TWI805721B - conductive paste - Google Patents

Abstract

The present invention provides an electroconductive paste in which problems such as abnormal crystal grain growth during firing are suppressed due to excellent dispersion stability. According to the present invention, a conductive paste can be provided, which is used for forming a conductive film and includes: conductive powder, dielectric powder and organic components. Regarding the centrifugal sedimentation behavior of the conductive powder and the dielectric powder when the conductive paste is subjected to the centrifugal sedimentation treatment, when the following transmittance change rate is evaluated, it is prepared so that the transmittance change rate becomes 0.003 or less, The transmittance change rate is defined as the amount of change per unit time of the integrated transmittance calculated based on the transmittance distribution along the centrifugal sedimentation direction.

Description

conductive paste

The present invention relates to a conductive paste. More specifically, the present invention relates to a conductive paste suitable for forming internal electrode layers of laminated ceramic electronic components.

This application claims priority based on Japanese Patent Application No. 2018-068733 for which it applied on March 30, 2018, and the entire content of this application is incorporated in this specification as a reference.

A multilayer ceramic capacitor (Multi-Layer Ceramic Capacitor, MLCC) has a structure in which a plurality of dielectric layers including ceramics and internal electrode layers are laminated. The MLCC is generally produced by printing a conductive paste for internal electrodes containing conductive powder on a dielectric green sheet containing dielectric powder and a binder to form an internal electrode layer, A plurality of dielectric green sheets on which the internal electrode layers were printed were laminated and bonded by pressure, followed by firing. Here, for example, Patent Document 1 discloses a conductive paste containing conductive particles and a coexisting material containing dielectric particles, and the coexisting material is provided with a non-conductive coating portion. According to the above structure, it is described that when the conductive particles are sintered to form the internal electrode layer, the abnormal grain growth of the conductive particles can be preferably suppressed without causing the coexisting materials existing between the conductive particles to react with each other. .

[Prior art literature]

[Patent Document]

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

In addition, along with the miniaturization and weight reduction of electronic equipment, each electronic component constituting the electronic equipment is also required to be smaller and thinner. In MLCC, it is required to enlarge the electrode area by further thinning the dielectric layer and further increasing the number of laminated layers, so as to reduce the size of the MLCC and increase the capacitance. By reducing the thickness of the dielectric layer and the internal electrode layer, for example, the average particle size of the powder used to form the internal electrode layer is reduced to the level of 10 nm in the coexistence material and to the level of several 100 nm in the conductive particle. Therefore, it becomes extremely difficult to prepare a coexisting material having 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 has become a problem. For example, due to excessive grain growth of the conductive particles during firing, the internal electrode layer expands and the dielectric layer is compressed, causing a decrease in withstand voltage of the dielectric layer or a decrease in reliability. In addition, if the conductive particles grow coarser, they will pierce the thinned dielectric layer, resulting in defective products and a decrease in yield. The grain growth of the conductive particles is considered to be caused by the fact that the conductive particles and the dielectric particles are unevenly present in the conductive paste film before firing, and there are many contact points between the conductive particles. parts (i.e., There are many portions where there are no dielectric particles), and the effect of suppressing sintering by the dielectric particles cannot be exhibited. In addition, the unevenness of the conductive particles and the dielectric particles may become more remarkable when the powders are finer and the surface activity is improved.

The present invention is made in view of the foregoing, and an object of the present invention is to provide a conductive paste in which problems such as abnormal crystal grain growth during firing are suppressed because the dispersion stability of conductive powder and dielectric powder is good.

According to the study of the present inventors, even if the raw materials used for the conductive paste are the same, 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. Furthermore, it was discovered that by variously controlling the paste preparation conditions so that the "transmittance rate of change" specified as follows is 0.003 or less, a conductive paste having an unprecedentedly high level of dispersion stability can be obtained. This technology is completed based on the knowledge mentioned above.

That is, by using the technology disclosed herein, a conductive paste can be provided, which is used for forming a conductive film and includes: conductive powder, dielectric powder and organic components. Here, regarding the centrifugal sedimentation behavior of the conductive powder and the dielectric powder when the conductive paste is subjected to centrifugal sedimentation treatment, the transmittance It was prepared so that the rate of change of the transmittance defined as the amount of change per unit time of the integrated transmittance calculated based on the transmittance distribution along the centrifugal sedimentation direction was 0.003 or less.

According to the above constitution, a conductive paste is realized in which the conductive powder and the dielectric powder are dispersed extremely stably in the organic component, and the dispersed state can be maintained for a long time state. According to the above-mentioned 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 aggregation or contact of the conductive powder can be preferably suppressed, and the Grain growth during firing of the coating film is suppressed. Thereby, the sizes of the conductive particles and the dielectric particles in the fired conductor film can be kept small, and the puncture of the dielectric layer caused by abnormal growth of the conductive particles, for example, can be suppressed. As a result, electronic parts excellent in quality and reliability can be manufactured.

In addition, in this specification, the so-called "transmittance rate of change" refers to the amount of change per unit time of the integrated light transmittance (T) obtained by acquiring the light transmittance distribution curve of the conductive paste over time ( ΔT/Δt). The light transmittance distribution curve can be obtained as follows: Regarding the sedimentation state of the particles contained in the paste when the conductive paste is subjected to centrifugal sedimentation treatment, using an optical detection method such as the light transmission method or the light reflection method, etc., on the entire paste Real-time and direct measurement of light transmittance or light reflectance along the centrifugal sedimentation direction in the area. In the invention disclosed herein, the rate of change in transmittance 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 Examples described later.

In a preferred aspect of the conductive paste disclosed herein, when the average particle size of the conductive powder based on the Buert (Brunauer Emmett Tellern, BET) method is set as D ₁ , the dielectric When the average particle diameter of the solid powder by the BET method is D ₂ , it satisfies 0.03×D ₁ ≦D ₂ ≦0.4×D ₁ . Thereby, even in the case of forming a thin conductive film, the dielectric particles can be preferably arranged in the gaps of the conductive particles, and the abnormal crystals of the conductive particles during firing can be preferably suppressed by the dielectric powder. Grains grow.

In a preferred aspect of the conductive paste disclosed herein, the average particle diameter D ₁ of the conductive powder based on 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 precision.

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 conductor 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 having excellent adhesion to a high-permittivity dielectric layer 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 layers disposed between the thin (for example, 1 μm or less) dielectric layers can be preferably formed with high surface flatness, electrical connection, and homogeneity by using the conductive paste disclosed herein. As a result, a compact, high-capacity, and high-quality MLCC in which short circuits, cracks, and the like in the dielectric layer are preferably suppressed can be realized.

1: Multilayer ceramic capacitor (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

t ₀ , t ₁ , t ₂ : time

S ₀ , S ₁ , S ₂ : integral transmittance

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

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

Fig. 2(a) to Fig. 2(c) illustrate the centrifugal sedimentation of the conductive paste A plot of the transmittance distribution during processing and how it changes over time.

