TW201942263A - Electroconductive paste - Google Patents

Abstract

An electroconductive paste is provided having good diffusion stability, whereby problems such as irregular particle growth during firing, etc., are suppressed. With the present invention, an electroconductive paste is provided that contains an electroconductive powder, a dielectric powder, and an organic component, and is used for forming a conductive film. When the centrifugal sedimentation behavior of the electroconductive powder and the dielectric powder when performing a centrifugal sedimentation process on the electroconductive paste is evaluated according to the transmission variation speed, defined as the amount of change per unit time of the calculated integrated transmittance on the basis of the transmittance distribution along the centrifugal sedimentation direction, the transmittance variation speed is adjusted to be 0.003 or less.

Description

Conductive paste

The present invention relates to a conductive paste. More specifically, the present invention relates to a conductive paste that is preferable for forming an internal electrode layer of a laminated ceramic electronic component.
This application claims priority based on Japanese Patent Application No. 2018-068733 filed on March 30, 2018, and incorporates the entire contents of this application into this specification by reference.

A multi-layer ceramic capacitor (MLCC) has a structure in which a dielectric layer including a ceramic and a plurality of internal electrode layers are laminated. The MLCC is generally produced by printing a conductive paste for an internal electrode containing a conductive powder on a dielectric green sheet including a dielectric powder, a binder, and the like to form an internal electrode layer. A plurality of dielectric green sheets printed with the internal electrode layer were laminated and pressure-bonded, and calcined. Here, for example, Patent Document 1 discloses a conductive paste containing a conductive particle and a coexisting material containing a dielectric particle, and the coexisting material includes a non-conductive coating portion. According to the above-mentioned configuration, when the conductive particles are sintered to form the internal electrode layer, it is described that abnormal grain growth of the conductive particles can be better suppressed without reacting the coexisting materials interposed between the conductive particles. .
[Prior Art Literature]
[Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2007-123198

[Problems to be Solved by the Invention]

In addition, with the miniaturization and weight reduction of electronic devices, miniaturization and thickness reduction of each electronic component constituting the electronic devices is also required. In MLCC, it is required to enlarge the electrode area by further thinning the dielectric layer and further increasing the number of layers, so that the volume of the MLCC is miniaturized and the electrostatic capacitance is increased. According to the thinning of the dielectric layer and the internal electrode layer, for example, the average particle diameter of the powder used to form the internal electrode layer is refined to a level of 10 nm in the coexisting material and a level of several hundred nm in the conductive particles. Therefore, it is extremely difficult to prepare a coexisting material including a non-conductive coating portion disclosed in Patent Document 1.

On the other hand, with the thinning of the dielectric layer and the internal electrode layer, grain growth of conductive particles at a level that has not been a problem until now becomes a problem. For example, due to excessive grain growth of the conductive particles during calcination, the internal electrode layer expands and the dielectric layer is pressed, which causes problems such as a decrease in withstand voltage of the dielectric layer or a decrease in reliability. In addition, if the conductive particles grow even coarser, they will pierce the thinned dielectric layer, causing problems such as defective products and a reduction in yield. It is considered that the grain growth of the conductive particles is caused by the fact that the conductive particles and the dielectric particles exist unevenly in the conductive paste coating film before the calcination, and there are many contacts between the conductive particles. There are multiple sites (i.e., parts where no dielectric particles are present), and the sintering suppression effect by the dielectric particles cannot be exhibited. In addition, as for the non-uniformity between the conductive particles and the dielectric particles, if these powders become finer and the surface activity is improved, they can become more significant.

The present invention has been made in view of the above-mentioned aspects, and an object thereof is to provide a conductive paste which has good dispersion stability of the conductive powder and the dielectric powder, and therefore suppresses problems such as abnormal grain growth during firing.
[Means for solving problems]

According to research by the present inventors, even if the same raw materials are used for the conductive paste, the dispersion state of the conductive powder and the dielectric powder in the paste can be changed by adjusting the preparation conditions of the paste. In addition, it has been found that by controlling the paste preparation conditions in various ways to achieve a "transmittance change rate" defined as described below, a conductive paste having an unprecedentedly high level of dispersion stability can be obtained. This technology was completed based on the said insight.

That is, by the technique disclosed herein, a conductive paste can be provided for forming a conductive film, and includes a conductive powder, a dielectric powder, and an organic component. Here, the centrifugal sedimentation behavior of the conductive powder and the dielectric powder when the centrifugal sedimentation treatment is performed on the conductive paste is evaluated by the transmittance change rate as described below. It is prepared so that the change rate becomes 0.003 or less, and the transmittance change rate is defined as a change amount per unit time of the integrated transmittance calculated based on the transmittance distribution in the centrifugal sedimentation direction.

According to the configuration, a conductive paste is realized in which a conductive powder and a dielectric powder are extremely stably dispersed in an organic component, and the dispersed state can be maintained for a long period of time. According to the conductive paste, the conductive powder and the dielectric powder are present in the organic component in a well-dispersed state. Therefore, when the coating film is formed, the conductive powders can also be prevented from agglomerating or contacting with each other, and can be greatly Grain growth is suppressed when the coating film is calcined. Thereby, the size of the conductive particles and the dielectric particles in the calcined conductor film can be kept small, and, for example, puncture of the dielectric layer due to abnormal growth of the conductive particles can be suppressed. As a result, electronic parts with excellent quality and reliability can be manufactured.

In addition, in the present specification, the "transmittance change rate" means a change amount per unit time of the integrated light transmittance (T) obtained by obtaining a light transmittance distribution curve of the conductive paste over time ( ΔT / Δt). The light transmittance distribution curve can be obtained as follows: About the sedimentation state of particles contained in the paste when the conductive paste is subjected to a centrifugal sedimentation process, an optical detection method such as a light transmission method or a light reflection method is used for the entire paste. The light transmittance or light reflectance is measured in real time and directly in the area along the centrifugal sedimentation direction. In the invention disclosed herein, the transmission rate change rate is used as an index for evaluating the dispersion stability of the conductive paste. The centrifugal sedimentation state of the particles can be accurately and quantitatively measured by the method specifically shown in the examples described later.

In a preferred aspect of the conductive paste disclosed herein, the average particle diameter of the conductive powder based on the Brunauer Emmett Tellern (BET) method is set to D ₁ , and the dielectric When the average particle diameter of the fine powder by the BET method is D ₂ , 0.03 × D ₁ ≦ D ₂ ≦ 0.4 × D _{1 is} satisfied. Thereby, even in the case of forming a thin conductive film, the dielectric particles can be preferably arranged in the voids of the conductive particles, and the dielectric powder can better suppress the abnormal crystals of the conductive particles at the time of firing. Grain grows.

In a preferred aspect of the conductive paste disclosed herein, the average particle diameter D ₁ of the conductive powder by the BET method is 0.5 μm or less. Thereby, for example, a conductor film having a thickness of about 3 μm or less can be formed with high accuracy.

In a preferred aspect of the conductive paste disclosed herein, the conductive powder is at least one of nickel, platinum, palladium, silver, and copper. Thereby, a conductive film excellent in electrical conductivity can be preferably realized.

In a preferred aspect of the conductive paste disclosed herein, the dielectric powder is at least one selected from the group consisting of barium titanate, strontium titanate, and calcium zirconate. Thereby, a conductive film excellent in adhesion with a dielectric layer having a high dielectric constant can be preferably realized.

