Method for manufacturing sensor element and slurry deposition device

Abstract

To prevent the front end side and / or rear end side of a porous protective layer that covers a predetermined region around the front end of an element body from becoming partially thin.SOLUTION: A method for manufacturing a sensor element 20 includes a first step of preparing an element body 60 and a second step of depositing a yet-to-be-fired slurry 77 on a predetermined region of the element body 60. The second step involves performing a first process once and then performing a second process at least once. The first process involves depositing the yet-to-be-fired slurry 77 on at least a portion of the predetermined region of the element body 60 using a slurry flow 85 flowing from above to below. The second process involves exposing the front end side or rear end side of the yet-to-be-fired slurry 77 from the slurry flow 85 to dry the exposed portion, and then returning the exposed portion to the slurry flow 85 to deposit the yet-to-be-fired slurry 77 on the at least a portion of the predetermined region.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a sensor element and a slurry deposition device. [Background technology]

[0002] A conventional method for manufacturing a sensor element is known, in which the front end of a substantially flat element body, specifically the portion exposed to the gas to be measured, is immersed in a slurry and then pulled up to form a porous protective layer (see, for example, Patent Document 1). In this method, the element body is immersed in the slurry and then pulled up, and the element body is moved not only up and down along the longitudinal axis direction but also in a direction perpendicular to the longitudinal axis direction. In this way, the shear stress generated when the element body moves through the slurry is increased, and the viscosity of the slurry is reduced, improving wettability, and the porous protective layer is formed on the surface of the element body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5533767 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described manufacturing method of the sensor element, the porous protective layer may easily become thin at the front end and / or rear end. Because the element body and the porous protective layer are exposed to the measurement gas containing water, if a part of the porous protective layer becomes thin, there is a concern that the water resistance of that part may be reduced.

[0005] The main purpose of the sensor element manufacturing method and slurry application device of the present invention is to prevent the front end side and / or rear end side of the porous protective layer covering a predetermined region around the front end of the element body from becoming partially thin. [Means for solving the problem]

[0006] The method for manufacturing a sensor element and the slurry deposition apparatus of the present invention employ the following means to achieve the above-mentioned main object.

[0007] [1] The method for manufacturing a sensor element of the present invention comprises: A method for manufacturing a sensor element comprising: an element body having a front end and a rear end which are both ends along a longitudinal direction and a side surface which is a surface along the longitudinal direction, the front end side being exposed to a gas to be measured; and a porous protective layer covering a predetermined region around the front end of the element body, a first step of preparing the element body before or after firing; a second step of applying a pre-fired slurry, which is a slurry that will become the porous protective layer after firing, to the predetermined region of the element body; Including, The second step comprises: After performing a first process of depositing the pre-fired slurry onto at least a part of the predetermined region of the element body using a slurry flow that flows from above to below, a second process of exposing a front end side or a rear end side of the pre-fired slurry from the slurry flow, drying the exposed portion, and returning the exposed portion to the slurry flow to adhere the pre-fired slurry to at least a part of the predetermined region, is performed at least once; The gist of this is as follows.

[0008] The method for manufacturing a sensor element of the present invention includes a first step of preparing an element body before or after firing, and a second step of applying a pre-firing slurry, which is a slurry that will become a porous protective layer after firing, to a predetermined region of the element body. The second step involves performing the first process once and then performing the second process at least once. The first process involves applying the pre-firing slurry to at least a portion of the predetermined region of the element body using a slurry flow that flows from above to below. The second process involves exposing the front end or rear end of the pre-firing slurry from the slurry flow, drying the exposed portion, and then returning the exposed portion to the slurry flow to apply the pre-firing slurry to at least a portion of the predetermined region. This prevents the front end and / or rear end of the applied slurry, and therefore the front end and / or rear end of the porous protective layer, from becoming partially thin.

[0009] [2] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element described in [1]), the second treatment may be performed by drying the exposed portion by applying hot air or infrared radiation to the exposed portion. This can reduce the time required to dry the exposed portion compared to when the exposed portion is naturally dried.

[0010] [3] In the above-mentioned method for manufacturing a sensor element (the method for manufacturing a sensor element described in [1] or [2]), the length of the exposed portion in the longitudinal direction per one treatment in the second treatment may be 10% or more of the length of the pre-fired slurry in the longitudinal direction after completion of the second step.

[0011] [4] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element according to any one of [1] to [3]), the second step may include rotating the element body around an axis extending in the longitudinal direction. This allows the pre-sintering slurry to be more uniformly applied in the circumferential direction to the side surface of the element body.

[0012] [5] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element according to any one of [1] to [3]), the element body may be rectangular and have four side surfaces, and in the second step, the element body may be arranged so that the side surface having the smallest area among the four side surfaces is on top. In this way, the pre-sintering slurry can be more sufficiently attached to the two side surfaces connected to the side surface having the smallest area among the four side surfaces.

