JP2006004675A - Composite conductive particle powder, conductive coating containing it, and stacked ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide composite conductive particle powder having an excellent heat contraction characteristic and excellent oxidation resistance while keeping electric characteristics as an internal electrode material and has excellent dispersibility in a conductive coating; and to provide a conductive coating and a stacked ceramic capacitor containing the composite conductive particle powder. <P>SOLUTION: This composite conductive particle powder is formed of composite particle powder where particle surfaces of nickel particles are uniformly coated with a dielectric substance. The composite conductive particle powder can be provided by adding a solution of metal alkoxide in a suspension liquid prepared by dispersing nickel particle powder in an organic solvent, then drying it with air and thereafter drying it at 60-120°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a composite conductive particle powder having excellent heat shrinkage characteristics and oxidation resistance while maintaining electrical characteristics as an internal electrode material, and having excellent dispersibility in a conductive paint, and containing the composite conductive particle powder An electrically conductive paint and a multilayer ceramic capacitor are provided.

  As is well known, a multilayer ceramic capacitor is a product in which a plurality of ceramic dielectric layers and internal electrode layers are alternately laminated and fired at a high temperature to integrate them, and is generally a metal that is an internal electrode material. Prepared by dispersing fine powder in a binder to form a paste, printing the paste on a ceramic green sheet, laminating multiple layers of the printed substrate, heat-pressing, and then firing in a reducing atmosphere Has been.

  Conventionally, noble metals such as gold, palladium and silver-palladium have been used as the internal electrodes of such multilayer ceramic capacitors, but in recent years, base metals such as nickel have been used from the viewpoint of cost reduction and the like. .

  However, when nickel powder is used, the heat shrinkage rate during firing is larger than when noble metal is used, and because the oxidation resistance is inferior, part of the nickel powder is oxidized during firing. Have the disadvantage of diffusing into the ceramic dielectric layer.

That is, the firing temperature when producing a multilayer ceramic capacitor depends on the type of ceramic dielectric, but when a ceramic dielectric such as BaTiO ₃ or SrTiO ₃ that is generally used is used, it is 1200 ° C. or higher. is required. On the other hand, since nickel powder starts thermal shrinkage from 400 to 500 ° C., when it is fired simultaneously with the ceramic dielectric layer, distortion occurs between the laminated ceramic dielectric layer and the nickel layer, and delamination and cracks occur. As a result, the performance of the multilayer ceramic capacitor deteriorates.

  In recent years, as the capacity of multilayer ceramic capacitors has increased, the number of multilayers tends to increase. On the other hand, in response to the demand for miniaturization of multilayer ceramic capacitors, the internal electrodes have become thinner as the ceramic layers become thinner. At present, further thinning is required for a single layer thickness of 1 to 2 μm.

  To date, nickel powders in which a composite oxide or oxide such as barium titanate is present on the nickel particle surface or inside the nickel particles have been disclosed in order to improve the heat shrink characteristics of the nickel powder (Patent Documents 1 to 3). ).

JP-A-11-124602 Japanese Patent Laid-Open No. 11-343501 JP 2000-282102 A

  In order to reduce the size and increase the performance of multilayer ceramic components and multilayer ceramic capacitors, while maintaining the electrical characteristics as the internal electrode material, the thermal contraction characteristics of the nickel powder as the internal electrode material are brought closer to the ceramic dielectric layer, A conductive particle powder excellent in oxidation resistance and dispersibility in a conductive coating is currently most demanded, but has not yet been obtained.

  That is, Patent Documents 1 to 3 describe nickel powder in which a composite oxide such as barium titanate or an oxide is present on the particle surface as an internal electrode material of a multilayer ceramic capacitor. However, since the surface of the nickel particles is not uniformly coated with a complex oxide such as barium titanate or an oxide, the oxidation resistance and the heat shrinkage characteristics during heating and firing are insufficient. In particular, the methods described in Patent Documents 2 and 3 increase the viscosity because of heating during the neutralization reaction, making uniform coating difficult. In addition, when a composite oxide or oxide such as barium titanate is present inside the particles, the function as an electrode material is not preferable because the composite oxide or oxide inhibits the function.

