JP7249367B2 - conductive paste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive paste that has excellent printability and is capable of forming a coating film with high surface smoothness and strength, and a multilayer ceramic capacitor using the conductive paste.

2. Description of the Related Art In recent years, electronic components mounted on various electronic devices have been miniaturized and laminated, and multilayer electronic components such as multilayer circuit boards, laminated coils, and laminated ceramic capacitors are widely used.

Among them, multilayer ceramic capacitors are generally manufactured through the following steps. First, a plasticizer, a dispersant, etc. are added to a solution of a binder resin such as polyvinyl butyral resin, poly(meth)acrylic acid ester resin, ethyl cellulose, etc. dissolved in an organic solvent, and then the ceramic raw material powder is added to obtain a ceramic slurry. obtain. Next, the ceramic slurry is cast on the release-treated surface of the support, and volatile matter such as an organic solvent is distilled off by heating or the like, and then separated from the support to obtain a ceramic green sheet.
Next, a conductive paste for forming internal electrodes is applied on the obtained ceramic green sheets by screen printing, and a plurality of these sheets are stacked and heat-pressed to form a laminate. Furthermore, after performing a process of thermally decomposing and removing the binder resin and the like contained in the laminate, a so-called degreasing process, the ceramic sintered body is fired to form an external electrode on the end surface of the ceramic sintered body. , to obtain a multilayer ceramic capacitor.

Along with miniaturization and higher capacity of multilayer ceramic capacitors, thinner layers of internal electrodes and smoothness of electrode surfaces are required. Therefore, as a conductive paste for forming a thin and smooth internal electrode, a metal material with a controlled particle size, such as the conductive paste disclosed in Patent Document 1, is used to form a thin and smooth electrode surface. It is stated that it can be smoothed.
However, since ethyl cellulose is used as a binder, the strength of the coating film is low, and there are problems such as cracking or chipping due to a slight impact.

The present inventors considered that the strength of the conductive paste coating film can be increased by using a polyvinyl acetal resin to solve the above-described problems.
In Patent Document 2, a low-polarity organic solvent is used to prevent sheet attack on ceramic green sheets. However, when such a low-polarity organic solvent and a conventional polyvinyl acetal resin are used as a binder for a conductive paste, the solubility 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 a 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.

WO2010/021202 JP 2005-243561 A Patent No. 5767923 Patent No. 5809505

An object of the present invention is to provide a conductive paste that has excellent printability and is capable of forming a coating film with high surface smoothness and 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 provides a conductive paste used for electrodes of a multilayer ceramic capacitor, which contains a polyvinyl acetal resin, an organic solvent, and a conductive powder, and the polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin. and the average degree of polymerization is 810 to 1600, the polyvinyl acetal resin is an acetalized product of two or more mixed polyvinyl alcohol resins having different degrees of polymerization, and the mixed polyvinyl alcohol resin has the highest degree of polymerization. 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 polymerization degree is a structural unit represented by the following formula (1-1), and the following formula ( A conductive paste containing a carboxylic acid-modified polyvinyl alcohol resin having at least one structural unit selected from the structural units represented by 1-2).

In the above formula (1-1), R ¹ and R ² each independently represent an alkylene group having 0 to 10 carbon atoms, and X ¹ and X ² each independently represent 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 It represents a hydrogen atom, a metal atom or a methyl group.
The present invention will be described in detail below.

As a result of extensive studies, the present inventors have found that a polyvinyl acetal resin containing a carboxylic acid-modified polyvinyl acetal resin having a specific structure and having a specific average polymerization degree is used as a binder resin for a conductive paste. By defining the structure of the mixed polyvinyl alcohol resin that constitutes, it is possible to obtain a conductive paste that has high printability, surface smoothness, and strength, and has completed the present invention.

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

In formula (2-3) above, 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 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.
They will be explained in order below.

The polyvinyl alcohol resin having the highest degree of polymerization is a carboxylic acid-unmodified polyvinyl alcohol resin. Further, the carboxylic acid-unmodified polyvinyl alcohol resin preferably has neither the structural unit represented by the formula (1-1) nor the structural unit represented by the 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 polymerization degree is 810, and the preferable upper limit thereof is 3,000. By setting the degree of polymerization to 810 or more, the strength of the obtained conductive paste can be effectively exhibited. By setting the degree of polymerization to 3000 or less, the influence on printability can be suppressed. A more preferable lower limit of the polymerization degree of the polyvinyl alcohol resin having the highest degree of polymerization is 1,200, and a more preferable upper limit thereof is 2,500. In addition, the said degree of polymerization means the polymerization degree of the individual polyvinyl alcohol resin, and it distinguishes it from the average polymerization degree mentioned later, and uses it.

