JP5387550B2 - Method for manufacturing gas sensor element - Google Patents

Description

  The present invention relates to a method for manufacturing a gas sensor element for detecting a specific gas concentration in a gas to be measured.

An exhaust system such as an internal combustion engine for a vehicle is provided with a gas sensor that detects a specific gas concentration (for example, oxygen concentration) in a measured gas such as exhaust gas.
Examples of the gas sensor include an oxygen ion conductive solid electrolyte body, a gas side electrode to be measured and a reference gas side electrode provided on one surface and the other surface of the solid electrolyte body, and a gas side electrode to be measured. And a gas sensor element having a porous diffusion resistance layer that allows the gas to be measured to pass therethrough.

  Some gas sensor elements have a structure in which an outer surface of a diffusion resistance layer serving as an inlet for a gas to be measured is covered with a porous protective layer. By adopting such a structure, poisonous substances (for example, lead, glass, phosphorus, etc.) in the exhaust gas that is the gas to be measured are trapped in the porous protective layer, and the gas-side electrode to be measured is deteriorated by poisoning. This prevents the deterioration of sensor characteristics.

  The gas sensor element having the above structure, for example, after laminating and firing a plurality of ceramic sheets constituting a solid electrolyte body, a diffusion resistance layer, etc., and producing an element main body, the outer surface of the diffusion resistance layer of the element main body It is manufactured by applying a paste-like material for forming a protective layer and baking it to form a protective layer (see Patent Documents 1 and 2).

JP 2006-126077 A JP 2007-248144 A

However, in the conventional method for manufacturing a gas sensor element, a paste-form protective layer forming material is applied to a previously produced element body and fired. That is, when the protective layer forming material is baked to form the protective layer, the element body portion that has been baked once and the protective layer forming material that has not been baked are simultaneously baked. The firing shrinkage varies greatly. As a result, there is a problem that the protective layer is peeled off at the interface with the element body.
Further, when the protective layer is peeled off, the function of the protective layer cannot be fully exhibited, and there is a problem that the poisoning resistance and sensor characteristics of the gas sensor element are deteriorated.

  This invention is made | formed in view of this problem, and it aims at providing the manufacturing method of the gas sensor element which can prevent peeling of the protective layer, maintaining the function of a protective layer.

The present invention provides an oxygen ion conductive solid electrolyte body, a measured gas side electrode and a reference gas side electrode provided on one surface and the other surface of the solid electrolyte body, and the measured gas side electrode, respectively. An element main body having a porous diffusion resistance layer that allows a gas to be measured to be in contact therewith, and a protective layer formed on the outer surface of the diffusion resistance layer that introduces the gas to be measured in the element main body; A method of manufacturing a gas sensor element comprising:
In forming the protective layer, it contains at least ceramic particles, acrylic resin particles and burnt-down particles burned off by firing, water or an organic solvent, and an organic binder resin soluble in the solvent. A protective layer forming material manufacturing step of manufacturing a protective layer forming material to be performed;
An application step of applying the protective layer forming material on the outer surface of the diffusion resistance layer of the element body;
Drying the protective layer forming material after the coating step, and removing the solvent in the protective layer forming material;
Firing the protective layer forming material, and performing a firing step to form the protective layer,
The content of the burnable particles in the protective layer-forming material after the drying step is 30 to 60% by volume,
In the method for producing a gas sensor element, the burning start temperature of the burnable particles in the protective layer forming material is higher than the burning start temperature of the organic binder resin.

  In the gas sensor element manufacturing method, the protective layer forming material preparation step, the coating step, and the baking step are performed when the protective layer is formed. Further, the protective layer forming material produced in the protective layer forming material producing step contains at least ceramic particles, burnable particles burned off by firing, a solvent, and an organic binder resin. And the burning start temperature of the burnable particles in the protective layer forming material is higher than the burning start temperature of the organic binder resin.

  Therefore, in the firing step, the burnable particles remain in the protective layer forming material at the stage where the organic binder resin starts to be burned out, and the skeleton of the protective layer forming material is formed together with the ceramic particles. ing. Therefore, the organic binder resin is burned out in a state where the skeleton of the protective layer forming material is maintained to some extent. Thereby, shrinkage | contraction of the protective layer forming material accompanying the burning-out of organic binder resin can be suppressed, and the baking shrinkage rate of the protective layer forming material can be reduced. As a result, the difference in firing shrinkage ratio between the element body and the protective layer forming material applied to the element body can be reduced, and peeling of the protective layer from the element body can be prevented.

  In addition, the burnable particles are finally burned off by firing, and thus do not exist in the formed protective layer. Thereby, the function of the protective layer is not impaired by the burnable particles. That is, it is possible to maintain the function of the protective layer to be originally obtained, for example, the function of trapping poisonous substances in the measurement gas.

