JP2017179358A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste that has excellent printability and can form a coated film having high surface smoothness and high strength, and to provide a multilayer ceramic capacitor using said conductive paste.SOLUTION: A conductive paste is a multilayer ceramic capacitor electrode conductive paste used in an electrode of a multilayer ceramic capacitor and contains a polyvinyl acetal resin, an organic solvent, and a conductive powder, and in which the polyvinyl acetal resin has an average polymerization degree of 810 to 1600 and is an acetalized product of two kinds or more mixed polyvinyl alcohol resins having different polymerization degrees, among the mixed polyvinyl alcohol resins, the polyvinyl alcohol resin having the highest degree of polymerization is a carboxylic acid-unmodified polyvinyl alcohol resin, and the polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization is a carboxylic acid-modified polyvinyl alcohol resin having a particular constitutional unit.SELECTED DRAWING: None

Description

The present invention relates to a conductive paste having excellent printability and capable of forming a coating film having high surface smoothness and high strength, and a multilayer ceramic capacitor using the conductive paste.

In recent years, electronic components mounted on various electronic devices have been reduced in size and stacked, and multilayer electronic components such as multilayer circuit boards, multilayer coils, and multilayer ceramic capacitors are widely used.

In particular, a multilayer ceramic capacitor is generally manufactured through the following processes. First, after adding a plasticizer, a dispersing agent, etc. to a solution in which a binder resin such as polyvinyl butyral resin, poly (meth) acrylic acid ester resin, and ethyl cellulose is dissolved in an organic solvent, ceramic raw material powder is added, and the ceramic slurry is added. obtain. Next, the ceramic slurry is cast on the release-treated support surface, and volatile components such as an organic solvent are distilled off by heating or the like, and then peeled from the support to obtain a ceramic green sheet.
Next, on the obtained ceramic green sheet, a conductive paste for forming internal electrodes is applied by screen printing, and a plurality of these are stacked and thermocompression bonded to produce a laminate. Furthermore, after performing a process of thermally decomposing and removing the binder resin and the like contained in the laminate, so-called degreasing treatment, firing to form a ceramic sintered body, and forming an external electrode on the end surface of the ceramic sintered body A multilayer ceramic capacitor is obtained.

With the reduction in size and increase in capacity of multilayer ceramic capacitors, thinning of the internal electrode and smoothness of the electrode surface have been demanded. Therefore, as a conductive paste for forming a thin and smooth internal electrode, for example, by using a metal material with a controlled particle size, such as the conductive paste disclosed in Patent Document 1, It is described that it can be smoothed.
However, since these use ethyl cellulose as a binder, the strength of the coating film is weak, and there are problems such as cracking and chipping caused by a slight impact.

In view of the above-mentioned problems, the present inventors considered that the strength of the conductive paste coating film can be increased by using a polyvinyl acetal resin.
In Patent Document 2, a low polarity organic solvent is used to prevent sheet attack on the ceramic green sheet. However, when such a low-polarity organic solvent and a conventional polyvinyl acetal resin are used as the binder of the conductive paste, the solubility of the inorganic powder is very poor due to the difference in polarity between the resin and the organic solvent. Dispersibility deteriorated and it was difficult to obtain good printability.

Therefore, the present inventors have developed a resin with excellent printability using polyvinyl acetal having a specific structure (see Patent Documents 3 and 4).
However, when the degree of polymerization of the resin is high, it takes a long time to dissolve the resin, resulting in poor productivity. On the other hand, when the degree of polymerization of the resin was reduced, a high level of strength could not be obtained.

International Publication No. 2010/021202 JP 2005-243561 A Japanese Patent No. 5767923 Japanese Patent No. 5809505

An object of the present invention is to provide a conductive paste having excellent printability and capable of forming a coating film having high surface smoothness and high strength, and a multilayer ceramic capacitor using the conductive paste.

上記式（１−１）中、Ｒ^１及びＲ^２は、それぞれ独立し、炭素数０〜１０のアルキレン基、Ｘ^１及びＸ^２は、それぞれ独立し、水素原子、金属原子又はメチル基を表す。上記式（１−２）中、Ｒ^３、Ｒ^４及びＲ^５は、それぞれ独立し、水素原子又は炭素数１〜１０のアルキル基、Ｒ^６は炭素数０〜１０のアルキレン基、Ｘ^３は水素原子、金属原子又はメチル基を表す。
以下、本発明を詳述する。 The present invention is a conductive paste used for an electrode of a multilayer ceramic capacitor, comprising a polyvinyl acetal resin, an organic solvent, and a conductive powder, wherein the polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin. The average degree of polymerization is 810 to 1600, and the polyvinyl acetal resin is an acetalized product of two or more types of mixed polyvinyl alcohol resins having different degrees of polymerization, and the highest degree of polymerization among the mixed polyvinyl alcohol resins. The polyvinyl alcohol resin is a carboxylic acid-unmodified polyvinyl alcohol resin, and the polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization is represented by the structural unit represented by the following formula (1-1) and the following formula ( It is selected from the structural units represented by 1-2) A conductive paste containing a carboxylic acid-modified polyvinyl alcohol resin having at least one.

In formula (1-1), R ¹ and R ² are each independently a C 0-10 alkylene group, X ¹ and X ² are each independently a hydrogen atom, a metal atom or a methyl group. . In the above formula (1-2), R ³ , R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ⁶ is an alkylene group having 0 to 10 carbon atoms, and X ³ is Represents a hydrogen atom, a metal atom or a methyl group.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have used a polyvinyl acetal resin having a specific average polymerization degree and containing a carboxylic acid-modified polyvinyl acetal resin having a specific structure as a binder resin of a conductive paste. It was found that a conductive paste having high printability and excellent surface smoothness and strength can be obtained by prescribing the structure of the mixed polyvinyl alcohol resin constituting the present invention, and the present invention has been completed.

The conductive paste of the present invention contains a polyvinyl acetal resin.
The polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin. In the present specification, the carboxylic acid-modified polyvinyl acetal resin means a polyvinyl acetal resin having a structural unit having a carboxyl group.
Further, in the present specification, the carboxylic acid-modified polyvinyl acetal resin is a structural unit having an acetyl group represented by the following formula (2-1) and a hydroxyl group represented by the following formula (2-2). And a resin having a structural unit having a carboxyl group in addition to the structural unit having an acetal group represented by the following formula (2-3).

In the above formula (2-3), ^{R 7} represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

In the present invention, the polyvinyl acetal resin is an acetalized product of two or more types of mixed polyvinyl alcohol resins having different degrees of polymerization.
The mixed polyvinyl alcohol resin is composed of a polyvinyl alcohol resin having the highest degree of polymerization and a polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization.
This will be described in order below.

The polyvinyl alcohol resin having the highest degree of polymerization is a carboxylic acid-unmodified polyvinyl alcohol resin. Moreover, it is preferable that the said carboxylic acid unmodified polyvinyl alcohol resin has neither the structural unit represented by the said Formula (1-1) nor the structural unit represented by the said Formula (1-2). . The structural unit represented by the above formula (1-1) and the structural unit represented by the above formula (1-2) will be described later.
By using a carboxylic acid-unmodified polyvinyl alcohol resin as the polyvinyl alcohol resin having the highest degree of polymerization, the resulting conductive paste can be made excellent in strength.

