JP6935997B2 - Conductive paste - Google Patents

Description

The present invention relates to a conductive paste having high printability and excellent surface smoothness, thread breakage and handleability.

In recent years, electronic components mounted on various electronic devices have been miniaturized and laminated, and laminated electronic components such as multilayer circuit boards, multilayer coils, and multilayer ceramic capacitors have been 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 prepared by dissolving a binder resin such as polyvinyl butyral resin, poly (meth) acrylic acid ester resin, and ethyl cellulose in an organic solvent, and then a ceramic raw material powder is added to prepare a ceramic slurry. obtain. Next, this ceramic slurry is cast on the surface of the support that has undergone the mold release treatment to distill off volatile components such as an organic solvent by heating or the like, and then peeled off from the support to obtain a ceramic green sheet.
Next, a conductive paste for forming an internal electrode is applied onto the obtained ceramic green sheet by screen printing, and a plurality of the conductive pastes are stacked and heat-bonded to prepare a laminate. Further, after performing a treatment of thermally decomposing and removing the binder resin and the like contained in the laminated body, that is, a so-called degreasing treatment, the ceramic sintered body is formed by firing, and an external electrode is formed on the end face of the ceramic sintered body. , Obtain a monolithic ceramic capacitor.

With the miniaturization and high capacity of multilayer ceramic capacitors, it has been required to make the internal electrodes thinner and to make the electrode surface smoother. Therefore, as the conductive paste for forming a thin layer and smooth internal electrode, the electrode surface is smoothed by using a metal material having a controlled particle size, for example, the conductive paste disclosed in Patent Document 1. It is stated that it can be done.
However, it is necessary to further improve the smoothness of the thinned electrode layer, which has been demanded in recent years, and even if a metal material having a controlled particle size as described above is used, the conductive paste If it is not well compatible with the organic solvent and the binder resin, which are other constituent materials of the above, the dispersibility becomes poor, and it is extremely difficult to smooth the electrode surface after printing.

Further, in Patent Document 2, a low-polarity organic solvent is used in order to prevent the sheet from attacking the ceramic green sheet.
However, it is effective to use a polyvinyl acetal resin capable of preventing delamination (delamination) for thinning the electrode. However, when a conventional polyvinyl acetal resin is used as a binder for a conductive paste, the polarity with an organic solvent is used. Due to the difference, the solubility is very poor, so that it is difficult to dissolve in the above-mentioned low-polarity organic solvent. Therefore, when a conventional polyvinyl acetal resin is applied to the electrode paste, the dispersibility of the inorganic powder deteriorates, the surface of the electrode after printing becomes rough, and it is difficult to smooth it.

In response to the above problems, the present inventors have developed a polyvinyl acetal having a specific structure (see Patent Documents 3 and 4).
However, even if the above resin is used, a high level of smoothness cannot be obtained when the degree of polymerization of the resin is high. Further, when the degree of polymerization of the resin is reduced, even if the electrode surface can be smoothed, the viscosity as a whole is also lowered, so that the handleability may be inferior.

International Release 2010/021202 Japanese Unexamined Patent Publication No. 2005-243561 Patent No. 5767923 Japanese Unexamined Patent Publication No. 2013-73689

An object of the present invention is to provide a conductive paste having high printability and excellent surface smoothness, thread breakage and handleability.

The present invention is a conductive paste used for an electrode 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. The polyvinyl acetal resin having an average degree of polymerization of 800 to 1600 is an acetal product of two or more kinds of mixed polyvinyl alcohol resins having different degrees of polymerization, and has the highest degree of polymerization among the mixed polyvinyl alcohol resins. The polyvinyl alcohol resin is a conductive paste having at least one selected from the structural unit represented by the following formula (1-1) and the structural unit represented by the following formula (1-2).

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。なお、炭素数０のアルキレン基とは、Ｒ^１、Ｒ^２又はＲ^６の両端の炭素が直接結合しているものを表す。
以下、本発明を詳述する。

In the above formula (1-1), R ¹ and R ² are independent of each other, and an alkylene group having 0 to 10 carbon atoms and X ¹ and X ² are independent of each other and 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 independent of each other, and hydrogen atom or 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 alkylene group having 0 carbon atoms means that the carbons at both ends of ^{R 1} , R ² or R ^{6 are directly bonded.}
Hereinafter, the present invention will be described in detail.

As a result of diligent studies, the present inventors have used a polyvinyl acetal resin containing a carboxylic acid-modified polyvinyl acetal resin and consisting of an acetal product of a mixed polyvinyl alcohol resin having a specific structure as a binder resin for the conductive paste. It has been found that a conductive paste having high printability and excellent surface smoothness, thread breakage and handleability can be obtained by setting the average degree of polymerization within a predetermined range.
Further, they have found that the above-mentioned effects can be obtained even when the degree of polymerization of the binder resin is high or low, and have completed the present invention.

The conductive paste of the present invention contains a polyvinyl acetal resin.
The polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin. By containing such a carboxylic acid-modified polyvinyl acetal resin, the interaction with the conductive powder can be enhanced, and a conductive paste having excellent dispersibility can be obtained.
In the present 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). , Means 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.

The polyvinyl acetal resin is an acetal product of two or more kinds 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 (hereinafter, also referred to as the highest degree of polymerization polyvinyl alcohol resin) is the structural unit represented by the above formula (1-1) and the above formula. It has at least one selected from the structural units represented by (1-2).
The polyvinyl alcohol resin having the highest degree of polymerization 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), whereby the polyvinyl acetal The interaction between the resin and the organic solvent, and the polyvinyl acetal resin and the conductive powder can be effectively strengthened. As a result, even if the polyvinyl acetal resin has a high degree of polymerization, it effectively exhibits appropriate viscosity and viscosity characteristics suitable for handleability without deteriorating the thread breakability of the conductive paste or adversely affecting the printability. Can be granted.

The polyvinyl alcohol resin having the highest degree of polymerization preferably has a structural unit represented by the above formula (1-1). When it has a structural unit represented by the above formula (1-1), the two carboxyl groups in the structural unit are present at positions sandwiching the carbon of the main chain, so that the obtained conductive paste is between the conductive powder and the conductive powder. It has an appropriate interaction and can also improve storage stability.

