JP2007137741A - Manufacturing method of ceramic slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic slurry from which extremely fine ceramic powder causing abnormal grain growth by firing is removed and to provide a manufacturing method of a laminated ceramic electronic component having an excellent performance such as voltage resistance and reliability even if the laminated ceramic electronic component prepared by using the ceramic slurry is a thin layer multilayered laminated ceramic electronic component. <P>SOLUTION: The ceramic slurry from which the extremely fine ceramic powder causing the abnormal grain growth by firing is removed is obtained by performing mixture while removing the fine powder in the ceramic slurry by causing aggregation in the ceramic slurry used for molding a green sheet, and the laminated ceramic electronic component obtained by laminating and firing the green sheet prepared by the ceramic slurry is the laminated ceramic electronic component having the excellent performance such as the voltage resistance and the reliability. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ceramic slurry used for a multilayer ceramic electronic component such as a multilayer ceramic capacitor, a method for manufacturing the same, and a method for manufacturing a multilayer ceramic electronic component using the ceramic slurry.

  A conventional method for manufacturing a multilayer ceramic electronic component will be described by taking a multilayer ceramic capacitor as an example.

  FIG. 2 is a partially cutaway perspective view of a general multilayer ceramic capacitor 21. Dielectric layers 22 and internal electrodes 23 are alternately stacked to form a multilayer body, and the end surface of the internal electrode 23 has a multilayer body. Are stacked so as to be alternately exposed at both opposite end faces, and are alternately connected to a pair of external electrodes 24 formed on both end faces of the laminate.

  In the production of such a multilayer ceramic capacitor, it is important to produce a green sheet that becomes a dielectric layer by firing. Therefore, the production technique of the ceramic slurry used for producing the green sheet is important.

For example, Patent Document 1 can be cited as a prior art document relating to the present invention.
JP 2001-106578 A

  However, as market demands have spurred downsizing and higher performance, the demand for larger capacity of multilayer ceramic capacitors has further increased, and along with this, it is required to use increasingly thinner green sheets. Therefore, the requirements for the dispersibility and quality of the ceramic slurry used to produce the green sheet are becoming stricter.

  In such a situation, for example, when a ceramic slurry is produced using the method shown in Patent Document 1, the force applied to the ceramic powder in the ceramic slurry may be excessive in order to increase dispersibility. .

  When an excessive force is applied to the ceramic powder, the ceramic powder is further pulverized and a very fine powder may be generated.

  This fine powder causes abnormal grain growth that excessively increases the crystal grain size during subsequent sintering of the laminate, and causes factors such as the breakdown voltage and reliability of the produced multilayer ceramic capacitor to deteriorate. It was.

  Accordingly, the present invention provides a ceramic slurry from which extremely fine ceramic powder that may cause abnormal grain growth by firing is removed, and a multilayer ceramic electronic component produced using this ceramic slurry has a thin multilayer structure. An object of the present invention is to provide a method for manufacturing a multilayer ceramic electronic component that is excellent in performance such as withstand voltage and reliability, even if it is a multilayer ceramic electronic component.

  In order to achieve this object, the method for producing a ceramic slurry according to the present invention is characterized in that in a ceramic slurry used for forming a green sheet, the fine powder in the ceramic slurry is mixed while being agglomerated and removed. This is a method for producing a ceramic slurry. In other words, very fine fine particles that cause abnormal grain growth by firing, even though the amount is very small, have a high activity on the surface of the particles, and thus act as a trigger for abnormal grain growth. It is considered that abnormally large crystal grains appear over a wide area of the component, which affects the performance of the multilayer ceramic electronic component.

  Therefore, the fine powder having a specific surface area of 5% or more with respect to the specific surface area of the entire ceramic powder in the ceramic slurry is mixed without removing the flocculant by using a means such as filter filtration. A multilayer ceramic electronic component laminated and fired using a green sheet produced from the ceramic slurry thus obtained can be a multilayer ceramic electronic component excellent in performance such as withstand voltage and reliability.

  According to the present invention, in the ceramic slurry used for forming the green sheet, the fine powder in the ceramic slurry is mixed while being agglomerated and removed. A ceramic slurry from which particles are removed is obtained, and a laminated ceramic electronic component laminated and fired using a green sheet produced from the ceramic slurry can be a laminated ceramic electronic component having excellent performance such as withstand voltage and reliability. .

(Embodiment 1)
Hereinafter, the first embodiment will be described using a multilayer ceramic capacitor as an example with reference to FIGS.

