JP6398741B2 - Gas sensor element manufacturing method and active solution dropping device - Google Patents

Description

The present invention relates to active solution dropping device which is suitable for preparation and its production of the gas sensor element for detecting the concentration of a specific gas component in a measurement gas.

  Conventionally, a gas sensor for detecting the concentration of a specific gas component such as oxygen contained in combustion exhaust gas has been provided in a combustion exhaust passage of an internal combustion engine such as an automobile engine, and the air-fuel ratio is determined by the detected concentration of the specific gas component. Control and temperature control of exhaust treatment catalyst are performed.

As such a gas sensor, a solid electrolyte substrate in which a solid electrolyte material having oxygen ion conductivity such as zirconia is formed in a bottomed cylindrical shape, an outer electrode layer in contact with a gas to be measured on its outer peripheral surface side, and an inner peripheral surface thereof It has a so-called cup-shaped detection element consisting of an inner electrode layer in contact with the atmosphere introduced as a reference gas on the side, and is generated between both electrodes due to the difference between the oxygen concentration in the gas to be measured and the oxygen concentration in the reference gas An oxygen sensor or the like that detects an electric potential difference to measure an oxygen concentration in a gas to be measured is widely used.
As a method for producing an inner electrode layer used in such a gas sensor, a method is known in which an active liquid is injected and sucked into an inner chamber of a solid electrolyte body and then a plating film is formed.

  For example, in Patent Document 1, a nucleation step of attaching nuclei to the inner peripheral surface of a bottomed cylindrical solid electrolyte body extending in the axial direction, and a plating solution in which the nuclei act as a catalyst, In the gas sensor element manufacturing method having a plating step for depositing the noble metal film on the inner peripheral surface of the solid electrolyte body, prior to the plating step, a resist is formed so as to cover portions other than the electrode predetermined portion where the electrode is to be formed in advance. A method of manufacturing a gas sensor element is disclosed in which the resist is burned off after plating.

JP 2011-247620 A

However, as disclosed in Patent Document 1, even if a resist is applied so as to cover a portion that is not planned to be plated, a strong acid or the like is used to remove the glass component deposited on the element surface in the firing step during the nucleation step. The grain boundary grooves are formed by the etching, and the plating solution permeates and diffuses due to the capillary phenomenon of the grain boundary grooves, and the plating solution bleeds to the portion covered with the resist.
Furthermore, in the conventional manufacturing method, since nucleation is performed over the entire inner peripheral surface of the solid electrolyte body, noble metal nuclei are also deposited in the portion covered with the resist.
For this reason, the plating solution that has permeated into the grain boundary grooves covered with the resist is precipitated by the catalytic action of the noble metal nuclei, and an inner electrode is formed in addition to the planned electrode portion.

As a result, variations occur in the shape and film thickness of the inner electrode.
In particular, when the variation in the width of the lead portion increases, the variation in the impedance characteristic increases, and when the variation in the film thickness of the inner electrode increases, the variation in the response may increase.

  Moreover, it is relatively easy to form an outer electrode of a predetermined shape on the outer peripheral surface of the solid electrolyte body exposed to the outside, but a resist of a desired shape is applied to the inner peripheral surface of the solid electrolyte body having a small inner diameter. It is not always easy to apply accurately.

  Furthermore, in the conventional manufacturing method, it is necessary to burn off the resist after plating, so that in addition to incurring an increase in manufacturing cost, the resist is not completely burned out, resulting in residual ash, or heating to burn out the resist. As a result, aggregation of the inner electrode occurs, which may cause a decrease in durability.

  Therefore, in view of such a situation, the present invention performs nucleation with extremely high accuracy only on the inner peripheral surface of the solid electrolyte body formed in a bottomed cylindrical shape within a necessary range for forming the electrode, and the inner electrode. An object of the present invention is to provide a method for manufacturing a gas sensor element in order to accurately form a layer into a desired shape.

Referring to FIGS. 1 (a) to 1 (f), the present invention provides a solid electrolyte body (2) formed in a bottomed cylindrical shape with one end closed and the other end opened, and an inner peripheral surface (200) thereof. A method for producing a gas sensor element (4) comprising an inner electrode (1) provided and an outer electrode (3) provided on an outer peripheral surface (201) thereof,
At least an etching step (P1; see FIGS. 3A and 3B) for eluting the grain boundary phase (GBP) of the solid electrolyte body to form a grain boundary groove (CP _GB ) on the inner peripheral surface; and A nucleation step (P2; see FIGS. 4A to 4C) in which a heat treatment is performed after applying the nucleation active solution (6) to be the core of the inner electrode, and a plating step (P3; see FIGS. 5A and 5B) to be performed thereafter. And
In the nucleation step,
While dropping a predetermined amount (V) of a liquid (DL) made of the nucleating active solution on the inner peripheral surface of the solid electrolyte body at a predetermined dropping pitch (P), A predetermined electrode range (AR1) having a predetermined electrode shape is defined.

Moreover, with reference to FIG. 6A, FIG. 8A, and 8B, the active solution dripping apparatus (5) which concerns on this invention formed the active solution for nucleation (6) for forming a noble metal nucleus in the shape of a bottomed cylinder. An active solution dropping device applied to the inner peripheral surface (200) of the solid electrolyte body (2),
A bottomed cylindrical nozzle (50) having an active solution introduction hole (500) partitioned on the inside and a nozzle hole (501) provided at the tip thereof in communication with the active solution introduction hole; A droplet dropping means (51) for dropping a predetermined amount (V) of droplets (DL) made of an active solution;
Active solution supply means (52) for supplying the cored active solution to the droplet dropping means;
Solid electrolyte body holding means (54, 59) for holding the solid electrolyte body;
An axial driving means (55) for generating a driving force that enables the solid electrolyte body holding means to move in the axial direction of the solid electrolyte body;
Axial drive transmission means (56) for transmitting the power of the axial drive means to the solid electrolyte body holding means;
A circumferential driving means (57) for generating a driving force that enables the solid electrolyte body holding means to move in the circumferential direction of the solid electrolyte body;
Circumferential drive transmission means (58) for transmitting the power of the circumferential drive means to the solid electrolyte body holding means;
A controller (53) for controlling driving and stopping of the droplet dropping means, the axial driving means, and the circumferential driving means;
While dropping and dropping the cored active solution droplets from the nozzle hole while moving and stopping the solid electrolyte body in the axial direction and the circumferential direction at a constant dropping pitch, the inner periphery of the solid electrolyte body The active solution film (60) is formed only in a predetermined electrode predetermined range (AR1) on the surface.

