WO2021059925A1 - Electroconductive paste and method for producing electronic component using same - Google Patents

Abstract

The present invention provides an electroconductive paste for use in gravure printing, the paste containing an electroconductive powder, a dielectric powder, a binder resin, a solvent, and a dispersant. The dispersant included in this electroconductive paste contains a prescribed dicarboxylic acid-based dispersant, and demonstrates a viscosity V₄₀ of 5 or less at 25°C, when the shear velocity of the electroconductive paste is 40s^-1.

Description

Conductive paste and manufacturing method of electronic parts using it

The present invention relates to a conductive paste and a method for manufacturing an electronic component using the conductive paste.
This application claims priority based on Japanese Patent Application No. 2019-174262 filed on September 25, 2019, and the entire contents of the application are incorporated herein by reference. There is.

In the manufacture of electronic components, a method of forming an electrode layer by applying a conductive paste on a base material to form a coating film and firing the coating film is widely used. For example, in an example of a method for manufacturing a multilayer ceramic capacitor (MLCC), first, a plurality of unfired dielectric green sheets containing a dielectric powder or the like are prepared. Next, a conductive paste containing a conductive powder and a resin binder or the like is applied onto the dielectric green sheet and dried to form a coating film. Next, a plurality of dielectric green sheets with a coating film are laminated and pressed in the stacking direction to be pressed against each other. Next, after cutting this into a predetermined size, it is fired and integrally sintered. Then, external electrodes are formed on both end faces of the composite after firing. In this way, an MLCC having a structure in which a large number of dielectric layers made of a dielectric powder and an internal electrode layer made of a fired body of a conductive paste are alternately laminated is produced (see, for example, Patent Documents 1 and 2). ).

Japanese Patent Application Publication No. 2014-122368 Japanese Patent Application Publication No. 2012-174977

By the way, in recent years, as the performance of various electronic devices has improved, each electronic component mounted on the electronic device is also required to be thinner, smaller, and have a higher density. For example, in MLCCs, it is required to increase the capacitance while reducing the volume of MLCCs by reducing the thickness of one layer of the internal electrode layer and increasing the number of layers.

Under these circumstances, the gravure printing method has come to be used instead of the screen printing method for applying the conductive paste for forming the internal electrode layer. Since the gravure printing method has a faster printing speed than the screen printing method, it is excellent in productivity and can form a thin film-like coating film with stable quality. As described above, since the printing speed of gravure printing is high, if the viscosity of the conductive paste is adjusted to the same level as that of screen printing, the surface of the coating film may become rough and the unevenness may become large. This leads to distortion of the laminated structure and may lead to defects such as short circuit defects. Therefore, the conductive paste for gravure printing needs to be adjusted to have a lower viscosity than that for screen printing. However, when the conductive paste contains inorganic powders having different particle sizes and specific gravities, for example, the conductive powder and the dielectric powder, these inorganic powders are easily separated in the conductive paste, and a homogeneous coating film is formed. Is difficult to form.

The present invention has been made in view of these points, and an object of the present invention is to provide a conductive paste having a low viscosity, excellent gravure printability, and capable of forming a homogeneous coating film, and an electronic component using the conductive paste. The purpose is to provide a manufacturing method.

According to the present invention, a conductive paste for gravure printing containing (A) a conductive powder, (B) a dielectric powder, (C) a binder resin, (D) a solvent, and (E) a dispersant. Is provided. The above (E) dispersant has the following formula (1):

^{(However, A 1} and A ² in the formula (1) are independently hydrogen, alkali metal or alkaline earth metal.); Contains a dicarboxylic acid-based dispersant having a structural portion represented by. .. In 25 ° C., the viscosity _{V 40} at a shear rate ^{40 s -1} of the conductive paste is less 5 Pa · s.

In the art disclosed herein, including the dispersing agent, and by adjusting to the viscosity V _40, thereby realizing a conductive paste having properties suitable for gravure printing. As a result, printing sagging and the like are less likely to occur, and a coating film can be quickly and stably formed on the base material. Further, for example, other anionic dispersants (for example, monocarboxylic acid-based dispersants, dicarboxylic acid-based dispersants having no structural portion of the above formula (1), polycarboxylic acid-based dispersants, sulfonic acid-based dispersants). Compared with the case of using a dispersant (dispersant, phosphoric acid-based dispersant, etc.) or an amine-based dispersant, the dispersibility between the conductive powder and the dielectric powder is good, and a coating film having a smooth surface can be obtained. Can be formed.

In a preferred embodiment of the conductive paste disclosed herein, the dispersant (E) is based on the following formula (2):

^{(However, A 1} and A ² in the formula (2) are independently hydrogen, alkali metal or alkaline earth metal, R has 3 to 30 carbon atoms, and is linear, branched or saturated. Alternatively, it is an unsaturated aliphatic group.); It is a compound represented by.

In one preferred embodiment of the conductive paste disclosed herein, the ratio of the viscosity _{V 4} at a shear rate ^{4s -1} of the conductive paste for the viscosity _{V 40 (V 4 / V 40} ) is 7 or less. Thereby, the printability of the conductive paste can be improved.

In a preferred embodiment of the conductive paste disclosed herein, the ratio of the average particle size D _{1 of the (A) conductive powder to the average particle size D 2 of the (B) dielectric powder (D 1} / D ₂ ). However, it is 2 or more. As described above, the large difference in particle size between the conductive powder and the dielectric powder tends to significantly reduce the dispersibility of the inorganic powder (particularly the dielectric powder) in the conductive paste. As a result, it is particularly difficult to form a homogeneous coating. Therefore, the application of the techniques disclosed herein is highly effective.

In a preferred embodiment of the conductive paste disclosed herein, the solvent (D) contains a hydrocarbon-based solvent and a solvent other than the hydrocarbon-based solvent, and the solvent other than the hydrocarbon-based solvent has a boiling point of 230 ° C. It contains a solvent having the following and a solubility parameter of Fedors of 9.9 (cal / cm ³ ) of ^{0.5 or less.} As a result, the sheet attack phenomenon in which the solvent erodes the green sheet can be suppressed at a high level. In addition, the quick-drying property of the coating film can be improved to improve the productivity.

In a preferred embodiment of the conductive paste disclosed herein, the solvent other than the hydrocarbon-based solvent has a boiling point of 200 ° C. or higher and a solubility parameter of 10.0 (cal / cm ³ ) ^0.5 or higher. A second solvent having a boiling point of 220 ° C. or lower and a solubility parameter of 9.5 (cal / cm ³ ) of ^0.5 or less is included. As a result, the above-mentioned effect of suppressing the sheet attack phenomenon and the effect of enhancing quick-drying can be achieved at a higher level.

In addition, in this specification, "Solubility Parameter (SP) of Fedors" means the so-called solubility parameter calculated by the Fedors method described in RFFedors, Polymer Engineering Science, 14, p147 (1974). .. In the Fedors method, it is considered that the aggregation energy density and the molar molecular weight depend on the type and number of substituents, and the solubility parameter is calculated by the following formula: δ = [ΣE _coh / ΣV] ^0.5 (here, Σ). _Ecoh represents the aggregation energy, and ΣV represents the molar molecular weight.); The solubility parameter is a value unique to each compound. In the following, the solubility parameter of Fedors may be simply referred to as "SP value". The SI unit of the SP value is (J / cm ³ ) ^0.5 or (MPa) ^{0.5 , but (cal / cm 3} ) ^0.5 , which is conventionally used in the present specification, is used. Use. The unit of the SP value can be converted by the following formula: 1 (cal / cm ³ ) ^0.5 ≈ 2.05 (J / cm ³ ) ^0.5 ≈ 2.05 (MPa) ^{0.5 ;.} ..

In a preferred embodiment of the conductive paste disclosed herein, the solubility parameter of the whole solvent other than the hydrocarbon-based solvent is 9.8 (cal / cm ³ ) ^0.5 or less. As a result, the binder resin can be suitably dissolved, and the above-mentioned sheet attack phenomenon can be better suppressed.

The solubility parameter δ _all of the entire solvent is calculated by the following formula: δ _all (cal / cm ³ ) ^0.5 = Σ [The unique solubility parameter δ (cal / cm ³ ) ^{0.5 of each solvent.} The mass ratio of each solvent based on the reference (1)]; can be calculated. In other words, first, the product of the unique solubility parameter δ (cal / cm ³ ) ^{0.5 of} each solvent and the mass ratio is obtained, and these are added up to obtain the solubility parameter δ _{all of the} entire solvent.