In the above formula (1-1), R ¹ and R ² are independent and represent an alkylene group having 0 to 10 carbon atoms, and X ¹ and X ² are independent and are hydrogen atoms, metal atoms or methyl groups, respectively. Represents.

In the above formula (1-1), if ^{the carbon number of the alkylene group represented by R 1} and R ² exceeds 10, the carboxyl group causes aggregation, so that it becomes difficult to dissolve in a low-polarity solvent. The preferable lower limit of the number of carbon atoms 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.

The above R ¹ and R ² may be the same or different, but different ones are preferable. Further, it is preferable that at least one of them is 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, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group and a decamethylene group. A branched alkylene group such as a linear alkylene group, a methylmethylene group, a methylethylene group, a 1-methylpentylene group and a 1,4-dimethylbutylene group, and a cyclic alkylene group such as a cyclopropylene group, a cyclobutylene group and a cyclohexylene group. The group etc. can be mentioned. Of these, linear alkyl groups such as an alkylene group having 0 carbon atoms, a methylene group, an ethylene group, an n-propylene group and an n-butylene group are 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, a potassium atom and the like. Of these, a sodium atom is preferable.

The structural unit represented by the above formula (1-1) is preferably derived from an α-dicarboxymonomer. Examples of the α-dicarboxymonomer include dicarboxylic acids having a radically polymerizable unsaturated double bond such as methylenemalonic acid, itaconic acid, 2-methyleneglutaric acid, 2-methyleneadipic acid, and 2-methylenesebacic acid, and dicarboxylic acids thereof. Examples thereof include metal salts or methyl esters thereof. Of these, itaconic acid is preferably used.
In the present specification, the α-dicarboxymonomer represents a monomer having two carboxyl groups at the α-carbon.

In the above formula (1-2), R ³ , R ⁴ and R ⁵ are independent of each other and represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ⁶ is an alkylene group having 0 to 10 carbon atoms. Represented, 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 number of carbon atoms of the alkyl group exceeds 10, the raw material is synthesized due to steric hindrance. Polymerization of time is less likely to occur. The preferred lower limit of the number of carbon atoms of the alkyl group represented by R ³ , R ⁴ and R ⁵ is 1, the preferred 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. Further, it is preferable that ^{R 3} , R ⁴ and R ^{5 are hydrogen atoms.}

Examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group, an n-butyl group, an n-pentyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and 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 groups, cyclopropyl groups, cyclopropylmethyl groups, cyclobutyl groups, cyclopentyl groups, cycloalkyl groups such as cyclohexyl groups and the like. Of these, linear 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), if ^{the carbon number of the alkylene group represented by R 6} exceeds 10, the carboxyl group causes aggregation, so that the resin is difficult to dissolve in the low-polarity solvent. The preferable lower limit of the number of carbon atoms 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 those similar to those exemplified in R 1} and R ² in the above formula (1-1), and among them, an alkylene group having 0 carbon atoms. Linear alkylene groups such as methylene group, ethylene group, n-propylene group and n-butylene group are preferable, alkylene group having 0 carbon number, methylene group and ethylene group are more preferable, and alkylene group having 0 carbon number is further preferable. ..

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

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

The highest degree of polymerization polyvinyl alcohol resin preferably has a degree of polymerization of 900 to 2500. Within the above range, the viscosity of the conductive paste can be effectively increased.

The content of the polyvinyl alcohol resin having the highest degree of polymerization in the mixed polyvinyl alcohol resin is not particularly limited as long as the amount of carboxyl groups of the polyvinyl acetal resin described later can be achieved, but the preferable lower limit is 10% by weight and the preferable upper limit is 90. The lower limit is 20% by weight, the more preferable upper limit is 80% by weight, the particularly preferable lower limit is 30% by weight, and the particularly preferable upper limit is 70% by weight.

The mixed polyvinyl alcohol resin contains a carboxylic acid-unmodified polyvinyl alcohol resin having neither a structural unit represented by the formula (1-1) nor a structural unit represented by the formula (1-2). Is preferable. By containing such a carboxylic acid-unmodified polyvinyl alcohol resin, the viscosity ratio of the obtained conductive paste can be made excellent in printability.
The carboxylic acid-unmodified polyvinyl alcohol resin preferably has the lowest degree of polymerization.

When the carboxylic acid-unmodified polyvinyl alcohol resin is contained, the difference in the degree of polymerization between the highest degree of polymerization polyvinyl alcohol resin and the carboxylic acid-unmodified polyvinyl alcohol resin is preferably 600 or more. When the difference in the degree of polymerization is 600 or more, the degree of polymerization of the carboxylic acid-unmodified polyvinyl alcohol resin can be reduced. As a result, it is possible to prevent the smoothness and the thread breakability from being affected. The difference in the degree of polymerization is more preferably 800 or more, and further preferably 1000 or more.
When two or more kinds of the carboxylic acid-unmodified polyvinyl alcohol resin are contained, the difference in the degree of polymerization is calculated by using the carboxylic acid-unmodified polyvinyl alcohol resin having the lowest degree of polymerization.

The carboxylic acid-unmodified polyvinyl alcohol resin preferably has a degree of polymerization of 200 to 800. By setting the content within the above range, the viscosity ratio can be made excellent in printability without adversely affecting the printability.

The content of the carboxylic acid-unmodified polyvinyl alcohol resin in the mixed polyvinyl alcohol resin is not particularly limited as long as the amount of carboxyl groups of the polyvinyl acetal resin described later can be achieved, but the preferable lower limit is 10% by weight, and the preferable upper limit is It is 90% by weight, the more preferable lower limit is 20% by weight, the more preferable upper limit is 80% by weight, the particularly preferable lower limit is 30% by weight, and the particularly preferable upper limit is 70% by weight.

The composition of the mixed polyvinyl alcohol resin is not particularly limited as long as it contains the highest degree of polymerization polyvinyl alcohol resin, but contains the above maximum degree of polymerization polyvinyl alcohol resin and the above carboxylic acid unmodified polyvinyl alcohol resin. It is preferable that it is one.
When the carboxylic acid-unmodified polyvinyl alcohol resin has the lowest degree of polymerization, a polyvinyl alcohol resin having a degree of polymerization between the highest degree of polymerization polyvinyl alcohol resin and the carboxylic acid-unmodified polyvinyl alcohol resin. (Hereinafter, also referred to as another polyvinyl alcohol resin) may be contained.