  Therefore, the present invention brings the thermal shrinkage characteristics of the nickel powder, which is the internal electrode material, close to the ceramic dielectric layer while maintaining the electrical characteristics as the internal electrode material, and also improves the oxidation resistance and dispersibility in the conductive paint. It is a technical subject to obtain excellent conductive particle powder.

  As a result of intensive studies to solve the above problems, the present inventors have found that the composite conductive particle powder in which the surface of the nickel particle is coated with the dielectric material by the method of the present invention is applied to the surface of the nickel particle. The thin and uniform coating of the dielectric substance maintains the electrical characteristics as the internal electrode material, while bringing the thermal shrinkage characteristics closer to the ceramic dielectric layer, and is resistant to oxidation and dispersion in the conductive paint. As a result, it was found that conductive particle powder having excellent properties can be obtained, and the present invention has been made.

  That is, the present invention is a composite conductive particle powder characterized by comprising a composite particle powder in which the surface of nickel particles is coated with a dielectric substance (Invention 1).

  In addition, the present invention provides the composite conductive particle powder, wherein the dielectric material is a ferroelectric (Invention 2).

  In the present invention, the metal alkoxide solution is added to a suspension in which nickel particle powder is dispersed in an organic solvent, and then air-dried and then dried at 60 to 120 ° C. 2 is a method for producing a composite conductive particle powder according to 2 (present invention 3).

  Moreover, the present invention uses a metal alkoxide containing at least one selected from Ti, Zr, Ba, Sr, Mg, and Ca, and the composite conductive particle powder according to the present invention 1 or 2, (Invention 4).

  Further, the present invention is a conductive paint containing at least conductive particle powder and a resin, wherein the conductive particle powder is the composite conductive particle powder (Invention 5). ).

  According to another aspect of the present invention, there is provided a multilayer ceramic capacitor having a structure in which ceramic dielectric layers and internal electrode layers are alternately stacked, wherein the composite electrode particles are contained in the internal electrode layer. (Invention 6).

  The composite conductive particle powder according to the present invention is excellent in heat shrinkage characteristics and oxidation resistance while maintaining electrical characteristics as an internal electrode material, and has excellent dispersibility in a conductive coating material. It is suitable as an electrode material.

  The conductive paint according to the present invention is suitable as a conductive paint for a multilayer ceramic capacitor because the electrode material is uniformly dispersed in the paint by using the composite conductive particle powder.

  In the multilayer ceramic capacitor according to the present invention, structural defects such as cracks and delamination are suppressed by using the conductive paint as an electrode paint for forming an internal electrode layer. It is suitable as a capacitor.

  The configuration of the present invention will be described in more detail as follows.

  First, the composite conductive particle powder according to the present invention will be described.

  The composite conductive particle powder according to the present invention comprises a composite particle powder in which the surface of nickel particles, which are particles to be processed, is uniformly coated with a dielectric substance.

  The nickel particle powder in the present invention is a powder obtained by a dry process in which a nickel salt vapor and a reducing gas are reacted in a gas phase, or a spray pyrolysis method in which a thermally decomposable nickel compound solution is sprayed to thermally decompose. Either the obtained one or a solution obtained by a wet method in which an aqueous solution containing a nickel salt is reduced and precipitated with a reducing agent under specific conditions may be used, and the nickel particle surface may be oxidized.

  The average particle diameter of the nickel particle powder in the present invention is preferably 0.009 to 5.0 μm, more preferably 0.025 to 3.0 μm, and still more preferably 0.045 to 1.0 μm.

The BET specific surface area value of the nickel particle powder in the present invention is preferably 0.01 to 50 m ² / g, more preferably 0.05 to 40 m ² / g.

  The thermal shrinkage start temperature of the nickel particle powder in the present invention is usually about 300 ° C., although it varies depending on the particle size.

  The oxidation start temperature of the nickel particle powder in the present invention is usually about 300 ° C.

  Although the fluidity of the nickel particle powder in the present invention varies depending on the particle size, the fluidity index described later is usually about 40.