According to the present invention, nucleation is not performed over the entire inner peripheral surface of the solid electrolyte body as in the prior art, but nucleation can be performed with a highly accurate and uniform thickness only in a necessary range. it can.
As a result, the inner electrode can be efficiently formed with extremely high dimensional accuracy.
Further, when the inner electrode is partially formed on the inner peripheral surface of the solid electrolyte body, the plating is not formed even if the non-nucleated portion is exposed to the plating solution in the plating process. Further, it is not necessary to mask a portion not subjected to plating, and it is not necessary to perform a wasteful work of burning the resist after forming the resist.

Sectional drawing of the gas sensor element formed using the manufacturing method of the gas sensor element of this invention, and the expansion | deployment schematic diagram which shows the structure of an inner side electrode The schematic diagram which shows the dripping method of the droplet which consists of an active solution for a nucleus which is the principal part of the manufacturing method of the gas sensor element of this invention Schematic diagram showing the termination method at the outer periphery of the nucleation range Sectional drawing and top view which show the outline | summary of the structure | tissue structure of the gas sensor element in which the manufacturing method of the gas sensor element of this invention is used Sectional drawing and top view which show the manufacturing method of the gas sensor element of this invention later on in order of a process, and show the outline | summary of the structure | tissue structure after etching the gas sensor element of FIG. 3A Sectional drawing and top view which show the active solution dripping process which dripping the active solution for a nucleus attached following FIG. 3B 4A is a cross-sectional view and a plan view showing a state in which the dropped active solution is diffused into the etching groove. FIG. 4B is a cross-sectional view and a plan view showing a state in which noble metal nuclei are deposited in a predetermined range by subjecting the droplets to heat treatment. FIG. 4C is a cross-sectional view and a plan view showing a plating process in which a plating solution is injected and plating is applied to a predetermined range that is nucleated. 5A is a cross-sectional view and a plan view showing a state in which the inner electrode is formed in a predetermined range. Sectional drawing which shows the relationship between the dropping method of an active solution, the contact angle with a solid electrolyte body, and the state of the droplet after dropping Sectional drawing which shows the state after dripping when the magnitude | size of a droplet is smaller than a solid electrolyte particle diameter Sectional drawing which shows the state after dripping when the contact angle of a droplet and a solid electrolyte body is small Sectional drawing which shows the state after dripping when the magnitude | size of a droplet is larger than a solid electrolyte particle diameter Plan view of FIG. 6D Characteristic diagram showing the relationship between the drop pitch and the presence or absence of disconnection Sectional drawing along the axial direction of a gas sensor element which shows the outline | summary of the droplet dropping apparatus for implement | achieving the manufacturing method of the gas sensor element of this invention Cross section of FIG. 8A Sectional view and plan view showing a state in which a manufacturing method of a conventional gas sensor element shown as a comparative example and its problems are shown in the order of processes and an active liquid for nucleation is injected 9A is a cross-sectional view and a plan view showing a state in which noble metal nuclei are deposited on the entire inner peripheral surface of the solid electrolyte body. 9B is a cross-sectional view and a plan view showing a state in which a plating resist is applied to a portion where the inner electrode is not formed and a plating solution is injected. 9C is a cross-sectional view and a plan view showing the state of the inner electrode formed when the plating solution is reduced 9D is an exploded view of the inner electrode formed by the conventional manufacturing method, following FIG. 9D.

With reference to FIG. 1, the outline | summary of the gas sensor element 4 with which the manufacturing method of the gas sensor element of this invention is applied, and the manufacturing method of the gas sensor element of this invention is demonstrated.
The present invention relates to a method of manufacturing a gas sensor element 4 used in a gas sensor that detects a specific gas component in a gas to be measured such as an oxygen sensor.
In particular, it is suitable for forming the inner electrode 1 with high accuracy by dividing it into a predetermined shape on the inner peripheral surface 200 of the bottomed cylindrical solid electrolyte body 2.

In the method for manufacturing the gas sensor element 4 of the present invention, the noble metal nucleus Nuc is nucleated on the inner peripheral surface 200 of the solid electrolyte body 2 using the nucleating active solution 6 in which the organic noble metal is dissolved.
Thereafter, a reduction reaction of the plating solution is caused by using the noble metal nucleus Nuc as a catalyst to form a noble metal plating film on the noble metal nucleus Nuc.
Further, in order to perform nucleation only on the predetermined electrode area AR1 forming the internal electrode 1 on the inner peripheral surface 200 of the solid electrolyte body 2, a predetermined amount of organic noble metal is dissolved in a solvent at a predetermined dropping pitch P interval. The greatest feature is that the active solution for nucleation 6 is dropped.

As shown in FIG. 1 (a), the gas sensor element 4 to which the manufacturing method of the present invention is applied has a bottomed cylindrical solid electrolyte body 2 having one end closed, the other end opened, and extending in the axial direction. The inner electrode 1 is formed on the inner peripheral surface 200 and partitioned into a predetermined shape, and the outer electrode 3 is formed on the outer peripheral surface 201 and partitioned into a predetermined shape.
The solid electrolyte body 2 is formed by a known molding method such as press molding using a known solid electrolyte material such as yttria partially stabilized zirconia having conductivity with respect to specific ions such as oxygen ions. Baked at temperature.

