JP2013114891A - Conductive paste and multilayer ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste which has excellent thixotropy and excellent printability such as resistance to stringiness, bleeding resistance and resistance to sheet attack, and further to provide a conductive paste with which a multilayer ceramic capacitor can be efficiently manufactured.SOLUTION: The conductive paste contains: conductive powder; an alkyl-modified vinyl alcohol polymer; and an aqueous solvent. The alkyl-modified vinyl alcohol polymer contains a monomer unit having an alkyl group having 5-29 carbon atoms, and has a viscosity-average polymerization degree P of 200 or more and 5,000 or less, a saponification degree of 20 mol% or more and 99.99 mol% or less, and an alkyl-modified rate S of 0.05 mol% or more and 5 mol% or less.

Description

  The present invention relates to a conductive paste used for forming an internal electrode layer of a multilayer electronic component such as a multilayer ceramic capacitor or a conductive layer of a solar cell, and a multilayer ceramic capacitor obtained by using the conductive paste and a ceramic green sheet. .

  The multilayer ceramic capacitor is a chip type ceramic capacitor in which a large number of dielectric layers such as titanium oxide and barium titanate and internal electrode layers are stacked. Such a multilayer ceramic capacitor is manufactured by the following method, for example. First, in an organic solvent in which ceramic powder is dispersed, a binder resin such as polyvinyl butyral resin and a plasticizer are added, and a slurry composition for a ceramic green sheet is prepared by uniformly mixing with a ball mill or the like. The slurry composition is cast on a releasable support such as a polyethylene terephthalate film, the solvent is removed by heating or the like, and then peeled from the support to produce a ceramic green sheet.

  The ceramic green sheet thus obtained is used after being peeled off from the peelable support. First, a plurality of laminates obtained by alternately applying a conductive paste serving as an internal electrode on the surface of a ceramic green sheet by screen printing or the like are heated and pressed to obtain a laminate. Furthermore, a laminated body is formed by various processes and cut into a predetermined shape. Then, through a process of thermally decomposing and removing the binder component contained in the laminate, so-called degreasing treatment, and then sintering the external electrode on the end face of the ceramic fired product obtained by firing. A multilayer ceramic capacitor can be manufactured.

  In recent years, ceramic green sheets have been made thinner and multilayered for the purpose of reducing the size and increasing the capacity of multilayer ceramic capacitors. However, as the ceramic green sheets become thinner and multi-layered, the difference between the part where the conductive paste is printed and the part where the conductive paste is not printed becomes larger. The deformation of the sheet and the internal electrode layer has occurred, causing a problem that the electrical characteristics and reliability of the multilayer ceramic capacitor are lowered. In addition, with the miniaturization and increase in capacity of multilayer ceramic capacitors, there has been a problem that printability is insufficient with conventional conductive pastes.

  In order to solve these problems, a conductive paste containing a specific modified polyvinyl acetal resin has been proposed (see Patent Document 1). However, in Patent Document 1, when printing the conductive paste on the ceramic green sheet, the binder such as polyvinyl butyral resin in the ceramic green sheet is dissolved by the organic solvent contained in the conductive paste, so that the sheet attack resistance is not good. It was enough. Further, the thixotropic property of the conductive paste was insufficient.

  Here, the thixotropic property of the conductive paste means a property that the apparent viscosity is low when the shear rate is high, and the apparent viscosity is high when the shear rate is low and when the shear rate is not sheared.

  On the other hand, in the manufacture of electronic components, the use of conventional organic solvents has caused problems such as human safety hazards, environmental pollution, fire, and explosion risks. In order to solve such problems, it has been proposed to use an aqueous slurry containing polyvinyl alcohol instead of an organic slurry as a slurry composition for ceramic green sheets (see Patent Document 2). However, Patent Document 2 does not describe the use of an aqueous solvent as a solvent for a conductive paste printed on a ceramic green sheet, and the thixotropy and sheet attack resistance of the conductive paste are still insufficient. .

  In order to solve these various problems, there has been a demand for a conductive paste that is excellent in thixotropy and sheet attack resistance and is safe for the human body and the environment.

JP 2008-143922 A JP 2002-284579 A

  An object of the present invention is to provide a conductive paste that is excellent in printability such as thixotropy, string resistance, bleed resistance, and sheet attack resistance. Furthermore, it aims at providing the electrically conductive paste which can manufacture a laminated ceramic capacitor efficiently.

