JP2008076282A - Manufacturing method of gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically apply insulating paste using an application device, which is achieved only by hand in the past, in a manufacturing method of a gas sensor for forming a protective film made of the insulating paste so as to prevent contact with a filling layer containing glass components on the rear end face of a sensor element. <P>SOLUTION: The manufacturing method of the gas sensor 1 comprises: an application process to apply the insulating paste P containing insulating ceramic powder with a specific surface area of 2.8-3.3 m<SP>2</SP>/g and ultraviolet curing resin and having its own viscosity of 20-200 Pa s onto the rear end face 112 of at least one of a detection element 11 and a heater element 12; a cured film forming process to form a cured film 133 for coating the rear end face 112 by irradiating ultraviolet onto the insulating paste P and curing the insulating paste P; and a protective film forming process to form the protective film 33 by heat-treating the cured film 133. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a gas sensor, and more particularly to a method for manufacturing a gas sensor such as an oxygen sensor, a full-range air-fuel ratio sensor, or a NOx sensor that is used for detecting the concentration of a specific gas component in a measurement target gas.

  2. Description of the Related Art Conventionally, a gas sensor having a sensor element whose electrical characteristics change according to the concentration of a specific gas component in exhaust gas discharged from an automobile is known. Among these, the sensor element includes a plate-like detection element that detects the concentration of oxygen or the like in the exhaust gas and outputs the detected concentration to the outside. This detection element is composed of a solid electrolyte base material mainly composed of zirconia. However, since such a solid electrolyte base material is not activated when the temperature is low, the sensor element is generally a detection element (solid electrolyte base material). A plate-like heater element is also provided. The heater element is formed of a ceramic substrate (insulating layer) mainly composed of alumina and a heating resistor. And the detection element and heater element in a sensor element are bonded together through bonding layers, such as cement, for example.

  Furthermore, a ceramic adapter having a through hole through which the sensor element is inserted is attached to the sensor element. The sensor element is inserted and held in a substantially cylindrical sensor holder through a mounted ceramic adapter. In addition, a plurality of filler layers are formed in the gap between the sensor element and the sensor holder by sequentially filling a plurality of fillers and performing heat treatment. In such a plurality of packed layers, the packed layer disposed at the rearmost in the sensor holder is obtained by melting and solidifying glass powder (glass 100%), and serves to keep the inside of the sensor holder airtight. I'm in charge. The filling layer made of glass is formed so as to surround the rear end portion of the sensor element to which the electrode wire is connected.

  For such a gas sensor, in general, since the solid electrolyte base material (zirconia) constituting the detection element has a larger thermal expansion coefficient than the glass component constituting the filling layer, the glass component of the filling layer is the rear end surface of the detection element. In direct contact with the unevenness present in the surface, stress due to the difference in thermal expansion between the two acts on the unevenness during the heat treatment, and cracks may occur in the detection element. Therefore, in order to prevent the filling layer containing the glass component from directly contacting the rear end surface of the detection element, an insulating protective film is formed on the entire rear end surface.

  Such a protective film is formed by applying an insulating paste made of insulating ceramic powder such as alumina powder, an organic solvent, a binder, a dispersing agent, and the like to the rear end face of the detection element, and drying and heat-treating it. However, when an insulating paste containing such an organic solvent is used, it must be dried for a long time at a relatively high temperature in order to remove the organic solvent. The existing bubbles may expand and the insulating paste may burst. In order to suppress such bursting of the insulating paste, it is effective to repeatedly apply and dry the insulating paste in a plurality of times, but this is not preferable because the number of work steps increases and productivity decreases. .

For this purpose, an insulating paste containing an insulating ceramic powder and an ultraviolet curable resin, which is substantially free of an organic solvent, is applied to the rear end surface of the detection element, and cured by irradiating it with ultraviolet rays. After that, the cured film is further heat-treated to form a protective film. According to such a method, it is not necessary to dry for a long time to remove the organic solvent, the working time can be greatly shortened, and the bursting of the insulating paste can be suppressed (for example, patents). Reference 1).
JP 2005-180923 A

  By the way, in order to manufacture such a gas sensor efficiently, it is preferable to automate the operation | work which apply | coats an insulating paste to the rear-end surface of a detection element as mentioned above using a coating device. An example of such a coating apparatus is a device that applies an insulating paste by discharging an insulating paste from a discharge nozzle, such as a dispenser.

  Since the insulating paste adheres to unnecessary portions when the coating amount of the insulating paste applied to the rear end surface of the detection element increases, the coating amount is preferably small. As the discharge nozzle, those having a small diameter capable of appropriately controlling the coating amount of the insulating paste are preferable.

  However, the conventional insulating ceramic powder and the ultraviolet curable resin, and the insulating paste substantially not containing the organic solvent has a viscosity of, for example, 400 MPa · s or more. It cannot be discharged from the nozzle. By expanding the inner diameter of the discharge nozzle, it is possible to discharge such a high-viscosity insulating paste, but as described above, it becomes difficult to control the coating amount when the inner diameter of the discharge nozzle is increased, There is a possibility that the insulating paste adheres to unnecessary portions.

