JP7152964B2 - Method for manufacturing gas sensor element - Google Patents

Description

The present invention relates to a method of manufacturing a gas sensor element.

A gas sensor for detecting the concentration of a specific component (such as oxygen) contained in the exhaust gas of an internal combustion engine is known. This type of gas sensor has an elongated plate-shaped gas sensor element inside. A detection part for detecting a specific component is provided at the tip of the gas sensor element. The detection section is composed of an electrode or the like, and the tip of the gas sensor element provided with such a detection section is exposed to the exhaust gas.

Exhaust gas contains poisonous substances such as silicon and phosphorus in addition to specific components, and such poisonous substances may adhere to the tip (detection part, etc.) of the gas sensor element. there were. In addition, the exhaust gas contains moisture, and such moisture and moisture such as condensed water in the exhaust pipe may adhere to the tip of the gas sensor element. If moisture adheres to the gas sensor element, damage such as cracks may occur in the gas sensor element. For this reason, a porous protective layer is formed at the tip of a conventional gas sensor element to suppress the adhesion of poisonous substances and the contact of moisture (water droplets). The porous protective layer is formed so as to cover the sensing portion at the tip of the gas sensor element.

As a conventional technique for forming such a porous protective layer on a gas sensor element, for example, a method of immersing the gas sensor element in slurry for the porous protective layer is known (see Patent Document 1). In this type of method, the tip of the gas sensor element is immersed in the slurry so that the slurry adheres to the tip. After that, by baking the deposited slurry, a porous protective layer is formed on the tip of the gas sensor element.

JP 2017-203716 A

In the method of immersing the gas sensor element in the slurry as described above, it is difficult to control the thickness of the porous protective layer, which poses a problem. For example, corners of the gas sensor element are portions to which slurry is less likely to adhere than other portions. Slurry more than necessary adheres to most of the parts. Firing the slurry in such a state results in the formation of a porous protective layer having a large thickness (volume). In this case, the heat capacity of the porous protective layer becomes too large, and activation of the gas sensor element by heating is delayed. Therefore, in the above-described prior art, in order to reduce the thickness of the porous protective layer, after firing, the surplus portion around the porous protective layer is cut with a cutter or the like. However, since the surplus portion cut after firing is discarded, there is also a problem that the disposal cost and man-hours for cutting increase.

An object of the present invention is to provide a method for manufacturing a gas sensor element that can adjust the thickness of a coating film made of the slurry to be small after the gas sensor element is immersed in slurry for a porous protective layer and before firing. is.

Means for solving the above problems are as follows. Namely
<1> A method for manufacturing a gas sensor element in which a detection portion disposed on the tip side of a gas sensor element extending in the axial direction is covered with a porous protective layer, wherein the tip side of the gas sensor element is used for forming a porous protective layer. an immersion step of forming a coating film of the slurry on the tip surface and the peripheral surface of the gas sensor element by immersing it in the slurry of; a scraping step of scraping off the coating film to remove a part of the coating film; and a baking step of baking the coating film after the scraping step to obtain the porous protective layer.

<2> The immersion step is performed multiple times before the baking step, and includes a drying step of drying the coating film between the previously performed immersion step and the subsequent immersion step. A method for manufacturing the gas sensor element according to claim 1 .

<3> In the scraping step, the gas sensor element is passed through a through-hole provided inside the scraping die, and an excess coating film of the peripheral surface coating film formed on the peripheral surface is exposed to the opening of the through-hole. 3. The method of manufacturing a gas sensor element according to claim 1, wherein the edge is abraded.

<4> In the scraping step, an excess coating film of the tip coating film formed on the tip surface is scraped off by a scraping blade that moves along a direction perpendicular to the axial direction. A method for manufacturing the gas sensor element according to claim 3 .

<5> Any one of claims 1 to 4, wherein the slurry has a shear rate of 43,000 mPa·s or more at a shear rate of 0.1 s ⁻¹ and a shear rate of 2,500 mPa·s or less at a shear rate of 10 s ⁻¹ . 10. A method for manufacturing the gas sensor element according to claim 1.

According to the present invention, there is provided a method for manufacturing a gas sensor element that can adjust the thickness of a coating film made of the slurry to be small after the gas sensor element is immersed in slurry for a porous protective layer and before firing. can be done.

Sectional view of the gas sensor according to the first embodiment cut along the axial direction FIG. 2 is an exploded perspective view schematically showing a detection element section and a heater section that constitute a gas sensor element; FIG. 2 is a cross-sectional view schematically showing the configuration of the tip side of the gas sensor element cut along the axial direction; FIG. 2 is a cross-sectional view schematically showing the configuration of the tip side of the gas sensor element cut in a direction orthogonal to the axial direction; Perspective view of the main body of the gas sensor element seen from the tip side Explanatory drawing showing a state in which the main body of the gas sensor element is waiting above the dipping tank in the dipping process. Top view of scraping type FIG. 6 is an explanatory view showing a state in which the tip of the gas sensor element main body lowered from the standby position is immersed in the slurry in the dipping tank in the immersion step; FIG. 10 is an explanatory view showing how a part of the peripheral surface coating (excess coating) formed on the peripheral surface of the tip portion of the gas sensor element body is removed using a scraping die in the scraping step; FIG. 6 is an explanatory view showing how a part of the tip coating (excess coating) formed on the tip surface of the tip of the gas sensor element main body is removed by using the scraping blade in the scraping step; Explanatory drawing showing how the scraping blade is returned to the retracted position after the scraping process. FIG. 8 is an explanatory view showing a state in which the gas sensor element main body is waiting above the dipping tank in the dipping step in the method for manufacturing the gas sensor element of Embodiment 2; In the scraping step in the method for manufacturing the gas sensor element of Embodiment 2, a scraping blade is used to remove part of the tip coating (excess coating) formed on the tip surface of the tip of the gas sensor element main body. Explanatory diagram showing the situation FIG. 11 is a cross-sectional view schematically showing the configuration of the distal end side of the gas sensor element according to Embodiment 3 cut along the axial direction; FIG. 11 is an explanatory view showing a state in which the gas sensor element main body is waiting above the dipping tank in the dipping step in the method for manufacturing the gas sensor element of Embodiment 3;