Fig. 3(a) is a diagram illustrating the temporal change of the transmittance distribution of the conductive paste, Fig. 3(b) is a diagram illustrating the temporal change of the integrated transmittance, and Fig. 3(c) is a diagram illustrating the transmittance change rate diagram.

Fig. 4 is the particle size of (a) nickel particles and (b) barium titanate particles measured based on scanning electron microscope (Scanning Electron Microscope, SEM) observation in the conductive film fired from the conductive paste of each example distributed.

5A and 5B are SEM observation images of the surfaces of the conductive films of Example 1 and Example 4, respectively.

6A and 6B are diagrams illustrating the measurement of the particle diameters of nickel (Ni) particles and barium titanate (BT) particles in the conductive film of Example 4, respectively.

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 the conductive paste or its properties) are matters required for the implementation of the present invention (for example, about the preparation of the raw materials of the paste and Specific methods of application to substrates, configurations of electronic components, etc.) can be implemented based on the technical content taught in this specification and the general technical knowledge of practitioners in this field. In addition, the expression "A~B" which shows a numerical range in this specification means A or more and B or less.

[conductive paste]

The conductive paste disclosed herein contains (A) conductive powder, (B) dielectric powder, and an organic component as main components. The so-called organic ingredients are typically A medium called a vehicle (vehicle) containing (C) a binder and (D) a dispersion medium. In addition, when the conductive paste is calcined, the organic components disappear, and the (A) conductive powder and (B) 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 components of the conductor film are usually dispersed in a vehicle as an organic component to form a paste, and are given appropriate viscosity and fluidity.

Furthermore, the conductive paste disclosed herein is prepared so that the rate of change in transmittance becomes 0.003 or less. Thereby, the (A) conductive powder and (B) dielectric powder are highly dispersed in the medium, and high dispersibility can be maintained for a long period of time. For example, even if the centrifugal sedimentation treatment at 4000rpm described later is applied for 100 minutes, the sedimentation of (A) conductive powder and (B) dielectric powder is suppressed, and the (A) conductive powder and (B) ) Complete separation of dielectric powder and organic components. It is considered that the unprecedentedly high dispersion stability is achieved not so much by the individual properties of the constituent materials of the conductive paste, but by the state of existence of each constituent material in the conductive paste. Hereinafter, the conductive paste disclosed herein will be described for each element.

(A) Conductive powder

Conductive powder is a material used to mainly form conductors (conductor films) with high electrical conductivity (hereinafter, simply referred to as "conductivity") such as electrodes, wires, or conductive films in electronic components and the like. Therefore, as the conductive powder, powders of various materials having desired conductivity can be used without particular limitation. As the conductive material, for example, nickel (Ni), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium ( Rh), osmium (Os), iridium (Ir), aluminum (Al), tungsten (W) and other gold Metallic monomers, alloys containing these metals, etc. Any one type of conductive powder may be used alone, or two or more types may be used in combination.

Furthermore, although it is not particularly limited, for example, regarding the conductive paste used for forming the MLCC internal electrode layer, it is preferable that the melting point of the conductive powder is lower than the sintering temperature of the dielectric layer (for example, about 1300°C). The use of metal species. Examples of the metal species include noble 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 preferable from the viewpoint of melting point and conductivity, but in consideration of stability and low price, it is more preferable to use nickel.

The method for producing the conductive powder, and properties such as the size and shape of the particles constituting the conductive powder are not particularly limited. For example, it may be included in the minimum dimension (typically, the thickness and/or width of the electrode layer) of the target electrode in consideration of the firing shrinkage. 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 ( _DB )" of the conductive powder and the dielectric powder refers to the specific surface area S measured based on the BET method and the specific surface area S of the powder, unless otherwise specified. The specific gravity ρ and the value 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 of forming the internal electrode layer of a small-sized, high-capacity MLCC, it is important that the average particle diameter of the conductive powder is smaller than the thickness of the internal electrode layer (dimension in the stacking direction). In other words, it is preferable that substantially no coarse particles exceeding the thickness of the internal electrode layer are included. From this point of view, as an example, the conductive powder preferably has a cumulative 90% particle size (D ₉₀ ) of not more than 3 μm, more preferably not more than 1 μm, for example, preferably not more than 0.5 μm. In addition, the average particle diameter (D ₅₀ ) may be approximately 1 μm or less, typically 0.5 μm or less, preferably 0.3 μm or less, more preferably 0.25 μm or less, for example 0.2 μm or less. When the average particle size is equal to or less than a predetermined value, a conductive film can be stably formed. In addition, the surface roughness of the formed conductor film can be preferably suppressed. For example, the arithmetic mean roughness Ra can be suppressed to a level of 5 nm or less.

The lower limit of the average particle size of the conductive powder is also not particularly limited, for example, it may be 0.005 μm or more, approximately 0.01 μm or more, typically 0.05 μm or more, preferably 0.1 μm or more, for example 0.12 μm or more. Since the average particle diameter is not 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 it is preferable to form a conductive film with high electrical conductivity and high density.

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, aggregation in the paste can be preferably suppressed, and the homogeneity, dispersibility, and storage stability of the paste can be improved more favorably. In addition, a conductor film having excellent electrical conductivity can be realized more stably. Furthermore, the specific surface area refers to the gas adsorption amount measured by, for example, a gas adsorption method (constant volume adsorption method) using nitrogen (N ₂ ) gas as an adsorbate, and is calculated by a BET method (such as a BET one-point method) out the value.

The shape of the conductive powder is not particularly limited. For example, the shape of the conductive powder in the conductive paste for the formation of some electrodes such as MLCC internal electrodes can be changed. It is spherical or roughly spherical. The average aspect ratio of the conductive powder may be typically 1 to 2, preferably 1 to 1.5. Thereby, the viscosity of the paste can be kept low, and the handleability of the paste and the workability at the time of film formation for forming a conductor film can be improved. In addition, the homogeneity of the paste can also be improved.

The "aspect ratio" in this specification is calculated based on electron microscope observation, and refers to the length (b) of the long side to the length (a) of the short side when drawing a rectangle circumscribing the particles constituting the powder. Ratio (b/a). The average aspect ratio is an arithmetic average of aspect ratios obtained with respect to 100 particles.

The content ratio of the conductive powder is not particularly limited, and when the entire conductive paste is 100% by mass, it may be approximately 30% by mass or more, typically 40% by mass to 95% by mass, for example, 45% by mass to 60% by mass. quality%. By satisfying the above-mentioned range, it is possible to preferably realize a conductive layer with high electrical conductivity and high density. In addition, the handleability of the paste and the workability at the time of film formation can also be improved.