（式（Ｉ）中、Ｒ^１は、炭素数５〜２９の直鎖状または分岐状アルキル基を表す。Ｒ^２は、水素原子またはメチル基を表す。）
［６］上記［１］〜［５］のいずれかの導電ペーストとセラミックグリーンシートとを用いて得られる積層セラミックコンデンサ；
に関する。 That is, the present invention
[1] An alkyl-modified vinyl alcohol polymer (hereinafter sometimes abbreviated as alkyl-modified PVA), a conductive paste containing conductive powder and an aqueous solvent, wherein the alkyl-modified vinyl alcohol polymer is carbon. A monomer unit having an alkyl group of 5 to 29, a viscosity average polymerization degree P of 200 or more and 5000 or less, a saponification degree of 20 mol% or more and 99.99 mol% or less, and an alkyl modification rate. A conductive paste having S of 0.05 mol% or more and 5 mol% or less;
[2] The conductive paste according to [1], wherein a content ratio of the alkyl-modified vinyl alcohol polymer is 0.1% by mass or more and 10% by mass or less;
[3] The conductive paste according to [1] or [2], wherein the content of water in the aqueous solvent is 60% by mass or more;
[4] The conductive paste according to any one of the above [1] to [3], wherein the alkyl group in the alkyl-modified vinyl alcohol polymer is an alkyl group having 15 to 26 carbon atoms;
[5] The conductive paste according to any one of [1] to [4], wherein the monomer unit is an N-alkyl (meth) acrylamide unit represented by the following formula (I):

(In Formula (I), R ¹ represents a linear or branched alkyl group having 5 to 29 carbon atoms. R ² represents a hydrogen atom or a methyl group.)
[6] A multilayer ceramic capacitor obtained using the conductive paste according to any one of [1] to [5] above and a ceramic green sheet;
About.

  The conductive paste of the present invention is excellent in printability such as thixotropy, yarn pulling resistance, bleeding resistance, and sheet attack resistance. Therefore, the conductive paste of the present invention can be suitably used as a conductive paste used for forming an internal electrode layer of a multilayer electronic component such as a multilayer ceramic capacitor or a conductive layer of a solar cell.

  The above-mentioned thread pulling resistance or bleeding resistance means that stringing or bleeding is unlikely to occur. Here, the stringing means that the conductive paste does not peel off cleanly from the plate used for printing, and the printing surface is in a state where the thread is pulled. This means that the apparent viscosity of the conductive paste is high in a state where the shear rate is high. Occurs when. On the other hand, blotting refers to a phenomenon in which a printed conductive paste flows on a ceramic green sheet and is printed in a state where it is wider than a target printed shape. This is a state in which the shear rate is low and unsheared. Occurs when the apparent viscosity of the conductive paste is low.

  Hereinafter, the conductive paste of the present invention, the manufacturing method thereof, and embodiments of the multilayer ceramic capacitor obtained by using the conductive paste will be described in detail.

[Conductive paste]
The electrically conductive paste of this invention contains specific alkyl modified PVA, electrically conductive powder, and an aqueous solvent, and may contain another component as needed. Hereinafter, each component contained in the electrically conductive paste of this invention is demonstrated.

(Alkyl-modified PVA)
The alkyl-modified PVA used in the present invention contains a monomer unit having an alkyl group having 5 to 29 carbon atoms. That is, the alkyl-modified PVA is a copolymer containing a monomer unit having an alkyl group having 5 to 29 carbon atoms and a vinyl alcohol unit (—CH ₂ —CHOH—). It may contain a monomer unit. When such an alkyl-modified PVA is used, the thixotropic property of the obtained conductive paste is improved by the hydrophobic group interaction in the alkyl-modified PVA. For this reason, when the conductive paste is printed, the printed portion is difficult to spread, and printability such as stringing resistance and bleeding resistance is improved. When the number of carbon atoms of the alkyl group is less than 5, the interaction between the alkyl groups is not sufficiently exhibited, so that the thixotropic property is lowered. On the other hand, when the carbon number of the alkyl group exceeds 29, the water solubility and handling property at high temperature of the alkyl-modified PVA are lowered. Among these, from the viewpoint of further improving thixotropy, an alkyl group having 8 to 29 carbon atoms is preferable, an alkyl group having 12 to 27 carbon atoms is more preferable, an alkyl group having 15 to 26 carbon atoms is further preferable, An alkyl group having 17 to 24 is particularly preferable.

