JP2009155142A - Method for producing ceramic slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing ceramic slurry having satisfactory dispersibility. <P>SOLUTION: The method for producing ceramic slurry comprises: a stage where a mixture at least comprising auxiliary component powder is subjected to a first dispersion treatment, so as to regulate auxiliary component slurry; and a stage where the main component powder is added to the auxiliary component slurry, and a second dispersion treatment is performed thereto, so as to prepare the ceramic slurry. The auxiliary component powder is composed of at least one kind of compound selected from the group consisting of a compound comprising either one kind of element among Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho and Yb, and the average grain size of the auxiliary component powder in the auxiliary component slurry is controlled to ≤0.1 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention can produce a green sheet having a small surface roughness and a high firing temperature stability, and in turn, a multilayer ceramic capacitor having a low short-circuit rate, and producing a ceramic slurry with good dispersibility. It is about the method.

A conventional multilayer ceramic capacitor uses a barium titanate (BaTiO ₃ ) -based ceramic dielectric material, which is formed into a sheet shape to produce a green sheet, and electrodes are printed on the green sheet. It is produced by repeating the lamination process.

  In recent years, with the miniaturization of electronic equipment products, the density of electronic circuits has been increasing, and as a result, there has been a strong demand for the reduction in size and capacity of multilayer ceramic capacitors. In order to realize this demand, attempts have been made to reduce the number of internal electrode layers and dielectric layers and increase the number of layers.

  Therefore, the green sheet forming the dielectric layer is also made thinner, and the surface roughness (unevenness) of the green sheet cannot be ignored with respect to the thickness. This is because if the thickness of the dielectric layer after firing varies due to the surface roughness, the electric field strength of the multilayer ceramic capacitor becomes non-uniform, causing a short circuit failure.

  Therefore, a technique for producing a green sheet having a smooth surface and a uniform thickness is indispensable for the production of multilayer ceramic capacitors. In order to smooth the surface of the thinned green sheet and make the thickness uniform, it is necessary to refine the ceramic powder in the green sheet and to increase the dispersibility of the ceramic powder in the green sheet. . Moreover, if the ceramic powder is not sufficiently dispersed in the green sheet, the stability of the particle size of the ceramic powder after firing and the stability of the electrical characteristics of the multilayer ceramic capacitor are also adversely affected.

  In order to increase the dispersibility of the ceramic powder in the green sheet, it is necessary to increase the dispersibility of the ceramic powder in the ceramic slurry as the raw material. Even if the ceramic powder containing is mixed with a dispersion medium, a dispersing agent, a binder, a plasticizer, etc. at a predetermined ratio, and mixed and pulverized using a dispersing machine such as a bead mill or a ball mill, the ceramic powder is mixed into the ceramic slurry. It is difficult to sufficiently disperse the powder. Further, even with a method of performing high-pressure dispersion treatment of ceramic powder of subcomponents as described in Patent Document 2, a uniformly dispersed ceramic slurry cannot be obtained.

Accordingly, there is a need for a method of preparing a ceramic slurry in which ceramic powder is uniformly dispersed.
JP 2001-106578 A JP2007-137693A

  Then, this invention makes it a subject to provide the manufacturing method of a ceramic slurry with favorable dispersibility in view of the said present condition.

  That is, the method for producing a ceramic slurry according to the present invention is a method for producing a ceramic slurry used as a dielectric material, and a mixture containing at least an auxiliary component powder is subjected to a first dispersion treatment to adjust the auxiliary component slurry. And a step of adding a main component powder to the subcomponent slurry and then performing a second dispersion treatment to prepare the ceramic slurry, and the subcomponent powder includes Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho, or Yb consisting of at least one compound selected from the group consisting of compounds containing any one element, An average particle diameter of the subcomponent powder in the component slurry is 0.1 μm or less.

  If it is such, by using nanoparticles having an average particle size of 0.1 μm or less as a subcomponent powder, by performing a dispersion treatment using a bead mill or the like, the coagulated subcomponent powder is loosened, A subcomponent slurry in which the subcomponent powder is uniformly dispersed can be obtained. Furthermore, by adding the main component powder to the subcomponent slurry and performing a dispersion treatment using a bead mill or the like, the agglomerated main component powder is loosened, and the main component powder and the subcomponent powder are uniformly dispersed. You can get a rally.