(B) Dielectric powder

The conductive paste disclosed herein may contain (B) dielectric powder as a component mainly constituting the conductive film after firing, in addition to the (A) conductive powder. The dielectric powder is a component that can suppress sintering of the conductive powder due to low temperature during firing of the conductive paste, or can adjust the thermal shrinkage rate and firing shrinkage history by being arranged between the particles constituting the conductive powder. Or the thermal expansion coefficient of the conductive film after firing. The role of the dielectric powder can be various. In particular, the dielectric powder contained in the conductive paste for the internal electrode layer of MLCC has the same or similar composition as the dielectric layer, This is preferable since it can function preferably as a coexistence material that improves the sintering bondability of the dielectric layer and the internal electrode layer.

The dielectric constant of the dielectric powder is not particularly limited, and can be appropriately selected according to the intended use. As an example, the relative dielectric constant of the dielectric powder used in the conductive paste for forming the internal electrode layer of the high dielectric constant MLCC is typically 100 or more, preferably 1000 or more, for example, 1000 to 20000 about. The composition of the dielectric powder is not particularly limited, and one kind or two or more kinds of various inorganic materials can be used as appropriate depending on the application or 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, calcium zirconate, etc. Metal oxide of perovskite structure represented by ABO ₃ , titanium dioxide (rutile), titanium pentoxide, hafnium oxide, zirconium oxide, aluminum oxide, forsterite, niobium oxide, barium neodymium titanate, rare earth Other metal oxides such as elemental oxides are typical examples. In the paste for the internal electrode layer, the dielectric powder can preferably be composed of, for example, barium titanate (BaTiO ₃ ), strontium titanate, and calcium zirconate (CaZrO ₃ ). On the other hand, of course, a dielectric material (further, an insulating material) having a relative permittivity of less than 100 can also be used.

The properties of the particles constituting the dielectric powder, such as the size and shape of the particles, are not particularly limited as long as they are included in the minimum dimension in the cross section of the electrode layer (typically, the thickness and/or width of the electrode layer). The average particle size of the dielectric powder can be appropriately selected according to the use of the paste, the size (fineness) of the electrode layer, and the like, for example. Regarding the target conductive layer, the average particle diameter of the dielectric powder is preferably smaller than the average particle diameter of the conductive powder from the viewpoint of easily ensuring predetermined conductivity. When D ₂ is the average particle size of the dielectric powder and D ₁ is the average particle size of the conductive powder, D ₁ and D ₂ are usually preferably D ₁ >D ₂ , more preferably D ₂ ≦0.5 ×D ₁ , more preferably D ₂ ≦0.4×D ₁ , for example, D ₂ ≦0.3×D ₁ . In addition, when 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 aspect, as a general standard, it is preferably 0.03×D ₁ ≦D ₂ , more preferably 0.05×D ₁ ≦D ₂ , for example, 0.1×D ₁ ≦D ₂ . For example, specifically, the average particle diameter of the dielectric powder is suitably not less than several nm, preferably not less than 5 nm, and may be not less than 10 nm. In addition, the average particle size of the dielectric powder may be approximately several μm or less, for example, 1 μm or less, preferably 0.3 μm or less. As an example, in the conductive paste for forming the internal electrode layer of MLCC, the average particle size of the dielectric powder may be approximately several nm to several hundreds of 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 MLCC, when the entire conductive paste is 100% by mass, it may be approximately 1% by mass to 20% by mass, for example, 3% by mass to 15% by mass. In addition, the ratio of the dielectric powder to 100 parts by mass of the conductive powder may be, for example, approximately 3 parts by mass to 35 parts by mass, preferably 5 parts by mass to 30 parts by mass, for example, 10 parts by mass to 25 parts by mass. Thereby, the firing of the conductive powder due to low temperature can be appropriately suppressed, and the electrical conductivity, denseness, and the like of the conductive film after firing can be improved.

(C) Adhesive

The binder is a material that functions as a binder among the organic components in the conductive paste disclosed herein. The binder typically contributes to the bonding of the powder contained in the conductive paste to the substrate and the bonding of particles constituting the powder. in addition, The binder is dissolved in a dispersion medium described later and functions as a vehicle (may be a liquid medium). Thereby, the viscosity of the conductive paste is increased, the powder components are uniformly and stably suspended in the medium, fluidity is imparted to the powder, and it contributes to the improvement of workability. The binder is a component that presupposes disappearing by firing. Therefore, the binder is preferably a compound that burns out during firing of the conductor film. Typically, it is preferable that the decomposition temperature is 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 resins, cellulose-based resins, polyvinyl alcohol-based resins, polyvinyl acetal-based resins, acrylic resins, urethane-based resins, epoxy-based resins, phenolic resins, 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 for a conductive paste containing inorganic oxide powder and the firing temperature is relatively high, cellulose-based resins and polyvinyl alcohol-based resins are preferable. , polyvinyl acetal resin, acrylic resin, etc.

The cellulose-based resin contributes to the improvement of the dispersibility of the inorganic oxide powder, and when the conductive paste is used for printing, etc., the shape characteristics of the printed body (wiring film) or the adaptability to the printing operation are excellent, etc., Therefore better. The cellulose-based resin refers to all polymers containing at least β-glucose as a repeating unit and derivatives thereof. 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 alkoxy groups, and derivatives thereof. A part or all of the alkyl group or aryl group (R) in the alkoxy group (RO ⁻ ) may be substituted with an ester group such as carboxyl group, nitro group, halogen, or other organic groups. Specific examples of cellulose-based resins include methyl cellulose, ethyl cellulose, propoxy cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl cellulose, and hydroxypropyl cellulose. Methylcellulose, hydroxypropylethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxypropylcellulose, carboxyethylmethylcellulose, cellulose acetate phthalate, nitrocellulose Su and so on.

The polyvinyl alcohol-based resin makes the dispersibility of the inorganic oxide powder good and soft, so when the conductive paste is used for printing, etc., it is excellent in the adhesiveness and printability of the printed body (wiring film), etc., so it is preferable. . The polyvinyl alcohol-based resin refers to all polymers and derivatives thereof containing at least a vinyl alcohol structure as a repeating unit. Typically, polyvinylalcohol (PVA) having a structure polymerized from vinyl alcohol, polyvinyl acetal resin obtained by acetalizing the PVA with alcohol, and derivatives thereof may also be used. things etc. Among them, polyvinyl butyral (PVB) having a structure in which PVA is acetalized with butanol is more preferable because it improves the shape characteristics of printed matter. In addition, these polyvinyl acetal resins may also be copolymers (including graft copolymers) that contain polyvinyl acetal as a main monomer and contain a sub-monomer that is copolymerizable with the main monomer. As a submonomer, ethylene, ester, (meth)acrylate, vinyl acetate etc. are mentioned, for example. The ratio of acetalization in the polyvinyl acetal resin is not particularly limited, but is preferably 50% or more, for example.