In a preferred aspect of the conductive paste disclosed herein, it can be used to form an internal electrode layer of a laminated ceramic electronic component. For example, wafer-type MLCCs require further thinning and high-layering of the dielectric layer. The internal electrode layer disposed between the thin (for example, 1 μm or less) dielectric layers can be preferably formed by using the conductive paste disclosed herein as one having high surface flatness, electrical connection, and homogeneity. As a result, a small-sized, large-capacity, and high-quality MLCC with suppressed occurrence of short-circuits, cracks, and the like of the dielectric layer can be preferably realized.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. Furthermore, matters other than those specifically mentioned in this specification (for example, the composition of a conductive paste or its properties) are matters required for the implementation of the present invention (for example, the preparation of raw materials for the paste and The specific method of applying the base material, the configuration of electronic components, etc.) can be implemented based on the technical content taught by this specification and the general technical common sense of those skilled in the art. In addition, the expression "A to B" which shows a numerical range in this specification means A or more and B or less.

[Conductive paste]
The conductive paste disclosed herein includes (A) a conductive powder, (B) a dielectric powder, and an organic component as main constituent components. The organic component is typically a medium called a vehicle containing (C) a binder and (D) a dispersion medium. In addition, when the conductive paste is calcined, organic components disappear, and (A) the conductive powder and (B) the dielectric powder are sintered to form a conductive sintered body (typically, a conductive film). The (A) conductive powder and (B) dielectric powder, which are the main body of the conductor film, are usually dispersed in a vehicle liquid as an organic component to form a paste, and are imparted with appropriate viscosity and fluidity.

Furthermore, the conductive paste disclosed herein is prepared so that the transmittance change rate becomes 0.003 or less. As a result, the conductive powder (A) and the dielectric powder (B) are highly dispersed in the medium, and high dispersibility can be maintained for a long period of time. For example, even if a centrifugal sedimentation treatment of 4000 rpm described later is applied for 100 minutes, sedimentation of (A) conductive powder and (B) dielectric powder is suppressed, and (A) conductive powder and ( B) The dielectric powder is completely separated from the organic components. The unprecedented high dispersion stability is considered to be achieved by the existence state of each constituent material in the conductive paste rather than the individual properties of the constituent materials of the conductive paste. Hereinafter, the conductive paste disclosed herein will be described according to each element.

(A) Conductive powder Conductive powder is mainly used to form conductive materials (such as conductive films) with high electrical conductivity (hereinafter, referred to as "conductivity") in electrodes, wires, or conductive films in electronic components and the like. material. Therefore, as the conductive powder, powders of various materials having desired conductivity can be used without particular limitation. Specific examples of the conductive material include nickel (Ni), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), and rhodium ( Rh), osmium (Os), iridium (Ir), aluminum (Al), tungsten (W) and other metals, and alloys containing these metals. The conductive powder may be used singly or in combination of two or more kinds.

In addition, although it is not particularly limited, for example, regarding a conductive paste used for the purpose of forming an MLCC internal electrode layer, a conductive powder having a melting point lower than the sintering temperature of the dielectric layer (for example, about 1300 ° C) is preferred. Use of metal species. Examples of the metal species include precious metals such as rhodium, platinum, palladium, copper, and gold, and base metals such as nickel. Among them, the use of noble metals such as platinum and palladium is preferred from the viewpoint of melting point and conductivity, but nickel is more preferably used in consideration of stability and low price.

There are no particular restrictions on properties such as the method for producing the conductive powder and the size or shape of particles constituting the conductive powder. For example, in consideration of the calcination shrinkage rate, it may be included in the range of the minimum size of the target electrode (typically, the thickness and / or width of the electrode layer). For example, the average particle diameter of the conductive powder may be about several nm to several tens of μm, for example, about 10 nm to 10 μm.
In addition, in this specification, the "average particle diameter (D _B )" of a conductive powder and a dielectric powder means a specific surface area S measured by a BET method and the powder unless otherwise specified. The specific gravity ρ is calculated by the following formula: D _B = 6 / (S × ρ). The specific surface area will be described later.

In addition, for example, in the application for forming an internal electrode layer of a small-sized, large-capacity MLCC, it is important that the average particle diameter of the conductive powder is smaller than the thickness (size in the stacking direction) of the internal electrode layer. In other words, it is preferable not to contain coarse particles that actually exceed the thickness of the internal electrode layer. From the viewpoint, as an example, the conductive powder preferably has a cumulative 90% particle diameter (D ₉₀ ) of not more than 3 μm, more preferably not more than 1 μm, and more preferably not more than 0.5 μm. The average particle diameter (D ₅₀ ) may be approximately 1 μm or less as a standard, and may be typically 0.5 μm or less, preferably 0.3 μm or less, more preferably 0.25 μm or less, such as 0.2 μm or less. When the average particle diameter is equal to or smaller than a predetermined value, a conductive film can be formed stably. In addition, the surface roughness of the formed conductor film can be preferably suppressed. For example, the arithmetic average roughness Ra can be suppressed to a level of 5 nm or less.

The lower limit of the average particle diameter of the conductive powder is also not particularly limited, and may be, for example, 0.005 μm or more, approximately 0.01 μm or more, typically 0.05 μm or more, preferably 0.1 μm or more, such as 0.12 μm or more. By preventing the average particle diameter from being too small, the surface energy (activity) of the particles constituting the conductive powder can be suppressed, and the aggregation of the particles in the conductive paste can be suppressed. In addition, the density of the paste coating layer can be increased, and a conductive film having high electrical conductivity and high density can be preferably formed.

The specific surface area of the conductive powder is not particularly limited, and may be approximately 10 m ² / g or less, preferably 1 m ² / g to 8 m ² / g, for example, 2 m ² / g to 6 m ² / g. Thereby, the aggregation in the paste can be better suppressed, and the homogeneity, dispersibility, and storage stability of the paste can be better improved. In addition, a conductive film excellent in electrical conductivity can be realized more stably. The specific surface area refers to a gas adsorption amount measured by a gas adsorption method (constant volume adsorption method) using, for example, nitrogen (N ₂ ) gas as an adsorbent, and is calculated by a BET method (for example, a BET one-point method). Out value.

The shape of the conductive powder is not particularly limited. For example, the shape of the conductive powder in the conductive paste for a part of an electrode forming application such as an MLCC internal electrode may be a spherical shape or a substantially spherical shape. The average aspect ratio of the conductive powder may be typically 1 to 2, and preferably 1 to 1.5. Thereby, the viscosity of the paste can be maintained low, and the operability of the paste or the workability when forming a conductive film can be improved. In addition, the homogeneity of the paste can be improved.
The "aspect ratio" in this specification is calculated based on observation with an electron microscope, and refers to the length of the long side (b) relative to the length of the short side (a) when drawing a rectangle circumscribed with the particles constituting the powder. Ratio (b / a). The average aspect ratio is an arithmetic average of the aspect ratios obtained for 100 particles.

The content ratio of the conductive powder is not particularly limited. When the entire conductive paste is 100% by mass, it may be approximately 30% by mass or more, typically 40% to 95% by mass, for example, 45% to 60% by mass. quality%. By satisfying the above range, a conductive layer having high electrical conductivity and high density can be preferably realized. In addition, the operability of the paste and the workability during film formation can be improved.

(B) Dielectric powder In addition to the (A) conductive powder, the conductive paste disclosed herein may include (B) a dielectric powder as a component mainly constituting a conductor film after calcination. The dielectric powder is composed of particles that are arranged between particles constituting the conductive powder, for example, to suppress sintering of the conductive powder from low temperature during the calcination of the conductive paste, or to adjust the thermal shrinkage rate and the calcination shrinkage history. Or the thermal expansion coefficient of the conductive film after calcination. The dielectric powder can have various functions. In particular, the dielectric powder contained in the conductive paste for the internal electrode layer of the MLCC has a composition common to or similar to that of the dielectric layer, so as to improve the dielectric layer and The coexisting material of the sintered bondability of the internal electrode layer is preferred because it functions well.