  Thus, according to the present invention, it is intended to provide a method for manufacturing a gas sensor element that can prevent peeling of the protective layer while maintaining the function of the protective layer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing a stacked gas sensor element in Example 1. FIG. 2 is a perspective development view showing an element main body in Example 1. FIG. 3 is an explanatory view showing a protective layer in Example 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing a gas sensor incorporating a gas sensor element in Example 1. FIG. 3 is an explanatory view showing a state in which a protective layer forming material is applied to the element body in Example 1. FIG. 3 is an explanatory diagram showing a protective layer forming material applied to the element body in Example 1. FIG. 3 is an explanatory diagram illustrating another example of the stacked gas sensor element in the first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing a stacked gas sensor element in Example 1. FIG. 3 is an explanatory view showing a protective layer in Example 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing a stacked gas sensor element in Example 1. FIG. 3 is an explanatory view showing a cup-type gas sensor element in the first embodiment. Explanatory drawing which shows a TG / DTA curve.

  The gas sensor element is disposed in an exhaust system such as an internal combustion engine for a vehicle, for example, and is based on a limiting current flowing between electrodes depending on a specific gas concentration (oxygen concentration) in a measured gas (exhaust gas). A / F sensor element for detecting the air-fuel ratio (A / F) of the air-fuel mixture supplied to the engine, depending on the specific gas concentration (oxygen concentration) ratio between the measured gas (exhaust gas) and the reference gas (atmosphere) Thus, the present invention is applied to an oxygen sensor element that detects an air-fuel ratio based on an electromotive force generated between electrodes.

In addition to the solid electrolyte body provided with the gas side electrode to be measured and the reference gas side electrode, the gas sensor element is, for example, a solid electrolyte for an oxygen pump for adjusting the oxygen concentration in a reference gas chamber into which a reference gas is introduced. A body or the like may be provided.
Further, the gas sensor element may be, for example, a stacked gas sensor element formed by laminating a solid electrolyte body, a diffusion resistance layer, or the like, or a solid electrolyte having a closed end and an open base end A cup-type gas sensor element having a body may be used.

  In the application step, a protective layer forming material is applied on the outer surface of the diffusion resistance layer of the element main body prepared in advance. Here, the element main body can be produced, for example, by laminating a plurality of ceramic sheets constituting a solid electrolyte body, a diffusion resistance layer, and the like, and firing them.

In the application step, for example, a paste-like protective layer forming material is applied by pad printing or screen printing, a slurry-like protective layer forming material is applied, or a slurry-like protective layer is formed. It can be applied by dipping the element body in the material.
In the application step, the protective layer forming material is applied at least on the outer surface of the diffusion resistance layer of the element body. For example, the protective layer forming material may be applied to a part of the outer peripheral surface of the element body including the outer surface of the diffusion resistance layer, or may be applied over the entire periphery.

  The protective layer is formed at least on the outer surface of the diffusion resistance layer that serves as an inlet for the gas to be measured in the element body, and the main function is poisoning in the exhaust gas that is the gas to be measured. It is to trap substances (for example, lead, glass, phosphorus, etc.) and prevent poisoning deterioration of the gas side electrode to be measured and accompanying sensor characteristics deterioration.

  In addition, when the protective layer is formed over a part or the entire circumference of the outer peripheral surface of the element body including the outer surface of the diffusion resistance layer, for example, the protective layer has the above-described poisoning prevention function. It also has the function of preventing water exposure. That is, the gas sensor element used at high temperatures has a problem that the element main body is cracked due to the occurrence of thermal shock due to water exposure, but the cracking of the element main body due to the water exposure is prevented by the protective layer. be able to.

  The burning start temperature of the burnable particles in the protective layer forming material is higher than the burning start temperature of the organic binder resin. For example, when the burnout start temperature of the burnable particles is lower than the burnout start temperature of the organic binder resin, the organic binder resin is burned away while maintaining the skeleton of the protective layer forming material to some extent due to the presence of the burnable particles. There is a possibility that the effect cannot be obtained sufficiently.

  Moreover, the burning start temperature of the burnable particles can be adjusted by changing the particle size of the burnable particles. For example, by increasing the particle size of the burnable particles, the burning start temperature of the burnable particles can be increased. Accordingly, if the burnout start temperature of the organic binder resin to be used is known, the particle size of the burnable particles may be adjusted so as to be higher than the burnout start temperature of the organic binder resin.

Moreover, the burning start temperature of the burnable particles and the organic binder resin can be determined, for example, by measuring differential heat and thermogravimetry by TG / DTA (differential heat / thermogravimetric simultaneous measurement method).
Specifically, it is assumed that, for example, a TG / DTA curve as shown in FIG. 12 is obtained by TG / DTA under the condition of a heating temperature increase rate of 10 ° C./min in an air atmosphere. Then, as shown in the figure, in the TG curve, the temperature T at the intersection Z between the extension line x of the baseline part X before weight reduction and the tangent line y of the first sudden weight loss part Y is obtained, and this is calculated as the burning start temperature. (Pyrolysis start temperature).

Moreover, it is preferable that the baking shrinkage rate of the said protective layer forming material is 8.0% or less.
In this case, the effect of preventing peeling of the protective layer from the element body can be sufficiently exhibited.
In addition, the firing shrinkage rate of the protective layer forming material is, for example, before and after firing when a square column (cuboid) sample is prepared using the protective layer forming material and the sample is fired under predetermined conditions. It can be determined by measuring the volume change rate.