In a preferred embodiment of the conductive paste disclosed herein, the dispersant (E) is 0.5% by mass or less when the total amount of the conductive paste is 100% by mass. As a result, an electrode layer having excellent electrical conductivity and denseness can be suitably realized.

In a preferred embodiment of the conductive paste disclosed herein, the binder resin (C) contains a polyvinyl acetal-based resin, and the weight average molecular weight of the polyvinyl acetal-based resin is 200,000 or less. As a result, the adhesiveness to the base material can be improved, and the uneven distribution of the dielectric powder can be suppressed.

The conductive paste disclosed herein can be used to form an internal electrode layer of a laminated ceramic electronic component. As a result, a smooth film in which the inorganic powder is homogeneously contained in the coating film can be preferably formed, and sheet attack can also be suppressed. As a result, it is possible to form an internal electrode layer having high continuity and homogeneity even in a thin film.

Further, the present invention provides a method for manufacturing an electronic component, which comprises applying the above-mentioned conductive paste onto a base material and firing the paste. By using the above-mentioned conductive paste, it is possible to suitably produce a small-sized, large-capacity, high-quality MLCC.

FIG. 1 is a cross-sectional view schematically showing the configuration of a multilayer ceramic capacitor. FIG. 2 is a cross-sectional view schematically showing the structure of the unfired laminate. FIG. 3A is an SEM observation image of Comparative Example 3, and FIG. 3B is an SEM observation image of Comparative Example 9. FIG. 4 is a conceptual diagram illustrating a method of calculating the dispersion index. FIG. 5 (A) is an SEM observation image of Example 5, and FIG. 5 (B) is an SEM observation image of Comparative Example 11. FIG. 6A is a cross-sectional profile of the surface roughness of Comparative Example 3, and FIG. 6B is a cross-sectional profile of the surface roughness of Example 1. FIG. 7 is a measurement chart of TG-DTA of Example 13, Example 19, and Example 9. 8 (A) is an SEM observation image of Example 19, FIG. 8 (B) is an SEM observation image of Example 16, and FIG. 8 (C) is an SEM observation image of Example 9.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification (for example, the constitution and properties of the conductive paste) and necessary for carrying out the present invention (for example, the method for preparing the conductive paste and the electrons). The configuration of parts, etc.) can be carried out based on the technical contents taught in this specification and the general technical common knowledge of those skilled in the art in the art. In the present specification, the notation of "X to Y (X, Y are arbitrary values)" indicating a numerical range means "preferably larger than X" and "preferably smaller than Y", as well as meaning X or more and Y or less. Includes the meaning of.

[Conductive paste for gravure printing]
The conductive paste disclosed herein contains (A) a conductive powder, (B) a dielectric powder, (C) a binder resin, (D) a solvent, and (E) a dispersant. .. In the following description, (A) conductive powder and (B) dielectric powder are referred to as components of "inorganic powder", and (C) binder resin, (D) solvent and (E) dispersant are referred to as "inorganic powder". Sometimes called "organic component". This conductive paste can be suitably used for gravure printing.

In the present specification, the term "coating film" refers to a conductive paste having a temperature lower than the boiling point of (C) binder resin and / or (E) dispersant, typically 200 ° C. or lower, for example 150 ° C. or lower. , Preferably a film-like body (dried product) dried at 120 ° C. or lower. When the conductive paste is dried at a temperature below the boiling point of the (C) binder resin and / or (E) dispersant, these components may remain in the coating film. The coating film includes all unfired (before firing) film-like bodies.
Further, in the present specification, the “electrode layer” refers to an inorganic powder such as (A) in which organic components in the conductive paste, for example, (C) binder resin, (D) solvent, and (E) dispersant disappear. ) A sintered body (fired product) obtained by firing a conductive powder and (B) a dielectric powder. The electrode layer includes a wiring (linear body), a wiring pattern, and a solid pattern. Hereinafter, each component will be described in order.

(A) Conductive powder The conductive powder is a component that imparts electrical conductivity to the electrode layer. The type of the conductive powder is not particularly limited, and among those conventionally known, one type can be used alone or two or more types can be appropriately used in combination depending on, for example, the use of the electrode layer. Examples of the conductive powder include simple base metals such as nickel (Ni), aluminum (Al), copper (Cu), and tungsten (W), gold (Au), silver (Ag), platinum (Pt), and palladium (Palladium). Examples thereof include simple precious metals such as Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os), and mixtures and alloys thereof. Examples of the alloy include nickel alloys such as nickel-copper (Ni-Cu) and nickel-aluminum (Ni-Al).

Although not particularly limited, for example, in an application for forming an internal electrode layer of MLCC, a metal species having a melting point lower than the sintering temperature of the dielectric layer (for example, about 1300 ° C.) may be used as the conductive powder. preferable. Of these, nickel-based particles are preferable because they are inexpensive and have an excellent balance between conductivity and cost. In addition, in this specification, "nickel-based particles" include all those containing a nickel component. Examples of nickel-based particles include a single nickel, the above-mentioned nickel alloy, and core-shell particles having nickel particles as a core, for example, core-shell particles in which the surface of nickel particles is coated with a noble metal such as silver.

The method for producing the conductive powder and the properties of the particles constituting the conductive powder, such as the size and shape of the particles, are not particularly limited. The size of the particles can be appropriately selected depending on, for example, the use of the conductive paste, the dimensions of the electrode layer, and the like. The size of the particles may be selected so as to be within the minimum dimensions of the target electrode layer (for example, the internal electrode layer), for example, the thickness and / or the width, in consideration of the firing shrinkage rate. Although not particularly limited, the average particle size D ₁ of the conductive powder may be approximately several nm to several μm, for example, 10 nm to 10 μm. In the present specification, the "average particle size" means a particle size corresponding to a cumulative total of 50% from the smallest particle size in the number-based particle size distribution based on electron microscope observation.

As an example, in an application for forming an internal electrode layer of an ultra-small to small MLCC, the average particle size D ₁ of the conductive powder is smaller than the thickness (length in the stacking direction) of the internal electrode layer, and is approximately 0.5 μm. Hereinafter, it may be typically 0.4 μm or less, preferably 0.3 μm or less. When the average particle size D ₁ is not more than a predetermined value, the surface irregularities can be suppressed to be small even in the thin film electrode layer. The average particle size D ₁ of the conductive powder may be approximately 0.01 μm or more, typically 0.05 μm or more, preferably 0.1 μm or more, for example 0.2 μm or more. When the average particle size D ₁ is equal to or greater than a predetermined value, the surface energy of the particles is suppressed, and aggregation in the conductive paste is suppressed. Therefore, a more homogeneous coating film can be realized.

The shape of the conductive powder may be, for example, substantially spherical, flake-shaped, needle-shaped, amorphous, or the like. Although not particularly limited, the conductive powder may be substantially spherical in applications for forming a thin-film electrode layer. As a result, the viscosity of the conductive paste can be kept low, and the handleability of the paste and the workability at the time of gravure printing can be improved. In addition, in this specification, "substantially spherical" means a form which can be regarded as a sphere (ball) as a whole, and has an average aspect ratio of about 1 to 2, for example, 1 to 1.5. Further, in the present specification, the "aspect ratio" is the length of the short side of the particles (a) when the particles constituting the conductive powder are observed with an electron microscope and a rectangle circumscribing the obtained observation image is drawn. ) To the ratio (b / a) of the length (b) of the long side. The average aspect ratio means the arithmetic mean value of the aspect ratios of a plurality of particles (for example, 100 particles).

Although not particularly limited, when the total content of the conductive paste is 100% by mass, the content ratio of the conductive powder is approximately 30 to 95% by mass, typically 35 to 80% by mass, for example, 40. It may be up to 60% by mass. By satisfying the above range, the handleability of the paste and the workability at the time of gravure printing can be improved. In addition, an electrode layer having excellent electrical conductivity and denseness can be preferably realized.

(B) Dielectric powder The dielectric powder is a component that is arranged between the conductive particles when the conductive paste is fired and relaxes the heat shrinkage of the conductive powder. Further, in the application of forming the internal electrode layer of the MLCC, it can also function as a co-material for improving the sintering bondability between the dielectric layer and the internal electrode layer. Although not particularly limited, the dielectric constant of the dielectric powder may be typically 100 or more, for example, about 1000 to 20000. However, the dielectric powder may have a relative permittivity of less than 100, and may be an insulating material.

