TWI819103B - Conductive glue - Google Patents

Abstract

The present invention provides a conductive adhesive that contains fine conductive powder, has good dispersibility of the conductive powder, and can form a highly flexible coating film. A conductive adhesive includes: conductive powder with an average particle size of less than 200 nm; a binder resin; a solvent to dissolve the binder resin; a carboxylic acid dispersant; and a nonionic surfactant. The HLB value of the nonionic surfactant in the conductive adhesive is 3 or more, and the amount of the nonionic surfactant added to the entire adhesive is 0.08 mass % or more and 1 mass % or less.

Description

Conductive glue

The invention relates to a conductive glue. Preferably, the present invention relates to a conductive adhesive that is suitable for forming internal electrode layers of laminated ceramic electronic components.

This application claims priority based on Japanese Patent Application No. 2018-233598 filed on December 13, 2018, and the entire content of this application is incorporated into this specification by reference.

A multi-layer ceramic capacitor (MLCC) has a structure in which a plurality of dielectric layers containing ceramics and internal electrode layers are laminated. This MLCC is generally manufactured by printing a conductive paste for internal electrodes containing conductive powder and a binder on a dielectric green sheet containing a dielectric powder and a binder to form a For the printing layer, a plurality of dielectric green sheets including the printing layer are laminated, pressed, and fired.

[Prior art documents]

[Patent Document]

[Patent Document 1] Japanese Patent No. 6119939

In addition, as electronic equipment becomes smaller and lighter, the components constituting the electronic equipment are Various electronic components are also required to be further miniaturized and thinned. In MLCC, it is required to expand the electrode area by further thinning the dielectric layer and further increasing the number of stacked layers, thereby miniaturizing the MLCC and increasing the electrostatic capacitance. Therefore, research is being conducted on miniaturizing the constituent materials of the dielectric green sheet and the printing layer to, for example, several hundred nm levels. Here, if the constituting materials of the green sheet or the printing layer are miniaturized, it is indispensable to use them in the slurry or glue used in their production to uniformly disperse the dielectric powder or conductive powder. of dispersants. However, when the content of the dispersant in the slurry or glue increases, the dielectric green sheet or printed layer tends to become hard and its flexibility decreases.

In particular, the conductive glue used to form the printing layer may contain a coexisting material that is finer than the conductive powder, and an increase in the amount of the dispersant added cannot be avoided. However, if the printed layer becomes hard and brittle, the adhesion or pressure-bonding properties to the dielectric green sheet will be damaged, and peeling or cracking will be induced in the fired laminate, resulting in a decrease in operability, so it is undesirable. . On the other hand, for example, if the dispersion amount of the conductive glue is insufficient, problems such as aggregation of the conductive powder, poor uniformity of the conductive powder and coexisting materials, excessive grain growth of the conductive powder during firing, and the like may occur. Reduce the withstand voltage of the dielectric layer. These phenomena become more significant as MLCC becomes thinner and conductive powder becomes more refined.

The present invention has been made in view of the above-mentioned points, and an object thereof is to provide a conductive adhesive that contains fine conductive powder, has good dispersibility of the conductive powder, and can form a highly flexible coating film.

According to research by the present inventors, it was found that if the average particle diameter of the conductive powder in the conductive glue is reduced to 200 nm or less, it is required to fully contain a dispersant for dispersing the powder. A dispersant amount with good dispersibility may adversely affect the flexibility of the printed coating layer (coating film) after drying. Furthermore, they found that in order to achieve both the dispersibility and softness of the conductive powder in the coating film, it is effective to use a carboxylic acid-based dispersant as a dispersant in combination with a predetermined nonionic surfactant, and completed this application. invention.

That is, the conductive adhesive disclosed herein includes conductive powder with an average particle diameter of 200 nm or less, a binder resin, a solvent that dissolves the binder resin, a carboxylic acid dispersant, and a nonionic surfactant. Furthermore, the HLB value of the nonionic surfactant is 3 or more, and the added amount of the nonionic surfactant relative to the entire glue is 0.08 mass % or more and 1 mass % or less. This makes it possible to realize a conductive adhesive in which the conductive powder has good dispersibility and can form a highly flexible coating film.

Furthermore, the so-called Hydrophilic-Lipophilic Balance (HLB) value is a value that indicates the degree of affinity of a surfactant for water and oil (water-insoluble organic compounds), and is represented by a value from 0 to 20. . The closer the HLB value is to 0, the higher the lipophilicity; the closer the HLB value is to 20, the higher the hydrophilicity. The HLB value in this specification adopts the value obtained based on Griffin's formula.

A preferred aspect of the conductive glue disclosed herein further includes dielectric powder. Furthermore, it is more preferable that the average particle diameter based on the Brunauer Emmett Tellern (BET) method of the conductive powder is D ₁ and the average particle diameter based on the BET method of the dielectric powder is D ₂ To satisfy 0.03×D ₁ ≦D ₂ ≦0.4×D ₁ . In this way, by including finer dielectric powder in addition to the conductive powder, the uniform dispersibility of the powder in the glue is likely to be significantly reduced, which may impair the quality of the formed internal electrode layer. However, even if the conductive adhesive disclosed herein contains such dielectric powder, the powder has good dispersibility and can form a highly flexible coating film, so it is preferable.

In a preferred aspect of the conductive adhesive disclosed herein, the binder resin includes cellulose-based resin and polyvinyl acetal. In addition, the proportion of the polyvinyl acetal in the total of the polyvinyl acetal and the cellulose resin is 15 mass% or more and 80 mass% or less. This configuration is preferable because the effect of polyvinyl acetal on improving the flexibility of the coating film can be effectively exhibited in a coating film formed of a glue containing only ethyl cellulose.

Furthermore, for example, Patent Document 1 discloses a resin that is a mixture of polyvinyl acetal and a cellulose derivative and contains In the case of a nickel paste having a predetermined composition of nickel powder with an average particle diameter of 300 nm, it is adjusted to achieve predetermined rheological characteristics. Furthermore, it is described that according to the binder resin, a conductive adhesive excellent in both printability and adhesion can be prepared compared to the case of using a cellulose derivative alone. However, according to the disclosure of Patent Document 1, for example, if the average particle diameter of the nickel powder is further refined to about 2/3, problems such as hardening of the formed coating film and aggregation of the nickel powder cannot be avoided. In contrast, the conductive glue disclosed herein realizes a glue that can form a better coating film even when the conductive powder is further refined.

In a preferred aspect of the conductive adhesive disclosed herein, the conductive powder includes at least one of nickel, platinum, palladium, silver and copper. This can preferably realize a conductor film with excellent electrical conductivity.

