JP2002293646A - 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 in each process before firing, and to provide a method of manufacturing the green ceramic sheet for the sensor device. SOLUTION: The green ceramic sheets for the sensor device are obtained by: mixing ceramic powder of a mass of A (g) and having a specific surface area of B (m<2> /g), an average particle diameter of 0.3 to 0.6 μm and containing >=80 mass% alumina with a binder of a mass of C (g) so that A×B/C becomes 35 to 55 m<2> /g; and forming a sheet by a doctor blade method. The resultant green ceramic sheets for the sensor device are free from the generation of cracks and the ruggedness on the surface of the sheet after being molded, do not stick to a cutting blade at the time of cutting and to each other even if being left adjacent to each other and are hardly deformed particularly in each process before being fired.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a green ceramic sheet for a sensor element and a method for producing the green ceramic sheet for a sensor element. More specifically, the present invention provides an unfired ceramic sheet which is excellent in handleability and hardly deforms in each step before firing, and a method for producing such an unfired ceramic sheet. The unfired ceramic sheet for a sensor element of the present invention is a laminated gas sensor element (oxygen sensor element, full area air-fuel ratio sensor element, nitrogen oxide sensor element, hydrocarbon sensor element, etc.) obtained by laminating various ceramic substrates. ) Can be used.

[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. As a ceramic substrate constituting the laminated gas sensor element, a substrate containing alumina at a high concentration may be used. For example, the ceramic substrate containing alumina at a high concentration is used as a base of a resistance change type sensor element using an oxide semiconductor, a base of a heater unit which is fired separately from a sensing unit, and the like.

[0003]

Heretofore, with respect to such an unfired ceramic sheet serving as a ceramic substrate containing alumina at a high concentration, a slurry is formed by mixing a ceramic powder mainly composed of alumina with a binder or the like. It is known that the slurry is used to form a sheet (plate) by a doctor blade method. In the past, in forming an unfired ceramic sheet, it has been general to form the sheet so that the sheet does not have excessive tackiness after the sheet is formed. However, in the unsintered ceramic sheet formed as described above, although it is left to cool after forming, microcracks may occur on the surface of the sheet.

[0004] On the other hand, the laminated gas sensor element is obtained by laminating and firing unfired ceramic sheets serving as a plurality of ceramic substrates, and microcracks may occur in the unfired ceramic sheet. And the following problems may occur. The laminated gas sensor element needs to be exposed to the exhaust gas in order to detect a specific component in the exhaust gas, and a portion (specifically, a sensing portion) exposed to the exhaust gas is exposed to a high temperature due to the influence of the exhaust gas and the like. Inevitably, a thermal shock is applied due to the addition of heater heating for activating the sensing unit. Further, in a portion of the laminated gas sensor element exposed to exhaust gas, a change in operating conditions of the internal combustion engine and a cooling cycle associated with repetition of the operation are greatly added. At this time, if microcracks exist on the ceramic substrate constituting the portion of the multilayer gas sensor element exposed to the exhaust gas, the element cracks may occur starting from the cracks.

[0005] Therefore, it is necessary to suppress the occurrence of microcracks in the ceramic substrate constituting the laminated gas sensor element. In order to suppress the occurrence of microcracks in the ceramic substrate, the microcracks at the stage of the unfired ceramic sheet are required. It is important how to suppress the occurrence of the phenomenon.

[0006] The present invention is to solve the above problems,
An object of the present invention is to provide an unfired ceramic sheet for a sensor element which is excellent in handling properties and in which microcracks do not occur particularly in a sheet state before firing, and a method for manufacturing such an unfired ceramic sheet for a sensor element.

[0007]

The unsintered ceramic sheet for a sensor element of the present invention (hereinafter, also simply referred to as "unsintered sheet") contains a ceramic powder containing 80% by mass or more of alumina and a binder. , 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), characterized in that A × B / C is 35~55m ² / g.

The above-mentioned “ceramic powder” contains 80 alumina.
The content is not particularly limited as long as it is contained by mass% or more, and as the ceramic component added in addition to alumina, zirconia, titania, yttria, silica, magnesia, mullite and the like can be contained. The amount of alumina contained in the ceramic powder may be 80 to 100% by mass.
It is preferable that it is 100 mass%, and it is especially preferable that it is 95-100 mass%. When the content of the alumina is less than 80% by mass, A × B / C (hereinafter, also referred to as “specific surface binder amount”) described later is 35 to 55 m ² /
In the range of g, sufficient good handling properties may not be obtained. The good handling property referred to here means that there is no irregularity on the surface of the unfired ceramic sheet for the sensor element after molding, a part of the sheet does not adhere to the cutting blade when cutting the sheet, and the sheet is adjacent to the cutting blade after cutting. This means that it does not adhere even if left unattended, and hardly deforms in the laminating step of the unfired ceramic sheet for the sensor element before firing.

