JP2002293647A - Green ceramic sheet for sensor device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a green ceramic sheet for a sensor device which has excellent handling properties and is hardly deformed particularly in the manufacture of a sensor requiring many times of lamination and/or printing, and to provide a manufacturing method thereof. SOLUTION: The green ceramic sheet for the sensor device is obtained by forming a paste sheet using a doctor blade process. The paste is obtained by feeding a polyvinyl butyral resin as a binder and n-butyl phthalate as a plasticizer to high purity alumina powder having 0.3-0.18 μm average particle diameter and 3-8 m<2> /g specific surface area so that the ratio of the plasticizer to the binder by mass is 35 to 50%, adding toluene and mixing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a green ceramic sheet for a sensor element and a method for producing the same. More specifically, the present invention provides an unsintered ceramic sheet for a sensor element which is excellent in handling properties and hardly deforms even when the number of laminations and / or the number of printings is large in a manufacturing process, and a method for manufacturing the same. The unfired ceramic sheet for a sensor element of the present invention can be used for forming a laminated gas sensor element (an oxygen sensor element, a full area air-fuel ratio sensor element, a nitrogen oxide sensor element, a hydrocarbon sensor element, and the like).

[0002]

2. Description of the Related Art Conventionally, oxygen sensors, HC sensors and NOx sensors have been known as gas sensors for detecting specific components in exhaust gas discharged from an internal combustion engine. As this kind of gas sensor, a gas sensor in which a laminated gas sensor element formed by laminating a plurality of plate-shaped ceramic substrates is assembled is put to practical use. The unfired ceramic sheet for a sensor element which becomes a fired ceramic substrate is obtained by forming a slurry obtained by mixing a ceramic powder with a binder, a plastic material, and the like into a sheet shape (plate shape) by a doctor blade method. . Conventionally, handling properties have been ensured by adding a plasticizer that exceeds half the amount of the binder added.

[0003]

However, in recent years, the structure of the laminated gas sensor element has become more complicated, and in the production of this element, a laminate and a paste (specifically, a paste for a conductive layer for forming electrodes and the like, The number of times of printing an insulating layer paste or the like for forming an insulating layer) is increasing.
For this reason, the number of times of crimping work performed for each lamination also increases,
In some cases, a sheet subjected to more crimping operations gradually deforms. Further, the paste used for printing contains a much larger amount of solvent to reduce the viscosity than the sheet. For this reason, as the number of times of printing of the paste increases, the stacked unfired ceramic sheets for sensor elements absorb the solvent contained in the paste, and gradually soften and deform. On the other hand, in order to achieve a complicated structure in the stacked gas sensor element, it is necessary to manufacture each sheet (ceramic substrate) with more precise dimensional accuracy. Also, high dimensional accuracy is required for miniaturization of the stacked gas sensor element.

[0004] The present invention is to solve the above problems,
An object of the present invention is to provide an unsintered ceramic sheet for a sensor element which hardly deforms in the production of a laminated gas sensor element which is excellent in handling properties, and particularly requires a large number of times of lamination and / or printing of a paste, and a method for producing the same. Aim.

[0005]

The unsintered ceramic sheet for a sensor element of the present invention (hereinafter also simply referred to as "unsintered sheet") comprises an unsintered ceramic element for a sensor element containing ceramic powder, a binder and a plasticizer. A ceramic sheet, wherein the mass of the plasticizer is 35 to 50% of the mass of the binder.
It is characterized by being.

The above-mentioned “ceramic powder” is not particularly limited and various types can be used. For example, alumina, zirconia, titania, yttria, silica, magnesia, mullite and the like can be mentioned. The ceramic powder may be composed of only one of them, or may be a mixture of two or more. The "binder" is not particularly limited as long as it imparts moldability to the ceramic powder, and various types of binders can be used, but a lipophilic binder is preferable. Examples of the lipophilic binder include a polyvinyl butyral resin and an acrylic resin. Among these, polyvinyl butyral resin has good dispersibility to the aggregate of the ceramic powder,
This is preferable from the viewpoint that the range of thermal use is wide and the amount of impurities mixed is small.