The conductive adhesive disclosed herein can be preferably used to form internal electrode layers of laminated ceramic electronic components. For example, chip-type MLCCs require further thinning and high-density lamination of dielectric layers. By using the conductive glue disclosed herein in the internal electrode layer disposed between such thin (for example, 1 μm or less) dielectric layers, fine conductive powder or dielectric powder can be dispersed in a good state and a coating film can be formed. The film has high flexibility. As a result, in the manufacturing steps of MLCC, the adhesion between the dielectric green sheet and the coating film of the conductive adhesive is good, and the coating film is difficult to crack or peel from the lamination of the green sheets to crimping or firing. As a result, the internal electrode layer can be preferably formed to be electrically continuous and homogeneous. In addition, it is possible to preferably realize a small, large-capacity, and high-quality MLCC in which the occurrence of short circuits, cracks, etc. in the dielectric layer is suppressed.

1: Multilayer ceramic capacitor (MLCC)

10: Multilayer wafer (capacitor part)

10': Unfired laminate

20: Dielectric layer

20':ceramic green sheet

30: Internal electrode layer

30': Conductive adhesive coating layer

40:External electrode

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

FIG. 2 is a schematic cross-sectional view schematically illustrating the structure of an unfired MLCC body.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, matters other than matters specifically mentioned in this specification (for example, the composition of the conductive adhesive or its properties) are matters necessary for the implementation of the present invention. (For example, specific methods regarding the preparation of raw materials for the glue and application to the substrate, the structure of electronic parts, etc.) can be implemented based on the technical content taught in this specification and the general technical knowledge of practitioners in the field. . In addition, the expression "A~B" indicating a numerical range in this specification means A or more and B or less.

[Conductive glue]

The conductive adhesive disclosed in this article contains (A) conductive powder, (C) binder resin, (D) solvent, (E) carboxylic acid dispersant, and (F) nonionic surfactant as main components . The conductive glue may additionally contain (B) dielectric powder. Then, the conductive paste is supplied to a base material and dried to form a coating film, and the coating film is fired to form a conductive sintered body (in other words, an electrode layer). The electrode layer is formed by sintering (A) conductive powder and (B) dielectric powder as optional components after the organic components in the conductive paste disappear. These (A) conductive powder and (B) dielectric powder, which are the main components of the electrode layer, are usually dispersed in organic components to form a gel and are imparted with appropriate viscosity and fluidity. The organic component here includes (C) binder resin, (D) solvent, (E) carboxylic acid dispersant, and (F) nonionic surfactant. Hereinafter, the conductive adhesive disclosed herein will be described based on each element.

(A) Conductive powder

Conductive powder is a material used mainly to form conductive objects (which may be conductive films) with high electrical conductivity (hereinafter referred to as "conductivity") such as electrodes, wires, or conductive films in electronic components. Therefore, powders of various materials having required conductivity can be used without particular limitation as the conductive powder. As such a conductive material, for example, Examples include: nickel (Ni), palladium (Pd), platinum (Pt), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium (Rh), osmium (Os), iridium ( Individual metals such as Ir), aluminum (Al), and tungsten (W), as well as 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, the conductive paste used for forming the internal electrode layer of the MLCC preferably contains conductive powder with a melting point lower than the sintering temperature of the dielectric layer (for example, about 1300 ℃) metal species. Examples of such metal species include noble metals such as rhodium, platinum, palladium, copper, and gold, and base metals such as nickel. These metals may suitably contain any one type or two or more types. Among them, from the viewpoint of melting point and electrical conductivity, it is preferable to contain noble metals such as platinum and palladium, and from the viewpoint of stability and low price, it is preferable to contain nickel. For example, particles in which the surface of nickel particles is coated with a noble metal such as silver may be included.

There are no particular limitations on the method for producing the conductive powder or the size or shape of the particles constituting the conductive powder. For example, considering the calcination shrinkage, the range may be limited to the minimum size of the target electrode (typically, the thickness and/or width of the internal electrode layer). The conductive glue disclosed herein is preferably a conductive powder having an average particle diameter of 200 nm or less because its advantages can be fully exerted. The average particle diameter of the conductive powder may be 180 nm or less, may be 160 nm or less, for example, may be 150 nm or less, or may be 100 nm or less.

In addition, in this specification, the "average particle diameter (D _B )" of conductive powder and 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 is the value calculated by the following formula: D _B =6/(S×ρ) (the sphere volume is equivalent to the diameter). The specific surface area will be described later.

For example, in the application of forming an internal electrode layer of a small and large-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 lamination direction). In other words, it is preferable to substantially not contain coarse particles exceeding the thickness of the internal electrode layer. From this viewpoint, for the conductive powder, for example, the cumulative 90% particle diameter (D ₉₀ ) is preferably not more than 0.8 μm, more preferably not more than 0.6 μm, for example, not more than 0.4 μm. If the cumulative 90% particle diameter is equal to or less than the specified value, the conductive film can be stably formed. In addition, the surface roughness of the formed conductive 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 diameter of the conductive powder is not particularly limited, and may be, for example, 5 nm or more, approximately 10 nm or more, for example, 30 nm or more, and typically is 50 nm or more, for example, 100 nm or more. By not having the average particle diameter be too small, an excessive increase in the surface energy (activity) of the particles constituting the conductive powder can be suppressed, and aggregation of the particles in the conductive glue can be suppressed. In addition, the density of the glue coating layer can be increased, and a conductor film with high electrical conductivity or high density can be preferably formed.

The specific surface area of the conductive powder also depends on the composition of the conductive powder, so it is not strictly limited. It can be about 30 m ² /g or less, for example, 20 m ² /g or less, typically 10 m ² /g or less, preferably It is ^1m2 /g~ ^8m2 /g, for example, it is ^2m2 /g~ ^6m2 /g. Thereby, aggregation in the glue can be better suppressed, and the homogeneity or dispersion and storage stability of the glue can be better improved. In addition, a conductor film excellent in electrical conductivity can be realized more stably. In addition, the specific surface area refers to the amount of gas adsorption measured by, for example, a gas adsorption method using nitrogen (N ₂ ) gas as an adsorbent (constant volume adsorption method), and is determined by the BET method (for example, the BET one-point method). calculated value.

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

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

The content ratio of the conductive powder is not particularly limited. When the total conductive adhesive is 100 mass %, it can be about 30 mass % or more, typically 40 mass % to 95 mass %, for example, 45 mass % to 60% by mass. By satisfying the above range, a conductor layer with high electrical conductivity or high density can be preferably realized. In addition, the workability of glue or film formation can be improved.