The dielectric constant of the dielectric powder is not particularly limited, and may be appropriately selected depending on the intended use. As an example, the relative dielectric constant of the dielectric powder used in the conductive paste for forming an internal electrode layer of a high-dielectric-constant MLCC is typically 100 or more, preferably 1,000 or more, such as 1,000 to 20,000. about. The composition of the dielectric powder is not particularly limited, and one kind or two or more kinds can be suitably used from various inorganic materials depending on applications and the like. Specific examples of the dielectric powder include barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, zirconium titanate, zinc titanate, barium magnesium niobate, and calcium zirconate. ABO ₃ metal oxide with perovskite structure, titanium dioxide (rutile), titanium pentoxide, hafnium oxide, zirconia, alumina, forsterite, niobium oxide, barium neodymium titanate, rare earth Element metal oxides and other metal oxides are typical examples. In the paste for use in the internal electrode layer, the dielectric powder may be preferably composed of barium titanate (BaTiO ₃ ), strontium titanate, calcium zirconate (CaZrO ₃ ), or the like. On the other hand, as a matter of course, a dielectric material (and thus an insulating material) having a relative dielectric constant of less than 100 can also be used.

The properties of the particles constituting the dielectric powder, such as the size or shape of the particles, are not particularly limited as long as they are included in the minimum size (typically, the thickness and / or width of the electrode layer) in the cross section of the electrode layer. The average particle diameter of the dielectric powder can be appropriately selected depending on, for example, the use of the paste, the size (fineness) of the electrode layer, and the like. The target conductive layer preferably has an average particle diameter of the dielectric powder that is smaller than the average particle diameter of the conductive powder, from the viewpoint of easily ensuring predetermined conductivity. When the average particle diameter of the dielectric powder is D ₂ and the average particle diameter of the conductive powder is D ₁ , D ₁ and D ₂ are usually preferably D ₁ > D ₂ , and more preferably D ₂ ≦ 0.5. × D ₁ , and more preferably D ₂ ≦ 0.4 × D _1. For example, D ₂ ≦ 0.3 × D ₁ . In addition, if the average particle diameter D _{2 of} the dielectric powder is too small, aggregation of the dielectric powder is likely to occur, which is not preferable. In this respect, as a rough standard, it is preferably 0.03 × D ₁ ≦ D ₂ , more preferably 0.05 × D ₁ ≦ D ₂ , and for example, 0.1 × D ₁ ≦ D ₂ . For example, the average particle diameter of the dielectric powder is suitably approximately several nm or more, preferably 5 nm or more, or 10 nm or more. The average particle diameter of the dielectric powder may be approximately several μm or less, for example, 1 μm or less, and preferably 0.3 μm or less. As an example, in the conductive paste for forming the internal electrode layer of the MLCC, the average particle diameter of the dielectric powder may be approximately several nm to several hundreds nm, for example, 5 nm to 100 nm.

The content ratio of the dielectric powder is not particularly limited. For example, in applications such as forming an internal electrode layer of an MLCC, when the entire conductive paste is 100% by mass, it may be approximately 1% to 20% by mass, for example, 3% to 15% by mass. The ratio of the dielectric powder to 100 parts by mass of the conductive powder may be, for example, approximately 3 to 35 parts by mass, preferably 5 to 30 parts by mass, for example, 10 to 25 parts by mass. Thereby, the low-temperature calcination of the conductive powder can be appropriately suppressed, and the electrical conductivity and the denseness of the conductor film after the calcination can be improved.

(C) Binder A binder is a material that functions as a binder among the organic components in the conductive paste disclosed herein. The binder typically helps to bond the powder contained in the conductive paste and the substrate, and to bond the particles constituting the powder to each other. The binder is dissolved in a dispersion medium to be described later and functions as a vehicle (which may be a liquid medium). Thereby, the viscosity of the conductive paste is increased, the powder component is suspended uniformly and stably in the vehicle liquid, fluidity is imparted to the powder, and workability is improved. The binder is a component premised on disappearance by calcination. Therefore, the adhesive is preferably a compound that burns out when the conductor film is fired. Typically, the decomposition temperature is preferably 500 ° C or lower regardless of the environment. The composition and the like of the adhesive are not particularly limited, and various known organic compounds used in such applications can be suitably used.

Examples of the binder include rosin-based resin, cellulose-based resin, polyvinyl alcohol-based resin, polyvinyl acetal-based resin, acrylic resin, urethane-based resin, epoxy-based resin, and phenol. Organic polymer compounds such as resins, polyester resins, and vinyl resins. It also depends on the combination with the solvent used, so it cannot be generalized. For example, as a binder containing a conductive paste containing inorganic oxide powder and a relatively high calcination temperature, cellulose resins and polyvinyl alcohol resins are preferred. , Polyvinyl acetal resin, acrylic resin, etc.

Cellulose-based resins contribute to the improvement of the dispersibility of inorganic oxide powders. When conductive paste is used for printing, the shape characteristics of printed matter (wiring film) and the adaptability to printing work are excellent. So better. The cellulose-based resin refers to all the polymers and their derivatives containing at least β-glucose as a repeating unit. Typically, it may be a compound obtained by substituting a part or all of the hydroxyl groups in the β-glucose structure as the repeating unit with an alkoxy group and a derivative thereof. Alkyl or aryl portion of the group (R) or all may be substituted by an ester group to a carboxyl group, a nitro group, a halogen, an organic group other ^- alkoxy (RO). Specific examples of the cellulose-based resin include methyl cellulose, ethyl cellulose, propoxy cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl. Methyl cellulose, hydroxypropyl ethyl cellulose, carboxy methyl cellulose, carboxy ethyl cellulose, carboxy propyl cellulose, carboxy ethyl methyl cellulose, cellulose acetate phthalate, nitro fibers Su et al.

The polyvinyl alcohol-based resin has good dispersibility of the inorganic oxide powder and is soft. Therefore, when a conductive paste is used for printing, the printed matter (wiring film) has excellent adhesion, printability, etc., and is therefore preferred. . The polyvinyl alcohol-based resin refers to all the polymers and derivatives thereof that contain at least a vinyl alcohol structure as a repeating unit. Typically, it may be a polyvinyl alcohol (PVA) containing a structure obtained by polymerizing vinyl alcohol, or a polyvinyl acetal resin obtained by acetalizing the PVA with an alcohol, and a derivative thereof. Things. Among them, a polyvinyl butyral (PVB) resin having a structure in which PVA is acetalized with butanol is more preferable because it improves the shape characteristics of a printed body. In addition, these polyethylene acetal resins may also be copolymers (including graft copolymers) and the like: a polyethylene acetal is a main monomer, and a secondary monomer having a copolymerizability with the main monomer is contained. Examples of the secondary monomer include ethylene, esters, (meth) acrylates, and vinyl acetate. The ratio of acetalization in the polyvinyl acetal resin is not particularly limited, but is preferably 50% or more.

The acrylic resin is preferable in that it is rich in adhesiveness and flexibility, and has fewer calcination residues regardless of the calcination environment. The acrylic resin refers to, for example, the entirety of the polymer and its derivatives containing at least an alkyl (meth) acrylate as a constituent monomer component. Typically, it may be a homopolymer containing 100% by mass of alkyl (meth) acrylate as a constituent monomer component, or a copolymer (including a graft copolymer), etc. The copolymer) is mainly composed of an alkyl (meth) acrylate, and contains a sub-monomer having copolymerizability with the main monomer. Examples of the secondary monomer include 2-hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, a vinyl alcohol-based monomer, a dialkylamino group, a carboxyl group, and an alkoxy group introduced. Copolymerizable monomers such as carbonyl. Specific examples of the acrylic resin include poly (meth) acrylic acid, vinyl chloride / acrylic acid graft copolymer resin, and ethylene acetal / acrylic acid graft copolymer resin. In addition, in this specification, expressions, such as "(meth) acrylate", are used as the term which shows that acrylate and / or methacrylate are included.