<Embodiment 1>
Embodiment 1 of the present invention will be described below with reference to FIGS. 1 to 11. FIG. First, the configuration of a gas sensor (oxygen sensor) 1 including a gas sensor element 100 manufactured by the method for manufacturing a gas sensor element according to this embodiment will be described. FIG. 1 is a cross-sectional view of the gas sensor 1 according to Embodiment 1 cut along the direction of the axis L, and FIG. It is an exploded perspective view. In this specification, the lower side of the gas sensor 1 shown in FIG. 1 is called "front end side", and the opposite side (upper side in FIG. 1) is called "rear end side".

As shown in FIG. 1, the gas sensor 1 includes a gas sensor element 100 composed of a laminate of a detection element section 300 and a heater section 200, a metal shell 30 for holding the gas sensor element 100 and the like in a manner to accommodate them, and A protector 24 attached to the tip of the metal shell 30 is provided. The gas sensor element 100 has an elongated plate shape as a whole, and is arranged such that its longitudinal direction is along the axis L direction. As will be described later, a porous protective layer 20 is formed on the tip side of the gas sensor element 100 .

As shown in FIG. 2, the heater section 200 has an elongated plate-like shape as a whole, and includes a first substrate 101 and a second substrate 103 mainly made of alumina, and a first substrate 101 and a second substrate. It is sandwiched between two substrates 103 and has a heating element 102 mainly made of platinum. The heating element 102 has a heating portion 102a located on the tip side and a pair of heater lead portions 102b extending from the heating portion 102a along the longitudinal direction (axis L direction) of the first substrate 101. As shown in FIG. The end of the heater lead portion 102b is electrically connected to the heater-side pad 120 via a conductor formed in the heater-side through-hole 101a provided in the first substrate 101. As shown in FIG.

As with the heater section 200 , the detection element section 300 has an elongated plate shape as a whole, and includes an oxygen concentration detection cell 130 and an oxygen pump cell 140 . The oxygen concentration detection cell 130 is composed of a first solid electrolyte body 105 and a first electrode 104 and a second electrode 106 formed on both sides of the first solid electrolyte body 105 . The first electrode 104 is composed of a first electrode portion 104a and a first lead portion 104b extending from the first electrode portion 104a along the longitudinal direction (axis L direction) of the first solid electrolyte body 105. As shown in FIG. The second electrode 106 is composed of a second electrode portion 106a and a second lead portion 106b extending from the second electrode portion 106a along the longitudinal direction of the first solid electrolyte body 105 (the direction of the axis L).

The ends of the first lead portions 104b are connected to a first through-hole 105a provided in the first solid electrolyte body 105, a second through-hole 107a provided in the insulating layer 107, which will be described later, and a fourth through-hole 107a provided in the second solid electrolyte body 109. The hole 109 a and the sixth through hole 111 a provided in the protective layer 111 are electrically connected to the detection element side pad 121 via conductors formed respectively. The ends of the second lead portion 106b are connected to a third through hole 107b provided in the insulating layer 107, a fifth through hole 109b provided in the second solid electrolyte body 109, and a seventh through hole 111b provided in the protective layer 111, which will be described later. They are electrically connected to the detection element side pads 121 via conductors formed respectively.

The oxygen pump cell 140 is composed of a second solid electrolyte body 109 and a third electrode 108 and a fourth electrode 110 formed on both sides of the second solid electrolyte body 109 . The third electrode 108 is composed of a third electrode portion 108a and a third lead portion 108b extending from the third electrode portion 108a along the longitudinal direction (axis L direction) of the second solid electrolyte body 109. As shown in FIG. The fourth electrode 110 is composed of a fourth electrode portion 110a and a fourth lead portion 110b extending from the fourth electrode portion 110a along the longitudinal direction of the second solid electrolyte body 109 (axis L direction).

The end of the third lead portion 108b is connected to the detecting element side pad 121 via conductors formed in the fifth through hole 109b provided in the second solid electrolyte body 109 and the seventh through hole 111b provided in the protective layer 111, respectively. is electrically connected to The end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in the eighth through hole 111c provided in the protective layer 111. FIG. The second lead portion 106b and the third lead portion 108b are at the same potential.

The first solid electrolyte body 105 and the second solid electrolyte body 109 are partially stabilized zirconia sintered bodies obtained by adding yttria (Y ₂ O ₃ ) or calcia (CaO) as a stabilizer to zirconia (ZrO ₂ ). Configured.

The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater-side pad 120, and the detection element-side pad 121 can be made of platinum group elements. Suitable platinum group elements forming these include Pt, Rh, Pd, and the like. In addition, you may use these platinum group elements individually or in combination of 2 or more types.

From the viewpoint of heat resistance and oxidation resistance, the heating element 102 and the like are preferably made mainly of Pt. In addition, the heating element 102 and the like preferably contain a ceramic component in addition to the platinum group element as the main component. From the viewpoint of fixation, this ceramic component is preferably the same component as the main material on the laminated side.