[0013] [6] In the above-mentioned method for manufacturing a sensor element (the method for manufacturing a sensor element described in any one of [1] to [5]), the first treatment may be performed by causing at least a part of the predetermined area of ​​the element body to enter the slurry flow and depositing the pre-fired slurry on at least a part of the predetermined area, or by directing the slurry flow at the element body with the longitudinal direction tilted relative to the flow direction of the slurry flow and depositing the pre-fired slurry on at least a part of the predetermined area.

[0014] [7] The method for manufacturing a sensor element described above (the method for manufacturing a sensor element described in any one of [1] to [6]) may further include a third step, after the second step, of disposing the element body so that one of the front end side and the rear end side of the pre-sintering slurry is on the lower side and the other is on the upper side, and drying the pre-sintering slurry. The second treatment may involve exposing and drying at least once the front end side or the rear end side of the pre-sintering slurry that will be on the upper side in the third step. This can prevent the film thickness of the front end side or the rear end side of the pre-sintering slurry that will be on the upper side in the third step from being thinned by exposure and drying in the second step. Furthermore, it can prevent the film thickness of the front end side or the rear end side of the pre-sintering slurry that will be on the lower side in the third step from being thinned by movement of the pre-sintering slurry due to its own weight in the third step.

[0015] [8] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element described in [7]), the second treatment may be performed such that the degree of drying of the front end side or the rear end side of the pre-sintered slurry, whichever is upper in the third step, when exposed from the slurry flow, is greater than the degree of drying of the rear end side, which is lower in the third step, when exposed from the slurry flow. This can further prevent the thickness of the front end side or the rear end side of the pre-sintered slurry, whichever is upper in the third step, from becoming thinner.

[0016] [9] In the method for manufacturing a sensor element described above (the method for manufacturing a sensor element described in [8]), the degree of drying may be a drying time or a number of drying times.

[0017]

[10] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element according to any one of [1] to [9]), the second step may include circulating the slurry that falls from the slurry flow without adhering to the element body above the element body so as to be reused in the slurry flow. In this way, the slurry that falls from the slurry flow without adhering to the element body can be effectively utilized.

[0018]

[11] In the above-described method for manufacturing a sensor element (the method for manufacturing a sensor element described in

[10] ), the second step may include adjusting the viscosity of the slurry that falls from the slurry flow without adhering to the element body, and then reusing the slurry in the slurry flow. In this way, the viscosity of the slurry flow can be adjusted.

[0019]

[12] The slurry deposition device of the present invention is A sensor element includes an element body having a front end and a rear end that are both ends along a longitudinal direction and a side surface that is a surface along the longitudinal direction, the front end side being exposed to a gas to be measured, and a porous protective layer that covers a predetermined region around the front end of the element body. The slurry deposition device deposits a pre-fired slurry, which becomes the porous protective layer after firing, onto the predetermined region of the element body, a holding part that holds the element body before or after firing; a drive unit that moves the holding unit; a control unit that controls the drive unit; Equipped with The control unit a first process for controlling the driving unit to move the holding unit while the holding unit is holding the element body, so that at least a part of the predetermined region of the element body enters the slurry flow and the pre-fired slurry adheres to at least a part of the predetermined region; a second process of controlling the driving unit at least once so as to expose a front end side or a rear end side of the pre-fired slurry from the slurry flow by moving the holding unit, dry the exposed portion, and then return the exposed portion into the slurry flow to adhere the pre-fired slurry to at least a part of the predetermined region; The gist of this is as follows.

[0020] In the slurry deposition device of the present invention, the control unit executes the first process once and then executes the second process at least once. In the first process, the control unit controls the drive unit to move the holding unit, while the holding unit is holding the element body, so that at least a portion of a predetermined region of the element body enters the slurry flow and deposits the pre-fired slurry on at least a portion of the predetermined region. In the second process, the control unit executes the second process at least once, controlling the drive unit to move the holding unit to expose the front end side or rear end side of the pre-fired slurry from the slurry flow, dry the exposed portion, and then return the exposed portion to the slurry flow, so that the pre-fired slurry is deposited on at least a portion of the predetermined region. This makes it possible to prevent the front end side and / or rear end side of the deposited slurry, and therefore the front end side and / or rear end side of the porous protective layer, from becoming partially thin. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. [Figure 2] FIG. 2 is a longitudinal cross-sectional view of the sensor element 20. [Figure 3] 3A to 3C are process diagrams of a method for manufacturing the sensor element 20. [Figure 4] 3A to 3C are explanatory diagrams illustrating the manufacturing process of the sensor element 20. [Figure 5] FIG. 2 is a schematic diagram of a slurry deposition device 80 and the like. [Figure 6] FIG. 10 is an explanatory diagram of step S110. DETAILED DESCRIPTION OF THE INVENTION

[0022] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a sensor element 20 manufactured by a sensor element manufacturing method according to an embodiment of the present invention, as viewed from the upper right front. FIG. 2 is a longitudinal cross-sectional view schematically showing a longitudinal cross-section of the sensor element 20. Note that upper connector electrodes 71, lower connector electrodes 72, and outer lead portions 75 are not shown in FIG. 1. In this embodiment, as shown in FIGS. 1 and 2, the longitudinal direction of the element body 60 of the sensor element 20 is defined as the front-rear direction (length direction), the stacking direction (thickness direction) of the solid electrolyte layers of the element body 60 is defined as the up-down direction, and the direction perpendicular to the front-rear direction and the up-down direction is defined as the left-right direction (width direction).