The saponification degree of the polyvinyl alcohol resin having the highest degree of polymerization has a preferred lower limit of 87.0 mol% and a preferred upper limit of 99.5 mol%. By setting the degree of saponification to 87.0 mol % or more, the solvent solubility of the obtained polyvinyl acetal resin can be improved. By setting the degree of saponification to 99.5 mol % or less, it is possible to improve the handling when synthesizing the polyvinyl acetal resin. A more preferable lower limit of the degree of saponification of the polyvinyl alcohol resin having the highest degree of polymerization is 90.0 mol%, and a more preferable upper limit thereof 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 polymerization degree is selected from structural units represented by the above formula (1-1) and structural units represented by the above formula (1-2). carboxylic acid-modified polyvinyl alcohol resin having at least one

The carboxylic acid-modified polyvinyl alcohol resin has at least one selected from structural units represented by the above formula (1-1) and structural units represented by the above formula (1-2). The carboxylic acid-modified polyvinyl acetal resin obtained by using the carboxylic acid-modified polyvinyl alcohol resin having the above structural unit dissolves in a low-polarity organic solvent, and is combined with a conductive powder, which is one of the constituent materials of the conductive paste. Since it is possible to improve the familiarity of the electrode, the surface of the electrode after printing can be smoothed.

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

In the above formula (1-1), R ¹ and R ² each independently represent an alkylene group having 0 to 10 carbon atoms, X ¹ and X ² each independently represent a hydrogen atom, a metal atom or a methyl group represents

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

R ¹ and R ² may be the same or different, but different ones are preferred. 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 , a cyclobutylene group, a cyclohexylene group, and the like. Among them, straight-chain alkylene groups such as alkylene, methylene, ethylene, trimethylene and tetramethylene groups having 0 carbon atoms are preferred, and alkylene, methylene and ethylene groups having 0 carbon atoms are more preferred.

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. Among them, a sodium atom is preferred.

The structural unit represented by formula (1-1) is preferably derived from an α-dicarboxy monomer. Examples of α-dicarboxy monomers include dicarboxylic acids having radically polymerizable unsaturated double bonds such as methylenemalonic acid, itaconic acid, 2-methyleneglutaric acid, 2-methyleneadipic acid and 2-methylenesebacic acid, and their metal salts or their methyl esters. Among them, itaconic acid is preferably used.
In this 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 constitutional unit represented by the formula (1-2), the solvent solubility can be further improved.
In formula (1-2) above, R ³ , R ⁴ and R ⁵ each independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁶ represents an alkylene group having 0 to 10 carbon atoms. and 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, raw material synthesis occurs due to steric hindrance if the number of carbon atoms in the alkyl group exceeds 10. Time polymerization becomes difficult to occur. The preferred lower limit for the number of carbon atoms in the alkyl group represented by R ³ , R ⁴ and R ⁵ is 1, the preferred upper limit is 5, and the more preferred upper limit is 3.

R ³ and R ⁴ may be the same or different, but are more preferably the same. Also, 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 groups 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 include branched alkyl groups such as 2-ethylhexyl group, cycloalkyl groups such as cyclopropyl group, cyclopropylmethyl group, cyclobutyl group, cyclopentyl group and cyclohexyl group. Among them, straight-chain alkyl groups such as methyl group, ethyl group, propyl group and n-butyl group are preferable, and methyl group and ethyl group are more preferable.

In the above formula (1-2), by setting the number of carbon atoms in the alkylene group represented by R ⁶ to 10 or less, aggregation due to carboxyl groups is prevented, and the resin becomes easier to dissolve in a low-polar solvent. The preferred lower limit for the number of carbon atoms in the alkylene group represented by R ⁶ is 0, the preferred upper limit is 5, the more preferred lower limit is 1, and the more preferred upper limit is 3.

Examples of R ⁶ in the above formula (1-2) include the same groups as those exemplified for R ¹ and R ² in the above formula (1-1), especially an alkylene group having 0 carbon atoms, Linear alkylene groups such as a methylene group, ethylene group, trimethylene group and tetramethylene group are preferred, alkylene groups having 0 carbon atoms, methylene groups and ethylene groups are more preferred, and alkylene groups having 0 carbon atoms are even more preferred.

When the above ^X3 is a metal atom, examples of the metal atom include sodium atom, lithium atom, potassium atom and the like. Among them, a sodium atom is preferred.

The structural unit represented by the above formula (1-2) is preferably derived from a monocarboxy monomer. Examples of monocarboxy monomers include monocarboxylic acids having a radically polymerizable unsaturated double bond such as acrylic acid, crotonic acid, methacrylic acid, and oleic acid, metal salts thereof, methyl esters thereof, and the like. Among them, crotonic acid is preferably used.

The carboxylic acid-modified polyvinyl alcohol resin may be used alone, or may be used by mixing different ones.

Although 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 above formula (1-1), A method of saponifying polyvinyl acetate obtained by copolymerizing vinyl acetate with an α-dicarboxy monomer, which is a structural unit represented by -1). Among them, when the α-dicarboxy monomer used in preparing the polyvinyl acetate by copolymerization is a methyl ester, the acetyl group derived from vinyl acetate is not hydrolyzed before saponification, so that the subsequent saponification can be performed. It is preferable because the saponification can be made higher when the polyvinyl alcohol resin is produced in the saponification step. Furthermore, since the amount of sodium hydroxide to be added in the saponification step can be reduced, it is possible to reduce the sodium ion content of the polyvinyl alcohol resin and the carboxylic acid-modified polyvinyl acetal resin.
Even if the α-dicarboxy monomer is a methyl ester, it is hydrolyzed in the subsequent saponification step, so that the resulting polyvinyl alcohol resin has carboxylic acid units containing no ester.
Among the α-dicarboxy monomers to be the structural units represented by the above formula (1-1), when using a monomer in which X ¹ and X ² are hydrogen atoms or metal atoms, when saponifying, vinyl acetate-derived Since a large amount of sodium hydroxide is consumed for hydrolysis of acetyl groups, the resulting carboxylic acid-modified polyvinyl alcohol resin may have a relatively large sodium ion content.
Further, when the carboxylic acid-modified polyvinyl alcohol resin has a structural unit represented by the above formula (1-2), a monocarboxy monomer to be the structural unit represented by the above formula (1-2) and vinyl acetate and a method of saponifying polyvinyl acetate obtained by copolymerizing with. Furthermore, a method of post-modification by reacting a polyvinyl alcohol resin with a compound having a carboxyl group such as mercaptopropionic acid can also be used.