As the dielectric material in the present invention, one or more oxides or composite oxides selected from Mg, Ca, Sr, Ba, Ti and Zr can be used. For example, magnesium oxide or Ca , Sr or Ba titanate or zirconate, etc., preferably BaTiO ₃ , SrTiO ₃ and ferroelectrics represented by solid solutions thereof. In view of heat shrinkage characteristics, it is preferable to select the same dielectric material as that used for the dielectric layer of the multilayer ceramic capacitor as dielectric particles as much as possible. In recent years, in particular, in order to improve the performance of multilayer ceramic capacitors, the ceramic dielectric layer has been mainly composed of barium titanate-based ferroelectrics, so it is made of a complex oxide such as barium titanate. It is preferable to use a barium titanate ferroelectric.

  The coating amount of the dielectric substance is preferably 0.01 to 30% by weight with respect to the composite conductive particle powder. When the amount is less than 0.01% by weight, the amount of the dielectric material attached is too small, and thus the heat shrinkage characteristics and the like cannot be improved. On the other hand, when the content exceeds 30% by weight, the dielectric material that is detached from the particle surface increases, dispersibility in the conductive coating is reduced, and there is too much dielectric material that adheres to the particle surface, leading to conduction. Since it worsens, it becomes disadvantageous as an electrode material. More preferably, it is 0.05-25 weight%, More preferably, it is 0.10-20 weight%.

  The average particle size of the composite conductive particle powder according to the present invention is preferably 0.01 to 5.0 μm. When the average particle diameter exceeds 5.0 μm, the thickness of one layer of the internal electrodes constituting the multilayer ceramic capacitor becomes too thick, making it difficult to reduce the size and increase the capacity. Considering the reduction in size and increase in capacity of the obtained multilayer ceramic capacitor, the thickness is more preferably 0.03 to 3.0 μm, and still more preferably 0.05 to 1.0 μm.

The BET specific surface area value of the composite conductive particle powder according to the present invention is preferably 0.01 to 50 m ² / g, more preferably 0.05 to 40 m ² / g.

  The heat shrinkage start temperature of the composite conductive particle powder according to the present invention is preferably 700 ° C. or higher. When the thermal shrinkage start temperature is less than 700 ° C., the difference in thermal shrinkage between the ceramic dielectric layer and the ceramic green sheet when the laminated body of the ceramic green sheets formed with the internal electrode layer is fired is fired. Therefore, cracks are likely to occur, which is not preferable. More preferably, it is 750 degreeC or more, More preferably, it is 800 degreeC or more, Most preferably, it is 850 degreeC or more.

  The oxidation start temperature of the composite conductive particle powder according to the present invention is 500 ° C. or higher, preferably 550 ° C. or higher, more preferably 600 ° C. When the oxidation start temperature is less than 500 ° C., the nickel particles are oxidized into the ceramic dielectric layer when firing the ceramic green sheet laminate formed with the internal electrode layer obtained by using this. Since it becomes easy to diffuse, it is not preferable.

  The fluidity of the composite conductive particle powder according to the present invention is preferably a fluidity index of 55 or more, more preferably 60 or more, and most preferably 65 to 90. When the fluidity index is less than 55, it is difficult to say that the fluidity is excellent, and it is difficult to disperse uniformly in the conductive paint.

  Next, a multilayer ceramic capacitor using the conductive paint according to the present invention will be described.

  The conductive paint according to the present invention is composed of the composite conductive particle powder according to the present invention, a resin and a solvent. If necessary, an additive such as a plasticizer may be added. The conductive paint according to the present invention will be described below.

  As the solvent in the present invention, terpineol, decyl alcohol, ethanol or the like can be used.

  As the resin in the present invention, cellulose resins such as ethyl cellulose and polyvinyl butyral resins can be used. A cellulose resin such as ethyl cellulose is preferable.

  The multilayer ceramic capacitor according to the present invention has a structure in which external electrodes are provided on a laminate in which ceramic dielectric layers and internal electrode layers are alternately laminated.

As the ceramic material used for the ceramic dielectric layer in the present invention, it is preferable to use a ferroelectric represented by BaTiO ₃ , SrTiO ₃ , yttrium oxide and their solid solutions in order to improve the performance of the multilayer ceramic capacitor. More preferably, it is a barium titanate ferroelectric such as barium titanate.

  The multilayer ceramic capacitor according to the present invention has a crack generation rate of 3% or less, preferably 2% or less, more preferably 1% or less.