The preferable lower limit of the polymerization degree of the polyvinyl alcohol resin having the highest degree of polymerization is 810, and the preferable upper limit is 3000. By setting the degree of polymerization to 810 or more, the strength of the obtained conductive paste can be effectively expressed. By setting the degree of polymerization to 3000 or less, it is possible to reduce the influence on the printability. The more preferable lower limit of the polymerization degree of the polyvinyl alcohol resin having the highest degree of polymerization is 1200, and the more preferable upper limit is 2500. In addition, the said polymerization degree means the polymerization degree of individual polyvinyl alcohol resin, and distinguishes and uses it from the average polymerization degree mentioned later.

The lower limit of the saponification degree of the polyvinyl alcohol resin having the highest degree of polymerization is preferably 87.0 mol%, and the upper limit is preferably 99.5 mol%. By making a saponification degree 87.0 mol% or more, the solvent solubility of the obtained polyvinyl acetal resin can be made excellent. By setting the degree of saponification to 99.5 mol% or less, the handling at the time of synthesizing the polyvinyl acetal resin can be improved. The more preferable lower limit of the saponification degree of the polyvinyl alcohol resin having the highest degree of polymerization is 90.0 mol%, and the more preferable upper limit is 99.0 mol%.

The mixed polyvinyl alcohol resin contains a polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization.
Further, the polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization is selected from the structural unit represented by the above formula (1-1) and the structural unit represented by the above formula (1-2). A carboxylic acid-modified polyvinyl alcohol resin having at least one of the following.

The carboxylic acid-modified polyvinyl alcohol resin has at least one selected from the structural unit represented by the formula (1-1) and the structural unit represented by the formula (1-2). By using the carboxylic acid-modified polyvinyl alcohol resin having the above structural unit, the resulting carboxylic acid-modified polyvinyl acetal resin is dissolved in a low-polar organic solvent, and the conductive powder is one of the constituent materials of the conductive paste. Since the familiarity can be improved, the electrode surface after printing can be smoothed.

When the carboxylic acid-modified polyvinyl alcohol resin has a structural unit represented by the above formula (1-1), since the two carboxyl groups in the structural unit are present at a position sandwiching the carbon of the main chain, the resulting conductivity is obtained. The paste has a moderate interaction with the conductive powder and can also improve the storage stability.

In the above formula (1-1), R ¹ and R ² are each independently a C 0-10 alkylene group, X ¹ and X ² are each independently a hydrogen atom, a metal atom or a methyl group. Represents.

In the above formula (1-1), by setting the number of carbon atoms of the alkylene group represented by R ¹ and R ² to 10 or less, aggregation due to a carboxyl group is prevented and solubility in a low-polar solvent is increased. be able to. The preferable lower limit of the carbon number of the alkylene group represented by R ¹ and R ² is 0, the preferable upper limit is 5, the more preferable lower limit is 1, and the more preferable upper limit is 3.

R ¹ and R ² may be the same or different, but are preferably different. At least one of them is preferably an alkylene group having 0 carbon atoms.

Examples of the alkylene group having 0 to 10 carbon atoms include an alkylene group having 0 carbon atoms, a methylene group, an ethylene group, a trimethylene group (n-propylene group), a tetramethylene group (n-butylene group), a pentamethylene group, Linear alkylene groups such as hexamethylene group, octamethylene group and decamethylene group, branched alkylene groups such as methylmethylene group, methylethylene group, 1-methylpentylene group and 1,4-dimethylbutylene group, cyclopropylene group And cyclic alkylene groups such as cyclobutylene group and cyclohexylene group. Among these, a linear alkylene group such as an alkylene group having 0 carbon atoms, a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group is preferable, and an alkylene group having 0 carbon atoms, a methylene group, and an ethylene group are more preferable.

When at least ^one of X ¹ and X ² is a metal atom, examples of the metal atom include a sodium atom, a lithium atom, and a potassium atom. Of these, a sodium atom is preferable.

The structural unit represented by the above formula (1-1) is preferably derived from an α-dicarboxy monomer. Examples of the α-dicarboxy monomer include dicarboxylic acids having a radical polymerizable unsaturated double bond such as methylene malonic acid, itaconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, 2-methylene sebacic acid, and the like. A metal salt or its methyl ester is mentioned. Of these, itaconic acid is preferably used.
In the present specification, the α-dicarboxy monomer represents a monomer having two carboxyl groups at the α-position carbon.

When the carboxylic acid-modified polyvinyl alcohol resin has a structural unit represented by the above formula (1-2), the solvent solubility can be further improved.
In said formula (1-2), R < ³ >, R < ⁴ > and R < ⁵ > respectively independently represent a hydrogen atom or a C1-C10 alkyl group, and R < ⁶ > represents a C0-C10 alkylene group. It represents, X ³ represents a hydrogen atom, a metal atom or a methyl group.

In the above formula (1-2), when at least one of R ³ , R ⁴ and R ⁵ is an alkyl group having 1 to 10 carbon atoms, if the alkyl group has more than 10 carbon atoms, the raw material synthesis is caused by steric hindrance. Time polymerization is less likely to occur. The preferable lower limit of the carbon number of the alkyl group represented by R ³ , R ⁴ and R ⁵ is 1, the preferable upper limit is 5, and the more preferable upper limit is 3.

R ³ and R ⁴ may be the same or different, but the same is more preferable. R ³ , R ⁴ and R ⁵ are preferably hydrogen atoms.

Examples of the alkyl group having 1 to 10 carbon atoms include methyl group, ethyl group, propyl group, n-butyl group, n-pentyl group, n-heptyl group, n-octyl group, n-nonyl group, n- Linear alkyl group such as decyl group, isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, 2,2-dimethylpropyl group, 1,1,3,3-tetramethylbutyl group, Examples thereof include branched alkyl groups such as 2-ethylhexyl group, cycloalkyl groups such as cyclopropyl group, cyclopropylmethyl group, cyclobutyl group, cyclopentyl group, and cyclohexyl group. Especially, linear alkyl groups, such as a methyl group, an ethyl group, a propyl group, n-butyl group, are preferable, and a methyl group and an ethyl group are more preferable.

In said formula (1-2), the carbon number of the alkylene group represented by R < ⁶ > shall be 10 or less, the aggregation by a carboxyl group is prevented and resin becomes easy to melt | dissolve in a low polarity solvent. The preferable lower limit of the carbon number of the alkylene group represented by R ⁶ is 0, the preferable upper limit is 5, the more preferable lower limit is 1, and the more preferable upper limit is 3.

Examples of R ⁶ in the above formula (1-2) include the same as those exemplified for R ¹ and R ² in the above formula (1-1). Among them, an alkylene group having 0 carbon atoms, A linear alkylene group such as a methylene group, an ethylene group, a trimethylene group and a tetramethylene group is preferred, an alkylene group having 0 carbon atoms, a methylene group and an ethylene group are more preferred, and an alkylene group having 0 carbon atoms is still more preferred.

When X ³ is a metal atom, examples of the metal atom include a sodium atom, a lithium atom, and a potassium atom. Of these, a sodium atom is preferable.

The structural unit represented by the formula (1-2) is preferably derived from a monocarboxy monomer. Examples of the monocarboxy monomer include monocarboxylic acid having a radical polymerizable unsaturated double bond such as acrylic acid, crotonic acid, methacrylic acid, oleic acid, a metal salt thereof, or a methyl ester thereof. Of these, crotonic acid is preferably used.

The said carboxylic acid modified polyvinyl alcohol resin may be used independently, and may mix and use a different thing.