Further, the above-mentioned "plasticizer" is not particularly limited as long as it imparts plasticity to the above-mentioned binder, and various types can be used. For example, butyl carbitol,
Di-n-butyl phthalate (DBP), DOP, DBS and the like. Among these, DBP, DOP, etc.
High vapor pressure, low volatility, and high boiling point are preferred.

The amount of the plasticizer may be 35 to 50% of the mass of the binder contained in the unsintered sheet.
%. If the mass ratio of the plasticizer to the mass of the binder is in the above range, the moldability of the unsintered sheet itself is not reduced, that is, microcracks are not easily generated after drying of the unsintered sheet and after drying, and There is no unevenness on the surface of the unfired sheet, and the unfired sheet (part of the unfired sheet) does not adhere to the cutting blade during cutting,
It does not adhere even if it is left next to it after cutting. Furthermore, even in the production of a laminated gas sensor element in which the number of times of lamination and / or the number of times of printing of the paste must be increased, the unsintered sheet is almost deformed (specifically, the unsintered sheet contracts or elongates). Nor.

Particularly, when the ceramic powder contains 80% by mass (particularly 90 to 100% by mass) of alumina,
The mass of the ceramic powder is A (g), the specific surface area of the ceramic powder is B (m ² / g), and the mass of the binder is C
A × B / C (hereinafter referred to as “specific surface binder amount”) in the case of (g) is 35 to 55 m ² / g (more preferably 3 to 55 m ² / g).
8 to 53 m ² / g, more preferably 40 to 50 m ² / g
g) is preferred. When the specific surface binder amount is 55
If it exceeds m ² / g, microcracks tend to occur in the unsintered sheet after forming the unsintered sheet and after drying (leaving). On the other hand, as it becomes smaller than 35 m ² / g, the adhesiveness of the unfired ceramic sheet for a sensor element tends to increase, and the amount of deformation due to pressure bonding or the like tends to increase, which is not preferable.

The specific surface area B of the ceramic powder is preferably 3 to 8 m ² / g (more preferably 4 to 7 m ² / g, and still more preferably 4 to 6 m ² / g). If the specific surface area is less than 3 m ² / g, the firing temperature must be increased to activate the reaction between the ceramic powders during firing of the unsintered sheet, and abnormal grain growth may occur. Further, the three-phase interface of the electrode portion provided for forming the sensing portion of the element may be reduced. On the other hand, if it exceeds 8 m ² / g, the slurry obtained by mixing the ceramic powder and the binder tends to solidify when casting, and the surface of the unsintered sheet tends to be uneven. When irregularities are generated on the surface of the unsintered sheet, when pastes such as a conductive layer paste and an insulating layer paste are printed, these pastes tend to be cut off on the sheet surface or the thickness tends to vary, which is not preferable. .

Further, the average particle size of the ceramic powder is 0.3 to 0.6 μm (more preferably, 0.35 to 0.5 μm).
5 μm, more preferably 0.4 to 0.5 μm). If the average particle size is less than 0.3 μm, it is necessary to raise the firing temperature to activate the reaction between the ceramic powders during firing of the unsintered sheet. However, if the firing temperature is excessively increased, abnormal grain growth tends to occur, and the performance of the three-phase interface of the electrodes constituting the sensing part of the sensor element tends to decrease.
On the other hand, when the thickness exceeds 0.6 μm, the slurry obtained by mixing the ceramic powder and the binder tends to be solidified when casting, and the surface of the unsintered sheet tends to be uneven. When irregularities are generated on the surface of the unsintered sheet, when pastes such as a conductive layer paste and an insulating layer paste are printed, these pastes tend to be interrupted on the sheet surface, and the thickness tends to vary, which is not preferable. .

The unsintered sheet of the present invention preferably has an actual density of 57 to 70% of the theoretical density. The actual density is a density measured by the Archimedes method. On the other hand, the theoretical density is a value calculated by adding the theoretical densities of all the constituent materials contained in the unsintered sheet for each content ratio of each constituent material. If the ratio of the actual density to the theoretical density is less than 57%, cracks are likely to occur in the unsintered sheet, and the difference in the difference in firing shrinkage tends to increase. On the other hand, the ratio of the real density to the theoretical density is 70
%, It becomes difficult to sufficiently degrease at the time of degreasing treatment (debinding process), and cracks may occur in the sheet during degreasing.