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

The saponification degree of the carboxylic acid-modified polyvinyl alcohol resin has a preferred lower limit of 87.0 mol% and a preferred upper limit of 99.5 mol%. By setting the degree of saponification to 87.0 mol % or more, the obtained conductive paste can have excellent solvent solubility. By setting the degree of saponification to 99.5 mol % or less, it is possible to improve the handling when synthesizing the polyvinyl acetal resin. A more preferable lower limit of the degree of saponification of the carboxylic acid-modified polyvinyl alcohol resin is 90.0 mol %, and a more preferable upper limit thereof is 99.0 mol %.

In the mixed polyvinyl alcohol resin, the preferable lower limit of 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 is 600. When the difference in polymerization degree of the mixed polyvinyl alcohol is 600 or more, each effect can be exhibited more effectively. When the carboxylic acid-modified polyvinyl alcohol resin and the polyvinyl alcohol resin with the highest degree of polymerization consist of a plurality of types, the difference when the difference is the smallest is taken as the degree of polymerization difference.

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 range, it is possible to prevent the characteristics of components with a high mixing ratio from appearing strongly and the characteristics of components with a low mixing ratio from not sufficiently appearing.
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.
The acetalization reaction is not particularly limited, and can be carried out by a conventionally known method. Examples thereof include a method of adding various aldehydes to an aqueous polyvinyl alcohol solution, an alcohol solution, a water/alcohol mixed solution, or a dimethylsulfoxide (DMSO) solution in the presence of an acid catalyst.
The above aldehydes are not particularly limited, and examples include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, and 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 to use acetaldehyde and butyraldehyde in combination.

The polyvinyl acetal resin may contain other polyvinyl acetal resins in addition to the carboxylic acid-modified polyvinyl acetal resin as long as the effects of the present invention are not impaired.
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 be adjusted to achieve the carboxyl group content of the polyvinyl acetal resin described later. Although not particularly limited, the preferable lower limit is 5% by weight, the preferable upper limit is 90% by weight, the more preferable lower limit is 10% by weight, the more preferable upper limit is 85% by weight, the particularly preferable lower limit is 15% by weight, and the particularly preferable upper limit is 15% by weight. 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 1,600. When the average degree of polymerization is 810 or more, the strength of the conductive paste can be increased and the required 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 the conductive paste is less likely to be stringy, resulting in excellent printability and surface smoothness. The preferable lower limit of the average polymerization degree 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 obtained from the average degree of polymerization of polyvinyl alcohol resin as a raw material.
Moreover, in this specification, the average degree of polymerization of the polyvinyl alcohol resin means the apparent average degree of polymerization of the entire 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 is obtained by summing 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 carboxyl group content of the polyvinyl acetal resin is 0.05 mol %, and the preferable upper limit thereof is 1 mol %. When the amount of carboxyl groups is 0.05 mol% or more, the effect of having carboxyl groups in the polyvinyl acetal resin is sufficiently exhibited, and the printability and surface smoothness of the conductive paste are improved, and storage stability is improved. can be improved. By setting the amount of carboxyl groups to 1 mol % or less, the solubility of the polyvinyl acetal resin in organic solvents is improved, and the interaction between the carboxyl groups and the conductive powder is moderate, so that it is possible to produce a conductive paste. becomes easier. The more preferable lower limit of the carboxyl group content of the polyvinyl acetal resin is 0.07 mol%, the more preferable upper limit is 0.8 mol%, the more preferable lower limit is 0.1 mol%, and the more preferable upper limit is 0.6 mol%. is.

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

Moreover, in this specification, the amount of carboxyl groups in the polyvinyl acetal resin means the apparent amount of carboxyl groups in the entire 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. It is obtained by summing each value.
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 content 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. and D represents the weight of the entire polyvinyl acetal resin.

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

When the polyvinyl acetal resin contains acetoacetal groups, the preferred upper limit of the amount of acetoacetal groups is 25 mol %. If the amount of acetoacetal groups exceeds 25 mol %, the solubility of the polyvinyl acetal resin in low-polarity organic solvents decreases, making it difficult to prepare a conductive paste. A more preferable upper limit of the amount of acetoacetal groups in the polyvinyl acetal resin is 22 mol %, and a still more preferable upper limit is 20 mol %.
The acetoacetal group is an acetal group in which R ⁷ is a methyl group among the acetal groups contained in the structural unit having the acetal group represented by the above formula (2-3). Moreover, in this specification, the amount of acetoacetal groups in the polyvinyl acetal resin means the apparent amount of acetoacetal groups in the entire polyvinyl acetal resin.