The acrylic resin is preferable in that it is rich in adhesiveness and flexibility, and has less firing residue regardless of the firing environment. The acrylic resin refers to, for example, a polymer containing at least an alkyl (meth)acrylate as a monomer component and derivatives thereof. all things. Typically, it may be a homopolymer containing 100% by mass of alkyl (meth)acrylate as a constituent monomer component, or a copolymer (including graft copolymer), etc., which Copolymer) contains an alkyl (meth)acrylate as a main monomer and contains a sub-monomer that is copolymerizable with the main monomer. Examples of sub-monomers include 2-hydroxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, vinyl alcohol-based monomers, dialkylamine groups, carboxyl groups, alkoxy Copolymerizable monomers such as carbonyl groups. Specific examples of the acrylic resin include poly(meth)acrylic acid, vinyl chloride/acrylic acid graft copolymer resin, vinyl acetal/acrylic acid graft copolymer resin, and the like. In addition, in this specification, expressions, such as "(meth)acrylate", are used as terms showing that acrylate and/or methacrylate are included.

Any one of these binders may be used, or two or more of them may be used in combination. In addition, although not specifically described, a copolymer, a block copolymer, or the like obtained by copolymerizing monomer components of any two or more resins described above can also be used. In addition, the content of the binder is not particularly limited. In order to finely adjust the properties of the conductive paste or the properties of the paste printed body (including the dry film), for example, the content of the binder may be 0.5 parts by mass or more, preferably 1 part by mass or more with respect to 100 parts by mass of the conductive powder. , more preferably at least 1.5 parts by mass, for example, at least 2 parts by mass. On the other hand, since the binder resin may increase the sintering residue, it is not preferable to contain it excessively. From this point of view, 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

The dispersion medium is a liquid medium for dispersing the powder among the organic components in the conductive paste disclosed herein, and is, for example, an element for imparting excellent fluidity while maintaining the dispersibility. In addition, the dispersion medium dissolves the binder and functions as a vehicle. The dispersion medium is also a component presupposed to disappear by drying and firing. There are no particular limitations on the dispersion medium, and organic solvents used in such conductive pastes can be suitably used. It also depends on, for example, the combination with a binder, but from the viewpoint of film formation stability, a high-boiling organic solvent with a boiling point of about 180°C to 300°C, for example, 200°C to 250°C can be used as Main components (components accounting for more than 50% by volume).

Specific examples of the dispersion medium include: sclareol, citronellol, phytol, geranyllinalool, texanol, benzyl alcohol, phenoxyethanol, 1-phenoxy-2-propane Alcohol solvents such as alcohol, terpineol, dihydroterpineol, isoborneol, butyl carbitol, diethylene glycol; terpineol acetate, dihydroterpineol acetate, isoborneol acetate Esters, carbitol acetate, diethylene glycol monobutyl ether acetate and other ester solvents; mineral spirits, etc. Among them, alcohol-based solvents or ester-based solvents can be preferably used.

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

(E) Other additives

Furthermore, the conductive paste disclosed herein may contain various organic additives known to be usable in general conductive pastes within a range that does not significantly impair the effects of the technology disclosed herein. The organic additives include, for example, dispersants, thickeners, plasticizers, pH adjusters, stabilizers, leveling agents, defoamers, antioxidants, preservatives, colorants (pigments, dyes, etc.) and the like. For example, in the case of using powders such as conductive powder and dielectric powder as the main body constituting the conductor film, if the average particle diameter is less than about 1 μm, the powder may be Agglomeration occurs during paste preparation and immediately after paste preparation. This tendency becomes more remarkable when using ultrafine powder or nanoparticle (for example, powder having an average particle diameter of 0.5 μm or less) that can significantly improve surface activity as the conductive powder. Therefore, the conductive paste disclosed herein may preferably contain a dispersant as other additives.

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

There are no particular limitations on the type and the like of the dispersant, and one or two or more of various known dispersants can be used as necessary. Typically, those having sufficient compatibility with the vehicle (a mixture of a binder and a dispersion medium) described later can be appropriately selected and used. There are many ways to classify dispersants. As dispersants, they can also be so-called Any of the surfactant-type dispersants (also known as low-molecular-weight dispersants), polymer-type dispersants, inorganic-type dispersants, etc. In addition, these dispersants may be any of anionic, cationic, amphoteric or 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, and typically can be a solid that can directly adsorb the functional groups to particles. surface compound. Furthermore, the so-called surfactant refers to the following amphiphilic substance: it has a hydrophilic part and an lipophilic part in its molecular structure, and has a chemical structure formed by these covalent bonds.

Regarding the dispersant, as a surfactant type dispersant, for example, specifically, a dispersant mainly composed of an alkyl sulfonate, a dispersant mainly composed of a quaternary ammonium salt, a dispersant mainly composed of a higher alcohol alkylene oxide compound, etc. Mainly dispersant, polyol ester compound-based dispersant, alkylpolyamine compound-based dispersant, etc. Examples of polymeric dispersants include: dispersants based on fatty acid salts such as carboxylic acid or polycarboxylic acid, and polycarboxylic acid moieties in which hydrogen atoms in a part of the carboxylic acid groups are substituted with alkyl groups. Dispersants based on alkyl ester compounds, dispersants based on polycarboxylate alkylamine salts, dispersants based on polycarboxylic acid partial alkyl ester compounds having a part of polycarboxylic acid having an alkyl ester bond, Dispersants based on polystyrene sulfonate, polyisoprene sulfonate, polyalkylene polyamine compounds, sulfonic acid compounds such as naphthalene sulfonate, naphthalene sulfonate formalin condensate salt Dispersants based on hydrophilic polymers such as polyethylene glycol, dispersants based on polyether compounds, poly(meth)acrylates, poly(meth)acrylamides, etc. A (meth)acrylic compound-based dispersant and the like. As an inorganic dispersant, for example For example, phosphates such as orthophosphate, metaphosphate, polyphosphate, pyrophosphate, tripolyphosphate, hexametaphosphate and organic phosphate, ferric sulfate, ferrous sulfate, ferric chloride and chlorinated Dispersants based on iron salts such as ferrous iron, 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 said dispersing agent may contain any one type individually, and may contain 2 or more types together. In addition, the type of dispersant is not particularly limited. For the purpose of effectively dispersing finer conductive powder and dielectric powder for a long period of time with the addition of a small amount of dispersant, if it is used, it may appear caused by steric hindrance. A high-molecular dispersant with good repelling effect is better. The weight-average molecular weight of the dispersant in this case is not particularly limited, but as a preferred example, it is preferably about 300 to 50,000, for example, 500 to 20,000.