The unsintered ceramic sheet for a sensor element of the present invention contains, in addition to the ceramic powder and the binder, a dispersant, an ionette and the like which are added when preparing a slurry for forming the unsintered sheet. It is general that it is contained.

The method for producing an unsintered ceramic sheet for a sensor element of the present invention is a method for producing an unsintered ceramic sheet for a sensor element containing ceramic powder, a binder, and a plasticizer. It is characterized in that it is adjusted to 35 to 50% of the mass of the binder.

The “ceramic powder”, the “binder”, and the “plasticizer” are the same as in the unsintered ceramic sheet for a sensor element of the present invention described above. According to the method for producing an unsintered ceramic sheet for a sensor element of the present invention, after the unsintered ceramic sheet is formed, cracks do not occur after drying, the surface of the unsintered sheet after molding has no irregularities, The sheet (part of the unsintered sheet) does not adhere to the cutting blade, and does not adhere even if left adjacent to after the cutting.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. [1] Production of 15 types of unsintered sheets having different amounts of the plasticizer with respect to the binder: 1000 g of alumina powder having a purity of 99.99% or more, an average particle size of 0.46 μm, and a specific surface area of 4.8 m ² / g; Mass shown in Table 1 (30 to 60 m ^{2 in} specific surface binder amount)
/ G) of polyvinyl butyral resin (binder), di-n-butyl phthalate (plasticizer) in an amount shown in Table 1, and an appropriate amount of toluene (solvent) were added and mixed by a ball mill to prepare a slurry. In addition, the compounding ratio of the binder and the plasticizer shown in Table 1 is a mass ratio converted into an external compound with respect to the mass of the ceramic powder.

[0017]

[Table 1] * IMG [T01]

The average particle size of the ceramic powder is a value measured by Microtrac (HRA). on the other hand,
The specific surface area of the ceramic powder is a value measured by a BET method (nitrogen adsorption amount method).

The slurry obtained above is opened with an opening of about 0.0
After passing through a 6 mm nylon mesh, the degree of vacuum was gradually increased while heating in a defoaming machine to perform defoaming. Next, the twelve types of slurries obtained so far were each formed into a sheet having a thickness of 0.4 to 0.5 mm on a resin film by a doctor blade method. The obtained sheet-like molded product was left to dry in a drying room (normal pressure, normal temperature, normal humidity) for 11 hours, and then the resin film was peeled off from the molded product, and the added amounts of the binder and the plasticizer were different. Various types of unsintered sheets (Examples 1 to 9 and Comparative Examples 1 to 6) were obtained. Then, the obtained unsintered ceramic sheet for each sensor element is subjected to an NC cutting machine at a plate temperature of 55 ° C. for 9 hours.
It was cut into 0 mm x 60 mm.

[2] Examination of cracks after molding of unsintered sheet The unsintered sheet of 90 mm × 60 mm obtained in [1]
Ten pieces of each of the five types were prepared. After applying the water-soluble red ink to the front and back surfaces of these 10 unsintered sheets, the front and back surfaces of each strip are visually checked using a magnifying glass, and the microscopic color can be checked by the permeation of the water-soluble red ink. The presence or absence of cracks was inspected. As a result, 1
An unsintered sheet in which cracks were observed at any of the places was indicated by “x” in the column of “Cracks generated by forming” in Table 1, and an unsintered sheet in which no cracks were observed was indicated by “○”. As a result, cracks were observed in Comparative Examples 1 and 2 in which the mass ratio of the plasticizer to the binder was 31.8% or less. On the other hand, no crack occurred in the unsintered sheet in which the mass ratio of the plasticizer to the binder exceeded 31.8%.

[3] Preparation of printing paste On the other hand, butyl carbidol and acetone are added to the unsintered sheet obtained in the same manner as in [1], dissolved and mixed, and then the acetone is evaporated. 120 viscosity
The paste of Pa was adjusted.