Moreover, it is preferable that the burning start temperature of the burnable particles is 35 ° C. or more higher than the burning start temperature of the organic binder resin.
In this case, the effect of burning out the organic binder resin while maintaining the skeleton of the protective layer forming material to some extent due to the presence of the burnable particles can be obtained more reliably.

In addition, after the coating step, the protective layer forming material is dried, a drying step of removing the solvent in the protective layer forming material is performed, and the burnout in the protective layer forming material after the drying step is performed. The content of the conductive particles is preferably 30 to 60% by volume .
In this case, the presence of the burnable particles can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material accompanying the burnout of the organic binder resin.

  When the content of the burnable particles in the protective layer forming material is less than 30% by volume, the effect of maintaining the skeleton of the protective layer forming material by the burnable particles cannot be sufficiently obtained, and organic There is a possibility that the shrinkage of the protective layer forming material due to the burnout of the binder resin cannot be suppressed. On the other hand, when the content of the burnable particles exceeds 60% by volume, the particle density in the protective layer forming material increases, and it is difficult to apply the protective layer forming material to the element body. There is a risk.

The average particle diameter of the burned particles is preferably smaller than the average particle diameter of the ceramic particles (claim 3).
In this case, the burnable particles can be burned out in a state where the skeleton of the protective layer forming material is maintained to some extent by the ceramic particles. Thereby, the baking shrinkage rate of the protective layer forming material can be further reduced.

  When the average particle size of the burnable particles is larger than the average particle size of the ceramic particles, the burnable particles are burned out while maintaining the skeleton of the protective layer forming material to some extent by the ceramic particles. May be difficult. That is, there is a possibility that the skeleton of the protective layer forming material cannot be maintained by the ceramic particles due to the burning of the burnable particles.

The average particle size of the burnable particles is preferably 0.5 to 4 μm.
In this case, the presence of the burnable particles can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material accompanying the burnout of the organic binder resin.

  When the average particle size of the burnable particles is less than 0.5 μm, the viscosity of the protective layer forming material increases, and the applicability of the protective layer forming material may decrease. On the other hand, when the average particle diameter of the burnable particles exceeds 4 μm, it is difficult to burn down the burnable particles while maintaining the skeleton of the protective layer forming material to some extent by the ceramic particles. There is a fear.

The burnable particles are preferably made of acrylic resin particles or carbon particles .
In this case, the presence of the burnable particles can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material due to the burnout of the organic binder resin, and the burnout is surely burned off, Can maintain the function.

  In addition, as the organic binder resin, for example, organic resins such as ethyl cellulose, methyl cellulose, polyvinyl butyral, and the like whose decomposition start temperature is less than 240 ° C. can be used.

Example 1
The manufacturing method of the gas sensor element concerning the Example of this invention is demonstrated using figures.
As shown in FIGS. 1 to 3, the gas sensor element 1 manufactured in this example includes an oxygen ion conductive solid electrolyte body 11, and a measurement target provided on one surface and the other surface of the solid electrolyte body 11. An element body 10 having a gas side electrode 12 and a reference gas side electrode 13, and a porous diffusion resistance layer 17 that allows a gas to be measured to be in contact with the gas to be measured 12 to be measured. And a protective layer 2 formed on the outer surface 171 of the diffusion resistance layer 17 for introducing gas.
This will be described in detail below.

As shown in FIG. 1, the gas sensor element 1 includes an air-fuel ratio (air-fuel ratio) of an air-fuel mixture supplied to an engine based on a limit current flowing between electrodes depending on a specific gas concentration (oxygen concentration) in a gas to be measured (exhaust gas). A / F sensor element for detecting (A / F).
The gas sensor element 1 has an element body 10. In the element body 10, a measured gas side electrode 12 made of platinum is provided on one surface of an oxygen ion conductive solid electrolyte body 11 made of zirconia. A reference gas side electrode 13 made of platinum is provided on the other surface of the solid electrolyte body 11.

  As shown in the figure, on the side of the reference gas side electrode 13 of the solid electrolyte body 11, a reference gas chamber forming layer 14 made of alumina which is electrically insulating and dense and does not transmit gas is laminated. A groove portion 141 is provided in the reference gas chamber forming layer 14, and a reference gas chamber 140 is formed by the groove portion 141. The reference gas chamber 140 is configured to be able to introduce a reference gas (atmosphere).

  A heater substrate 15 is laminated on the surface of the reference gas chamber forming layer 14 opposite to the solid electrolyte body 11. On the heater substrate 15, a heating element (heater) 151 that generates heat when energized is provided so as to face the reference gas chamber forming layer 14. The heating element 151 is configured to heat the gas sensor element 1 to an activation temperature by generating heat by energization.