An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130 described above. The insulating layer 107 is composed of an insulating portion 114 and a diffusion resistance portion 115 . A hollow measurement chamber 107c is formed in the insulating portion 114 of the insulating layer 107 at a position corresponding to the second electrode portion 106a and the third electrode portion 108a. This measurement chamber 107c communicates with the outside in the width direction of the insulating layer 107, and a diffusion resistance portion for realizing gas diffusion between the outside and the measurement chamber 107c under a predetermined rate-determining condition is provided in the communicating portion. 115 are arranged.

The insulating part 114 is not limited as long as it is a ceramic sintered body having insulating properties, and is made of, for example, an oxide-based ceramic such as alumina or mullite.

The diffusion resistance section 115 is a porous body made of alumina, and the diffusion resistance section 115 made of this porous body adjusts the velocity of the detection gas flowing into the measurement chamber 107c.

A protective layer 111 is formed on the surface of the second solid electrolyte body 109 so as to sandwich the fourth electrode 110 therebetween. The protective layer 111 sandwiches the fourth electrode portion 110a, a porous electrode protection portion 113a for protecting the fourth electrode portion 110a from poisoning, and the fourth lead portion 110b. and a reinforcing portion 112 for protecting the second solid electrolyte body 109 . It should be noted that the gas sensor element 100 of the present embodiment is designed so that the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 has a predetermined value (for example, 450 mV). The direction and size are adjusted, and the oxygen sensor element linearly detects the oxygen concentration in the gas to be measured according to the current flowing through the oxygen pump cell 140 .

Returning to FIG. 1, the metal shell 30 is made of SUS430, and has a male threaded portion 31 for attaching the gas sensor 1 to an exhaust pipe, and a hexagonal portion 32 to which an attachment tool is applied during attachment. The metal shell 30 is provided with a metal fitting side stepped portion 33 projecting radially inward, and the metal fitting side stepped portion 33 supports a metal holder 34 for holding the gas sensor element 100 . . Inside the metal holder 34, a ceramic holder 35 and a talc 36 are arranged in order from the tip side. This talc 36 consists of a first talc 37 arranged in the metal holder 34 and a second talc 38 arranged at the rear end of the metal holder 34 . The gas sensor element 100 is fixed to the metal holder 34 by compressing and filling the first talc 37 in the metal holder 34 . In addition, since the second talc 38 is compressed and filled in the metal shell 30 , sealing between the outer surface of the gas sensor element 100 and the inner surface of the metal shell 30 is ensured. A sleeve 39 made of alumina is arranged on the rear end side of the second talc 38 . This sleeve 39 is formed in a multistage cylindrical shape, and is provided with a shaft hole 39a along the axis L, and the gas sensor element 100 is inserted through the sleeve 39 including the shaft hole 39a. A crimping portion 30a on the rear end side of the metal shell 30 is bent inward, and the crimping portion 30a allows the sleeve 39 to move toward the front end of the metal shell 30 via a ring member 40 made of stainless steel. is pressed by

A protector 24 made of metal is attached to the outer circumference of the metal shell 30 on the front end side by welding. The protector 24 has a double structure, and an outer protector 41 having a uniform outer diameter and having a bottomed cylindrical shape is arranged on the outer side, and an inner outer protector 41 having a rear end portion 42a whose outer diameter is the outer diameter of the tip portion 42b. A bottomed cylindrical inner protector 42 formed to be larger than the diameter is arranged. Such a protector 24 covers the tip of the gas sensor element 100 protruding from the tip of the metallic shell 30 and has a plurality of gas intake holes 24a.

The front end side of an outer cylinder 25 made of SUS430 is inserted into the rear end side of the metallic shell 30 . The outer cylinder 25 has a distal end portion 25a with an enlarged diameter on the distal end side, and the distal end portion 25a is fixed to the metal shell 30 by laser welding or the like. A separator 50 is arranged inside the rear end side of the outer cylinder 25 , and a holding member 51 is interposed in a gap formed between the separator 50 and the outer cylinder 25 . The holding member 51 is fixed between the caulked outer cylinder 25 and the separator 50 while engaging with the protruding portion 50a rising outward from the peripheral surface of the separator 50 .

Further, through holes 50b for inserting various lead wires 11, 12 and 13 for the detection element section 300 and the heater section 200 are provided in the separator 50 so as to penetrate from the front end side to the rear end side. It is For convenience of explanation, only three lead wires 11, 12, and 13 are shown in FIG. 1, and illustration of other lead wires is omitted. Connection terminals 16 for connecting the lead wires 11 and the like to the detection element side pads 121 of the detection element section 300 and the heater side pads 120 of the heater section 200 are accommodated in the through holes 50b. Each lead wire 11 and the like is configured to be externally connectable to a connector (not shown), and electrical signals are input between an external device such as an ECU and each lead wire 11 and the like via such a connector. Output is done.

Further, on the rear end side of the separator 50, a substantially cylindrical rubber cap 52 for closing the rear end side opening 25b of the outer cylinder 25 is arranged. The rubber cap 52 is fixed to the outer cylinder 25 by crimping the outer cylinder 25 radially inward while being accommodated in the rear end of the outer cylinder 25 . The rubber cap 52 is also provided with through holes 52a for inserting the lead wires 11 and the like so as to penetrate from the front end side to the rear end side.

3 is a cross-sectional view schematically showing the configuration of the tip side of the gas sensor element 100 cut along the direction of the axis L, and FIG. 4 is a cross-sectional view of the gas sensor element 100 cut in a direction orthogonal to the direction of the axis L. Fig. 2 is a cross-sectional view schematically showing the configuration of the distal end side of the. As shown in FIGS. 3 and 4, a porous protective layer 20 is formed on the tip side of the gas sensor element 100 . In this specification, the gas sensor element 100 in which the porous protective layer 20 is not formed may be particularly referred to as "gas sensor element main body 100a".