When the polyvinyl acetal resin contains butyral groups, the preferred lower limit of the butyral group content is 40 mol %, and the preferred upper limit is 80 mol %. By setting the butyral group content to 40 mol % or more, it is possible to prevent the residual hydroxyl group content from becoming too large and improve the solubility of the polyvinyl acetal resin in low-polar solvents. When the amount is 80 mol % or less, the amount of residual hydroxyl groups increases and the viscosity of the obtained conductive paste increases, so that the storage stability can be improved. A more preferable lower limit of the butyral group content of the polyvinyl acetal resin is 50 mol %, and a more preferable upper limit thereof is 70 mol %.
The butyral group is an acetal group in which R ⁷ is a propyl group among the acetal groups contained in the structural unit having the acetal group represented by the above formula (2-3). In the present specification, the butyral group weight of the polyvinyl acetal resin means the apparent butyral group weight of the entire polyvinyl acetal resin.

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

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

In the polyvinyl acetal resin, the preferred lower limit of the ratio of the amount of acetyl groups to the amount of hydroxyl groups is 0.01, and the preferred upper limit thereof 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 be 0.01 or more or 0.15 or less, the solubility in low-polarity organic solvents can be improved. A more preferable lower limit of the ratio of the amount of acetyl groups to the amount of hydroxyl groups in the polyvinyl acetal resin is 0.03, and a more preferable upper limit thereof is 0.13.

In the polyvinyl acetal resin, the total amount of the carboxyl group content, the degree of acetalization, the hydroxyl group content and the acetyl group content 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 exhibited more favorably.

The polyvinyl acetal resin preferably has a sodium ion content of less than 50 ppm. If the content of sodium ions in the polyvinyl acetal resin is less than 50 ppm, the conductive paste will have excellent conductivity, and the viscosity will not change significantly over time.

The conductive paste of the present invention may contain other resins such as acrylic resin and ethyl cellulose in addition to the polyvinyl acetal resin as long as the effects of the present invention are not impaired.
Due to the effect of the carboxyl group, the polyvinyl acetal resin of the present invention is also more compatible with other resins than ordinary polyvinyl acetal resins.

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

It is preferable that the nickel powder has an average particle size of 50 to 300 nm and a substantially spherical shape. By setting the average particle size 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 made smooth. In addition, the substantially spherical shape includes particles having a nearly spherical shape as well as a truly spherical shape.

The amount of the conductive powder to be blended is not particularly limited, but the preferred lower limit is 100 parts by weight and the preferred upper limit is 10000 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin. 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. If the blending amount of the conductive powder exceeds 10,000 parts by weight, the dispersibility of the conductive powder in the conductive paste may deteriorate, and the printability may deteriorate. As for the amount of the conductive powder to be blended, a more preferable lower limit is 200 parts by weight and a more preferable upper limit is 5000 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin.

The conductive paste of the present invention preferably contains ceramic powder in addition to the conductive powder. By containing the ceramic powder, it becomes easier to match the shrinkage behavior of the conductive powder during firing with that of the ceramic green sheet.
Although the ceramic powder is not particularly limited, barium titanate used for green sheets is preferable. Although the particle size of the ceramic powder is not particularly limited, it is preferably smaller than the particle size of the conductive powder, specifically 30 nm to 200 nm.

The conductive paste of the present invention contains an organic solvent.
As the organic solvent, an organic solvent generally used for conductive paste can be used. In order to prevent the sheet attack phenomenon in particular, a non-phase organic solvent that does not swell or dissolve the polyvinyl butyral resin contained in the ceramic green sheet is used. It is preferably a soluble low-polarity organic solvent and its solubility parameter is 8.0 to 11.0 (cal/cm ³ ) ^0.5 . As the solubility parameter, one calculated by the Fedors method is used.
Examples of the organic solvent include terpineol (terpineol), dihydroterpineol (dihydroterpineol), terpinyl acetate, isobornyl acetate, dihydroterpineol acetate (dihydroterpinyl acetate), dihydroterpineol methyl ether, terpineol Terpineol derivatives such as nylmethyl ether, hydrocarbon solvents such as mineral spirits, 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.

The amount of the organic solvent to be blended is not particularly limited, but the preferred lower limit is 100 parts by weight and the preferred upper limit is 10000 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin. When the blending amount of the organic solvent is 100 parts by weight or more, the viscosity of the conductive paste is lowered, and the printability can be improved. By setting the blending amount of the organic solvent to 10,000 parts by weight or less, it is possible to sufficiently exhibit the performance of the polyvinyl acetal resin in the conductive paste. The more preferable lower limit of the amount of the organic solvent compounded is 200 parts by weight, and the more preferable upper limit thereof is 5000 parts by weight with respect to 100 parts by weight of the polyvinyl acetal resin.

The conductive paste of the present invention may contain plasticizers, lubricants, antistatic agents, dispersants, surfactants and the like as appropriate within a range that does not impair the effects of the present invention.