The method for synthesizing the carboxylic acid-modified polyvinyl alcohol resin is not particularly limited. For example, when the carboxylic acid-modified polyvinyl acetal resin has a structural unit represented by the formula (1-1), the formula (1) Examples thereof include a method of saponifying polyvinyl acetate obtained by copolymerizing an α-dicarboxy monomer serving as a structural unit represented by -1) and vinyl acetate. In particular, if the α-dicarboxy monomer used when the polyvinyl acetate is prepared by copolymerization is a methyl ester, the acetyl group derived from vinyl acetate is not hydrolyzed before saponification. It is possible to make the saponification higher when producing the polyvinyl alcohol resin in the crystallization step, which is preferable. Furthermore, since the amount of sodium hydroxide to be added can be reduced in the saponification step, it is possible to reduce the sodium ion content of the polyvinyl alcohol resin and thus the carboxylic acid-modified polyvinyl acetal resin.
Even when the α-dicarboxy monomer is a methyl ester, hydrolysis is performed in a subsequent saponification step, and thus the obtained polyvinyl alcohol resin has a carboxylic acid unit containing no ester.
In addition, among the α-dicarboxy monomers that are structural units represented by the above formula (1-1), when a monomer in which X ¹ and X ² are hydrogen atoms or metal atoms is used, it is derived from vinyl acetate at the time of saponification. Since the amount of sodium hydroxide consumed for hydrolysis of acetyl groups increases, the resulting carboxylic acid-modified polyvinyl alcohol resin may have a relatively high sodium ion content.
In addition, when the carboxylic acid-modified polyvinyl alcohol resin has a structural unit represented by the above formula (1-2), a monocarboxy monomer that becomes a structural unit represented by the above formula (1-2), and vinyl acetate And a method of saponifying polyvinyl acetate obtained by copolymerization of Furthermore, the method etc. which make polyvinyl alcohol resin react with the compound which has carboxyl groups, such as mercaptopropionic acid, and post-modify | denaturate are mentioned.

The preferable lower limit of the degree of polymerization of the carboxylic acid-modified polyvinyl alcohol resin is 300, and the preferable upper limit is 900. By setting the degree of polymerization to 300 or more, the storage stability of the obtained conductive paste can be made excellent. By setting the degree of polymerization to 900 or less, the viscosity of the obtained conductive paste can be made suitable for printing. The minimum with a more preferable polymerization degree of the said carboxylic acid modification polyvinyl alcohol resin is 500, and a more preferable upper limit is 800.

The preferable lower limit of the saponification degree of the carboxylic acid-modified polyvinyl alcohol resin is 87.0 mol%, and the preferable upper limit is 99.5 mol%. By setting the saponification degree to 87.0 mol% or more, the solvent solubility of the obtained conductive paste can be made excellent. By setting the degree of saponification to 99.5 mol% or less, the handling at the time of synthesizing the polyvinyl acetal resin can be improved. The minimum with a more preferable saponification degree of the said carboxylic acid modification polyvinyl alcohol resin is 90.0 mol%, and a more preferable upper limit is 99.0 mol%.

The mixed polyvinyl alcohol resin has a preferable lower limit of 600 for the difference in the degree of polymerization between the carboxylic acid-modified polyvinyl alcohol resin and the polyvinyl alcohol resin having the highest degree of polymerization. When the difference in the degree of polymerization of the mixed polyvinyl alcohol is 600 or more, each effect can be more effectively expressed. When the carboxylic acid-modified polyvinyl alcohol resin and the polyvinyl alcohol resin having the highest degree of polymerization are composed of a plurality of types, the difference when the difference is the smallest is the difference in polymerization degree.

In the mixed polyvinyl alcohol resin, the mixing ratio of the polyvinyl alcohol resin having the highest degree of polymerization and the carboxylic acid-modified polyvinyl alcohol resin is preferably 10:90 to 90:10 by weight. When the mixing ratio is within the above-described range, it is possible to prevent the characteristics of components having a large mixing ratio from appearing strongly or the characteristics of components having a small mixing ratio from becoming insufficient.
The mixed polyvinyl alcohol resin may contain polyvinyl alcohol other than the polyvinyl alcohol resin having the highest degree of polymerization and the carboxylic acid-modified polyvinyl alcohol resin.

In the present invention, the acetalized product of the mixed polyvinyl alcohol resin is obtained by acetalizing the mixed polyvinyl alcohol resin.
It does not specifically limit as said acetalization reaction, It can carry out by a conventionally well-known method. For example, a method in which various aldehydes are added to an aqueous solution of polyvinyl alcohol, an alcohol solution, a water / alcohol mixed solution, or a dimethyl sulfoxide (DMSO) solution in the presence of an acid catalyst.
The aldehyde is not particularly limited. For example, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde , 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde and the like. Among these aldehydes, it is preferable to use butyraldehyde alone or a combination of acetaldehyde and butyraldehyde.

If the said polyvinyl acetal resin is in the range which does not inhibit the effect of this invention, in addition to the said carboxylic acid modification polyvinyl acetal resin, you may contain other polyvinyl acetal resin.
When the polyvinyl acetal resin contains another polyvinyl acetal resin, the content of the carboxylic acid-modified polyvinyl acetal resin in the polyvinyl acetal resin can achieve the carboxyl group amount of the polyvinyl acetal resin described later. Although not particularly limited, a preferred lower limit is 5% by weight, a preferred upper limit is 90% by weight, a more preferred lower limit is 10% by weight, a more preferred upper limit is 85% by weight, a particularly preferred lower limit is 15% by weight, and a particularly preferred upper limit. Is 80% by weight.

The average degree of polymerization of the polyvinyl acetal resin has a lower limit of 810 and an upper limit of 1600. When the average degree of polymerization is 810 or more, the strength of the conductive paste can be increased and a necessary viscosity can be imparted. When the average degree of polymerization is 1600 or less, the solubility of the polyvinyl acetal resin in an organic solvent is improved, and stringing or the like is less likely to occur in the conductive paste, resulting in excellent printability and surface smoothness. The preferable lower limit of the average degree of polymerization of the polyvinyl acetal resin is 900, the preferable upper limit is 1500, the more preferable lower limit is 1000, the more preferable upper limit is 1400, the still more preferable lower limit is 1050, and the further preferable upper limit is 1350.

In this specification, the average degree of polymerization of polyvinyl acetal resin is calculated | required from the average degree of polymerization of polyvinyl alcohol resin which is a raw material.
Moreover, in this specification, the average polymerization degree of polyvinyl alcohol resin means the average average polymerization degree of the whole polyvinyl alcohol resin. That is, the average degree of polymerization of two or more types of mixed polyvinyl alcohol resins having different degrees of polymerization can be obtained by summing up each value obtained by multiplying the degree of polymerization of each polyvinyl alcohol resin by the content ratio of the resin. .

The preferable lower limit of the amount of carboxyl groups in the polyvinyl acetal resin is 0.05 mol%, and the preferable upper limit is 1 mol%. When the amount of the carboxyl group is 0.05 mol% or more, the polyvinyl acetal resin sufficiently exhibits the effect of having a carboxyl group, and the printability and surface smoothness of the conductive paste are improved, and the storage stability is improved. Can be improved. Making the amount of carboxyl groups 1 mol% or less improves the solubility of the polyvinyl acetal resin in an organic solvent, and the interaction between the carboxyl groups and the conductive powder becomes moderate, so that a conductive paste is prepared. Becomes easy. The more preferred lower limit of the amount of carboxyl groups of the polyvinyl acetal resin is 0.07 mol%, the more preferred upper limit is 0.8 mol%, the still more preferred lower limit is 0.1 mol%, and the more preferred upper limit is 0.6 mol%. It is.