Examples of the monomer unit having an alkyl group having 5 to 29 carbon atoms include monomer units derived from α-olefins such as 1-octene and 1-decene; pentyl vinyl ether, octyl vinyl ether, nonyl vinyl ether, Monomer units derived from vinyl ethers such as dodecyl vinyl ether and octadecyl vinyl ether; alkyl (meth) acrylates; N-alkyl (meth) acrylamide units represented by the following formula (I) are preferred, and R ¹ below has 8 carbon atoms. More preferred are N-alkyl (meth) acrylamide units that are -29 alkyl groups.

In formula (I), R ¹ represents a linear or branched alkyl group having 5 to 29 carbon atoms. R ² represents a hydrogen atom or a methyl group. In addition, R ¹ and R ² may have a substituent such as a halogen atom as long as the effects of the present invention are not impaired, but preferably do not have these substituents. .

Examples of the alkyl group having 5 to 29 carbon atoms represented by R ¹ include a pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group, pentadecyl group, and nonadecyl group. . Among these, from the viewpoint of further improving thixotropy, an alkyl group having 8 to 29 carbon atoms is preferable, an alkyl group having 12 to 27 carbon atoms is more preferable, an alkyl group having 15 to 26 carbon atoms is further preferable, An alkyl group having 17 to 24 is particularly preferable.

R ² is a hydrogen atom or a methyl group from the viewpoint of ease of synthesis and the like.

  The method for producing the alkyl-modified PVA is not particularly limited, but an alkyl-modified vinyl ester polymer obtained by copolymerizing an unsaturated monomer represented by the following formula (II) and a vinyl ester monomer. A method of saponifying is preferred.

In the formula (II), the definitions of R ¹ and R ² are the same as in the above formula (I).

  Examples of the unsaturated monomer represented by the above formula (II) include N-octylacrylamide, N-decylacrylamide, N-dodecylacrylamide, N-octadecylacrylamide, N-hexacosylacrylamide, and N-octylmethacrylamide. N-decyl methacrylamide, N-dodecyl methacrylamide, N-octadecyl methacrylamide, N-hexacosyl methacrylamide and the like. Of these, N-octadecyl acrylamide, N-octyl methacrylamide, N-decyl methacrylamide, N-dodecyl methacrylamide, N-octadecyl methacrylamide, N-hexacosyl methacrylamide are preferred, and N-octadecyl acrylamide, N- Dodecyl methacrylamide and N-octadecyl methacrylamide are more preferable, and N-octadecyl acrylamide and N-octadecyl methacrylamide are more preferable.

  The temperature when copolymerizing the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is not particularly limited, but is preferably 0 ° C or higher and 200 ° C or lower, and 30 ° C or higher and 140 ° C or lower. Is more preferable. When the copolymerization temperature is lower than 0 ° C., it is difficult to obtain a sufficient polymerization rate. Moreover, when the temperature which performs superposition | polymerization is higher than 200 degreeC, the alkyl modification PVA which has the alkyl modification rate S prescribed | regulated by this invention is hard to be obtained. As a method for controlling the temperature employed in the copolymerization to 0 ° C. or more and 200 ° C. or less, for example, by controlling the polymerization rate, the heat generated by the polymerization is balanced with the heat released from the surface of the reactor. Examples thereof include a method and a method of controlling by an external jacket using an appropriate heat medium, but the latter method is preferable from the viewpoint of safety.

  The polymerization method employed for copolymerizing the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is batch polymerization, semi-batch polymerization, continuous polymerization, or semi-continuous polymerization. Either is acceptable. As the polymerization method, an arbitrary method can be adopted from known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among these, a bulk polymerization method or a solution polymerization method in which polymerization is performed in the absence of a solvent or in the presence of an alcohol solvent is preferably employed. For the purpose of producing a copolymer having a high degree of polymerization, an emulsion polymerization method is employed. As the alcohol solvent used in the bulk polymerization method or the solution polymerization method, methanol, ethanol, n-propanol or the like can be used, but is not limited thereto. These solvents can be used in combination of two or more.