Although the plasticizer is not particularly limited, examples include phthalate 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 the dispersant is not particularly limited, for example, fatty acids, aliphatic amines, alkanolamides, and phosphate esters are suitable. A silane coupling agent or the like may also be added.
The above fatty acids are not particularly limited, and examples include saturated fatty acids such as behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, capric acid, caprylic acid, coconut fatty acid; oleic acid, linoleic acid, linolenic acid, sorbic acid. , beef tallow fatty acid, castor hardened fatty acid and other unsaturated fatty acids. Among them, lauric acid, stearic acid, oleic acid and the like are preferable.
The above-mentioned aliphatic amine is not particularly limited, and examples thereof include laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, alkyl (coconut) amine, alkyl (hardened beef tallow) amine, alkyl (beef tallow) amine, and 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.
The phosphate is not particularly limited, and examples thereof include polyoxyethylene alkyl ether phosphate and polyoxyethylene alkyl allyl ether phosphate.

The above-mentioned surfactant is not particularly limited, but examples of anionic surfactants include carboxylic acid-based fatty acid sodium salts and the like, sulfonic acid-based linear alkylbenzenesulfonate sodium, sodium lauryl sulfate, and alkylpolyoxysulfate. Monoalkyl phosphate etc. are mentioned as a salt etc. and a phosphoric acid type|system|group. Examples of cationic surfactants include alkyltrimethylammonium salts, dialkyldimethylammonium salts, and alkylbenzyldimethylammonium salts. Examples of amphoteric surfactants include alkyldimethylamine oxides and alkylcarboxybetaines. Examples of surfactants include polyoxyethylene alkyl ethers, fatty acid sorbitan esters, alkyl polyglucosides, fatty acid diethanolamides, alkyl monoglyceryl ethers, and the like.
The above dispersant and surfactant are also effective in suppressing an increase in the viscosity of the paste or resin solution over time.

The method for producing the conductive paste of the present invention is not particularly limited. are mixed using a mixer such as a ball mill, blender mill, or three rolls.

The conductive paste of the present invention is applied to a ceramic green sheet by a printing process such as screen printing, die coating, or gravure offset, and a plurality of these sheets are stacked and heat-pressed to form a laminate, which is then degreased and fired. A laminated ceramic capacitor can be obtained by forming a ceramic sintered body, and forming external electrodes on the end faces of the ceramic sintered body. Such a laminated ceramic capacitor is also one aspect of the present invention.

Although the method for printing the conductive paste of the present invention is not particularly limited, it can be performed by a printing process such as screen printing, die coating, or gravure printing as described above. The optimum viscosity at that time varies depending on each printing process, so it 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 gravure printing, the viscosity at a shear rate of 10000 s ⁻¹ is preferably 0.05 to 0.5 Pa·s.

Since the conductive paste of the present invention contains a polyvinyl acetal resin containing a carboxylic acid-modified polyvinyl acetal resin as described above, the surface after printing can be made smooth even if a low-polarity organic solvent is used. , the multilayer ceramic capacitor can be made thinner, and excellent conductivity can be obtained.
Moreover, since the polyvinyl acetal resin used in the conductive paste of the present invention has a very low sodium ion content, it can also be suitably used as a binder for silver salts.

An organic silver salt is used as the silver salt. The above organic silver salt is not particularly limited, and examples thereof include silver salts of organic compounds having a mercapto group, a thione group or a carboxyl group, silver benzotriazole, and the like. Specifically, silver salts of compounds having a mercapto group or a thione group, silver salts of 3-mercapto-4-phenyl 1,2,4-triazole, silver salts of 2-mercapto-benzimidazole, and 2-mercapto-5 -silver salts of dithiocarboxylic acids such as silver salts of aminothiazole, silver salts of 1-phenyl-5-mercaptotetrathiazole, silver salts of 2-mercaptobenzothiazole, silver salts of thioglycolic acid, silver salts of dithioacetic acid , thioamide silver, thiopyridine silver salt, 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., silver aromatic carboxylate, silver thiocarboxylate, silver aliphatic carboxylate having a thioether group, silver salt of tetrazaindene, silver S-2-aminophenylthiosulfate, etc. metal aminoalcohols, organic acid metal chelates, and the like.

ADVANTAGE OF THE INVENTION According to this invention, it has excellent printability and can provide the electrically conductive paste which can form a coating film with high surface smoothness and strength, and the laminated ceramic capacitor using this electrically conductive paste.

EXAMPLES The aspects of the present invention will be described in more detail with reference to Examples below, but the present invention is not limited only to these Examples.

(Example 1)
(Production of polyvinyl acetal resin)
Carboxylic acid-modified polyvinyl alcohol resin G (degree of polymerization 300, carboxyl group content 1.0 mol%, acetyl group content 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 (35% strength 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 the acetalization reaction was carried out while maintaining this temperature. After completing the reaction, after neutralization, washing with water and drying, polyvinyl acetal resin (average degree of polymerization 1350, acetyl group content 1.8 mol%, residual hydroxyl group content 21.3 mol%, acetoacetal group content 23.0 mol %, butyral group content: 53.5 mol %, carboxyl group content: 0.5 mol %).