  Next, a method for producing the composite conductive particle powder according to the present invention will be described.

  The composite conductive particle powder according to the present invention is obtained by adding a metal alkoxide solution to a suspension obtained by dispersing nickel particle powder, which is a particle powder to be treated, in a water-soluble organic solvent, stirring, air drying, and then 60 to 120 ° C. The composite conductive particle powder in which the surface of the nickel particles is uniformly coated with the dielectric substance can be obtained by the above-described manufacturing method.

  Any organic solvent may be used as long as it is generally used, but a water-soluble organic solvent is preferable. Specifically, alcohol solvents such as ethyl alcohol, propyl alcohol or butyl alcohol, ketone solvents such as acetone or methyl ethyl ketone, glycol ether solvents such as methyl cellosolve, ethyl cellosolve, propyl cellosolve or butyl cellosolve, diethylene glycol, triethylene glycol , Oxyethylene such as polyethylene glycol, dipropylene glycol or tripropylene glycol, polypropylene glycol, oxypropylene addition polymer, alkylene glycol such as ethylene glycol, propylene glycol or 1,2,6-hexanetriol, glycerin, 2-pyrrolidone, etc. Can be preferably used, but more preferably ethyl alcohol, propyl alcohol, butyl alcohol, etc. Alcohol solvents, acetone, ketone solvents such as methyl ethyl ketone.

  As the metal element constituting the metal alkoxide used in the present invention, any metal element can be used as long as it can form a dielectric, but barium, titanium, strontium, magnesium, calcium and the like are preferable. Moreover, as a kind of alkoxide, methoxide, ethoxide, propoxide, isopropoxide, oxyisopropoxide, butoxide, etc. can be used.

  The metal alkoxide is preferably used after being dispersed or dissolved in advance in the above-mentioned organic solvent in order to perform a more uniform treatment.

  In addition, the hydrolysis of the metal alkoxide does not require any particular addition of water in order to adhere or coat the inorganic compound more uniformly on the particle surface of the nickel particles, depending on the moisture in the organic solvent and the moisture of the nickel particles. Hydrolysis is preferably performed.

  Next, a method for producing a conductive paint according to the present invention will be described.

  The conductive paint according to the present invention can be obtained by adding the composite conductive particle powder according to the present invention to an organic solvent and a resin and kneading them.

  For the dispersion in the present invention, a three-roll mill, a ball mill, a kneader or the like can be used.

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

  A ceramic slurry is obtained by adding a resin and an organic solvent to a ceramic dielectric and kneading them with a ball mill or the like into a sheet shape to obtain a ceramic green sheet. Next, a conductive paint is printed on the ceramic green sheet by screen printing or the like to form an internal electrode layer. Next, a plurality of ceramic green sheets on which internal electrode layers are formed can be laminated, heated and integrated to be fired, and then external electrodes can be baked.

<Action>
In the present invention, the most important point is that the composite conductive particle powder having a dielectric substance attached or coated on the particle surface of the nickel particle maintains the electrical characteristics as the internal electrode material, while maintaining the heat shrinkage characteristics. In addition, the oxidation resistance is excellent, and the dispersibility in the conductive paint is excellent.

  The reason why the composite conductive particle powder according to the present invention has excellent heat shrinkage characteristics is that the present inventor considered that the particle surface of the nickel particles could be coated more uniformly with the dielectric substance. Yes.

  As the reason why the composite conductive particle powder according to the present invention is excellent in oxidation resistance, the present inventor was able to reduce the contact with oxygen by uniformly coating the particle surface of the nickel particles with a dielectric substance. I think it is due to this.

  In addition, it is a fact that the multilayer ceramic capacitor obtained using the composite conductive particle powder according to the present invention has a low crack generation rate.

  As the reason for the low crack generation rate of the multilayer ceramic capacitor according to the present invention, the present inventor used the composite conductive particle powder according to the present invention as an internal electrode material, so that the starting temperature of heat shrinkage is more ceramic dielectric. This is thought to be due to the closeness of the layer and the difference in thermal shrinkage between the internal electrode material and the ceramic dielectric layer being reduced.

  Hereinafter, the present invention will be described in detail with reference to examples.