  For this reason, conventionally, it is difficult to apply the insulating paste by using a coating apparatus, and the insulating paste is applied by hand to each detection element, which takes time and is not excellent in productivity. There is a problem.

  The present invention has been made in order to solve the above-described problems, and in the past, an application of an insulating paste to the rear end surface of a detection element, which could be performed only by hand coating, It is an object of the present invention to provide a method for manufacturing a gas sensor that can be applied automatically, thereby shortening the working time and improving the productivity.

The gas sensor manufacturing method of the present invention comprises a plate-like detection element that detects the concentration of a specific gas component in a gas to be measured, and a plate-like heater element that is stacked on the detection element and heats the detection element. And a cylindrical element that penetrates the sensor element along the axial direction in a state in which the front end side of the sensor element protrudes from the front end of the sensor element and accommodates the rear end portion of the sensor element inside the sensor element. A gas sensor manufacturing method comprising: a sensor holder; and a filling layer filled between the sensor element and the sensor holder so as to surround at least a rear end portion of the sensor element and containing at least a glass component. The rear end face of the element on the side composed of a base material having a large difference between at least the thermal expansion coefficient of the glass component among the detection element and the heater element constituting the sensor element. Applying an insulating paste containing alumina powder and an ultraviolet curable resin, and curing the insulating paste by irradiating the insulating paste with ultraviolet rays to form a cured film that covers the rear end face In the method for manufacturing a gas sensor, comprising: a cured film forming step for forming a protective film by heat-treating the cured film; and the specific surface area of the alumina powder in the insulating paste in the coating step is 2. The viscosity is 8 m ² / g or more and 3.3 m ² / g or less, and its own viscosity is 20 Pa · s or more and 200 Pa · s or less.

  In the gas sensor manufacturing method of the present invention, it is preferable that the viscosity of the ultraviolet curable resin constituting the insulating paste is 500 mPa · s or more and 1000 mPa · s or less. Further, in the gas sensor manufacturing method of the present invention, after the protective film forming step inserts the sensor element on which the cured film is formed into the sensor holder, between the sensor element and the sensor holder, It is preferable that the filling layer and the protective film are formed at the same time by filling the powder to be the filling layer containing at least the glass component and performing a heat treatment. Furthermore, in the gas sensor manufacturing method of the present invention, the base material constituting the detection element is preferably mainly made of zirconia, and the base material constituting the heater element is preferably mainly made of alumina.

According to the present invention, the specific surface area is 2 on the rear end face of the element constituted by the base material having a large difference between the thermal expansion coefficient of the glass component among the detection element and the heater element constituting the sensor element. By applying an insulating paste having an alumina powder of not less than 0.8 m ² / g and not more than 3.3 m ² / g and an ultraviolet curable resin and having a viscosity of 20 Pa · s to 200 Pa · s, Insulating paste can be applied by an application device such as a dispenser, which has been difficult in the past, thereby significantly reducing the work time for manufacturing the gas sensor and improving productivity.

  Hereinafter, the present invention will be described in detail. First, a gas sensor manufactured by applying the gas sensor manufacturing method of the present invention will be described. In the following, it is a kind of gas sensor, which is attached to the exhaust pipe, and is used for detecting the oxygen gas concentration in the exhaust gas to be measured, and is used as a whole area air-fuel ratio sensor 1 (hereinafter referred to as air-fuel ratio sensor 1). .).

  FIG. 1 is a longitudinal sectional view showing the air-fuel ratio sensor 1. The air-fuel ratio sensor 1 includes a detection element 11 capable of detecting oxygen concentration. By attaching the air-fuel ratio sensor 1 to an exhaust pipe of an automobile, an exhaust pipe in which exhaust gas flows through the front end side of the detection element 11 is provided. It is used by placing it in

  The air-fuel ratio sensor 1 is inserted and held except for the plate-like sensor element 14 and the tip end side (the lower side shown in FIG. 1) of the sensor element 14, and has a substantially cylindrical shape extending along the axial direction of the sensor element 14. The ceramic holder 13, the metal shell 3 that inserts and holds the front end side of the ceramic holder 13, the bottomed cylindrical protector 19 joined to the front end side of the metal shell 3, and the rear end side of the metal shell 3 (FIG. 1) An outer cylinder 5 that surrounds and protects the rear end side of the ceramic holder 13, and a substantially columnar separator 16 that is disposed so as to close the rear opening of the outer cylinder 5. The outer peripheral surface of the separator 16 is surrounded, and the protective outer cylinder 7 is attached to the rear end side of the outer cylinder 5.