The other polyvinyl alcohol resin is not particularly limited as long as it has a degree of polymerization between the highest degree of polymerization polyvinyl alcohol resin and the carboxylic acid-unmodified polyvinyl alcohol resin, and is composed of two or more different resins. It may be one.
The other polyvinyl alcohol resin is selected from the structural unit represented by the formula (1-1) and the structural unit represented by the formula (1-2), similarly to the polyvinyl alcohol resin having the highest degree of polymerization. It may or may not have at least one of these.

When the other polyvinyl alcohol resin is an unmodified polyvinyl alcohol resin, the degree of polymerization is preferably 800 or less. When another polyvinyl alcohol resin such as an unmodified polyvinyl alcohol resin is used, the thread breakability and printability deteriorate as the degree of polymerization increases, but the degree of polymerization of the other polyvinyl alcohol resin is 800 or less. , The deterioration can be minimized.

As for the other polyvinyl alcohol resin, the difference in the degree of polymerization between the highest degree of polymerization polyvinyl alcohol resin and the other polyvinyl alcohol resin is preferably 600 or more. When the difference in the degree of polymerization is 600 or more, the degree of polymerization of the other polyvinyl alcohol resin can be reduced. As a result, it is possible to prevent the smoothness and the thread breakability from being affected. The difference in the degree of polymerization is more preferably 800 or more, and further preferably 1000 or more.

The content of the other polyvinyl alcohol resin in the mixed polyvinyl alcohol resin is not particularly limited as long as the amount of carboxyl groups of the polyvinyl acetal resin described later can be achieved, but the preferable lower limit is 5% by weight and the preferable upper limit is 95% by weight. The more preferable lower limit is 10% by weight, the more preferable upper limit is 90% by weight, the particularly preferable lower limit is 15% by weight, and the particularly preferable upper limit is 85% by weight.

The method for synthesizing the carboxylic acid-modified polyvinyl acetal resin is not particularly limited. For example, when the highest degree of polymerization polyvinyl alcohol resin has a structural unit represented by the above formula (1-1), the above formula is used. A polyvinyl alcohol resin obtained by saponifying polyvinyl acetate obtained by copolymerizing α-dicarboxymonomer, which is a constituent unit represented by (1-1), and vinyl acetate, and the second or the second thereof. Examples thereof include a method in which a polyvinyl alcohol resin having the following degree of polymerization is mixed and acetalized by a conventionally known method.

When the polyvinyl alcohol resin having the highest degree of polymerization has a structural unit represented by the above formula (1-2), the monocarboxymonomer which is the structural unit represented by the above formula (1-2) and acetic acid A polyvinyl alcohol resin obtained by saponifying polyvinyl acetate obtained by copolymerizing with vinyl and a polyvinyl alcohol resin having a second or lower degree of polymerization are mixed and acetalized by a conventionally known method. There is a way to do it.

Further, there is also a method of acetalizing a carboxylic acid-modified polyvinyl alcohol resin obtained by reacting a polyvinyl alcohol resin having the highest degree of polymerization with a compound having a carboxyl group such as mercaptopropionic acid and post-modifying it by a conventionally known method. Can be mentioned.

Further, after the above-mentioned highest degree of polymerization polyvinyl alcohol resin, carboxylic acid-unmodified polyvinyl alcohol resin, and other polyvinyl alcohol resin are acetalized by a conventionally known method, the average degree of polymerization is within a predetermined range. , A method of mixing the acetal products of the respective polyvinyl alcohol resins may be used.

The acetalization reaction is not particularly limited, and can be carried out by a conventionally known method. For example, a method of adding various aldehydes 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 can be mentioned.
The above aldehyde is not particularly limited, and for example, formaldehyde, acetaldehyde, propionaldehyde, butylaldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glioxal, glutaaldehyde, 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 in combination with acetaldehyde and butyraldehyde.

The polyvinyl acetal resin used in the present invention has an average degree of polymerization of 800 at the lower limit and 1600 at the upper limit. By setting the average degree of polymerization to 800 or more, it is possible to increase the viscosity and improve the handleability. By setting the value to 1600 or less, it is possible to prevent stringing and improve printability. In addition, surface smoothness is improved. The preferable lower limit of the average degree of polymerization of the polyvinyl acetal resin is 850, the preferable upper limit is 1500, the more preferable lower limit is 900, and the more preferable upper limit is 1400.

In the present specification, the average degree of polymerization of the polyvinyl acetal resin is obtained from the average degree of polymerization of polyvinyl alcohol as a raw material.
Further, in the present specification, the average degree of polymerization of the polyvinyl acetal resin means the apparent average degree of polymerization of the entire polyvinyl acetal resin. That is, for example, when the polyvinyl acetal resin contains a plurality of resins having different average degrees of polymerization, the average degree of polymerization of the polyvinyl acetal resin can be obtained by multiplying the average degree of polymerization of each resin by the content ratio of the resin. It is obtained by summing each value.

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 effect of having the carboxyl group in the polyvinyl acetal resin can be obtained, the printability of the conductive paste is improved, the surface smoothness is improved, and the inorganic powder is formed. It can be prevented from settling and deteriorating stability during storage. By setting the amount of the carboxyl group to 1 mol% or less, the solubility of the polyvinyl acetal resin in an organic solvent is improved, and the interaction between the carboxyl group and the conductive powder becomes appropriate. Therefore, a conductive paste is prepared. It becomes easy and can prevent gelation and deterioration of stability. The preferable lower limit of the amount of carboxyl groups of the polyvinyl acetal resin is 0.07 mol%, the preferable upper limit is 0.9 mol%, the more preferable lower limit is 0.1 mol%, and the more preferable upper limit is 0.8 mol%. ..