The solid electrolyte body 2 has a large diameter between the cylindrical leg portion 20, a bottom portion 21 closed at the distal end side thereof, a head portion 22 opened at the proximal end side, and the leg portion 20 and the head portion 22. The large-diameter portion 23 that expands as described above.
The inner electrode 1 to which the manufacturing method of the present invention is applied uses a known noble metal such as platinum, and is formed on the inner peripheral surface 200 of the solid electrolyte body 2 as shown in FIG. The electrode detection part 10, the inner electrode lead part 11, and the inner electrode terminal part 12 are comprised.
The inner electrode detection unit 10 has a certain width in the axial direction on the closed end side of the solid electrolyte body 2 and is formed over the entire circumference in the circumferential direction.

The inner electrode lead portion 11 is formed to extend in the axial direction with a constant width W11 so as to connect the inner electrode lead portion 11 to the inner electrode terminal portion 12 from the proximal end side of the inner electrode detection portion 10.
By the manufacturing method described later, the width W11 of the inner electrode lead portion 11 is formed with extremely high accuracy with a variation of 200 μm or less, preferably 100 μm or less, with respect to a set value of 0.5 mm or more and 3.0 mm or less. Yes.
The inner electrode terminal portion 12 is provided on the proximal end side of the inner electrode lead portion 11, and has a certain width in the axial direction on the inner peripheral surface of the head portion 22 on the opening end side. It is formed over the circumference.

The outer electrode 3 is made of a known noble metal such as platinum, and is formed on the outer peripheral surface 201 of the solid electrolyte body 2. The outer electrode 3 includes an outer electrode detection unit 30, an outer electrode lead unit 31, and an outer electrode terminal unit 32. ing.
The outer electrode detection unit 30 has a certain width in the axial direction at the front end side of the leg portion 20 and faces the inner electrode detection unit 20 via the leg portion 20, and the entire circumference of the outer peripheral surface 201. It is formed over.

The outer electrode lead portion 31 is formed to extend in the axial direction with a certain width so as to connect the outer electrode terminal portion 32 to the outer electrode terminal portion 32 from the proximal end side of the outer electrode detection portion 30.
The outer electrode terminal portion 32 is provided on the base end side of the outer electrode lead portion 31, has a constant width in the axial direction on the outer peripheral surface 201 of the head portion 22, and is formed over the entire periphery of the outer peripheral surface 201. ing. In the method for manufacturing a gas sensor element of the present invention, when forming the inner electrode 1, as shown in FIG. 5C, the noble metal nucleus that serves as a catalyst is provided only in the predetermined electrode area AR1 where the inner electrode 1 is to be formed. Nuc is precipitated.

In the present invention, as shown in FIG. 4 (d), a film of the active solution 6 for nucleation (active solution film 60) in which the organic noble metal is dissolved is formed only in the predetermined electrode area AR1, and this is formed at 400 ° C. By performing the heat treatment at a heat treatment temperature of 600 ° C. or less, it is possible to deposit the noble metal nucleus Nuc only in the predetermined electrode area AR1.
Further, in order to form a film of the active solution 6 for nucleation in which the organic noble metal is dissolved only in the predetermined electrode area AR1, as shown in FIGS. (E) and (f), the axial direction of the solid electrolyte body 2 and at intervals of a predetermined dropping pitch P in the circumferential direction, a predetermined amount of nucleation for the active solution 6 where the organic noble metal is dissolved in a solvent by dropwise addition dropwise, spreading droplets DL having a predetermined diffusion diameter D _{2 The} electrode planned area AR1 is completely filled with the aggregate of _DF .

With reference to FIG. 2A and FIG. 2B, the dripping method of the active solution 6 with a nucleus is demonstrated still in detail.
Droplet DL predetermined amount has a substantially spherical shape having a predetermined droplet diameter [phi] D _1.
When such droplets DL is dropped to the inner peripheral surface 200 of the solid electrolyte body 2, a hemispherical or convex shaped contact droplet DL _CN with a predetermined contact diameter [phi] D.

Further, the contact droplet DL _CN diffuses into a grain boundary groove formed on the surface of the solid electrolyte body 2 by capillary action, and becomes a diffusion droplet DL _DF having a predetermined diffusion diameter φD ₂ .
At this time, in addition to a constant amount of the dropped droplets DL, since the nucleating active solution 6 uses a volatile solvent, the solvent volatilizes at the same time as the diffusion. [phi] D ₂ is suppressed within a predetermined range.

Therefore, a predetermined amount of the liquid droplet DL is moved in the axial direction and the circumferential direction of the solid electrolyte body 2 at intervals of a predetermined dropping pitch P along the predetermined electrode range AR1 set in advance so as to have a predetermined electrode shape. However, by dropping one drop at a time, it is possible to form a droplet film of the nucleating active solution 6 evenly in the planned electrode area AR1 while suppressing excessive diffusion of the droplets. At the time of dropping, the solid electrolyte body 2 can be preheated.
At this time, if dripping is continued at a constant dripping pitch P, it may not be divisible by the dripping pitch P at the edge of the planned electrode area AR1, so the terminal dropping pitch P with the dripping pitch adjusted is shown in FIG. 2B. the outer peripheral edge of the spread droplets _{DL DF} is to match the edge of the electrode will range AR1 is changed to _END.
Note that the terminal dropping pitch _PEND can be appropriately changed between the circumferential direction and the axial direction.