In addition, the said organic additive may contain any one type individually, and may contain 2 or more types together. In addition, the content of the organic additive can be appropriately adjusted within the range that does not significantly hinder the properties of the conductive paste disclosed herein. For example, it can be contained in an appropriate ratio according to the properties and purpose of the organic additive. Generally speaking, for example, the dispersant is usually contained in a ratio of about 5 mass % or less, for example, 3 mass % or less, typically 1 mass % or less and about 0.01 mass % or more, based on 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 the inorganic powder, or an additive that inhibits them. From this point of view, when organic additives are included, the total content of these components is preferably about 10% by mass or less of the entire conductive paste, more preferably 5% by mass or less, and most preferably 3% by mass or less .

Conductive paste can usually be prepared in the following way: in the organic component (C) binder and (D) dispersion medium are mixed in advance to prepare a vehicle, and (A) conductive powder and (B) dielectric powder are mixed and kneaded in the vehicle. In the conductive paste disclosed herein, it is most important to blend The constituent materials. The preparation method of the conductive paste is not particularly limited as long as the change speed of the transmittance can be realized. As an example of the preparation method of the conductive paste, which will be described in detail in the examples described later, (A) conductive powder and (B) dielectric powder can be pre-dispersed in different (D) dispersion media and prepared as In the form of a slurry, the conductive powder and the dielectric powder are then mixed in the form of a slurry, whereby the two can be blended with good dispersibility.

Furthermore, if the (C) binder in the organic component is initially added to the slurry containing (A) conductive powder (hereinafter referred to as conductive powder slurry) or the slurry containing (B) dielectric powder ( Hereinafter, it is referred to as a dielectric powder slurry), which prevents these powders from being highly dispersed. Therefore, with regard to (C) binder, it is preferable to prepare a vehicle liquid in advance by mixing with a part of (D) dispersion medium, and to use the vehicle liquid for the mixed slurry of conductive powder slurry and dielectric powder slurry The state is mixed. The rate of change in transmittance of the conductive paste prepared in this manner is preferably less than 0.003, more preferably less than 0.0025, and most preferably less than 0.002. The above-mentioned conductive paste (mixed slurry) is preferable because it can strongly maintain its highly dispersed state for a long period of time.

Here, the pre-prepared conductive powder slurry and dielectric powder slurry are preferably highly dispersed conductive powder or dielectric powder in the respective slurries in an unprecedentedly preferable state. The so-called dispersion condition also depends on the object The material (composition, etc.) of the conductive powder and dielectric powder, the average particle size, the paste concentration, the structure of the stirring device or dispersing device used, etc., cannot be generalized. For example, as an example, if the diffusion intensity in the previous diffusion treatment is set to 1, the stirring intensity when preparing the conductive powder slurry and the dielectric powder slurry in the technology disclosed herein can be set to 0.1 (times. ) or more, may also be 0.5 or more, for example, preferably 1 or more, more preferably 1.5 or more, further preferably 1.8 or more, especially preferably 2 or more. The upper limit of the stirring intensity can be set as the upper limit of the apparatus configuration. For example, if the diffusion intensity in the previous diffusion treatment is set to 1, about 5 can be used as a standard. Moreover, when adjusting the rate of change in transmittance, for example, a desired prepared conductive paste may be prepared in advance and the rate of change in transmittance may be confirmed, and the rate of change in transmittance may be adjusted little by little so that the rate of change in transmittance becomes 0.003 or less. Stirring conditions of the conductive paste. More specifically, for example, in the case of preparing a paste by setting the stirring intensity at about 30 m/s by a conventional method, the range of about 30 m/s to 60 m/s, for example, about 45 m/s to 60 m/s is exemplified. Increase the stirring intensity within the range. In addition, on the other hand, in the case of preparing the paste by setting the stirring intensity at about 7 m/s by the conventional method, the range of about 7 m/s to 20 m/s, for example, about 10 m/s to 20 m/s is exemplified. Increase the stirring intensity within the range.

In addition, at this time, at least the conductive powder slurry can be stirred and dispersed using a non-medium stirring device or a dispersing device. Furthermore, the so-called mediumless stirring device or dispersing device refers to the following stirring or dispersing device: it does not have a hard medium (for example, also called a crushing member) for stirring and dispersing such as impact on the fluid as the stirring or dispersing object. , movable member, medium (media), etc.). The media-free The driving force of the stirring or dispersing device is, for example, high-speed fluid such as compressed air, steam, heated air, ultrasonic waves, cavitation bubbles, etc., by utilizing the impact or collision of the driving force, the collision of particles, Mutual friction, etc. may show stirring or dispersing effect. For example, jet mill, jet mill, ultrasonic jet mill, cross jet mill (Cross Jet Mill) etc. are illustrated. If the above medium-less stirring and dispersing device is used, the hard medium directly contacts and acts on the solid primary particles contained in the fluid to be stirred and dispersed, and does not cause deformation, such as foiling, of the primary particles.

Regarding the other dielectric slurry, there is no limitation on the stirring device or the dispersing device. For example, the aforementioned non-medium stirring device or dispersing device may be used, or a media type stirring device or dispersing device may be used. Without further illustration, examples of media-type stirring and dispersing devices include ball mills, bead mills, colloid mills, hammer mills, mortars, disk mills, and roll mills.

By separating the conductive powder and the dielectric powder in advance to prepare a highly dispersed slurry in the above manner, the agglomeration of either particle can be preferably suppressed when the two are mixed, and a highly dispersed state can be achieved. As a result, even when, for example, centrifugal sedimentation treatment is performed on the conductive paste to accelerate the sedimentation, the conductive paste disclosed herein can highly suppress the sedimentation of the conductive powder and the dielectric powder. In addition, in the form containing a dispersant, a dispersant may or may not be contained regarding any one of the conductive powder slurry, the dielectric powder slurry, and the conductive paste. Regarding the slurry containing the dispersant, the powder material and the dispersant may be stirred and dispersed in the dispersion medium at the same timing or at different timings.

Regarding the conductive paste disclosed herein, the dispersion stability of the conductive powder and the dielectric powder is extremely high as described above. Therefore, various well-known supply methods can be employ|adopted for supplying an electroconductive paste to a base material in particular, without limitation. As said supply method, printing methods, such as screen printing, gravure printing, offset printing, and inkjet printing, a spraying method, a dip coating method, etc. are mentioned, for example. Especially when forming the internal electrode layer of MLCC, the gravure printing method which can print at high speed, the screen printing method, etc. can be suitably used.