As shown in the figure, an insulating layer 16 having an opening 161 is laminated on the measured gas side electrode 12 side of the solid electrolyte body 11. The insulating layer 16 is made of alumina that is electrically insulative and dense and does not transmit gas.
On the surface of the insulating layer 16 opposite to the solid electrolyte body 11, a porous diffusion resistance layer 17 made of a gas-permeable alumina porous body is laminated.

A measured gas chamber 160 is formed at a location covered by the solid electrolyte body 11, the opening 161 of the insulating layer 16, and the diffusion resistance layer 17. The measured gas chamber 160 is configured so that the measured gas (exhaust gas) can be introduced from the diffusion resistance layer 17.
On the surface of the diffusion resistance layer 17 opposite to the insulating layer 16, a shielding layer 18 made of alumina that is electrically insulating and dense and does not transmit gas is laminated.

As shown in FIG. 2, the measured gas side electrode 12 provided on one surface of the solid electrolyte body 11 passes through the conductive lead portion 121, the terminal portion 122, and the through hole 188 formed in the shielding layer 18. The terminal portion 123 is electrically connected.
Further, the reference gas side electrode 13 provided on the other surface of the solid electrolyte body 11 is formed on the conductive lead portion 131, the terminal portions 132 and 133, the solid electrolyte body 11, the insulating layer 16, and the shielding layer 18, respectively. The through holes 119, 169, and 189 are electrically connected to the terminal portion 134.
The heat generating portion 151 provided on the heater substrate 15 is electrically connected to the terminal portion 153 through a pair of conductive lead portions 152 and a pair of through holes 159 formed in the heater substrate 15. .

As shown in FIG. 1, the protective layer 2 is formed on the outer surface 171 of the diffusion resistance layer 17 serving as an inlet for the gas to be measured in the element body 10.
As shown in FIG. 3, the protective layer 2 is composed of ceramic particles 21 mainly composed of alumina, catalytic noble metal particles 29 such as Pt, Pd, and Rh supported on the ceramic particles 21 and glass particles. Is a porous layer of 36 to 48%. In FIG. 3, the glass particles are not shown.

The protective layer 2 traps poisonous substances (for example, lead, glass, phosphorus, etc.) in the gas to be measured (exhaust gas) introduced from the outer surface 171 of the diffusion resistance layer 17 into the gas chamber 160 to be measured. The gas-side electrode 12 is configured to be able to prevent poisoning deterioration and accompanying sensor characteristic deterioration.
Further, the protective layer 2 is configured such that the catalyst noble metal particles 29 supported on the ceramic particles 21 can burn the hydrogen gas in the gas to be measured (exhaust gas) to prevent output deviation caused by the hydrogen gas. ing.

Next, the gas sensor 8 provided with the gas sensor element 1 of this example will be described.
As shown in FIG. 4, the gas sensor 8 is disposed on the base end side of the gas sensor element 1, an insulator 81 that inserts and holds the gas sensor element 1 inside, a housing 82 that inserts and holds the insulator 81 inside, and a housing 82. It has an atmosphere-side cover 83 provided and an element cover 84 that is disposed on the front end side of the housing 82 and protects the gas sensor element 1.

As shown in the figure, the element cover 84 is constituted by a double-structured cover including an outer cover 841 and an inner cover 842.
The outer cover 841 and the inner cover 842 are provided with a conduction hole 843 in the side surface and the bottom surface for conducting the gas to be measured.

Next, the manufacturing method of the gas sensor element 1 of this example is demonstrated.
In forming the protective layer 2 in the method of manufacturing the gas sensor element 1 of the present example, as shown in FIGS. 5 and 6, the ceramic particles 21, the burnable particles 22 burned off by firing, and a solvent made of an organic solvent, A protective layer forming material preparation step for preparing a protective layer forming material 20 containing an organic binder resin 23 soluble in a solvent, and an outer surface of the diffusion resistance layer 17 of the element body 10 on the protective layer forming material 20. A coating process for coating on 171 and a firing process for firing the protective layer forming material 20 coated on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 to form the protective layer 2 are performed.
The burning start temperature of the burnable particles 22 in the protective layer forming material 20 is higher than the burning start temperature of the organic binder resin 23.
This will be described in detail below.

  In manufacturing the gas sensor element 1 of the present example, first, the element main body 10 is manufactured. Specifically, the ceramic sheets constituting the heater substrate 15, the reference gas chamber forming layer 14, the solid electrolyte body 11, the insulating layer 16, the diffusion resistance layer 17, and the shielding layer 18 are sequentially laminated to produce an element intermediate. . Then, the element intermediate is fired under conditions of 1400 to 1500 ° C. for 1 to 3 hours, and the element body 10 (see FIG. 1) is manufactured.

  Next, ceramic particles 21 (10.9% by volume) made of alumina, catalytic noble metal particles 29 (1.1% by volume) made of noble metals such as Pt, Pd, Rh, and glass particles (5.7% by volume) Burnout particles 22 made of acrylic resin (17% by volume), a solvent made of terpineol as an organic solvent (62.3% by volume), and an organic binder resin 23 made of ethyl cellulose soluble in the solvent (3% by volume) Are mixed and kneaded to prepare a paste-like protective layer forming material 20 (see FIGS. 5 and 6) (protective layer forming material preparing step).