In this specification, the amount of carboxyl groups of the polyvinyl acetal resin means the proportion of structural units having a carboxyl group in the entire structural units of the polyvinyl acetal resin. For example, in the structural unit represented by the above formula (1-1), two carboxyl groups exist, but the entire structural unit of the polyvinyl acetal resin regardless of the number of carboxyl groups present in one structural unit. The proportion of structural units having a carboxyl group in the amount is defined as the amount of carboxyl groups.

Moreover, in this specification, the carboxyl group amount of polyvinyl acetal resin means the apparent carboxyl group amount of the whole polyvinyl acetal resin. That is, for example, when the polyvinyl acetal resin contains a plurality of resins having different carboxyl group amounts, the carboxyl group amount of the polyvinyl acetal resin is obtained by multiplying the carboxyl group amount of each resin by the content ratio of the resin. Each value is obtained by summing.
In particular, for example, when the polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin and an unmodified polyvinyl acetal resin, the carboxyl group amount of the polyvinyl acetal resin is calculated by the following formula (3).
A = B × (C / D) (3)
In the above formula (3), A represents the carboxyl group amount (mol%) of the polyvinyl acetal resin, B represents the carboxyl group amount (mol%) of the carboxylic acid-modified polyvinyl acetal resin, and C represents the carboxylic acid-modified polyvinyl acetal resin. D represents the weight of the entire polyvinyl acetal resin.

The amount of carboxyl groups of the carboxylic acid-modified polyvinyl acetal resin represented by B in the above formula (3) is not particularly limited as long as the amount of carboxyl groups of the polyvinyl acetal resin described above can be achieved, but a preferable lower limit is 0.03. The preferred upper limit is 4% by mole.

When the said polyvinyl acetal resin contains an acetoacetal group, the upper limit with the preferable amount of acetoacetal groups is 25 mol%. When the amount of acetoacetal groups exceeds 25 mol%, the solubility of the polyvinyl acetal resin in a low-polar organic solvent is lowered, making it difficult to produce a conductive paste. The upper limit with the more preferable amount of acetoacetal groups of the said polyvinyl acetal resin is 22 mol%, and a more preferable upper limit is 20 mol%.
Note that the acetal group, of the acetal groups contained in the structural unit having an acetal group represented by the above formula (2-3), an acetal group where R ⁷ is a methyl group. Moreover, in this specification, the acetoacetal group amount of polyvinyl acetal resin means the apparent acetoacetal group amount of the whole polyvinyl acetal resin.

When the said polyvinyl acetal resin contains a butyral group, the minimum with the preferable amount of butyral groups is 40 mol%, and a preferable upper limit is 80 mol%. By setting the amount of butyral group to 40 mol% or more, it is possible to prevent the amount of residual hydroxyl group from being excessively increased and improve the solubility of the polyvinyl acetal resin in a low-polar solvent. By setting it to 80 mol% or less, the amount of residual hydroxyl groups increases and the viscosity of the resulting conductive paste increases, so that storage stability can be improved. The more preferable lower limit of the butyral group amount of the polyvinyl acetal resin is 50 mol%, and the more preferable upper limit is 70 mol%.
In addition, a butyral group is an acetal group in case R < ⁷ > is a propyl group among the acetal groups contained in the structural unit which has an acetal group represented by the said Formula (2-3). Moreover, in this specification, the butyral group amount of polyvinyl acetal resin means the apparent butyral group amount of the whole polyvinyl acetal resin.

In the polyvinyl acetal resin, a preferable lower limit of the amount of hydroxyl groups is 16 mol%, and a preferable upper limit is 25 mol%. By making the amount of the hydroxyl group 16 mol% or more, aggregation of the conductive powder can be prevented, the dispersibility of the obtained conductive paste can be improved, and a smooth printed coating film can be obtained. By setting it to 25 mol% or less, solubility in a low-polar organic solvent used in the present invention can be improved. A more preferable lower limit of the hydroxyl group content of the polyvinyl acetal resin is 17 mol%, and a more preferable upper limit is 23 mol%.

In the polyvinyl acetal resin, the preferable lower limit of the amount of acetyl groups is 0.1 mol%, and the preferable upper limit is 5 mol%. When the amount of the acetyl group is 0.1 mol% or more, the acetalization reaction is facilitated, and when the amount is 5 mol% or less, the solubility in the low-polar organic solvent used in the present invention is improved. The minimum with the preferable amount of acetyl groups of the said polyvinyl acetal resin is 0.2 mol%, and a preferable upper limit is 2.5 mol%.

In the polyvinyl acetal resin, the preferable lower limit of the ratio of the amount of acetyl groups to the amount of hydroxyl groups is 0.01, and the preferable upper limit is 0.15. When the ratio of the amount of acetyl groups to the amount of hydroxyl groups is within the above range, the polyvinyl acetal resin can be dissolved in a low polarity organic solvent described later. By setting the ratio of the amount of acetyl groups to the amount of hydroxyl groups to 0.01 or more or 0.15 or less, the solubility in a low-polar organic solvent can be improved. The more preferable lower limit of the ratio of the amount of acetyl groups to the amount of hydroxyl groups of the polyvinyl acetal resin is 0.03, and the more preferable upper limit is 0.13.

In the polyvinyl acetal resin, the total amount of the carboxyl group amount, the degree of acetalization, the hydroxyl group amount, and the acetyl group amount is preferably 99.1 mol% or more.
When the total amount is 99.1 mol% or more, the content of other structural units is reduced, and the effects of the present invention can be more suitably exhibited.

The polyvinyl acetal resin preferably has a sodium ion content of less than 50 ppm. When the content of sodium ions in the polyvinyl acetal resin is less than 50 ppm, the conductive paste is excellent in conductivity, and it is difficult for a significant change in viscosity over time to occur.

The conductive paste of the present invention may contain other resins such as an acrylic resin and ethyl cellulose in addition to the polyvinyl acetal resin as long as the effect of the present invention is not impaired.
The polyvinyl acetal resin of the present invention is excellent in compatibility with other resins as compared with a normal polyvinyl acetal resin due to the effect of the carboxyl group.

The conductive paste of the present invention contains a conductive powder.
The conductive powder is not particularly limited, and examples thereof include powder made of nickel, aluminum, silver, copper, silver salt, and alloys thereof. These conductive powders may be used alone or in combination of two or more. Among these, nickel is preferable because of its excellent conductivity.

The nickel powder preferably has an average particle diameter of 50 to 300 nm and a substantially spherical shape. By setting the average particle diameter to 50 nm or more, the specific surface area of the nickel powder is reduced, and the dispersibility of the aggregated nickel powder is improved. By setting the average particle size to 300 nm or less, the surface after printing can be smoothed. The substantially spherical shape includes particles having a shape close to a sphere in addition to a true sphere shape.

Although the compounding quantity of the said electroconductive powder is not specifically limited, The preferable minimum with respect to 100 weight part of said polyvinyl acetal resins is 100 weight part, and a preferable upper limit is 10000 weight part. By setting the blending amount of the conductive powder to 100 parts by weight or more, the density of the conductive powder in the conductive paste can be increased, and the conductivity can be improved. When the blending amount of the conductive powder exceeds 10,000 parts by weight, the dispersibility of the conductive powder in the conductive paste may be decreased, and the printability may be decreased. As for the compounding quantity of the said electroconductive powder, the more preferable minimum with respect to 100 weight part of said polyvinyl acetal resins is 200 weight part, and a more preferable upper limit is 5000 weight part.