  As the initiator used for copolymerization, conventionally known azo initiators, peroxide initiators, redox initiators and the like are appropriately selected according to the polymerization method. As the azo initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethyl valeronitrile) and the like, and peroxide initiators include perisopropyl compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; t-butyl Perester compounds such as peroxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxydecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc. Is mentioned. Furthermore, the initiator can be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form an initiator. Moreover, as a redox-type initiator, what combined said peroxide and reducing agents, such as sodium hydrogen sulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, Rongalite, is mentioned.

  In addition, when copolymerization of the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer is performed at a high temperature, coloring of PVA due to decomposition of the vinyl ester monomer may occur. It may be seen. In that case, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of 1 ppm to 100 ppm (with respect to the mass of the vinyl ester monomer) for the purpose of preventing coloring.

  Vinyl ester monomers used for copolymerization include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, and lauric acid. Examples thereof include vinyl, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like. Of these, vinyl acetate is most preferred.

  When the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer are copolymerized, other monomers may be copolymerized within a range not impairing the gist of the present invention. Examples of monomers that can be used include α-olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, and i-propyl acrylate. Acrylic acid esters such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate; methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate , Methacrylic acid esters such as n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate; acrylamide; N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane Sulfo Acrylamide derivatives such as acid and salts thereof, acrylamidopropyldimethylamine and salts thereof or quaternary salts thereof, N-methylolacrylamide and derivatives thereof; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid And methacrylamide derivatives such as methacrylamide dimethyldimethylamine and quaternary salts thereof, N-methylol methacrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n- Vinyl ethers such as butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane; Nitriles such as rilonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl acetate, 2,3-diacetoxy-1-allyloxypropane And allyl compounds such as allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid, and salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like.

  Further, for the purpose of adjusting the degree of polymerization of the resulting alkyl-modified vinyl ester polymer upon copolymerization of the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer, Copolymerization may be performed in the presence of a chain transfer agent as long as the gist of the invention is not impaired. Chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; halogenated hydrocarbons such as trichloroethylene and perchloroethylene; sodium phosphinate 1 And phosphinic acid salts such as hydrates. Among these, aldehydes and ketones are preferably used. What is necessary is just to determine the addition amount of a chain transfer agent according to the chain transfer constant of the chain transfer agent to add, and the polymerization degree of the target vinyl ester polymer. In general, the content is preferably 0.1% by mass or more and 10% by mass or less based on the vinyl ester monomer.

  The saponification reaction of the alkyl-modified vinyl ester polymer may be an alcoholysis decomposition reaction using a conventionally known basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxide or an acidic catalyst such as p-toluenesulfonic acid. Hydrolysis reactions can be applied. Examples of the solvent that can be used in this reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene. These can be used alone or in combination of two or more. Among them, it is convenient and preferable to perform the saponification reaction using methanol or a methanol / methyl acetate mixed solution as a solvent and sodium hydroxide as a catalyst.

  In the alkyl-modified PVA used in the present invention, the content of the monomer unit having an alkyl group having 5 to 29 carbon atoms, that is, the alkyl modification rate (S) needs to be 0.05 mol% or more and 5 mol% or less. 0.1 mol% or more and 2 mol% or less is preferable, and 0.2 mol% or more and 1 mol% or less are more preferable. In addition, the alkyl modification rate S in this specification is the ratio of the number of moles of monomer units having an alkyl group having 5 to 29 carbon atoms in the number of moles of all structural units constituting the alkyl-modified PVA.

  When the alkyl modification rate S exceeds 5 mol%, the proportion of hydrophobic groups contained in one molecule of the alkyl-modified PVA increases, and the water solubility of the alkyl-modified PVA decreases. On the other hand, when the alkyl modification rate S is less than 0.05 mol%, the water content of the alkyl-modified PVA is excellent, but the number of alkyl groups contained in the alkyl-modified PVA is small, and the conductive paste is based on the alkyl modification. The thixotropy, yarn-drawing resistance and bleeding resistance are not fully expressed.