A detection unit 150 for detecting a specific component (such as oxygen) contained in the exhaust gas is provided at the tip portion 100b of the gas sensor element main body 100a. The detection section 150 is mainly composed of each electrode section (the first electrode section 104a, the second electrode section 106a, the third electrode section 108a, and the fourth electrode section 110a) of the detection element section 300, and the measurement chamber 107c. be. A porous protective layer 20 is formed on the tip portion 100b of the gas sensor element main body 100a so as to cover the periphery of such a detection portion 150. As shown in FIG. The porous protective layer 20 is formed with pores having a three-dimensional network structure so as to allow gas permeation.

FIG. 5 is a perspective view of the gas sensor element main body 100a viewed from the tip side. For convenience of explanation, the porous protective layer 20 is shown virtually in FIG. The porous protective layer 20 is formed on the tip portion 100b of the gas sensor element main body 100a so as to cover the tip surface 100c and the peripheral surface 100d of the tip portion 100b of the gas sensor element main body 100a.

The porous protective layer 20 can be formed, for example, by bonding ceramic particles of one or more selected from the group consisting of titania, alumina, spinel, zirconia, mullite, zircon and cordierite by firing or the like. By sintering a slurry containing these particles, pores can be formed between the ceramic particles. It should be noted that a burnable pore-forming material made of carbon, resin beads, organic or inorganic binders, or the like may be added to the slurry containing the particles.

The gas sensor element 100 manufactured by the manufacturing method of this embodiment is used for the gas sensor 1 as described above.

Next, a method for manufacturing the gas sensor element according to Embodiment 1 will be described. The method for manufacturing the gas sensor element of the present embodiment includes an immersion step, a scraping step, and a baking step.

In the immersion step, the tip end side of the gas sensor element main body 100a (gas sensor element 100) is immersed in the slurry S for forming the porous protective layer 20 (hereinafter simply referred to as "slurry"), so that the tip end of the gas sensor element main body 100a In this step, a coating film 700 of the slurry S is formed on the tip surface 100c and the peripheral surface 100d of the portion 100b.

Slurry S is a solution containing ceramic particles of one or more kinds, for example selected from the group consisting of titania, alumina, spinel, zirconia, mullite, zircon and cordierite, similar to those conventionally used in this type of dipping process. consists of However, the slurry S is preferably set to have a higher viscosity when the shear rate is 0.1 s ^-1 than that used conventionally, and the viscosity when the shear rate is 10 s ^-1 is set low. preferably. The viscosity (mPa s) of the slurry S is preferably set to 43000 mPa s or more when the shear rate is 0.1 s ⁻¹ under room temperature (23° C.) conditions, and the shear rate is 10 s. When ⁻¹ , it is preferably set to 2500 mPa·s or less. The ^viscosity of the slurry S is not particularly limited as long as it does not impair the purpose of the present invention. is set to 2400 mPa·s when the shear rate is 10 s ⁻¹ . When the viscosity of the slurry S is set in this way, it becomes easier to adjust the thickness of the coating film 700 made of the slurry S formed on the gas sensor element main body 100a in the scraping step, which will be described later. The viscosity of the slurry S is appropriately adjusted by adding, for example, an organic binder made of a synthetic resin or natural polymer, alumina sol, water, or the like. The viscosity of the slurry S was measured using a viscometer (Rheometer MCR102: manufactured by Anton-Paar).

Here, an example of preparation of the slurry used in the immersion step will be described. Titania powder, spinel powder, alumina sol, organic binder (e.g., acrylic copolymer), dispersant (e.g., anionic polymer dispersant), antifoaming agent (e.g., amide wax antifoaming agent), and water , are blended in predetermined proportions, and mixed for a predetermined period of time to obtain the desired slurry.

FIG. 6 is an explanatory view showing a state in which the gas sensor element main body 100a stands by above the dipping tank 400 in the dipping step. FIG. 6 shows the state of the gas sensor element main body 100a and the like before the immersion process is started. FIG. 6 shows a container-like dipping tank 400 that contains slurry S and has an upward opening, and a gas sensor element main body 100a standing by above the dipping tank 400 in a stationary state. The gas sensor element main body 100a is fixed using a predetermined jig so that its longitudinal direction is along the vertical direction and its tip portion 100b faces downward. The tip portion 100b of the gas sensor element main body 100a faces the slurry S contained in the dipping tank 400. As shown in FIG. In FIG. 6, of the surfaces of the gas sensor element main body 100a, the surface on which the electrode protection portion 113a is formed faces the front side of the paper. As shown in FIG. 6, the position where the gas sensor element main body 100a stands still above the dipping tank 400 and stands by is referred to as a "standby position".

The gas sensor element main body 100a is fixed to a predetermined jig, and along the up-down direction (vertical direction), between the standby position and the position inside the dipping bath 400 below it (immersion position described later). is configured to be able to move back and forth. The mechanism for reciprocating the gas sensor element main body 100a is not particularly limited as long as the object of the present invention is not impaired, and a known reciprocating mechanism using a servomotor or the like is applied.