(B) Dielectric powder

In addition to the (A) conductive powder, the conductive glue disclosed herein may contain (B) dielectric powder as an optional component as a component that mainly constitutes the fired conductor film. The dielectric powder is a component that, by being disposed between the particles constituting the conductive powder, suppresses low-temperature heat transfer of the conductive powder when, for example, the conductive glue is fired. Sintering, or the thermal shrinkage rate and calcining shrinkage history or the thermal expansion coefficient of the calcined conductive film can be adjusted. The role of dielectric powder can be various. In particular, the dielectric powder contained in the conductive glue used for the internal electrode layer of MLCC has the same or similar composition as the dielectric layer, thereby improving the performance of the dielectric layer and It is preferable that the coexisting material of the internal electrode layer is sintered to function better.

The dielectric constant of the dielectric powder is not particularly limited and can be appropriately selected depending on the intended use. As an example, regarding the dielectric powder used in the conductive paste for forming the internal electrode layer of a high-dielectric-constant MLCC, the relative dielectric constant is typically 100 or more, preferably 1000 or more, for example, 1000~ Around 20,000. The composition of such dielectric powder is not particularly limited, and one or two or more types of inorganic materials or amorphous materials can be appropriately used depending on the application. 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. with ABO ₃ Metal oxides with a perovskite structure, or titanium dioxide (rutile), titanium pentoxide, hafnium oxide, zirconium oxide, alumina, forsterite, niobium oxide, barium neodymate titanate, rare earths Element oxides and other metal oxides are typical examples. In the paste for the internal electrode layer, the dielectric powder may preferably be composed of barium titanate (BaTiO ₃ ), strontium titanate, calcium zirconate (CaZrO ₃ ), or the like. On the other hand, of course, a dielectric material (and therefore an insulating material) whose relative dielectric constant is 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 limited to the minimum size 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 depending on the use of the glue, the size (fineness) of the electrode layer, and the like. Regarding the target conductive layer, from the viewpoint of easily ensuring predetermined conductivity, the average particle size of the dielectric powder is preferably smaller than the average particle size of the conductive powder. 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 , 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 may easily occur, which is not preferable. In this regard, as a rough standard, 0.03×D ₁ ≦D ₂ is preferred, 0.05×D ₁ ≦D ₂ is more preferred, and for example, 0.1×D ₁ ≦D ₂ may be used. For example, specifically, the average particle diameter of the dielectric powder is suitably approximately several nm or more, preferably 5 nm or more, and may be 10 nm or more. 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 used to form the internal electrode layer of the MLCC, the average particle size of the dielectric powder may be approximately several nm to several hundred nm, for example, 5 nm to 100 nm.

The content ratio of the dielectric powder is not particularly limited. For example, in the use of forming the internal electrode layer of MLCC, when the total conductive paste is 100 mass%, it can be about 0.2 mass% to 20 mass%, for example, 1 mass% to 15 mass%, 3 mass% ~10% by mass, etc. In addition, the ratio of the dielectric powder to 100 parts by mass of the conductive powder can 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, it is possible to appropriately suppress the low-temperature calcination of the conductive powder and improve the electrical conductivity, density, etc. of the calcinated conductor film.

(C)Binder resin

The binder resin is a material that functions as a binder among the organic components in the conductive adhesive disclosed herein. The binder resin typically contributes to the bonding between the powder contained in the conductive glue and the base material, and the bonding between the particles constituting the powder. In addition, the binder resin is dissolved in a solvent described below and functions as a medium (which may be a liquid medium). Thereby, the viscosity of the conductive glue is increased and the powder components are uniformly and stably suspended in the medium, which imparts fluidity to the powder and contributes to improvement in operability. The binder resin is a component that is premised on disappearing by calcination. Therefore, it is preferable that the binder resin is a compound burned when the conductor film is fired. Typically, it is preferable that the decomposition temperature is 500°C or lower regardless of the environment.

The composition of the binder resin is not particularly limited, and various known organic compounds used in such applications can be suitably used. Examples of such binder resins include rosin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyvinyl acetal-based resins, acrylic resins, urethane-based resins, and epoxy-based resins. Organic polymer compounds such as phenol resin, polyester resin, and vinyl resin. Any one of these may be used, or two or more types may be used in combination. It also depends on the combination with the solvent used, so it cannot be generalized. As mentioned above, as a binder resin for a conductive glue containing fine conductive powder or the like, for example, a cellulose-based resin and a polyvinyl acetal are preferred. combination.

Cellulose-based resin contributes to the improvement of the dispersibility of powder components such as conductive powder or dielectric powder in the medium. In addition, when the conductive adhesive is used for printing, etc., the shape of the printed body (coating film) Excellent characteristics or adaptability to printing operations etc., so it is better. Cellulose-based resin refers to all linear polymers and derivatives thereof containing at least β-glucose as a repeating unit. Typically, the compound may be a compound in which part or all of the hydroxyl groups in the β-glucose structure as a repeating unit are substituted with alkoxy groups, and derivatives thereof. Part or all of the alkyl group or aryl group (R) in the alkoxy group (RO-) may be substituted with ester groups such as carboxyl groups, nitro groups, halogens, or other organic groups, or may be unsubstituted. Specific examples of the cellulose-based resin include methylcellulose, ethylcellulose, propoxycellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylcellulose. Methylcellulose, hydroxypropyl ethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxypropylcellulose, carboxyethylmethylcellulose, cellulose acetate, cellulose butyrate, fiber Cellulose propionate, cellulose acetate phthalate, cellulose nitrate, cellulose sulfate, cellulose phosphate, etc.

The molecular weight of the cellulose-based resin is not particularly limited. For example, the number average molecular weight (Mn) may be 10,000 or more, more preferably 15,000 or more, for example, 20,000 or more, 30,000 or more, 50,000 or more, etc. The number average molecular weight (Mn) may be, for example, approximately 120,000 or less, for example, 110,000 or less, 100,000 or less, 80,000 or less, for example, 70,000 or less. The molecular weight distribution (Mw/Mn), which is the ratio of the number average molecular weight (Mn) and the weight average molecular weight (Mw), can be about 2 to 4, for example.

Polyvinyl acetal is preferable because the powder component has good dispersibility and is soft, and therefore has excellent adhesion to the printed body (wiring film), printability, etc. when the conductive adhesive is used for printing or the like. Polyvinyl acetal is a resin obtained by reacting an aldehyde with a polyvinyl alcohol-based resin and acetalizing it. Polyvinyl acetal contains may include Any one or more of a structural unit in which a continuous vinyl alcohol structural unit is acetalized with an aldehyde compound, an unreacted vinyl alcohol structural unit, and a vinyl acetate structural unit that is an unsaponified portion of a polyvinyl alcohol-based resin. All polymers and their derivatives. Typically, it may be a polyvinyl butyral resin (PVB) having a structure in which polyvinyl alcohol is acetalized with butanol. PVB improves both the flexibility and shape characteristics of the printed body, so it is better. In addition, the polyvinyl acetal may be a copolymer (including graft copolymerization) containing polyvinyl acetal as the main monomer and a secondary monomer copolymerizable with the main monomer. Examples of the submonomer include ethylene, ester, (meth)acrylate, vinyl acetate, and the like. The acetalization ratio in the polyvinyl acetal resin is not particularly limited, but is preferably 50% or more, for example.