The alkyl modification rate S may be obtained from the alkyl-modified PVA or may be obtained from an alkyl-modified vinyl ester polymer that is a precursor thereof, and both can be obtained from proton NMR. For example, when obtaining from an alkyl-modified vinyl ester polymer, specifically, after reprecipitation and purification of the alkyl-modified vinyl ester polymer with n-hexane / acetone three or more times sufficiently, under reduced pressure at 50 ° C. Dry for 2 days to prepare a sample for analysis. This sample is dissolved in CDCl ₃ and measured at room temperature using proton NMR.

In this case, for example, when the alkyl-modified monomer unit other than the monomer unit is not included, R ¹ is linear, and R ² is a hydrogen atom, it can be calculated by the following method. That is, the peak α (4.7 to 5.2 ppm) derived from the main chain methine of the alkyl-modified vinyl ester polymer and the peak β (0.8 to 1.0 ppm) derived from the terminal methyl group of the alkyl group R ¹ From these, the alkyl modification rate S is calculated using the following equation.
Alkyl modification rate S (mol%) = {(number of protons of β / 3) / (number of protons of α + (number of protons of β / 3))} × 100

  The alkyl-modified PVA has a viscosity average degree of polymerization (P) (hereinafter, the viscosity average degree of polymerization may be simply referred to as a degree of polymerization) of 200 to 5000, preferably 500 to 4000, preferably 1000 or more. 3000 or less is more preferable. When the degree of polymerization of the alkyl-modified PVA exceeds 5000, the productivity of the alkyl-modified PVA is lowered, which is not practical. On the contrary, when the degree of polymerization of the alkyl-modified PVA is less than 200, the thixotropic property of the obtained conductive paste is not sufficiently developed.

This viscosity average polymerization degree P is measured according to JIS-K6726. That is, after re-saponifying and purifying the alkyl-modified PVA, it is obtained by the following formula from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C.
Viscosity average polymerization degree P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

  The saponification degree of the alkyl-modified PVA needs to be 20 mol% or more and 99.99 mol% or less, preferably 40 mol% or more and 99.9 mol% or less, more preferably 60 mol% or more and 99.5 mol%. 80 mol% or more and 99 mol% is more preferable. When the saponification degree of the alkyl-modified PVA is less than 20 mol%, it is difficult to prepare a conductive paste because the water solubility of the alkyl-modified PVA decreases. On the other hand, when the saponification degree of the alkyl-modified PVA exceeds 99.99 mol%, production of the alkyl-modified PVA becomes difficult, which is not practical. The saponification degree of the alkyl-modified PVA is a value that can be measured according to JIS-K6726.

  The content ratio of the alkyl-modified PVA in the conductive paste of the present invention is preferably 0.1% by mass or more and 10% by mass or less from the viewpoint of further improving the thixotropic property of the obtained conductive paste.

(Conductive powder)
The conductive powder used in the present invention is not particularly limited as long as it exhibits conductivity, and examples thereof include nickel, palladium, platinum, gold, silver, copper, and powders made of these alloys. As the conductive powder, it is preferable to use a conductive powder in which an insoluble inorganic oxide that is an oxide containing silicon, aluminum, or zirconium is adsorbed on the surface. By using such a conductive powder, the conductive powder is stably dispersed at a high concentration in the aqueous slurry without being re-agglomerated, so that it can be suitably used as a conductive paste for firing, particularly a conductive paste for forming a multilayer ceramic capacitor. The said electrically conductive powder may be used independently, or may use 2 or more types together.

  The content of the conductive powder in the conductive paste of the present invention is preferably 30% by mass or more and 80% by mass or less from the viewpoint of further improving the thixotropic property of the obtained conductive paste.

(Aqueous solvent)
In the conductive paste of the present invention, it is important to use an aqueous solvent as a solvent. The reason for this is that the alkyl-modified PVA has a high polarity because it has a large number of hydroxyl groups in the molecule, and tends to be hardly dissolved in an organic solvent. Therefore, the conductive paste of the present invention can be easily produced by using an aqueous solvent.

  In addition, by using a water-based solvent as a solvent, as described later, when a laminated ceramic capacitor is produced by printing a conductive paste on a ceramic green sheet, a resin such as polyvinyl acetal contained in the ceramic green sheet is reduced. There is also an advantage that it is difficult to dissolve in the conductive paste, and particularly excellent in sheet attack resistance.

  The aqueous solvent is not particularly limited, but from the viewpoints of safety to human body, environmental pollution, possibility of fire, possibility of explosion, etc., those mainly composed of water are preferable. Specifically, in the aqueous solvent The content of water is more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and may be 100% by mass. The water is preferably distilled water or ion exchange water, and more preferably ion exchange water.