  The average particle diameters of the nickel particle powder and the composite conductive particle powder were both measured by measuring the particle diameters of 350 particles shown in the electron micrograph, and indicating the average value.

  The specific surface area value was indicated by a value measured by the BET method.

  The coating amount of the dielectric material adhering to the composite conductive particles is determined using the amount of metal constituting the dielectric material by using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.). The measurement was carried out in accordance with K0119 "General X-ray fluorescence analysis rules".

  The thermal shrinkage start temperatures of the nickel particle powder and the composite conductive particle powder were measured using “Thermal analyzer EXSTAR6000 TMA / SS (thermal / application / strain measuring device)” (manufactured by Seiko Electronics Co., Ltd.).

  The oxidation start temperatures of the nickel particle powder and the composite conductive particle powder were measured using a “thermal analyzer EXSTAR6000 TG / DTA (differential thermogravimetric simultaneous measuring device)” (manufactured by Seiko Denshi Kogyo Co., Ltd.).

  The flowability of the nickel particle powder and the composite conductive particle powder is determined by using a powder tester (trade name, manufactured by Hosokawa Micron Co., Ltd.), each of the angle of repose (degree), the degree of compression (%), the spatula angle (degree), and the degree of aggregation. The powder characteristic value was measured, and each index was obtained by replacing each measured value with a numerical value of the same standard, and each index was expressed as a total fluidity index. The closer the fluidity index is to 100, the better the fluidity.

  The crack generation rate of the multilayer ceramic capacitor was determined by cutting the multilayer ceramic capacitor produced by the method described later, and visually checking for the occurrence of delamination and / or cracks using a metal microscope for 100 samples. The incidence was determined.

<Example 1-1: Production of composite conductive particle powder>
Nickel particle powder (Processed particle 1 Particle shape: spherical, average particle diameter: 0.22 μm, BET specific surface area value: 3.3 m ² / g, heat shrinkage start temperature: 405 ° C., oxidation start temperature: 360 ° C., fluidity Index: 40) 500 g of acetone was poured into 500 ml of acetone using a stirrer to obtain an acetone slurry containing nickel particle powder.

  Next, 200 ml of an acetone solution in which 60.85 g of titanium tetraisopropoxide is dispersed and 200 ml of an acetone solution in which 54.80 g of barium isopropoxide are dispersed are added to the slurry of acetone containing the nickel particle powder, and the mixture is added for 60 minutes. Stir and mix.

  The obtained mixed solution was air-dried in a fume hood for 3 hours, and then dried at 80 ° C. for 60 minutes using a dryer to obtain composite conductive particle powder.

The obtained composite conductive particle powder was a spherical particle having an average particle diameter of 0.26 μm. The BET specific surface area value was 4.7 m ² / g, the heat shrinkage start temperature was 950 ° C., the oxidation start temperature was 620 ° C., and the fluidity was 68. The amount of the adhered dielectric material was 9.08% by weight (corresponding to 10 parts by weight in terms of BaTiO _{3 with} respect to 100 parts by weight of the nickel particle powder).

<Example 2: Production of conductive paint>
100 parts by weight of the composite conductive particle powder, 115 parts by weight of terpineol, and 100 parts by weight of a terpineol solution of ethyl cellulose (ethyl cellulose content: 20% by weight) are mixed and dispersed using a three-roll mill, and conductive paint Got.

<Example 3-1: Production of multilayer ceramic capacitor>
A ceramic slurry prepared by a conventional method using a dielectric (type: BaTiO ₃ , particle shape: granular, average particle diameter: 30 nm, BET specific surface area value: 31.5 m ² / g) is formed into a sheet shape, and the thickness A ceramic green sheet of about 2.8 μm was obtained. Next, the conductive paint was printed on the ceramic green sheet by screen printing to form an internal electrode layer. Next, a plurality of ceramic green sheets on which the internal electrode layer is formed are laminated, and the heat-integrated one is fired in a reducing atmosphere at 1300 ° C. for 2 hours, and then the external electrode is baked to obtain a laminated ceramic. A capacitor was obtained.

  The crack generation rate of the obtained multilayer ceramic capacitor was 0%.