(Preparation of conductive paste)
A resin solution was obtained by dissolving 20 parts by weight of the obtained polyvinyl acetal resin in 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 conductive powder, the obtained resin solution is mixed and dispersed by a triple roll, A conductive paste was obtained.

(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, 70 g of carboxylic acid-modified polyvinyl alcohol resin G and 30 g of unmodified polyvinyl alcohol resin A were used to perform the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization: 930, acetyl group content: 1.9 mol%, residual hydroxyl group content: 22.1 mol%, 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 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 10 g of carboxylic acid-modified polyvinyl alcohol resin G and unmodified polyvinyl alcohol resin D (degree of polymerization: 900, acetyl group content: 2.7 Polyvinyl acetal resin (average degree of polymerization 840, acetyl group content 2.7 mol%, residual hydroxyl group content 21.5 mol%, acetoacetal group content A white powder having a content of 23.5 mol %, a butyral group content of 52.3 mol %, and a carboxyl group content 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 4)
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 J (degree of polymerization: 800, carboxyl group content: 1.0 mol %, acetyl group content: 1.0 mol %) was used. 8 mol%, 70 g of a structural unit represented by the above general formula (4-1) (X is a sodium ion)), and 30 g of unmodified polyvinyl alcohol resin A are used to perform an acetalization reaction. , Polyvinyl acetal resin (average degree of polymerization 1280, acetyl group content 1.7 mol%, residual hydroxyl group content 22.0 mol%, A white powder having an acetoacetal group content of 18.5 mol %, a butyral group content of 57.2 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 5)
Same as Example 1, except that 90 g of carboxylic acid-modified polyvinyl alcohol resin J and 10 g of unmodified polyvinyl alcohol resin A were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Then, polyvinyl acetal resin (average degree of polymerization 960, acetyl group content 1.8 mol%, residual hydroxyl group content 20.8 mol%, acetoacetal group content 23.9 mol%, butyral group content 52.7 mol%, carboxyl A white powder having a basis weight 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 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 10 g of carboxylic acid-modified polyvinyl alcohol resin J and 90 g of unmodified polyvinyl alcohol resin D were used to carry out the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization 890, acetyl group content 2.6 mol%, residual hydroxyl group content 21.3 mol%, butyral A white powder having a base content of 76.0 mol % and a carboxyl group content 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)
Same as Example 1, except that 90 g of carboxylic acid-modified polyvinyl alcohol resin J and 10 g of unmodified polyvinyl alcohol resin D were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Then, polyvinyl acetal resin (average degree of polymerization 810, acetyl group content 1.9 mol%, residual hydroxyl group content 22.7 mol%, acetoacetal group content 22.8 mol%, butyral group content 51.7 mol%, carboxyl A white powder having a basis weight 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 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 10 g of carboxylic acid-modified polyvinyl alcohol resin J and unmodified polyvinyl alcohol resin C (degree of polymerization: 1400, acetyl group content: 1.7 mol) %) in the same manner as in Example 1, except that 90 g of the 0.2 mol %, butyral group content 54.5 mol %, carboxyl group content 0.1 mol %).
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 9)
Same as Example 1, except that 90 g of carboxylic acid-modified polyvinyl alcohol resin J and 10 g of unmodified polyvinyl alcohol resin C were used in place of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Then, polyvinyl acetal resin (average degree of polymerization 860, acetyl group content 1.8 mol%, residual hydroxyl group content 21.9 mol%, acetoacetal group content 22.7 mol%, butyral group content 52.7 mol%, carboxyl A white powder having a basis weight 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 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 H (degree of polymerization: 500, carboxyl group content: 1.0 mol %, acetyl group content: 2.0 mol %) was used. 10 g of unmodified polyvinyl alcohol resin B (having a degree of polymerization of 1700 and an acetyl group content of 2.0 mol %) 90 g Polyvinyl acetal resin (average degree of polymerization 1580, acetyl group content 2.0 mol%, residual hydroxyl group content 21.5 mol%, acetoacetal group content 22.3 mol% , a butyral group content of 54.1 mol %, and a carboxyl group content of 0.1 mol %).
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 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 H and 50 g of unmodified polyvinyl alcohol resin B were used, and the aldehyde used when performing the acetalization reaction was changed to 15 g of acetaldehyde and 70 g of n-butyraldehyde, in the same manner as in Example 1, polyvinyl acetal resin (average degree of polymerization 1100, acetyl group content 2.0 mol%, residual hydroxyl group content 20.9 mol% , an acetoacetal group content of 13.4 mol %, a butyral group content of 63.2 mol %, and a carboxyl group content of 0.5 mol %).
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 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 70 g of carboxylic acid-modified polyvinyl alcohol resin H and 30 g of unmodified polyvinyl alcohol resin B were used, and the aldehyde used when performing the acetalization reaction Polyvinyl acetal resin (average degree of polymerization 860, acetyl group content 2.0 mol%, residual hydroxyl group content 22.2 mol%) was prepared in the same manner as in Example 1, except that acetaldehyde 5 g and n-butyraldehyde 75 g , an acetoacetal group content of 4.6 mol %, a butyral group content of 70.5 mol %, and a carboxyl group content of 0.7 mol %).
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 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 N (degree of polymerization: 500, carboxyl group content: 1.0 mol%, acetyl group: 4.5 Polyvinyl acetal was prepared in the same manner as in Example 1, except that 30 g of a structural unit represented by the following general formula (4-2) (X is a sodium ion) and 70 g of unmodified polyvinyl alcohol resin B were used. Resin (average degree of polymerization 1340, acetyl group content 2.8 mol%, residual hydroxyl group content 22.4 mol%, acetoacetal group content 23.6 mol%, butyral group content 51.0 mol%, carboxyl group content 0.3 %) of white powder was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 14)
In Example 1, the procedure was the same as in Example 1, except that 70 g of carboxylic acid-modified polyvinyl alcohol resin N and 30 g of unmodified polyvinyl alcohol resin B were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Polyvinyl acetal resin (average degree of polymerization 860, acetyl group content 3.8 mol%, residual hydroxyl group content 21.7 mol%, acetoacetal group content 22.5 mol%, butyral group content 51.4 mol%, carboxyl group 0.7 mol %) of white powder 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 (degree of polymerization: 500, carboxyl group content: 0.5 mol %, acetyl group content: 2.5 mol %) was used. 5 mol%, using 70 g of the structural unit (X is a sodium ion) represented by the general formula (4-1) and 30 g of the unmodified polyvinyl alcohol resin B, the aldehyde used when performing the acetalization reaction, Polyvinyl acetal resin (average degree of polymerization 860, acetyl group content 2.4 mol%, residual hydroxyl group content 20.7 mol%, aceto A white powder having an acetal group content of 9.5 mol %, a butyral group content of 67.1 mol %, and a carboxyl group content of 0.4 mol % was obtained.
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Example 16)
Same as Example 1, except that 10 g of carboxylic acid-modified polyvinyl alcohol resin M and 90 g of unmodified polyvinyl alcohol resin B were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Then, polyvinyl acetal resin (average degree of polymerization 1580, acetyl group content 2.1 mol%, residual hydroxyl group content 21.0 mol%, acetoacetal group content 23.3 mol%, butyral group content 53.6 mol%, carboxyl A white powder having a basis weight 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 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 30 g of carboxylic acid-modified polyvinyl alcohol resin J, 40 g of carboxylic acid-modified polyvinyl alcohol resin G, and 30 g of unmodified polyvinyl alcohol resin A were used. In the same manner as in Example 1, polyvinyl acetal resin (average degree of polymerization: 1080, acetyl group content: 1.8 mol%, residual hydroxyl group content: 21.3 mol%, acetoacetal group content: 22.8 mol%, A white powder having a butyral group content of 53.4 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 18)
In Example 1, instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, 30 g of carboxylic acid-modified polyvinyl alcohol resin G, 30 g of unmodified polyvinyl alcohol resin A, and 40 g of unmodified polyvinyl alcohol resin D were used. , Polyvinyl acetal resin (average degree of polymerization 1170, acetyl group content 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 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 G and 50 g of unmodified polyvinyl alcohol resin C were used to perform the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization 850, acetyl group content 2.0 mol%, residual hydroxyl group content 19.5 5.3 mol % of acetoacetal groups, 72.7 mol % of butyral groups, and 0.5 mol % of carboxyl groups).
A conductive paste was obtained in the same manner as in Example 1, except that the obtained polyvinyl acetal resin was used and the solvent was changed to dihydroterpineol.