Any of these adhesives can be used, or two or more of them can be used in combination. Although not explicitly described, a copolymer, a block copolymer, or the like obtained by copolymerizing monomer components of any two or more of the resins may be used. The content of the binder is not particularly limited. In order to properly adjust the properties of the conductive paste or the properties of the paste printing body (including the dry film), for example, the content of the binder may be 0.5 parts by mass or more, and preferably 1 part by mass or more, based on 100 parts by mass of the conductive powder. The ratio is more preferably 1.5 parts by mass or more, for example, 2 parts by mass or more. On the other hand, since the binder resin may increase the calcination residue, the excessive content is not preferable. From this viewpoint, the content of the binder may be 10 parts by mass or less, preferably 7 parts by mass or less, more preferably 5 parts by mass or less, for example 4 parts by mass or less, based on 100 parts by mass of the conductive powder.

(D) Dispersion medium A dispersion medium is a liquid medium used to disperse a powder among organic components in the conductive paste disclosed herein, and is used to impart excellent flow while maintaining the dispersibility. Elements of sex. The dispersing medium dissolves the binder and functions as a vehicle. The dispersion medium is also a component premised on disappearance by drying and calcination. The dispersion medium is not particularly limited, and an organic solvent used in such a conductive paste can be suitably used. Although it also depends on the combination with, for example, a high-boiling-point organic solvent having a boiling point of about 180 ° C or higher and 300 ° C or lower, such as 200 ° C or higher and 250 ° C or lower, from the viewpoint of film formation stability and the like. The main component (component that accounts for more than 50% by volume).

Specific examples of the dispersion medium include sclareol, citronellol, phytol, geranyl linalool, texanol, benzyl alcohol, phenoxyethanol, and 1-phenoxy-2-propane Alcohol solvents such as alcohol, terpineol, dihydroterpineol, isobornyl, butylcarbitol, diethylene glycol; terpineol acetate, dihydroterpineol acetate, isobornyl acetate Ester solvents such as esters, carbitol acetate, diethylene glycol monobutyl ether acetate; mineral spirits, etc. Among them, an alcohol-based solvent or an ester-based solvent can be preferably used.

The proportion of the (C) dispersion medium in the conductive paste is not particularly limited. When the entire paste is 100% by mass, it may be approximately 70% by mass or less, typically 5 to 60% by mass, for example, 30% by mass. % To 50% by mass. By satisfying the above range, moderate fluidity can be imparted to the paste, and workability during film formation can be improved. In addition, the self-levelling of the paste can be improved and a smoother surface conductor film can be realized.

(E) Other additives In addition, the conductive paste disclosed herein may include various organic additives that can be used in general conductive pastes within a range that does not significantly impair the effect of the technology disclosed herein. The organic additives include, for example, a dispersant, a thickener, a plasticizer, a pH adjuster, a stabilizer, a leveling agent, a defoamer, an antioxidant, a preservative, and a colorant (pigment, dye, etc.). For example, when using powders such as conductive powder and dielectric powder as the main body of the conductive film, if the average particle diameter is less than about 1 μm, the powder may be provided without special surface treatment or the like. Aggregation sometimes occurs during the preparation of the paste and immediately after the preparation of the paste. This tendency is more significant when using ultrafine powder or nano particles (for example, a powder having an average particle diameter of 0.5 μm or less) as the conductive powder or the like, which can significantly improve the surface activity. Therefore, the conductive paste disclosed herein may preferably include a dispersant as other additives.

The dispersant is a component that suppresses agglomeration of particles constituting the powder when the powder is dispersed in a dispersion medium, and uniformly disperses the particles in the dispersion medium. The dispersant has a function of directly adsorbing on the solid surface of the particles and stabilizing the solid-liquid interface between the particles and the dispersion medium. The dispersant is preferably burned off during the calcination of the conductive paste. In other words, the dispersant preferably has a decomposition temperature sufficiently lower than the calcination temperature of the conductive paste (typically, 600 ° C. or lower).

The type of the dispersant is not particularly limited, and one or two or more kinds can be used as needed from various known dispersants. Typically, those having sufficient compatibility with a vehicle (a mixture of a binder and a dispersion medium) described later can be appropriately selected and used. There are a variety of methods for classifying dispersants. As the dispersant, any one of a so-called surfactant-type dispersant (also referred to as a low-molecular-type dispersant), a polymer-type dispersant, and an inorganic dispersant may be used. . These dispersants may be any of anionic, cationic, amphoteric, and nonionic. In other words, the dispersant is a compound having at least one functional group among anionic groups, cationic groups, amphoteric groups, and nonionic groups in the molecular structure. Typically, the dispersant may be a solid in which the functional group can be directly adsorbed to particles. Surface compounds. The term “surfactant” refers to an amphiphilic substance that includes a hydrophilic portion and a lipophilic portion in a molecular structure and has a chemical structure formed by covalent bonding.

Regarding the dispersant, examples of the surfactant-type dispersant include a dispersant mainly composed of an alkyl sulfonate, a dispersant mainly composed of a quaternary ammonium salt, and an alkylene oxide compound composed of a higher alcohol. A main dispersant, a main dispersant including a polyol ester compound, a main dispersant including an alkyl polyamine compound, and the like. Examples of the polymer-based dispersant include a dispersant mainly composed of a fatty acid salt such as a carboxylic acid or a polycarboxylic acid, and a polycarboxylic acid moiety in which a hydrogen atom in a part of the carboxylic acid group is substituted with an alkyl group. Dispersant mainly composed of alkyl ester compounds, dispersant composed mainly of polycarboxylic acid alkylamine salts, dispersant composed mainly of polycarboxylic acid partially alkyl ester compounds having alkyl ester bonds in part of polycarboxylic acids, Dispersants mainly composed of polystyrene sulfonate, polyisoprene sulfonate, and polyalkylene polyamine compounds, and sulfonic acid compounds such as naphthalene sulfonate and formalin condensate salt Dispersant mainly composed of hydrophilic polymers such as polyethylene glycol, dispersant composed mainly of hydrophilic polymers such as polyethylene glycol, dispersant composed mainly of polyether compounds, poly (meth) acrylates, poly (meth) acrylamides, etc. A (meth) acrylic compound-based dispersant and the like. Examples of the inorganic dispersant include phosphates such as orthophosphate, metaphosphate, polyphosphate, pyrophosphate, tripolyphosphate, hexametaphosphate, and organic phosphate; ferric sulfate; ferrous sulfate; Dispersants mainly composed of iron salts such as ferric chloride and ferrous chloride, aluminum salts such as aluminum sulfate, polyaluminum chloride and sodium aluminate, and calcium salts such as calcium sulfate, calcium hydroxide, and calcium hydrogen phosphate.

In addition, the dispersant may include any one kind alone, or may include two or more kinds in combination. In addition, the type of the dispersant is not particularly limited. For the purpose of dispersing finer conductive powders and dielectric powders efficiently for a long period of time with the addition of a small amount of a dispersant, the use of the dispersant may cause a three-dimensional obstacle A polymer-type dispersant having a repellent effect is preferred. The weight average molecular weight of the dispersant in this case is not particularly limited, and as a preferred example, it is preferably set to about 300 to 50,000, for example, 500 to 20,000.