The active solution 6 for nucleation includes organic noble metal or noble metal halide soluble in an organic solvent such as organic platinum or platinum halide, such as dichloroethane, chloroform, methyl ethyl ketone, cyclohexane, isopropyl alcohol, isobutyl alcohol, dipentene, terpineol. What was melt | dissolved in organic solvents, such as, can be used. Preferably, when a compound containing an organoplatinum complex that is easy to adjust the viscosity is dissolved in a highly volatile (low boiling point) solvent, the control of the diffusion diameter φD ₂ is easy and the variation is small.

In the present invention, as to reduce the droplet volume V per 1 dot, the contact diameter [phi] D, more diffuse diameter [phi] D ₂ decreases, the dimensional accuracy of the active solution film 60 is formed on the electrode will range AR1 is higher. Inevitably, the dimensional accuracy of the inner electrode 1 also increases, but on the other hand, the productivity decreases.
Similarly, the smaller the dropping pitch P is, the higher the dimensional accuracy of the inner electrode 1 is. On the other hand, the number of times of dropping for dropping a certain range increases, so the productivity is lowered.

For this reason, there exists an optimum range of the diffusion diameter φD ₂ per dot and an optimum range of the droplet pitch P. In the present invention, the droplet diameter φD ₁ is determined by the drop amount V of the droplet DL of the cored active solution 6 dropped per dot, and the diffusion diameter φD ₂ is changed by changing the type of solvent. This by the solvent, since a change in the spread between the contact diameter [phi] D, as the dimensional accuracy and productivity becomes a desired range, the diffusion diameter [phi] D ₂ is normally 1～250Myuemu, preferably in the range of 10~150μm It can be set appropriately. Diffusion diameter [phi] D ₂ is 1μm less, productivity is significantly reduced, and 250μm greater than the variation in dimensional accuracy decreases increases.
At this time, the droplet diameter φD ₁ that becomes the desired diffusion diameter φD ₂ can be appropriately set in the range of usually about 1 μm to about 200 μm, preferably about 10 μm to about 100 μm, depending on the type of solvent.

Further, dropping the pitch P can be set appropriately 3/4 times or less of the range of spread diameter [phi] D _2. When the range is preferably 1/4 times or more and 3/4 times or less, good results can be obtained regardless of the type of solvent.
In particular, when the diffusion diameter φD ₂ is smaller than 10 μm, if the dropping pitch P is made smaller than ¼ times the diffusion diameter φD ₂ , the productivity is remarkably lowered. When the dropping pitch P larger than 3/4 times the diffusion diameter [phi] D _2, will be not only the dimensional accuracy of the inner electrode 1 drops, the nucleation that are not part electrode will range AR1 interspersed There is a risk of disconnection of the internal electrode 1.

With reference to FIG. 3A and FIG. 3B, the etching process P1 will be described.
As shown in FIG. 3A, in the solid electrolyte body 2, a grain boundary phase GBP is formed between solid electrolyte particles G made of zirconia and yttria arranged with a certain particle size distribution.
A range defined by dotted lines in the plan view in the figure is an electrode formation scheduled range AR1, and an example in which the inner electrode 1 is formed with high accuracy in this range will be described.

Next, as shown in FIG. 3B, a part of the grain boundary phase GBP existing on the inner peripheral surface 200 of the solid electrolyte body 2 is eluted by etching using a known strong acid. This treatment increases the three-phase boundary point where the noble metal such as platinum contacts with the solid electrolyte and the exhaust gas, thereby contributing to an improvement in output and a reduction in resistance value. However, by forming the grain boundary groove CP _GB , variation due to diffusion of the solution is caused. Is likely to occur. Therefore, in the present invention, in the next step, the diffusion diameter φD ₂ and the dropping pitch P of the active solution 6 are controlled to facilitate electrode formation.

With reference to FIG. 4A-FIG. 5B, the nucleation process P2 is demonstrated.
As shown in FIG. 4A, while the solid electrolyte body 2 is relatively moved at a predetermined dropping pitch, the droplet DL of the nucleating active solution 6 is dropped from the nozzle 50 one dot at a time so as to draw a point drawing. The droplet DL of the active solution 6 is applied to the electrode formation scheduled area AR1.
Next, as shown in FIG. 4B, the droplets dropped at a constant dropping pitch diffuse and penetrate into the grain boundary grooves CP _GB formed on the inner peripheral surface of the solid electrolyte body 2 by etching.

At this time, since droplet volume V dripped is constant, the magnitude of the diffusion droplet DL _DF is larger it is not more than necessary depends on the type of solvent.
Furthermore, since a volatile organic solvent is used as the solvent, the solvent diffuses while volatilizing, and each droplet is maintained in a certain size range. As a result, sequence spreading droplets DL _DF having a substantially constant diffusion diameter D ₂ is in a predetermined dropping pitch P, will be distributed uniformly over a predetermined electrode formation planned range AR1.

As described above this time, dropping the pitch P is preferably set in a range of 1 / 4-3 / 4 times the diffusion diameter _{D 2} that is set in the range of 1～250Myuemu.
By spreading droplets DL _DF of adjacent droplets DL overlap at a constant rate, it prevents the portion not nucleation occurs, it is possible to prevent the internal breakage of the inner electrode 1.
In addition, by preheating the solid electrolyte body 2 to an appropriate temperature higher than room temperature in advance, the volatilization of the solvent component in the active solution 6 is promoted, and the spread due to the capillary phenomenon is reduced, thereby suppressing variation. improves.

Next, as shown in FIG. 5A, by heating at a predetermined heat treatment temperature, the solvent is removed and the organic noble metal dissolved in the active solution is decomposed while the organic components are removed to form a noble metal as a nucleus. Only precipitate.
At this time, by limiting the range of the heat treatment temperature to 350 ° C. or more and 600 ° C. or less, it is possible to suppress a decrease in catalytic action due to aggregation of the deposited noble metal nuclei Nuc.