(Example 20)
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 M and 50 g of unmodified polyvinyl alcohol resin B were used to perform the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization: 1100, acetyl group content: 2.3 mol%, residual hydroxyl group content: 21.1 mol%, A white powder having a butyral group content of 76.3 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, except that the obtained polyvinyl acetal resin was used and the solvent was changed to dihydroterpineol.

(Example 21)
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 M and 50 g of unmodified polyvinyl alcohol resin A were used to perform the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization: 1450, acetyl group content: 1.9 mol%, residual hydroxyl group content: 20.4 11.9 mol % of acetoacetal groups, 65.5 mol % of butyral groups, and 0.3 mol % of carboxyl groups).
A conductive paste was obtained in the same manner as in Example 1, except that the obtained polyvinyl acetal resin was used and the solvent was changed to dihydroterpineol.

(Comparative example 1)
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 L (degree of polymerization: 1700, carboxyl group content: 1.0 mol %, acetyl group content: 1.0 mol %) was used. 5 mol%, 50 g of a structural unit represented by the above general formula (4-1) (where X is a sodium ion), and 50 g of unmodified polyvinyl alcohol resin F (degree of polymerization: 500, acetyl group: 2.5 mol%) Polyvinyl acetal resin (average polymerization degree 1100, acetyl group content 2.0 mol%, residual hydroxyl group content 20.8 mol%, acetoacetal group content 23.9 mol) was prepared in the same manner as in Example 1 except that %, a butyral group content of 52.8 mol %, and a carboxyl group content of 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 (degree of polymerization: 800, acetyl groups: 2.0 mol % ) in the same manner as in Example 1, except that 50 g of acetaldehyde and 75 g of n-butyraldehyde were used as the aldehydes used during the reaction. , 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%).
A conductive paste was obtained in the same manner as in Example 1 using the obtained polyvinyl acetal resin.