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 unfired ceramic sheet for a sensor element, and abnormal grain growth occurs. There is a possibility that 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 be solidified when casting, and the sheet surface is likely to have irregularities. Even when the insulating pastes are printed, the pastes are likely to be interrupted on the sheet surface or to have a thickness variation.

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). When the average particle size is less than 0.3 μm, when firing the unfired ceramic sheet for a sensor element,
The firing temperature must be increased to activate the reaction between the ceramic powders, which may cause abnormal grain growth, and the three-phase interface of the electrodes provided to form the sensing part of the element is It may decrease. On the other hand, when the thickness exceeds 0.6 μm, the slurry in which the ceramic powder and the binder are mixed is easily solidified when casting, and the surface of the sheet is likely to be uneven, and the surface of the unfired ceramic sheet for the sensor element has a conductive paste or an insulating material. Even when the pastes are printed, the pastes are likely to be interrupted on the sheet surface or to vary in thickness.

The "binder" is not particularly limited as long as the specific surface binder amount described later is a predetermined amount, and various types 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 ceramic powder, and has a wide range of thermal use.
Further, it is preferable from the viewpoint that the amount of impurities mixed is small.

The above “A × B / C” indicates the surface area of the ceramic powder that needs to be covered by 1 g of the binder. The Himen amount of binder may be any 35~55m ² / g, is preferably 38~53m ² / g, 40
More preferably, it is で 50 m ² / g. If the specific surface binder amount exceeds 55 m ² / g, the probability of occurrence of microcracks after forming and leaving the unfired sensor element ceramic sheet undesirably increases. On the other hand, as the specific surface binder amount 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 unsintered ceramic sheet for the sensor element contains, in addition to the ceramic powder and the binder, a plasticizer and a dispersant added when preparing a slurry for forming the unsintered sheet. That is common.

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 comprising a ceramic powder containing at least 80% by mass of alumina and a binder. 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
(G), A × B / C is 35 to 55 m ² / g
The ceramic powder and the binder are mixed so that The “ceramic powder”, the “binder”, and the “A × B / C (specific surface binder amount)” are the same as those of the unfired ceramic sheet for a sensor element of the present invention described above.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. [1] Manufacture of 12 types of unsintered sheets A mass (specific surface) shown in Table 1 with respect to 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. 30-60m ^{2 in} binder amount
/ G) of polyvinyl butyral (binder) and half of the mass of polyvinyl butyral shown in Table 1
Butyl (plasticizer) and an appropriate amount of toluene (solvent) were added and mixed by a ball mill to form a slurry.

[0016]

[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 the BET method (nitrogen adsorption amount method).

[0018] The slurry obtained above is
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, and then the resin film was peeled off from the molded product to obtain 12 types of sensor elements having different specific surface binder amounts. Unsintered ceramic sheet (Examples 1 to 7, Comparative Examples 1 to 3)
5) was obtained.

[2] Attachment of unsintered ceramic sheet for sensor element to cutting blade at the time of cutting Each unsintered ceramic sheet for sensor element obtained in [1] was cut by a NC cutting machine at a plate temperature of 55 ° C. at 6 mm.
It was cut into a grid of 100 × 6 mm strips. At this time,
It was visually observed whether or not the unfired ceramic sheet for the sensor element adhered to the cutting blade and floated from the mounting surface (plate). As a result, those in which the unsintered ceramic sheet for the sensor element floated from the mounting surface were marked with “x” in the column of “floating by cutting (attachment to the cutting blade)” in Table 1, and those that did not float. Wrote "〇".

As a result, the specific surface binder amount was 34.3 m ²
/ G in Comparative Examples 3 to 5, it was found that the unsintered ceramic sheet for the sensor element may adhere to the cutting blade. In particular, in Comparative Example 1 and Comparative Example 2, in a state where the unfired ceramic sheet for the sensor element adhered to the cutting blade,
Since the cutting of the next uncut unfired ceramic sheet for a sensor element was started, a normal cutting step could not be performed.

[3] Adhesion of unsintered ceramic sheets for sensor elements by leaving after cutting [12] Twelve types of unsintered sheets cut into 100 pieces of 6 mm x 6 mm in a grid in [2] In a state in which the unsintered sheets are in contact with each other on the side). After a lapse of one hour in a completely cooled sheet state, the strip-shaped unfired ceramic sheets for sensor elements were separated from each other. At this time, those which adhered to each other and did not separate were marked with "x" in Table 1. Those that adhered but could be easily separated were marked with “○”, and those where no adhesion was observed were marked with “◎”.