  FIG. 1 is a schematic diagram of an example of a ceramic slurry filter filtration apparatus, which includes a filter 11, a pump 12 for circulating the slurry, and a tank 13 for storing the slurry. The arrows in FIG. 1 indicate the direction in which the ceramic slurry flows.

  FIG. 2 is a partially cutaway perspective view of a general multilayer ceramic capacitor 21. Dielectric layers 22 and internal electrodes 23 are alternately stacked to form a multilayer body, and the end surface of the internal electrode 23 has a multilayer body. Are stacked so as to be alternately exposed at both opposite end faces, and are alternately connected to a pair of external electrodes 24 formed on both end faces of the laminate.

  Next, the manufacturing method of the multilayer ceramic capacitor according to the present invention will be described in detail.

  First, a ceramic slurry is prepared by mixing a ceramic powder containing barium titanate as a main component, a polyvinyl butyral resin as a binder, a solvent, a plasticizer, a dispersant, and the like using an apparatus such as a medium stirring mill.

  The ceramic slurry was filtered through two filters in succession as shown in (Table 1).

  As the filter used, a filter having an absolute filtration accuracy of 99.99% in which 99.99% of the particles of the slurry after filtration were 1.5 μm or less was used.

  This filter is a kind of filter called a cartridge filter, and the inside of the filter has a fiber structure and has a height of about 10 inches.

  The filter is generally used for removing coarse particles having a particle diameter equal to or larger than a predetermined particle diameter, and it has been said that a fine powder having a predetermined particle diameter or less cannot be removed.

  However, such fine powder in the ceramic slurry has a large surface area and high activity, so that it easily aggregates. The present inventors have found that the fine powder can be removed using a filter by utilizing such properties of the fine powder that is likely to cause aggregation, thereby achieving the present invention.

  For example, even when the ceramic slurry is allowed to stand for a long time after mixing, such fine powders agglomerate, but in this case, component separation in the ceramic slurry occurs, which is not preferable.

  In addition, a method of removing fine powder using an aggregating agent such as alum is also conceivable. In this case, it is not only difficult to remove the aggregating agent from the ceramic slurry, but also a desired particle size other than the fine powder. It is not preferable because even the powder having the above is removed.

  Therefore, it is most preferable in the production of the ceramic slurry to remove the agglomerated fine powder using filter filtration.

  Using the ceramic slurry filtered through the number of times shown in (Table 1), a green sheet having a thickness of 2 μm to be the dielectric layer 22 after firing is produced by a doctor blade method.

  Here, although the filter configuration shown in FIG. 1 has two stages, the number of times of passing through these two filters is defined as the number of times of filtration.

  Moreover, the specific surface area of the ceramic powder before filter filtration and the ceramic powder remaining in the filter on the right side of FIG. 1 (the filter closer to the tank 13) after filter filtration was measured using the BET method (Table 1). It is shown to match.

  Here, the specific surface area increase rate is the percentage difference between the specific surface area of the ceramic powder remaining in the filter and the specific surface area of the ceramic powder before filter filtration.

  On the other hand, an electrode paste is prepared by mixing Ni alone or a metal powder containing an additive such as Cu with Ni as a main component and a solvent, a resin, a plasticizer, etc., and this electrode paste is screen printed. To form a conductor layer to be the internal electrode 23 by coating on the green sheet.

  Next, 250 green sheets on which the conductor layer is formed are stacked, and then one or more green sheets not coated with electrode paste are stacked on top and bottom to form upper and lower protective layers. A body green block (not shown) was prepared.

  Next, this multilayer green block was cut into dimensions of 1.9 mm length × 1.0 mm width × 1.0 mm thickness, and a multilayer ceramic green chip (not shown) to be the multilayer ceramic capacitor 21 was produced by firing. . At this time, both end surfaces of the multilayer ceramic green chip have a structure in which one end portion of the conductor layer is exposed on different end surfaces alternately facing each other with the green sheet interposed therebetween.

  Next, the multilayer ceramic green chip is put into a batch-type atmosphere firing furnace, and after debinding, it is fired in the range of 1200 ° C. to 1250 ° C. in a reducing atmosphere with a mixed gas of nitrogen gas and hydrogen gas, Multilayer ceramic capacitors of sample numbers 1 to 5 shown in Table 1 were obtained.

Thereafter, a pair of external electrodes 24 was formed on 100 multilayer ceramic capacitors of sample numbers 1 to 5. The insulation resistance was measured for 100 monolithic ceramic capacitors on which external electrodes were formed, and the number of insulation resistances of 10 ⁶ Ω or less is shown in Table 1 as the short-circuit rate.