  Further, in addition to the above configuration, the air-fuel ratio sensor 1 includes a supporting soot pipe 18 and an insulating soot pipe 27 attached to the sensor element 14, a protective film 33 applied to the rear end surface of the detecting element 11, and an opening behind the protective outer cylinder 7. The rubber cap 20 etc. which are arrange | positioned in order to block | close is provided. In addition, a first filling layer 302 is formed inside the ceramic holder 13 to hold from the middle part of the sensor element 14 to the vicinity of the rear end part of the sensor element 14, and behind the first filling layer 302 is a sensor. A second filling layer 312 is formed to be sealed so as to surround the rear end portion of the element 14 and the electrode wire 22 connected to the rear end portion. In the following description, the front end of the sensor element 14 is referred to as “sensor front end 141”, and the rear end is referred to as “sensor rear end 142”.

  Next, the sensor element 14 will be described with reference to FIGS. 1 and 2. FIG. 2 is a perspective view of the sensor element 14 to which the support rod 18 is attached. As shown in FIGS. 1 and 2, the sensor element 14 includes a plate-like detection element 11 that detects a gas concentration and a plate-like heater element 12 that heats the detection element 11 as a bonding layer (not shown). ) To form a single laminate. In addition, since the structure of the sensor element 14 used for the air-fuel ratio sensor 1 is a conventionally well-known thing, although details, such as the internal structure, are abbreviate | omitted, schematic structure is as follows.

  First, the detection element 11 includes an oxygen concentration cell element in which a porous electrode mainly composed of Pt is formed on both sides of a plate-shaped solid electrolyte substrate, and a porous electrode mainly composed of Pt on both sides of the solid electrolyte substrate. And an insulating spacer that is stacked between the two elements and forms a hollow measurement gas chamber. This solid electrolyte base material is mainly formed of zirconia in which yttria is dissolved as a stabilizer. The spacer forming the measurement gas chamber is mainly composed of alumina, and inside the hollow measurement gas chamber is one porous electrode of the oxygen concentration cell element and one porous electrode of the oxygen pump element. It arrange | positions with the form which an electrode exposes. The measurement gas chamber is formed so as to be positioned on the sensor tip portion 141 side of the detection element 11, and is configured such that exhaust gas can be introduced through a porous diffusion resistance portion separately formed on the spacer. ing.

  In addition, on the rear end side of such a detection element 11, three electrode wires 22 for inputting / outputting electric signals to / from each electrode formed on the detection element 11 are provided. One of the electrode wires 22 is electrically connected so as to be shared with one electrode of the oxygen concentration cell element exposed to the inside of the measurement gas chamber and one electrode of the oxygen pump element. The remaining two electrode wires 22 are electrically connected to the other electrode of the oxygen concentration cell element and the other electrode of the oxygen pump element, respectively.

  Next, the heater element 12 is formed such that a heating resistor mainly composed of Pt is sandwiched between plate-like insulating base materials mainly composed of alumina. Two electrode wires 22 electrically connected to both ends of the heating resistor are provided on the rear end side of the heater element 12.

  And the detection element 11 and the heater element 12 are mutually adhere | attached through a bonding layer (for example, phosphate cement). As shown in FIGS. 1 and 2, the rear end surface 122 of the heater element 12 is bonded so as to protrude to the rear end side from the rear end surface 112 of the detection element 11. In addition, a porous protective layer (not shown) for preventing poisoning is formed on at least the surface of the electrode exposed to the exhaust gas in the detection element 11. Further, the electrode wires 22 drawn from the rear end sides of the detection element 11 and the heater element 12 are each connected to the lead terminal 25 by spot welding as shown in FIG.

  Next, the support rod 18 will be described. As shown in FIG. 2, the support rod 18 is a member that extends in parallel with the axial direction of the detection element 11 and has a substantially U-shaped cross section in a direction orthogonal to the extended axial direction. As shown in FIGS. 1 and 2, the supporting rod 18 has the concave surface side directed toward the side surface near the electrode line 22 of the detection element 11, and the detection element 11 is interposed through a heat resistant cement (for example, phosphate cement). It is glued to. As the material of the support rod 18, a material close to the thermal expansion coefficient of the glass component constituting the second filling layer 312, specifically, alumina is used. This is because the thermal expansion difference between the detection element 11 made of a solid electrolyte base material mainly composed of zirconia and the second filling layer 312 made of a glass component is large, and cracks are generated in the detection element 11 when they are in direct contact with each other. For this reason, the difference in thermal expansion is buffered by the support rod 18.

  Next, the insulating soot tube 27 will be described with reference to FIGS. 1 and 3. FIG. 3 is a perspective view of the sensor element 14 showing a state in which the insulating rod 27 is attached to the sensor element 14 shown in FIG. As shown in FIG. 3, the insulating soot tube 27 is made of a ceramic member having a bottomed cylindrical shape, and the end surface side of the opening of the cylinder is directed toward the sensor rear end 142 side of the sensor element 14. It is attached to the tip side slightly from the middle part.