[0023] The sensor element 20 is used as part of a gas sensor. In addition to the sensor element 20, the gas sensor includes a protective cover that protects the front end of the sensor element 20 and a sensor assembly that houses the sensor element. This gas sensor is attached to, for example, an exhaust gas pipe of an internal combustion engine of a vehicle, and is used to detect the concentration (specific gas concentration) of a specific gas such as NOx, O2, or ammonia in the exhaust gas from the internal combustion engine. Of the two ends (front and rear ends) along the longitudinal direction of the sensor element 20, the front end is exposed to the measurement gas.

[0024] As shown in FIGS. 1 and 2, the sensor element 20 includes an element body 60, a detection unit 63, a heater 69, a plurality of upper connector electrodes 71, a plurality of lower connector electrodes 72, and a porous protective layer 76. The element body 60 has a laminated body in which a plurality of (six in this embodiment) oxygen ion conductive solid electrolyte layers such as zirconia (ZrO) are stacked. The element body 60 has a rectangular parallelepiped shape with its longitudinal direction aligned with the front-rear direction, and has first to sixth faces 60a to 60f as outer surfaces on the top, bottom, left, right, front, and rear sides, respectively. The first to fourth faces 60a to 60d are surfaces aligned with the longitudinal direction of the element body 60 and correspond to the side faces (top, bottom, left, and right faces) of the element body 60. The fifth face 60e is the front end face of the element body 60, and the sixth face 60f is the rear end face of the element body 60. The dimensions of element body 60 may be, for example, a length in the front-rear direction of 25 mm to 100 mm, a width in the left-right direction of 2 mm to 10 mm, and a thickness in the up-down direction of 0.5 mm to 5 mm. Element body 60 is formed with a measurement gas inlet 61 that opens to fifth surface 60e and introduces a measurement gas into itself, and a reference gas inlet 62 that opens to sixth surface 60f and introduces a reference gas (here, air) that serves as a reference for detecting the concentration of a specific gas into itself.

[0025] The detection unit 63 is for detecting the concentration of a specific gas in the gas to be measured. The detection unit 63 has a plurality of electrodes 64 to 68 disposed on the front end side of the element body 60. In this embodiment, the detection unit 63 includes an outer electrode 64 disposed on the first surface 60a, and an inner main pump electrode 65, an inner auxiliary pump electrode 66, a measurement electrode 67, and a reference electrode 68 disposed inside the element body 60. The inner main pump electrode 65 and the inner auxiliary pump electrode 66 are disposed on the inner circumferential surface of the space inside the element body 60, and have a tunnel-like structure.

[0026] The principle by which the detection unit 63 detects the concentration of a specific gas in a measurement gas is well known, and therefore a detailed description thereof will be omitted. The detection unit 63 detects the concentration of a specific gas, for example, as follows. The detection unit 63 pumps oxygen from the measurement gas around the inner main pump electrode 65 to the outside based on the voltage applied between the outer electrode 64 and the inner main pump electrode 65. The detection unit 63 also pumps oxygen from the measurement gas around the inner auxiliary pump electrode 66 to the outside based on the voltage applied between the outer electrode 64 and the inner auxiliary pump electrode 66. As a result, the measurement gas, whose oxygen concentration has been adjusted to a predetermined concentration, reaches the vicinity of the measurement electrode 67. The measurement electrode 67 functions as a NOx reduction catalyst and reduces the specific gas (NOx) in the measurement gas that has reached it. The detection unit 63 then generates an electromotive force between the measurement electrode 67 and the reference electrode 68 in accordance with the oxygen concentration after reduction, or generates a current flowing between the measurement electrode 67 and the outer electrode 64 based on the electromotive force, as an electrical signal. The electrical signal generated by the detection unit 63 in this manner is a signal indicating a value corresponding to the concentration of a specific gas in the measured gas (a value from which the concentration of the specific gas can be derived), and corresponds to the detection value detected by the detection unit 63.

[0027] The heater 69 is an electric resistor disposed inside the element body 60. When power is supplied from the outside, the heater 69 generates heat to heat the element body 60. The heater 69 heats and keeps warm the solid electrolyte layer that forms the element body 60, and can adjust the temperature to a temperature (e.g., 800°C) at which the solid electrolyte layer is activated.

[0028] Each of the plurality of upper connector electrodes 71 and the plurality of lower connector electrodes 72 is disposed on the rear end side of the side surface of the element body 60 and serves as an electrode for electrical conduction with the outside. The plurality of upper connector electrodes 71 and the plurality of lower connector electrodes 72 are exposed without being covered by the porous protective layer 76. In this embodiment, the four upper connector electrodes 71 are disposed side by side in the left-right direction on the rear end side of the first surface 60a (upper surface). The four lower connector electrodes 72 are disposed side by side in the left-right direction on the rear end side of the second surface 60b (lower surface). Each of the four upper connector electrodes 71 and the four lower connector electrodes 72 is electrically connected to one of the plurality of electrodes 64 to 68 of the detection unit 63 and the heater 69. An upper connector electrode 71 and an outer electrode 64 are electrically connected to each other via an outer lead portion 75 disposed on the first surface 60a. The other connector electrodes are each electrically connected to a corresponding electrode or heater 69 via a lead wire or through hole disposed inside the element body 60 .