The plating step P3 will be described with reference to FIG. 5B.
When the plating solution and the reducing agent are injected into the inner space of the solid electrolyte body 2 while being nucleated only in the predetermined range AR1, as shown in FIG. 5B, the noble metal nucleus Nuc is catalyst only in the specific range AR1. The reduction reaction of the plating solution proceeds from the noble metal nucleus Nuc as a starting point, and a plating film is formed, so that the inner electrode 1 can be accurately formed in a preset shape.
According to the present invention, since the noble metal nucleus Nuc is not nucleated in a portion other than the predetermined range AR1, even if the inner peripheral surface 200 of the etched solid electrolyte body 2 is in contact with the plating solution, The reduction reaction does not proceed, and the inner electrode 1 is not formed on an unnecessary portion of the inner peripheral surface 200 of the solid electrolyte body 2.
Masking with a resist and removal of the resist are not required as in the prior art, and the manufacturing cost can be reduced.

6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E, and FIG. 6F, the droplet after the droplet DL of the nucleus-attached active solution 6 is dropped on the inner peripheral surface 200 of the solid electrolyte body 2 I will explain the spread of the process step by step.
When the core-attached active solution 6 introduced into the active solution introduction space 500 partitioned inside the nozzle 50 is repeatedly pressurized at a predetermined pressure Pr, a predetermined amount V of liquid droplets from the nozzle hole 501 provided at the tip. DL is discharged.

The active solution for nucleation 6 used in the present invention is a solution in which a nucleation source such as an organic noble metal is completely dissolved in a solvent, so that it is different from a dispersion slurry in which noble metal powder is dispersed in a solvent. Therefore, the behavior of the droplet DL depends on the nature of the solvent, and a relatively uniform liquid film can be formed.
Droplet DL is a substantially spherical, between the liquid droplet amount per grain V and the droplet diameter D _{1,
V = 4/3 · π ·} (D 1/2) 3 relation holds.

The contact droplet DL _{CN at} the moment when the droplet DL is in contact with the inner peripheral surface 200 of the solid electrolyte body 2 has a lens shape with a radius R, and can be regarded as a part of the phantom sphere (spherical crown). At this time, the diameter of the bottom surface in contact with the inner peripheral surface 200 of the solid electrolyte body 2 is defined as the contact diameter D, the contact angle θ between the solid electrolyte body 2 and the inner peripheral surface 200, and the height of the contact droplet DL _CN are represented as H. Then, between the droplet volume V and the contact diameter D,
^{V = π · R · H 2} -π · H 3/3
D = R · cos (θ / 2) = 2√H · (2R−H)
A relationship of H = (1-cos θ) · D / 2 is established. From these relationships, the contact diameter D can be calculated from the droplet amount V and the contact angle θ.

When the contact angle θ is relatively small (for example, when 0 <θ ≦ 45 °), the droplet DL is relatively easily wetted with the inner peripheral surface 200 of the solid electrolyte body 2 and the contact diameter D corresponding to the contact angle θ. It becomes.
The contact angle θ of the droplet DL can be arbitrarily set by selecting a solvent that dissolves the organic noble metal complex.

However, in the present invention, the presence of the grain boundary groove CP _GB formed in the etching step P1, not necessarily remain in contact droplet DL _CN of the aforementioned spherical crown model are fixed. Depending on whether or not the droplet DL penetrates into the grain boundary groove CP _GB , the drying property of the solvent, and the presence or absence of preheating, there is a difference in the spread and variation of the diffusion droplet DL _DF , and the droplet volume V is particularly small or large. Sometimes the effect is thought to increase. This will be discussed next.

How the droplet DL diffuses after contacting the inner peripheral surface 200 of the solid electrolyte body 2 depends on the contact diameter D, the particle diameter GS of the solid electrolyte particles G such as zirconia constituting the solid electrolyte body 2, and etching. Therefore, it varies depending on the relationship with the grain boundary groove CP _GB formed in the grain boundary _GB .
As shown in FIG. 6B, a particle diameter GS> contact diameter D, and, if the droplet DL is dropped on the grain boundary groove CP _GB, the most of the droplets in the grain boundary groove CP _GB by capillarity becomes sucked by it, diffusion diameter D ₂ is smaller.

Further, the particle diameter GS> contact diameter D, and, when a droplet DL is dropped on the particles G, the diffusion diameter D ₂ do not change much from the contact diameter D.
Whether the droplet DL is dropped on the grain boundary groove CP _GB or the particle G appears randomly, so that the diffusion diameter D ₂ of the diffusion droplet DL _DF is averaged and constant diffusion has a diameter D _2, it can be approximated as a constant state of dropping pitch coated with P at an average liquid film thickness aT _DS.

On the other hand, even in droplet diameter D ₁ is constant, if there is a difference in wettability of the solvent, as shown in FIG. 6C, when the contact angle theta is relatively small (e.g., θ = 20 °), the diffusion diameter D ₂ is relatively large. Thus, when the droplet DL is smaller than the particle diameter GS, the dispersion increases due to suction into the grain boundary groove CP _GB , so that the diffusion droplet DL is smaller than the grain boundary groove CP _GB (diameter 2r). _The droplet amount V may be set so that the _DF becomes sufficiently large.

Furthermore, as shown in FIG. 6D, FIG. 6E, and when droplet volume V is large, the contact diameter D is larger than the particle diameter GS, contact droplet _{DL CN} so as to straddle the large number of grain boundaries groove _{CP GB} When spreading, droplets are simultaneously sucked into the plurality of grain boundary grooves CP _GB and diffused in the outer diameter direction, so that the diffusion diameter D ₂ becomes relatively large.
Further, in such a case, it becomes easy to occur at the same time evaporation of the solvent and diffusion, but is never excessively enlarged diffusion diameter D _2, unevenness is likely to occur in the spread. For this reason, it is preferable to set the droplet amount V so that the droplet DL does not become significantly larger than the particle diameter GS.
The difference in the solvent, for either diffusion diameter D ₂ is determined by a degree of divergence for a constant droplet volume V, by the following examples, it will be described with reference to the drawings.