As shown in FIG. 6, between the gas sensor element main body 100a at the standby position and the dipping tank 400, a scraping die 500 and a scraping blade 600 used in the scraping process performed after the dipping process are arranged. ing. FIG. 7 is a plan view of the scraping die 500. FIG. The scraping die 500 includes a plate-shaped scraping main body 501 arranged along the horizontal direction, a through hole 502 provided inside the scraping main body 501 so as to penetrate in the thickness direction, and and an opening edge 503 surrounding 502 . The sizes of the through hole 502 and the opening edge 503 are set so that the gas sensor element main body 100 a can pass through the through hole 502 in the opening edge 503 . At the standby position, the tip portion 100b of the gas sensor element main body 100a is arranged so as to be accommodated inside the opening edge portion 503 when viewed from above. FIG. 7 virtually shows the tip portion 106 of the gas sensor element main body 100a in a state of being accommodated inside the opening edge portion 503 when viewed from above. As shown in FIG. 6, the scraping blade 600 is retracted to a position outside the through hole 502 so as not to overlap the through hole 502 in the vertical direction. ”. In addition, in the case of the present embodiment, the scraping blade 600 is arranged on the upper surface 500 a side of the scraping die 500 . The scraping blade 600 is arranged at a height position such that a clearance is formed between the scraping blade 500 and the upper surface 500 a of the scraping die 500 .

FIG. 8 is an explanatory diagram showing a state in which the tip portion 100b of the gas sensor element main body 100a lowered from the standby position is immersed in the slurry in the dipping bath 400 in the immersion step. When the gas sensor element main body 100a (see FIG. 6) waiting at the standby position moves downward, the tip portion 100b passes through the through hole 502 in the opening edge portion 503 of the scraping die 500 from above to below. . At that time, the tip portion 100 b passes through the through hole 502 without contacting the opening edge portion 503 . After that, the gas sensor element main body 100 a further moves downward, and the tip portion 100 b is immersed in the slurry contained in the dipping bath 400 . The height position of the tip portion 100b immersed in the slurry is set so that it does not contact the bottom of the dipping tank 40 and the slurry evenly adheres to the tip surface 100c and the peripheral surface 100d of the tip portion 100b. . As shown in FIG. 8, the position of the gas sensor element main body 100a immersed in the slurry so that the slurry adheres to the tip surface 100c and the peripheral surface 100d is referred to as the "immersion position". The gas sensor element main body 100a may, if necessary, remain stationary at the immersion position for a predetermined time, or may be pulled up immediately after reaching the immersion position.

By dipping tip portion 100b of gas sensor element main body 100a in the slurry by such an immersion step, slurry coating 700 can be formed on tip surface 100c and peripheral surface 100d of tip portion 100b. The tip portion 100b of the gas sensor element main body 100a immersed in the slurry is then pulled up and subjected to the next scraping step.

The scraping step is a step of scraping off the coating film 700 of the slurry adhering to the tip portion 100b of the gas sensor element main body 100a to remove a part of the coating film 700. FIG. As described above, when the tip portion 100b of the gas sensor element main body 100a is pulled up from the slurry after the immersion step, the coating film 700 made of the slurry deposit is formed on the tip portion 100b. After the immersion step, if the thickness of the coating film 700 formed on the tip portion 100b exceeds the thickness required for the porous protective layer 20, the excess coating film is removed by the scraping step. be. In this specification, the thickness of the coating film 700 required as the porous protective layer 20 is referred to as "required thickness".

In this specification, of the coating film 700 adhering to the tip portion 100b after the immersion step, the coating film formed on the peripheral surface 100d of the tip portion 100b is referred to as the “peripheral coating film 701”, and the tip portion 100b The coating film formed on the tip end surface 100c of is referred to as "tip coating film 702". In the present specification, the tip coating film 702 is the coating film on the front side of the tip surface 100c of the tip portion 100b in the axial direction (the direction of the axis L).

In the scraping step of the present embodiment, of the coating film 700 adhering to the tip portion 100b, part of the peripheral surface coating film 701 formed on the peripheral surface 100d of the tip portion 100b (excess coating film) 701a is scraped off. 500 is used to remove (peripheral surface scraping step), and a portion of the tip coating 702 (excess coating) 702a formed on the tip surface 100c of the tip 100b is removed using the scraping blade 600. and a removing step (tip surface scraping step). In this embodiment, the circumferential surface scraping step is performed first, and then the tip surface scraping step is performed.

FIG. 9 shows that in the scraping step, a scraping die 500 is used to remove a portion (excess coating film) 701a of the peripheral surface coating film 701 formed on the peripheral surface 100d of the tip portion 100b of the gas sensor element main body 100a. It is an explanatory view showing a state of FIG. 9 shows the contents of the above-described peripheral surface scraping process. After the immersion step, if the peripheral coating film 701 exceeding the required thickness adheres to the tip portion 100b of the gas sensor element main body 100a that has been pulled up, the excess coating film (excess coating film) 701a is The tip 100b is scraped off by the opening edge 503 as it passes through the opening edge 503 (through hole 502) of the scraping die 500 from the lower side to the upper side. In this way, when the tip portion 100b passes through the opening edge portion 503, the excess coating film 701a is separated from the peripheral coating film 701 of the required thickness.

A part of the separated excess coating film 701a drops due to its own weight or the like and is returned into the dipping tank 400. FIG. The scraping die 500 is made of, for example, a metal plate processed into a predetermined shape. The size of the opening edge portion 503 (the size of the through hole 502) of the scraping die 500 is such that the gas sensor element main body 100a can pass therethrough and the thickness required for forming the porous protective layer 20 is sufficient as described above. A coating film 700 (peripheral coating film 701) is set to be formed around the tip portion 100b after the peripheral surface scraping process. In the case of this embodiment, the opening edge 503 has a rectangular shape in plan view, and is fixed using a fixing device (not shown). The longitudinal direction (long side direction) of the opening edge portion 503 is arranged along the short side direction (width direction) of the gas sensor element main body 100a, and the short side direction (short side direction) of the opening edge portion 503 is arranged along the gas sensor element main body. It is arranged along the thickness direction of 100a.