The molecular weight of the polyvinyl acetal is not particularly limited. For example, the number average molecular weight (Mn) can be 10,000 or more, more preferably 15,000 or more, for example, 20,000 or more, 30,000 or more, 50,000 or more, etc. The number average molecular weight (Mn) may be, for example, approximately 120,000 or less, for example, 110,000 or less, 100,000 or less, 80,000 or less, for example, 70,000 or less. The molecular weight distribution (Mw/Mn), which is the ratio of the number average molecular weight (Mn) and the weight average molecular weight (Mw), can be about 2 to 4, for example.

These cellulose-based resins and polyvinyl acetal generally have poor compatibility. Therefore, a preferred aspect may be a configuration in which only a cellulose-based resin is used as the binder resin. However, as mentioned above, the polyvinyl acetal itself may have the function of imparting flexibility to the dried coating film of the conductive adhesive. In addition, it is considered that the combination of a carboxylic acid-based dispersant and a nonionic surfactant described below can also contribute to the uniform mixing of these cellulose-based resins and polyvinyl acetal. From the stated point of view, as a bond Agent resin, including both cellulose resin and polyvinyl acetal can also be a better form. The proportion of polyvinyl acetal in the total of polyvinyl acetal and cellulose resin is preferably about 80 mass% or less, more preferably about 70 mass% or less, and particularly preferably, for example, about 60 mass% or less. The proportion of polyvinyl acetal may be 0% by mass. However, for example, if it is 5% by mass or more, the effect of improving the flexibility of the coating film is easily exhibited, so it is preferable, more preferably 10% by mass or more, and particularly preferably 10% by mass or more. For example, 15% by mass or more.

The content of the binder resin is not particularly limited. In order to well adjust the properties of the conductive adhesive or the properties of the offset printing body (including the dry film), for example, the content of the binder resin may be 0.5 parts by mass or more, preferably 1 part by mass or more, based on 100 parts by mass of the conductive powder. , more preferably, the ratio is 1.5 parts by mass or more, for example, 2 parts by mass or more. On the other hand, the binder resin has the possibility of increasing the calcined residue, so it is undesirable to contain it excessively. From this viewpoint, the content of the binder resin can be 10 parts by mass or less, preferably 7 parts by mass or less, more preferably 6 parts by mass or less, for example, 5 parts by mass or less based on 100 parts by mass of the conductive powder. . Therefore, for example, the content of the binder resin in the conductive glue can be, for example, 0.1 mass% or more, preferably 1 mass% or more, for example, 2 mass% or more. In addition, the content of the binder resin in the conductive glue may be, for example, 5 mass% or less, preferably 4 mass% or less, for example, 3 mass% or less.

(D)Solvent

The solvent is a liquid medium used to bring the powder into a dispersed state among the organic components in the conductive adhesive disclosed herein. For example, it is an element used to impart excellent fluidity while maintaining the dispersibility. In addition, the solvent dissolves the binder resin and serves as Function for the medium liquid. This solvent is also a component that is presupposed to disappear by drying and calcining. The solvent is not particularly limited, and organic solvents used in such conductive adhesives can be suitably used. Although it also depends on the combination with a binder, for example, from the viewpoint of film formation stability, a high boiling point organic solvent with a boiling point of about 180°C or more and 300°C or less, for example, about 200°C or more and 250°C or less can be used. As the main component (component accounting for more than 50% by volume).

Specific examples of the solvent include: sclareol, citronellol, phytol, geranyllinalool, texanol, benzyl alcohol, phenoxyethanol, 1-phenoxy-2-propanol, and terpene Alcohol solvents such as pinol, dihydroterpineol, isoborneol, butylcarbitol, diethylene glycol; terpineol acetate, dihydroterpineol acetate, isoborneol acetic acid Ester solvents such as ester, carbitol acetate, diethylene glycol monobutyl ether acetate, etc.; mineral spirit, etc. Among these, alcohol-based solvents or ester-based solvents are preferably used.

The proportion of the (D) solvent in the conductive adhesive is not particularly limited. When the entire adhesive is 100% by mass, it may be approximately 70% by mass or less, typically 5% by mass to 60% by mass, for example, 30% by mass. Mass%~50 mass%. By satisfying the above range, appropriate fluidity can be imparted to the glue, and workability during film formation can be improved. In addition, the self-leveling properties of the glue can be improved to achieve a smoother surface conductor film.

(E) Carboxylic acid dispersant

The conductive adhesive disclosed herein is characterized by containing a carboxylic acid-based dispersant as a dispersant. The carboxylic acid-based dispersant is a preferable dispersant in terms of preferably suppressing the aggregation of the conductive powder in the conductive glue. For example, the carboxylic acid dispersant is a compound having one or more carbonyl groups (-C(=O) ^- ) in its molecular structure or a salt thereof. The carbonyl group is preferentially bonded to the surface of the particles constituting the conductive powder or dielectric powder, imparts an electric charge to the particle surface, and suppresses aggregation of the particles by its electrical repulsion. Carboxylic acid-based dispersants are preferred because they contribute to improving the uniform dispersibility of the powder in the glue in the above manner. The carboxylic acid-based dispersant is not limited thereto, and examples thereof include dispersants mainly composed of fatty acid salts such as carboxylic acid or polycarboxylic acid, and dispersants in which hydrogen atoms in a part of the carboxylic acid groups are substituted with alkyl groups. A dispersant based on a polycarboxylic acid partial alkyl ester compound, a dispersant based on a polycarboxylic acid alkylamine salt, and a polycarboxylic acid partial alkyl ester compound based on a part of the polycarboxylic acid having an alkyl ester bond. As the main dispersant, etc. Examples of carboxylic acid salts include alkali metal salts (for example, sodium salts or potassium salts) or alkaline earth metal salts (for example, magnesium salts or calcium salts). These compounds may be used individually by 1 type, and may be used in combination of 2 or more types suitably. The number average molecular weight of the carboxylic acid dispersant may be, for example, about 30,000 or less, preferably about 20,000 or less, for example, about 15,000 or less. The number average molecular weight of the carboxylic acid-based dispersant may be, for example, about 100 or more, may be about 200 or more, for example, may be about 400 or more.