The type of the dielectric powder is not particularly limited, and among conventionally known inorganic materials, for example, one type may be used alone or two or more types may be used in combination depending on the intended use. Examples of the dielectric powder include barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, zirconium titanate, zinc titanate, barium titanate niobate, calcium zirconate, and strontium zirconate. A metal oxide having a perovskite structure represented by ABO ₃ and other metal oxides such as titanium dioxide, titanium pentoxide, hafnium oxide, zirconium oxide, aluminum oxide, forsterite, niobium oxide, and barium titanate. Can be mentioned. As an example, in the application of forming the internal electrode layer of MLCC, for example, barium titanate, strontium titanate, calcium zirconate and the like can be preferably used.

The method for producing the dielectric powder and the properties of the particles constituting the dielectric powder, such as the size and shape of the particles, are not particularly limited. The size of the particles can be appropriately selected depending on, for example, the use of the conductive paste, the dimensions of the electrode layer, and the like. The size of the particles may be selected so as to be within the minimum dimensions of the target electrode layer (for example, the internal electrode layer), for example, the thickness and / or the width, in consideration of the firing shrinkage rate. Although not particularly limited, the average particle size D ₂ of the dielectric powder may be approximately several nm to several μm, for example, 1 nm to 1 μm. As an example, in an application for forming an internal electrode layer of an MLCC, the average particle size D ₂ of the dielectric powder may be approximately 5 nm or more, typically 10 nm or more, for example, 20 nm or more, 50 nm or more, and is approximately 0. It may be 5.5 μm or less, typically 0.3 μm or less, for example 0.2 μm or less, 0.1 μm or less.

Although not particularly limited, from the viewpoint of forming an electrode layer having excellent electrical conductivity, it is preferable that the average particle size D ₂ of the dielectric powder is smaller than the average particle size D _{1 of the conductive powder.} That is, D ₁ and D ₂ are preferably D ₁ > D ₂ . D ₁ and D ₂ preferably satisfy (D ₁ / D ₂ ) ≥ 2, more preferably (D ₁ / D ₂ ) ≥ 3, for example, (D ₁ / D ₂ ) ≥ 4. You may be. When the average particle size is significantly different in this way, the application of the techniques disclosed herein is particularly effective. Further, D ₁ and D ₂ may satisfy 50 ≧ (D ₁ / D ₂ ) or 20 ≧ (D ₁ / D ₂ ), for example, 10 ≧ (D ₁ / D _2). ) May be satisfied.

Although not particularly limited, when the total content of the conductive paste is 100% by mass, the content ratio of the dielectric powder is approximately 0.2 to 20% by mass, typically 1 to 15% by mass. For example, it may be 3 to 10% by mass. The content ratio of the dielectric powder to 100 parts by mass of the conductive powder may be approximately 3 to 35 parts by mass, typically 5 to 30 parts by mass, for example, 10 to 25 parts by mass. By satisfying the above range, it is possible to suitably suppress the heat shrinkage of the conductive powder and preferably realize a conductive layer having excellent electrical conductivity and denseness.

(C) Binder resin The binder resin is a component that adjusts the viscosity (fluidity) of the conductive paste and imparts adhesiveness to the coating film to bring the inorganic powders into close contact with each other and the inorganic powder and the base material. The binder resin is dissolved in the solvent (D) described later and can function as a vehicle. The binder resin is a component that is typically lost by firing. In other words, the binder resin is a compound that burns through when the coating film is fired. The binder resin may have, for example, a thermal decomposition temperature of 500 ° C. or lower.

The type of the binder resin is not particularly limited, and among the conventionally known organic compounds used for this type of application, for example, one type may be used alone or two or more types may be appropriately combined depending on the application. be able to. The binder resin is typically a thermoplastic resin. However, it may be a thermosetting resin. Examples of the binder resin include cellulose-based resin, polyvinyl acetal-based resin, polyvinyl alcohol-based resin, acrylic resin, urethane-based resin, epoxy-based resin, phenol-based resin, rosin-based resin, polyester-based resin, and ethylene-based resin. Examples include organic polymer compounds. Among them, it is preferable to contain (C1) a cellulosic resin as the binder resin from the viewpoint of improving the burn-through property at the time of firing and the surface smoothness of the electrode layer. Further, in the conductive paste containing the inorganic powder having a fine particle size as described above, (C2) polyvinyl is used as the binder resin from the viewpoint of improving the adhesiveness between the coating film and the base material and the integrity of the coating film. It is preferable to contain an acetal-based resin, and for example, it is preferable to use a combination of (C1) cellulose-based resin and (C2) polyvinyl acetal-based resin.

(C1) Cellulose-based resin includes a linear polymer (cellulose) containing β-glucose as a repeating unit and its derivatives in general. The (C1) cellulosic resin can typically be a compound in which a part or all of the hydroxy groups in the β-glucose structure, which is a repeating unit, is replaced with an alkoxy group, and a derivative thereof (modified product, etc.). The alkyl group or aryl group (R) in the alkoxy group (RO-) may be partially or wholly substituted with an ester group such as a carboxyl group, a nitro group, a halogen, or another organic group. Examples of the cellulose-based resin include methyl cellulose (MC), ethyl cellulose (EC), hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxyethyl methyl cellulose, cellulose acetate, nitrocellulose and the like. Can be mentioned. Of these, MC and EC are preferable. By containing the cellulosic resin, workability during gravure printing can be improved, and a coating film having excellent surface smoothness can be stably formed.

The properties of the cellulosic resin are not particularly limited. The weight average molecular weight (Mw) of the cellulosic resin may be approximately 10,000 or more, for example, 60,000 or more, 80,000 or more, 120,000 or more, or 200,000 or more. The weight average molecular weight (Mw) of the cellulosic resin may be approximately 800,000 or less, for example, 600,000 or less, 400,000 or less, or 320,000 or less. The "weight average molecular weight (Mw)" is a number-based average molecular weight, which can be measured by, for example, gel chromatography (GPC) and calculated using a standard polystyrene calibration curve.

(C2) The polyvinyl acetal-based resin is a resin obtained by reacting a polyvinyl alcohol-based resin with an aldehyde to acetalize it. The polyvinyl acetal-based resin has a continuous vinyl alcohol structural unit having a structural unit acetalized by an aldehyde compound, and has an unreacted vinyl alcohol structural unit and acetic acid which is an unsaken portion of the polyvinyl alcohol-based resin. It includes a polymer having one or more of vinyl structural units, and a derivative thereof (modified product, etc.) in general. The ratio of acetalized structural units (degree of acetalization) in the polyvinyl acetal-based resin may be, for example, 50 mol% or more. Polyvinyl acetal-based resins are superior in adhesiveness and flexibility to, for example, cellulose-based resins.

Examples of the polyvinyl acetal resin include polyvinyl butyral resin (PVB) having a structure in which polyvinyl alcohol is acetalized with butanol. By including PVB, the shape characteristics of the coating film can be improved. The polyvinyl acetal-based resin is a copolymer (graft) in which the polyvinyl acetal-based resin is used as the main monomer (a component that occupies 50% or more of the total monomer; the same applies hereinafter) and the main monomer contains a copolymerizable submonomer. (Including copolymerization) may be used. Examples of the submonomer include ethylene, ester, (meth) acrylate, vinyl acetate and the like.

The properties of the polyvinyl acetal resin are not particularly limited. The weight average molecular weight (Mw) of the polyvinyl acetal-based resin may be approximately 50,000 or more, and may be, for example, 75,000 or more, 85,000 or more, 100,000 or more, or 150,000 or more. The weight average molecular weight (Mw) of the polyvinyl acetal resin may be approximately 1 million or less, for example, 750,000 or less, 500,000 or less, preferably 300,000 or less, 250,000 or less, for example, 200,000 or less. You may. By setting the weight average molecular weight to a predetermined value or less, an increase in paste viscosity can be suitably suppressed. Therefore, it is possible to achieve both gravure printability and the shape characteristics of the coating film at a high level.

Although not particularly limited, the binder resin may be composed of (C2) polyvinyl acetal-based resin as the main component (the component that occupies the largest amount; the same shall apply hereinafter). The (C2) polyvinyl acetal-based resin may occupy approximately 50% by mass or more, for example, 60 to 80% by mass, when the total amount of the binder resin is 100% by mass. When (C1) cellulose-based resin and (C2) polyvinyl acetal-based resin are simultaneously contained as the binder resin, the (C2) polyvinyl acetal-based resin becomes 100% by mass when (C1) + (C2) is 100% by mass. , Approximately 10 to 90% by mass, typically 20 to 80% by mass, for example 50 to 70% by mass.