Here, the burning start temperature of the burnable particles 22 in the protective layer forming material 20 is higher than the burning start temperature of the organic binder resin 23. In this example, the burnout start temperature of the burnable particles 22 is about 280 ° C., and the burnout start temperature of the organic binder resin 23 is about 200 ° C. That is, the burning start temperature of the burnable particles 22 is 35 ° C. or more higher than the burning start temperature of the organic binder resin 23.
Further, the average particle size of the burnable particles 22 is smaller than the average particle size of the ceramic particles 21. In this example, the average particle size of the burnable particles 22 is about 1.0 μm, and the average particle size of the ceramic particles 21 is about 4.0 μm.

Next, as shown in FIG. 5, the paste-like protective layer forming material 20 is applied onto the outer surface 171 of the diffusion resistance layer 17 of the element body 10 (application step). In this example, the paste-like protective layer forming material 20 was applied by a method such as pad printing or screen printing.
Next, the protective layer forming material 20 applied on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 is dried at 140 ° C. for 15 minutes, and the organic solvent (solvent) in the protective layer forming material 20 is then dried. Are removed by evaporation (drying step).

  As a result, as shown in FIG. 6, the protective layer forming material 20 applied on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 has a skeleton formed by the ceramic particles 21 and the burnable particles 22. The organic binder resin 23 exists between the ceramic particles 21 and the burnable particles 22 forming the skeleton. At this time, the content of the burnable particles 22 in the protective layer forming material 20 is 45.1% by volume. In FIG. 6, illustration of glass particles is omitted.

Thereafter, the protective layer forming material 20 applied on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 is fired under the conditions of 900 ° C. and 1 hour (firing step).
In this firing process, first, the organic binder resin 23 in the protective layer forming material 20 starts to burn out. At this time, the protective layer forming material 20 is in a state where a skeleton is formed by the ceramic particles 21 and the burnable particles 22. Next, the burnable particles 22 in the protective layer forming material 20 start to burn out. Finally, the organic binder resin 23 and the burnable particles 22 are burned out, and a porous protective layer 2 (see FIG. 3) composed of the remaining ceramic particles 21 and the catalyst noble metal 29 is formed.
As described above, the gas sensor element 1 (see FIG. 1) is manufactured.

Next, the effect in the manufacturing method of the gas sensor element 1 of this example is demonstrated.
In the manufacturing method of the gas sensor element 1 of this example, when forming the protective layer 2, the protective layer forming material preparation process, the coating process, and the baking process are performed. Further, the protective layer forming material 20 produced in the protective layer forming material production step contains ceramic particles 21, burnable particles 22 burned off by firing, a solvent, and an organic binder resin 23. The burning start temperature of the burnable particles 22 in the protective layer forming material 20 is higher than the burning start temperature of the organic binder resin 23.

  Therefore, in the firing step, the burnable particles 22 remain in the protective layer forming material 20 at the stage where the organic binder resin 23 starts to be burned out, and the skeleton of the protective layer forming material 20 is the ceramic particles 21. It forms with. Therefore, the organic binder resin 23 is burned out in a state where the skeleton of the protective layer forming material 20 is maintained to some extent. Thereby, shrinkage | contraction of the protective layer forming material 20 accompanying the burning of the organic binder resin 23 can be suppressed, and the baking shrinkage rate of the protective layer forming material 20 can be reduced. As a result, the difference in firing shrinkage between the element body 10 and the protective layer forming material 20 applied to the element body 10 can be reduced, and the protective layer 2 can be prevented from peeling off from the element body 10. be able to.

  Further, the burnable particles 22 are finally burned off by firing, and thus are not present in the formed protective layer 2. Thereby, the function of the protective layer 2 is not impaired by the burnable particles 22. That is, it is possible to maintain the function of the protective layer 2 to be originally obtained, for example, the function of trapping poisonous substances in the measurement gas as in this example.

  Moreover, in this example, after the coating process, the protective layer forming material 20 is dried, and a drying process for removing the organic solvent (solvent) in the protective layer forming material 20 is performed. The content rate of the burnable particles 22 in the material 20 is in the range of 30 to 60% by volume. Therefore, the presence of the burnable particles 22 can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material 20 due to the burnout of the organic binder resin 23.

  Moreover, the burning start temperature of the burnable particles 22 is 35 ° C. or more higher than the burning start temperature of the organic binder resin 23. Therefore, the effect of burning off the organic binder resin 23 in a state where the skeleton of the protective layer forming material 20 is maintained to some extent due to the presence of the burnable particles 22 can be obtained more reliably.

  Further, the average particle size of the burnable particles 22 is smaller than the average particle size of the ceramic particles 21. Therefore, the burnable particles 22 can be burned out in a state where the skeleton of the protective layer forming material 20 is maintained to some extent by the ceramic particles 21. Thereby, the baking shrinkage rate of the protective layer forming material 20 can be further reduced.