[4] Examination of deformation of unsintered sheet due to printing of paste Examples 1 to 4 in which cracks did not occur obtained in [1]
9 and the paste obtained in [3] was printed on the entire surface of one side of each of the unsintered sheets in Comparative Examples 3 to 6.
Dry at 0 ° C. for 2 hours. Thereafter, similarly, printing and drying of the paste obtained in [3] were repeated four times each to obtain a laminate in which the paste was printed five times in total. The same operation was performed for each of the ten unsintered sheets for each example and comparative example to obtain a laminate. The size (90 mm before printing) in the longitudinal direction of each of the obtained 10 laminates was measured, and the average value of the deformation ratio from the same size before printing was calculated.

As a result, in Examples 1 to 9 in which the mass ratio of the plasticizer to the binder was 35 to 50%, the rate of change could be suppressed to 0.02 to 0.4. In Examples 3 to 6, it is larger than 1.6. That is, the mass ratio of the plasticizer to the binder is 50%.
From the above, it can be seen that the deformation rate sharply increases. Therefore, according to the results of [2] and [4], the deformation rate caused by the printing of the paste is reduced to 0 even if there is no crack at the time of molding and there are many paste printing steps on the surface of the unsintered sheet. It can be seen that the unsintered sheet that can be suppressed to less than 0.5 has a mass ratio of the plasticizer to the binder of 35 to 50%.

[5] Production of 7 types of unsintered sheets having different binder amounts with respect to the ceramic powder: 1000 g of alumina powder having a purity of 99.99% or more, an average particle size of 0.46 μm and a specific surface area of 4.8 m ² / g. Te, mass shown in Table 1 (specific surface binder amount is 30 to 60 m ²
/ G) of polyvinyl butyral resin (binder), di-n-butyl phthalate (plasticizer) in half the mass of polyvinyl butyral resin shown in Table 2, and an appropriate amount of toluene (solvent) are added and mixed by a rotary machine. did. The average particle size and specific surface area of the alumina powder were measured in the same manner as in [1].

[0025]

[Table 2] * IMG [T02]

The slurry obtained above is opened with an opening of about 0.0
After passing through a 6 mm nylon mesh, the degree of vacuum was gradually increased while heating in a defoaming machine to perform defoaming. Next, the twelve types of slurries obtained so far were each formed into a sheet having a thickness of 0.4 to 0.5 mm on a resin film by a doctor blade method. The obtained sheet-like molded product was left to dry in a drying chamber (normal pressure, normal temperature, normal humidity) for 11 hours, then the resin film was peeled off from the molded product, and seven types of non-specific binders having different specific surface binder amounts were used. Fired sheets (Examples 10 to 16) were obtained.

[6] Attachment of unsintered sheet to cutting blade during cutting Each unsintered sheet obtained in [5] is cut into 100 pieces of 6 mm × 6 mm strips at a plate temperature of 55 ° C. by an NC cutting machine. Cut into a grid. At this time, it was visually observed whether the unsintered sheet adhered to the cutting blade and floated from the mounting surface (plate). As a result, it was found that the unsintered sheet could be cut without floating above the mounting surface.

[7] Attachment of unsintered sheets by leaving after cutting The 7 types of unsintered sheets cut into 100 pieces of 6 mm × 6 mm strips in a lattice form in [6] as they are (strip-shaped unsintered sheets) The two were touching each other on the sides). Then, in a completely cooled sheet state, 1
After a lapse of time, the strip-shaped unsintered sheets were separated from each other. As a result, it was possible to adhere to the film in Example 16 but to remove the film without any problem ("O" in Table 2).
As shown). Further, in Examples 1 to 6, no adhesion was observed at all (in Table 2, it was described as “◎”).

[8] Examination of occurrence of crack due to cutting of unsintered sheet 100 pieces of each of the seven types of strip-shaped unsintered sheets obtained in [7] were prepared. After applying the water-soluble red ink to the front and back surfaces of the unfired sheets in the form of 100 strips, the front and back surfaces of each strip are visually checked using a magnifying glass, and the water-soluble red ink penetrates. The presence or absence of cracks (microcracks) that can be confirmed by the above was inspected. as a result,
In Example 1, cracks were observed in 3% of the unsintered sheet, but this occurrence rate is considered to be at a level that does not cause any problem in production. In addition, in Examples 2 to 7 other than the above, cracks did not occur and good inspection results were obtained.