Although not particularly limited, when the total amount of the conductive paste is 100% by mass, the content ratio of the binder resin is approximately 0.1 to 5% by mass, typically 1 to 4% by mass, for example. It may be 2 to 3% by mass. The content ratio of the binder resin to 100 parts by mass of the conductive powder is approximately 0.1 to 10 parts by mass, typically 0.5 to 8 parts by mass, for example, 1 to 7 parts by mass and 2 to 5 parts by mass. There may be. By satisfying the above range, it becomes easy to adjust the conductive paste to a property suitable for gravure printing. In addition, the adhesion between the coating film and the base material can be improved, and a conductive layer having excellent electrical conductivity and denseness can be stably realized.

(D) Solvent The solvent is a liquid medium for dispersing the inorganic powder and imparting a viscosity (fluidity) suitable for gravure printing to the conductive paste. The solvent can also function as a vehicle that dissolves the above-mentioned (C) binder resin and / or (E) dispersant described later. Solvents are components that are typically lost by drying and firing. The solvent is a component that burns out when the conductive paste is dried and / or when the coating film is fired. The type of the solvent is not particularly limited, and among the conventionally known organic solvents used for this type of application, for example, one type may be used alone or depending on the type of the (C) binder resin and the like. Two or more types can be used in combination as appropriate. Examples of the solvent include an alcohol solvent having an -OH group, an ether solvent having an ether bond (R-OR'), and an ester having an ester bond (RC (= O) -OR'). Examples thereof include a system solvent, a hydrocarbon solvent composed of a carbon atom and a hydrogen atom, and the like.

Examples of alcohol-based solvents and ether-based solvents include tarpineol, texanol, dihydroterpineol, benzyl alcohol, 3-methoxy-3-methyl-1-butanol, phenoxyethanol, 1-phenoxy-2-propanol, isobornol, diethylene glycol, and diethylene glycol. Examples thereof include monoethyl ether, diethylene glycol monobutyl ether (butyl carbitol), propylene glycol monobutyl ether, dipropylene glycol methyl-n-propyl ether and the like. Examples of the ester solvent include 3-methoxy-3-methyl-1-butanol acetate, 3-methoxybutyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol diacetate, cyclohexanol acetate, and isobol. Nyl acetate, carbitol acetate, ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate), tarpineol acetate, dihydroterpineol acetate and the like can be mentioned. Examples of the hydrocarbon solvent include aromatic hydrocarbon solvents such as toluene and xylene; paraffin solvents such as normal paraffins and isoparaffins, naphthen solvents such as monocyclic naphthenes and bicyclic naphthenes, and paraffin / paraffin / Examples thereof include naphthen mixed solvents and aliphatic hydrocarbon solvents such as mineral spirits.

Although not particularly limited, when a conductive paste is applied on the green sheet, a hydrocarbon solvent is used as the solvent from the viewpoint of suppressing a sheet attack phenomenon (a phenomenon in which the solvent erodes the green sheet). It is preferable to include, for example, a hydrocarbon solvent and a solvent other than the hydrocarbon solvent, for example, at least one of an alcohol solvent and an ester solvent are preferably used in combination. Among them, the hydrocarbon solvent preferably contains a naphthenic solvent, and the hydrocarbon solvent may be composed mainly of a naphthenic solvent. When the total amount of the hydrocarbon solvent is 100% by mass, the naphthenic solvent may occupy about 50% by mass or more, for example, 60 to 80% by mass. When a hydrocarbon solvent and a non-hydrocarbon solvent are simultaneously contained as the solvent, when the total of the hydrocarbon solvent and the non-hydrocarbon solvent is 100% by mass, the non-hydrocarbon solvent is used. The content of the solvent may be approximately 10 to 95% by mass, typically 20 to 90% by mass, for example 50 to 80% by mass.

Although not particularly limited, solvents other than hydrocarbons have a boiling point of approximately 100 ° C. or higher, for example 200 ° C. or higher, from the viewpoint of improving storage stability of the conductive paste and workability during gravure printing. It may contain a high boiling point solvent. Further, from the viewpoint of rapidly drying the coating film to improve productivity, it is preferable to use a high boiling point solvent having a boiling point of about 100 to 300 ° C., for example, 200 to 250 ° C., preferably 230 ° C. or lower as a main component. The high boiling point solvent may occupy approximately 50% by mass or more, for example 90% by mass or more, when the total amount of the solvent other than the hydrocarbon solvent is 100% by mass, and substantially the entire solvent (95% by mass or more). ) May be composed of a high boiling point solvent.

^{For solvents other than hydrocarbons, the SP value is approximately 10.5 (cal / cm 3} ) from the viewpoint of adjusting the conductive paste to properties suitable for gravure printing and achieving a well-balanced sheet attack property. ^0.5 or less, for example 10 (cal / cm ³ ) ^0.5 or less, preferably 9.9 (cal / cm ³ ) ^0.5 or less, for example 8 to 9.9 (cal / cm ³ ) ^0.5 It may contain a solvent. From the viewpoint of resin solubility, the SP value of all solvents other than hydrocarbon solvents is approximately 8 (cal / cm ³ ) ^0.5 or more, for example 8.5 (cal / cm ³ ) ^0.5 or more, 9 ( cal / cm ³ ) It ^{may be 0.5} or more. Further, from the viewpoint of better suppressing the sheet attack phenomenon, the SP value of the entire solvent other than the hydrocarbon system is approximately 9.8 (cal / cm ³ ) ^0.5 or less, for example, 9.7 (cal / cm ^3). ) It ^{may be 0.5} or less.

The solvent other than the hydrocarbon solvent may contain a first solvent and a second solvent having different boiling points and / or SP values. As an example, a first solvent having excellent solubility of the binder resin and a second solvent having excellent quick-drying property may be contained. The first solvent has a higher SP value than the second solvent and may be approximately 10.0 (cal / cm ³ ) ^0.5 or more, for example, 10 to 10.5 (cal / cm ³ ) ^0.5. .. Further, the first solvent may have a boiling point of about 200 ° C. or higher, for example, 200 to 230 ° C. The boiling point of the second solvent is equal to or lower than that of the first solvent, and may be approximately 220 ° C. or lower, for example 140 to 215 ° C. Further, the second solvent may have an SP value of approximately 9.5 (cal / cm ³ ) ^0.5 or less, for example, 8.5 to 9.5 (cal / cm ³ ) ^0.5 . Thereby, the dispersibility of the inorganic powder in the conductive paste, the solubility of the binder resin, and the dryness of the coating film can be combined at a high level. The content ratio of the first solvent is approximately 10 to 95% by mass, typically 20 to 90% by mass, for example, 50 to 80% by mass, when the total of the first solvent and the second solvent is 100% by mass. It may be.

Although not particularly limited, when the total amount of the conductive paste is 100% by mass, the content ratio of the solvent is approximately 80% by mass or less, typically 10 to 70% by mass, for example, 30 to 60% by mass. May be%. By satisfying the above range, it is possible to impart appropriate fluidity to the conductive paste, and it is possible to improve workability during gravure printing. In addition, the self-leveling property can be improved, and a coating film having excellent surface smoothness can be stably formed even during high-speed printing.

(E) Dispersant The dispersant is a parent for uniformly dispersing the above-mentioned inorganic powders, that is, (A) conductive powder and (B) dielectric powder in a conductive paste, and suppressing aggregation of these components. It is a medium compound. The dispersant can be dissolved in the solvent (D) described above and function as a vehicle. As a result, the inorganic powder can be uniformly and stably dispersed.

The conductive paste disclosed herein can be used as a dispersant according to the following formula (1):

It contains a dicarboxylic acid-based dispersant having a structural portion represented by. In the formula (1), A ¹ and A ² are independent of hydrogen (H); alkali metals such as sodium (Na) and potassium (K); or magnesium (Mg), calcium (Ca) and the like. Alkaline earth metal; Among ^{them, both A 1} and A ² are preferably hydrogen.

In structural part of formula (1), the second and third carbon atoms from the right, respectively carboxylate group (-C (= O) O ^-) is attached. That is, the carboxylate group is bonded to each adjacent carbon atom. Further, no substituent is bonded to the fourth carbon atom (leftmost carbon atom) adjacent to the third carbon atom. That is, it is represented by _{-CH 2.} Although the details are not clear, by using a dicarboxylic acid-based dispersant having such a structural portion, another anionic dispersant (for example, a monocarboxylic acid-based dispersant, the structural portion of the above formula (1)) can be obtained. Compared to the case of using a dicarboxylic acid-based dispersant, a polycarboxylic acid-based dispersant, a sulfonic acid-based dispersant, a phosphoric acid-based dispersant, etc.) or an amine-based dispersant, the inorganic powder in the conductive paste It is considered that the uniform dispersibility of the above is specifically enhanced.