This kind of carboxylic acid dispersant is more effective than other anionic dispersants (such as sulfonic acid dispersants, phosphoric acid dispersants, etc.). Compared with other anionic dispersants, it can be added in a small amount to Exhibit the prescribed dispersion effect. However, if the carboxylic acid-based dispersant acts excessively on fine conductive powder and dielectric powder, the bonding between particles caused by the binder resin will be hindered, making it difficult to realize the bonding between particles caused by the binder resin. The soft bond is therefore suboptimal. From this viewpoint, the addition amount of the carboxylic acid dispersant may be 0.05% by mass or more, for example, preferably 0.1% Quality% or more. The addition amount of the carboxylic acid dispersant may be 1.5% by mass or less, for example, preferably 1% by mass or less.

(F)Nonionic surfactant

In addition, the conductive adhesive is characterized by containing a nonionic surfactant together with the carboxylic acid-based dispersant. By coexisting with the carboxylic acid dispersant, the nonionic surfactant has the following effect: it does not adversely affect the dispersion effect of the conductive powder and the like brought by the carboxylic acid dispersant and better assists the dispersion effect. , improve the flexibility of the formed coating film. The details are not clear, but it is assumed that not only the carboxylic acid-based dispersant but also the nonionic surfactant is bonded to the surface of the conductive powder, etc., so that the binder resin effectively acts on the conductive powder, etc., maintaining the softness between the particles. combine.

Here, the nonionic surfactant preferably has an HLB value of 3 or more. When the HLB value is 3 or more, the effect of improving the flexibility of the coating film can be better exerted. The HLB value is preferably 3 or more, more preferably 5 or more, still more preferably 8 or more, and particularly preferably 10 or more. The upper limit of the HLB value is not particularly limited, and may be 20, for example. Examples of such nonionic surfactants include: glycerol monostearate [3], sorbitan monostearate [4.7], sorbitan monolaurate [8.6], sorbitol Anhydride monopalmitate [6.7], sorbitan monostearate [4.7], sorbitan distearate [4.4], sorbitan monooleate [4.3], sorbitol Anhydride sesquioleate [3.7], polyoxyethylene (20) sorbitan monolaurate [16.7], polyoxyethylene (6) sorbitan monolaurate [13.3], polyoxyethylene sorbitan Sugar alcohol anhydride monopalmitate [15.6], polyoxyethylene (20) sorbitan monostearate [14.9], polyoxyethylene (6) sorbitan monostearate [9.6], polyoxyethylene (6) sorbitan monostearate [9.6], oxyethylene mountain Ribitol tristearate [14.9], polyoxyethylene (20) sorbitan monooleate [14.9], polyoxyethylene (6) sorbitan monooleate [10], polyoxyethylene Oxyethylene sorbitan trioleate [11.0], polyoxyethylene oleyl ether [12.4], polyoxyethylene lauryl ether [9.5], polyoxyethylene stearate [15.0], etc. In addition, the numerical value shown in parentheses after the substance name of the nonionic surfactant exemplifies the HLB value.

The amount of nonionic surfactant added also depends on the type of nonionic surfactant used, so it is not strict. However, as a range in which the effect of improving the flexibility of the coating film can be confirmed, for example, relative to the conductive adhesive It can be about 0.08 mass% or more, preferably 0.1 mass% or more, more preferably, for example, 0.15 mass% or more. On the other hand, if the addition amount of the nonionic surfactant is too large, the coating film will stretch too much and the film hardness cannot be obtained, which is undesirable from this point of view. The nonionic surfactant may be added in an amount of approximately 1% by mass or less relative to the conductive adhesive, preferably 0.9% by mass or less, more preferably 0.8% by mass or less, for example.

Other additives

Furthermore, the conductive adhesive disclosed herein may contain various organic additives that can be used in known general conductive adhesives within the scope that does not significantly impair the essence of the present invention. Examples of such organic additives include thickeners, plasticizers, pH adjusters, stabilizers, leveling agents, defoaming agents, antioxidants, preservatives, and colorants (pigments, dyes, etc.). These organic additives may be contained individually, or may be contained in combination of 2 or more types. In addition, the content of the organic additive can be appropriately adjusted within a range that does not significantly hinder the properties of the conductive adhesive disclosed herein. For example, the organic additive may be contained in an appropriate proportion depending on the properties and purpose of the organic additive. For example, additive one Generally speaking, it can be included 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, relative to the total mass of the powder component. Furthermore, it is not preferable to contain components that inhibit the sinterability of the conductive powder or inorganic powder, or additives in amounts that inhibit these. From this point of view, when organic additives are included, the total content of these components is preferably about 5% by mass or less of the entire conductive adhesive, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. .

Such conductive glue can be preferably prepared by, for example, preliminarily combining (A) conductive powder, (B) dielectric powder, and (C) binder resin or (E) carboxylic acid dispersant. , (F) nonionic surfactant, etc. are dispersed in (D) solvent respectively, and these slurries are mixed. When preparing the slurry, mixing devices or dispersing devices such as ball mills, bead mills, colloid mills, hammer mills, mortars, disc crushers, roller mills, etc. can be appropriately used. The conductive adhesive can be supplied to the base material by various known supply methods without particular limitation. Examples of such supply methods include printing methods such as screen printing, gravure printing, offset printing, and inkjet printing, spray coating methods, dip coating methods, and the like. In particular, when forming the internal electrode layer of an MLCC, a gravure printing method, a screen printing method, or the like that enables high-speed printing can be preferably used.

[use]

As described above, the conductive glue disclosed herein has good dispersibility of the particles contained in the conductive glue even when a glue containing fine conductive powder with an average particle diameter of 200 nm or less is prepared. In addition, when a coating film is formed from the conductive glue, the dispersibility of particles in the coating film can be preferably maintained and flexibility can be imparted to the coating film. Due to this characteristic, when printing the conductive glue onto the dielectric green sheet When the conductive powder is used, a coating film (printed body) with good continuity and good adhesion can be formed. In addition, since the coating film has sufficient flexibility, problems such as cracking or peeling of the coating film are unlikely to occur even when the dielectric green sheets on which the coating film is formed are overlapped, pressed, or cut. Furthermore, even when the cut dielectric green sheet (laminate) is fired, the growth of crystal grains of the conductive powder can be preferably suppressed, and the fired dielectric can be maintained at a high level. The withstand voltage of the layer. As a result, the internal electrode layer in the laminated ceramic electronic component can be formed into a thin layer with low resistance. The conductive adhesive disclosed herein can be preferably used to form the internal electrode layer of a small MLCC with each side being 5 mm or less, for example, 1 mm or less. In particular, it can be suitably used to produce the internal electrodes of a small, large-capacity MLCC in which the thickness of the dielectric layer is 1 μm or less.