  The content ratio of the aqueous solvent in the conductive paste of the present invention is preferably 20% by mass or more and 70% by mass or less from the viewpoint of further improving the thixotropic property of the obtained conductive paste.

(Other ingredients)
The electrically conductive paste of the present invention is a water-soluble polymer such as various known PVAs (excluding the alkyl-modified PVA used in the present invention), starch, carboxymethylcellulose, methylcellulose, and hydroxymethylcellulose, as long as the gist of the present invention is not impaired. Other components such as a plasticizer, a lubricant, a dispersant, and an antistatic agent may be contained.

  The method for producing the conductive paste of the present invention is not particularly limited. For example, the conductive powder, the alkyl-modified PVA, the aqueous solvent and other components are supplied to a known mixer such as a blender mill or a three-roll. The manufacturing method of the electrically conductive paste to knead | mix can be employ | adopted.

The viscosity of the conductive paste of the present invention is not particularly limited, but the viscosity ratio η ₂ / η between the viscosity η ₁ at a shear rate of 1 (1 / sec) and the viscosity η ₂ at a shear rate of 100 (1 / sec). ₁ is preferably 0.8 or less, more preferably 0.5 or less, further preferably 0.3 or less, and particularly preferably 0.1 or less. When the viscosity ratio η ₂ / η ₁ is within the above range, the thixotropy is further enhanced, and a conductive paste that is more excellent in string resistance and bleed resistance can be obtained.

(Use)
The conductive paste of the present invention is suitably used for forming an internal electrode layer of a multilayer electronic component such as a multilayer ceramic capacitor or a conductive layer of a solar cell. Therefore, a multilayer ceramic capacitor obtained using the conductive paste and ceramic green sheet of the present invention is also one aspect of the present invention. Since the conductive paste of the present invention is excellent in printability such as thixotropy, string pull resistance, bleeding resistance and sheet attack resistance, a multilayer ceramic capacitor can be efficiently produced by using the conductive paste.

  The method for producing the slurry composition used for the ceramic green sheet is not particularly limited. For example, a binder resin such as polyvinyl acetal resin, ceramic powder, an organic solvent, and various additives to be added as necessary are ball mill, blender, etc. The method of mixing using various mixers, such as a mill and a 3 roll, is employ | adopted.

  The method for producing the ceramic green sheet is not particularly limited and can be produced by a conventionally known production method. For example, the ceramic green sheet slurry composition is cast on a peelable support such as a polyethylene terephthalate film. A method of forming and removing the solvent by heating or the like and then peeling off from the support is employed.

  A multilayer ceramic capacitor can be manufactured by laminating the ceramic green sheet obtained in this way with the printed (coated) conductive paste of the present invention. Specifically, for example, a plurality of sheets obtained by applying the conductive paste of the present invention to the surface of the ceramic green sheet by screen printing or the like are alternately stacked and heat-pressed to form a laminate, and the resin contained in the laminate For example, a method of sintering an external electrode on the end face of the ceramic fired product obtained by pyrolyzing and removing (degreasing treatment) and the like is employed.

  Hereinafter, the present invention will be described in detail by way of examples and comparative examples. In the following Examples and Comparative Examples, “part” and “%” mean mass basis unless otherwise specified.

  PVA (alkyl-modified PVA and non-modified PVA) obtained by the following production examples was evaluated according to the following method.

[Viscosity average polymerization degree P and degree of saponification of PVA]
The viscosity average polymerization degree P and saponification degree of PVA were determined by the method described in JIS-K6726.

[Alkyl modification rate S of PVA]
The alkyl modification rate S of PVA was determined according to the method using proton NMR described above. For proton NMR, 500 MHz JEOL GX-500 was used.