  In addition, an insertion hole (not shown) through which the sensor element 14 is inserted is provided substantially at the center of the bottom of the insulating soot tube 27. With the sensor element 14 being inserted into this insertion hole, the insulating soot tube 27 The sensor element 14 is held by the insulating rod 27 by filling the adhesive 28 inside the recess. As shown in FIG. 1, the insulating rod 27 holding the sensor element 14 is adapted to engage with a flange 131 erected on the inner peripheral surface of the ceramic holder 13.

  Next, the protective films 33 and 34 which are the main parts of the present invention will be described with reference to FIG. The protective film 33 is formed on the rear end surface 112 of the detection element 11 in the sensor element 14. The protective film 33 is made of a material close to the thermal expansion coefficient of the glass component contained in the second filling layer 312, specifically, alumina. This protective film 33 is cracked in the detection element 11 when the glass component constituting the second filling layer 312 is in direct contact with the rear end surface of the detection element 11 composed of zirconia as a base material, as in the support rod 18. In order to suppress this, it is formed so as to cover the entire rear end surface 112 of the detection element 11. In other words, the detection element 11 is prevented from being cracked by buffering the difference in coefficient of thermal expansion between the detection element 11 and the second filling layer 312 with the protective film 33. For the same reason, the protective film 34 is also provided in a certain range from the rear end surface 122, for example, about 6 mm, in the vicinity of the corner formed by the side surface of the heater element 12 and the concave end surface of the support rod 18. It is formed. A method of forming such protective films 33 and 34 will be described later.

  Next, the ceramic holder 13 will be described with reference to FIG. As shown in FIG. 1, the ceramic holder 13 is a substantially cylindrical ceramic body. The sensor holder 14 is inserted and held therein, and is itself housed and held in the metal shell 3. The ceramic holder 13 corresponds to a “sensor holder” in the claims. As a material of the ceramic holder 13, it is preferable to select a material having a thermal expansion coefficient close to that of the first filling layer 302 and the second filling layer 312 formed in the ceramic holder 13. This is because when the difference in thermal expansion between the ceramic holder 13 and the first filling layer 302 and the second filling layer 312 is large, an excessive amount between the ceramic holder 13 and the first filling layer 302 and the second filling layer 312 is excessive. This is because the compressive stress works and a crack is generated in the ceramic holder 13. In the present embodiment, the ceramic holder 13 is mainly formed of alumina close to the thermal expansion coefficient of the glass component because both the first filling layer 302 and the second filling layer 312 contain a glass component. ing.

  A flange 131 is erected on the inner peripheral surface on the front end side of the ceramic holder 13 toward the inner diameter direction of the ceramic holder 13. The insulating rod 27 attached to the sensor element 14 is engaged with a flange 131 in the ceramic holder 13. At this time, the sensor tip portion 141 of the sensor element 14 protrudes from the tip side of the ceramic holder 13 by a predetermined length, and the sensor tip portion 141 is exposed to the exhaust gas. Thus, the sensor element 14 is held coaxially by the ceramic holder 13. It is to be noted that a portion other than the sensor tip 141 of the sensor element 14 is accommodated by being inserted into the ceramic holder 13.

  The first packed layer 302 filled between the ceramic holder 13 and the sensor element 14 melts and solidifies a mixture powder composed of one or more powders of talc, magnesia, alumina, and the like and glass powder. It is formed by that. For example, the first packed bed 302 is obtained by melting and solidifying talc mixed powder containing 12% by mass of a glass component. The second filling layer 312 filled between the ceramic holder 13 and the sensor element 14 so as to surround the sensor rear end portion 142 of the sensor element 14 is made of crystallized glass powder (for example, silica magnesium borate glass based glass). ) Is melted and solidified. The second filling layer 312 corresponds to the “filling layer” in the claims.

  Next, the metal shell 3 will be described. As shown in FIG. 1, the metallic shell 3 is a substantially cylindrical mounting member made of SUS430. A ceramic holder 13 having a sensor element 14 is attached to the metal shell 3 and attached to an exhaust pipe through which exhaust gas flows. A double bottomed cylindrical protector 19 is provided in the opening on the front end side of the metal shell 3 so as to cover the sensor front end portion 141 of the protruding sensor element 14. A plurality of gas inlets are provided on the outer periphery of the protector 19. Thus, the exhaust gas passes through this gas inlet and is introduced into the protector 19.

  Further, in the gap between the metal shell 3 and the ceramic holder 13, a talc layer 24 compressed and filled with talc powder is provided. Furthermore, a substantially ring-shaped fastener 23 is fitted behind the talc layer 24. And the front end side of the outer cylinder 5 is engage | inserted between the metal shell 3 and the fastener 23, and the rear-end part of the metal shell 3 is crimped toward the inner side. Thus, the ceramic holder 13 and the outer cylinder 5 are attached to the metal shell 3.

