JP2013114890A - 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; a polyoxyalkylene-modified vinyl alcohol polymer having a polyoxyalkylene group in a side chain; and an aqueous solvent. The polyoxyalkylene-modified vinyl alcohol polymer 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 a polyoxyalkylene group modification rate S of 0.05 mol% or more and 10 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, resulting in 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は水素原子またはメチル基である。Ｒ^２は水素原子または炭素数１〜８のアルキル基である。ｍおよびｎは、それぞれオキシアルキレンユニットの繰り返し単位数を表し、１≦ｍ≦３０、１≦ｎ≦２０である。）
［７］上記［１］〜［６］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] A polyoxyalkylene-modified vinyl alcohol polymer having a polyoxyalkylene group (hereinafter sometimes abbreviated as POA group) in the side chain (hereinafter abbreviated as POA-modified PVA), conductive. A conductive paste containing a powder and an aqueous solvent, wherein the polyoxyalkylene-modified vinyl alcohol polymer 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 mol% or less. A conductive paste having a polyoxyalkylene group modification rate S of 0.05 mol% or more and 10 mol% or less;
[2] The conductive paste according to [1], wherein a content ratio of the POA-modified PVA 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 [1] to [3], wherein the POA group is at least one group selected from the group consisting of a polyoxyethylene group, a polyoxypropylene group, and a polyoxybutylene group. ;
[5] The conductive paste according to any one of [1] to [4], wherein the number of units of the POA group is 2 to 50;
[6] The conductive paste according to any one of [1] to [5], wherein the POA group is a POA group represented by the following formula (I):

(In Formula (I), R ¹ is a hydrogen atom or a methyl group. R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. M and n each represent the number of repeating units of an oxyalkylene unit. 1 ≦ m ≦ 30 and 1 ≦ n ≦ 20.)
[7] A multilayer ceramic capacitor obtained using the conductive paste according to any one of [1] to [6] 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 POA 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.

(POA-modified PVA)
The POA-modified PVA used in the present invention has a POA group in the side chain. By using POA-modified PVA having a POA group in the side chain as described above, the thixotropic property of the obtained conductive paste is improved. 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. As said POA group, it is preferable that it is a POA group which has a C1-C8 alkylene group, for example, At least 1 sort (s) selected from the group which consists of a polyoxyethylene group, a polyoxypropylene group, and a polyoxybutylene group The POA group is more preferable. Note that the POA-modified PVA in the conductive paste functions as a binder.

  When the POA-modified PVA has two or more types of oxyalkylene groups in the molecule, the two or more types of oxyalkylene groups may be either random or block. Among them, the block shape is preferable from the viewpoint of easily expressing the physical properties based on the POA group.

  The average number of oxyalkylene groups in the POA group is preferably 2 to 50, more preferably 5 to 40, still more preferably 8 to 30, and particularly preferably 10 to 25. . Thus, the thixotropic property of the obtained electrically conductive paste improves further because the average unit number of an oxyalkylene group exists in the said range. In addition, when the said POA group consists of 2 or more types of oxyalkylene groups, let the total number of units of each oxyalkylene group be the number of units of an oxyalkylene group.

Among these, the POA group is particularly preferably a POA group represented by the above formula (I). In the above formula (I), R ¹ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom from the viewpoint of productivity.

In the above formula (I), ^{R 2} is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. R ² is preferably a hydrogen atom, a methyl group or a butyl group, more preferably a hydrogen atom or a methyl group.

  In the above formula (I), m and n each represent the average number of repeating units of the oxyalkylene group, and preferably 1 ≦ m ≦ 30 and 1 ≦ n ≦ 20. Here, a unit having the number of repeating units m is referred to as unit 1, and a unit having the number of repeating units n is referred to as unit 2.

  The number m of repeating units 1 of the POA group unit 1 represented by the above formula (I) is preferably 1 ≦ m ≦ 30, more preferably 1 ≦ m ≦ 20, further preferably 1 ≦ m ≦ 10, and 1 ≦ m ≦ 5. Is particularly preferred. When the number m of repeating units is in the above range, the thixotropy of the obtained conductive paste is further improved.

  The number of repeating units n of the POA group unit 2 represented by the above formula (I) is preferably 1 ≦ n ≦ 20, more preferably 5 ≦ n ≦ 18, and further preferably 8 ≦ n ≦ 15. When the number of repeating units n is in the above range, the thixotropic property of the obtained conductive paste is further improved.

  The method for producing the POA-modified PVA of the present invention is not particularly limited, but the POA-modified vinyl ester polymer obtained by copolymerizing an unsaturated monomer having a POA group in the side chain and a vinyl ester monomer is obtained. A method of saponifying the coalescence is preferred.