  Moreover, the average particle diameter of the burnable particles 22 is 0.5 to 4 μm. Therefore, the presence of the burnable particles 22 can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material 20 due to the burnout of the organic binder resin 23.

  The burnable particles 22 are made of acrylic resin particles. Therefore, the presence of the burnable particles 22 can sufficiently exhibit the effect of suppressing the shrinkage of the protective layer forming material 20 due to the burning of the organic binder resin 23, and the burning of the protective layer 2 is ensured by burning. The original function can be maintained.

  Thus, according to the manufacturing method of this example, it is possible to obtain the gas sensor element 1 that can prevent the protective layer 2 from peeling while maintaining the function of the protective layer 2.

In this example, as shown in FIGS. 1 and 5, the protective layer forming material 20 is applied on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 to form the protective layer 2 in the coating process. However, for example, as shown in FIG. 7, the protective layer forming material 20 is applied over the entire outer peripheral surface 100 of the element body 10 including the outer surface 171 of the diffusion resistance layer 17 to form the protective layer 2. You can also
In this case, the protective layer 2 has a function of preventing water in addition to the function of preventing poisoning. That is, the protective layer 2 can prevent the element main body 10 from being cracked due to moisture.

(Example 2)
In this example, as shown in FIGS. 8 and 9, the configuration of the gas sensor element 1 is changed.
In this example, as shown in FIG. 8, the covering layer 3 is formed on the outer peripheral surface 100 of the element body 10 so as to cover the protective layer 2 formed on the outer surface 171 of the diffusion resistance layer 17 of the element body 10. It is formed all around.

As shown in FIG. 9, the coating layer 3 is a dense layer made of ceramic particles 31 mainly composed of alumina and having a porosity of about 60%. The coating layer 3 is configured such that the outer surface 301 can prevent the element body 10 from being cracked by water.
Other configurations are the same as those in the first embodiment.

Next, the manufacturing method of the gas sensor element 1 of this example is demonstrated.
In this example, similarly to Example 1, after the element body 10 is manufactured, a protective layer forming material manufacturing process, a coating process, and a drying process are sequentially performed.

Next, the covering layer forming material is coated on the outer peripheral surface 100 of the element body 10 over the entire circumference so as to cover the protective layer forming material 20 applied on the outer surface 171 of the diffusion resistance layer 17 of the element body 10. Apply. In this example, the coating layer forming material was applied by dipping.
Here, the coating layer forming material is a mixture of ceramic particles 31 made of alumina (see FIG. 9), a solvent made of water as a solvent, and an inorganic binder made of aluminum hydroxide dihydrate soluble in the solvent.・ Made by kneading.

Next, the coating layer forming material is dried at 140 ° C. for 15 minutes, and the solvent (solvent) in the coating layer forming material is evaporated and removed.
Thereafter, the protective layer forming material 20 (see FIGS. 5 and 6) and the coating layer forming material applied to the element body 10 are fired at 900 ° C. for 1 hour. Thereby, the gas sensor element 1 (refer FIG. 8) is produced.
Others are the same manufacturing methods as Example 1, and have the same effect.

(Example 3)
In this example, as shown in FIG. 10, the configuration of the gas sensor element 1 is changed.
As shown in the figure, the gas sensor element 1 includes a solid electrolyte body 11, a measured gas side electrode 12, and a reference gas side electrode 13 as in the first embodiment. The measured gas side electrode 12 is disposed facing the measured gas chamber 160.
A porous diffusion resistance layer 17 having an opening 172 is laminated on the gas electrode 12 to be measured side of the solid electrolyte body 11. In addition, an insulating layer 191 and a heater substrate 15 are stacked on the reference gas side electrode 13 side of the solid electrolyte body 11. The heater substrate 15 is provided with a heating element 151.

  The gas sensor element 1 has a pump cell 4 that adjusts the oxygen concentration in the measured gas chamber 160. The pump cell 4 has an oxygen ion conductive solid electrolyte body 41 for pumping, and a pair of pump electrodes 42 and 43 provided on one surface and the other surface of the solid electrolyte body 41 for pumping, respectively. One pump electrode 42 is arranged facing the gas chamber 160 to be measured.

A solid electrolyte body for pump 41 is laminated on the surface of the diffusion resistance layer 17 opposite to the solid electrolyte body 11. One pump electrode 42 is covered with a porous layer 44. In addition, an insulating layer 192 is disposed outside the porous layer 44.
Further, the protective layer 2 is formed on the outer peripheral surface 100 of the element body 10 including the outer surface 171 of the diffusion resistance layer 17 over the entire periphery.
The other configuration is the same as that of the first embodiment, and has the same operation and effect.

Example 4
This example is an example of a bottomed cylindrical cup-shaped gas sensor element 1 as shown in FIG.
As shown in the figure, the gas sensor element 1 includes a bottomed cylindrical solid electrolyte body 11, a measured gas side electrode 12 provided on the outer surface of the solid electrolyte body 11, and a reference gas side electrode 13 provided on the inner surface. And have. A reference gas chamber 140 is formed inside the solid electrolyte body 11, and a heating element 151 is inserted into the reference gas chamber 140.