  Next, the outer cylinder 5 and the protective outer cylinder 7 will be described. As shown in FIG. 1, the substantially cylindrical outer cylinder 5 is made of SUS304 and is attached to the rear end side of the metal shell 3. The outer cylinder 5 protects the rear end side from the middle of the ceramic holder 13. In addition, an insulating member support portion 51 is provided at the peripheral portion on the rear end side of the outer tube 5 and is erected and bent at a substantially right angle inside the outer tube 5. The insulating member support portion 51 supports the separator 16 disposed on the rear end side of the outer cylinder 5 from the front end side (lower side shown in FIG. 1). On the other hand, the substantially cylindrical protective outer cylinder 7 is also made of SUS304, and is attached by fitting the substantially cylindrical protective outer cylinder 7 from the rear end side of the outer cylinder 5. And the outer cylinder 5 and the protection outer cylinder 7 are firmly connected by crimping the fitting part (overlap part) of the outer cylinder 5 and the protection outer cylinder 7 toward radial inside.

  A separator 16 that houses and protects the connecting portion between the lead terminal 25 and the lead wire 50 described above is disposed inside the protective outer cylinder 7. A substantially cylindrical rubber cap 20 for closing the opening is disposed in the opening on the rear end side of the protective outer cylinder 7. The rubber cap 20 is fixed to the protective outer cylinder 7 by crimping the outer periphery of the protective outer cylinder 7 radially inward while being attached to the inner side of the rear end side of the protective outer cylinder 7. ing. The rubber cap 20 is provided with a plurality of insertion holes, and lead wires 50 drawn from the separator 16 are respectively inserted into the insertion holes.

Next, a method for manufacturing the air-fuel ratio sensor 1 will be described.
First, the sensor element 14 is formed by bonding the plate-shaped detection element 11 and the heater element 12 obtained by firing in advance through a bonding layer. As shown in FIG. 2, a support rod 18 is bonded to the sensor element 14 on the side surface in the vicinity of the electrode wire 22 of the detection element 11 using heat-resistant cement. Further, as shown in FIG. 3, an insulating soot tube 27 is attached via a bonding body 28 around the radial direction slightly on the tip side from the middle portion of the sensor element 14. Further, each electrode line 22 drawn from the rear end side of the detection element 11 and the heater element 12 is aligned into a predetermined shape as shown in FIG. Thereafter, the lead terminal 25 is welded to each electrode wire 22. Note that the state in which the lead terminals 25 are connected is omitted in the drawing.

  Among such sensor elements 14, the coating film 233 is formed on the rear end surface 112 of the detection element 11 by applying an insulating paste. In addition, a coating film 234 is formed by applying an insulating paste to a certain range from the rear end surface 122 in the vicinity of the corner formed by the side surface of the heater element 12 and the end surface on the concave side of the support rod 18. (Application process). These coating films 233 and 234 become the cured films 133 and 134 by ultraviolet irradiation in the cured film forming process described later, and further become the protective films 33 and 34 by the heat treatment in the protective film forming process.

In the present invention, as an insulating paste used to form such coating films 233 and 234, an alumina powder having a specific surface area of 2.8 m ² / g to 3.3 m ² / g and an ultraviolet curable resin are used. And having a viscosity of 20 Pa · s to 200 Pa · s. In the present invention, by using such an insulating paste, the insulating paste can be easily discharged from the discharge nozzle of a coating device such as a dispenser, and conventionally, a detection element that could only be performed by hand coating 11 can be automated using a coating apparatus. For this reason, the manufacturing time of the air-fuel ratio sensor 1 can be shortened, and productivity can be improved. Further, in the present invention, by using such an insulating paste, it is possible to form the protective films 33 and 34 having stress relaxation characteristics substantially equivalent to those of a conventional protective film made of an insulating paste. Moreover, it is preferable that this insulating paste does not contain an organic solvent substantially. This eliminates the need for long-time drying to remove the organic solvent, can significantly reduce the working time, and can also suppress the rupture of the insulating paste. In this embodiment, the insulating paste is substantially free of organic solvent.

Here, when the specific surface area of the alumina powder exceeds 3.3 m ² / g, it is difficult to make the viscosity of the insulating paste 200 Pa · s or less, and it is difficult to discharge the insulating paste from a discharge nozzle such as a dispenser. For example, in a conventional insulating paste, an alumina powder having an average particle size of 0.65 to 0.67 μm and a specific surface area of 6.47 to 7.24 m ² / g is used. However, when such an alumina powder is used, the viscosity of the insulating paste becomes 400 Pa · s or more even when a low viscosity UV curable resin is applied. For this reason, it becomes difficult to discharge the conventional insulating paste from a discharge nozzle such as a dispenser.

On the other hand, when the specific surface area of the alumina powder is reduced, the viscosity of the insulating paste is likely to be lowered and discharged from a discharge nozzle such as a dispenser. However, when the alumina powder is excessively small, such as less than 2.8 m ² / g, the protective film When 33 is formed, the contact area between the detection element 11 and the insulating ceramic powder is reduced, and as a result, the detection element 11 is easily cracked.