  The insulation resistance was measured at an applied voltage of 6.3 V using an insulation resistance meter.

  Next, a reliability test was performed for 1000 hours while applying a rated voltage of 6.3 V to the multilayer ceramic capacitors of Sample Nos. 1 to 5 after measuring the insulation resistance in an atmosphere at a temperature of 85 ° C.

100 samples were measured for each sample after the end of the 1000-hour reliability test, and the number of short-circuited states (resistance value of 10 ⁶ Ω or less) is shown as a percentage in the same manner as described above (Table 1).

As is clear from the results of (Table 1), lamination of sample numbers 2 to 5 produced using a ceramic slurry mixed while removing fine powder having a specific surface area of 8.00 m ² / g or more by performing filter filtration. A ceramic capacitor has a low short-circuit rate with an insulation resistance of 10 ⁶ Ω or less, and no short-circuit occurs in a reliability test. In this case, the number of times of filter filtration is 3 to 15 passes, and the powder specific surface area remaining inside the filter is increased by 5.3% to 12.8% with respect to the powder specific surface area before filtration. . Therefore, it shows that very fine ceramic powder with high activity on the particle surface is removed during filtration. Repeating filter filtration causes the fine ceramic powder to agglomerate. You can see that it is trapped. For this reason, the multilayer ceramic capacitor produced using the slurry from which fine ceramic powder has been removed has no appearance of abnormally large crystal particles after firing, has a low short-circuit rate, and has excellent reliability. It can be done.

  However, the multilayer ceramic capacitor of Sample No. 1 has a high short-circuit rate of 37%, and a short-circuit after the reliability test has also occurred. This sample No. 1 slurry has a filter filtration frequency of 1 pass, and the powder specific surface area remaining inside the filter is only 1.3% higher than the powder specific surface area before filtration. It is considered that the fine ceramic powder has not been removed. In this case, after firing, crystal particles that have become abnormally large due to the fine ceramic powder appear, and it is considered that short-circuiting and reliability deterioration are caused.

  Therefore, the rate of increase in the specific surface area of the fine ceramic powder that remains in the filter and is removed is preferably 5% or more, that is, the fine surface powder having a specific surface area that is 5% or more larger than the specific surface area of the entire ceramic powder in the ceramic slurry. By removing the powder, the occurrence of short-circuit defects can be further suppressed and the reliability can be improved.

  In the first embodiment, the same two filters are used for filtration. However, the present invention is not limited to this, and the number of filters may be one, and the number of times of filtration may be doubled. . Further, it is not necessary to use the same filter. For example, a filter that is upstream with respect to the direction in which the slurry flows and a filter that is coarse with respect to the downstream filter may be used.

  Furthermore, the number of filters can be used with an arbitrary number of three or more.

  If the number of filters increases, the number of times of filtration can be reduced, but the size of the apparatus increases as the number of filters increases.

  A method for producing a ceramic slurry according to the present invention comprises mixing a ceramic slurry used for forming a green sheet while agglomerating and removing fine powder in the ceramic slurry. This is a method for producing a ceramic slurry in which fine powder that causes abnormal grain growth is removed without using a flocculant, for example, by removing the powder using means such as filter filtration. A multilayer ceramic electronic component laminated and fired using a sheet can be made into a multilayer ceramic electronic component excellent in performance such as withstand voltage and reliability, and is useful in a method for manufacturing a multilayer ceramic electronic component.

The schematic diagram which shows the filter filtration apparatus in one embodiment of this invention Partial cutaway perspective view of a general ceramic capacitor

Explanation of symbols

11 Filter 12 Pump 13 Tank 21 Multilayer Ceramic Capacitor 22 Dielectric Layer 23 Internal Electrode 24 External Electrode

Claims (4)

A method for producing a ceramic slurry comprising mixing at least a ceramic powder, a binder, and a solvent, wherein the fine powder in the ceramic slurry is mixed while being removed by agglomeration. . The method for producing a ceramic slurry according to claim 1, wherein the fine powder in the ceramic slurry is mixed while being removed by agglomeration without using a flocculant. 3. The method for producing a ceramic slurry according to claim 2, wherein the ceramic slurry containing at least the ceramic powder, the binder, and the solvent is filtered and mixed while removing fine powder in the ceramic slurry. . The method for producing a ceramic slurry according to claim 1, wherein the fine powder having a specific surface area larger by 5% or more than the specific surface area of the entire ceramic powder in the ceramic slurry is mixed while being removed.

Images