As shown in the figure, a porous diffusion resistance layer 17 is provided on the outer surface of the solid electrolyte body 11 so as to cover the entire outer surface. In addition, the protective layer 2 is formed on the outer surface 171 of the diffusion resistance layer 17 of the element body 10 so as to cover the entire outer surface 171.
The other configuration is the same as that of the first embodiment, and has the same operation and effect.

(Example 5)
In this example, the effect of the method for producing the gas sensor element of the present invention is examined.
In this example, as shown in Table 1, among the components of the protective layer forming material, the content of ceramic particles, glass particles, catalytic noble metal particles, and organic solvent (solvent) is constant, and burnout particles and organic binder resin. A protective layer was formed using a plurality of protective layer forming materials having different contents (ratio), and gas sensor elements (samples A1 to A12) were produced.
And about the produced gas sensor (sample A1-A12), peeling of a protective layer and the ease of formation of a protective layer were evaluated, and the baking shrinkage rate of the protective layer (protective layer formation material) was also investigated.

The basic configuration of the gas sensor elements (samples A1 to A12) manufactured in this example and the manufacturing method thereof are the same as those in the first embodiment.
Moreover, the material which comprises each component (burnable particle | grains, organic binder resin, ceramic particle | grains, glass particle | grains, catalyst noble metal particle | grains) of the material for protective layer formation is the same as that of Example 1, The content rate is shown in Table 1. It is as follows. However, the content rate of each component shown in Table 1 is the content rate of each component after drying the protective layer forming material and removing the organic solvent (solvent) in the protective layer forming material (after the drying step). is there.

Next, an evaluation method for each item will be described.
About "peeling of a protective layer", the state of the protective layer of the produced gas sensor element is observed using SEM (scanning electron microscope), and the presence or absence of peeling of a protective layer is confirmed.
The determination of “peeling of the protective layer” is as follows. When there is no gap of 10 μm or more between the diffusion resistance layer and the protective layer of the element main body part, peeling of 10 μm or more occurs. When it was, it was set as x.

With respect to “ease of forming protective layer”, the viscosity of the paste-like protective layer forming material before being applied to the element body is measured. That is, the viscosity in a state where an organic solvent (solvent) is present in the protective layer forming material is measured. And it evaluates based on the value of the measured viscosity.
The determination of “ease of forming a protective layer” is determined when the viscosity A (Pa · s) of the protective layer forming material is 10 ≦ A ≦ 35 in consideration of the ease of application by a method such as pad printing. A: When 5 ≦ A <10 or 35 <A ≦ 40, it was evaluated as “◯”, and when A <5 or A> 40, it was evaluated as “X”.

  “The firing shrinkage ratio of the protective layer (protective layer forming material)” is a method of preparing a square column (cuboid) sample using the protective layer forming material and firing the sample at 900 ° C. for 1 hour. . Then, by measuring the volume change rate before and after firing, the firing shrinkage rate of the protective layer (protective layer forming material) is obtained.

Next, the evaluation result of each item will be described.
As shown in Table 1, it can be seen that the higher the content of the burnable particles in the protective layer forming material, the smaller the firing shrinkage rate of the protective layer. This is because the organic binder resin is burned out in a state where the skeleton of the protective layer forming material is maintained to some extent due to the presence of the burnable particles, and the shrinkage of the protective layer forming material accompanying the burning of the organic binder resin can be suppressed. It shows that.

And in samples A4 to A12 in which the content of burnable particles in the protective layer forming material was 30% by volume or more, no peeling of the protective layer was observed (peeling of the protective layer: determination ○). This indicates that peeling of the protective layer can be prevented by reducing the firing shrinkage rate of the protective layer.
On the other hand, in samples A1 to A3 in which the content of the burnable particles in the protective layer forming material was less than 30% by volume, the protective layer was peeled off (protective layer peeling: judgment x). That is, it is shown that the effect of suppressing the peeling of the protective layer due to the presence of the burnable particles could not be obtained sufficiently.

  Moreover, from the same table, in the samples A11 and A12 in which the content of the burnable particles in the protective layer forming material exceeds 60% by volume, the determination of the ease of forming the protective layer was x. This indicates that the increase in the content of burnable particles increases the particle density in the protective layer forming material, which makes it difficult to apply the protective layer forming material. For example, in the case of pad printing, a paste-like protective layer forming material is hardly adsorbed on the pad, and a desired transfer performance cannot be obtained.

Based on the above results, according to the method for manufacturing a gas sensor element of the present invention, the shrinkage of the protective layer forming material due to the burnout of the organic binder resin can be suppressed by the presence of the burnable particles, and the peeling of the protective layer is prevented. I found out that I can do it.
In addition to the effect of preventing the peeling of the protective layer, when considering the ease of forming the protective layer, the protective layer forming material is dried and the organic solvent (solvent) in the protective layer forming material is removed. It turned out that it is preferable that the content rate of the burnable particle | grains after having been 30-30 volume%.