(Comparative Example 3)
Example 1, except that 30 g of carboxylic acid-modified polyvinyl alcohol resin J and 70 g of unmodified polyvinyl alcohol resin A were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Similarly, polyvinyl acetal resin (average polymerization degree 1920, acetyl group content 1.5 mol%, residual hydroxyl group content 23.3 mol%, acetoacetal group content 23.4 mol%, butyral group content 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)
Example 1, except that 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin D were used instead of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A. Similarly, polyvinyl acetal resin (average polymerization degree 600, acetyl group content 2.5 mol%, residual hydroxyl group content 22.1 mol%, acetoacetal group content 24.1 mol%, butyral group content 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 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 K (degree of polymerization: 1500, carboxyl group content: 1.0 mol %, acetyl group content: 2.0 mol %) was used. Polyvinyl acetal resin (average degree of polymerization: 1500 , acetyl group content 2.5 mol%, residual hydroxyl group content 20.5 mol%, acetoacetal group content 22.6 mol%, butyral group content 53.4 mol%, carboxyl group content 1.0 mol%) white powder. 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, 100 g of carboxylic acid-modified polyvinyl alcohol resin J was used in place of 50 g of carboxylic acid-modified polyvinyl alcohol resin G and 50 g of unmodified polyvinyl alcohol resin A, and 80 g of n-butyraldehyde was used as the aldehyde used in the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization 800, acetyl group content 1.8 mol%, residual hydroxyl group content 21.7 mol%, butyral group content 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, in place 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 L and 50 g of carboxylic acid-modified polyvinyl alcohol resin G were used to perform the acetalization reaction. Polyvinyl acetal resin (average degree of polymerization: 1000, acetyl group content: 1.9 mol%, residual hydroxyl group content: 23.0%) 5 mol %, 11.1 mol % of acetoacetal groups, 62.5 mol % of butyral groups, and 1.0 mol % of carboxyl groups) were obtained as a white powder.
A conductive paste was obtained in the same manner as in Example 1, except that the obtained polyvinyl acetal resin was used and the solvent was changed to dihydroterpineol.

<Evaluation>
The polyvinyl acetal resins and conductive pastes obtained in Examples and Comparative Examples were evaluated as follows. Table 2 shows the results.

(1) Solvent solubility of resin (a) Examples 1 to 18, Comparative Examples 1 to 6
10 parts by weight of the polyvinyl acetal resins obtained in Examples 1 to 18 and Comparative Examples 1 to 6 were dissolved in 90 parts by weight of dihydroterpineol acetate with stirring at room temperature. The time required 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 △: 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 19-21, Comparative Example 7
10 parts by weight of the polyvinyl acetal resins obtained in Examples 19 to 21 and Comparative Example 7 were dissolved in 90 parts by weight of dihydroterpineol with stirring at room temperature. The time required 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 △: 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 The conductive paste sheets obtained in Examples and Comparative Examples were subjected to tensile speed of 20 mm/min using TENSILON (manufactured by Shimadzu Corporation, AUTOGRAPHcAGS-J) in accordance with JIS K 7113. The tensile elastic modulus (Mpa) was measured at and evaluated according to the following criteria.
○: 1000 Mpa or more △: 700 Mpa or more and less than 1000 Mpa ×: less than 700 Mpa

(3) Paste Coating Strength Evaluation The conductive pastes obtained in Examples and Comparative Examples were applied to a thickness of 5 μm on a glass plate, and the solvent was dried in a blower oven at 100° C. for 30 minutes. . Using the obtained coating film, the scratch hardness (pencil method) was measured according to JIS K 5600-5-4 and evaluated according to the following criteria.
○: Pencil hardness is 9H or more △: Pencil hardness is 7H or more and less than 9H ×: Pencil hardness is less than 7H

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

ADVANTAGE OF THE INVENTION According to this invention, it has excellent printability and can provide the electrically conductive paste which can form a coating film with high surface smoothness and strength, and the laminated ceramic capacitor using this electrically conductive paste.

Claims (7)

A conductive paste used for electrodes 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 polymerization degree of 930 to 1600 and a hydroxyl group content of 25 mol% or less,
The polyvinyl acetal resin is an acetalized product of two or more 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 polymerization degree is at least selected from structural units represented by the following formula (1-1) and structural units represented by the following formula (1-2) A conductive paste comprising a carboxylic acid-modified polyvinyl alcohol resin having one.

In the above formula (1-1), R ¹ and R ² each independently represent an alkylene group having 0 to 10 carbon atoms, and X ¹ and X ² each independently represent 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 It represents a hydrogen atom, a metal atom or a methyl group. Carboxylic acid-unmodified polyvinyl alcohol resin is characterized in that it has neither the structural unit represented by the formula (1-1) nor the structural unit represented by the formula (1-2). 1. The conductive paste according to 1. 3. The conductive paste according to claim 1, wherein the difference in the degree of polymerization between the polyvinyl alcohol resin having the highest degree of polymerization and the carboxylic acid-modified polyvinyl alcohol resin is 600 or more. 4. The conductive paste according to claim 1, 2 or 3 , wherein the conductive powder is made of nickel. 5. The conductive paste according to claim 1 , further comprising ceramic powder. 6. The conductive paste according to claim 1 , 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 or 6 .