  Moreover, if the viscosity of the insulating paste is 200 Pa · s or less, it can be easily discharged from a discharge nozzle such as a dispenser, but if it becomes too low, such as less than 20 Pa · s, it is applied only to the desired portion. For example, as described above, a coating film 234 is formed by applying an insulating paste near the corner formed by the side surface of the heater element 12 and the end surface on the concave side of the support rod 18. Insulating paste may sag and adhere to unnecessary parts.

The specific surface area of the alumina powder is measured by the BET single point method. Specifically, for example, using a direct-reading specific surface area measurement device (monosoap) manufactured by Cantachrome, a sample (0.5 to 1.0 g) is placed in a sample cell, and an N ₂ -He (30:70) carrier is used. After degassing under gas flow (250 ° C., 20 minutes), N ₂ in the carrier gas is adsorbed at liquid nitrogen temperature. Thereafter, the temperature is raised to room temperature, and the amount of desorption is measured with a thermal conductivity detector to determine the surface area of the sample. The sample weight is measured immediately after the measurement. Then, the specific surface area (m ² / g) is obtained by dividing the surface area of the sample by the sample weight. On the other hand, the viscosity of the insulating paste is measured by a method based on JIS K7117-2.

The alumina powder is not necessarily limited as long as the specific surface area is 2.8 m ² / g or more and 3.3 m ² / g or less. For example, the average particle diameter is 0.5 μm or more and 0.8 μm or less. Are preferably used. As the alumina powder having such a specific surface area and average particle diameter, a commercially available product can be used. For example, a product commercially available from Sumitomo Chemical Co., Ltd. under the trade name Sumiko Random AA-05 is used. be able to.

  Further, the ultraviolet curable resin may be any resin that is cured by irradiating ultraviolet rays, and includes, for example, a prepolymer, a photopolymerizable monomer, and a photoinitiator.

  Examples of the prepolymer include polyester polyacrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate, oligo acrylate, alkyd acrylate, melamine acrylate, and silicon acrylate.

  Examples of the photopolymerizable monomer include monofunctional compounds such as n-lauryl acrylate, ethyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 1,6-hexanediol monoacrylate, dicyclopentadiene acrylate, and cyclohexyl acrylate. Monomers (monofunctional acrylate), dicyclopentenyl acrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, carboepoxy acrylate, 1,6-hexanediol eye acrylate, ethylene glycol acrylate, nonaethylene glycol diacrylate, etc. A functional monomer (polyfunctional acrylate) etc. can be mentioned. These photopolymerizable monomers are also referred to as reactive diluents.

  Examples of the photoinitiator include acetophenones, benzophenones, Michler ketones, benzoins, and benzoin ethers.

  Such an ultraviolet curable resin may contain various additives such as a stabilizer, a sensitizer, and a pigment in addition to the prepolymer, the photopolymerization monomer, and the photoinitiator. Moreover, when using an ultraviolet curable resin, a commercially available ultraviolet curable resin (ultraviolet curable adhesive) can also be used. Examples of commercially available ultraviolet curable resins include products marketed under the trade names of “3Bond 3121” and “3Bond 3130” from ThreeBond Co., Ltd., and commercially available under the tradename of “Loctite” from Henkel Japan Co., Ltd. Can be used.

  In the present invention, among such ultraviolet curable resins, it is particularly preferable to use those having a viscosity of 500 mPa · s to 1000 mPa · s. When the viscosity of the ultraviolet curable resin exceeds 1000 mPa · s, the viscosity of the insulating paste easily exceeds 200 Pa · s, and it may be difficult to discharge from a discharge nozzle such as a dispenser. Further, when the viscosity of the ultraviolet curable resin is less than 500 mPa · s, the viscosity of the insulating paste tends to be less than 20 Pa · s, and it may be difficult to apply the insulating paste only to a desired portion. The viscosity of the ultraviolet curable resin is measured using an E-type viscometer with a rotor cone of 3 ° × R9.7.

The insulating paste having a viscosity of 20 Pa · s or more and 200 Pa · s or less used in the present invention comprises an alumina powder having a specific surface area of 2.8 m ² / g or more and 3.3 m ² / g or less, and an ultraviolet curable resin. It can be obtained by blending and kneading. At this time, as described above, an ultraviolet curable resin having a viscosity of 500 mPa · s or more and 1000 mPa · s or less is used, and further, 20 parts by weight or more of the ultraviolet curable resin with respect to 100 parts by weight of the insulating ceramic powder. By blending at a ratio of 50 parts by weight or less, an insulating paste having a viscosity of 20 Pa · s to 200 Pa · s as described above can be easily prepared.

