mass or less, and still more preferably 0% by mass. The lower Pb content can allow the air heated by contact with the heat-generating partition walls 14 to be safely applied to organisms such as humans, for example. In the outer peripheral wall 11 and the partition walls 14, the Pb content is preferably less than 0.03% by mass, and more preferably less than 0.01% by mass, and further preferably 0% by mass, as converted to PbO. The lead content can be determined by ICP-MS (inductively coupled plasma mass spectrometry).
The material making up the outer peripheral wall 11 and the partition walls 14 preferably have a lower limit of a Curie point of 100° C. or more, and more preferably 110° C. or more, and even more preferably 125° C. or more, in terms of efficiently heating the air. Further, the upper limit of the Curie point is preferably 250° C. or more, and preferably 225° C. or more, and even more preferably 200° C. or more, and still more preferably 150° C. or more, in terms of safety as a component placed in the vehicle interior or near the vehicle interior.
The Curie point of the material making up the outer peripheral wall 11 and the partition walls 14 can be adjusted by the type of shifter and an amount of the shifter added. For example, the Curie point of barium titanate (BaTIO3) is about 120° C., but the Curie point can be shifted to the lower temperature side by substituting a part of Ba and Ti with one or more of Sr, Sn and Zr.
As used herein, the Curie point is measured by the following method. A sample is attached to a sample holder for measurement, mounted in a measuring tank (e.g., MINI-SUBZERO MC-810P, from ESPEC), and a change in electrical resistance of the sample as a function of a temperature change when the temperature is increased from 10° C. is measured using a DC resistance meter (e.g., Multimeter 3478A, from YOKOGAWA HEWLETT PACKARD, LTD.). Based on an electrical resistance-temperature plot obtained by the measurement, a temperature at which the resistance value is twice the resistance value at room temperature (20° C.) is defined as the Curie point.
A pair of electrodes 20a, 20b are provided on the first end face 12a and the second end face 12b.
Applying of a voltage between the pair of electrodes 20a, 20b allows the honeycomb structure 10 to generate heat by Joule heat.
The pair of electrodes 20a, 20b may employ, 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 capable of ohmic contact with the outer peripheral wall 11 and/or the partition walls 14 which have the PTC property. The ohmic electrode may employ an ohmic electrode containing, for example, at least one selected from Al, Au, Ag and In as a base metal, and containing at least one selected from Ni, Si, Zn, Ge, Sn, Se and Te for n-type semiconductors as a dopant. Further, the pair of electrodes 20a, 20b may have a single-layer structure, or may have a laminated structure of two or more layers. When the pair of electrodes 20a, 20b have the laminated structure of two or more layers, the materials of the respective layers may be of the same type or of different types.
The thickness of the pair of electrodes 20a, 20b may be appropriately set according to the method for forming the pair of electrodes 20a, 20b. The method for forming the pair of electrodes 20a, 20b includes metal deposition methods such as sputtering, vapor deposition, electrolytic deposition, and chemical deposition. Alternatively, the pair of electrodes 20a, 20b can be formed by applying an electrode paste and then baking it, or by thermal spraying. Furthermore, the pair of electrodes 20a, 20b may be formed by joining metal sheets or alloy sheets.
Each of the thicknesses of the pair of electrodes 20a, 20b is, for example, about 5 to 80 μm for baking the electrode paste, and about 100 to 1000 nm for dry plating such as sputtering and vapor deposition, and about 10 to 100 μm for thermal spraying, and about 5 μm to 30 μm for wet plating such as electrolytic deposition and chemical deposition. Further, when joining the metal sheet or alloy sheet, each of the thicknesses is preferably about 5 to 100 μm.
The functional material-containing layer 30 is provided on the surfaces of the partition walls 14 (in the case of the outermost cells 13, the partition walls 14 that define the outermost cells 13 and the outer peripheral wall 11) parallel to the extending direction of the cells 13. By thus providing the functional material-containing layer 30, the functional material can be easily heated, so that the functional material can exert its desired function.
The functional material contained in the functional material-containing layer 30 is not particularly limited as long as it is a material that can exhibit a desired function, and examples that can be used herein include adsorbents, catalysts, and the like. The adsorbent preferably has a function of adsorbing one or more components selected from components to be removed in the air, such as water vapor, carbon dioxide, and volatile components. Also, the use of the catalyst can purify the components to be removed. Furthermore, the adsorbent and the catalyst may be used together for the purpose of enhancing the function of the absorbent to capture the components to be removed.