Here, referring to Tables 1 to 9, in the gas sensor element manufacturing method of the present invention, the width variation (μm) of the inner electrode lead portion 11 is reduced in accordance with the organic solvent used for the cored active solution 6. However, the optimum diffusion diameter D ₂ (μm) and dropping pitch (μm) for increasing productivity will be described.
In accordance with the production method described above, each of the steps P1 to P1 was performed on the test solid electrolyte 2 using dichloroethane, chloroform, methyl ethyl ketone, cyclohexane, isopropyl alcohol, isobutyl alcohol, dipentene, terpineol as the solvent for the nucleating active solution 6. Conduct P3 and test investigation on diffusion diameter (drop mark diameter) D ₂ , productivity, inner electrode lead part 11 width variation, and lead part 11 breakage due to difference in organic solvent and drop volume Went. The results are shown in Tables 2 to 9, respectively. Diffusion diameter D ₂ is the diameter when forming a plating film after degreasing liquid droplets dropped on the solid electrolyte body 2 was measured and noted in the table as a drop mark diameter D _2. Similarly, the lead portion 11 was also measured for the maximum width-minimum width after plating to obtain width variation.

In each solvent, an organic noble metal complex serving as a nucleus as a solute is dissolved at a predetermined concentration.
In addition, the noble metal used as the solute of the nucleation-use active solution 6 is not only an organic noble metal complex but also a solvent that is soluble in a solvent such as a halogenated noble metal. Can be used.
Preferably, an organic platinum complex, platinum halide or the like can be used, but a noble metal different from the plating layer can be used as a nucleus.
Table 1 shows typical physical properties of each solvent. In addition, as shown in Table 1, these organic solvents have a surface tension of 10 mN / m or more and 40 mN / m or less, and the contact angle θ is 45 ° or less.

In Tables 2 to 9, when the variation (μm) in the width of the inner electrode lead portion 11 is 100 μm or less, it is determined that the effect is sufficient, and the condition where the variation is 200 μm or less is determined to be effective. It was judged that there was no effect.
In Tables 2 to 9, the productivity is determined to be sufficiently effective when the number of drops required to cover a distance of 1 mm is 100 times or less, and 200 times or less is determined to be effective, and 1000 times. When it exceeded, it was determined that there was no effect. The judgment column is marked with a double circle when both conditions are sufficiently effective, with a circle when both are effective, and otherwise marked with a cross. It is.
As is apparent from the table, regardless of the type of solvent, the drop marks diameter [phi] D ₂ double circle determined in the range of 10 to 150 m, and has a round determination in 1～250Myuemu. If the drop mark diameter φD ₂ is less than 1 μm, the productivity deteriorates and the width variation increases, which is not preferable. It can be seen that the drop mark diameter φD ₂ can be controlled to a desired diameter by adjusting the amount of liquid droplets according to the solvent, and it is possible to achieve both dimensional accuracy and productivity.
In the tests shown in Tables 2 to 9, the solid electrolyte body 2 is at room temperature and is not preheated. Also, dropping the pitch P has been compared with conditions set to be 3/4 of the diffusion diameter (drop mark diameter) D _2, also disconnection of the lead portions 11 in any of the test has not occurred.

With reference to Tables 10 and 11 and FIG. 7, the relationship between the dropping pitch and the presence or absence of disconnection will be described. Tables 10 and 11 show that for methyl ethyl ketone (droplet diameter D ₂ 50 μm) and terpineol (droplet diameter D ₂ 5.5 μm), the drop pitch P is 1/10, 1/8, 1 and 1 of the drop mark diameter D ₂ , respectively. / 4, 1/2, 3/4, 1, 5/4 are set and the results of similar tests are shown, the resistance is measured after plating, and the presence or absence of disconnection is evaluated. (The resistance ∞ is marked as having a break and marked with a cross).
As shown in FIG. 7, it has been found that if the dropping pitch P is widened, the productivity is improved, but if the dropping pitch P is too wide, the lead portion 11 is disconnected.
Specifically, when dropping the pitch P is drop marks diameter (diffusion diameter) D ₂ or more, a gap is formed between the diffusion droplets part nucleation is not performed occurs not plated on its part, the inner It has been found that there is a possibility of disconnection in the electrode 1 (particularly the lead portion 11).
While maintaining a constant productivity irrespective of the size of the droplets, in order to prevent disconnection, based on the spread diameter D ₂ at the time of dropwise for active solution 6 with nuclei, dropping the pitch P diffusion diameter D It was found that it is desirable to set it to 1/4 or more and 2/4 or less of ₂ .
This is because when the dropping pitch P exceeds 3 / 4D ₃ , none of the solvents are nucleated and a portion that cannot be plated is generated. On the other hand, since dropping pitch P tends to decrease the productivity and smaller than 1/4, especially when the spread diameter D ₂ is smaller than 10 [mu] m (see Table 11), it is significantly reduced productivity.

With reference to Tables 12-18, the influence at the time of providing the pre-heating process which heats the solid electrolyte body 2 previously is demonstrated.
Prior to the nucleation step P2, the temperature of the solid electrolyte body 2 is preliminarily heated to 80 ° C., the nucleation active solution 6 is dropped, and the dropping pitch P is set to 3/4 of the diffusion diameter (droplet mark diameter) D ₂ . The test was performed under the same conditions. As the results shown in Table 12 to 18, in any of the solvents, for the case was dropped the same droplet amount at ordinary temperature, the diffusion diameter (drop mark diameter) D ₂ is reduced, relatively inner electrode lead The variation in the width of the portion 11 is small.
This is because when the temperature of the element is increased, the solvent is likely to volatilize, the penetration depth into the grain boundary groove CP _GB due to capillary action becomes shallow, and the drying speed increases due to preheating. It is considered that diffusion due to capillary action of the active solution film formed on the inner peripheral surface 200 of the electrolyte body 2 is reduced.