The conductive paste of the present invention preferably further contains a ceramic powder in addition to the conductive powder. By containing ceramic powder, it becomes easy to match the shrinkage behavior of the conductive powder during firing with the ceramic green sheet.
Although it does not specifically limit as said ceramic powder, The barium titanate used for a green sheet is preferable. Although it does not specifically limit as a particle size of ceramic powder, It is preferable that it is a thing smaller than the particle size of the said electroconductive powder, and it is preferable that it is specifically 30 nm-200 nm.

The conductive paste of the present invention contains an organic solvent.
As the organic solvent, an organic solvent generally used for a conductive paste can be used. In particular, in order to prevent a sheet attack phenomenon, a polyvinyl butyral resin contained in a ceramic green sheet is not swollen or dissolved. It is a soluble low-polarity organic solvent, and its solubility parameter is preferably 8.0 to 11.0 (cal / cm ³ ) ^0.5 . Note that the solubility parameter is calculated by the Fedors method.
Examples of the organic solvent include terpineol (terpineol), dihydroterpineol (dihydroterpineol), terpinyl acetate, isobornyl acetate, dihydroterpineol acetate (dihydroterpinyl acetate), dihydroterpinyl methyl ether, terpineol. Examples thereof include terpineol derivatives such as nilmethyl ether, hydrocarbon solvents such as mineral spirit, ethers and esters such as dipropylene glycol monomethyl ether and dipropylene glycol monomethyl ether acetate. These organic solvents may be used alone or in combination of two or more.

Although the compounding quantity of the said organic solvent is not specifically limited, The preferable minimum with respect to 100 weight part of said polyvinyl acetal resins is 100 weight part, and a preferable upper limit is 10000 weight part. When the blending amount of the organic solvent is 100 parts by weight or more, the viscosity of the conductive paste becomes low, and the printability can be improved. By setting the blending amount of the organic solvent to 10000 parts by weight or less, the performance of the polyvinyl acetal resin can be sufficiently exhibited in the conductive paste. As for the compounding quantity of the said organic solvent, the more preferable minimum with respect to 100 weight part of said polyvinyl acetal resins is 200 weight part, and a more preferable upper limit is 5000 weight part.

The conductive paste of the present invention may appropriately contain a plasticizer, a lubricant, an antistatic agent, a dispersant, a surfactant and the like as long as the effects of the present invention are not impaired.

The plasticizer is not particularly limited. For example, phthalic acid diesters such as bis (2-ethylhexyl) phthalate, dioctyl phthalate and dibutyl phthalate, adipic acid diesters such as dioctyl adipate, and alkylene glycol diesters such as triethylene glycol 2-ethylhexyl Etc.

Although it does not specifically limit as said dispersing agent, For example, a fatty acid, an aliphatic amine, an alkanolamide, and phosphate ester are suitable. Moreover, you may mix | blend a silane coupling agent etc.
The fatty acid is not particularly limited, and examples thereof include saturated fatty acids such as behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, capric acid, caprylic acid, and coconut fatty acid; oleic acid, linoleic acid, linolenic acid, sorbic acid And unsaturated fatty acids such as beef tallow fatty acid and castor-cured fatty acid. Of these, lauric acid, stearic acid, oleic acid and the like are preferable.
The aliphatic amine is not particularly limited. For example, laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, alkyl (coconut) amine, alkyl (cured beef tallow) amine, alkyl (beef tallow) amine, alkyl (soybean) amine Etc.
The alkanolamide is not particularly limited, and examples thereof include coconut fatty acid diethanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, and oleic acid diethanolamide.
It does not specifically limit as said phosphate ester, For example, polyoxyethylene alkyl ether phosphate ester and polyoxyethylene alkyl allyl ether phosphate ester are mentioned.

The surfactant is not particularly limited, and examples of the anionic surfactant include a sodium salt of a fatty acid as a carboxylic acid, a sodium linear alkylbenzene sulfonate, a sodium lauryl sulfate, and an alkyl polyoxysulfate as a sulfonic acid. Examples of phosphoric acid salts such as salts include monoalkyl phosphates. Examples of cationic surfactants include alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzyldimethylammonium salts. Examples of amphoteric surfactants include alkyldimethylamine oxide and alkylcarboxybetaine. Examples of the surfactant include polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglucoside, fatty acid diethanolamide, alkyl monoglyceryl ether and the like.
The dispersant and the surfactant are also effective in suppressing the increase in viscosity of the paste or resin solution with time.

The method for producing the conductive paste of the present invention is not particularly limited. For example, the polyvinyl acetal resin containing the carboxylic acid-modified polyvinyl acetal resin, the conductive powder, the organic solvent, and other components added as necessary. And the like using a mixer such as a ball mill, a blender mill, or a three roll.

The conductive paste of the present invention is applied on a ceramic green sheet by a printing process such as screen printing, die coating, gravure offset, etc., and a plurality of these are stacked and thermocompression bonded to produce a laminate, followed by degreasing and firing. A multilayer ceramic capacitor can be obtained by forming a ceramic sintered body and further forming external electrodes on the end face of the ceramic sintered body. Such a multilayer ceramic capacitor is also one aspect of the present invention.

Although it does not specifically limit as a method to print the electrically conductive paste of this invention, It can carry out by printing processes, such as the above-mentioned screen printing, die coating, and gravure printing. The optimum viscosity at that time is different depending on each printing process and may be adjusted as appropriate. For example, in the case of screen printing, the viscosity at a shear rate of 10000 s ⁻¹ is 0.5 to 1.0 Pa · s. For example, in the case of gravure printing, the viscosity at a shear rate of 10,000 s ⁻¹ is preferably 0.05 to 0.5 Pa · s.

Since the conductive paste of the present invention contains the polyvinyl acetal resin containing the carboxylic acid-modified polyvinyl acetal resin as described above, the surface after printing can be smoothed even if a low polarity organic solvent is used. In addition, the multilayer ceramic capacitor can be thinned, and excellent conductivity can be obtained.
Moreover, since the polyvinyl acetal resin to be used has a very low sodium ion content, the conductive paste of the present invention can be suitably used as a silver salt binder.

An organic silver salt is used as the silver salt. It does not specifically limit as said organic silver salt, For example, the silver salt of the organic compound which has a mercapto group, a thione group, or a carboxyl group, benzotriazole silver, etc. are mentioned. Specifically, a silver salt of a compound having a mercapto group or a thione group, a silver salt of 3-mercapto-4-phenyl1,2,4-triazole, a silver salt of 2-mercapto-benzimidazole, 2-mercapto-5 -Silver salt of aminothioazole, silver salt of 1-phenyl-5-mercaptotetrathiazole, silver salt of 2-mercaptobenzothiazole, silver salt of thioglycolic acid, silver salt of dithiocarboxylic acid such as silver salt of dithioacetic acid , Silver thioamide, silver salt of thiopyridine, silver salt of dithiohydroxybenzol, silver salt of mercaptotriazine, silver salt of mercaptooxadiazole, silver salt of aliphatic carboxylic acid: silver caprate, silver laurate, silver myristate, palmitic acid Silver, silver stearate, silver behenate, silver maleate, silver fumarate, silver tartrate, silver furoate, silver linoleate Silver oleate, silver hydroxystearate, silver adipate, silver sebacate, silver succinate, silver acetate, silver butyrate, silver camphorate, etc., aromatic carboxylic acid silver, thione carboxylic acid silver, aliphatic carboxylic acid having thioether group Examples thereof include silver acid, silver salt of tetrazaindene, silver S-2-aminophenylthiosulfate, metal-containing amino alcohol, and organic acid metal chelate.