In addition, the organic additives may include any one kind alone, or may include two or more kinds in combination. In addition, the content of the organic additive may be appropriately adjusted within a range that does not significantly hinder the properties of the conductive paste disclosed herein. For example, it may be contained in an appropriate ratio according to the properties of the organic additive and its purpose. Generally, for example, the dispersant is contained in a proportion of about 5 mass% or less, for example, 3 mass% or less, typically 1 mass% or less and about 0.01 mass% or more with respect to the total mass of the powder component. Furthermore, it is not preferable to contain a component that inhibits the sinterability of the conductive powder or inorganic powder or the like, or an additive that inhibits these amounts. From the viewpoint, when organic additives are included, the total content of these components is preferably about 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. .

The conductive paste can generally be prepared by mixing the (C) binder and (D) dispersion medium as organic components in advance to prepare a vehicle solution, and then (A) the conductive powder and (B) The dielectric powder is mixed and kneaded. In the conductive paste disclosed herein, in order to suppress the rate of change in transmittance to 0.003 or less and achieve high dispersion stability of (A) conductive powder and (B) dielectric powder in the paste, the most important thing is blending. The constituent material. The method for preparing the conductive paste is not particularly limited within a range in which the transmittance change rate can be achieved. As an example of a method for preparing a conductive paste, detailed description will be given in Examples described later. The conductive powder (A) and the dielectric powder (B) may be dispersed in different (D) dispersion media in advance and prepared into The slurry is then mixed with the conductive powder and the dielectric powder in the form of a slurry, whereby the two are blended with good dispersibility.

In addition, if the (C) binder in the organic component is first added to a slurry containing conductive powder (A) (hereinafter referred to as a conductive powder slurry) or a slurry containing (B) a dielectric powder ( In the following, referred to as a dielectric powder slurry), the high dispersion of these powders is prevented. Therefore, it is preferable that the (C) binder is prepared in advance by mixing with a part of the (D) dispersion medium, and the mixed slurry of the conductive powder slurry and the dielectric powder slurry is prepared by using the medium liquid. State mixed. The rate of change in transmittance of the conductive paste prepared as described above is preferably less than 0.003, more preferably 0.0025 or less, and even more preferably 0.002 or less. The conductive paste (mixed paste) is preferred because it can maintain its high dispersion state strongly for a long period of time.

Here, it is preferable that the conductive powder or the dielectric powder slurry prepared in advance has the conductive powder or the dielectric powder highly dispersed in the respective slurry in a better state than ever before. The above-mentioned dispersion conditions also depend on the materials (composition, etc.), average particle diameter, paste concentration, and configuration of the stirring device or dispersion device used for the target conductive powder and dielectric powder, so they cannot be generalized. For example, if the diffusion strength in the previously performed diffusion treatment is set to 1, for example, the stirring strength when preparing the conductive powder slurry and the dielectric powder slurry in the technique disclosed herein can be set to 0.1 (times) ) Or more may be 0.5 or more, for example, preferably 1 or more, more preferably 1.5 or more, still more preferably 1.8 or more, and even more preferably 2 or more. The upper limit of the stirring intensity can be set to the upper limit of the device configuration. For example, if the diffusion intensity in the previously performed diffusion process is set to 1, the standard may be about 5. In addition, when adjusting the transmittance change rate, for example, it is possible to prepare a conductive paste to be prepared in advance and confirm the transmittance change rate, and adjust the transmittance rate little by little so that the transmittance change rate becomes 0.003 or less. Stirring conditions for conductive paste. More specifically, for example, when a paste is prepared by setting the stirring intensity to about 30 m / s by a conventional method, a range of about 30 m / s to 60 m / s, for example, 45 m / s to 60 is exemplified. Increase the stirring intensity in the range of about m / s. On the other hand, in the case where a paste is prepared by setting the stirring intensity to about 7 m / s by a conventional method, a range of about 7 m / s to 20 m / s, for example, 10 m / s to 20 is exemplified. Increase the stirring intensity in the range of about m / s.

In addition, at this time, at least the conductive powder slurry can be stirred and dispersed using a medium-less stirring device or a dispersing device. In addition, the medium-free stirring device or dispersing device refers to a stirring or dispersing device that does not have a rigid medium (such as a pulverizing member) that does not have a stirring or dispersing effect such as to impinge on a fluid to be stirred or dispersed. , Movable members, media, etc.). The driving force of the medium-free stirring or dispersing device is, for example, high-speed fluid such as compressed air, steam, or heated airflow, ultrasonic waves, or cavitation bubbles, and the like. Collision, friction, etc., can show agitation or dispersion. For example, jet mills, jet mills, ultrasonic jet mills, cross jet mills, and the like are exemplified. When the medium-free stirring and dispersing device is used, the hard medium and the primary solid particles contained in the fluid to be stirred and dispersed are brought into direct contact with each other and act, without causing deformation of the primary particles, such as foiling.

Regarding the other dielectric paste, there are no restrictions on the stirring device or the dispersing device. For example, the medium-free stirring device or dispersion device may be used, or a medium-type stirring device or dispersion device may be used. Without further exemplification, examples of the media-type stirring and dispersing device include a ball mill, a bead mill, a colloid mill, a hammer mill, a mortar, a disk mill, and a roll mill.

In this way, the conductive powder and the dielectric powder are separated in advance to prepare a highly-dispersed slurry, whereby the agglomeration of any one kind of particles can be better suppressed when the two are mixed, and a highly-dispersed state can be achieved. As a result, even when the conductive paste is subjected to a centrifugal sedimentation treatment to accelerate the sedimentation, the conductive paste disclosed herein can highly suppress the sedimentation of the conductive powder and the dielectric powder. Furthermore, in the aspect including a dispersant, any of the conductive powder slurry, the dielectric powder slurry, and the conductive paste may contain a dispersant or may not contain it. Regarding the slurry containing a dispersant, the powder material and the dispersant can be stirred and dispersed in a dispersion medium at the same time or at different times.

As for the conductive paste disclosed herein, the dispersion stability of the conductive powder and the dielectric powder as described above is extremely high. Therefore, the supply of the conductive paste to the substrate can be performed by any of various known supply methods without any particular limitation. Examples of the supply method include printing methods such as screen printing, gravure printing, lithographic printing, and inkjet printing, spray coating methods, and dip coating methods. In particular, in the case of forming the internal electrode layer of the MLCC, a gravure printing method, a screen printing method, or the like capable of high-speed printing can be preferably used.

[use]
As described above, even if the conductive paste is subjected to centrifugal sedimentation treatment at 4000 rpm for 100 minutes as described above, the particles contained in the conductive paste are not completely settled and separated from the dispersion medium. inhibition. The conditions of the centrifugal sedimentation treatment are, for example, an accelerated test corresponding to several months to several years in a sedimentation treatment process performed by leaving the conductive paste to stand. Therefore, the conductive paste is excellent in long-term storage after the preparation of the paste, and for example, a large amount of paste can be prepared at one time in a mass production step and used for a long time (for printing). This feature also stabilizes the printability of the printed coating film formed using the conductive paste, and for example, contributes to the improvement of the uniformity of the thickness and density of the printed coating film. In addition, the state in which the conductive powder and the dielectric powder are highly dispersed can also be maintained in the printed coating film. As a result, even if the printed coating film is calcined, sintering of the conductive particles and abnormal grain growth can be better suppressed. In this aspect, the conductive paste can also be preferably used in applications where homogeneity or surface smoothness of a conductor film after calcination is particularly required. Typical applications include formation of an electrode layer in a multilayer ceramic electronic component. The conductive paste disclosed herein can be preferably used, for example, for forming an internal electrode layer of a small MLCC having sides of 5 mm or less, for example, 1 mm or less. In particular, it can be preferably used for the production of internal electrodes of small, large-capacity MLCCs with a dielectric layer thickness of 1 μm or less.