  Patent Document 2 discloses a slurry of subcomponent powder having an average particle size of 0.1 μm or less obtained by pulverizing a raw material of subcomponent powder (paragraph numbers [0043] and [0095]). However, the “subcomponent powder” in the present invention corresponds to the “raw material” of the subcomponent powder in Patent Document 2, and there are substantially two types. It does not contain the above metal elements. And although the method of patent document 2 prepares a ceramic slurry through such a complicated process, the particle size distribution of the obtained ceramic slurry is only D50 = 0.37 micrometer (paragraph number [ 0100]), the effect is very inadequate. This seems to be because even if the average particle size of the subcomponent powder was 0.1 μm or less, the variation in the particle size was large, and a large particle size was included in a considerable proportion. On the other hand, as will be described later, the ceramic slurry produced by using the method according to the present invention has a D99 value of 0.35 μm or less, and the ceramic powders of the main component and the subcomponent are dispersed very uniformly. Is.

  In the present invention, the dispersion treatment is preferably performed using a bead mill.

  The dispersion treatment using the bead mill is preferably performed using beads having a particle size of 0.03 to 0.3 mm at a peripheral speed v of 5 m / s <v <15 m / s.

  The main component powder is preferably a barium titanate-based dielectric powder.

  The average particle diameter of the barium titanate-based dielectric powder before the second dispersion treatment is preferably 0.3 μm or less.

  The maximum particle size of the subcomponent powder in the subcomponent slurry is preferably 3/4 or less of the average particle size of the main component powder before the second dispersion treatment.

  The mixture containing at least the subcomponent powder preferably contains a first mixed solvent and a first dispersant.

  When adding the main component powder to the subcomponent slurry, it is preferable to add a second dispersant.

  The slurry obtained by adding and mixing the second mixed solvent and the binder to the ceramic slurry obtained by the production method according to the present invention is also one aspect of the present invention.

  The green sheet manufactured by apply | coating the slurry which concerns on this invention on a base material in a sheet form is also one of this invention.

  A sintered body produced by firing the green sheet according to the present invention is also one aspect of the present invention.

  A ceramic capacitor including a plurality of electrodes and a dielectric layer made of a sintered body according to the present invention provided between the electrodes is also one aspect of the present invention.

  The electrode preferably contains Ni or a Ni alloy.

  According to the present invention, ceramic powder can be agglomerated and a ceramic slurry with good dispersibility can be obtained. The green sheet produced using such a ceramic slurry has a low surface roughness due to the high dispersibility of the main component powder and subcomponent powder, so the dielectric layer thickness after sintering becomes uniform, and the multilayer ceramic Capacitor short-circuit rate is reduced. In addition, since the green sheet produced using such a ceramic slurry has a dense structure and a uniform particle size, the particle size after firing is stable, the electrical characteristics are stabilized, and an effective firing temperature is achieved. The temperature range is also widened.

  A multilayer ceramic capacitor 1 according to an embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the multilayer ceramic capacitor 1 according to this embodiment is provided on a capacitor chip body 2 in which dielectric layers 3 and internal electrodes 4 are alternately stacked, and on the surface of the capacitor chip body 2. An external electrode 5 electrically connected to the internal electrode 4. The internal electrodes 4 are laminated so that the ends thereof are alternately exposed on the two opposing surfaces of the capacitor chip body 2, and are formed on the surfaces of the capacitor chip body 2 to form a predetermined capacitor circuit. The electrode 5 is electrically connected.

  The dielectric layer 3 is made of a sintered body of ceramic powder, and in the present embodiment, the ceramic powder is obtained as a ceramic slurry. In order to obtain the ceramic powder as a ceramic slurry, first, a mixture containing at least an auxiliary component powder is subjected to a dispersion treatment (first dispersion treatment) to prepare an auxiliary component slurry.

  Examples of the sub-component powder include powders of compounds such as oxides and carbonates containing any one of Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho, and Yb. . As for the powder of such a compound, 1 type may be used and 2 or more types may be used together.

  The first dispersion treatment is preferably performed using a bead mill. Such a dispersion treatment using a bead mill is preferably performed at a peripheral speed v of 5 m / s <v <15 m / s using beads having a particle size of 0.03 to 0.3 mm. If the particle size and peripheral speed of the cobblestone are smaller than this range, it is difficult to sufficiently disperse and disperse the agglomerated subcomponent powder, while if the particle size and peripheral speed of the cobblestone are larger than this range, the subcomponent The crystallinity of the powder is reduced and it becomes fine powder.