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

Further, in the present specification, the carboxyl group amount of the polyvinyl acetal resin means the apparent carboxyl group amount of the entire polyvinyl acetal resin. That is, for example, when a polyvinyl acetal resin contains a plurality of resins having different carboxyl group amounts, the carboxyl group amount of the polyvinyl acetal resin can be 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 amount of carboxyl groups in the polyvinyl acetal resin is calculated by the following formula (3).
A = B × (C / D) (3)
In the above formula (3), A represents the amount of carboxyl groups (mol%) of the polyvinyl acetal resin, B represents the amount of carboxyl groups (mol%) of the carboxylic acid-modified polyvinyl acetal resin, and C represents the amount of carboxyl groups (mol%) of the carboxylic acid-modified polyvinyl acetal resin. Represents the weight of, and 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 above-mentioned polyvinyl acetal resin can be achieved, but the preferable lower limit is 0.03. Mol%, preferably the upper limit is 4 mol%.

When the polyvinyl acetal resin contains an acetal acetal group, the upper limit of the amount of the acetal acetal group is preferably 25 mol%. When the amount of the acetoacetal group is 25 mol% or less, the solubility of the polyvinyl acetal resin in a low-polarity organic solvent is improved, and the production of a conductive paste becomes easy. The preferable upper limit of the acetal acetal group amount of the polyvinyl acetal resin is 22 mol%, and the more preferable upper limit is 20 mol%.
The acetal acetal group is an acetal group in the case where ^{R 7} is a methyl group among the acetal groups contained in the structural unit having an acetal group represented by the above formula (2-3). Further, in the present specification, the acetal acetal group amount of the polyvinyl acetal resin means the apparent acetal acetal group amount of the entire polyvinyl acetal resin.

When the polyvinyl acetal resin contains a butyral group, the preferable lower limit of the butyral group amount is 40 mol%, and the preferable upper limit is 80 mol%. When the butyral group amount is 40 mol% or more, the residual hydroxyl group amount does not become too large, and the solubility of the polyvinyl acetal resin in a low polar solvent can be improved. When it is 80 mol% or less, the amount of residual hydroxyl groups becomes high, the viscosity of the obtained conductive paste does not become too low, and the 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%.
The butyral group is an acetal group in the case where ^{R 7} is a propyl group among the acetal groups contained in the structural unit having an acetal group represented by the above formula (2-3). Further, in the present specification, the butyral group amount of the polyvinyl acetal resin means the apparent butyral group amount of the entire polyvinyl acetal resin.

In the polyvinyl acetal resin, the preferable lower limit of the amount of hydroxyl groups is 16 mol%, and the preferable upper limit is 25 mol%. When the amount of hydroxyl groups is 16 mol% or more, 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. When the amount of the hydroxyl groups is 25 mol% or less, the solubility in the low-polarity organic solvent used in the present invention is improved. The preferable lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin is 17 mol%, and the preferable upper limit is 23 mol%. Further, in the present specification, the hydroxyl group amount of the polyvinyl acetal resin means the apparent hydroxyl group amount of the entire polyvinyl acetal resin.

In the polyvinyl acetal resin, the lower limit of the amount of acetyl groups is preferably 0.1 mol% and the upper limit is preferably 5 mol%. When the amount of the acetyl group is 0.1 mol% or more, the acetalization reaction is facilitated, and when it is 5 mol% or less, the solubility in the low-polarity organic solvent used in the present invention can be enhanced. can. The preferable lower limit of the amount of acetyl groups in the polyvinyl acetal resin is 0.2 mol%, and the preferable upper limit is 4 mol%. Further, in the present specification, the acetyl group amount of the polyvinyl acetal resin means the apparent acetyl group amount of the entire polyvinyl acetal resin.

In the polyvinyl acetal resin, the total amount of the above-mentioned carboxyl group amount, acetalization degree (total of acetoacetal group amount and butyral group amount), hydroxyl group amount and acetyl group amount is preferably 99.1 mol% or more.
When the total amount is 99.1 mol% or more, the content of other constituent units is reduced, and the effects of the present invention can be more preferably exhibited.

The conductive paste of the present invention may contain other resins such as acrylic resin and ethyl cellulose in addition to the above-mentioned 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 has excellent compatibility with other resins as compared with ordinary polyvinyl acetal resins.

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

The average particle size of the nickel powder is preferably 50 to 300 nm, and the shape is preferably substantially spherical. If the average particle size is less than 50 nm, the specific surface area of the nickel powder becomes large, and the agglomerated nickel powder may not be able to be dispersed. If the average particle size exceeds 300 nm, the surface after printing may not be smooth. The substantially spherical shape includes particles having a shape close to a sphere as well as a true sphere.

The blending amount of the conductive powder is not particularly limited, but the preferable lower limit with respect to 100 parts by weight of the polyvinyl acetal resin is 100 parts by weight, and the preferable upper limit is 10,000 parts by weight. If the blending amount of the conductive powder is less than 100 parts by weight, the density of the conductive powder in the conductive paste may be low, and the conductivity may be lowered. 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 decrease, and the printability may decrease. Regarding the blending amount of the conductive powder, 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 further contains a ceramic powder in addition to the above conductive powder. By containing the ceramic powder, it becomes easy to match the shrinkage behavior of the conductive powder at the time of firing with the ceramic green sheet.
The ceramic powder is not particularly limited, but barium titanate used for the green sheet is preferable. The particle size of the ceramic powder is not particularly limited, but it is preferably smaller than the particle size of the conductive powder, and specifically, it is preferably 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 a conductive paste can be used, but in order to prevent a sheet attack phenomenon in particular, the polyvinyl butyral resin contained in the ceramic green sheet is not swollen or dissolved, and is non-phase. It is a low-polarity organic solvent that dissolves, and its solubility parameter is preferably 8.0 to 11.0 (cal / cm ³ ) ^0.5 . As the solubility parameter, the one calculated by the Fedors method is used.
Examples of the organic solvent include terpineol (turpineol) derivatives such as tarpinyl acetate, isovonyl acetate, dihydroterpineol acetate, dihydroterpineol, dihydroterpinyl methyl ether, and tarpinyl methyl ether, and hydrocarbons such as mineral spirit. Examples include solvents, 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 blending amount of the organic solvent is not particularly limited, but the preferable lower limit with respect to 100 parts by weight of the polyvinyl acetal resin is 100 parts by weight, and the preferable upper limit is 10,000 parts by weight. If the blending amount of the organic solvent is less than 100 parts by weight, the viscosity of the conductive paste may increase and the printability may decrease. If the blending amount of the organic solvent exceeds 10,000 parts by weight, the performance of the polyvinyl acetal resin may not be sufficiently exhibited in the conductive paste. Regarding the blending amount of the organic solvent, 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 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, and is, for example, a phthalate diester such as bis (2-ethylhexyl) phthalate, dioctyl phthalate, or dibutyl phthalate, an adiponic acid diester such as dioctyl adipate, or an alkylene glycol diester such as triethylene glycol 2-ethylhexyl. And so on.