That is, when the two carboxylate groups are close to each other in the same molecule, the probability of binding to the surfaces of the (A) conductive powder and the (B) dielectric powder increases. Therefore, it is considered that the dispersant is more adsorbed on the surface of the inorganic powder and the inorganic particles are stabilized. Further, in the dispersant having the structural portion of the above formula (1), both of the two carboxylate groups are adsorbed on the inorganic particles, and one is adsorbed on the inorganic particles and the other is in an unadsorbed state by an equilibrium reaction. However, the latter is stochastically predominant. Thus, for example, when the (B) dielectric powder is finer than the (A) conductive powder, the dispersant disclosed herein is charged by unadsorbed carboxylate groups ( B) It is considered that it is easily adsorbed on the surface of the dielectric powder. Then, it is considered that the unadsorbed carboxylate group electrically interacts with the conductive powder (A) so that the conductive powder (A) and the dielectric powder (B) are uniformly and uniformly dispersed. ..

The properties of the dispersant are not particularly limited. The molecular weight of the dispersant may be approximately 100 or more, and may be, for example, 150 or more, 200 or more, or 230 or more. The molecular weight of the dispersant may be approximately 20,000 or less, for example, about 10,000 or less, 5000 or less, 2000 or less, 1000 or less, or 500 or less. By setting the molecular weight to a predetermined value or more, the effect of enhancing the uniform dispersibility of the above-mentioned inorganic powder can be better exhibited. Further, by setting the molecular weight to a predetermined value or less, an increase in paste viscosity can be suitably suppressed. The dispersant is preferably a low molecular weight compound having a molecular weight of less than 10,000 rather than a high molecular weight compound having a molecular weight of 10,000 or more. Thereby, the above-mentioned effect can be exhibited at a higher level.

In the present specification, the term "molecular weight" simply means a value calculated from the sum of the atomic weights of each atom based on the molecular formula. The molecular formula of the compound can be specified by appropriately selecting an analysis method according to the molecular structure. Examples of analysis methods include infrared spectroscopy (IR: Infrared Spectroscopy), nuclear magnetic resonance (NMR: Nuclear Magnetic Resonance), mass spectrometry (MS: Mass Spectrometry), and gas chromatography-mass spectrometry (GC-). MS: Gas Chromatography-Mass spectrometry), gas chromatography (GC: Gas Chromatography), gel permeation chromatography (GPC: Gel Permeation Chromatography), CHN element spectrometry, and the like can be mentioned.

The dispersant is not particularly limited except that it has a structural portion of the formula (1), and one of the conventionally known amphipathic compounds used for this kind of application may be used alone or in combination of two. The above can be used in combination as appropriate. As an example of the dispersant, for example, the following formula (2):

Examples thereof include compounds represented by ;. In the formula (2), A ¹ and A ² are the same as those in the above formula (1). In addition, R is a saturated or unsaturated aliphatic group having 3 to 30 carbon atoms. The number of carbon atoms may be, for example, 4 or more, 5 or more, 6 or more, further 7 or more, and for example, 29 or less, 28 or less, 27 or less, or even 25 or less. The aliphatic group may be linear or branched chain having branches. Examples of the aliphatic group include an alkyl group, an alkenyl group, an alkynyl group and the like. The aliphatic group may contain a vinylene group (-CH = CH-).

Specific examples of the dispersing agent represented by the above formula (2), for example, octa polybutenyl butane diacid represented by the following formula _{(3) (C 12 H 20} O 4: molecular weight = 228), the following equation (4) in octadecenyl Seni butane diacid represented _{(C 22 H} 40 _{O 4:} molecular weight = 368), the following equation hexamethylene co Seni butane diacid represented by _{(5) (C 30 H 56} O 4: molecular weight = 480) And so on. In the following formula (3), the R portion of the formula (2) is a linear alkenyl group having 7 carbon atoms, and in the following formula (4), the R portion of the formula (2) is a linear chain having 17 carbon atoms. In the following formula (5), the R moiety of the formula (2) is a linear alkenyl group having 25 carbon atoms.

The dispersant may be mainly composed of a compound having the structural portion of the above formula (1). The compound having the structural portion of the formula (1) may occupy approximately 50% by mass or more when the total amount of the dispersant is 100% by mass, and substantially the entire dispersant (95% by mass or more) is used. It is preferable that it is composed of a compound having a structural portion of the formula (1). However, the dispersant may supplementally contain other compounds as long as the effects of the techniques disclosed herein are not significantly reduced. Examples of auxiliary dispersants include monocarboxylic acid-based dispersants, dicarboxylic acid-based dispersants that do not have the structural portion of the above formula (1), polycarboxylic acid-based dispersants, and sulfonic acid-based dispersants. Examples thereof include anionic dispersants such as agents and phosphoric acid-based dispersants, and amine-based dispersants. These auxiliary dispersants may be suppressed to approximately 50% by mass or less, 30% by mass or less, 10% by mass or less, for example, 5% by mass or less of the total dispersant.

Although not particularly limited, the content ratio of the dispersant is approximately 0.01 to 5% by mass, typically 0.05 to 3% by mass, assuming that the entire conductive paste is 100% by mass. For example, it may be 0.1 to 2% by mass, preferably 0.5% by mass or less, for example, 0.3% by mass or less, 0.2% by mass or less. By setting the content ratio of the dispersant to a predetermined value or more, the dispersant can be sufficiently acted on the fine inorganic powder. Further, by setting the content ratio of the dispersant to a predetermined value or less, an electrode layer having excellent electrical conductivity and denseness can be suitably realized.

(F) Other Additives The conductive paste disclosed here may be composed of the above four components, and can be used for a general conductive paste as long as the essence of the present invention is not significantly impaired. Various known additives can be included. Examples of such additives include viscosity regulators, thickeners, defoamers, plasticizers, leveling agents, pH regulators, stabilizers, antioxidants, preservatives, colorants (pigments, dyes). Etc.) etc. These additives may be used alone or in combination of two or more, if necessary.

The additive can be contained in an appropriate ratio according to the purpose of addition and the like. Although not particularly limited, when the total amount of the conductive paste is 100% by mass, the content ratio of the additive is approximately 5% by mass or less, typically 3% by mass or less, for example, 1% by mass or less. It is good to suppress it to. As a result, an electrode layer having excellent electrical conductivity and denseness can be suitably realized.

(G) Properties of Conductive Paste The conductive paste disclosed here is adjusted to have a low viscosity for gravure printing having a high printing speed. Specifically, at 25 ° C., the viscosity V _{40 at} ^{a shear rate of 40 s -1} is adjusted to 5 Pa · s or less. From the viewpoint of increasing the printing speed and increasing the productivity, the viscosity V ₄₀ may be adjusted to, for example, 4.5 Pa · s or less, 4 Pa · s or less, 3.5 Pa · s or less, 3 Pa · s or less. .. From the viewpoint of suppressing print sagging and improving workability, the viscosity V ₄₀ may be adjusted to, for example, 0.1 Pa · s or more and 0.2 Pa · s or more. The viscosity of the conductive paste is determined by, for example, the type and content ratio of the binder resin, the type and content ratio of the dispersant, the type and content ratio of the solvent, and the addition of other additives (for example, viscosity modifiers and thickeners). Can be adjusted by.

Although not particularly limited, at 25 ° C., the viscosity _{V 4} at a shear rate of ^{4s -1} is approximately 20 Pa · s or less, 18 Pa · s or less, 15 Pa · s or less, it is adjusted to below 13 Pa · s Good. The viscosity V ₄ may be adjusted to, for example, 0.1 Pa · s or more, 0.2 Pa · s or more, and 0.4 Pa · s or more. The ratio of viscosity V ₄ to viscosity V _{40 (V 4} / V ₄₀ ) may be approximately 7 or less, typically 6 or less, for example 5.5 or less, 5 or less, 4.5 or less. As a result, the storage stability and handleability of the conductive paste can be improved.

For such a conductive paste, for example, a vehicle in which (C) a binder resin and (E) a dispersant are dispersed or dissolved in (D) a solvent is prepared, and (A) a conductive powder and (B) are prepared therein. It can be suitably prepared by adding the dielectric powder and then stirring and mixing. In preparing the conductive paste, various conventionally known stirring devices and dispersing devices such as a ball mill, a bead mill, a roll mill, a magnetic stirrer, a planetary mixer, a dispenser, a high-pressure disperser, and a mortar can be appropriately used.