For example, 100 parts by weight of alumina powder having an average particle diameter of 0.5 μm or more and 0.8 μm or less and a specific surface area of 2.8 m ² / g or more and 3.3 m ² / g or less has a viscosity of 500 mPa · s or more. An insulating paste having a viscosity of about 80 Pa · s can be obtained by blending an ultraviolet curable resin of 1000 mPa · s or less in a proportion of 35 parts by mass.

  The insulating paste thus prepared can be applied to the rear end surface 112 or the like of the detection element 11 using a coating device such as a dispenser, for example, as follows. First, as shown in FIG. 5, the sensor element 14 (hereinafter simply referred to as the sensor element 14) to which the supporting soot pipe 18 and the insulating soot pipe 27 are bonded as shown in FIG. Fix it.

  Then, as shown in FIG. 6, the insulating paste P is discharged from the discharge nozzle 411 of the dispenser 410, and the insulating paste P is applied to the rear end surface 112 of the detection element 11. At this time, as shown in an enlarged view in FIG. 7, the insulating paste P is applied only to, for example, the edge portion on the opposite side of the heater element 12 in the rear end surface 112 of the detection element 11. 8 is a view of the sensor element 14 and the like shown in FIG. 6 as viewed from the detection element 11 side (left side in FIG. 6). When applying the insulating paste P, for example, the discharge nozzle 411 is detected. The insulating paste P is applied by moving in the horizontal direction from one side surface side to the other side surface side of the rear end surface 112 of the element 11.

  The discharge nozzle 411 of the dispenser 410 as described above preferably has an inner diameter of 0.48 mm or more and 0.70 mm or less. If the inner diameter of the discharge nozzle 411 exceeds 0.70 mm, the inner diameter is too large, and it becomes difficult to appropriately control the coating amount of the insulating paste P. Further, when the inner diameter of the discharge nozzle 411 is less than 0.48 mm, it is difficult to discharge from the discharge nozzle 411 even if the viscosity of the insulating paste P is 20 Pa · s or more and 200 Pa · s or less.

  For the case where the insulating paste P is applied to the edge portion in this way, as shown in FIG. 9, the air blow is performed from the edge side using the air blow device 430, and is expanded to FIG. 10. As shown, the insulating paste P applied to the edge is spread to the heater element 12 side, and the coating film 233 made of the insulating paste P is formed on the entire rear end surface 112 of the detection element 11.

  Moreover, as shown in FIGS. 11 and 12 (FIG. 12 is a partially enlarged view of FIG. 11) in the vicinity of the corner formed by the side surface of the heater element 12 and the end surface on the concave side of the support rod 18. The coating film 234 made of the insulating paste P is formed by discharging the insulating paste P from the discharge nozzle 411 while moving the discharge nozzle 411 of the dispenser 410 in the vertical direction.

The sensor element 14 (see also FIG. 4) on which the coating films 233 and 234 made of the insulating paste P are formed in this way uses an ultraviolet irradiation device (light source: ultrahigh pressure mercury lamp, wavelength 365 nm) as in the conventional case. For example, by irradiating ultraviolet rays at an output of 950 mW / cm ² for about 5 seconds, the coating films 233 and 234 are photocured to form cured films 133 and 134 (cured film forming step).

  Then, the sensor element 14 is inserted inside the separately formed ceramic holder 13, and the insulating rod 27 of the sensor element 14 is engaged with the flange 131 of the ceramic holder 13.

  As shown in FIG. 13, talc mixed powder 301 containing, for example, 12% by mass of a glass component serving as the first packed layer 302 is supplied to the gap in the ceramic holder 13 in which the sensor element 14 is inserted. The talc mixed powder 301 is lowered by applying mechanical vibration to 13. Further, crystallized glass powder 311 to be the second packed layer 312 is supplied to the gap in the ceramic holder 13 filled with the talc mixed powder 301.

  The ceramic holder 13 filled with the talc mixed powder 301 and the crystallized glass powder 311 is housed in a heating furnace and heat-treated at 800 ° C. for 1 hour in an air atmosphere (protective film forming step). After the heat treatment is completed, the sensor holder 13 is removed from the heating furnace and allowed to cool. Through a series of processes including this heat treatment, as shown in FIG. 14, the cured films 133 and 134 become the protective films 33 and 34, respectively, and the talc mixed powder 301 and the crystallized glass powder 311 are melted and solidified, respectively. The layer 302 and the second filling layer 312 are formed. The ultraviolet curable resin constituting the cured films 133 and 134 is degreased (burned out) at the time of temperature rise during the heat treatment.

  The ceramic holder 13 that has been heat-treated in this manner is mounted inside the metal shell 3, and the separator 16, outer cylinder 5, and protective outer cylinder 7 are appropriately assembled by a known procedure, and an air-fuel ratio as shown in FIG. This is sensor 1.