The dispersant is not particularly limited, but for example, fatty acids, aliphatic amines, alkanolamides, and phosphoric acid esters are suitable. Further, a silane coupling agent or the like may be blended.
The fatty acid is not particularly limited, and for example, saturated fatty acids such as behenic acid, stearic acid, palmitic acid, myristic acid, lauric acid, capric acid, capric acid, and coconut fatty acid; oleic acid, linoleic acid, linolenic acid, and sorbic acid. , Unsaturated fatty acids such as beef fatty acid and hardened sardine fatty acid. Of these, lauric acid, stearic acid, oleic acid and the like are preferable.
The aliphatic amine is not particularly limited, and for example, lauryl amine, myristyl amine, cetyl amine, stearyl amine, oleyl amine, alkyl (palm) amine, alkyl (hardened beef tallow) amine, alkyl (beef tallow) amine, and alkyl (soybean) amine. And so on.
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 phosphoric acid ester is not particularly limited, and examples thereof include polyoxyethylene alkyl ether phosphoric acid ester and polyoxyethylene alkyl allyl ether phosphoric acid ester.

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

Since the viscosity of the conductive paste of the present invention differs depending on each printing process, it may be adjusted as appropriate, but it is preferable that the viscosity η60 at a ^{share rate of 60s -1 is 0.1 to 10 Pa · s.}
In particular, when used for screen printing, η60 is preferably 1.0 to 10.0 Pa · s, and when used for gravure printing, η60 is preferably 0.1 to 1.0 Pa · s. ..

In the conductive paste of the present invention, ^{the ratio of the viscosity η60 measured under the condition of share rate 60s -1} to the viscosity η600 measured under the condition of share rate 600s ^-1 (η60 / η600, hereinafter also referred to as TI value) is 2. It is preferably 0.0 or more and less than 4.5. If the above η60 / η600 is 2.0 or more, the viscosity at the time of coating is too low to spread evenly, or the static viscosity of the conductive paste contained in the plate pattern is too high to be contained in the pattern. It is possible to prevent problems such as not spreading evenly. When the η60 / η600 is less than 4.5, it is possible to prevent the viscosity at the time of coating from being too high and the coating not being spread uniformly. The preferred lower limit is 2.3 and the preferred upper limit is 3.5.
Η60 / η600 is one of the indexes showing thixotropy.
In order to ensure handleability, a certain high viscosity is required so that it can be easily spread or recovered during coating or cleaning. On the other hand, the conductive paste contained in the pattern of the plate needs to be uniformly filled in the pattern without being biased, and the viscosity must be sufficiently low in order to print uniformly. That is, a large change in viscosity is required before and after the process. Such a property is called thixotropy, and by setting η60 / η600 within the above range, a conductive paste having excellent thixotropy can be obtained.

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

The conductive paste of the present invention is applied onto a ceramic green sheet by a printing process such as screen printing, die coating, gravure offset, etc., and a plurality of sheets are stacked and heat-bonded to prepare a laminate, which is then degreased and fired. A multilayer ceramic capacitor can be obtained by forming a ceramic sintered body and further forming an external electrode on the end face of the ceramic sintered body. Such a monolithic ceramic capacitor is also one of the present inventions.

The method for printing the conductive paste of the present invention is not particularly limited, but it can be performed by a printing process such as screen printing, die coating, or gravure printing as described above.

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. , The multilayer ceramic capacitor can be thinned, and excellent conductivity can be obtained.

An object of the present invention is to provide a conductive paste having high printability and excellent surface smoothness, thread breakage and handleability.

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

(Example 1)
(Preparation of polyvinyl acetal resin)
Carboxylic acid-modified polyvinyl alcohol resin A (average degree of polymerization 2500, carboxyl group amount 1.0 mol%, acetyl group amount 1.5 mol%, structural unit represented by the general formula (4-1) (X is sodium ion) 30 g and 70 g of unmodified polyvinyl alcohol resin J (average degree of polymerization 200, acetyl group amount 2.2 mol%) are added to 1000 g of pure water and stirred at a temperature of 90 ° C. for about 2 hours to dissolve. rice field. The solution was cooled to 40 ° C., and 90 g of hydrochloric acid (concentration 35% by weight), 20 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, the polyvinyl acetal resin (average polymerization degree 890, acetyl group amount 2.0 mol%, residual hydroxyl group amount 20.7 mol%, acetoacetal group amount 23.5) was subjected to neutralization, washing with water and drying. A white powder having a molar%, a butyral group amount of 53.5 mol%, and a carboxyl group amount of 0.3 mol%) was obtained.

(Preparation of conductive paste)
A resin solution was obtained by dissolving 10 parts by weight of the obtained polyvinyl acetal resin in 90 parts by weight of dihydroterpineol acetate. 180 parts by weight of nickel powder, 20 parts by weight of barium titanate, and 50 parts by weight of dihydroterpineol acetate were mixed as a conductive powder, and then the obtained resin solution was mixed and dispersed by three rolls. A conductive paste was obtained.

(Example 2)
In Example 1, when the acetalization reaction is carried out by using 50 g of the carboxylic acid-modified polyvinyl alcohol resin A and 50 g of the unmodified polyvinyl alcohol resin J instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J. The polyvinyl acetal resin (average polymerization degree 1350, acetyl group amount 1.9 mol%, residual hydroxyl group amount 22.0 mol%,) was the same as in Example 1 except that the aldehyde used was changed to 80 g of n-butyl aldehyde. A white powder having a butyral group amount of 75.6 mol% and a 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.