According to the present invention, it is possible to provide a conductive paste having excellent printability and capable of forming a coating film having high surface smoothness and high strength, and a multilayer ceramic capacitor using the conductive paste.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
(Preparation of polyvinyl acetal resin)
Carboxylic acid modified polyvinyl alcohol resin G (polymerization degree 300, carboxyl group amount 1.0 mol%, acetyl group amount 2.2 mol%, structural unit represented by the following general formula (4-1) (X is sodium ion) And 50 g of unmodified polyvinyl alcohol resin A (degree of polymerization 2400, acetyl group content 1.3 mol%) were added to 1000 g of pure water and stirred at a temperature of 90 ° C. for about 2 hours to dissolve. . The solution was cooled to 40 ° C., and 90 g of hydrochloric acid (concentration 35% by weight), 25 g of acetaldehyde and 55 g of n-butyraldehyde were added to the solution. The liquid temperature was lowered to 10 ° C., and this temperature was maintained to carry out the acetalization reaction. After completing the reaction, neutralization, washing with water and drying were performed to obtain a polyvinyl acetal resin (average polymerization degree 1350, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.3 mol%, acetoacetal group amount 23.0). White powder having a mol%, butyral group amount of 53.5 mol%, and carboxyl group amount of 0.5 mol%) was obtained.

(Preparation of conductive paste)
A resin solution was obtained by dissolving 20 parts by weight of the obtained polyvinyl acetal resin with 80 parts by weight of dihydroterpineol acetate. After mixing 90 parts by weight of nickel powder, 10 parts by weight of barium titanate and 50 parts by weight of dihydroterpineol acetate as a conductive powder, the resulting resin solution is mixed and dispersed by a three roll, A conductive paste was obtained.

(Example 2)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin G70g and the unmodified polyvinyl alcohol resin A30g were used to perform the acetalization reaction. A polyvinyl acetal resin (average degree of polymerization 930, acetyl group amount 1.9 mol%, residual hydroxyl group amount 22.1 mol%, except that the aldehyde used was changed to 80 g of n-butyraldehyde) A white powder having a butyral group content of 75.3 mol% and a carboxyl group content of 0.7 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 3)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin G10 g and unmodified polyvinyl alcohol resin D (polymerization degree 900, acetyl group amount 2.7) Except for using 90 g, a polyvinyl acetal resin (average degree of polymerization 840, acetyl group amount 2.7 mol%, residual hydroxyl group amount 21.5 mol%, acetoacetal group amount) was used except that 90 g was used. 23.5 mol%, butyral group amount 52.3 mol%, carboxyl group amount 0.1 mol%) was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

Example 4
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin J (polymerization degree 800, carboxyl group amount 1.0 mol%, acetyl group amount 1. The aldehyde used when the acetalization reaction is performed using 8 mol%, 70 g of the structural unit represented by the general formula (4-1) (X has a sodium ion) and 30 g of unmodified polyvinyl alcohol resin A. Except for changing to 20 g of acetaldehyde and 65 g of n-butyraldehyde, a polyvinyl acetal resin (average polymerization degree 1280, acetyl group amount 1.7 mol%, residual hydroxyl group amount 22.0 mol%, Acetoacetal group amount 18.5 mol%, butyral group amount 57.2 mol%, cal To obtain a white powder of hexyl group amount 0.7 mole%).
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 5)
In Example 1, carboxylic acid-modified polyvinyl alcohol resin J90g and unmodified polyvinyl alcohol resin A10g were used instead of carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin A50g. Polyvinyl acetal resin (average polymerization degree 960, acetyl group amount 1.8 mol%, residual hydroxyl group amount 20.8 mol%, acetoacetal group amount 23.9 mol%, butyral group amount 52.7 mol%, carboxyl A white powder having a base amount of 0.9 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 6)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin J10g and the unmodified polyvinyl alcohol resin D90g are used to perform the acetalization reaction. A polyvinyl acetal resin (average degree of polymerization 890, acetyl group amount 2.6 mol%, residual hydroxyl group amount 21.3 mol%, butyral, in the same manner as in Example 1 except that the aldehyde was changed to 80 g of n-butyraldehyde. A white powder having a base amount of 76.0 mol% and a carboxyl group amount of 0.1 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 7)
In Example 1, carboxylic acid modified polyvinyl alcohol resin J90 g and unmodified polyvinyl alcohol resin D10 g were used instead of carboxylic acid modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g. Polyvinyl acetal resin (average degree of polymerization 810, acetyl group amount 1.9 mol%, residual hydroxyl group amount 22.7 mol%, acetoacetal group amount 22.8 mol%, butyral group amount 51.7 mol%, carboxyl A white powder having a base amount of 0.9 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 8)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin J10 g and unmodified polyvinyl alcohol resin C (polymerization degree 1400, acetyl group amount 1.7 mol) %) 90 g in the same manner as in Example 1, except that polyvinyl acetal resin (average polymerization degree 1340, acetyl group amount 1.7 mol%, residual hydroxyl group amount 20.5 mol%, acetoacetal group amount 23) 2 mol%, butyral group amount 54.5 mol%, carboxyl group amount 0.1 mol%) was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

Example 9
In Example 1, carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g were used instead of carboxylic acid-modified polyvinyl alcohol resin J90 g and unmodified polyvinyl alcohol resin C10 g, as in Example 1. Polyvinyl acetal resin (average polymerization degree 860, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.9 mol%, acetoacetal group amount 22.7 mol%, butyral group amount 52.7 mol%, carboxyl A white powder having a base amount of 0.9 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 10)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin H (polymerization degree 500, carboxyl group content 1.0 mol%, acetyl group content 2. 0 mol%, 10 g of the structural unit represented by the above general formula (4-1) (X has a sodium ion) and unmodified polyvinyl alcohol resin B (polymerization degree 1700, acetyl group amount 2.0 mol%) 90 g In the same manner as in Example 1, except for using polyvinyl acetal resin (average polymerization degree 1580, acetyl group amount 2.0 mol%, residual hydroxyl group amount 21.5 mol%, acetoacetal group amount 22.3 mol%). White powder having a butyral group amount of 54.1 mol% and a carboxyl group amount of 0.1 mol%) was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 11)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin A50g, carboxylic acid-modified polyvinyl alcohol resin H50g and unmodified polyvinyl alcohol resin B50g are used, and an aldehyde used when performing an acetalization reaction Was changed to 15 g of acetaldehyde and 70 g of n-butyraldehyde in the same manner as in Example 1 to obtain a polyvinyl acetal resin (average degree of polymerization 1100, acetyl group amount 2.0 mol%, residual hydroxyl group amount 20.9 mol%). A white powder having an acetoacetal group amount of 13.4 mol%, a butyral group amount of 63.2 mol% and a carboxyl group amount of 0.5 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