(H) Properties of the coating film The coating film made of the conductive paste disclosed here can have less surface irregularities than the conventional ones. Although it depends on the particle size of the inorganic powder and the like, the maximum roughness Rmax of the coating film can be, for example, 0.7 μm or less, preferably 0.65 μm or less, 0.6 μm or less. Further, the coating film made of the conductive paste disclosed herein has better dispersibility of the inorganic powder than the conventional one and can have a homogeneous composition. Although it depends on the particle size of the inorganic powder and the like, the dispersity index of the inorganic powder in the coating film can be, for example, 80% or more, preferably 83% or more, 89% or more. The method for measuring the maximum roughness Rmax and the method for calculating the dispersion index will be described in Examples described later.

[Use of conductive paste]
The conductive paste disclosed herein can be used to form a coating film by applying it on an arbitrary substrate by a gravure printing method and drying it, and then firing the coating film to form an electrode layer. .. Among them, it can be preferably used in applications where surface smoothness and homogeneity of the electrode layer are required. Typical uses include the formation of an internal electrode layer of a small laminated ceramic electronic component having a side of 5 mm or less, for example, 1 mm or less. In particular, it can be suitably used for forming an internal electrode layer of a small-sized and large-capacity MLCC in which the thickness of the dielectric layer is thinned to a level of 2 μm or less.

In the present specification, the "ceramic electronic component" includes a general electronic component having a crystalline ceramic base material and / or an amorphous ceramic base material. For example, ceramic capacitors including ceramic substrates, chip inductors, high-frequency filters, high-temperature co-fired ceramics (HTCC) substrates, low-temperature co-fired ceramics (LTCC). ) The base material and the like are typical examples included in the "ceramic electronic parts" referred to here.

Examples of the ceramic material constituting the ceramic substrate include barium titanate (BaTIO ₃ ), strontium titanate (SrTIO ₃ ), calcium titanate (CaTIO ₃ ), calcium zirconate (CaZrO ₃ ), and strontium zirconate (SrZrO). ₃ ), Zirconium oxide (Zirconia: ZrO ₂ ), Magnesium oxide (Magnesia: MgO), Aluminum oxide (Alumina: Al ₂ O ₃ ), Silicon dioxide (Silica: SiO ₂ ), Zinc oxide (ZnO), Titanium oxide (Titania) : TiO ₂ ), cerium oxide (Celia: CeO ₂ ), Ittrium oxide (Itria: Y ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ) and other oxide-based materials; Cordierite ( ₂ MgO ・ 2Al 2 O ₃₎ · 5SiO _2), mullite _{(3Al 2 O 3 · 2SiO 2} ), forsterite (2MgO · _SiO 2), steatite (MgO · _SiO 2), sialon _{(Si 3 N 4 -AlN-Al} 2 O 3), lead zirconate Composite oxide-based materials such as (ZrO ₂ · SiO ₂ ) and ferrite (M ₂ O · Fe ₂ O ₃ ); silicon nitride (silicon nitride: Si ₃ N ₄ ), aluminum nitride (aluminum nitride: AlN), boron nitride hydroxide-based material hydroxyapatite and the like;:;:: (B 4 C , boron _carbide) carbide-based material such as (boron nitride BN) nitride material such as silicon carbide (silicon carbide SiC), boron carbide ; Etc. can be mentioned. These may be contained alone, as a mixture of two or more types, or as a composite of two or more types.

[Multilayer ceramic capacitor]
FIG. 1 is a cross-sectional view schematically showing the configuration of a multilayer ceramic capacitor (MLCC) 1. The MLCC1 is a chip-type capacitor in which a large number 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 surface of the laminated chip 10 composed of the dielectric layer 20 and the internal electrode layer 30. As an example, the internal electrode layer 30 is connected to external electrodes 40 which are alternately different in the stacking order. As a result, the capacitor structure composed of the dielectric layer 20 and the pair of internal electrode layers 30 sandwiching the dielectric layer 20 is connected in parallel, and a small-sized and large-capacity MLCC1 is constructed. The dielectric layer 20 of the MLCC1 is made of, for example, a dielectric material. The internal electrode layer 30 is composed of a fired body of the conductive paste disclosed herein. Such MLCC1 can be produced, for example, by the following procedure.

FIG. 2 is a cross-sectional view schematically showing the configuration of the unfired laminated body 10a (in other words, the unfired laminated chip 10). In the production of MLCC1, first, a dielectric green sheet as a base material is prepared. Here, for example, a ceramic powder as a dielectric material, a binder resin, a solvent, or the like is mixed to prepare a paste for forming a dielectric layer. Next, the unfired dielectric green sheet 20a is prepared by applying the prepared paste in a thin layer on the carrier sheet by a doctor blade method or the like. Next, the conductive paste disclosed here is prepared. Then, the prepared conductive paste is applied onto the dielectric green sheet 20a in a predetermined pattern so as to have a desired thickness (for example, 1 μm or less) to form the coating film 30a. According to the conductive paste disclosed herein, the coating film 30a having good dispersibility of the inorganic powder, excellent surface smoothness, and good adhesion to the dielectric green sheet can be stably formed. it can.

Next, a plurality of (for example, several hundred to several thousand) dielectric green sheets 20a with the prepared coating film 30a are laminated and pressure-bonded. As a result, a laminated pressure-bonded body is produced. The laminated pressure-bonded body is cut into a chip shape as needed. Since the surface unevenness of the coating film 30a is small, distortion of the laminated structure is unlikely to occur even when the coating film 30a is laminated or crimped. Further, since the coating film 30a has good adhesion to the dielectric green sheet 20a, problems such as cracking and peeling of the coating film 30a are unlikely to occur even if the coating film 30a is laminated, crimped, or cut. Thereby, the unfired laminated body 10a can be stably obtained.

Next, the unfired laminate 10a is fired under appropriate heating conditions (for example, in a nitrogen-hydrogen-containing atmosphere, at a temperature of about 1000 to 1300 ° C.). As a result, the dielectric green sheet 20a is fired to form the dielectric layer 20 (see FIG. 1). Further, the coating film 30a is fired to become an internal electrode layer 30 (see FIG. 1). In this way, the dielectric layer 20 and the internal electrode layer 30 are integrally sintered, and the laminated chip 10 can be obtained. According to the technique disclosed herein, the internal electrode layer 30 can be formed as electrically continuous and homogeneous. Then, the external electrode material is applied to the side surface of the laminated chip 10 and baked to form the external electrode 40. As described above, it is possible to manufacture a high-quality MLCC1 in which defects such as short-circuit defects are unlikely to occur.

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

<Test Example I>
[Preparation of conductive paste]
In this test example, (E) is obtained by stirring and mixing (A) a conductive powder, (B) a dielectric powder, (C) a binder resin, (D) a solvent, and (E) a dispersant. ) Conductive pastes (Comparative Examples 1 to 9, Examples 1 to 3) in which only the types of dispersants were different were prepared.

As the conductive powder, nickel powder (Ni) having an average particle diameter of 0.2 μm was used so as to have a ratio of 50% by mass with respect to the entire conductive paste.
As the dielectric powder, barium titanate powder (BT) having an average particle diameter of 50 nm was used at a ratio of 15 parts by mass with respect to 100 parts by mass of nickel powder.
As the binder resin (C), ethyl cellulose (EC) and polyvinyl butyral (PVB, weight average molecular weight (Mw): 85,000) were mixed and used. In Comparative Examples 1 and 2, the viscosity was adjusted to high by using a part of high molecular weight ethyl cellulose. EC was used so as to have a ratio of 2 parts by mass with respect to 100 parts by mass of nickel powder, and PVB was used so as to have a ratio of 3 parts by mass with respect to 100 parts by mass of nickel powder.
As the solvent (D), a hydrocarbon solvent (naphthenic solvent), a first solvent (dihydroterpineol) which is a solvent other than the hydrocarbon solvent, and a second solvent (3-methoxy-3-methyl-1-butanol acetate) ) Is mixed and used in a mass ratio of 1st solvent: 2nd solvent: hydrocarbon solvent = 45:30:25, (A) conductive powder, (B) dielectric powder, (C) binder resin. , (E) The balance after subtracting the dispersant was used as the ratio of the solvent (D) in the conductive paste.

As the dispersant (E), those shown in Table 1 were used so as to have a ratio of 0.2% by mass with respect to the entire paste. The "comb-shaped carboxylic acid" used in Comparative Example 4 is a polymer of hydroxystearic acid, and "N-oleic sarcosine", "malonic acid", and "citric acid" used in Comparative Examples 5 to 8. , The structural formulas of "oleic acid" are as shown in the following formulas (6), (7), (8) and (9), respectively.