  The manufacturing method of the present invention has been described above. However, the present invention is not necessarily limited to the above-described manufacturing method, and the configuration thereof is appropriately changed as necessary and within the scope not departing from the spirit of the present invention. be able to. For example, in the manufacturing method described above, the insulating paste P is applied to the edge of the rear end surface 112 of the detection element 11, and the coating film 233 is formed by performing air blowing on the insulating paste P. However, such a method is not necessarily required as long as it can be formed. Moreover, in the said manufacturing method, after forming the coating film 233, the coating film 234 was formed, However, The formation order of such a coating film can also be changed suitably.

  Further, the air-fuel ratio sensor 1 is configured such that the thermal expansion coefficient of the second packed bed 302 is closer to the thermal expansion coefficient of the heater element 12 than the detection element 11. May be configured so as to be closer to the thermal expansion coefficient of the detection element 11 than the heater element 12. In this case, it is necessary to form a protective film so as to cover the rear end surface 122 of the heater element 12. In addition, the sensor element 14 is configured such that the detection element 11 and the heater element 12 are bonded via the bonding layer, but the detection element and the heater element may be integrated by simultaneous firing.

The longitudinal cross-sectional view which shows an example of the gas sensor (all area | region air fuel ratio sensor) manufactured by the manufacturing method of this invention. The perspective view which shows the sensor element with which the supporting soot tube was mounted | worn. The perspective view which shows the sensor element with which the insulated soot pipe was mounted | worn. The perspective view which shows the sensor element in which the coating film which consists of insulating paste was formed. The figure which shows a mode that the sensor element was fixed to the jig | tool. The figure which shows a mode that an insulating paste is apply | coated to the rear end surface of a detection element. The enlarged view which expands and shows the mode of application | coating of the insulating paste shown in FIG. The figure which shows a mode that application | coating of the insulating paste shown in FIG. 6 was seen from another direction. The figure which shows the mode of application | coating of the insulating paste by an air blow. The enlarged view which expands and shows the mode of application | coating of the insulating paste shown in FIG. The figure which shows a mode that an insulating paste is apply | coated to the side part of the rear end side of a heater element. The enlarged view which expands and shows the mode of application | coating of the insulating paste shown in FIG. The longitudinal cross-sectional perspective view which shows the state which supplied the talc mixed powder and the crystallized glass powder in the ceramic holder in which the sensor element was inserted. The longitudinal cross-sectional perspective view which shows the state after heat processing of the ceramic holder etc. which are shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Air-fuel ratio sensor (gas sensor), 3 ... Main metal fitting, 11 ... Detection element, 12 ... Heater element, 13 ... Ceramic holder (sensor holder), 14 ... Sensor element, 18 ... Support pipe, 22 ... Electrode wire, 27 ... Insulating soot tube 33, 34 ... Protective film, 112 ... Rear end surface of detection element, 122 ... Rear end surface of heater element, 133, 134 ... Hardened film, 141 ... Sensor front end portion, 142 ... Sensor rear end portion, 233, 234 ... Coating film, 301 ... talc mixed powder, 302 ... first packed layer, 311 ... crystallized glass powder, 312 ... second packed layer (filled layer), 400 ... jig, 410 ... dispenser, 411 ... nozzle, 430 ... air Blowing device, P ... insulating paste

Claims (4)

A sensor element composed of a plate-like detection element that detects the concentration of a specific gas component in the gas to be measured, and a plate-like heater element that is stacked on the detection element and heats the detection element;
A cylindrical sensor holder that penetrates the sensor element along the axial direction in a state in which the front end side of the sensor element protrudes from the front end of the sensor element, and accommodates a rear end portion of the sensor element inside itself,
A filling layer filled between the sensor element and the sensor holder so as to surround at least a rear end portion of the sensor element, and containing at least a glass component;
A method of manufacturing a gas sensor comprising:
Among the detection element and the heater element constituting the sensor element, alumina powder and UV-curing property are formed on the rear end surface of the element composed of a base material having a large difference in coefficient of thermal expansion of at least the glass component. An application step of applying an insulating paste containing a resin;
A cured film forming step of forming a cured film covering the rear end surface by irradiating the insulating paste with ultraviolet rays to cure the insulating paste;
In a gas sensor manufacturing method comprising a protective film forming step of forming a protective film by heat-treating the cured film,
The insulating paste in the coating step has a specific surface area of the alumina powder of 2.8 m ² / g to 3.3 m ² / g and a viscosity of 20 Pa · s to 200 Pa · s. A method for manufacturing a gas sensor.   The method for producing a gas sensor according to claim 1, wherein the ultraviolet curable resin has a viscosity of 500 mPa · s to 1000 mPa · s.   In the protective film forming step, after the sensor element with the cured film formed is inserted into the sensor holder, the filling layer including at least the glass component is formed between the sensor element and the sensor holder. 3. The method of manufacturing a gas sensor according to claim 1, wherein the filling layer and the protective film are formed simultaneously by filling a powder and performing a heat treatment.   4. The method of manufacturing a gas sensor according to claim 1, wherein the base material forming the detection element is mainly made of zirconia, and the base material forming the heater element is mainly made of alumina. 5.

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