Example 12
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin A50g, carboxylic acid-modified polyvinyl alcohol resin H70g and unmodified polyvinyl alcohol resin B30g are used to perform an acetalization reaction. Was changed to 5 g of acetaldehyde and 75 g of n-butyraldehyde in the same manner as in Example 1, except that the polyvinyl acetal resin (average polymerization degree 860, acetyl group amount 2.0 mol%, residual hydroxyl group amount 22.2 mol%) A white powder having an acetoacetal group amount of 4.6 mol%, a butyral group amount of 70.5 mol%, and a carboxyl group amount of 0.7 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 13)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin N (polymerization degree 500, carboxyl group amount 1.0 mol%, acetyl group 4.5 Polyvinyl acetal in the same manner as in Example 1, except that 30 g of mol%, a structural unit represented by the following general formula (4-2) (X has a sodium ion) and 70 g of unmodified polyvinyl alcohol resin B were used. Resin (average polymerization degree 1340, acetyl group amount 2.8 mol%, residual hydroxyl group amount 22.4 mol%, acetoacetal group amount 23.6 mol%, butyral group amount 51.0 mol%, carboxyl group amount 0.3 Mol%) of white powder.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 14)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin A50g, carboxylic acid-modified polyvinyl alcohol resin N70g and unmodified polyvinyl alcohol resin B30g were used in the same manner as in Example 1. Polyvinyl acetal resin (average polymerization degree 860, acetyl group amount 3.8 mol%, residual hydroxyl group amount 21.7 mol%, acetoacetal group amount 22.5 mol%, butyral group amount 51.4 mol%, carboxyl group A white powder in an amount of 0.7 mol%) was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 15)
In Example 1, instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, carboxylic acid-modified polyvinyl alcohol resin M (polymerization degree 500, carboxyl group content 0.5 mol%, acetyl group content 2. An aldehyde used for performing an acetalization reaction using 5 mol%, 70 g of the structural unit represented by the general formula (4-1) (X has a sodium ion) and 30 g of unmodified polyvinyl alcohol resin B, A polyvinyl acetal resin (average degree of polymerization 860, acetyl group amount 2.4 mol%, residual hydroxyl group amount 20.7 mol%, acetoacetate was obtained in the same manner as in Example 1 except that 10 g of acetaldehyde and 75 g of n-butyraldehyde were used. Acetal group amount 9.5 mol%, butyral group amount 67.1 mol%, carboxy Of white powder was obtained based on the amount 0.4 mole%).
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 16)
In Example 1, carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g were used instead of carboxylic acid-modified polyvinyl alcohol resin M10 g and unmodified polyvinyl alcohol resin B 90 g, as in Example 1. Polyvinyl acetal resin (average polymerization degree 1580, acetyl group amount 2.1 mol%, residual hydroxyl group amount 21.0 mol%, acetoacetal group amount 23.3 mol%, butyral group amount 53.6 mol%, carboxyl A white powder having a base amount of 0.1 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 17)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin J30 g, carboxylic acid-modified polyvinyl alcohol resin G40 g, and unmodified polyvinyl alcohol resin A30 g Except for the use, polyvinyl acetal resin (average polymerization degree 1080, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.3 mol%, acetoacetal group amount 22.8 mol%, A white powder having a butyral group amount of 53.4 mol% and a carboxyl group amount of 0.7 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 18)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin G30 g, unmodified polyvinyl alcohol resin A30 g, and unmodified polyvinyl alcohol resin D40 g were used. , Except that the aldehyde used for the acetalization reaction was changed to 80 g of n-butyraldehyde, the same procedure as in Example 1 was repeated, except that polyvinyl acetal resin (average polymerization degree 1170, acetyl group amount 2.1 mol%, residual A white powder having a hydroxyl group content of 19.8 mol%, a butyral group content of 77.8 mol%, and a carboxyl group content of 0.3 mol% was obtained. A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 19)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin C50g were used to perform the acetalization reaction. A polyvinyl acetal resin (average polymerization degree 850, acetyl group amount 2.0 mol%, residual hydroxyl group amount 19.5, remaining amount 19.5%) was obtained in the same manner as in Example 1 except that 6 g of acetaldehyde and 75 g of n-butyraldehyde were used. White powder having a mol%, acetoacetal group amount of 5.3 mol%, butyral group amount of 72.7 mol%, carboxyl group amount of 0.5 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1 except that the solvent was changed to dihydroterpineol.

(Example 20)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin M50g and the unmodified polyvinyl alcohol resin B50g were used to perform the acetalization reaction. A polyvinyl acetal resin (average polymerization degree 1100, acetyl group amount 2.3 mol%, residual hydroxyl group amount 21.1 mol%, except that the aldehyde used was changed to 80 g of n-butyraldehyde, A white powder having a butyral group content of 76.3 mol% and a carboxyl group content of 0.3 mol% was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1 except that the solvent was changed to dihydroterpineol.

(Example 21)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin M50g and the unmodified polyvinyl alcohol resin A50g were used to perform the acetalization reaction. A polyvinyl acetal resin (average polymerization degree 1450, acetyl group amount 1.9 mol%, residual hydroxyl group amount 20.4) was obtained in the same manner as in Example 1 except that the aldehyde used was changed to 15 g of acetaldehyde and 70 g of n-butyraldehyde. White powder having a mol%, an acetoacetal group amount of 11.9 mol%, a butyral group amount of 65.5 mol%, and a carboxyl group amount of 0.3 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1 except that the solvent was changed to dihydroterpineol.

(Comparative Example 1)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin L (degree of polymerization 1700, carboxyl group amount 1.0 mol%, acetyl group amount 1. 5 mol%, 50 g of the structural unit represented by the above general formula (4-1) (X has a sodium ion) and 50 g of unmodified polyvinyl alcohol resin F (degree of polymerization 500, acetyl group 2.5 mol%) In the same manner as in Example 1, except for using polyvinyl acetal resin (average polymerization degree 1100, acetyl group amount 2.0 mol%, residual hydroxyl group amount 20.8 mol%, acetoacetal group amount 23.9 mol) %, Butyral group amount 52.8 mol%, carboxyl group amount 0.5 mol%).
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 2)
In Example 1, instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 50 g of carboxylic acid-modified polyvinyl alcohol resin J and unmodified polyvinyl alcohol resin E (polymerization degree 800, acetyl group 2.0 mol%) ), And the aldehyde used in the reaction was changed to 5 g of acetaldehyde and 75 g of n-butyraldehyde in the same manner as in Example 1, except that the polyvinyl acetal resin (degree of polymerization 800, acetyl group amount 1.9 mol%) was used. A white powder having a residual hydroxyl group content of 21.5 mol%, an acetoacetal group content of 4.5 mol%, a butyral group content of 71.6 mol%, and a carboxyl group content of 0.5 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 3)
In Example 1, Example 1 except that carboxylic acid-modified polyvinyl alcohol resin J30 g and unmodified polyvinyl alcohol resin A70 g were used instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g. Similarly, a polyvinyl acetal resin (average polymerization degree 1920, acetyl group amount 1.5 mol%, residual hydroxyl group amount 23.3 mol%, acetoacetal group amount 23.4 mol%, butyral group amount 51.6 mol%, A white powder having a carboxyl group content of 0.3 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 4)
In Example 1, Example 1 was used except that carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin D50g were used instead of carboxylic acid-modified polyvinyl alcohol resin G50g and unmodified polyvinyl alcohol resin A50g. Similarly, polyvinyl acetal resin (average polymerization degree 600, acetyl group amount 2.5 mol%, residual hydroxyl group amount 22.1 mol%, acetoacetal group amount 24.1 mol%, butyral group amount 50.9 mol%, A white powder having a carboxyl group content of 0.5 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 5)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, carboxylic acid-modified polyvinyl alcohol resin K (polymerization degree 1500, carboxyl group amount 1.0 mol%, acetyl group amount 2. A polyvinyl acetal resin (average polymerization degree 1500) was obtained in the same manner as in Example 1 except that 100 g of 5 mol% and a structural unit represented by the above general formula (4-1) (X has a sodium ion) was used. White powder having an acetyl group amount of 2.5 mol%, a residual hydroxyl group amount of 20.5 mol%, an acetoacetal group amount of 22.6 mol%, a butyral group amount of 53.4 mol%, and a carboxyl group amount of 1.0 mol%) Got. A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 6)
In Example 1, instead of carboxylic acid-modified polyvinyl alcohol resin G50 g and unmodified polyvinyl alcohol resin A50 g, an aldehyde used for carrying out the acetalization reaction using carboxylic acid-modified polyvinyl alcohol resin J100 g was used as an n-butyraldehyde 80 g. In the same manner as in Example 1 except that the polyvinyl acetal resin (average polymerization degree 800, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.7 mol%, butyral group amount 75.5 mol%, A white powder having a carboxyl group content of 1.0 mol% was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 7)
In Example 1, instead of the carboxylic acid-modified polyvinyl alcohol resin G50g and the unmodified polyvinyl alcohol resin A50g, the carboxylic acid-modified polyvinyl alcohol resin L50g and the carboxylic acid-modified polyvinyl alcohol resin G50g are used to perform the acetalization reaction. The polyvinyl acetal resin (average polymerization degree 1000, acetyl group amount 1.9 mol%, residual hydroxyl group amount 23.3%) was changed in the same manner as in Example 1 except that the aldehyde used in the above was changed to 15 g of acetaldehyde and 65 g of n-butyraldehyde. 5 mol%, acetoacetal group amount 11.1 mol%, butyral group amount 62.5 mol%, carboxyl group amount 1.0 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1 except that the solvent was changed to dihydroterpineol.