[use]

In the conductive paste disclosed herein, even when the centrifugal sedimentation treatment at 4000 rpm is continuously applied for 100 minutes, for example, the particles contained in the conductive paste are not completely settled and separated from the dispersion medium, and the sedimentation is suppressed. . The conditions of the centrifugal sedimentation treatment are, for example, an accelerated test of several months to several years equivalent to the sedimentation treatment process performed by standing the conductive paste. Therefore, the conductive paste has excellent long-term storage properties after paste preparation, and for example, a large amount of paste can be prepared at once in a mass production process and used for a long time (for printing). These features also stabilize the printability of a printed coating film formed using the conductive paste, and contribute to, for example, improvement of the uniformity of the printed coating film in thickness, density, and the like. In addition, the highly dispersed state of the conductive powder and the dielectric powder can also be maintained in the printed coating film. As a result, even if the said printed coating film is calcined, the sintering of electroconductive particle and abnormal crystal grain growth can be preferably suppressed. In this aspect, the conductive paste can be preferably used also in applications where the homogeneity, surface smoothness, and the like of the conductive film after firing are particularly required. Typical applications include formation of electrode layers in laminated ceramic electronic components. The conductive paste disclosed herein, for example, can be preferably used for those whose sides are less than 5 mm, such as less than 1 mm. Formation of internal electrode layers of small MLCCs. In particular, it can be suitably used for production of internal electrodes of small-sized and large-capacity MLCCs in which the thickness of the dielectric layer is on the order of 1 μm or less.

In addition, in this specification, a "ceramic electronic component" is a common term which means the electronic component which has a crystalline ceramic base material or an amorphous ceramic (glass-ceramic) base material. For example, chip inductors, high-frequency filters, ceramic capacitors, high-temperature fired laminated ceramics (High Temperature Co-fired Ceramics, HTCC) substrates, low-temperature fired laminated ceramics (Low Temperature Co-fired Ceramics, LTCC) substrates, etc. are typical examples included in the "ceramic electronic parts" described here.

Examples of ceramic materials constituting the ceramic substrate include barium titanate (BaTiO ₃ ), zirconia (ZrO ₂ ), magnesium oxide (MgO), alumina (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 materials; cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ ), Mo Alite (3Al ₂ O ₃ .2SiO ₂ ), forsterite (2MgO.SiO ₂ ), steatite (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) Nitride-based materials such as silicon carbide (SiC) and boron carbide (B ₄ C) and other carbide-based materials; hydroxide-based materials such as hydroxyapatite, etc. These may be contained individually by 1 type, and may be contained as a mixture of 2 or more types, or as a complex which combined 2 or more types.

[Laminated Ceramic Capacitors]

FIG. 1A is a cross-sectional view schematically showing a multilayer ceramic capacitor (MLCC) 1 . The MLCC 1 is a wafer-type capacitor configured by laminating a plurality of dielectric layers 20 and internal electrode layers 30 alternately and integrally. A pair of external electrodes 40 are provided on the side of the laminated 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 the order of lamination. Thereby, a small-sized and large-capacity MLCC 1 is constructed in which 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. Dielectric layer 20 of MLCC1 is made of ceramics. The internal electrode layer 30 is composed of a calcined body of the conductive paste disclosed herein. The MLCC1 is preferably produced, for example, by the following procedure.

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

Next, prepare the conductive paste disclosed herein. Specifically, at least conductive powder (A), dielectric powder (B), binder (C), and dispersion medium (D) are prepared, and these are prepared in a predetermined ratio so that the transmittance change rate becomes 0.003 or less Stir and mix in a manner to prepare a conductive paste. Then, the prepared paste is supplied onto the prepared ceramic green sheet 20' so as to form a predetermined pattern and have a desired thickness (for example, 1 μm or less), to form a conductive paste coating layer 30'. Conductive The dispersion stability of the paste is significantly improved. Therefore, in the mass production of MLCC, even if the formation (printing) of the conductive paste coating layer 30' on the ceramic green sheet 20' is continued for a long time, the properties of the conductive paste are stable, so the printing quality can also be improved. stable.

A plurality of prepared ceramic green sheets 20 ′ with conductive paste coating layers 30 ′ (for example, hundreds to thousands of sheets) are laminated and bonded by pressure. The laminated pressure-bonded body is cut into wafer shapes as necessary. Thereby, an unfired laminate 10' can be obtained. Next, the prepared unfired laminate 10' is calcined under appropriate heating conditions (for example, a temperature of about 1000° C. to 1300° C. in a nitrogen-containing atmosphere). Thereby, the ceramic green sheet 20' and the conductive paste coating layer 30' are calcined simultaneously. The ceramic green sheet 20 ′ is fired to form the dielectric layer 20 . The conductive paste coating layer 30 ′ is fired to form the internal electrode layer 30 . The dielectric layer 20 and the internal electrode layer 30 are integrally sintered to obtain a sintered body (laminated wafer 10). Furthermore, before the calcination, in order to make the organic components such as binder and dispersion medium disappear, it is also possible to implement binder removal treatment (for example, in an oxygen-containing environment, at a temperature lower than the calcination temperature: for example, about 250 ° C ~ heat treatment at 700°C). Thereafter, external electrodes 40 are formed by applying an external electrode material to the side surface of laminated wafer 10 and firing. Thereby, MLCC1 can be manufactured.

Hereinafter, some examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

[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 nickel slurry is prepared by performing a dispersion process using a medialess high-speed disperser.

Next, (2) Barium titanate powder, an organic solvent, and a dispersant are prepared, and dispersion treatment is performed using a media mill to prepare a barium titanate slurry.

Moreover, (3) Use a medium-less high-speed dispersion device to disperse and mix the prepared nickel slurry, barium titanate slurry and dispersant, thereby making nickel. Barium titanate mixed slurry.

Subsequently, (4) in the nickel. The additionally prepared vehicle liquid 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, when preparing the paste, in formulation A, nickel powder (Ni) was used with an average particle diameter of 180nm, and barium titanate powder (BT) was used with an average particle diameter of 10nm. The ratio of the powder was 10% by mass. In addition, these nickel powders and barium titanate powders were not subjected to dispersion treatment such as special surface treatment. In addition, dihydroterpineol was used as an organic solvent, and a carboxylic acid-based dispersant was used as a dispersant. As for the vehicle, what was obtained by heating and mixing ethyl cellulose as a binder and an organic solvent in advance according to a conventional method was used.

(Example 2~Example 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) nickel slurry and (2) barium titanate slurry was changed, and the ratio of the dispersant was changed. , so that the dispersion state of nickel powder or barium titanate powder in the paste Variety. And other conditions were made the same as Example 1, and the electroconductive paste of Example 2-Example 4 was obtained by this.

However, regarding the conductive pastes of Examples 1 to 4, as the dispersion treatment conditions, the stirring speed was changed within the range of about 8 m/s to 60 m/s.

(Example 5)

In the preparation of the conductive paste of Example 1, the formulation B shown in Table 1 was used instead of the formulation A, and the dispersion treatment conditions and other conditions were the same as those of Example 1 to obtain the conductive paste of Example 5. In addition, in preparation B, nickel powder with an average particle diameter of 300 nm was used, and barium titanate powder with 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 amount of dispersant was decreased.