[0029] The porous protective layer 76 is a porous body that covers a predetermined region around the front end of the element body 60 (a region within a predetermined range from the front end to the rear end), specifically, a part of the first to fourth surfaces 60a and the entire fifth surface 60e of the element body 60. The porous protective layer 76 covers the portions of the element body 60 that are exposed to the measurement gas, including the measurement gas inlet 61 and the outer electrode 64. The porous protective layer 76 covers and protects a portion of the element body 60. Specifically, the porous protective layer 76 serves as a protective layer that prevents, for example, water in the measurement gas from adhering to the element body 60 and causing cracks in the element body 60.

[0030] The porous protective layer 76 is made of a ceramic porous body such as porous alumina, porous zirconia, porous spinel, porous cordierite, porous titania, or porous magnesia. The thickness of the porous protective layer 76 may be, for example, 40 μm or more and 800 μm or less. The porosity of the porous protective layer 76 may be 10% or more and 85% or less. The porous protective layer 76 covers the measurement gas inlet 61, but because it is porous, the measurement gas can flow through the porous protective layer 76 and reach the measurement gas inlet 61.

[0031] The porosity of the porous protective layer 76 is a value derived as follows using an image (SEM image) obtained by observation using a scanning electron microscope (SEM). First, the sensor element 20 is cut along the thickness direction of the porous protective layer 76 so that the cross section of the porous protective layer 76 serves as the observation surface. The cut surface is then filled with resin and polished to obtain an observation sample. Next, an SEM image of the porous protective layer 76 is obtained by photographing the observation surface of the observation sample with the SEM magnification set to 1000x to 10000x. The obtained image is then analyzed to determine a threshold value using discriminant analysis (Otsu's binarization) based on the brightness distribution of the brightness data of the pixels in the image. Next, each pixel in the image is binarized into an object portion and a pore portion based on the determined threshold value, and the area of ​​the object portion and the area of ​​the pore portion are calculated. The porosity (unit: %) is then derived as the ratio of the area of ​​the pore portion to the total area (the total area of ​​the object portion and the pore portion).

[0032] Next, a method for manufacturing the sensor element 20 will be described. FIG. 3 is a process chart showing an example of the steps of the method for manufacturing the sensor element 20. FIG. 4 is an explanatory diagram showing an example of the manufacturing process of the sensor element 20. As shown in FIG. 3, in the method for manufacturing the sensor element 20, first, a fired element body 60 is prepared (step S100, see FIG. 4(a)). Next, a pre-fired slurry 77, which is a slurry that will become the porous protective layer 76 after firing, is attached to a predetermined region of the element body 60 (step S110, see FIG. 4(b)). Then, the pre-fired slurry 77 attached to the element body 60 is dried (step S120, see FIG. 4(b)). Furthermore, the pre-fired slurry 77 is fired to form the porous protective layer 76 (step S130, see FIG. 4(c)), thereby obtaining the sensor element 20.

[0033] Step S100 will be described. In step S100, first, a plurality of unsintered ceramic green sheets (six in this embodiment) corresponding to the element body 60 are prepared. Next, notches, through-holes, grooves, etc. are formed in each green sheet by punching or the like, and wiring patterns such as electrodes 64-68 and outer lead portions 75 are formed by screen printing, as needed. Each green sheet is then dried, and thereafter, the plurality of green sheets are stacked to form a laminate. The laminate thus obtained includes a plurality of element bodies 60. The laminate is cut into pieces the size of the element bodies 60, and fired at a predetermined firing temperature to obtain the element bodies 60. Note that in step S100, instead of manufacturing and preparing the element bodies 60, a pre-manufactured, fired element body 60 may be prepared.

[0034] Step S110 will now be described. Fig. 5 is a schematic diagram of a slurry deposition device 80 used in step S110. In Fig. 5, the left-right direction is the X-axis direction, the front-to-back direction (the direction penetrating the paper surface) is the Y-axis direction, and the up-down direction is the Z-axis direction. In step S110, the pre-fired slurry 77 is deposited on a predetermined region of the element body 60 using the slurry deposition device 80.

[0035] The slurry deposition device 80 includes a holding unit 81, a driving unit 82, an upper slurry tank 83, a lower slurry tank 88, a pump 90, fans 91 and 92, and a control unit 94. The holding unit 81 holds the element body 60 so that the longitudinal direction of the element body 60 is along the X-axis direction. The driving unit 82 includes an X-axis motor and a movement mechanism that moves the holding unit 81 in the X-axis direction as the X-axis motor rotates. The driving unit 82 also includes a position sensor that detects the position of the holding unit 81 in the X-axis direction.