In addition, in this specification, "ceramic electronic component" is a general term indicating an electronic component having 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 (HTCC) substrates, low temperature fired laminated ceramics (Low Temperature Co-fired) including ceramic base materials Ceramics, LTCC) substrates, etc. are typical examples included in the "ceramic electronic components" described here.

Examples of ceramic materials constituting the ceramic base material include barium titanate (BaTiO ₃ ), zirconium oxide (zirconium dioxide: ZrO ₂ ), magnesium oxide (magnesium oxide: MgO), and alumina (alumina: Al ₂ O ₃ ), silicon dioxide (silicon oxide: SiO ₂ ), zinc oxide (ZnO), titanium oxide (titanium dioxide: TiO ₂ ), cerium oxide (cerium dioxide: CeO ₂ ), yttrium oxide (yttrium trioxide: Y ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), dysprosium oxide (Dy ₂ O ₃ ), tungsten oxide (Ho ₂ O ₃ ), gallium oxide (Gd ₂ O ₃ ) and other oxide materials; cordierite (2MgO. 2Al ₂ O ₃ .5SiO ₂ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), forsterite (2MgO.SiO ₂ ), 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 (silicon nitride: Si ₃ N ₄ ), nitride-based materials such as aluminum nitride (aluminum nitride: AlN), boron nitride (boron nitride: BN); silicon carbide (silicon carbide: SiC), boron carbide Carbide-based materials such as (tetraboron monocarbide: B ₄ C); hydroxide-based materials such as hydroxyapatite, etc. These may be contained individually by 1 type, may be contained in the form of a mixture of 2 or more types, or may be contained in the form of a complex which combined 2 or more types.

[Multilayer Ceramic Capacitors]

FIG. 1 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 are provided on the side surfaces of the multilayer wafer (capacitor portion) 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, which is a capacitor structure including a dielectric layer 20 and a pair of internal electrode layers 30 sandwiching the dielectric layer 20 and connected in parallel. The dielectric layer 20 of the MLCC 1 is made of ceramic. The internal electrode layer 30 is composed of a calcined body of the conductive paste disclosed herein. Such MLCC1 is preferably produced by the following procedure, for example.

FIG. 2 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) as a base material is first prepared. Here, for example, ceramic powder as a dielectric material is mixed with a binder, an organic solvent, and the like to prepare a paste for forming a dielectric layer. Next, a plurality of unfired ceramic green sheets 20' are prepared by supplying the prepared glue in a thin layer on a carrier sheet using a doctor blade method or the like.

Next, prepare the conductive glue disclosed in this article. Specifically, at least conductive powder (A), dielectric powder (B), binder resin (C), solvent (D), and (E) carboxylic acid dispersant and (F) nonionic interface are prepared The activating agent is prepared in a predetermined ratio, stirred and mixed, thereby preparing a conductive adhesive. Then, the prepared glue is supplied to the prepared ceramic green sheet 20' so as to have a predetermined pattern and a required thickness (for example, 1 μm or less) to form the conductive glue coating layer 30'. The dispersion stability of the conductive adhesive disclosed in this article is significantly improved. Therefore, during mass production of MLCC, even if the formation (printing) of the conductive adhesive coating layer 30' on the ceramic green sheet 20' continues for a long time, the properties of the conductive adhesive are stable, so the printing quality can be improved. Well stabilized.

The prepared ceramic green sheets 20' with the coating layer 30' are laminated in multiple sheets (for example, hundreds to thousands of sheets) and are pressure-bonded. The laminated pressure-bonded body is cut into a wafer shape if necessary. Thereby, the unfired laminated body 10' can be obtained. Then, the produced unfired laminated body 10' is fired under appropriate heating conditions (for example, a temperature of approximately 1000°C to 1300°C in a nitrogen-containing environment). Thereby, the ceramic green sheet 20' and the conductive paste coating layer 30' are fired simultaneously. The ceramic green sheet is fired to become the dielectric layer 20 . Conductive glue The coating layer 30' is fired to become the internal electrode layer 30. The dielectric layer 20 and the 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 the binder and dispersion medium disappear, a binder removal treatment can also be performed (for example, in an oxygen-containing environment and at a temperature lower than the calcination temperature: for example, about 250°C~ Heat treatment at 700°C). Thereafter, the external electrode material is applied to the side surface of the laminated wafer 10 and burned to form the external electrode 40 . With this, MLCC1 can be manufactured.

Several embodiments related to the present invention will be described below, but the present invention is not intended to be limited to those shown in the embodiments.

[Preparation of conductive adhesive]

The conductive adhesives of Examples 1 to 35 were prepared by mixing conductive powder, dielectric powder, binder resin, anionic dispersant, nonionic surfactant, and solvent.

As the conductive powder, nickel powder with an average particle diameter of 180 nm was used at a ratio of 50% by mass relative to the entire glue. As the dielectric powder, barium titanate powder with an average particle diameter of 50 nm was used at a ratio of 5% by mass relative to the entire gel. In addition, dihydroterpineol was used as a solvent, and the remainder minus the following binder resin, anionic dispersant, and nonionic surfactant was used as the solvent.

The binder resin is used in a proportion of 2.5% by mass relative to the entire glue. As a binder resin, ethyl cellulose (EC) and polyvinyl butyraldehyde (PVB) were mixed and used in the formulation shown in Tables 1 to 3 below. Furthermore, by Since the molecular weight of PVB has a range, we are going to calculate the following three types of PVB with different molecular weights.

PVB1: about 2.3×10 ⁴

PVB2: about 5.3×10 ⁴

PVB3: about 6.6×10 ⁴

As anionic dispersants, the following four types are prepared. There are typically three types of anionic dispersants: carboxylic acid-based, sulfonic acid-based, and phosphoric acid-based surfactants. Among these, carboxylic acid-based surfactants range from those with smaller molecular weights to those with larger molecular weights. In contrast, sulfonic acid-based surfactants And the molecular weight of phosphoric acid-based surfactants becomes relatively smaller. Therefore, two types of carboxylic acid-based surfactants are prepared: one with a large molecular weight and one with a small molecular weight. In addition, the proportion of the anionic dispersant relative to the entire gel is shown in the following Tables 1 to 3, and varies between 0.1 mass % and 1.4 mass %.