As a result, the specific surface binder amount was 37 m ² / g.
Below, sticking of the strip-shaped unfired ceramic sheets for sensor elements was observed. However, in the seventh embodiment, the adhesion is such that it is separated by its own weight, and there is no particular problem in the manufacture of the laminated gas sensor element.
However, in Comparative Examples 3 to 5, the sheets could not be separated from each other.

[4] Examination of presence or absence of cracks due to cutting of unsintered sheet 100 pieces of each of the twelve types of strip-shaped unsintered ceramic sheets for sensor elements obtained in [3] were prepared. This 10
After applying water-soluble red ink to the front and back surfaces of the unsintered ceramic sheet for sensor elements in the form of 0 strips, visually check the front and back surfaces of each strip with a magnifying glass, and use the water-soluble red ink. The presence or absence of cracks (microcracks) that can be confirmed by permeation of the particles was examined. As a result, Table 1 shows the number of unfired ceramic sheets for sensor elements in which cracks were observed at any one of the front and back sides.

From the results shown in Table 1, the specific surface binder amount is 53.
Example 1, Comparative Example 1 and Comparative Example 2 which are 3 m ² / g or more
In the cracks were observed. However, the occurrence rate in Example 1 was as low as 3%, and it is considered that there is no problem in manufacturing. On the other hand, no cracks were observed in Examples 2 to 7 and Comparative Examples 3 to 5 in which the specific surface binder amount was 55 m ² / g or less. In Comparative Example 1, cracks were already visually observed after forming and drying by the doctor blade method.

[5] Examination of deformation due to pressure bonding In the same manner as in [1] to [3], 90 mm long and 60 mm wide
Six unsintered ceramic sheets for sensor elements having a thickness of 0.4 to 0.5 mm, which were cut into pieces, were prepared for each specific surface binder amount. 1 of the obtained unfired ceramic sheet for sensor element
6 pieces of each type are placed on the crimping device, and 90.4 mm long,
Cover a metal plate of 60.4 mm wide and 0.5 mm thick with 50
Crimping was performed at 0.8 ° C. under the conditions of 0.8 MPa.
Thereafter, the elongation in the vertical direction of the unsintered sheet before the pressing operation was 90 mm was measured, and the amount of deformation was calculated.

As a result, the specific surface binder amount was 37 m ² / g.
In the following Example 7 and Comparative Examples 3 to 5, deformation occurred. However, among them, the deformation amount of Example 7 was 0.05%
It is considered that the deformation of the unfired laminate due to the lamination is within an allowable range if the amount of deformation is such a degree. On the other hand, when the specific surface binder amount is 34.3 m ² / g or less, the deformation amount is gradually increased to 0.16 to 5.3%.

[0027]

According to the method for producing an unsintered ceramic sheet for a sensor element of the present invention, a crack (microcrack) hardly occurs after molding and an unsintered ceramic sheet for a sensor element having good handling properties 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, the laminated gas sensor element obtained using the unfired ceramic sheet for a sensor element of the present invention is a highly durable element that does not cause element cracking even when subjected to severe thermal shock and cooling / heating cycles. Will work.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Awano 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi Inside Japan Specialty Ceramics Co., Ltd. F term (reference) 4G030 AA36 BA07 CA08 GA11 GA14 GA15 GA17 4G052 DA02 DA08 DB02

Claims (6)

[Claims] 1. A ceramic powder containing 80% by mass or more of alumina and a binder, wherein the mass of the ceramic powder is A (g), and the specific surface area of the ceramic powder is B (m ² / g). An unfired ceramic sheet for a sensor element, wherein A × B / C is in the range of 35 to 55 m ² / g, where C (g) is the mass of the binder. 2. The specific surface area B of the ceramic powder is 3 to 3.
The unsintered ceramic sheet for a sensor element according to claim 1, which is 8 m ² / g. 3. An average particle diameter of the ceramic powder is 0.3.
The unsintered ceramic sheet for a sensor element according to claim 1, wherein the thickness is from 0.6 to 0.6 μm. 4. A method for producing a green ceramic sheet for a sensor element containing a ceramic powder containing 80% by mass or more of alumina and a binder, wherein the mass of the ceramic powder is A (g), The specific surface area of the powder is B (m ² / g), and the mass of the binder is C (g).
Wherein the ceramic powder and the binder are mixed such that A × B / C is in the range of 35 to 55 m ² / g. 5. The method according to claim 4, wherein the ceramic powder having a specific surface area B of 3 to 8 m ² / g is used. 6. The method for producing a green ceramic sheet for a sensor element according to claim 4, wherein the ceramic powder having an average particle diameter of 0.3 to 0.6 μm is used.