[0036] The upper slurry tank 83 stores the slurry and drops the slurry as a slurry flow 85 downward in the Z-axis direction through a rectangular slit 84 formed in the bottom. The length of the slurry flow 85 in the X-axis direction is shorter than the length of a predetermined region of the element body 60 in the X-axis direction. The length of the slurry flow 85 in the Y-axis direction is longer than the length of the element body 60 in the Y-axis direction. The speed of the slurry flow 85 can be adjusted by the depth of the slurry in the upper slurry tank 83 and the distance from the slit 83 to the element body 60 (the position of the holding unit 81 in the Z-axis direction). The speed of the slurry flow 85 may be increased by applying positive pressure to the slurry in the upper slurry tank 83 or decreased by applying negative pressure. The upper slurry tank 83 may be provided with a valve capable of closing the slit 84. The slurry contains the material of the porous protective layer 76, a solvent, a binder (sintering aid), a pore-forming material, etc. Examples of materials for the porous protective layer 76 include at least some of alumina, zirconia, spinel, cordierite, titania, and magnesia. Examples of solvents include organic solvents such as acetone and inorganic solvents such as water. Examples of binders include silicon dioxide and calcium carbonate. Examples of pore-forming materials that disappear during sintering include theobromine and acrylic resin. The particle size and amount of the pore-forming material are determined based on, for example, the desired porosity of the porous protective layer 76.

[0037] The lower slurry tank 88 is disposed below the upper slurry tank 83 and stores the slurry. The pump 90 pumps the slurry in the lower slurry tank 88 to the upper slurry tank 83. As a result, the slurry that falls from the upper slurry tank 83 and reaches the lower slurry tank 88 can be returned to the upper slurry tank 83 and reused as the slurry flow 85. As a result, the slurry can be used effectively. The blower 91 is disposed on the left side of the slurry flow 85 in the X-axis direction and blows hot air to a first predetermined range. The blower 92 is disposed on the right side of the slurry flow 85 in the X-axis direction and blows hot air to a second predetermined range. The first predetermined range and the second predetermined range will be described later.

[0038] The control unit 94 includes a microprocessor having a CPU, a memory unit, etc. The control unit 94 receives an input of the position of the holder 81 in the X-axis direction from the position sensor of the drive unit 82. The control unit 94 controls the position and movement of the holder 81 by controlling the drive unit 82. The control unit 94 controls the pump 90 and also controls the blowers 91 and 92.

[0039] FIG. 6 is an explanatory diagram showing an example of step S110. In step S110, first, as shown in FIG. 6(a), the element body 60 is positioned on the right side of the slurry flow 85 in the X-axis direction, and the element body 60 is held by the holder 81 so that the fifth surface 60e (front end surface) of the element body 60 faces the slurry flow 85 (left side in the X-axis direction) and the longitudinal direction of the element body 60 is horizontal. Note that the orientation of the element body 60 is not limited to the horizontal direction, as long as the longitudinal direction of the element body 60 is inclined with respect to the flow direction (falling direction) of the slurry flow. Hereinafter, movement of the element body 60 toward the front end side (movement toward the left side in the X-axis direction) is referred to as forward movement, and movement toward the rear end side (movement toward the right side in the X-axis direction) is referred to as backward movement.

[0040] 6(b), the control unit 94 controls the driving unit 82 to move the element body 60 forward by moving the holding unit 81, so that a part of the predetermined region of the element body 60 (including the front end of the predetermined region) enters the slurry flow 85. As a result, the pre-fired slurry 77 adheres to a part of the predetermined region of the element body 60.

[0041] Then, as shown in FIG. 6(c), the control unit 94 controls the drive unit 82 to move the holding unit 81 to further advance the element body 60 and expose the front end side of the pre-fired slurry 77 from the slurry flow 85, and also controls the blower 91 to blow hot air onto the front end exposed portion of the pre-fired slurry 77, which is the portion of the pre-fired slurry 77 exposed from the slurry flow 85, to dry the front end exposed portion. Here, the periphery of the front end exposed portion corresponds to the first predetermined range described above. The longitudinal length of the front end exposed portion may be 10% or more of the final longitudinal length of the pre-fired slurry 77 after completion of step S110 (see FIG. 6(e)).

[0042] Thereafter, as shown in FIG. 6(d), the control unit 94 moves the holding unit 81 to move the element body 60 backward, returning the front-end exposed portion into the slurry flow 85 and controlling the drive unit 82 to expose the rear end side of the pre-fired slurry 77 from the slurry flow 85, and also controls the blower 92 to blow hot air onto the rear-end exposed portion, which is the portion of the pre-fired slurry 77 exposed from the slurry flow 85, to dry it. Here, the periphery of the rear-end exposed portion corresponds to the second predetermined range described above. The longitudinal length of the rear-end exposed portion may be 10% or more of the final longitudinal length of the pre-fired slurry 77 after completion of step S110 (see FIG. 6(e)). In Figures 6(c) and 6(d), by applying warm air to the front end exposed portion and the rear end exposed portion to dry them, the time required to dry the front end exposed portion and the rear end exposed portion can be shortened compared to when the front end exposed portion and the rear end exposed portion are allowed to dry naturally.