The adsorbent preferably has a function that can adsorb the components to be removed, such as water vapor, carbon dioxide and volatile components at −20 to 40° C. and release them at an elevated temperature of 60° C. or more. Examples of the adsorbent having such functions include zeolite, silica gel, activated carbon, alumina, silica, low-crystalline clay, amorphous aluminum silicate complexes, and the like. The type of the adsorbent may be appropriately selected depending on the types of the components to be removed. The adsorbent may be used alone, or in combination with two or more types.
The catalyst preferably has a function capable of promoting the oxidation-reduction reaction. The catalysts having such functions include metal catalysts such as Pt, Pd and Ag, and oxide catalysts such as CeO2 and ZrO2. The catalyst may be used alone, or in combination with two or more types.
The volatile components contained in the air in the vehicle interior include, for example, volatile organic compounds (VOCs), and odor components other than the VOCs Specific examples of the volatile components include ammonia, acetic acid, isovaleric acid, nonenal, formaldehyde, toluene, xylene, paradichlorobenzene, ethylbenzene, styrene, chlorpyrifos, di-n-butyl phthalate, tetradecane, and di-2-ethylhexyl phthalate, diazinon, acetaldehyde, 2-(1-methylpropyl)phenyl N-methylcarbamate, and the like.
The thickness of the functional material-containing layer 30 may be determined according to the size of the cells 13, and is not particularly limited. For example, the thickness of the functional material-containing layer 30 is preferably 20 μm or more, and more preferably 25 μm or more, and even more preferably 30 μm or more, from the viewpoint of ensuring sufficient contact with air. On the other hand, the thickness of the functional material-containing layer 30 is preferably 400 μm or less, and more preferably 380 μm or less, and even more preferably 350 μm or less, from the viewpoint of suppressing separation of the functional material-containing layer 30 from the partition walls 14 and the outer peripheral wall 11.
The thickness of the functional material-containing layer 30 is measured using the following procedure. Any cross section parallel to the flow path direction of the honeycomb structure 10 is cut out, and a cross-sectional image at magnifications of about 50 is acquired using a scanning electron microscope or the like. Also, this cross section is made to pass through the center of gravity position in the cross section orthogonal to the flow path of the honeycomb structure 10. The thickness of each functional material-containing layer 30 visually recognized from the cross-sectional image is calculated by dividing the cross-sectional area by the length of the cells 13 in the flow path direction. This calculation is performed for all the functional material-containing layers 30 visually recognized from the cross-sectional image, and an average value thereof is determined to be the thickness of the functional material-containing layer 30.
From the viewpoint that the functional material exhibits a desired function in the heater element 100, an amount of the functional material-containing layer 30 is preferably 50 to 500 g/L, and more preferably 100 to 400 g/L, and even more preferably 150 to 350 g/L, based on the volume of the honeycomb structure 10. It should be noted that the volume of the honeycomb structure 10 is a value determined by the external dimensions of the honeycomb structure 10.
The heater element 100 satisfies the following equations (1) and (2):
in which y is a time [seconds] until a temperature reaches 80° C. when a voltage of 10 to 13.5 V is applied to the heater element 100, and x is a heating characteristic factor represented by the following equation (3):
heating characteristic factor=a volume resistivity [Ω·cm] of the honeycomb structure 10/an opening ratio [%] of the honeycomb structure 10×a specific heat [J/kg·K] of the honeycomb structure 10×a density [g/m3] of the honeycomb structure 10. (3)
The above equations (1) and (2) are relational expressions experimentally derived from measurement results obtained by preparing various samples of the heater element 100, and measuring whether or not cracks are generated during heating (during a regeneration treatment of the functional material) (thermal shock resistance), a temperature increase property (heating rate), and a pressure loss. The measurement results will be described.
Various samples of the heater element 100 were prepared as follows:
First, as ceramic raw materials, BaCO3 powder, TiO2 powder and La(NO3)3·6H2O powder were prepared. These powders were weighed so as to have the predetermined composition after firing, and dry-mixed to obtain a mixed powder. The dry mixing was carried out for 30 minutes. Subsequently, 3 to 30 parts by weight of water, a binder, a plasticizer and a dispersant in total were added by a proper amount, based on 100 parts by mass of the obtained mixed powder, such that a ceramic formed body having a relative density of 64.8% were obtained after extrusion, and then kneaded to obtain a green body. Methyl cellulose was used as the binder. Polyoxyalkylene alkyl ether was used as the plasticizer and the dispersant.
The obtained green body was then introduced into an extrusion molding machine and extruded using a predetermined die to obtain a honeycomb structure 10 having the shape as shown below after the firing.