[Measurement of paste viscosity]
The viscosity of the conductive paste was measured using a rotary vibration rheometer MARS III manufactured by HAAKE. The measurement conditions are as follows. The viscosity _V 40 at a shear rate of ^{40s -1} (Pa · s), and the viscosity _V 4 at a shear rate of ^{4s -1} a (Pa · s), shown in the column "Viscosity" of Table 1. The ratio of viscosity V ₄ to viscosity V _{40 (V 4} / V ₄₀ ) is shown in the “Viscosity ratio” column of Table 1.
Measurement mode: Shear velocity dependence measurement Sensor: Cone plate (φ20 mm, angle 1 °)
Measurement temperature: 25 ° C
Gap: 0.052 mm
Shear velocity: 10000-0.01s ^-1
Measurement time: 3 minutes

[Evaluation of dispersion index]
A coating film was formed by the following procedure, and the dispersibility of the inorganic powder (here, the conductive powder) in the coating film was evaluated. Specifically, first, the conductive paste of each example is applied onto a PET substrate with a thickness of about 250 μm using an applicator, and dried at 110 ° C. for about 15 minutes to form a coating film (about 50 μm). did. Then, this coating film was SEM-observed from the surface on the PET substrate side, and an SEM observation image was acquired. The acceleration voltage at the time of observation was 20 kV, and the observation magnification was 10,000 times. FIG. 3 is an example of an SEM observation image, FIG. 3 (A) is for Comparative Example 3, and FIG. 3 (B) is for Comparative Example 9.

Next, based on the obtained SEM observation image, the dispersity index of the conductive powder was calculated according to a conventionally known dispersibility evaluation method (see, for example, Japanese Patent Application Publication No. 2015-7542). That is, first, the SEM observation image was binarized with a predetermined threshold value to generate an evaluation image. FIG. 4 is a conceptual diagram illustrating a method of calculating the dispersion index. Next, the evaluation image was divided into equal sizes until the number of divisions reached a predetermined number, and the evaluation image variation coefficient CVb and the complete separation variation coefficient CVa were calculated for each partition size. The evaluation image coefficient of variation CVb was calculated based on the area value x and the standard deviation σ of the object (for example, the white portion after binarization representing the conductive powder). Further, the coefficient of variation CVa at the time of complete separation was calculated based on the area value of the object assuming that the object and the non-object other than the object were completely separated. Further, here, the evaluation image was divided until the evaluation image variation coefficient CVb became the same value as the variation coefficient CVa at the time of complete separation. In addition, the coefficient of variation CVc at the time of complete mixing was calculated based on the area value of the object assuming that the object and the non-object other than the object were completely mixed for each section size.

Next, the partition size and the evaluation image coefficient of variation CVb are plotted on the two-dimensional coordinates, and the values of the evaluation image variation coefficient CVb are connected by a straight line between the adjacent partition sizes, and the “first relationship b” in FIG. Was graphed. Similarly, the partition size and the coefficient of variation CVa during complete separation are plotted on the two-dimensional coordinates, and the values of the coefficient of variation CVa during complete separation are connected by a straight line between adjacent partition sizes, and the “second relationship” in FIG. a ”was graphed. Further, the partition size and the coefficient of variation CVc during complete mixing are plotted on the two-dimensional coordinates, and the values of the coefficient of variation CVc during complete mixing are connected by a straight line between adjacent partition sizes, and the “third relationship c” in FIG. Was graphed.

Next, in the first relationship b, the second relationship a, and the third relationship c, from the minimum value of the partition size (that is, the maximum value of the number of divisions) to the maximum value of the partition size (that is, the minimum value of the number of divisions). The integrated values in the range up to are calculated respectively. That is, as shown in FIG. 4, the area surrounded by the first relationship b and the horizontal axis is B, the area surrounded by the second relationship a and the horizontal axis is A, and the area surrounded by the third relationship c and the horizontal axis is horizontal. The area surrounded by the shaft was defined as C. Then, the dispersion index was calculated based on the following equation: dispersion index α [%] = (1- (BC) / (AC)) × 100 ;. The results are shown in the column of "Dispersity index α" in Table 1. It can be said that the closer the dispersion index α is to 100%, the better the dispersibility of the conductive powder in the coating film (that is, the higher the dispersion of the conductive powder is close to the completely mixed state).

Then, the dispersibility of the coating film of each example was evaluated based on the following indexes. The results are shown in the "Dispersity Index-Judgment" column of Table 1.
×: α is less than 89% ○: α is 89% or more

[Evaluation of gravure printability]
A coating film was formed by the following procedure, and the surface roughness of the coating film was measured. Specifically, first, a dielectric green sheet containing barium titanate was prepared. Next, the conductive paste whose dispersity index was judged to be "○" was applied onto a dielectric green sheet with a thickness of about 1 μm by a gravure printing method, and dried at 80 ° C. for about 5 minutes to form a coating film. Formed. The conditions for gravure printing are as follows.
Print pattern: 1005 type (2000 μm x 500 μm)
Printing speed: 30m / min
Printing pressure: 0.3MPa

Next, the surface roughness of the coating film was measured using a super-resolution non-contact three-dimensional surface shape measurement system (model: BW-A501) manufactured by Nikon Corporation. The measurement conditions are as follows. Then, the height image of the coating film was captured and the image was analyzed to obtain a cross-sectional profile. Five cross-sectional profiles were prepared (at n = 5) for each sample. Then, the difference between the highest point and the lowest point of the obtained cross-sectional profile was obtained, and the arithmetic mean value of n = 5 was defined as "maximum roughness Rmax". The results are shown in the "Rmax" column of Table 1.
・ Optical microscope: Interference microscope manufactured by Nikon Corporation (model: ECLIPSE LV150)
-Objective lens magnification: 10 times-Measurement range: 50 μm x 1000 μm

FIG. 6 is an example of a cross-sectional profile of surface roughness, FIG. 6 (A) is for Comparative Example 3, and FIG. 6 (B) is for Example 1. Then, the gravure printability of the conductive paste of each example was evaluated based on the following indexes. The results are shown in the "Gravure printability-judgment" column of Table 1.
X: Rmax exceeds 0.7 μm ○: Rmax is 0.7 μm or less

[Comprehensive judgment]
In addition, a comprehensive evaluation was performed based on the evaluation result of the dispersion index and the evaluation result of the gravure printability. The overall evaluation was given as "○" when both of the above two evaluation results were ○, and as "x" when even one of them contained x. The results are shown in the "Comprehensive Judgment" column of Table 1.

As shown in Table 1, the conductive pastes of Comparative Examples 1 to 3 were excellent in the dispersibility of the coating film, but had large irregularities on the surface of the coating film and lacked gravure printability. Further, the conductive pastes of Comparative Examples 4 to 9 lacked the dispersibility of the coating film. In contrast, in the conductive paste examples 1-3, it includes a predetermined dicarboxylic acid dispersant, by adjusting the viscosity V ₄₀ below the low-viscosity 5 Pa · s, the homogeneity of the coating and the gravure printing It was compatible with sex.

<Test Example II>
In this test example, as the solvent (D), a first solvent (dihydroterpineol) and a hydrocarbon solvent (naphthenic solvent) are mixed at a mass ratio of first solvent: hydrocarbon solvent = 75:25. A conductive paste (Example 4) was prepared in the same manner as in Example 2 except that it was used in the above manner, and evaluated in the same manner as in Test Example I. The results are shown in Table 2.

As shown in Table 2, even in Example 4 in which the second solvent (3-methoxy-3-methyl-1-butanol acetate) is not used, both the homogeneity of the coating film and the gravure printability are compatible as in Example 2. It was confirmed that it could be done.

<Test Example III>
In this test example, a conductive paste (Comparative Example 11, Examples 5 to 8) was prepared using an inorganic powder having a particle size larger than that of Test Examples I and II. Specifically, as the conductive powder (A), nickel powder (Ni) having an average particle diameter of 0.3 μm was used so as to have a ratio of 50% by mass with respect to the entire conductive paste. Further, as the (B) dielectric powder, barium titanate powder (BT) having an average particle diameter of 100 nm was used at a ratio of 25 parts by mass with respect to 100 parts by mass of the nickel powder. In Comparative Examples 11 and 5, other than this, a conductive paste was prepared in the same manner as in Comparative Examples 4 and 2, respectively. Further, in Examples 6 and 7, a conductive paste was prepared in the same manner as in Example 5 except that the composition of the binder resin (C) was different as shown in Table 3. Further, in Example 8, the content ratio of the conductive powder (A) was 57% by mass with respect to the entire conductive paste, and the conductive paste was prepared in the same manner as in Example 5.