FIG. 10 shows that in the scraping step, a scraping blade 600 is used to remove a portion (excess coating) 702a of the tip coating 702 formed on the tip surface 100c of the tip portion 100b of the gas sensor element main body 100a. It is explanatory drawing which shows a state. FIG. 10 shows the content of the tip surface scraping process described above. After the circumferential surface scraping step, the gas sensor element main body 100a that has passed through the opening edge portion 503 of the scraping die 500 from the bottom to the upper side has the tip surface 100c of the tip portion 100b at a predetermined position for the tip surface scraping step. move upward to the predetermined height position. The predetermined height position of the tip surface 100c for the tip surface scraping step is such that the thickness of the tip coating film 702 formed on the tip surface 100c becomes the thickness necessary for the porous protective layer 20 after the tip surface scraping step. is set to In the case of this embodiment, the height position of the tip surface 100c when the step of scraping the tip surface is performed is set to be the same as the height position of the tip surface 100c of the gas sensor element main body 100a stationary at the standby position described above. It is In another embodiment, the height position of the tip face 100c when the step of scraping the tip face is performed may differ from the height position of the tip face 100c of the gas sensor element main body 100a stationary at the standby position.

FIG. 10 shows the gas sensor element main body 100a in a stationary state at the standby position. At the tip portion 100b of the gas sensor element main body 100a in this state, a coating film 700 including a peripheral coating film 701 whose thickness has been adjusted by removing an excess coating film 701a is formed. Among such coating films 700, if the tip coating film 702 formed on the tip surface 100c exceeds the required thickness, the excess coating film (excess coating film 702a) is removed by the scraping blade 600. be worn out.

The scraping blade 600 is made of, for example, a metal plate processed into a predetermined shape. The scraping blade 600 is configured using a known reciprocating mechanism or the like so that the tip portion 601 thereof can reciprocate along the horizontal direction. In the scraping step, the height position of the tip portion 601 of the scraping blade 600 and the height position of the tip portion 100b of the gas sensor element main body 100a are set so that the tip coating film 702 of the required thickness is left on the tip surface 100c. be done. In FIG. 6, the gas sensor element main body 100a is arranged such that its longitudinal direction extends along the vertical direction (vertical direction). The axial direction (the direction of the axis L) of such a gas sensor element main body 100a is along the vertical direction. Therefore, it can be said that the scraping blade 600 moves along a direction perpendicular to the axial direction of the gas sensor element main body 100a.

The scraping blade 600 is stationary at the retracted position as shown in FIG. When the gas sensor element main body 100a is returned to the standby position and stands still after the peripheral surface scraping process, the scraping blade 600 moves horizontally so as to scrape off the excess coating film 702a of the tip coating film 702. FIG. The tip 601 of the scraping blade 600 horizontally moves from the retracted position toward the sensor element main body 100a, and further moves horizontally above the opening edge 503 so as to cross the opening edge 503 in the longitudinal direction. When the scraping blade 600 horizontally moves across the opening edge 503, the tip 601 scrapes off the excess coating 702a exceeding the required thickness from the tip coating 702 of the required thickness. In this way, if the tip coating film 702 formed on the tip surface 100c exceeds the required thickness, the excess coating film (excess coating film 702a) is scraped off by the scraping blade 600. FIG.

FIG. 11 is an explanatory view showing how the scraping blade 600 is returned to the retracted position after the scraping process. After scraping off the excess coating film 702a of the tip coating film 702, the scraping blade 600 moves horizontally in a direction opposite to that during scraping so as to return to the retracted position.

Through the scraping process (peripheral surface scraping process, tip surface scraping process) as described above, the coating film 700 formed on the tip portion 100b of the gas sensor element main body 100a is adjusted so as not to be too thick. .

After the scraping process, when the coating film 700 having a sufficient thickness for forming the porous protective layer 20 is formed on the tip portion 100b of the gas sensor element main body 100a, the gas sensor element main body 100a is subjected to a firing process. .

The firing step is a step of firing the coating film 700 after the scraping step to obtain the porous protective layer 20 . Various conditions such as the firing temperature and firing time in the firing step are not particularly limited as long as the coating film 700 is sintered to obtain the porous protective layer 20, and are appropriately set according to the purpose. . The firing process is performed, for example, at 1000° C. for 3 hours.

As described above, in the method for manufacturing the gas sensor element of the present embodiment, the tip portion 100b of the gas sensor element 100 (gas sensor element main body 100a) where the detection section 150 is arranged is subjected to the immersion process, the scraping process, and the baking process. , the porous protective layer 20 can be coated, and the gas sensor element 100 (see FIGS. 3 to 5) provided with the porous protective layer 20 as described above is obtained. According to the method for manufacturing the gas sensor element of the present embodiment, the thickness of the coating film 700 made of slurry can be adjusted to a desired thickness by the scraping process before the firing process. Therefore, according to the method for manufacturing the gas sensor element of the present embodiment, it is possible to manufacture the gas sensor element 100 with a smaller volume of the entire porous protective layer 20 and a shorter active time than the conventional technique.

In addition, compared with the second embodiment described later, the scraping blade 600 is arranged on the upper surface 500a side of the scraping die 500 and separated from the upper surface 500a as in the present embodiment, and the tip surface scraping step is performed. is preferred. This is because the horizontal movement of the scraping blade 600 is less likely to be hindered due to the influence of the cured material such as the removed excess coating film 702a.

<Embodiment 2>
Next, a method for manufacturing a gas sensor element according to Embodiment 2 will be described with reference to FIGS. 12 and 13. FIG. Embodiment 2 differs from Embodiment 1 described above in the configuration and the like of the scraping blade 600A used in the scraping step (tip surface scraping step). Here, the peripheral surface scraping process of the second embodiment will be mainly described. In the subsequent embodiments such as the second embodiment, the same reference numerals are given to the same parts as those explained in the first embodiment, and the explanation thereof will be omitted.