Shape of the cross section and each end face of the honeycomb structure 10 orthogonal to the flow path direction: quadrangular;
Subsequently, after dielectric drying and hot air drying of the obtained honeycomb formed body, it was degreased in an air atmosphere in a firing furnace (at 450° C. for 4 hours), and then fired in an air atmosphere to obtain a honeycomb structure. The firing was carried out by maintaining it at 950° C. for 1 hour, and then increasing the temperature to 1200° C. and maintaining it at 1200° C. for 1 hour, and then increasing the temperature at a heating rate of 200° C./hour to 1400° C. (the maximum temperature) and maintaining it at 1400° C. for 2 hours.
The pair of electrodes 20a, 20b were then formed on both end faces (first end face 12a and second end face 12b) of the obtained honeycomb structure 10. The pair of electrodes 20a, 20b were formed as follows. First, an electrode slurry containing aluminum (electrode material), ethyl cellulose, and diethylene glycol monobutyl ether (organic binder) was prepared, and the first end face 12a was coated with the slurry. Subsequently, after removing an excess electrode slurry on the outer periphery of the honeycomb structure 10 by blowing and wiping, the electrode slurry was dried to form the electrode 20a on the first end face 12a. In the same way, the electrode 12b was also formed on the second end face 12b to form the heater element 100.
The heater element 100 thus obtained was evaluated as follows:
After conducting a heating rate test as described below, the presence or absence of cracks in the partition walls 14 was visually observed. In this evaluation, a sample in which no crack was observed in the partition walls 14 is represented as A, and a sample in which cracks were observed in the partition walls 14 is represented as B.
The time until the temperature reaches 80° C. when the voltage shown in Table 1 was applied to the heater element 100 was measured. The measurement of the temperature was performed using thermocouples at five positions (one position at the central portion and four positions at the outer periphery of the cross section orthogonal to the extending direction of the cells (flow path) of the honeycomb structure forming the heater element). It should be noted that the temperature was an average of the temperatures at the five positions. In this evaluation, a sample in which the time to reach the temperature was within 185 seconds is represented as A, and a sample to reach the temperature exceeded 185 seconds is represented as B.
Differential pressure gauges were installed on upstream and downstream sides of each sample, air was passed through at a flow rate of 45 m3/h, and a pressure loss (pressure on upstream side—pressure on downstream side) was determined. In this evaluation, a sample having a pressure loss of 100 Pa or less is represented as A, and a sample having a pressure loss more than 100 Pa is represented as B.
Table 1 shows the above evaluation results. Also,
As shown in Table 1 and
The method for producing the heater element 100 according to the embodiment of the present invention is not particularly limited as long as it is the method that can produce the heater element 100 having the above features, and it can be performed according to a known method. Hereinafter, the method for producing the heater element 100 according to an embodiment of the present invention will be illustratively described.
A method for producing the honeycomb structure 10 forming the heater element 100 includes a forming step and a firing step.
In the forming step, a green body containing a ceramic raw material including BaCO3 powder, TiO2 powder, and rare earth nitrate or hydroxide powder is formed to prepare a honeycomb formed body having a relative density of 60% or more.
The ceramic raw material can be obtained by dry-mixing the powders so as to have a desired composition.
The green body can be obtained by adding a dispersion medium, a binder, a plasticizer and a dispersant to the ceramic raw material and kneading them. The green body may optionally contain additives such as shifters, metal oxides, property improving agents, and conductor powder.
The blending amount of the components other than the ceramic raw material is not particularly limited as long as the relative density of the honeycomb formed body is 60% or more.
As used herein, the “relative density of the honeycomb formed body” means a ratio of the density of the honeycomb formed body to the true density of the entire ceramic raw material. More particularly, the relative density can be determined by the following equation:
The density of the honeycomb formed body can be measured by the Archimedes method using pure water as a medium. Further, the true density of the entire ceramic raw material can be obtained by dividing the total mass of the respective raw materials (g) by the total volume of the actual volumes of the respective raw materials (cm3).
Examples of the dispersion medium include water or a mixed solvent of water and an organic solvent such as alcohol, and more preferably water.
Examples of the binder include organic binders such as methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. In particular, it is preferable to use methyl cellulose in combination with hydroxypropoxyl cellulose. The binder may be used alone, or in combination of two or more, but it is preferable that the binder does not contain an alkali metal element.
Examples of the plasticizer include polyoxyalkylene alkyl ethers, polycarboxylic acid-based polymers, and alkyl phosphate esters.
The dispersant that can be used herein includes surfactants such as polyoxyalkylene alkyl ether, ethylene glycol, dextrin, fatty acid soaps, and polyalcohol. The dispersant may be used alone or in combination of two or more.
The honeycomb formed body can be produced by extrude the green body. In the extrusion, a die having a desired overall shape, cell shape, partition wall thickness, cell density and the like can be used.