In addition, in this specification, a "ceramic electronic component" means the term common to the electronic component which has a crystalline ceramic substrate or an amorphous ceramic (glass ceramic) substrate. For example, chip inductors including ceramic-based substrates, high-frequency filters, ceramic capacitors, High Temperature Co-fired Ceramics (HTCC) substrates, and Low Temperature Co-fired ceramics Ceramics (LTCC) substrates are typical examples included in the "ceramic electronic components" described herein.

Examples of the ceramic material constituting the ceramic substrate include barium titanate (BaTiO ₃ ), zirconia (ZrO ₂ ), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), and silicon dioxide (SiO ₂ ). , Zinc oxide (ZnO), titanium oxide (TiO ₂ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ) and other oxide-based materials; cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), Mo Lairite (3Al ₂ O ₃ · 2SiO ₂ ), forsterite (2MgO · SiO ₂ ), block talc (MgO · SiO ₂ ), sialon (Si ₃ N ₄ -AlN-Al ₂ O ₃ ), zircon ( ZrO ₂ · SiO ₂ ), ferrite (M ₂ O · Fe ₂ O ₃ ) and other composite oxide materials; silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), boron nitride (BN) And other nitride-based materials; silicon carbide (SiC), boron carbide (B ₄ C) and other carbide-based materials; hydroxyapatite and other hydroxide-based materials. These may be contained singly, or as a mixture of two or more kinds, or in the form of a composite of two or more kinds.

[Multilayer Ceramic Capacitor]
FIG. 1A is a cross-sectional view schematically showing a multilayer ceramic capacitor (MLCC) 1. MLCC1 is a chip-type capacitor in which a plurality of dielectric layers 20 and internal electrode layers 30 are alternately and integrally laminated. A pair of external electrodes 40 is provided on a side surface of the multilayer wafer 10 including the dielectric layer 20 and the internal electrode layer 30. As an example, the internal electrode layers 30 are alternately connected to different external electrodes 40 in a stacking order. Thereby, a small and large-capacity MLCC 1 is constructed, and a capacitor structure including a dielectric layer 20 and a pair of internal electrode layers 30 sandwiching the dielectric layer 20 is connected in parallel. The dielectric layer 20 of the MLCC1 is made of ceramic. The internal electrode layer 30 is made of a fired body of the conductive paste disclosed herein. The MLCC1 is preferably manufactured by the following procedure, for example.

FIG. 1B is a cross-sectional view schematically showing an unfired laminated wafer 10 (unfired laminated body 10 ′). When manufacturing MLCC1, a ceramic green sheet (dielectric green sheet) is first prepared as a base material. Here, for example, a ceramic powder as a dielectric material, a binder, an organic solvent, and the like are mixed to prepare a dielectric layer forming paste. Next, a plurality of unfired ceramic green sheets 20 'are prepared by supplying the prepared paste in a thin layer onto a carrier sheet by a doctor blade method or the like.

Next, prepare the conductive paste disclosed herein. Specifically, at least the conductive powder (A), the dielectric powder (B), the binder (C), and the dispersion medium (D) are prepared, and these are blended at a predetermined ratio so that the transmission rate change rate becomes 0.003 or less. The conductive paste is prepared by stirring and mixing in the same manner. Then, the prepared paste is supplied onto the prepared ceramic green sheet 20 ′ so as to have a predetermined pattern and a desired thickness (for example, 1 μm or less) to form a conductive paste coating layer 30 ′. The dispersion stability of the conductive paste disclosed herein has been significantly improved. Therefore, in mass production of MLCC, even if the formation (printing) of the conductive paste coating layer 30 ′ on the ceramic green sheet 20 ′ is continuous and elapsed over a long period of time, the properties of the conductive paste are stable, so that the printing quality can be improved.地 stable.

The prepared ceramic green sheet 20 'with the conductive paste coating layer 30' is laminated on a plurality of sheets (for example, hundreds to thousands) and pressure-bonded. The laminated body is cut into a wafer shape as necessary. Thereby, the unfired laminated body 10 'can be obtained. Next, the produced unfired laminated body 10 'is fired under appropriate heating conditions (for example, a temperature of about 1000 ° C to 1300 ° C in a nitrogen-containing environment). Thereby, the ceramic green sheet 20 'and the conductive paste coating layer 30' are simultaneously fired. The ceramic green sheet 20 ′ is fired to form the dielectric layer 20. The conductive paste coating layer 30 ′ is fired to become the internal electrode layer 30. The dielectric layer 20 and the internal electrode layer 30 are sintered integrally to obtain a sintered body (multilayer wafer 10). In addition, before the calcination, in order to eliminate organic components such as the binder and the dispersion medium, a de-binder treatment may be performed (for example, in an oxygen-containing environment, at a temperature lower than the calcination temperature: for example, about 250 ° C to 700 ° C heat treatment). Thereafter, the external electrode 40 is formed by applying an external electrode material to the side surface of the laminated wafer 10 and performing firing. Thereby, MLCC1 can be manufactured.

Hereinafter, several embodiments related to the present invention will be described, but it is not intended to limit the present invention to those shown in the embodiments.

[Preparation of conductive paste]
(example 1)
The conductive paste of Example 1 of Formulation A shown in Table 1 below was prepared in the following procedure.
That is, first, (1) nickel powder, an organic solvent, and a dispersant are prepared, and a dispersion process is performed using a mediumless high-speed dispersing device to prepare a nickel slurry.
Next, (2) prepare a barium titanate slurry by preparing a barium titanate powder, an organic solvent, and a dispersant, and performing a dispersion treatment using a media mill.

In addition, (3) disperse and mix the prepared nickel slurry, barium titanate slurry and dispersant using a medium-free high-speed dispersing device to produce nickel. Barium titanate mixed slurry.
Thereafter, (4) in said nickel. A separately prepared vehicle and organic solvent are added to the barium titanate mixed slurry, and mixed with a medium-free high-speed dispersing device to obtain a conductive paste.

Furthermore, in the preparation of the paste, in Formulation A, the average particle diameter of nickel powder (Ni) was 180 nm, and the average particle diameter of barium titanate powder (BT) was 10 nm. The proportion of nickel powder was 10% by mass. In addition, these nickel powders and barium titanate powders are not subjected to a dispersion treatment such as a special surface treatment. As the organic solvent, dihydroterpineol was used, and as the dispersant, a carboxylic acid-based dispersant was used. The vehicle was prepared by heating and mixing ethyl cellulose as an adhesive and an organic solvent according to a conventional method.

(Examples 2 to 4)
Next, in the preparation of the conductive paste of Example 1, the intensity (peripheral speed or rotation speed) of the dispersion treatment during the preparation of (1) the nickel slurry and (2) the barium titanate slurry was changed, and the ratio of the dispersant was changed. Thus, the dispersion state of the nickel powder or barium titanate powder in the paste is changed. Further, other conditions were set to be the same as those of Example 1, thereby obtaining conductive pastes of Examples 2 to 4.
However, regarding the conductive pastes of Examples 1 to 4, the stirring speed was changed within a range of about 8 m / s to 60 m / s as a dispersion treatment condition.

(Example 5)
In the preparation of the conductive paste of Example 1, Formulation B shown in Table 1 was used instead of Formulation A. The dispersion treatment conditions and other conditions were the same as in Example 1, and a conductive paste of Example 5 was obtained. In Formulation B, a nickel powder having an average particle diameter of 300 nm was used, and a barium titanate powder having an average particle diameter of 50 nm was used. In order to increase the particle size of the powder used, the ratio of the barium titanate powder to the nickel powder was increased to 15% by mass, and the dispersing amount was reduced.