(Example 6)
In this example, the effect of the method for producing the gas sensor element of the present invention is examined.
In this example, as shown in Table 2, a protective layer is formed using a plurality of protective layer forming materials having different burnout particle sizes (different burnout start temperatures), and gas sensor elements (samples B1 to B7) are formed. Produced.
And about the produced gas sensor (sample B1-B7), peeling of a protective layer and the ease of formation of a protective layer were evaluated similarly to Example 5, and the baking shrinkage rate of a protective layer (protective layer forming material) together I also investigated.

The basic configuration of the gas sensor elements (samples B1 to B7) manufactured in this example and the manufacturing method thereof are the same as those in the first embodiment.
Moreover, the material which comprises each component (burnable particle | grains, organic binder resin, ceramic particle | grains, glass particle | grains, catalyst noble metal particle | grains) of the material for protective layer formation is the same as that of Example 1, The content rate is shown in Table 1. It is the same as sample A4. In particular, the content of burnable particles is 30% by volume.
Moreover, the content rate of each component is a content rate of each component after drying the protective layer forming material and removing the organic solvent (solvent) in the protective layer forming material (after a drying process).
Moreover, the burning start temperature of the organic binder resin (ethyl cellulose) is about 200 ° C.

Next, an evaluation method for each item will be described.
Evaluation methods, determinations, and the like of “peeling of protective layer”, “ease of forming protective layer”, and “firing shrinkage rate of protective layer (protective layer forming material)” are the same as in Example 5.

Next, the evaluation result of each item will be described.
As shown in Table 2, peeling of the protective layer was not observed in samples B1 to B4 in which the particle size of the burnable particles in the protective layer forming material was 4 μm or less (the difference in burning start temperature was 35 ° C. or more). Layer peeling: Determination ○).
On the other hand, in Samples B5 to B7 in which the particle size of the burnable particles in the protective layer forming material exceeded 4 μm, the protective layer was peeled off (protective layer peeling: judgment x). This is because if the particle size of the burnable particles increases, it becomes difficult to burn the burnable particles while maintaining the skeleton of the protective layer forming material to some extent by the ceramic particles.

Moreover, from the same table, in the samples B2 to B7 in which the particle size of the burnable particles in the protective layer forming material was 0.5 μm or more, the determination of the ease of forming the protective layer was “good”.
On the other hand, in the sample B1 in which the particle size of the burnable particles in the protective layer forming material was less than 0.5 μm, the determination of the ease of forming the protective layer was good. This indicates that, as the particle size of the burnable particles is reduced, the viscosity in the protective layer forming material is increased, and the applicability of the protective layer forming material is slightly reduced.

From the above results, it was found that the particle size of the burnable particles in the protective layer forming material is preferably 4 μm or less in order to obtain the effect of preventing the protective layer from peeling off. In addition, this indicates that the burning start temperature of the burnable particles is preferably 35 ° C. or more higher than the burning start temperature of the organic binder resin.
Moreover, when the ease of formation of a protective layer was considered, it turned out that it is preferable to make the particle diameter of the burnable particle | grains in the material for protective layer formation into 0.5 micrometer or more.

DESCRIPTION OF SYMBOLS 1 Gas sensor element 10 Element main-body part 17 Diffusion resistance layer 171 Outer surface (outer surface of a diffusion resistance layer)
20 Protective layer forming material 21 Ceramic particles 22 Burnable particles 23 Organic binder resin

Claims (4)

An oxygen ion conductive solid electrolyte body, a gas side electrode to be measured and a reference gas side electrode respectively provided on one surface and the other surface of the solid electrolyte body, and a surface to be brought into contact with the gas side electrode to be measured A gas sensor comprising an element body having a porous diffusion resistance layer that allows measurement gas to pass therethrough, and a protective layer formed on the outer surface of the diffusion resistance layer through which the gas to be measured is introduced in the element body A method for manufacturing an element, comprising:
In forming the protective layer, it contains at least ceramic particles, acrylic resin particles and burnt-down particles burned off by firing, water or an organic solvent, and an organic binder resin soluble in the solvent. A protective layer forming material manufacturing step of manufacturing a protective layer forming material to be performed;
An application step of applying the protective layer forming material on the outer surface of the diffusion resistance layer of the element body;
Drying the protective layer forming material after the coating step, and removing the solvent in the protective layer forming material;
Firing the protective layer forming material, and performing a firing step to form the protective layer,
The content of the burnable particles in the protective layer-forming material after the drying step is 30 to 60% by volume,
A method for producing a gas sensor element, wherein a burning start temperature of the burnable particles in the protective layer forming material is higher than a burning burning start temperature of the organic binder resin.   2. The method of manufacturing a gas sensor element according to claim 1, wherein the burnout start temperature of the burnable particles is 35 ° C. or more higher than the burnout start temperature of the organic binder resin. 3. The method for manufacturing a gas sensor element according to claim 1, wherein an average particle diameter of the burnable particles is smaller than an average particle diameter of the ceramic particles. 4. The method for manufacturing a gas sensor element according to any one of claims 1 to 3, wherein an average particle diameter of the burnable particles is 0.5 to 4 µm.

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