[Production Example 1] Production of PVA1 Into a 3 L reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropping port and initiator addition port, 750 g of vinyl acetate, 250 g of methanol and N-octadecylmethacrylamide 1 .1 g was charged, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. Further, a comonomer solution in which N-octadecylmethacrylamide was dissolved in methanol to a concentration of 5% was prepared as a delay solution, and this comonomer solution was purged with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The delay solution was added dropwise to the reactor so that the monomer composition in the polymerization solution was constant, and polymerization was performed at 60 ° C. for 3 hours, followed by cooling to stop the polymerization. The total amount of comonomer added until the polymerization was stopped was 4.8 g. The solid content concentration when the polymerization was stopped was 29.9%. Subsequently, unreacted vinyl acetate monomer was removed while occasionally adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of an alkyl-modified vinyl acetate polymer (alkyl-modified PVAc). Further, 777.9 g of alkyl-modified PVAc methanol solution prepared by adding methanol (200.0 g of alkyl-modified PVAc in the solution) was added to 27.9 g of an alkali solution (sodium hydroxide in 10% methanol). Saponification was carried out by addition (concentration of alkyl-modified PVAc in the saponification solution was 25%, and the molar ratio of sodium hydroxide to vinyl acetate units in the alkyl-modified PVAc was 0.03). A gel was formed about 1 minute after the addition of the alkaline solution. The gel-like material was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to allow saponification to proceed. Then, 500 g of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this white solid, 2000 g of methanol was added and washed at room temperature for 3 hours. This washing operation was repeated three times, and then the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain alkyl-modified PVA (PVA1). PVA1 had a viscosity average polymerization degree P of 1700, a saponification degree of 98.5 mol%, and an alkyl modification rate S of 0.4 mol%.

[Production Examples 2 to 4] Production of PVA 2 to 4 Kinds of N-alkyl (meth) acrylamide units and their amounts used, polymerization rate, concentration of alkyl-modified PVAc during saponification, and molar ratio of sodium hydroxide to vinyl acetate units Except for having changed as shown in Table 1, various PVA (PVA2-4) was manufactured by the same method as the manufacture example 1.

[Example 1]
(Manufacture of conductive paste)
2 g of PVA1 obtained in Production Example 1 and 98 g of ion-exchanged water were supplied to a separable flask equipped with a stirring blade, stirred for 2 hours while heating in a 90 ° C. water bath, and 2% PVA1 An aqueous solution of was prepared. Next, the total amount of the prepared 2% PVA1 aqueous solution and 100 g of nickel powder (Mitsui Metal Mining Co., Ltd .; 2020SS) as a conductive powder were supplied to three rolls to prepare a conductive paste.

(Evaluation)
The conductive paste produced in Example 1 was evaluated by the following method. The evaluation results are shown in Table 2.

(Production of ceramic green sheets)
10 parts of polyvinyl butyral resin (manufactured by Kuraray Co., Ltd .; Mobital B60H) was added to a mixed solvent of 30 parts of toluene and 15 parts of ethanol and dissolved by stirring. Subsequently, 3 parts of dibutyl phthalate was added as a plasticizer and dissolved by stirring. To the obtained solution, 100 parts of barium titanate (manufactured by Sakai Chemical Industry Co., Ltd .; BT-01 (average particle size 0.1 μm)) is added as a ceramic powder, and mixed for 48 hours with a ball mill to obtain a ceramic slurry composition. It was. The obtained slurry composition was applied onto a release-treated polyester film so that the thickness after drying was about 1 μm, air-dried at room temperature for 1 hour, a hot-air dryer at 80 ° C. for 3 hours, then After drying at 120 ° C. for 2 hours, a ceramic green sheet was produced by peeling off from the polyester film.

(1) Viscosity As an index of thixotropy of the conductive paste produced in Example 1, the viscosity of the conductive paste was measured in the FLOW SWEEP mode under the following measurement conditions using a rotary rheometer (manufactured by TA INSTRUMENT; ARES G2). , Shear rate: 1 (1 / sec), and shear rate: 100 (1 / sec). The viscosity η ₁ at a shear rate of 1 (1 / sec) is 25 Pa · s, the viscosity η ₂ at a shear rate of 100 (1 / sec) is 1.5 Pa · s, and the viscosity ratio η ₂ / η ₁ was 0.06.
<Measurement conditions>
Diameter of rotating disk: 40mm
Rotating disk (upper): Cone angle of rotating disk (lower): 0.02 rad
Traction gap: 0.0262mm

(2) Yarn pulling resistance The conductive paste produced in Example 1 was printed on the ceramic green sheet with a screen printer, and then dried in an oven at 100 ° C. for 30 minutes. Thereafter, the stringiness of the printed portion was observed with an optical microscope and evaluated according to the following criteria.
A: There is no stringing of 20 μm or more in length.
X: There is stringing of 20 μm or more in length.