  The mixture preferably further contains a first mixed solvent and a first dispersant in addition to the subcomponent powder.

  The first mixed solvent is not particularly limited, and examples thereof include glycols such as ethyl carbitol, butanediol, and 2-butoxyethanol: alcohols such as methanol, ethanol, propanol, and butanol: acetone, methyl ethyl ketone, diacetone alcohol, and the like. Ketones: Esters such as methyl acetate and ethyl acetate: Aromatics such as toluene, xylene and benzyl acetate.

  The first dispersant is not particularly limited. For example, a polyvinyl butyral dispersant, a polyvinyl acetal dispersant, a polycarboxylic acid dispersant, a maleic acid dispersant, a polyethylene glycol dispersant, an allyl ether copolymer dispersant. Agents and the like.

  The average particle size of the subcomponent powder in the subcomponent slurry obtained by the first dispersion treatment is 0.1 μm or less, preferably 0.02 to 0.06 μm. When it exceeds 0.1 μm, a green sheet with low surface smoothness and non-uniform thickness can be obtained.

  In order to obtain the ceramic slurry, the main component powder is then added to the subcomponent slurry and a dispersion treatment (second dispersion treatment) is performed.

Wherein there is no particular limitation on the major component powder, for _{example, Ba x Ca 1-x TiO} 3 (0 <x ≦ 1) barium titanate-based dielectric powder comprising the like are suitably used.

  The barium titanate-based dielectric powder preferably has an average particle size of 0.3 μm or less. When it exceeds 0.3 μm, a green sheet with low surface smoothness and non-uniform thickness can be obtained.

  Before the second dispersion treatment, it is preferable that the maximum particle size of the subcomponent powder in the subcomponent slurry is 3/4 or less of the average particle size of the main component powder. When the maximum particle size of the subcomponent powder in the subcomponent slurry exceeds this range, the sintering reaction between the main component powder and the subcomponent powder hardly occurs uniformly during firing.

  When adding the main component powder to the subcomponent slurry, it is preferable to further add a second dispersant. It does not specifically limit as a 2nd dispersing agent, For example, the same thing as a 1st dispersing agent is mentioned.

  The second dispersion process is preferably performed using, for example, a bead mill in the same manner as the first dispersion process.

  A slurry for forming a green sheet is obtained by adding and mixing the second mixed solvent and the binder to the ceramic slurry thus obtained.

  It does not specifically limit as a 2nd mixed solvent, For example, the same thing as the said 1st mixed solvent is mentioned.

  The binder is not particularly limited, and examples thereof include acrylic resin, polyvinyl butyral resin, polyvinyl acetal resin, and ethyl cellulose resin.

  It is preferable that the binder is previously dissolved in the second mixed solvent and filtered to obtain a solution, and the ceramic slurry is added to the solution. A binder resin having a high degree of polymerization is difficult to dissolve in a solvent, and the dispersibility of the slurry tends to be deteriorated by an ordinary method. Dispersibility of each component in the slurry for green sheet formation can be improved by dissolving the binder resin having a high degree of polymerization in a solvent and then adding other components to the solution. Can also be suppressed. In the case of a solvent other than the second mixed solvent, the solid content concentration cannot be increased and the change in lacquer viscosity with time tends to increase.

  The green sheet is formed by applying the slurry for forming the green sheet thus produced on a base material made of polyethylene terephthalate or the like. The dielectric layer 3 is made of a sintered body obtained by firing the obtained green sheet.

  The internal electrode 4 is not particularly limited, and examples thereof include metals such as Cu, Ni, W, Mo, Ag, and alloys thereof.

  The external electrode 5 is not particularly limited, and examples thereof include metals such as Cu, Ni, W, Mo, and Ag or alloys thereof; alloys such as In—Ga and Ag-10Pd; carbon, graphite, and a mixture of carbon and graphite. The thing which consists of etc. is mentioned.

  Although it does not specifically limit as a manufacturing method of the multilayer ceramic capacitor which concerns on this embodiment, For example, it manufactures as follows. First, the conductive paste for the internal electrode 4 containing the various metals described above is screen-printed in a predetermined shape on the green sheet to form the conductive paste film for the internal electrode 4.