[9] Examination of deformation due to pressure bonding In the same manner as in [1], six unsintered sheets having a thickness of 0.4 to 0.5 mm cut into 90 mm in length and 60 mm in width are prepared for each specific surface binder amount. did. Six sheets of each of the seven types of unsintered sheets obtained were placed on a crimping device, and each was 90.4 mm in length and 6 in width.
A metal plate having a thickness of 0.4 mm and a thickness of 0.5 mm was put on and subjected to a pressure bonding operation at 50 ° C. under a condition of 0.8 MPa. Thereafter, the elongation in the longitudinal direction of the unsintered sheet, which had a length of 90 mm before the pressure bonding operation, was measured, and the amount of deformation was calculated. As a result, in Example 7, although very small, 0.0
Deformation of 5% was observed, but with such an amount of deformation, it is considered that deformation of the unfired laminate due to lamination is within an allowable range. On the other hand, Examples 1 to 6 were at the deformation level without any problem in production.

[0031]

According to the method for producing an unfired ceramic sheet for a sensor element of the present invention, cracks do not occur after molding, and almost no deformation occurs even when the number of laminations and / or the number of paste printings is large. Thus, an unsintered ceramic sheet for a sensor element on which lamination and printing of a paste can be performed can be obtained. Further, according to such an unsintered ceramic sheet for a sensor element, it is possible to perform the lamination with high dimensional accuracy even for a sensor element having a large number of laminations during manufacturing. Furthermore, lamination can be performed with high dimensional accuracy even in the manufacture of a small sensor element.
For this reason, a sensor element with excellent measurement accuracy and high durability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/416 G01N 27/46 331 27/419 325Z 327Z (72) Inventor Yoshiaki Kuroki Takatsuji-cho, Mizuho-ku, Nagoya-shi No. 14-18 Japan Special Ceramics Co., Ltd. F-term (reference) 2G004 BB04 BM07 2G046 AA03 AA07 AA13 AA18 BB02 BB06 EA07 EA18 FB02 FE03 2G060 AA03 AB05 AB10 AB15 AE19 BD10 JA01 4G030 AA07 AA12 AA17 GA17 AGA17 GAA HA04 PA22

Claims (9)

[Claims] An unsintered ceramic sheet for a sensor element containing ceramic powder, a binder and a plasticizer, wherein the mass of the plasticizer is 35 to 50% of the mass of the binder.
An unfired ceramic sheet for a sensor element, characterized in that: 2. The ceramic powder contains at least 80% by mass of alumina, the mass of the ceramic powder is A (g), the specific surface area of the ceramic powder is B (m ² / g), and the mass of the binder is Is C (g), A ×
B / C is unfired ceramic sheet sensor element according to claim 1, wherein the 35~55m ² / g. 3. The method according to claim ^{2, wherein} B is 3 to 8 m ² / g.
An unfired ceramic sheet for a sensor element as described in the above. 4. The ceramic powder has an average particle size of 0.3.
4. The method according to claim 1, wherein the thickness is about 0.6 μm.
An unfired ceramic sheet for a sensor element according to item 8. 5. An unfired ceramic sheet for a sensor element having an actual density of 57 to 70% of a theoretical density. 6. A method for producing a green ceramic sheet for a sensor element, comprising a ceramic powder, a binder and a plasticizer, wherein the mass of the plasticizer is 35% of the mass of the binder.
A method for producing an unfired ceramic sheet for a sensor element, which is adjusted to 50%. 7. An alumina as the ceramic powder,
A powder containing 0% by mass or more is used, the mass of the ceramic powder is A (g), and the specific surface area of the ceramic powder is B
^(M 2 / g) and then, the mass of the binder in the case of the C (g), A × B / C the 35~55m ² / g according to claim 6 sensor element green ceramic sheet according to adjust to Production method. 8. The method for producing an unfired ceramic sheet for a sensor element according to claim 6, wherein the ceramic powder in which B is 3 to 8 m ² / g is used. 9. The method for producing an unfired ceramic sheet for a sensor element according to claim 6, wherein the ceramic powder having an average particle size of 0.3 to 0.6 μm is used.