FIG. 12 is an explanatory diagram showing a state in which the gas sensor element main body 100a stands by above the dipping tank 400 in the dipping step in the method for manufacturing the gas sensor element of the second embodiment. As shown in FIG. 12, between the gas sensor element main body 100a at the standby position and the dipping tank 400, a scraping die 500 similar to that of the first embodiment is arranged. The scraping blade 600A is made of a metal plate processed into a predetermined shape, as in the first embodiment, and is configured such that the tip portion 601A thereof can reciprocate along the horizontal direction. As shown in FIG. 12, the scraping blade 600A is retracted to a position outside the through hole 502 so as not to overlap the through hole 502 in the vertical direction. However, the scraping blade 600A of this embodiment is arranged on the lower surface 500b side of the scraping die 500, not on the upper surface 500a side, and is configured to be movable along the lower surface 500b.

FIG. 13 shows a front end coating formed on the front end surface 100c of the front end portion 100b of the gas sensor element main body 100a by using the front end coating 600A in the front end coating (peripheral surface front end) in the method of manufacturing the gas sensor element according to the second embodiment. FIG. 7 is an explanatory diagram showing how a part (excess coating film) 702a of the film 702 is removed; In the present embodiment, the same dipping process as in the first embodiment is performed, and then the gas sensor element main body 100a is lifted out of the dipping bath 400 with the slurry coating film 700 adhering to the tip portion 100b. Then, as in the first embodiment, the tip portion 100b to which the coating film 700 is attached is passed through the opening edge portion 503 (the through hole 502) of the scraping die 500 from the bottom to the top, so that the opening edge portion 503 is A part (excess coating film) 701a of the peripheral surface coating film 701 is removed by this. However, in the circumferential surface scraping step of the present embodiment, before the tip portion 100b to which the coating film 700 is adhered completely passes through the opening edge portion 503, the tip surface 100c of the tip portion 100b is removed for the tip surface scraping step. reaches a predetermined height position, the movement of the gas sensor element main body 100a is stopped.

The predetermined height position of the tip surface 100c for the tip surface scraping step is such that the thickness of the tip coating film 702 formed on the tip surface 100c becomes the thickness necessary for the porous protective layer 20 after the tip surface scraping step. is set to When the tip surface 100c stops at the predetermined height position, if part of the tip coating 702 adhering to the tip surface 100c protrudes below the lower surface 500b of the scraping die 500, the protrusion The excess coating film 702a is scraped off by the scraping blade 600A. FIG. 13 shows how the extra coating film 702a is scraped off by the tip 601A of the scraping blade 600A moving along the lower surface 500b of the scraping die 500 and removed. After the excess coating film 702a is removed by the scraping blade 600A, the scraping blade 600A is returned to the retracted position.

After the tip surface scraping process is completed, the peripheral surface scraping process is restarted, the gas sensor element main body 100a is lifted, the tip part 100b having the coating film 700 formed thereon passes through the opening edge part 503, and the gas sensor element main body 100a is ready for standby. returned to position. In this way, the scraping blade 600A may be arranged on the side of the lower surface 500b of the scraping die 500 to perform the tip surface scraping step.

<Embodiment 3>
Next, a method for manufacturing a gas sensor element according to Embodiment 3 will be described with reference to FIGS. 14 and 15. FIG. First, the configuration of the gas sensor element 100A manufactured by the method for manufacturing a gas sensor element according to this embodiment will be described. FIG. 14 is a cross-sectional view schematically showing the configuration of the distal end side of the gas sensor element 100A according to Embodiment 3 cut along the axial direction. A gas sensor element 100A of this embodiment includes a gas sensor element main body 100a having the same configuration as that of the first embodiment. The gas sensor element 100A of the present embodiment includes a porous protective layer 20A around the tip portion 100b (detection section 150) of the gas sensor element 100A, as in the first embodiment. The configuration is different from that of the first embodiment. The porous protective layer 20A is composed of the inner porous protective layer 21 formed directly on the distal end surface 100c and the peripheral surface 100d of the distal end portion 100b, and the inner porous protective layer 21 on the inner porous protective layer 21 so as to cover the inner porous protective layer 21. and an outer porous protective layer 22 formed on. In other words, the porous protective layer 20A is of a multi-layer type unlike the single-layer type of the first embodiment. The inner porous protective layer 21 of the porous protective layer 20</b>A has a lower density and a higher porosity (%) than the outer porous protective layer 22 .

The outer porous protective layer 22 can be formed using, for example, slurry similar to that of the first embodiment described above. On the other hand, the inner porous protective layer 21 is formed using another slurry (slurry for the inner porous protective layer 21) different from the slurry for the outer porous protective layer 22. As the slurry for the inner porous protective layer 21, for example, a slurry containing a larger amount of pore-forming material than the slurry for the outer porous protective layer 22 is used.

In the method for manufacturing the gas sensor element of the present embodiment, only the outermost porous protective layer 22 among the porous protective layers 20A has its thickness adjusted by the scraping process before the firing process.

FIG. 15 is an explanatory view showing a state in which the gas sensor element main body 100a stands by above the dipping tank 400 in the dipping step in the method for manufacturing the gas sensor element of the third embodiment. In the present embodiment, as shown in FIG. 15, a slurry coating 800 for the inner porous protective layer 21 is applied in advance so as to cover the front end surface 100c and the peripheral surface 100d of the front end portion 100b of the gas sensor element main body 100a. formed. As described above, the gas sensor element 100A (gas sensor element main body 100a) used in the method of manufacturing the gas sensor element of the present embodiment has a slurry different in composition from the slurry for the outer porous protective layer 22 and is previously applied to the tip portion 100b. A slurry coated film 800 is used. Note that the coating film 800 may be formed on the tip surface 100c and the peripheral surface 100d of the tip portion 100b through a so-called dipping process, or may be formed by another coating process (for example, , spray coating).