(Example 3)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, the carboxylic acid-modified polyvinyl alcohol resin B (average polymerization degree 900, carboxyl group amount 1.0 mol%, acetyl group amount 2) Same as in Example 1 except that 90 g of .5 mol%, which has a structural unit (X is a sodium ion) represented by the general formula (4-1), and 10 g of an unmodified polyvinyl alcohol resin J were used. , Polyvinyl acetal resin (average degree of polymerization 830, acetyl group amount 2.5 mol%, residual hydroxyl group amount 20.8 mol%, acetoacetal group amount 23.2 mol%, butyral group amount 52.6 mol%, carboxyl group amount 0.9 mol%) of white powder was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 4)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 6 g of the carboxylic acid-modified polyvinyl alcohol resin A and the unmodified polyvinyl alcohol resin K (average degree of polymerization 800, acetyl group amount 2. Polyvinyl acetal resin (average degree of polymerization 902, acetyl group amount 2.0 mol%, residual hydroxyl group amount 21.2 mol%, acet acetal group) in the same manner as in Example 1 except that 94 g (0 mol%) was used. A white powder having an amount of 23.5 mol%, a butyral group amount of 53.2 mol%, and a carboxyl group amount of 0.06 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 5)
In Example 1, the same as in Example 1 except that 30 g of carboxylic acid-modified polyvinyl alcohol resin A and 70 g of unmodified polyvinyl alcohol resin K were used instead of 30 g of carboxylic acid-modified polyvinyl alcohol resin A and 70 g of unmodified polyvinyl alcohol resin J. Polyvinyl acetal resin (average degree of polymerization 1310, acetyl group amount 1.9 mol%, residual hydroxyl group amount 21.5 mol%, acetal acetal group amount 24.0 mol%, butyral group amount 52.3 mol%, carboxyl A white powder having a base weight 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.

(Example 6)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 10 g of the carboxylic acid-modified polyvinyl alcohol resin B and 90 g of the unmodified polyvinyl alcohol resin K are used to carry out the acetalization reaction. Polyvinyl acetal resin (average polymerization degree 810, acetyl group amount 2.1 mol%, residual hydroxyl group amount 22.2 mol%, butyral) in the same manner as in Example 1 except that the aldehyde was changed to 80 g of n-butyl aldehyde. A white powder having a group amount of 75.6 mol% and a carboxyl group amount of 0.1 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 7)
In Example 1, the same as in Example 1 except that 90 g of carboxylic acid-modified polyvinyl alcohol resin B and 10 g of unmodified polyvinyl alcohol resin K were used instead of 30 g of carboxylic acid-modified polyvinyl alcohol resin A and 70 g of unmodified polyvinyl alcohol resin J. Polyvinyl acetal resin (average degree of polymerization 890, acetyl group amount 2.5 mol%, residual hydroxyl group amount 22.0 mol%, acet acetal group amount 23.8 mol%, butyral group amount 50.8 mol%, carboxyl A white powder having a base content of 0.9 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 8)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, the carboxylic acid-modified polyvinyl alcohol resin C (average polymerization degree 1400, carboxyl group amount 1.0 mol%, acetyl group amount 2) In the same manner as in Example 1, except that 10 g of 0.0 mol% having a structural unit (X is a hydrogen atom) represented by the general formula (4-1) and 90 g of unmodified polyvinyl alcohol resin K were used. Polyvinyl acetal resin (average degree of polymerization 860, acetyl group amount 2.0 mol%, residual hydroxyl group amount 20.3 mol%, acetoacetal group amount 24.0 mol%, butyral group amount 53.6 mol%, carboxyl group amount 0 .1 mol%) of white powder was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 9)
In Example 1, the same as in Example 1 except that 90 g of carboxylic acid-modified polyvinyl alcohol resin C and 10 g of unmodified polyvinyl alcohol resin K were used instead of 30 g of carboxylic acid-modified polyvinyl alcohol resin A and 70 g of unmodified polyvinyl alcohol resin J. Polyvinyl acetal resin (average degree of polymerization 1340, acetyl group amount 2.0 mol%, residual hydroxyl group amount 21.0 mol%, acet acetal group amount 23.5 mol%, butyral group amount 52.6 mol%, carboxyl A white powder having a base content of 0.9 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 10)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, the carboxylic acid-modified polyvinyl alcohol resin D (average degree of polymerization 1700, carboxyl group amount 1.0 mol%, acetyl group amount 1). .8 mol%, 30 g of structural unit (X is sodium ion) represented by the general formula (4-1) and unmodified polyvinyl alcohol resin L (average degree of polymerization 500, acetyl group amount 2.0 mol%) Polyvinyl acetal resin (average degree of polymerization 860, acetyl group amount 1.9 mol%, residual hydroxyl group amount 21.5 mol%, acet acetal group amount 22.8 mol) in the same manner as in Example 1 except that 70 g was used. %, Butyral group amount 53.5 mol%, carboxyl group amount 0.3 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 11)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 50 g of the carboxylic acid-modified polyvinyl alcohol resin D and 50 g of the unmodified polyvinyl alcohol resin L were used, and the aldehyde used in the reaction was 15 g of acetaldehyde. Polyvinyl acetal resin (average polymerization degree 1100, acetyl group amount 1.9 mol%, residual hydroxyl group amount 20.8 mol%, acetacetal group amount) in the same manner as in Example 1 except that the n-butyl aldehyde was changed to 70 g. A white powder having 13.8 mol%, a butyral group amount of 63.0 mol%, and a 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.