  Next, a plurality of green sheets on which the conductive paste film for the internal electrode 4 is formed as described above are stacked, and a green sheet on which no conductive paste film is formed is stacked so as to sandwich the green sheets. After pressure bonding, the laminate (green chip) is obtained by cutting as necessary.

  And after performing a binder removal process to the obtained green chip, the said green chip is baked, for example in reducing environment, and the capacitor chip body 2 is obtained. In the capacitor chip body 2, dielectric layers 3 and internal electrodes 4 made of a sintered body obtained by firing a green sheet are alternately laminated.

  The obtained capacitor chip body 2 is preferably subjected to an annealing treatment to reoxidize the dielectric layer 3.

  Next, an electrode made of the above-mentioned various metals or the like on the end surface of the capacitor chip body 2 so that the external electrode 5 is electrically connected to each end edge of the internal electrode 4 exposed from the end surface of the capacitor chip body 2. The external electrode 5 is formed by coating. Then, if necessary, a coating layer is formed on the surface of the external electrode 5 by plating or the like.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

BaCO ₃ , MgO, SiO ₂ , Mn ₃ O ₄ and Dy ₂ O ₃ were prepared as subcomponents. The addition amount of Ba element is 0.95 mol%, the addition amount of Si element is 1.55 mol%, and the Dy element is added to the main component barium titanate (BaTiO ₃ ) to be added to the subcomponent later. The addition amount of Mg is 0.65 mol%, the addition amount of Mg element is 1.2 mol%, and the addition amount of Mn element is 0.13 mol%.

  Next, 390 parts by weight of a mixed solution of ethanol and toluene as a solvent and 6 parts by weight of a polyvinyl butyral dispersant (BL-1 manufactured by Sekisui Chemical Co., Ltd.) as a dispersant with respect to 100 parts by weight of the prepared subcomponent. Add and mix with homogenizer. Next, these mixtures were dispersed and pulverized under the conditions shown in Table 1 using a vertical bead mill having a function of separating beads and slurry by centrifugal force. The sample supply rate is 100 ml / min.

  Next, with respect to 100 parts by weight of the main component barium titanate powder, the subcomponent slurry after the dispersion and pulverization treatment was added so that each element had the above-described addition amount. The particle sizes of the subcomponent powder and the main component powder in the subcomponent slurry are as shown in Table 2. The particle sizes shown in Table 2 were determined by observing each powder with a scanning electron microscope, measuring the particle size of 300 particles, and calculating the average value.

  Furthermore, 0.87 wt% of the above BL-1 was added as a dispersant to 100 parts by weight of the barium titanate powder, and mixed with a homogenizer. Next, these mixtures were dispersed and pulverized under the conditions shown in Table 3 using a vertical bead mill having a function of separating beads and slurry by centrifugal force. The sample supply rate is 100 ml / min.

  Next, the obtained ceramic slurry was put into a ball mill and mixed with a toluene-ethanol mixed solvent, a polyvinyl butyral binder and a plasticizer until an appropriate viscosity was obtained, thereby preparing a green sheet forming slurry. And the said slurry was apply | coated by the doctor blade method on the polyethylene terephthalate film, and the green sheet was produced.

  Next, on each green sheet, a conductive paste for an internal electrode made of Ni powder is screen-printed in a predetermined shape, and then a plurality of green sheets on which a conductive paste film is formed are laminated, thermocompression bonded and integrated, A laminate was produced.

Then, the laminate was heated in air at 300 ° C. for 10 hours to remove the organic binder, and then fired in a reducing atmosphere at 1100 ° C. for 2 hours, and further in an N ₂ gas atmosphere at 1000 ° C. The capacitor chip body was obtained by reoxidation treatment for 2 hours and sintering. Next, after polishing the end surface of the obtained capacitor chip body by sand blasting, an external electrode is formed by applying an In-Ga electrode to the end surface, and a multilayer ceramic capacitor having the structure illustrated in FIG. 1 is obtained. Produced.

  Various characteristics of the ceramic slurry, the green sheet, and the multilayer ceramic capacitor were evaluated as follows, and the results are shown in Table 4.

<Evaluation of ceramic slurry>
The particle size distribution of the prepared ceramic slurry was measured with LA-920 manufactured by Horiba. A sample having a D99 value exceeding 0.35 μm was evaluated as NG.