In the method for manufacturing the gas sensor element of the present embodiment, the dipping process, the scraping process and the baking process are performed in the same manner as in the first embodiment except that the gas sensor element main body 100a with the coating film 800 is used. A gas sensor element 100A having a multi-layered porous protective layer 20A may be manufactured by the method for manufacturing a gas sensor element of this embodiment.

<Other embodiments>
The present invention is not limited to the embodiments explained by the above description and drawings, and the following embodiments are also included in the technical scope of the present invention.

(1) In Embodiment 1 and the like, the case where the immersion step is performed only once was exemplified, but the present invention is not limited to this, and in other embodiments, the immersion step and the scraping step are performed before the baking step. , may be performed twice or more. For example, in one immersion step, the coating film 700 having a thickness sufficient to form the porous protective layer 20 is applied to all the surfaces (the front end surface 100c and the peripheral surface 100d) of the front end portion 100b of the gas sensor element main body 100a. If it cannot be formed, an additional dipping step may be performed. The immersion step is performed until a coating film 700 having a sufficient thickness is formed on all surfaces (tip surface 100c and peripheral surface 100d) of tip portion 100b of gas sensor element main body 100a. When the thickness of the peripheral coating 701 is smaller than the required thickness, the peripheral coating 701 is not scraped off in the peripheral scraping process, and the thickness of the tip surface coating 702 is less than the required thickness. is smaller, the tip coating 702 will not be scraped off during the tip scraping process.

(2) In Embodiment 1 and the like, the baking process is performed immediately after the scraping process, but in other embodiments, the drying process may be performed between the scraping process and the baking process. By performing the drying process, the water content in the coating film 700 formed on the tip portion 100b of the gas sensor element main body 100a is reduced, and further, the organic binder and the like in the coating film 700 are thermally cured, so that the coating film 700 is dried. becomes hard to some extent, and the shape of the coating film 700 is easily maintained. Various conditions such as drying temperature and drying time in the drying step are not particularly limited, but for example, drying may be performed at 90° C. for 1 minute or more. In particular, when the immersion process is performed multiple times before the baking process, it is preferable to perform a drying process for drying the coating film 700 between the first immersion process and the subsequent immersion process. . When the drying step is performed after the previous dipping step, it is easy to form a new slurry coating film on top of the already formed coating film in the next dipping step, thereby forming a porous protective layer. It is easy to obtain a sufficiently thick coating film 700 for forming.

(3) In another embodiment, when the scraping process is performed twice or more, scraping dies having different sizes, shapes, etc. of the opening edges may be used in each scraping process (peripheral surface scraping process). In another embodiment, when the scraping process is performed twice or more, scraping blades having different height positions may be used in each scraping process (tip surface scraping process). In another embodiment, after the immersion step, the tip surface scraping step may be performed first, and then the peripheral surface scraping step may be performed.

(4) In the above Embodiment 1, the opening edge of the scraping type has a rectangular shape, but in other embodiments, it is not limited to this. It may be set in other forms.

(5) If necessary, the porous protective layer of the gas sensor element manufactured by the manufacturing method of Embodiment 1 or the like is subjected to cutting or the like using a laser or a blade to finely shape the porous protective layer. may be adjusted.

DESCRIPTION OF SYMBOLS 1... Gas sensor 100... Gas sensor element 100a... Gas sensor element main body 100b... Tip part 100c... Tip surface 100d... Peripheral surface 150... Detection part 500... Scraping die 503... Opening edge part 600... Scraping blade , 700... Slurry coating film 701... Peripheral surface coating film 702... Tip surface coating film 701a, 702a... Excess coating film

Claims (5)

A method for manufacturing a gas sensor element in which a detecting portion disposed on the tip side of a plate-shaped gas sensor element extending in an axial direction is covered with a porous protective layer,
an immersion step of immersing the tip side of the gas sensor element in slurry for forming a porous protective layer to form a coating film of the slurry on the tip surface and the peripheral surface of the gas sensor element;
A scraping step of scraping off the coating film to remove a portion of the coating film;
and a baking step of baking the coating film after the scraping step to obtain the porous protective layer. A method for manufacturing a gas sensor element in which a detecting portion disposed on the tip side of the gas sensor element extending in the axial direction is covered with a porous protective layer,
an immersion step of immersing the tip side of the gas sensor element in slurry for forming a porous protective layer to form a coating film of the slurry on the tip surface and the peripheral surface of the gas sensor element;
A scraping step of scraping off the coating film to remove a portion of the coating film;
a baking step of baking the coating film after the scraping step to obtain the porous protective layer,
The dipping step is performed multiple times before the firing step,
A method for manufacturing a gas sensor element, comprising a drying step of drying the coating film between the first dipping step and the subsequent dipping step. In the scraping step, the gas sensor element is passed through a through hole provided inside a scraping die, and an excess coating film of the peripheral surface coating film formed on the peripheral surface is removed by the opening edge of the through hole. 3. The method for manufacturing the gas sensor element according to claim 1, wherein the gas sensor element is abraded. In the scraping step, an excess coating film of the tip coating film formed on the tip surface is scraped off by a scraping blade moving along a direction perpendicular to the axial direction. A method for manufacturing a gas sensor element according to any one of 1. 5. The slurry according to any one of claims 1 to 4, wherein the slurry has a shear rate of 43000 mPa·s or more at a shear rate of 0.1 s ⁻¹ and a shear rate of 2500 mPa·s or less at a shear rate of 10 s ⁻¹ . of the gas sensor element.

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