  The unsaturated monomer having a POA group in the side chain is preferably an unsaturated monomer having a POA group represented by the above formula (I) in the side chain, for example, an unsaturated monomer represented by the following formula (II) A monomer is preferred. That is, the POA-modified vinyl ester system obtained by copolymerizing an unsaturated monomer represented by the following formula (II) having a POA group represented by the above formula (I) and a vinyl ester monomer. A method of saponifying the polymer is more preferable.

In the formula (II), R ¹ , R ² , m and n are the same as those in the above formula (I). R ³ represents a hydrogen atom or a —COOM group, where M represents a hydrogen atom, an alkali metal or an ammonium group. R ⁴ represents a hydrogen atom, a methyl group or a —CH ₂ —COOM group, where M is as defined above. X is _{-O -, - CH 2 -O -} , - CO -, - (CH 2) k -, - COO -, - CO-NR 5 - or ^-CO-NR 5 -CH ₂ - represents a. When X is asymmetric, the direction is not limited. Here, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and 1 ≦ k ≦ 15.

In the unsaturated monomer represented by the above formula (II), preferred examples and numerical ranges of R ¹ , R ² , m and n are the same as those described above in the description of the formula (I). R ³ is preferably a hydrogen atom, and R ⁴ is preferably a hydrogen atom or a methyl group. X is preferably —CH ₂ —O—, —CO—NR ⁵ — or —CO—NR ⁵ —CH ₂ —, and is —CO—NR ⁵ — or —CO—NR ⁵ —CH ₂ —. More preferably. Furthermore, R ⁵ is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom.

For example, when R ^{2 in the} formula (II) is a hydrogen atom, R ³ is a hydrogen atom, and R ⁴ is a hydrogen atom or a methyl group, the unsaturated monomer represented by the formula (II) Examples include mono (meth) acrylic acid amide, polyoxyalkylene mono (meth) allyl ether, polyoxyalkylene monovinyl ether, and polyoxyalkylene mono (meth) acrylate. Specifically, polyoxyethylene polyoxybutylene monoacrylic acid Amide, N-methylene polyoxyethylene polyoxybutylene monoacrylic acid amide, Polyoxyethylene polyoxybutylene monomethacrylamide, N-methylene polyoxyethylene polyoxybutylene monomethacrylamide, Polyoxyethylene polyoxybutylene monoallyl ether The Oxyethylene polyoxybutylene monomethallyl ether, polyoxyethylene polyoxybutylene monovinyl ether, polyoxyethylene polyoxybutylene monoacrylate, polyoxyethylene polyoxybutylene monomethacrylate, polyoxypropylene polyoxybutylene monoacrylic amide, N- Methylene polyoxypropylene polyoxybutylene monoacrylic amide, polyoxypropylene polyoxybutylene monomethacrylamide, N-methylene polyoxypropylene polyoxybutylene monomethacrylamide, polyoxypropylene polyoxybutylene monoallyl ether, polyoxypropylene Polyoxybutylene monomethallyl ether, polyoxypropylene polyoxybutylene monovinyl ether , Polyoxypropylene polyoxybutylene monoacrylate, polyoxypropylene polyoxybutylene monomethacrylate, and the like. Among these, polyoxyethylene polyoxybutylene monoacrylic amide, N-methylene polyoxyethylene polyoxybutylene monoacrylic amide, polyoxyethylene polyoxybutylene monomethacrylamide, N-methylene polyoxyethylene polyoxybutylene mono Methacrylic acid amide, polyoxyethylene polyoxybutylene monoallyl ether are preferably used, polyoxyethylene polyoxybutylene monomethacrylamide, N-methylene polyoxyethylene polyoxybutylene monomethacrylamide, polyoxyethylene polyoxybutylene Monoallyl ether is more preferably used, and polyoxyethylene polyoxybutylene monomethacrylamide, N-methylene polyoxyethylene polyoxybutylene module Methacrylamide are more preferred.

When R ^{2 in the} above formula (II) is an alkyl group having 1 to 8 carbon atoms, R ³ is a hydrogen atom, and R ⁴ is a hydrogen atom or a methyl group, the unsaturated monomer represented by the above formula (II) Specific examples include those in which the terminal hydroxyl group of the unsaturated monomer exemplified when R ^{2 in the} formula (II) is a hydrogen atom is substituted with an alkoxy group having 1 to 8 carbon atoms. Among these, polyoxyethylene polyoxybutylene monomethacrylamide, N-methylene polyoxyethylene polyoxybutylene monomethacrylamide, polyoxyethylene polyoxybutylene monoallyl ether, a hydroxyl group at the terminal is substituted with a methoxy group. Saturated monomers are preferably used, and unsaturated monomers in which the hydroxyl groups at the ends of polyoxyethylene polyoxybutylene monomethacrylamide and N-methylene polyoxyethylene polyoxybutylene monomethacrylamide are substituted with methoxy groups Is particularly preferably used.