AD1: Carboxylic acid dispersant, molecular weight 14,000

AD2: Carboxylic acid dispersant, molecular weight 490

AD3: Sulfonic acid dispersant, molecular weight 490

AD4: Phosphoric acid dispersant, molecular weight 420

As the nonionic surfactant, prepare the following three types, mix them appropriately, and use them by changing HLB between 1.8 and 12.4 as shown in Table 1 to Table 3 below. In addition, the HLB when a plurality of surfactants are blended is calculated by weighting the HLB of each surfactant based on the blending amount. In addition, the proportion of the nonionic surfactant relative to the entire gel is as shown in Table 1 to Table 3 below, and varies between 0.05 mass % and 1.2 mass %.

ND1: Polyoxyethylene (10) oleyl ether, HLB is 14.5

ND2: Sorbitan monooleate, HLB is 4.3

ND3: Sorbitan trioleate, HLB is 1.8

[Evaluation of softness]

In order to evaluate the flexibility of the electrode film obtained by printing the conductive glue, dried coating films of the conductive glue of each example were prepared. Specifically, the conductive adhesive of each example was supplied onto a PET film with a thickness of approximately 250 μm using a film applicator, and dried at 100° C. for 15 minutes to form a dry coating film.

Next, a test piece with a size of 40 mm × 10 mm was cut out from the obtained dry coating film, and both ends of the test piece in the longitudinal direction were fixed to a pair of sample fixing base materials for tensile testing using double-sided tape. The test piece and the base material for fixing the sample are placed on a hot plate set at 70°C. With one of the base materials fixed, the other base material is moved at a certain speed in the horizontal direction to measure The elongation of the test piece at break. Furthermore, the elongation of the dried coating film of each example was standardized based on the elongation of the dried coating film of Example 4, and the results of evaluation based on the following indexes are shown in the "Softness" section of Tables 1 to 3. bar. Furthermore, the evaluation of the elongation indicates whether the relative value of the elongation of the dry coating film in each example is as shown in the following four stages when the elongation of the dry coating film in Example 4 is taken as "100%". Any range. In addition, the index "●" indicates that when the relative value of the elongation is 160% or more, the dry coating film is excessively elongated and the strength is too weak, so it is judged to be unsatisfactory characteristics.

×: Less than 110% (hard and brittle)

△: More than 110% and less than 120% (softness is acceptable)

○: 120% or more and less than 160% (good softness)

●: More than 160% (excessive elongation)

[Evaluation of dispersion]

The dispersibility of the particles of the conductive powder and the dielectric powder in the electrode film obtained by printing the conductive paste was evaluated according to the following procedure. Specifically, the prepared conductive adhesive of each example was supplied to a PET base material with a thickness of about 250 μm using an applicator, and dried at 110° C. for about 15 minutes to form a dry coating film. Then, the dried coating film was hollowed out into a disc shape with a diameter of 20 mm, and five measurement samples for each example were prepared. Then, the mass, radius, and thickness of the measurement sample are measured, and the dry density (bulk density) of the dried coating film is calculated based on the following equation.

(Dry density)=(mass)/{π×(radius) ² ×(thickness)}

In addition, the mass and radius were measured once for each measurement sample. The thickness was measured at three places on each measurement sample using a digital electronic micrometer (K351C manufactured by Anritsu Co., Ltd.), and the average value was used. The dry density is the arithmetic mean of values obtained for five measurement samples.

Then, the relative density of the dried coating film of each example was calculated when the dry density of the dried coating film of Example 3 was 100, and the dispersibility was evaluated in four stages based on the following indexes. Furthermore, for the dry coating film with a relative density of 95 or more, use a scanning electron microscope (SEM) to observe the dry coating film from the PET substrate side (10,000 times), and remove the conductive particles in the dry film. Whether there is no obvious unevenness in the filling properties of dielectric particles will be reflected in the evaluation. The results are shown in the "Dispersibility" column of Tables 1 to 3.

×: Relative density is less than 90

△: Relative density is more than 90 and less than 95

○: The relative density is 95 or more, and there is no unevenness in filling properties as measured by SEM observation.

●: The relative density is above 95, and the filling property observed by SEM is obviously uneven.

[Comprehensive evaluation]

In addition, for the dry coating film, it was evaluated whether the softness and dispersibility were balanced in a good balance. When the balance was achieved, "○" was indicated in the "Comprehensive" column of Tables 1 to 3. When the balance was not achieved, "○" was indicated. In the case of , "×" is indicated in the "General" column of Tables 1 to 3. In addition, regarding the comprehensive evaluation, when both softness and dispersibility evaluation results are ○, or a combination of ○ and Δ, it is determined that both softness and dispersibility are achieved. Furthermore, when one × or ● is included, or when both are Δ and there is no ○, it is determined that both flexibility and dispersibility cannot be achieved.

As shown in Table 1, Examples 1 to 5 are examples in which a nonionic surfactant is not added to a conductive adhesive that uses both EC and PVB as a binder resin, and the amount of an anionic dispersant is changed. In this case, it was found that when the addition amount of the anionic dispersant is a small amount of 0.1% by mass, the flexibility of the obtained dry coating film is high, but the dry density of the coating film becomes low.

This is considered to be because the absolute amount of the dispersant was too small, so the conductive powder and dielectric powder agglomerated and the dispersion state was not good, and a dense electrode film could not be obtained. Furthermore, it was found that as the added amount of the anionic dispersant increases to about 0.5% by mass, the softness of the dry coating film decreases, and the dispersibility of the conductive powder and dielectric powder in the dry coating film tends to improve. Discovered dispersion that improves both softness and dispersibility The amount of agent added. Furthermore, it was found that if the added amount of the dispersant is excessively high and is 1.4% by mass, the dispersibility of the conductive powder and the dielectric powder will be worsened. From these results, it was confirmed that the dry coating films of Examples 1 to 5 that did not contain a nonionic surfactant were unable to achieve both flexibility and dispersibility in a well-balanced manner.

On the other hand, Examples 6 to 11 are examples in which a nonionic surfactant is included in various addition amounts in addition to an anionic dispersant. The addition amount of the anionic dispersant was set to 0.5% by mass, which confirmed good dispersibility of the conductive powder and the dielectric powder in Examples 1 to 5. According to Examples 6 to 11, it was confirmed that by adding a nonionic surfactant in addition to the anionic dispersant, a dry coating was obtained while maintaining good dispersibility of the conductive powder and the dielectric powder. The flexibility of the film tends to increase together with the added amount of the nonionic surfactant. However, it was found that when the added amount of the nonionic surfactant is 0.05% by mass, the flexibility of the dry coating film may not be sufficiently improved. The amount of the nonionic surfactant added can be, for example, 0.1% by mass or more. In addition, it was found that if the added amount of the nonionic surfactant is too high, the flexibility of the dried coating film will be too high and the coating film will be excessively stretched, which is undesirable. The amount of the nonionic surfactant added may be, for example, less than 1.2% by mass, for example, about 1% by mass or less. Furthermore, for example, it can be seen from the comparison between Example 8 and Example 12 that even if the nonionic surfactant is added alone to the conductive glue, it does not show the effect of improving the dispersibility of the conductive powder and the dielectric powder. Therefore, it can be seen that It is necessary to use an anionic dispersant and a nonionic surfactant in combination.