(Example 12)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 90 g of the carboxylic acid-modified polyvinyl alcohol resin D and 10 g of the unmodified polyvinyl alcohol resin L were used, and the aldehyde used in the reaction was 5 g of acetaldehyde. Polyvinyl acetal resin (average polymerization degree 1580, acetyl group amount 1.8 mol%, residual hydroxyl group amount 22.0 mol%, acetacetal group amount) in the same manner as in Example 1 except that the n-butyl aldehyde was changed to 75 g. A white powder having 4.5 mol%, a butyral group amount of 70.8 mol%, and a carboxyl group amount of 0.9 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 13)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, the carboxylic acid-modified polyvinyl alcohol resin H (average polymerization degree 1700, carboxyl group amount 1.0 mol%, acetyl group 4. Polyvinyl acetal in the same manner as in Example 1 except that 0 mol%, 30 g of a structural unit represented by the general formula (4-2) (where X is a sodium ion) and 70 g of an unmodified polyvinyl alcohol resin L were used. Resin (average degree of polymerization 860, acetyl group amount 2.6 mol%, residual hydroxyl group amount 22.1 mol%, acetal acetal group amount 23.0 mol%, butyral group amount 52.0 mol%, carboxyl group amount 0.3 Mol%) of white powder was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 14)
In Example 1, the same as in Example 1 except that carboxylic acid-modified polyvinyl alcohol resin H70 g and unmodified polyvinyl alcohol resin L30 g were used instead of carboxylic acid-modified polyvinyl alcohol resin A 30 g and unmodified polyvinyl alcohol resin J 70 g. Polyvinyl acetal resin (average degree of polymerization 1340, acetyl group amount 3.4 mol%, residual hydroxyl group amount 21.8 mol%, acetal acetal group amount 22.5 mol%, butyral group amount 51.6 mol%, carboxyl group An amount of 0.7 mol%) of white powder was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 15)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, the carboxylic acid-modified polyvinyl alcohol resin E (average polymerization degree 1700, carboxyl group amount 0.5 mol%, acetyl group amount 1) Using 30 g of .5 mol%, a structural unit represented by the general formula (4-1) (where X is a sodium ion) and 70 g of unmodified polyvinyl alcohol resin L, the aldehyde used in the reaction was 15 g of acetaldehyde and n-. Polyvinyl acetal resin (average polymerization degree 860, acetyl group amount 1.9 mol%, residual hydroxyl group amount 20.6 mol%, acetacetal group amount 13. A white powder having 4 mol%, a butyral group amount of 64.0 mol%, and a carboxyl group amount of 0.2 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 16)
In Example 1, the same as in Example 1 except that 90 g of carboxylic acid-modified polyvinyl alcohol resin E and 10 g of unmodified polyvinyl alcohol resin L were used instead of 30 g of carboxylic acid-modified polyvinyl alcohol resin A and 70 g of unmodified polyvinyl alcohol resin J. Polyvinyl acetal resin (average polymerization degree 1580, acetyl group amount 1.6 mol%, residual hydroxyl group amount 22.4 mol%, acetal acetal group amount 22.4 mol%, butyral group amount 53.2 mol%, carboxyl A white powder having a base content of 0.4 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Example 17)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and the carboxylic acid-modified polyvinyl alcohol resin F (average polymerization degree 800, carboxyl group amount 0). Except for using 30 g of .5 mol%, 2.0 mol% of acetyl group, a structural unit represented by the general formula (4-1) (where X is a hydrogen atom), and 40 g of an unmodified polyvinyl alcohol resin J. In the same manner as in Example 1, a polyvinyl acetal resin (average polymerization degree 1070, acetyl group amount 1.9 mol%, residual hydroxyl group amount 21.3 mol%, acetoacetal group amount 21.7 mol%, butyral group amount A white powder of 54.6 mol% and a 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.

(Example 18)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 30 g of the carboxylic acid-modified polyvinyl alcohol resin A, 30 g of the unmodified polyvinyl alcohol resin K, and 40 g of the unmodified polyvinyl alcohol resin J are used. Polyvinyl acetal resin (average degree of polymerization 1070, acetyl group amount 1.9 mol%, residual hydroxyl group amount 22.9 mol%, acetoacetal group amount 23.0 mol%, butyral) in the same manner as in Example 1. A white powder having a base content of 51.9 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.

(Example 19)
In Example 1, 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J were replaced with 50 g of the carboxylic acid-modified polyvinyl alcohol resin C and 50 g of the unmodified polyvinyl alcohol resin J. Similarly, polyvinyl acetal resin (average degree of polymerization 800, acetyl group amount 2.1 mol%, residual hydroxyl group amount 23.3 mol%, acetal acetal group amount 23.3 mol%, butyral group amount 50.8 mol%, A white powder having a carboxyl group content 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, when the acetalization reaction is carried out by using 50 g of the carboxylic acid-modified polyvinyl alcohol resin E and 50 g of the unmodified polyvinyl alcohol resin K instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J. The polyvinyl acetal resin (average polymerization degree 1250, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.1 mol%,) was the same as in Example 1 except that the aldehyde used was changed to 80 g of n-butyl aldehyde. A white powder having a butyral group amount of 76.9 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.

(Example 21)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 50 g of the carboxylic acid-modified polyvinyl alcohol resin H and 50 g of the unmodified polyvinyl alcohol resin K were used, and the aldehyde used in the reaction was acetaldehyde. Polyvinyl acetal resin (average polymerization degree 1250, acetyl group amount 1.8 mol%, residual hydroxyl group amount 21.4 mol%, acetacetal) in the same manner as in Example 1 except that it was changed to 15 g and 70 g of n-butyl aldehyde. A white powder having a group amount of 12.8 mol%, a butyral group amount of 63.5 mol%, and a 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.

(Comparative Example 1)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 50 g of the unmodified polyvinyl alcohol resin M (average polymerization degree 1700, acetyl group amount 1.5 mol%) and carboxylic acid. It has a modified polyvinyl alcohol resin G (average degree of polymerization 500, carboxyl group amount 1.0 mol%, acetyl group amount 2.5 mol%, structural unit represented by the general formula (4-1) (X is sodium ion). ) 50 g, and the same as in Example 1, polyvinyl acetal resin (average polymerization degree 1100, acetyl group amount 2.0 mol%, residual hydroxyl group amount 21.5 mol%, acet acetal group amount 22. A white powder having 9 mol%, a butyral group amount of 53.1 mol%, and a 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.

(Comparative Example 2)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 50 g of the carboxylic acid-modified polyvinyl alcohol resin F and 50 g of the unmodified polyvinyl alcohol resin K were used, and the aldehyde used in the reaction was 5 g of acetaldehyde. Polyvinyl acetal resin (average polymerization degree 800, acetyl group amount 2.0 mol%, residual hydroxyl group amount 22.0 mol%, acet acetal group) in the same manner as in Example 1 except that it was changed to 75 g of n-butyl aldehyde. A white powder having an amount of 13.5 mol%, a butyral group amount of 62.3 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.