  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, it is difficult to obtain POA modified PVA which has the POA group modification rate (S) prescribed | regulated by this invention. 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, 2-ethylhexyl acrylate, dodecyl acrylate and octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, methacryl Methacrylic acid such as ethyl acetate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Esters; N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salt, acrylamide propyl dimethylamine and its salt or its quaternary salt, N-methylol acrylamide and its Acrylamide derivatives such as derivatives; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacrylamide and Methacrylamide derivatives such as derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether , N-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, vinyl ethers such as 2,3-diacetoxy-1-vinyloxypropane; nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane and allyl chloride; maleic acid, Examples thereof include unsaturated dicarboxylic acids such as itaconic acid and fumaric acid and salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like.

  In addition, for the purpose of adjusting the degree of polymerization of the resulting POA-modified vinyl ester polymer in the copolymerization of the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer, Copolymerization may be carried out 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.

  For the saponification reaction of the POA-modified vinyl ester polymer, an alcohololysis 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 or the like. 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.

  The POA-modified PVA used in the present invention needs to have a POA group modification rate S of 0.05 mol% or more and 10 mol% or less, preferably 0.1 mol% or more and 5 mol% or less, preferably 0.15 mol%. More preferably, it is 2 mol% or less. The POA group modification rate S is represented by the mole fraction of POA groups with respect to the total of monomer units constituting the POA-modified PVA. When the POA group modification rate S exceeds 10 mol%, the ratio of the POA groups contained in one molecule of the POA modified PVA is increased, so that the water solubility of the POA modified PVA is lowered and the preparation of the conductive paste becomes difficult. . On the other hand, when the POA group modification rate S is less than 0.05 mol%, the proportion of POA groups contained in one molecule of the POA-modified PVA is low, and the resulting paste has thixotropy, string resistance and bleeding resistance. Not fully expressed.

Here, the POA group modification rate S of the POA-modified PVA obtained by saponification after copolymerizing the unsaturated monomer represented by the above formula (II) and the vinyl ester monomer will be described. The POA group modification rate S of the POA-modified PVA may be determined from the POA-modified PVA or from the precursor POA-modified vinyl ester polymer, and both can be determined from proton NMR. For example, when obtaining from a POA-modified vinyl ester polymer, specifically, after sufficiently reprecipitation purification of the POA-modified vinyl ester polymer three or more times using an n-hexane / acetone mixed solvent. Then, drying is performed under reduced pressure at 50 ° C. for 2 days to prepare a sample of POA-modified vinyl ester polymer for analysis. The sample is then dissolved in CDCl ₃ and measured at room temperature using proton NMR. The peak α derived from the proton of the main chain methine of the vinyl ester monomer unit (4.7 to 5.2 ppm) and the peak β derived from the proton of the terminal methyl group of the unit 2 (0.8 to 1. 0 ppm), the POA group modification rate S can be calculated using the following formula. In the following formula, n represents the number of repeating units of unit 2.
POA group modification rate S (mol%) = {(β peak area / 3n) / (α peak area + (β peak area / 3n))} × 100

  The POA-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 1000 to 4000, and preferably 2000 or more. 3000 or less is more preferable. When the polymerization degree of the POA-modified PVA exceeds 5000, the productivity of the POA-modified PVA is lowered and is not practical. On the other hand, when the degree of polymerization of the POA-modified PVA is less than 200, the thixotropic property of the obtained conductive paste is not sufficiently developed.

The viscosity average polymerization degree P of the POA-modified PVA is measured according to JIS-K6726. That is, after re-saponifying and purifying the 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 POA-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% are more preferable. When the saponification degree of the POA-modified PVA is less than 20 mol%, it is difficult to prepare a conductive paste because the water solubility of the POA-modified PVA decreases. On the other hand, when the saponification degree of the POA-modified PVA exceeds 99.99 mol%, it is not practical because the production of the POA-modified PVA becomes difficult. The saponification degree of the POA-modified PVA is a value that can be measured according to JIS-K6726.

  The content of the POA-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 is that the POA-modified PVA has a large number of hydroxyl groups in the molecule and thus has a high polarity and is difficult to dissolve 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 water-based solvents are preferred from the viewpoints of human safety, environmental pollution, fire, explosion risk, and the like. Specifically, the water-based solvent contains water. The rate 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 conductive paste of the present invention is a water-soluble polymer such as various known PVAs (excluding POA-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 POA-modified PVA, the aqueous solvent, and other components are supplied to a known mixer such as a blender mill, three rolls or the like. 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 in the production of 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 milled. , A method of mixing using various mixers such as a blender mill, three rolls or the like is employed.