  In accordance with Examples 1-1 to 31-1, composite conductive particle powder, conductive paint and multilayer ceramic capacitor were prepared. Various characteristics of each manufacturing condition and the obtained composite conductive particle powder and multilayer ceramic capacitor are shown.

Processed particles 1-3:
Nickel particle powder having the characteristics shown in Table 1 was prepared as the particle powder to be treated.

Examples 1-2 to 1-6, Comparative Example 1:
A composite conductive particle powder was obtained in the same manner as in Example 1-1 except that the type of particle powder to be treated, the type of organic solvent in the surface treatment step, the type of surface treatment agent and the amount added were variously changed. .

  The production conditions at this time are shown in Table 2, and the characteristics of the obtained composite conductive particle powder are shown in Table 3.

Comparative example 2 (Japanese Unexamined Patent Publication No. 11-343501, Example 6 additional test)
Nickel particle powder (particle shape: spherical, average particle size: 0.22 μm, BET specific surface area value: 3.3 m ² / g, heat shrinkage start temperature: 405 ° C., oxidation start temperature: 360 ° C., fluidity index: 40) 100 g was added to 1 L of pure water and stirred to form a slurry. After stirring for 30 minutes, 100 g of hydrogen peroxide solution was added all at once, and when the reaction was completed and no bubbles were generated, stirring was stopped, filtered, and dried to obtain surface-oxidized nickel fine powder.

100 g of surface oxidized nickel fine powder was added to 1 L of pure water and stirred to form a slurry. After heating to 60 ° C., 3.9 g of titanium sulfate solution (Ti: 5 wt%) was added all at once. Further, an aqueous sodium hydroxide solution (NaOH: 1N) was added to adjust the pH to 8, and the mixture was stirred for 1 hour. Then, this was filtered, and after repulping once, it was filtered again. The cake thus obtained was added to 1 L of pure water to make a slurry. Then, a solution obtained by dissolving 2.62 g of barium chloride in hot water was added all at once. Further, an aqueous sodium hydroxide solution (NaOH: 1N) was added to adjust the pH to 12 or more, and the mixture was stirred as it was for about 1 hour, and then filtered and dried to obtain a composite nickel fine powder containing BaTiO ₃ oxide.

  Table 3 shows various characteristics of the obtained composite nickel fine powder.

<Multilayer ceramic capacitor>
Examples 3-2 to 3-6, Comparative Examples 3 to 7:
A laminate was obtained in the same manner as in the production of the multilayer ceramic capacitor of Example 3-1, except that the type of conductive particle powder was variously changed.

  Table 4 shows the manufacturing conditions and the characteristics of the obtained multilayer ceramic capacitor.

  The composite conductive particle powder according to the present invention is suitable as an electrode material for a multilayer ceramic capacitor because it has excellent heat shrinkage characteristics and oxidation resistance and is excellent in dispersibility in a conductive paint.

  The conductive paint according to the present invention is suitable as a conductive paint for a multilayer ceramic capacitor because the electrode material is uniformly dispersed in the paint by using the composite conductive particle powder.

In the multilayer ceramic capacitor according to the present invention, structural defects such as cracks and delamination are suppressed by using the conductive paint as an electrode paint for forming an internal electrode layer. It is suitable as a capacitor.

Claims (6)

A composite conductive particle powder comprising a composite particle powder having a surface of nickel particles coated with a dielectric substance. 2. The composite conductive particle powder according to claim 1, wherein the dielectric substance is a ferroelectric substance. 3. The composite electroconductivity according to claim 1, wherein a solution of the metal alkoxide is added to a suspension in which nickel particle powder is dispersed in an organic solvent, and then air-dried and then dried at 60 to 120 [deg.] C. Production method of particle powder. The method for producing a composite conductive particle powder according to claim 1 or 2, wherein a metal alkoxide containing at least one selected from Ti, Zr, Ba, Sr, Mg, and Ca is used. The conductive paint containing at least the conductive particle powder and a resin, wherein the conductive particle powder is the composite conductive particle powder according to claim 1 or 2. 3. A laminated ceramic capacitor having a structure in which ceramic dielectric layers and internal electrode layers are alternately laminated, wherein the internal electrode layer contains the composite conductive particle powder according to claim 1 or 2. Ceramic capacitor.