Then, the evaluation was performed in the same manner as in Test Example I. The results are shown in Table 3. FIG. 5 is an example of an SEM observation image, FIG. 5 (A) is for Example 5, and FIG. 5 (B) is for Comparative Example 11. Since this test example uses an inorganic powder having a larger particle size than that of test examples I and II, the dispersity index was determined based on the following indexes.
×: α is less than 83% ○: α is 83% or more

As shown in Table 3, the coatings were also applied in Examples 5 to 8 in which (A) the size and content ratio of the conductive powder, (B) the size and content ratio of the dielectric powder, and (C) the blending of the binder resin were different. It was confirmed that both the homogeneity of the film and the gravure printability can be achieved.

<Test Example IV>
In this test example, the solvent (D) was further investigated. As the solvent (D), in addition to the hydrocarbon solvent (naphthenic solvent), as the solvent other than the hydrocarbon solvent, the first solvent and the second solvent shown in Table 4 are prepared, and these are shown in Table 4. Conductive pastes (Examples 9 to 24) were prepared in the same manner as in Example 5 except that they were mixed and used in a blending ratio. Then, the dryness and the sheet attack property were evaluated. _{The total SP value δ all} of the first solvent and the second solvent in Table 4 is calculated by the following formula:
δ _all = (SP value of first solvent x content ratio of first solvent (%) + SP value of second solvent x content ratio of second solvent (%) / (content ratio of first solvent (%) + first 2 Solvent content (%));
Calculated from.

[Evaluation of dryness]
The conductive paste was analyzed by differential thermal-Differential Thermal Analysis (TG-DTA). The measurement conditions are as follows.
Sample amount: Conductive paste 5 mg
Gas flow rate: Air 200 ml / min
Program: Heat from room temperature to 85 ° C at 20 ° C / min and then maintain 85 ° C

As an example, FIG. 7 shows measurement charts of TG-DTA of Example 13, Example 19, and Example 9. Then, from the measurement chart, the time when the weight change disappeared (the weight change rate became 0.1% by mass or less) was determined as the drying time. The results are shown in the "Drying time" column of Table 4. Then, the dryness of the conductive paste of each example was evaluated based on the following indexes. The results are shown in the column of "Judgment result-dryness" in Table 1.
Δ: Drying time is less than 15 minutes or more than 25 minutes ○: Drying time is 15 minutes or more and 25 minutes or less

[Evaluation of seat attack]
Similar to Test Example I, the conductive paste of each example was gravure-printed on a dielectric green sheet containing barium titanate and dried at 80 ° C. for about 5 minutes to form a coating film. Then, this coating film was SEM-observed from the side of the dielectric green sheet, and an SEM observation image was acquired. The acceleration voltage was 20 kV and the observation magnification was 1000 times. FIG. 8 is an example of an SEM observation image, FIG. 8 (A) is for Example 19, FIG. 8 (B) is for Example 16, and FIG. 8 (C) is for Example 9. Next, the area of the black portion (resin pool) was compared based on the SEM observation image. Then, the seat attack property was evaluated based on the following indexes. The results are shown in the column of "Judgment result-Sheet attackability" in Table 1.
Δ: Area of black part is 20% or more ○: Area of black part is 5% or more and less than 20% ◎: Area of black part is less than 5%

[Comprehensive judgment]
In addition, a comprehensive evaluation was performed based on the above-mentioned evaluation results of dryness and sheet attackability. In the overall evaluation, in the above two evaluation results, "◎" is 2 points, "○" is 1 point, "△" is 0 points, and the total score is 0 points, "△", and 1 point. Was "○", the case of 2 points was "○", and the case of 3 points was "◎". The results are shown in the "Judgment-Comprehensive" column of Table 4.

As shown in Table 4, in Examples 12 and 13 in which texanol or decanol was used as the second solvent, both the drying property and the sheet attack property were relatively poor as compared with the other examples. On the other hand, the solvent (D) contains, as the second solvent, a solvent having a boiling point of 230 ° C. or less and an SP value of 9.9 (cal / cm ³ ) of ^0.5 or less. Compared with 13, at least one of drying property and sheet attack property could be improved. Among them, as in Examples 17 to 24, the first solvent having a boiling point of 200 ° C. or higher and an SP value of 10.0 (cal / cm ³ ) ^0.5 or higher and the SP value having a boiling point of 220 ° C. or lower By using a second solvent having a temperature of 9.5 (cal / cm ³ ) of ^0.5 or less in combination, the sheet attack property could be further improved.

<Test Example V>
In this test example, the binder resin (C) was further examined. As the binder resin (C), two types of polyvinyl butyral (Sekisui Chemical's Eslek (registered trademark)) having different weight average molecular weights shown in Table 5 were used. Conductive pastes (Examples 25 and 26) were prepared in the same manner as in Example 2 except for the above, and evaluated in the same manner as in Test Example I. The results are shown in Table 5.

As shown in Table 5, it was confirmed that in Examples 25 and 26 in which the weight average molecular weight of (C2) PVB is 100,000 to 200,000, both the homogeneity of the coating film and the gravure printability can be achieved as in Example 2. Was done.

The preferred embodiment of the present invention has been described above. However, the above embodiments are merely examples, and the present invention can be implemented in various other embodiments. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. The techniques described in the claims include various modifications and modifications of the embodiments illustrated above. For example, it is possible to combine some of the above-described embodiments or replace them with other modifications. Further, if the technical feature is not explained as essential, it can be deleted as appropriate.

1 Multilayer ceramic capacitor (MLCC)
10 Laminated chip 10a Unfired laminated body 20 Dielectric layer 20a Dielectric green sheet 30 Internal electrode layer 30a Coating film 40 External electrode

Claims (11)

1. A conductive paste for gravure printing containing (A) a conductive powder, (B) a dielectric powder, (C) a binder resin, (D) a solvent, and (E) a dispersant.
   The dispersant (E) has the following formula (1):
   

   

   ^{(However, A 1} and A ² in the formula (1) are independently hydrogen, alkali metal or alkaline earth metal.); Contains a dicarboxylic acid-based dispersant having a structural portion represented by. ,
   A conductive paste for gravure printing, wherein the viscosity V _{40 at} ^{a shear rate of 40 s -1} of the conductive paste at 25 ° C. is 5 Pa · s or less.
2. The dispersant (E) has the following formula (2):
   

   

   ^{(However, A 1} and A ² in the formula (2) are independently hydrogen, alkali metal or alkaline earth metal, and R has 3 to 30 carbon atoms and is linear, branched or saturated. Or an unsaturated aliphatic group.); A compound represented by;
   The conductive paste according to claim 1.
3. The ratio of the viscosity _{V 4} at a shear rate ^{4s -1} of the conductive paste for the viscosity _{V 40 (V 4 / V 40} ) is 7 or less,
   The conductive paste according to claim 1 or 2.
4. The ratio (D ₁ / D ₂ ) of the average particle size D ₁ of the (A) conductive powder to the average particle size D ₂ of the (B) dielectric powder is 2 or more.
   The conductive paste according to any one of claims 1 to 3.
5. The solvent (D) contains a hydrocarbon-based solvent and a solvent other than the hydrocarbon-based solvent.
   The solvent other than the hydrocarbon-based solvent contains a solvent having a boiling point of 230 ° C. or lower and a solubility parameter of Fedors of 9.9 (cal / cm ³ ) of ^0.5 or less.
   The conductive paste according to any one of claims 1 to 4.
6. Solvents other than the hydrocarbon type
   A first solvent having a boiling point of 200 ° C. or higher and a solubility parameter of 10.0 (cal / cm ³ ) of ^{0.5 or higher.}
   A second solvent having a boiling point of 220 ° C. or lower and a solubility parameter of 9.5 (cal / cm ³ ) of ^{0.5 or lower.}
   including,
   The conductive paste according to claim 5.
7. The solubility parameter of the whole solvent other than the hydrocarbon system is 9.8 (cal / cm ³ ) ^0.5 or less.
   The conductive paste according to claim 5 or 6.
8. The dispersant (E) is 0.5% by mass or less when the total amount of the conductive paste is 100% by mass.
   The conductive paste according to any one of claims 1 to 7.
9. The binder resin (C) contains a polyvinyl acetal-based resin.
   The weight average molecular weight of the polyvinyl acetal resin is 200,000 or less.
   The conductive paste according to any one of claims 1 to 8.
10. Used to form the internal electrode layer of laminated ceramic electronic components,
    The conductive paste according to any one of claims 1 to 9.
11. A method for manufacturing an electronic component, which comprises applying the conductive paste according to any one of claims 1 to 10 onto a base material and firing the paste.

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