Next, Examples 8 and 13 to 17 are examples of changing the HLB value of the nonionic surfactant. According to the results of Examples 13 to 17, it can be seen that the dry coating film Softness is roughly proportional to the HLB value of the nonionic surfactant. The larger the HLB value, the higher the softness. Furthermore, it is found that the HLB value of the nonionic surfactant is 1.8, which is too low, and a sufficient flexibility-improving effect of the coating film cannot be obtained. For example, it can be set to 2 or more or 3 or more. Furthermore, although not shown specifically, the relationship between the HLB value of the nonionic surfactant and the softness-improving effect was confirmed. There was almost no influence of component differences due to different manufacturers of the nonionic surfactant. .

As shown in Table 2, Examples 18 to 21 are examples in which PVB is not used as the binder resin, and only the conventional EC is used as the binder resin, and the addition amount of the nonionic surfactant is changed. PVB has the effect of improving the softness of the dried coating film and improving the adhesion. Therefore, although it is not clearly shown in Table 2, in Example 18 which does not contain PVB, for example, compared with Example 3, the elongation of the dry coating film decreased by about 5% or more. In these Examples 18 and 3, the addition amount of the anionic dispersant was 0.2% by mass, and the dispersion state of the conductive powder and the dielectric powder was good, but the flexibility of the dried coating film was insufficient. In contrast, it was found that the combination of anionic dispersant and nonionic interfacial activity In Examples 20 to 22 of the agent, only EC was used as the binder resin, but the flexibility of the dried coating film was improved. In addition, it was also confirmed that, similarly to the case of using EC and PVB in combination, if the added amount of the nonionic surfactant is excessive, the flexibility of the dried coating film becomes too high and the coating film stretches excessively, which is undesirable. Furthermore, it was confirmed that even when the composition of the binder resin is different, the added amount of the nonionic surfactant can be less than about 1.2 mass %, for example, about 1 mass % or less.

In addition, Examples 22 to 23 are examples in which the ratio of EC and PVB of the binder resin was changed relative to Example 8. Compared with the case of using only EC, PVB has the effect of imparting flexibility to the dry coating film and improving the adhesion. It was confirmed that in Example 22 in which the amount of PVB was small, it was difficult to exhibit the effect of improving the flexibility of the dry coating film by the combined use of the nonionic surfactant, similarly to the cases of Examples 18 to 21. However, the greater the proportion of PVB in Examples 22 to 23, the higher the actual elongation of the dry coating film, and the combined use effect of the nonionic surfactant is easily exhibited. In addition, Examples 24 to 25 are examples in which the molecular weight of PVB in the binder resin was changed. It was confirmed that as the molecular weight of PVB becomes smaller, the elongation of the dry coating film becomes larger, and the dispersibility of the conductive powder and the dielectric powder also becomes higher. On the contrary, it was confirmed that when the molecular weight of PVB becomes large, the elongation of the dry coating film decreases, and the dispersibility of the conductive powder and the dielectric powder also becomes relatively poor. According to these opinions, the amount of PVB added should not be too much, and the molecular weight should not be too large.

As shown in Table 3, Examples 4, 8, and 26 to 35 are examples in which the type of anionic dispersant and the amount of added nonionic surfactant were changed. From these results, it was confirmed that in order to achieve both flexibility and dispersibility of the dry coating film, the most important dispersant used in combination with the nonionic surfactant is the carboxylic acid dispersant. It is also known that even if the anionic dispersant is the same, the effect of improving the dispersion state of the conductive powder and the dielectric powder in the sulfonic acid or phosphoric acid dispersant is small, and even in the case of improving the dispersion (for example 35), the softness of the coating film cannot be improved by using a nonionic surfactant in combination. Furthermore, it was confirmed that as long as the dispersant combined with the nonionic surfactant is a carboxylic acid dispersant, the molecular weight can be increased or decreased.

By using the conductive glue disclosed herein, even when the average particle size of the conductive powder is fine, the dispersibility of the powder in the dry coating film can be maintained well, and the flexibility of the dry coating film can be improved. Thus, for example, in the manufacturing of MLCC, the conductive paste is used to print internal electrodes on the dielectric green sheet. Under this condition, the adhesion and adhesion between the green sheet and the dry coating film can be well maintained. As a result, it is possible to suppress the occurrence of cracks or peeling of the electrode layer, or the decrease in withstand voltage in the subsequent steps of lamination, pressure bonding, and baking. This enables the manufacture of MLCCs with high quality and reliability such as withstand voltage. Although the present invention has been described in detail above, these are merely examples, and various changes can be made without departing from the gist of the present invention.

1: Multilayer ceramic capacitor (MLCC)

10: Multilayer wafer (capacitor part)

20: Dielectric layer

30: Internal electrode layer

40:External electrode

Claims (7)

A conductive adhesive, including: conductive powder with an average particle size of less than 200 nm; a binder resin; a solvent in which the binder resin is dissolved; a carboxylic acid dispersant; and a nonionic surfactant, the conductive In the glue, the hydrophilic-lipophilic balance value of the nonionic surfactant is 10 or more, and the added amount of the nonionic surfactant relative to the entire conductive glue is 0.08 mass% or more and 1 mass% or less. . The conductive glue described in item 1 of the patent application further includes dielectric powder. The conductive adhesive described in claim 2, wherein the average particle diameter of the conductive powder based on the Boett method is D ₁ and the average particle diameter based on the Boett method of the dielectric powder is When the average particle diameter is D ₂ , 0.03×D ₁ ≦D ₂ ≦0.4×D ₁ is satisfied. The conductive adhesive as described in any one of items 1 to 3 of the patent application, wherein the binder resin includes cellulose-based resin and polyvinyl acetal. The conductive adhesive as described in Item 4 of the patent application, wherein the proportion of the polyvinyl acetal in the total of the polyvinyl acetal and the cellulose resin is 15 mass% or more and 80 mass% %the following. Conductive materials as described in any one of items 1 to 3 of the patent application scope The conductive powder includes at least one selected from the group consisting of nickel, platinum, palladium, silver and copper. The conductive adhesive described in any one of items 1 to 3 of the patent application is used to form internal electrode layers of laminated ceramic electronic components.