(Example 6)

In the preparation of the conductive paste of Example 4, the formulation B shown in Table 1 was used instead of the formulation A, and the dispersion treatment conditions and other conditions were the same as those of Example 4 to obtain the conductive paste of Example 6.

The preparation of the conductive pastes of Example 5 and Example 6 was substantially the same, but the conditions of the dispersion treatment were different for Example 1 and Example 4, respectively.

[Measurement of Transmittance Change Speed]

Regarding the prepared conductive pastes of Examples 1 to 6, the rate of change in transmittance 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, a solid content concentration of 10% by mass. Dihydroterpineol was used as an organic solvent for dilution. Furthermore, at the time of dilution, in order not to cause a so-called solvent shock (solvent shock), an organic solvent was added dropwise and mixed with a burette while stirring the conductive paste. Specifically, measure 10 g of the conductive paste in a 100 mL beaker, use a small mixer (using 6 blades, and rotate at about 200 rpm), and stir the conductive paste in the beaker while stirring the conductive paste in the beaker. Add organic solvent for the interval. The amount of the organic solvent added is, for example, 45 g with respect to 10 g of the conductive paste of Example 1.

The transmittance characteristics of the prepared diluted paste were measured using a dispersion stability analyzer (LUMiFuge manufactured by LUM GmbH). A polyamide angular tubular disposable sample cell (cell code (cell code) 3, LUM 2mmPA, measurement volume 0.4mL-0.5mL, measurement optical path length 2mm) for analysis equipment was used for the measurement. The sample tank is configured to hold 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 with a total length of 82 mm. The diluted paste weighed 0.4 mL using a syringe, and after filling the tank slowly from the bottom of the tank, it was capped and used for measurement.

The sample tank was set horizontally (so that the longitudinal direction of the tank coincided with the centrifugal direction) on the rotor of the dispersion stability analyzer, and the measurement was started.

The dispersion stability analysis device performs centrifugal sedimentation treatment on the slurry contained in the sample tank by rotating the rotor, and at the same time optically detects the liquid level of the slurry and the sedimentation state of the particles in the slurry, thereby enabling on-the-spot Measured directly. Moreover, the optical detection of the particle sedimentation state is implemented by the following method: using a line source of oscillating near-infrared laser to irradiate the laser light in a manner parallel to the longitudinal direction of the sample chamber, and using a charge-coupled device (Charge-Coupled Device, CCD) line sensor detects the intensity of the transmitted light. In the present embodiment, the transmitted light intensity was measured so as to include a region 19 mm from the liquid surface of the slurry in a sample present in a centrifugal state within a range of 23 mm from the bottom of the sample tank. In addition, in this embodiment, the time curve of the transmittance can be obtained by acquiring the position information of the sample tank and the transmittance curve at the position in real time during a predetermined measurement period. The measurement conditions are as follows.

Measuring temperature: 25.0°C

Transmittance measurement wavelength: 865nm

Light source intensity: 1 (standard)

Speed: 4000rpm

Measurement interval: 10 seconds

Measurement time: 6200 seconds (among them, the analysis object is up to 6000 seconds)

For example, as shown in FIG. 2( a ), the slurry contained in the sample tank initially has particles dispersed at a uniform concentration, and the transmittance is also constant. However, as shown in (b) and (c), the particles in the slurry move (sediment) toward the bottom surface of the tank (outside in the direction of the radius of rotation) as centrifugal sedimentation proceeds. Thereby, the slurry concentration at a predetermined position of the sample tank gradually decreases from the inner side in the direction of the rotation radius, and the transmittance of the slurry at the position gradually increases. In the measurement, a time variation curve of the transmittance distribution across the total measurement length of the sample tank can be obtained.

Therefore, as shown in FIG. 3(a), the transmittance (light transmittance) is integrated for a predetermined measurement area of the sample tank, and when the relationship between the integrated transmittance and the measurement time is plotted, for example, as shown in (b). The inclination of is defined as "transmittance change speed", where t ₀ , t ₁ , t ₂ represent time; S ₀ , S ₁ , S ₂ represent the time along the direction of centrifugal sedimentation at time t ₀ , t ₁ , t ₂ Integral of transmittance (integrated transmittance). The sedimentation of the particles proceeded stably at the beginning of the centrifugal sedimentation treatment, but stopped when the particles reached the bottom of the tank and became saturated. In the technology disclosed herein, as shown in (c), for this paste, the integral transmittance (T) per unit time in the measurement period from 0 seconds to 6000 seconds, which can be considered to be substantially stable in the sedimentation of the particles The amount of change (ΔT/Δt) is adopted as the "transmittance change rate". With regard to the rate of change in transmittance, a larger value indicates faster sedimentation and poorer 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 was calculated for the region of the sample tank 19 mm from the upper surface (liquid surface) of the sample. Based on this, the results of calculating the rate of change in transmittance for each conductive paste are shown in Table 2 below. In addition, the wavelength of the light (laser light here) used for the measurement of transmittance is not limited to the said 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, conductive films of each conductive paste were produced, and the sinterability was evaluated.

First, about 3 g of the conductive paste of each example was coated on a film made of polyethylene terephthalate (PET) with a film thickness of 250 μm by a film applicator. Thereafter, a dry coating film was obtained by processing the set temperature at 100° C. and drying time for 15 minutes using a warm air dryer. Next, the dried coating film was peeled off from the PET film, heated at a heating rate of 200°C/h in an N ₂ atmosphere, and held at a temperature of 600°C for 20 minutes to perform binder removal treatment. Then, in a (N ₂ +1%H ₂ ) atmosphere, heating was performed at a heating rate of 200° C./h, and the temperature was kept at 1200° C. for 10 minutes to perform main firing to obtain a conductive film.

Using a scanning electron microscope (Scanning Electron Microscope: SEM) to observe the surface of the conductive film after firing (the surface on the side that is not in contact with the PET film), and measure the sintering of the nickel particles and barium titanate particles after firing. The average particle size.

Specifically, first, Au vapor deposition was performed on the surface of the conductive film after firing for about 30 seconds, thereby preparing a sample for SEM observation. Then, based on the SEM image obtained by setting the observation magnification to 10,000 times, the area-equivalent circle diameters (Heywood diameters) of the nickel particles and the barium titanate particles were determined. The circle equivalent diameter is calculated by selecting about 70 nickel particles and barium titanate particles whose grain boundaries can be identified from SEM images of about 4 to 6 fields of view, and setting the contour of each particle using image processing software Out of the circle is equivalent to the diameter (refer to FIG. 6A and FIG. 6B ). In addition, the cumulative 50% particle diameter (D ₅₀ ) in the particle size distribution based on the number of area-circle-equivalent diameters obtained for each of about 70 particles is defined as the nickel particles or barium titanate particles in the conductive film. the average particle size. In addition, 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 Table 3 and Table 4 below.