(3) Smear resistance The conductive paste produced in Example 1 was printed on the ceramic green sheet with a screen printer, and then dried in an oven at 100 ° C. for 30 minutes. Thereafter, the bleeding resistance of the printed portion was observed with an optical microscope and evaluated according to the following criteria.
○: The amount of bleeding is less than 20 μm.
X: The amount of bleeding is 20 μm or more.

(4) Sheet Attack Resistance After the conductive paste produced in Example 1 was printed on the ceramic green sheet with a screen printer, it was dried in an oven at 100 ° C. for 30 minutes. Thereafter, the sheet attack property of the ceramic green sheet with respect to the conductive paste was evaluated by observing swelling and distortion of the back side of the printed sheet with a stereomicroscope and according to the following criteria.
○: Almost no swelling or distortion.
X: There exists swelling and distortion.

[Example 2]
A conductive paste was produced in the same manner as in Example 1 except that PVA2 was used instead of PVA1. With respect to the obtained conductive paste, the viscosity, yarn pull resistance, bleeding resistance and sheet attack resistance were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[Example 3]
A conductive paste was produced in the same manner as in Example 1 except that PVA3 was used instead of PVA1. With respect to the obtained conductive paste, the viscosity, yarn pull resistance, bleeding resistance and sheet attack resistance were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[Comparative Example 1]
A conductive paste was produced in the same manner as in Example 1 except that PVA4 was used instead of PVA1. With respect to the obtained conductive paste, the viscosity, yarn pull resistance, bleeding resistance and sheet attack resistance were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[Comparative Example 2]
Instead of water used as the aqueous solvent in the conductive paste, an attempt was made to produce a conductive paste in the same manner as in Example 1 except that α-terpineol was used, but PVA1 was not completely dissolved, A uniform solution could not be prepared.

[Comparative Example 3]
92 g of α-terpineol was heated with a heater to a temperature of 60 ° C., and 8 g of ethyl cellulose (manufactured by Dow Chemical; STD-200) was gradually added while stirring with a stirring blade to prepare an 8% ethyl cellulose solution. Next, the total amount of the prepared 8% ethyl cellulose solution and 100 g of nickel powder (Mitsui Metal Mining Co., Ltd .; 2020SS) as a conductive powder were supplied to three rolls to prepare a conductive paste. With respect to the obtained conductive paste, the viscosity, yarn pull resistance, bleeding resistance and sheet attack resistance were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

  The conductive paste of the present invention is excellent in thixotropy, has little stringiness and bleeding at the time of printing, and is also excellent in sheet attack resistance against ceramic green sheets. Therefore, the internal electrode of multilayer electronic components such as multilayer ceramic capacitors It can be suitably used as a conductive paste used for forming a layer or a conductive layer of a solar cell.

Claims (6)

A conductive paste containing an alkyl-modified vinyl alcohol polymer, a conductive powder and an aqueous solvent,
The alkyl-modified vinyl alcohol polymer contains a monomer unit having an alkyl group having 5 to 29 carbon atoms, has a viscosity average polymerization degree P of 200 or more and 5000 or less, and a saponification degree of 20 mol% or more and 99.99. The electrically conductive paste which is 99 mol% or less and whose alkyl modification rate S is 0.05 mol% or more and 5 mol% or less.   2. The conductive paste according to claim 1, wherein a content ratio of the alkyl-modified vinyl alcohol polymer is 0.1% by mass or more and 10% by mass or less.   The electrically conductive paste of Claim 1 or 2 whose content rate of the water in the said aqueous solvent is 60 mass% or more.   The conductive paste according to any one of claims 1 to 3, wherein the alkyl group in the alkyl-modified vinyl alcohol polymer is an alkyl group having 15 to 26 carbon atoms. The conductive paste according to claim 1, wherein the monomer unit is an N-alkyl (meth) acrylamide unit represented by the following formula (I).

(In Formula (I), R ¹ represents a linear or branched alkyl group having 5 to 29 carbon atoms. R ² represents a hydrogen atom or a methyl group.)   A multilayer ceramic capacitor obtained by using the conductive paste according to any one of claims 1 to 5 and a ceramic green sheet.