[0043] The control unit 94 performs a set of processes, each of which involves exposing and drying the front end side of the pre-firing slurry 77 shown in FIG. 6(c) and exposing and drying the rear end side of the pre-firing slurry 77 shown in FIG. 6(d), a predetermined number of times, and then controls the driving unit 82 to move the holding unit 81 to move the element body 60 backward, as shown in FIG. 6(e), to expose the entire pre-firing slurry 77 from the slurry flow 85. Here, the predetermined number of times is determined based on the desired film thickness of the pre-firing slurry 77, and may be one or more times. By adhering the pre-firing slurry 77 to a predetermined region of the element body 60 in this manner, it is possible to prevent the front and rear end sides of the pre-firing slurry 77 (see the dashed lines in FIG. 6(e)) from becoming partially thin.

[0044] Step S120 will be described. In step S120, the pre-firing slurry 77 attached to a predetermined region of the element body 60 is dried. In this embodiment, the element body 60 is arranged so that one of the front end side and the rear end side of the pre-firing slurry 77 is on the lower side and the other is on the upper side, and the pre-firing slurry 77 is dried. This makes it possible to further prevent the film thickness of the lower one of the front end side and the rear end side of the pre-firing slurry 77 from becoming thin due to movement of the pre-firing slurry 77 due to its own weight. In step S120, the pre-firing slurry 77 may be dried by applying hot air, by irradiating it with infrared rays, or by natural drying.

[0045] Step S130 will be described. In step S130, the pre-fired slurry 77 that has adhered to a predetermined region of the element body 60 and dried is fired at a predetermined firing temperature. As a result, the pre-fired slurry 77 is sintered to form the porous protective layer 76, and the sensor element 20 is obtained. As described above, by preventing the front and rear end sides of the pre-fired slurry 77 from becoming partially thin, it is possible to prevent the front and rear end sides of the porous protective layer 76 from becoming partially thin. As a result, it is possible to prevent a decrease in the water resistance of the front and rear end sides of the porous protective layer 76.

[0046] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. In this embodiment, the element body 60 corresponds to the element body, the porous protective layer 76 corresponds to the porous protective layer, step S100 corresponds to the first step, step S110 corresponds to the second step, and step S120 corresponds to the third step. Furthermore, the slurry deposition device 80 corresponds to the slurry deposition device, the holding unit 81 corresponds to the holding unit, the driving unit 82 corresponds to the driving unit, and the control unit 94 corresponds to the control unit.

[0047] According to the manufacturing method of the sensor element 20 of this embodiment described above in detail, the pre-firing slurry 77, which is a slurry that will become the porous protective layer 76 after firing, is applied to a predetermined region of the fired element body 60. In this case, the pre-firing slurry 77 is applied to at least a part of the predetermined region of the element body 60 using a slurry flow 85 flowing from above to below, and then the front end side or the rear end side of the pre-firing slurry 77 is exposed from the slurry flow 85 to dry the exposed portion (the front end side exposed portion or the rear end side exposed portion), and the exposed portion is returned to the slurry flow 85 to apply the pre-firing slurry 77 to at least a part of the predetermined region. This makes it possible to prevent the front end side and the rear end side of the pre-firing slurry 77, and therefore the front end side and the rear end side of the porous protective layer 76, from becoming partially thin.

[0048] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0049] For example, in the above-described embodiment, the fired element body 60 is prepared in step S100, and the pre-fired slurry 77 is fired in step S120 to obtain the sensor element 20. However, the present invention is not limited to this. For example, the pre-fired element body 60 may be prepared in step S100, and the element body 60 and the pre-fired slurry 77 may be fired together in step S120 to obtain the sensor element 20.

[0050] In the embodiment described above, in step S110, as shown in Fig. 6(b), the element body 60 is moved forward to cause a part of the predetermined region of the element body 60 (including the front end of the predetermined region) to enter the slurry flow 85. However, the present invention is not limited to this. For example, a valve capable of closing the slit 84 may be provided in the upper slurry tank 83 of the slurry deposition device 80, and the element body 60 may be placed in the state shown in Fig. 6(b) and then the valve may be opened to allow the slurry flow 85 to hit a part of the predetermined region of the element body 60.

[0051] In the embodiment described above, in step S110, as shown in Fig. 6(c), hot air is blown onto the front-end exposed portion by air blower 91 to dry the front-end exposed portion, and as shown in Fig. 6(d), hot air is blown onto the rear-end exposed portion by air blower 92 to dry the rear-end exposed portion, but this is not limiting. For example, the front-end exposed portion and / or the rear-end exposed portion may be dried by irradiating them with infrared rays, or the front-end exposed portion and / or the rear-end exposed portion may be allowed to dry naturally.