  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 (POA-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.

[POA group modification rate S of PVA]
The POA group 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 A 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, a monomer dropping port and an initiator addition port has 750 g of vinyl acetate, 250 g of methanol, and a POA group. Monomer A which is an unsaturated monomer (monomer A is an unsaturated monomer represented by the following formula (III)) is charged with 3.3 g, and the system is maintained for 30 minutes while bubbling nitrogen. Replaced with nitrogen. Moreover, the solution which made the density | concentration 20% by melt | dissolving the monomer A in methanol as a delay solution was prepared, and nitrogen substitution was carried out by bubbling of 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.
While the delay solution was added dropwise so that the monomer composition (ratio of vinyl acetate and monomer A) in the polymerization solution was constant, polymerization was performed at 60 ° C. for 3 hours and then cooled to stop the polymerization. The total amount of monomer A added until the polymerization was stopped was 17.6 g. The solid content concentration when the polymerization was stopped was 24.4%. Subsequently, unreacted vinyl acetate monomer was removed while occasionally adding methanol at 30 ° C. under reduced pressure to obtain a methanol solution (concentration 35%) of POA-modified vinyl ester polymer (POA-modified PVAc). Furthermore, 55.6 g of an alkali solution (10% methanol solution of sodium hydroxide) was added to 453.4 g of POA-modified PVAc methanol solution prepared by adding methanol to this (100.0 g of POA-modified PVAc in the solution). Saponification was carried out (POA modified PVAc concentration of saponified solution 20%, molar ratio of sodium hydroxide to vinyl acetate unit in POA modified PVAc 0.1). A gel-like product was formed in about 1 minute after the addition of the alkaline solution. This was pulverized with a pulverizer and allowed to stand at 40 ° C. for 1 hour to proceed with saponification, and then 500 g of methyl acetate was added to leave the remaining alkali. Neutralized. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this, 2000 g of methanol was added, and the mixture was left to wash at room temperature for 3 hours. After the above washing operation was repeated three times, the white solid obtained by centrifugal drainage was left in a dryer at 65 ° C. for 2 days to obtain POA-modified PVA (PVA1). PVA1 had a viscosity average polymerization degree P of 1700, a saponification degree of 98.7 mol%, and a POA group modification rate of 0.4 mol%.

[Production Examples 2 to 3] Production of PVA 2 to 3 The amount of unsaturated monomer having a POA group used during polymerization, the polymerization rate, the concentration of POA-modified PVAc during saponification, and the mole of sodium hydroxide relative to the vinyl acetate unit Various PVA (PVA2-3) was manufactured by the same method as Example 1 except having changed ratio as shown in Table 1.

[Example 1]
(Manufacture of conductive paste)
4 g of PVA1 obtained in Production Example 1 and 96 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 4% PVA1 An aqueous solution of was prepared. Next, the total amount of the prepared 4% 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 30 Pa · s, the viscosity η ₂ at a shear rate of 100 (1 / sec) is 2 Pa · s, and the viscosity ratio η ₂ / η ₁ is 0.07.
<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.

[Comparative Example 1]
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 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 stringing and bleeding at the time of printing, and has excellent sheet attack resistance against a ceramic green sheet. Therefore, the internal electrode layer of a multilayer electronic component such as a multilayer ceramic capacitor Can be suitably used as a conductive paste used for forming a conductive layer of a solar cell or the like.

Claims (7)

A conductive paste containing a polyoxyalkylene-modified vinyl alcohol polymer having a polyoxyalkylene group in the side chain, a conductive powder and an aqueous solvent,
The polyoxyalkylene-modified vinyl alcohol polymer has 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 a polyoxyalkylene group modification rate S of 0. Conductive paste having a content of 0.05 mol% or more and 10 mol% or less.   The conductive paste according to claim 1, wherein a content ratio of the polyoxyalkylene-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 claim 1, wherein the polyoxyalkylene group is at least one group selected from the group consisting of a polyoxyethylene group, a polyoxypropylene group, and a polyoxybutylene group.   The conductive paste according to any one of claims 1 to 4, wherein the number of units of the polyoxyalkylene group is 2 to 50. The conductive paste according to claim 1, wherein the polyoxyalkylene group is a polyoxyalkylene group represented by the following formula (I).

(In Formula (I), R ¹ is a hydrogen atom or a methyl group. R ² is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. M and n each represent the number of repeating units of an oxyalkylene unit. 1 ≦ m ≦ 30 and 1 ≦ n ≦ 20.)   A multilayer ceramic capacitor obtained by using the conductive paste according to any one of claims 1 to 6 and a ceramic green sheet.