<Evaluation of Green Sheet>
The surface roughness (Rz) of the green sheet was measured with a scanning probe microscope (SPM-9500J3 manufactured by Shimadzu Corporation). Samples with Rz exceeding 0.4 μm were evaluated as NG.

<Evaluation of multilayer ceramic capacitor>
The resistance value of 100 samples for each multilayer ceramic capacitor was measured with an insulation resistance meter, and a sample having a resistance value of 100 kΩ or less was determined as a defective product, thereby obtaining a short-circuit rate. A sample having a short-circuit rate exceeding 10% was evaluated as NG.

<Production method and measurement conditions of single plate sample>
A single plate evaluation sample was prepared as follows. The green sheets were cut into 1 cm squares and stacked so as to have a thickness of 1 mm. Next, it was molded at a pressure of 1000 kg / cm ³ . Next, in order to incinerate the resin component, baking was performed in the air at 300 ° C. for 10 hours, and then baking was performed in the baking temperature and reducing atmosphere shown in Table 5 for 2 hours. Then, it was stabilized at 1000 ° C. in nitrogen gas and reoxidation treatment was performed for 2 hours.

  For the obtained single plate sample, the density, particle size, and effective firing temperature range were evaluated as follows, and the results are shown in Table 5.

The density (g / cm ³ ) was measured using the Archimedes method.

  The presence or absence of particles having a particle size of 0.5 μm or more was determined by measuring the particle size of the sintered body with a scanning electron microscope.

The effective firing temperature range indicates the effective range of the firing temperature on condition that there are no particles having a density of 5.8 g / cm ³ or more and a particle size of 0.5 μm or more.

Desired characteristics can be obtained when the density is not less than 5.8 g / cm ³ , the sintered particle size is less than 0.5 μm, and the effective firing temperature range is not less than 20 ° C. The evaluation result was “NG”.

1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 2 ... Capacitor chip body 3 ... Laminate body layer 4 ... Internal electrode 5 ... External electrode

Claims (13)

A method for producing a ceramic slurry for use as a dielectric material, comprising:
Subjecting the mixture containing at least the subcomponent powder to a first dispersion treatment to prepare a subcomponent slurry; and
A step of adding a main component powder to the subcomponent slurry, and then performing a second dispersion treatment to prepare the ceramic slurry, and
The subcomponent powder is at least one compound selected from the group consisting of compounds containing any one element of Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho, or Yb. It consists of
The method for producing a ceramic slurry, wherein an average particle size of the subcomponent powder in the subcomponent slurry is 0.1 μm or less.   The method for producing a ceramic slurry according to claim 1, wherein the dispersion treatment is performed using a bead mill.   The ceramic slurry production according to claim 2, wherein the dispersion treatment using the bead mill is performed using beads having a particle diameter of 0.03 to 0.3 mm at a peripheral speed v of 5 m / s <v <15 m / s. Method.   4. The method for producing a ceramic slurry according to claim 1, wherein the main component powder is a barium titanate dielectric powder.   The method for producing a ceramic slurry according to claim 4, wherein an average particle diameter of the barium titanate-based dielectric powder before the second dispersion treatment is 0.3 µm or less.   The maximum particle size of the subcomponent powder in the subcomponent slurry is 3/4 or less of the average particle size of the main component powder before the second dispersion treatment. Of manufacturing ceramic slurry.   The method for producing a ceramic slurry according to claim 1, 2, 3, 4, 5 or 6, wherein the mixture containing at least the subcomponent powder contains a first mixed solvent and a first dispersant.   The method for producing a ceramic slurry according to claim 1, 2, 3, 4, 5, 6 or 7, wherein a second dispersant is further added to the subcomponent slurry when the main component powder is added.   A slurry obtained by adding a second mixed solvent and a binder to the ceramic slurry obtained by the production method according to claim 1, 2, 3, 4, 5, 6, 7 or 8.   The green sheet manufactured by apply | coating the slurry of Claim 9 on a base material in a sheet form.   The sintered compact manufactured by baking the green sheet of Claim 10.   A ceramic capacitor comprising: a plurality of electrodes; and a dielectric layer made of the sintered body according to claim 11 provided between the electrodes.   The ceramic capacitor according to claim 12, wherein the electrode contains Ni or a Ni alloy.