[0052] In the above-described embodiment, in step S110, the element body 60 is moved forward and backward to deposit the pre-fired slurry 77 on a predetermined region of the element body 60, as shown in FIGS. 6(b) to 6(e). However, this is not limiting. For example, in addition to moving the element body 60 forward and backward, the element body 60 may be rotated about an axis extending in the longitudinal direction (front-rear direction) to deposit the pre-fired slurry 77 on a predetermined region of the element body 60. In this way, the upper side of the element body 60 (the upstream side of the slurry flow 85) switches between the first surface 60a, the third surface 60c, the second surface 60b, and the fourth surface 60d, or vice versa, thereby allowing the pre-fired slurry 77 to be more uniformly deposited on the first to fourth surfaces 60a to 60d of the element body 60. Alternatively, the element body 60 may be moved forward or backward with a certain surface (for example, the first surface 60a) of the element body 60 facing upward to deposit the pre-fired slurry 77 on a predetermined area of ​​the element body 60, and then the element body 60 may be moved forward or backward with a surface other than the certain surface (for example, the second surface 60b) facing upward to deposit the pre-fired slurry 77 on a predetermined area of ​​the element body 60.

[0053] Although not described in the above-described embodiment, in step S110, the element body 60 may be arranged so that the side with the smallest area among the four side surfaces of the element body 60, i.e., the first to fourth surfaces 60a to 60d, is on the upper side. For example, if the element body 60 has a rectangular parallelepiped shape and is ordered in order of length in the front-to-rear direction, length in the left-to-right direction (width), and length in the up-to-down direction (thickness), the element body 60 may be arranged so that the third surface 60c or the fourth surface 60c is on the upper side. This allows the pre-sintering slurry 77 to adhere more sufficiently to the first surface 60a and the second surface 60b.

[0054] In the embodiment described above, in step S110, a process of exposing the front end side of the pre-firing slurry 77 and drying the exposed front end side portion, and a process of exposing the rear end side of the pre-firing slurry 77 and drying the exposed rear end side portion are performed. However, only one of these processes may be performed. In this case, it is preferable to perform the process of exposing and drying the front end side or rear end side of the pre-firing slurry 77, whichever will be the upper side in the third step, at least once. This makes it possible to prevent the film thickness of the front end side or rear end side of the pre-firing slurry 77, which will be the upper side in the third step, from becoming thin.

[0055] In the embodiment described above, in step S110, a process of exposing the front end side of the pre-firing slurry 77 and drying the exposed front end side portion, and a process of exposing the rear end side of the pre-firing slurry 77 and drying the exposed rear end side portion are performed, but at this time, the degree of drying of the front end side or the rear end side of the pre-firing slurry 77, whichever is upper in the third step, when exposed from the slurry flow 85, may be greater than the degree of drying of the rear end side of the pre-firing slurry 77, whichever is lower in the third step, when exposed from the slurry flow 85. This makes it possible to prevent the film thickness of the front end side or the rear end side of the pre-firing slurry 77, whichever is upper in the third step, from becoming thin. Here, examples of methods for adjusting the degree of drying include a method of adjusting the exposure time of the front end side and rear end side of the pre-calcination slurry 77, i.e., the drying time of the front end side exposed portion and the rear end side exposed portion; a method of adjusting the number of times the front end side and rear end side of the pre-calcination slurry 77 are exposed, i.e., the number of times the front end side exposed portion and the rear end side exposed portion are dried; and a method of drying one of the front end side exposed portion and the rear end side exposed portion with hot air and allowing the other to dry naturally.

[0056] In the above-described embodiment, the slurry deposition device 80 uses the pump 90 to pump the slurry in the lower slurry tank 88 to the upper slurry tank 83 for reuse in the slurry flow 85, but is not limited to this. For example, the slurry deposition device 80 does not need to be equipped with the pump 90. In this case, an operator or the like may transfer the slurry in the lower slurry tank 88 to the upper slurry tank 83, or a slurry different from the slurry in the lower slurry tank 88 may be supplied to the upper slurry tank 83.

[0057] In the above-described embodiment, the slurry deposition device 80 uses the pump 90 to pump the slurry in the lower slurry tank 88 into the upper slurry tank 83 for reuse in the slurry flow 85. In this case, however, the viscosity of the slurry may be adjusted before reuse in the slurry flow 85. This is because, when the slurry is used as the slurry flow 85, the viscosity of the slurry may change when it comes into contact with air. One method for adjusting the viscosity of the slurry is, for example, to add a solvent.

[0058] In the above-described embodiment, the element body 60 has a rectangular parallelepiped shape, but is not limited to this. For example, the element body 60 may have a cylindrical or columnar shape. In this case, the element body 60 has only one side surface. [Industrial Applicability]

[0059] The present invention can be used in the manufacturing industry of sensor elements for detecting the concentration of a specific gas such as NOx in a measurement gas such as exhaust gas from an internal combustion engine. [Explanation of symbols]

[0060] 20 sensor element, 60 element body, 60a first surface, 60b second surface, 60c third surface, 60d fourth surface, 60e fifth surface, 60f sixth surface, 61 measured gas inlet, 62 reference gas inlet, 63 detection unit, 64 outer electrode, 65 inner main pump electrode, 66 inner auxiliary pump electrode, 67 measurement electrode, 68 reference electrode, 69 heater, 71 upper connector electrode, 72 lower connector electrode, 75 outer lead portion, 76 porous protective layer, 77 pre-fired slurry, 80 slurry deposition device, 81 holding unit, 82 drive unit, 83 upper slurry tank, 84 slit, 85 slurry flow, 88 lower slurry tank, 90 pump, 91, 92 blower, 94 control unit.