In addition, for reference, SEM observation images (20,000 magnifications) of conductive films produced using the conductive pastes of Examples 1 and 4 are shown in FIGS. 5A and 5B , respectively. In addition, in FIG. 6A and FIG. 6B , regarding the SEM observation image (10000 times) of the conductive film of Example 4, in order to measure the average particle diameter of nickel particles (Ni) and barium titanate particles (BT), The case where the outline of the particles is drawn is also shown.

As shown in Table 2, it can be seen that even if the raw materials used are the same, the change speed of the transmittance of the obtained conductive paste can be significantly different by changing the preparation method. In this embodiment, the stirring intensity of the nickel slurry and the barium titanate slurry of Examples 1 to 4 were changed within the range of 8 m/s to 60 m/s, respectively. Similarly, the stirring intensity of the nickel slurry and the barium titanate slurry in Examples 5 to 6 were also changed within the range of 8 m/s to 60 m/s, respectively. As a result, for the conductive pastes of Examples 1 and 5, for example, the rate of change in transmittance was reduced and the dispersion stability was improved, and the rate of change in transmittance was increased and the dispersion stability was reduced in the conductive pastes of Examples 4 and 6. . In this way, it is considered that when the dispersion state and dispersion stability of Ni particles and BT particles in the obtained conductive paste are changed, the dispersion stability of these particles can be preferably expressed by using the rate of change in transmittance as an index ( digitized).

On the other hand, as shown in Table 2 and Table 3, it can be seen that the lower the transmittance change rate of the paste, the smaller the _D50 and _D90 of the Ni particles and BT particles in the conductor film obtained after firing, for example, as shown in As shown in Example 1 of FIG. 5A , the grain growth of each particle caused by calcination was suppressed. In addition, it can be seen that the higher the transmittance change rate of the paste, the larger the D ₅₀ and D ₉₀ of the Ni particles and BT particles in the conductor film obtained after firing. For example, as shown in Example 4 of FIG. The induced grain growth cannot be suppressed. From this, it can be seen that the rate of change in the transmittance of the conductive paste disclosed herein can also be preferably used as an index for grasping the grain growth behavior during firing of the conductive paste in advance.

More specifically, as shown in FIG. 4( a ), the maximum frequency of the particle size distribution of Ni particles in the conductor films of Examples 1 and 5 was high and extremely sharp. Regarding Examples 1 and 5, it can be seen that although the average particle diameter of the Ni powder used as a raw material is 180 nm and 300 nm, the particle size distribution of the Ni particles after sintering is approximately the same shape. If the rate of change in transmittance is small, the Ni particles growth was suppressed at a high level. Regarding the particle size distribution of Ni particles in the conductor film of Example 2, the width of the peak with a slightly lower maximum frequency was maintained at the same width as in Example 1. On the other hand, for example, regarding the particle size distribution of Ni particles in the conductive films of Examples 3 and 4, it can be seen that the presence of coarse particles increases and broadens, and in Example 4, the number of coarse particles increases significantly, forming a left shoulder in the particle size distribution ( second peak). It can be seen that the Ni particles in the conductive film of Example 6 significantly progressed in grain growth by sintering compared to the Ni particles of Example 4. In addition, as shown in FIG. 4( b ), since the BT particles are finer than the Ni particles, although the grain growth caused by sintering becomes remarkable, as shown in Table 3, it shows approximately the same behavior as that of the Ni particles. Behavior.

From this, it can be seen that the conductive film formed by using the conductive paste of Example 1 with a small transmittance change rate suppresses the grain growth of the raw material particles during sintering, and can form a uniform conductive film with a thinner surface and a flat surface. . Details are vague, such as Regarding the conductive pastes of Examples 1 and 5, it is considered that, for example, Ni particles and fine BT particles do not aggregate, and even in a paste state, BT particles can be preferably arranged between Ni particles when forming a coating film. In addition, it is considered that sintering and grain growth of Ni particles during sintering can be favorably suppressed by this. On the other hand, regarding the conductive pastes of Examples 4 and 6, which have a large rate of change in transmittance, it is considered that, for example, aggregation of fine BT particles cannot suppress the contact of Ni particles well. It is considered that the Ni particles and the BT particles each remarkably progress in grain growth at the time of sintering. For example, if the rate of change in 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 conductive film composed of finer sintered particles can be obtained. In addition, it is considered that 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 particles of the same type are in contact with each other at a higher frequency when forming a coating film, which 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. Thereby, for example, in the manufacture of MLCCs, expansion of internal electrode layers and penetration of thinned dielectric layers by conductive particles can be suppressed, and MLCCs with high withstand voltage and reliability can be manufactured.

As mentioned above, although this invention was demonstrated in detail, these are only an illustration, and various changes can be added to this invention in the range which does not deviate from the summary.

1‧‧‧Multilayer Ceramic Capacitors (MLCC)

10‧‧‧layer chip

10'‧‧‧Uncalcined laminate

20‧‧‧dielectric layer

20'‧‧‧ceramic green sheet

30‧‧‧internal electrode layer

30'‧‧‧Conductive paste coating layer

40‧‧‧External electrodes

Claims (6)

A conductive paste, which is used to form a conductive film, and includes: conductive powder, dielectric powder, and organic components, and the dilution of the conductive paste to a solid content concentration of 10% by mass is carried out at a rotation speed of 4000rpm for 6200 seconds The centrifugal sedimentation behavior of the conductive powder and the dielectric powder during the centrifugal sedimentation treatment was prepared so that the transmittance change rate was 0.003 or less when evaluating the following transmittance change rate. The transmittance rate of change is defined as the amount of change per unit time of the integrated transmittance calculated based on the transmittance distribution in the measurement period from 0 seconds to 6000 seconds along the centrifugal sedimentation direction. The conductive paste as described in claim 1, wherein the average particle diameter of the conductive powder based on the Buert (BET) method is set to D ₁ , and the average particle size of the dielectric powder based on the cloth When the average particle diameter of the Erter's method is D ₂ , it satisfies 0.03×D ₁ ≦D ₂ ≦0.4×D ₁ . The conductive paste according to claim 1 or 2, wherein the average particle diameter D ₁ of the conductive powder based on the Buert method is 0.5 μm or less. The conductive paste as described in claim 1 or claim 2, wherein the conductive powder is at least one selected from the group consisting of nickel, platinum, palladium, silver and copper. The conductive paste as described in item 1 or item 2 of the patent application, wherein the dielectric powder is selected from the group consisting of barium titanate, strontium titanate and calcium zirconate at least one of the The conductive paste as described in claim 1 or claim 2, which is used to form an internal electrode layer of a laminated ceramic electronic component.

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