(Example 6)
In the preparation of the conductive paste of Example 4, Formulation B shown in Table 1 was used instead of Formulation A. The dispersion treatment conditions and other conditions were the same as those of Example 4, and a conductive paste of Example 6 was obtained.
The blending of the conductive pastes of Example 5 and Example 6 is almost the same, but the conditions of the dispersion treatment differ according to Examples 1 and 4, respectively.

[Table 1]

Table 1

[Measurement of transmission rate change rate]
Regarding the prepared conductive pastes of Examples 1 to 6, the transmittance change rate was measured in the following procedure.
First, the conductive paste of each example was diluted to a concentration suitable for evaluating the dispersion stability of such a conductive paste, that is, the solid content concentration was 10% by mass. Dihydroterpineol was used as an organic solvent for dilution. In addition, during the dilution, in order not to cause so-called solvent shock, an organic solvent was added dropwise with a burette while stirring the conductive paste, and mixed. Specifically, measure 10 g of conductive paste in a 100 mL beaker, and use a small mixer (using 6 blades at a rotation speed of about 200 rpm), while stirring the conductive paste in the beaker, while using 2 mL as the unit, Organic solvents were added at intervals of about 5 seconds. The amount of the organic solvent added is, for example, 45 g for 10 g of the conductive paste of Example 1.

About the prepared dilution paste, the transmittance characteristic was measured using the dispersion stability analyzer (LUMiFuge made by LUM GmbH). The measurement was performed using an angular rectangular disposable sample cell (cell code 3, LUM 2 mmPA, measurement volume 0.4 mL to 0.5 mL, and measurement optical path length 2 mm) made of polyamine for an analysis device. The sample tank is configured to receive a 0.4 mL sample for measurement, and the upper surface of the 0.4 mL sample is located at a position 23 mm from the bottom of the sample tank having a total length of 82 mm. The diluted paste was weighed with a syringe using a syringe and weighed 0.4 mL. After the bottom of the tank was slowly filled in the tank, it was capped and used for measurement.

The sample cell is set horizontally (so that the longitudinal direction of the cell coincides with the centrifugal direction) on the rotor of the dispersion stability analysis device and measurement is started.
The dispersion stability analysis device performs a centrifugal sedimentation treatment on the slurry contained in the sample tank by rotating the rotor, and simultaneously performs an optical detection on the liquid surface of the slurry and the sedimentation state of particles in the slurry, thereby enabling the spot Direct measurement. Furthermore, the optical detection of the particle sedimentation state is performed by using a linear light source of an oscillating near-infrared laser to irradiate laser light in a manner parallel to the longitudinal direction of the sample slot, and using a charge-coupled element Device (CCD) line sensor detects the intensity of transmitted light. In the present embodiment, the transmitted light intensity is measured so as to include a region of 19 mm from the liquid surface of the slurry in a sample that exists in a range of 23 mm from the bottom of the sample tank in a centrifuge state. In addition, in this embodiment, a time curve of transmittance can be obtained by acquiring a curve of the position information of the sample slot and the transmittance of the position in real time during a predetermined measurement period. The measurement conditions are as follows.

Measurement temperature: 25.0 ℃
Transmittance measurement wavelength: 865 nm
Light source intensity: 1 (standard)
Speed: 4000 rpm
Measurement interval: 10 seconds Measurement time: 6200 seconds (of which the analysis target is 6000 seconds)

For example, as shown in FIG. 2 (t ₀ ), the slurry contained in the sample tank is initially dispersed with particles at a uniform concentration, and the transmittance is also fixed. However, as shown in (t ₁ ) and (t ₂ ), with the centrifugal sedimentation, the particles in the slurry move (sediment) toward the bottom of the tank (outer side in the direction of the radius of rotation). Thereby, the slurry concentration in the predetermined position of the sample tank gradually decreases from the inner side in the radial direction of rotation, and the transmittance of the slurry in the position gradually increases. In the measurement, a time change curve of the transmittance distribution across the total measurement length of the sample tank can be obtained.

Therefore, as shown in FIG. 3 (a), transmittance (light transmittance) is integrated for a predetermined measurement area of the sample slot. For example, as shown in (b), the relationship between the integrated transmittance and the measurement time is plotted. Is defined as the "transmittance change rate". The sedimentation of the particles is performed steadily at the beginning of the centrifugal sedimentation treatment, but when the particles reach the bottom surface of the tank, it does not proceed and becomes saturated. In the technique disclosed herein, as shown in (c), with respect to this paste, the sedimentation of particles can be considered to be performed approximately stably, and the unit transmittance (T) per unit time during the measurement period from 0 to 6000 seconds is considered to be substantially stable. The amount of change (ΔT / Δt) is adopted as the "transmittance change rate". Regarding the rate of change in transmittance, a larger value indicates faster sedimentation and worse dispersion stability, and a smaller value indicates slower sedimentation and better dispersion stability. In addition, in the present embodiment, the rate of change in transmittance is calculated for the area of the sample groove 19 mm from the upper surface (liquid surface) of the sample. Accordingly, the results of calculating the rate of change in transmittance for each conductive paste are shown in Table 2 below. The wavelength of light (here, laser light) used for the measurement of transmittance is not limited to the above-mentioned example.

[Evaluation of Sinterability]
Next, in order to confirm the influence of the dispersion state of the particles in the prepared conductive pastes of Examples 1 to 6 on the sinterability, each conductive paste conductive film was produced and evaluated for sinterability.
First, about 3 g of the conductive paste of each example was coated on a polyethylene terephthalate (PET) film with a film applicator at a film thickness of 250 μm. Thereafter, a dry coating film was obtained by processing with a warm air dryer at a set temperature of 100 ° C. and a drying time of 15 minutes. Then, the dried coating film was peeled from the PET film, and heated in a N ₂ environment at a heating rate of 200 ° C./h, and maintained at a reaching temperature of 600 ° C. for 20 minutes, thereby performing a debinding treatment. Then, in a (N ₂ + 1% H ₂ ) environment, heating was performed at a temperature increase rate of 200 ° C./h, and the temperature was maintained at 1200 ° C. for 10 minutes, thereby subjecting it to formal firing to obtain a conductive film.

A scanning electron microscope (Scanning Electron Microscope: SEM) was used to observe the surface of the conductive film (the surface on the side not in contact with the PET film) after calcination, and measure the calcined nickel particles and barium titanate particles after sintering. The average particle size.
Specifically, first, the surface of the fired conductive film was subjected to Au vapor deposition for about 30 seconds to prepare a sample for SEM observation. Then, based on the SEM image obtained by setting the observation magnification to 10,000 times, the area circle equivalent diameter (Heywood diameter) of the nickel particles and the barium titanate particles was determined. The circle equivalent diameter is calculated by selecting approximately 70 nickel particles and barium titanate particles that can recognize grain boundaries from SEM images of about 4 to 6 fields of view, and setting the contour of each particle using image processing software. The diameter of the circle is quite large (see Figure 6). In addition, the cumulative 50% particle diameter (D ₅₀ ) in the particle size distribution based on the number-of-area-circle-equivalent-diameter-based particle size distribution obtained for about 70 particles was defined as nickel particles or barium titanate particles in the conductive film. Average particle size. The cumulative 90% particle size (D ₉₀ ) in the number-based particle size distribution was calculated in the same manner, and the results are shown in Tables 3 and 4 below.

In addition, for reference, an SEM observation image (20,000 times) of a conductive film produced using the conductive pastes of Examples 1 and 4 is shown in FIG. 5. In addition, in FIG. 6, the SEM observation image (10,000 times) of the conductive film of Example 4 is shown together to measure the average particle diameters of the nickel particles (Ni) and barium titanate particles (BT). A case where the outline of a particle is drawn.