Claims

1. A method for manufacturing a sensor element comprising: an element body having a front end and a rear end which are both ends along a longitudinal direction and a side surface which is a surface along the longitudinal direction, the front end side being exposed to a gas to be measured; and a porous protective layer covering a predetermined region around the front end of the element body, a first step of preparing the element body before or after firing; a second step of applying a pre-fired slurry to the predetermined region of the element body, the pre-fired slurry being a slurry that will become the porous protective layer after firing; Including, The second step comprises: After performing a first process of depositing the pre-fired slurry onto at least a part of the predetermined region of the element body using a slurry flow flowing from above to below, a second process of exposing a front end side or a rear end side of the pre-fired slurry from the slurry flow, drying the exposed portion, and returning the exposed portion to the slurry flow to adhere the pre-fired slurry to at least a part of the predetermined region, is performed at least once; A method for manufacturing a sensor element.

2. A method for manufacturing the sensor element according to claim 1, The second treatment is drying the exposed portion by applying hot air or infrared radiation to the exposed portion. A method for manufacturing a sensor element.

3. A method for manufacturing the sensor element according to claim 1 or 2, the length of the exposed portion in the longitudinal direction per one second treatment is 10% or more of the length of the pre-fired slurry after completion of the second step; A method for manufacturing a sensor element.

4. A method for manufacturing the sensor element according to claim 1 or 2, The second step includes rotating the element body around an axis extending in the longitudinal direction. A method for manufacturing a sensor element.

5. A method for manufacturing the sensor element according to claim 1 or 2, the element body has a rectangular parallelepiped shape and has four of the side surfaces; the second step is to arrange the element body so that the side surface having the smallest area among the four side surfaces is on the upper side; A method for manufacturing a sensor element.

6. A method for manufacturing the sensor element according to claim 1 or 2, The first treatment is to cause at least a part of the predetermined region of the element body to enter into the slurry flow, thereby causing the pre-fired slurry to adhere to at least a part of the predetermined region, or to cause the slurry flow to hit the element body in a state in which the longitudinal direction is inclined with respect to the flow direction of the slurry flow, thereby causing the pre-fired slurry to adhere to at least a part of the predetermined region. A method for manufacturing a sensor element.

7. A method for manufacturing the sensor element according to claim 1 or 2, a third step of, after the second step, disposing the element body so that one of the front end side and the rear end side of the pre-sintering slurry is on the lower side and the other is on the upper side, and drying the pre-sintering slurry; In the second treatment, one of the front end side and the rear end side of the pre-fired slurry, which will be the upper side in the third step, is exposed and dried at least once. A method for manufacturing a sensor element.

8. A method for manufacturing a sensor element according to claim 7, In the second treatment, the degree of drying of the front end side or the rear end side of the pre-fired slurry when exposed from the slurry flow, whichever is on the upper side in the third step, is made greater than the degree of drying of the rear end side when exposed from the slurry flow, whichever is on the lower side in the third step. A method for manufacturing a sensor element.

9. A method for manufacturing a sensor element according to claim 8, The degree of drying is the drying time or the number of drying times. A method for manufacturing a sensor element.

10. A method for manufacturing the sensor element according to claim 1 or 2, In the second step, the slurry that falls from the slurry flow without adhering to the element body is circulated above the element body and reused in the slurry flow. A method for manufacturing a sensor element.

11. A method for manufacturing a sensor element according to claim 10, In the second step, the viscosity of the slurry that has fallen from the slurry flow without adhering to the element body is adjusted, and then the slurry is reused in the slurry flow. A method for manufacturing a sensor element.

12. A sensor element includes an element body having a front end and a rear end that are both ends along a longitudinal direction and a side surface that is a surface along the longitudinal direction, the front end side being exposed to a gas to be measured, and a porous protective layer that covers a predetermined region around the front end of the element body. The slurry deposition device deposits a pre-fired slurry, which becomes the porous protective layer after firing, onto the predetermined region of the element body, a holding part that holds the element body before or after firing; a drive unit that moves the holding unit; a control unit that controls the drive unit; Equipped with The control unit a first process for controlling the driving unit to move the holding unit while the holding unit is holding the element body, so that at least a part of the predetermined region of the element body enters the slurry flow and the pre-fired slurry adheres to at least a part of the predetermined region; a second process of controlling the driving unit at least once so as to expose a front end side or a rear end side of the pre-fired slurry from the slurry flow by moving the holding unit, dry the exposed portion, and then return the exposed portion into the slurry flow to adhere the pre-fired slurry to at least a part of the predetermined region; Slurry deposition device.

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