With reference to FIG. 8A and FIG. 8B, an example of the active solution dripping apparatus 5 with a nucleus for implement | achieving the manufacturing method of the gas sensor element of this invention is demonstrated.
For details of the nozzle 50, refer to FIG. 6A.
The nucleus-attached active solution dropping device 5 includes a nozzle 50, a droplet dropping means 51, an active solution supplying means 52, a control device 53, a solid electrolyte body holding means 54, an axial driving means 55, and an axial driving. The transmission means 56, the circumferential direction rotation means 57, and the circumferential direction drive transmission means 58 are comprised.

  The nozzle 50 has an active solution introduction space 500 for introducing the nucleus-attached active solution 6 inside, and an opening 501 having a predetermined opening diameter communicating with the active solution introduction space 500 on the tip side. Yes.

  The droplet dropping means 51 is provided at the tip of the nozzle 50 by using a piezo actuator, a solenoid actuator, a heater or the like to increase the internal pressure of the nucleus-attached active solution 6 introduced into the active solution introduction space 500 of the nozzle 50. A predetermined amount of the active solution 6 is dropped from the nozzle hole 501 one by one.

At this time, the droplet DL may be naturally dropped by gravity, or may be caused to collide with the inner peripheral surface 200 of the solid electrolyte body 2 at a constant speed by increasing the injection pressure.
Using the collision energy, increase the drying rate of the solvent in the droplets, it is possible to suppress the spread of the diffusion diameter D _2.
The active solution supply means 52 supplies the nucleus-attached active solution 6 to the droplet dropping means 51.

The control device 53 transmits a drop signal Drop, an axial movement signal MO, and a circumferential movement signal ROT at a predetermined timing to control the driving and stopping of the droplet dropping means 51, and to drive the axial driving means 55. The stop and the drive and stop of the circumferential driving means 57 are controlled, and a predetermined amount of the active solution 6 is made from the nozzle 50 to the inner peripheral surface of the solid electrolyte body 2 at a predetermined dropping interval.
The solid electrolyte body holding means 54 holds the solid electrolyte body 2 so as to be movable in the axial direction and the circumferential direction.

The axial direction drive means 55 may be anything as long as it generates a driving force, and a known drive means such as a servo motor can be used.
The axial direction drive transmission means 56 may be anything as long as it can transmit the generated driving force to the solid electrolyte body holding means 54, and a known drive transmission means such as a linear guide can be used.
By driving and stopping the axial drive means 55, the solid electrolyte holding means 54 fixed to the axial drive transmission means 56 can be moved in the axial direction at a predetermined dropping interval.

A known drive means such as a servomotor can be used for the circumferential direction rotation means 57, and a known drive transmission means such as a gear can be used for the circumferential direction drive transmission means 58.
By driving and stopping the circumferential rotation means 57, the circumferential drive transmission means 58 is rotated at a predetermined rotation angle, and the solid electrolyte body holding means 54 is interlocked to rotate the solid electrolyte body 2 at a predetermined rotation angle. be able to.
The solid electrolyte body holding means 54 is provided with a pressing portion 59 so that the solid electrolyte body 2 can be attached and detached.

Here, with reference to FIGS. 9A to 9E, a conventional gas sensor element, which is shown as a comparative example, is provided with a resist 8 inside the solid electrolyte body 2 and plated to form an inner electrode in a predetermined shape. The manufacturing method and its problems will be described.
In the comparative example, in the same manner as shown in FIGS. 4A and 4B, through the etching process, in the space partitioned inside the solid electrolyte body 2 in which the grain boundary grooves CP _GB are formed on the surface, FIG. As shown in FIG. 3, the noble metal nuclei are precipitated by injecting the nucleus-attached active solution 6 and heating to a predetermined temperature.

As a result, in the comparative example, as shown in FIG. 9B, the noble metal nucleus Nuc is deposited over the entire inner peripheral surface of the solid electrolyte body 2.
In particular, the grain boundary groove portion CP _GB formed by etching has higher activity than the particle surface, the noble metal nucleus Nuc is likely to precipitate, and the grain boundary groove portion CP _GB has a high concentration distribution of the noble metal nucleus.

As shown in FIG. 9C, even if the portion where the inner electrode is not planned to be formed is covered with the resist 8, the grain boundary formed between the resist 8 and the surface of the solid electrolyte body when the plating solution is injected. The plating solution is sucked into the groove CP _GB by capillary action.
As shown in FIG. 9D, the plating liquid is reduced by the catalytic action of the noble metal nuclei Nuc the plating solution penetrates into the lower side is present in the grain boundary groove CP _GB to resist 8 through the grain boundary groove CP _GB, plating solution The bleeding part 14 is formed by the amount of penetration.

As a result, as shown in FIG. 9E, a bleed portion 14 that spreads with a width of 100 μm or more is formed around the inner electrode 1z formed by the conventional manufacturing method.
For this reason, the width of the inner electrode lead portion 11z is increased by the blur portion 14, and the DC resistance component RI of the inner electrode lead portion 11z is reduced.
Further, since the variation of the inner electrode 1z increases will result in a variation in the AC impedance Z _AC between the inner electrode 1z and the outer electrode 3.