[Table 2]

Table 2

[table 3]

table 3

As shown in Table 2, it can be seen that even if the same raw materials are used, the rate of change in transmittance of the obtained conductive paste can be significantly different by changing the preparation method. In this embodiment, the stirring strength of the nickel slurry and the barium titanate slurry of Examples 1 to 4 is changed within a range of 8 m / s to 60 m / s, respectively. Similarly, the stirring strength of the nickel slurry and the barium titanate slurry of Examples 5 to 6 was also changed within the range of 8 m / s to 60 m / s. As a result, it was found that, for the conductive pastes of Examples 1 and 5, the transmittance change rate becomes smaller and the dispersion stability is improved, and for the conductive pastes of Examples 4 and 6, the transmittance change rate becomes larger and the dispersion stability becomes lower. . In this way, when the dispersion upper body and dispersion stability of Ni particles and BT particles in the obtained conductive paste are changed, it is considered that the dispersion stability of these particles can be better exhibited by using the rate of change in transmittance as an index. (Numerical).

On the other hand, as shown in Tables 2 and 3, it can be seen that the D ₅₀ and D ₉₀ of the Ni particles and the BT particles in the conductor film obtained after calcination are smaller as the paste having a lower change rate in transmittance is smaller, for example, as As shown in Example 1 of FIG. 5, grain growth of each particle due to calcination is suppressed. In addition, it can be seen that the D ₅₀ and D ₉₀ of the Ni particles and BT particles in the conductor film obtained after calcination are larger as the paste having a larger transmission rate change rate. For example, as shown in Example 4 of FIG. The induced grain growth cannot be suppressed. It can be seen from this that the rate of change in transmittance of the conductive paste disclosed herein can also be used as an index for grasping in advance the grain growth behavior of the conductive paste during calcination, and is preferably used.

More specifically, as shown in FIG. 4 (a), the maximum frequency of the particle size distribution of the Ni particles in the conductor films of Examples 1 and 5 is high and extremely sharp. Regarding Examples 1 and 5, although the average particle size of the Ni powder used as the raw material is different between 180 nm and 300 nm, the particle size distribution of the sintered Ni particles is approximately the same shape. If the rate of change in transmittance is small, The growth of Ni particles is suppressed at a high level. Regarding the particle size distribution of the Ni particles of the conductor film of Example 2, the peak width with a slightly lower maximum frequency maintained the same width as that of Example 1. In contrast, for example, regarding the particle size distribution of the Ni particles in the conductive films of Examples 3 and 4, it can be seen that the presence of coarse particles increases and widens. As for Example 4, the number of coarse particles increased significantly, forming a left shoulder in the particle size distribution ( Second peak). It can be seen that, compared with the Ni particles of Example 4, the Ni particles in the conductive film of Example 6 undergo significant grain growth by sintering. In addition, as shown in FIG. 4 (b), the BT particles are finer than the Ni particles. Although the grain growth caused by the calcination becomes significant, as shown in Table 3, it shows that they are approximately the same as the Ni particles. behavior.

From this, it can be seen that the conductor film formed using the conductive paste of Example 1 having a small transmittance change rate can suppress the grain growth during the calcination of the raw material particles, the thickness is thinner, the surface is flat, and a uniform conductor film can be formed. . Although the details are not clear, for example, regarding the conductive pastes of Examples 1 and 5, it is considered that, for example, Ni particles and fine BT particles do not agglomerate, and even in a paste state, Ni particles can be preferably formed between the Ni particles during coating film formation. Configure BT particles. In addition, it is considered that the sintering and grain growth of the Ni particles at the time of calcination can be better suppressed by this. On the other hand, regarding the conductive pastes of Examples 4 and 6 in which the rate of change of transmittance is large, it is considered that, for example, the fine BT particles are agglomerated, and the contact between the Ni particles cannot be satisfactorily suppressed. It is considered that the Ni grains and BT grains each significantly undergo grain growth during the calcination. For example, if the rate of change of the transmittance of the conductive paste is 0.003 or less, it can be said that the dispersion stability of the particles in the paste is high, and a conductor film composed of finer sintered particles can be obtained. In addition, if the rate of change of the transmittance of the conductive paste is higher than 0.003, the dispersion stability of the particles in the paste is low, and the same kind of particles contact each other at a higher frequency during the formation of the coating film, and it is easily carried out by firing Grain growth.

By using the conductive paste disclosed herein, abnormal grain growth of conductive particles can be suppressed to form a conductive film. This makes it possible, for example, to suppress expansion of the internal electrode layer or puncture of the thinned dielectric layer caused by conductive particles in the production of the MLCC, thereby producing an MLCC with high withstand voltage and reliability.
The present invention has been described in detail above, but these are merely examples, and the present invention can be modified in various ways without departing from the spirit thereof.

1‧‧‧Multilayer Ceramic Capacitors (MLCC)

10‧‧‧Laminated Wafer

10'‧‧‧Unfired laminate

20‧‧‧ Dielectric layer

20'‧‧‧ceramic green sheet

30‧‧‧Internal electrode layer

30'‧‧‧ conductive paste coating layer

40‧‧‧External electrode

FIG. 1A is a schematic cross-sectional view illustrating the structure of an MLCC.

FIG. 1B is a schematic cross-sectional view schematically illustrating the structure of an uncalcined MLCC body.

(T ₀ ) to (t ₂ ) of FIG. 2 are diagrams illustrating a change in transmittance distribution and a change in time when the conductive paste is subjected to a centrifugal sedimentation treatment.

(A) is a figure explaining the time change of the transmittance distribution of a conductive paste, (b) is a figure explaining the time change of an integrated transmittance, and (c) is a figure explaining the change rate of the transmittance Illustration.

FIG. 4 is the particle size of (a) nickel particles and (b) barium titanate particles measured in a conductive film obtained by calcining the conductive paste of each example based on a scanning electron microscope (SEM) observation. distributed.

FIG. 5 is an SEM observation image of the surfaces of the conductive films of Examples 1 and 4. FIG.

FIG. 6 is a diagram illustrating the measurement of particle diameters of nickel (Ni) particles and barium titanate (BT) particles in the conductive film of Example 4. FIG.

Claims (6)

A conductive paste for forming a conductive film, and comprising: a conductive powder, a dielectric powder, and an organic component, The centrifugal sedimentation behavior of the conductive powder and the dielectric powder when the conductive paste is subjected to a centrifugal sedimentation treatment is evaluated at the rate of change in transmittance when the rate of change in transmittance is evaluated as follows. It is prepared in a manner below 0.003, and the transmission rate change rate is defined as a change amount per unit time of the integrated transmission rate calculated based on the transmission rate distribution in the centrifugal sedimentation direction. The conductive paste according to item 1 of the scope of patent application, wherein the average particle diameter of the conductive powder based on the Boutte (BET) method is set to D ₁ , and the base powder of the dielectric powder is based on a cloth. When the average particle diameter of the Ute method is set to D ₂ , 0.03 × D ₁ ≦ D ₂ ≦ 0.4 × D _{1 is} satisfied. The conductive paste according to item 1 or 2 of the scope of application for a patent, wherein the average particle diameter D ₁ of the conductive powder based on the Boutte method is 0.5 μm or less. The conductive paste according to any one of claims 1 to 3, wherein the conductive powder is at least one selected from the group consisting of nickel, platinum, palladium, silver, and copper. The conductive paste according to any one of claims 1 to 4, wherein the dielectric powder is selected from the group consisting of barium titanate, strontium titanate, and calcium zirconate. At least one. The conductive paste according to any one of claims 1 to 5, which is used to form an internal electrode layer of a laminated ceramic electronic part.