The relative density of the honeycomb formed body obtained by extrusion is 60% or more, and preferably 65% or more. By controlling the relative density of the honeycomb formed body to such a range, the honeycomb formed body can be densified and the electrical resistance at room temperature can be reduced. The upper limit of the relative density of the honeycomb formed body is not particularly limited, but it may generally be 80%, and preferably 75%.
The honeycomb formed body can be dried before the firing step. Non-limiting examples of the drying method include conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, drying under reduced pressure, drying in vacuum, and freeze drying. Among these, a drying method that combines the hot air drying with the microwave drying or dielectric drying is preferable in that the entire formed body can be rapidly and uniformly dried.
The firing step includes maintaining the formed body at a temperature of from 1150 to 1250° C., and then increasing the temperature to a maximum temperature of from 1360 to 1430° C. at a heating rate of 20 to 600° C./hour, and maintaining the temperature for 0.5 to 10 hours.
The maintaining of the honeycomb formed body at the maximum temperature of from 1360 to 1430° C. for 0.5 to 10 hours can provide the honeycomb structure 10 containing, as a main component, BaTiO3-based crystal particles in which a part of Ba is substituted with the rare earth element.
Further, the maintaining at the temperature of from 1150 to 1250° C. can allow the Ba2TiO4 crystal particles generated in the firing process to be easily removed, so that the honeycomb structure 10 can be densified.
Further, the heating rate of 20 to 600° C./hour from the temperature of 1150 to 1250° C. to the maximum temperature of 1360 to 1430° C. can allow 1.0 to 10.0% by mass of Ba6Ti17O40 crystal particles to be formed into the honeycomb structure 10.
The maintaining time at 1150 to 1250° C. is not particularly limited, but it may preferably be from 0.5 to 10 hours. Such a maintaining time can lead to stable and easy removal of Ba2TiO4 crystal particles generated in the firing process.
The firing step preferably includes maintaining at 900 to 950° C. for 0.5 to 5 hours during the increasing of the temperature. The maintaining at 900 to 950° C. for 0.5 to 5 hours can lead to sufficient decomposition of BaCO3, so that the honeycomb structure 10 having a predetermined composition can be easily obtained.
Prior to the firing step, a degreasing step for removing the binder may be performed. The degreasing step may preferably be performed in an air atmosphere in order to decompose the organic components completely.
Also, the atmosphere of the firing step may preferably be the air atmosphere in terms of control of electrical characteristics and production cost.
A firing furnace used in the firing step and the degreasing step is not particularly limited, but it may be an electric furnace, a gas furnace, or the like.
By forming a pair of electrodes 20a, 20b on the honeycomb structure 10 obtained as described above, the heater element 100 can be produced.
The pair of electrodes 20a, 20b can be formed by metal deposition methods such as sputtering, vapor deposition, electrolytic deposition, and chemical deposition. Further, 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, but may also be composed of a plurality of electrode layers having different compositions. A typical method for forming the pair of electrodes 20a, 20b will be described below.
First, an electrode slurry containing an electrode material, an organic binder, and a dispersion medium is prepared, and the surfaces of the outer peripheral wall 11 and the partition walls 14 on the first end face 12a or the second end face 12b of the honeycomb structure 10 are coated with the slurry. 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. An excess slurry on the periphery of the honeycomb structure 10 is removed by blowing and wiping. The slurry can be then dried to form the pair of electrodes 20a, 20b on the first end face 12a or the second end face 12b of the honeycomb structure 10. The drying can be performed while heating the heater element 100 to a temperature of about 120 to 600° C., for example. Although a series of steps of coating, slurry removal, and drying may be performed only once, the steps can be repeated multiple times to provide the pair of electrodes 20a, 20b having desired thicknesses.
The functional material-containing layer 30 can be then formed on the surfaces of the partition walls 14 and the like of the heater element 100 thus obtained to provide the heater element 100 with the functional material-containing layer 30.
Although the method for forming the functional material-containing layer 30 is not particularly limited, it can be formed, for example, by the following steps. The heater element 100 is immersed in a slurry containing a functional material, an organic binder, and a dispersion medium for a predetermined period of time, and an excess slurry on the end faces and the outer periphery of the honeycomb structure 10 is removed 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 can be then dried to form the functional material-containing layer 30 on the surfaces of the partition walls 14. The drying can be performed while heating the heater element 100 to a temperature of about 120 to 600° C., for example. Although a series of steps of immersion, slurry removal, and drying may be performed only once, the steps can be repeated multiple times to provide the functional material-containing layer 30 having the desired thickness on the surfaces of the partition walls 14 and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-208619 | Dec 2022 | JP | national |