DESCRIPTION OF SYMBOLS 1 Inner electrode 10 Inner electrode detection part 11 Inner electrode lead part 12 Inner electrode terminal part 2 Solid electrolyte body 20 Solid electrolyte body leg part 21 Solid electrolyte body bottom part (closed end)
200 Inner peripheral surface 201 Outer peripheral surface 22 Solid electrolyte body head (open end)
23 Solid Electrode Large Diameter Part 3 Outer Electrode 30 Outer Electrode Detection Part 31 Outer Electrode Lead Part 32 Outer Electrode Terminal Part 4 Gas Sensor Element 5 Active Solution Drop Device 50 Nozzle 51 Droplet Dropping Unit (Piezo Actuator, Solenoid Actuator, Heater)
52 Active solution supply means 53 Control devices 54 and 59 Solid electrolyte body holding means 55 Axial direction drive means (servo motor)
56 Axial direction drive transmission means (linear guide)
57 Circumferential rotation means (servo motor)
58 Circumferential drive transmission means (gear)
6 Active solution for nucleation 7 Plating solution AR1 Electrode planned range CP _GB grain boundary groove DL active solution droplet DL _CN contact droplet DL _DF diffusion droplet D ₁ droplet diameter D ₂ diffusion diameter GBP Grain boundary phase Nuc Noble metal nucleus P1 Etching process P2 Nucleation process P3 Plating process

Claims (12)

A solid electrolyte body (2) formed in a bottomed cylindrical shape with one end closed and the other end opened, an inner electrode (1) provided on the inner peripheral surface (200), and an outer peripheral surface (201) A method for producing a gas sensor element (4) comprising an outer electrode (3),
At least an etching step (P1) for eluting the grain boundary phase (GBP) of the solid electrolyte body to form a grain boundary groove (CPGB) on the inner peripheral surface, and a nucleus serving as a core of the inner electrode on the inner peripheral surface After applying the attachment active solution (6), it comprises a nucleation step (P2) in which heat treatment is performed, and a plating step (P3) to be performed thereafter,
In the nucleation step,
While dropping a predetermined amount (V) of a liquid (DL) made of the nucleating active solution on the inner peripheral surface of the solid electrolyte body at a predetermined dropping pitch (P), A method for manufacturing a gas sensor element, wherein a predetermined electrode range (AR1) having a predetermined electrode shape is defined.   When the droplet contacts the inner peripheral surface of the solid electrolyte body and then diffuses into a grain boundary groove existing on the surface of the solid electrolyte body to form a diffusion droplet (DLDF), the adjacent diffusion liquid The method for manufacturing a gas sensor element according to claim 1, wherein the dropping pitch is set so as to overlap with a droplet.   3. The method of manufacturing a gas sensor element according to claim 2, wherein a drop pitch of the droplets is not less than 1/4 times and not more than 3/4 times the diffusion diameter when the diameter of the diffusion droplet is a diffusion diameter (φD2). .   The method for manufacturing a gas sensor element according to claim 3, wherein the diffusion diameter is 1 μm or more and 250 μm or less.   The method for manufacturing a gas sensor element according to claim 3, wherein the diffusion diameter is 10 μm or more and 150 μm or less.   Based on the contact angle (θ) when the droplet contacts the inner peripheral surface of the solid electrolyte body and becomes a contact droplet (DLCN), and the size of the grain boundary groove, the size of the diffusion droplet 6. The method of manufacturing a gas sensor element according to claim 2, wherein the amount of the droplet corresponding to the same is set.   7. The active solution for nucleation according to any one of claims 1 to 6, wherein an organic noble metal complex and a halogenated noble metal are used as a solute, volatilized by the heat treatment, and no residue remains on the inner peripheral surface. A method for manufacturing a gas sensor element.   The method for producing a gas sensor element according to any one of claims 1 to 7, wherein the nucleating active solution uses an organic solvent having a surface tension of 10 mN / m or more and 40 mN / m or less as a solvent.   The gas sensor element according to any one of claims 1 to 8, wherein the active solution for nucleation uses an organic solvent selected from dichloroethane, chloroform, methyl ethyl ketone, cyclohexane, isopropyl alcohol, isobutyl alcohol, dipentene, and terpineol as a solvent. Manufacturing method.   The method for manufacturing a gas sensor element according to any one of claims 1 to 9, wherein the heat treatment temperature is 400 ° C or higher and 600 ° C or lower.   The method of manufacturing a gas sensor element according to any one of claims 1 to 10, further comprising a preheating step of heating the solid electrolyte body to a predetermined temperature in advance when dropping the cored active solution. An active solution dropping device for applying an active solution for nucleation (6) for forming a noble metal nucleus to an inner peripheral surface (200) of a solid electrolyte body (2) formed into a bottomed cylindrical shape,
A bottomed cylindrical nozzle (50) having an active solution introduction space (500) partitioned inward and a nozzle hole (501) provided at the tip thereof in communication with the active solution introduction space;
A droplet dropping means (51) for dropping a predetermined amount (V) of a droplet (DL) made of the cored active solution from the nozzle hole;
Active solution supply means (52) for supplying the cored active solution to the droplet dropping means;
Solid electrolyte body holding means (54, 59) for holding the solid electrolyte body;
An axial driving means (55) for generating a driving force that enables the solid electrolyte body holding means to move in the axial direction of the solid electrolyte body;
Axial drive transmission means (56) for transmitting the power of the axial drive means to the solid electrolyte body holding means;
A circumferential driving means (57) for generating a driving force that enables the solid electrolyte body holding means to move in the circumferential direction of the solid electrolyte body;
Circumferential drive transmission means (58) for transmitting the power of the circumferential drive means to the solid electrolyte body holding means;
A controller (53) for controlling driving and stopping of the droplet dropping means, the axial driving means, and the circumferential driving means;
While dropping and dropping the cored active solution droplets from the nozzle hole while moving and stopping the solid electrolyte body in the axial direction and the circumferential direction at a constant dropping pitch, the inner periphery of the solid electrolyte body An active solution dropping device (5) characterized in that an active solution film (60) is formed only in a predetermined electrode predetermined range (AR1) on the surface.

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