<Evaluation>
The following evaluation was performed about the polyvinyl acetal resin and electrically conductive paste obtained by the Example and the comparative example. The results are shown in Table 2.

(1) Solvent solubility of resin (a) Examples 1 to 18 and Comparative Examples 1 to 6
10 parts by weight of the polyvinyl acetal resin obtained in Examples 1 to 18 and Comparative Examples 1 to 6 were dissolved in 90 parts by weight of dihydroterpineol acetate while stirring at room temperature. The time taken for dissolution was evaluated according to the following criteria.
◎: Time required for dissolution is less than 1 hour ○: Time required for dissolution is 1 hour or more and less than 2 hours Δ: Time required for dissolution is 2 hours or more and less than 3 hours ×: Time required for dissolution is 3 hours or more

(B) Examples 19 to 21, Comparative Example 7
10 parts by weight of the polyvinyl acetal resin obtained in Examples 19 to 21 and Comparative Example 7 was dissolved in 90 parts by weight of dihydroterpineol while stirring at room temperature. The time taken for dissolution was evaluated according to the following criteria.
◎: Time required for dissolution is less than 1 hour ○: Time required for dissolution is 1 hour or more and less than 2 hours Δ: Time required for dissolution is 2 hours or more and less than 3 hours ×: Time required for dissolution is 3 hours or more

(2) Tensile Modulus Evaluation Examples of conductive paste sheets obtained in Examples and Comparative Examples are based on JIS K 7113, using TENSILON (manufactured by Shimadzu Corporation, AUTOGRAPHc AGS-J), and a tensile speed of 20 mm / min. The tensile elastic modulus (Mpa) was measured at 1 and evaluated according to the following criteria.
○: 1000 Mpa or more Δ: 700 Mpa or more and less than 1000 Mpa ×: less than 700 Mpa

(3) Paste coating film strength evaluation The conductive paste obtained in Examples and Comparative Examples was coated on a glass plate with a thickness of 5 μm, and the solvent was dried in a blowing oven at 100 ° C. for 30 minutes. . Using the obtained coating film, scratch hardness (pencil method) was performed based on JIS K 5600-5-4, and evaluated according to the following criteria.
○: Pencil hardness is 9H or more Δ: Pencil hardness is 7H or more and less than 9H ×: Pencil hardness is less than 7H

(4) Surface roughness (3) Measured at 10 locations with a surface roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.) using a coating film prepared in the same manner as the coating film used for evaluation of paste coating film strength. And evaluated according to the following criteria.
A: Average surface roughness Ra at 10 locations is less than 0.150 μm ○: Average surface roughness Ra at 10 locations is 0.150 μm or more and less than 0.175 μm Δ: Average surface roughness Ra at 10 locations 0.175 μm or more and less than 0.200 μm ×: Average surface roughness Ra of 10 locations is 0.200 μm or more

According to the present invention, it is possible to provide a conductive paste having excellent printability and capable of forming a coating film having high surface smoothness and high strength, and a multilayer ceramic capacitor using the conductive paste.

Claims (8)

A conductive paste used for an electrode of a multilayer ceramic capacitor,
Containing a polyvinyl acetal resin, an organic solvent, and a conductive powder;
The polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin and has an average degree of polymerization of 810 to 1600,
The polyvinyl acetal resin is an acetalized product of two or more types of mixed polyvinyl alcohol resins having different degrees of polymerization,
Among the mixed polyvinyl alcohol resins, the polyvinyl alcohol resin having the highest degree of polymerization is a carboxylic acid-unmodified polyvinyl alcohol resin,
The polyvinyl alcohol resin other than the polyvinyl alcohol resin having the highest degree of polymerization is at least selected from a structural unit represented by the following formula (1-1) and a structural unit represented by the following formula (1-2). A conductive paste comprising a carboxylic acid-modified polyvinyl alcohol resin having one kind.

In formula (1-1), R ¹ and R ² are each independently a C 0-10 alkylene group, X ¹ and X ² are each independently a hydrogen atom, a metal atom or a methyl group. . In the above formula (1-2), R ³ , R ⁴ and R ⁵ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R ⁶ is an alkylene group having 0 to 10 carbon atoms, and X ³ is Represents a hydrogen atom, a metal atom or a methyl group. The carboxylic acid-unmodified polyvinyl alcohol resin does not have any of the structural unit represented by the formula (1-1) and the structural unit represented by the formula (1-2). The conductive paste according to 1. The conductive paste according to claim 1 or 2, wherein a difference in polymerization degree between the polyvinyl alcohol resin having the highest degree of polymerization and the carboxylic acid-modified polyvinyl alcohol resin is 600 or more. The polyvinyl acetal resin has a carboxyl group amount of 0.05 to 1 mol%, a hydroxyl group amount of 16 to 25 mol%, an acetyl group amount of 0.1 to 5 mol%, and an acetoacetal group amount of 25 mol% or less. The conductive paste according to claim 1, 2, or 3. The conductive paste according to claim 1, wherein the conductive powder is made of nickel. Furthermore, ceramic powder is contained, The electrically conductive paste of Claim 1, 2, 3, 4 or 5 characterized by the above-mentioned. The conductive paste according to claim 1, 2, 3, 4, 5 or 6, wherein the organic solvent has a solubility parameter of 8.0 to 11.0 (cal / cm ³ ) ^0.5 . A multilayer ceramic capacitor obtained by using the conductive paste according to claim 1, 2, 3, 4, 5, 6 or 7.