(Comparative Example 3)
Example 1 except that carboxylic acid-modified polyvinyl alcohol resin A 70 g and carboxylic acid-modified polyvinyl alcohol resin F 30 g were used instead of carboxylic acid-modified polyvinyl alcohol resin A 30 g and unmodified polyvinyl alcohol resin J 70 g. In the same manner as above, the polyvinyl acetal resin (average degree of polymerization 1990, acetyl group amount 1.7 mol%, residual hydroxyl group amount 20.7 mol%, acetoacetal group amount 23.8 mol%, butyral group amount 53.0 mol%). , A white powder having a carboxyl group content of 0.9 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Comparative Example 4)
In Example 1, 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J were replaced with 50 g of the carboxylic acid-modified polyvinyl alcohol resin B and 50 g of the unmodified polyvinyl alcohol resin J. Similarly, polyvinyl acetal resin (average degree of polymerization 550, acetyl group amount 2.3 mol%, residual hydroxyl group amount 22.2 mol%, acetoacetal group amount 24.0 mol%, butyral group amount 51.0 mol%, A white powder having a carboxyl group content 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.

(Comparative Example 5)
In Example 1, the polyvinyl acetal resin (average) was the same as in Example 1 except that 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J were used instead of 100 g of the carboxylic acid-modified polyvinyl alcohol resin C. Degree of polymerization 1400, acetyl group amount 2.0 mol%, residual hydroxyl group amount 21.6 mol%, acetal acetal group amount 22.5 mol%, butyral group amount 52.9 mol%, carboxyl group amount 1.0 mol%) White powder was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Comparative Example 6)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 100 g of the carboxylic acid-modified polyvinyl alcohol resin B was used, and the aldehyde used in the acetalization reaction was 80 g of n-butylaldehyde. Polyvinyl acetal resin (average polymerization degree 900, acetyl group amount 2.5 mol%, residual hydroxyl group amount 22.5 mol%, butyral group amount 74.0 mol%, A white powder having a carboxyl group content of 1.0 mol%) was obtained.
Using the obtained polyvinyl acetal resin, a conductive paste was obtained in the same manner as in Example 1.

(Comparative Example 7)
In Example 1, instead of 30 g of the carboxylic acid-modified polyvinyl alcohol resin A and 70 g of the unmodified polyvinyl alcohol resin J, 50 g of the unmodified polyvinyl alcohol resin M and 50 g of the carboxylic acid-modified polyvinyl alcohol resin F were used, and the aldehyde used in the reaction was acetaldehyde. Polyvinyl acetal resin (average polymerization degree 850, acetyl group amount 1.8 mol%, residual hydroxyl group amount 23.0 mol%, acet acetal) in the same manner as in Example 1 except that the values were changed to 15 g and 70 g of n-butyl aldehyde. A white powder having a group amount of 12.1 mol%, a butyral group amount of 62.9 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.

<Evaluation>
The polyvinyl acetal resin or conductive paste obtained in Examples and Comparative Examples was evaluated as follows. The results are shown in Table 2.

(1) Solvent solubility of resin 10 parts by weight of the polyvinyl acetal resin obtained in Examples and Comparative Examples was dissolved in 90 parts by weight of dihydroterpineol acetate, and the haze value of the obtained solution was measured with a haze meter. It was evaluated according to the criteria of.
◯: Haze value is less than 8.0 Δ: Haze value is 8.0 or more and less than 15.0 ×: Haze value is 15.0 or more

(2) Paste Viscosity Ratio The viscosities of the conductive pastes obtained in Examples and Comparative Examples at 20 ° C. were measured under the conditions of ^{share rate 60s -1} and share rate 600s ^{-1 respectively.} The ratio (η60 / η600) of the viscosity η60 measured at the share rate 60s ^{-1 to the viscosity η600 measured under the condition of the share rate 600s -1 was evaluated according to the following criteria.}
◯: 2.3 or more and less than 3.5 Δ: 2.0 or more and less than 2.3, or 3.5 or more and less than 4.5 ×: less than 2.0 or 4.5 or more

(3) Evaluation of Thread Breakability The thread breakability of the conductive pastes obtained in Examples and Comparative Examples was measured at 20 ° C. using an elongation viscometer (manufactured by HAAKE, Caver1) and evaluated according to the following criteria.
◯: Thread break time is less than 1.0 seconds Δ: Thread break time is 1.0 seconds or more and less than 3.0 seconds ×: Thread break time is 3.0 seconds or more

(4) Printability evaluation Screen printing machine (MT-320TV, manufactured by Microtech), screen plate (manufactured by Tokyo Process Service, ST500, emulsion 2 μm, 2012 pattern, screen frame 320 mm × 320 mm), printing glass substrate (soda glass) , 150 mm × 150 mm, thickness 1.5 mm), the conductive paste was printed in an environment of temperature 23 ° C. and humidity 50%, and solvent-dried in a blower oven under the conditions of 100 ° C. for 30 minutes. .. The print pattern was observed visually or with a magnifying microscope, the shape of the edge of the print surface was confirmed, and the evaluation was made according to the following criteria.
◯: The print was performed according to the print pattern, and no thread-like disordered portion was confirmed at the printed end.
Δ: The print was performed according to the print pattern, and one portion where the printed end was disordered in a thread shape was confirmed.
X: It was confirmed that the print was not performed according to the print pattern, or that the printed end was disturbed in a thread-like manner at two or more places.

(5) Surface Roughness Evaluation Using the print pattern of the conductive paste obtained in "(4) Printability Evaluation", 10 points were measured with a surface roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.), and the following Evaluated by criteria.
◯: Average surface roughness Ra of 10 places is less than 0.125 μm Δ: Average surface roughness Ra of 10 places is 0.125 μm or more and less than 0.150 μm ×: Average surface roughness Ra of 10 places Is 0.150 μm or more

According to the present invention, it is possible to provide a conductive paste having high printability and excellent surface smoothness, thread breakage and handleability.

Claims (5)

A conductive paste used for the electrodes of multilayer ceramic capacitors.
Containing a polyvinyl acetal resin, an organic solvent, and a conductive powder,
The polyvinyl acetal resin contains a carboxylic acid-modified polyvinyl acetal resin, has an average degree of polymerization of 800 to 1600, a carboxyl group amount of 0.05 to 0.9 mol%, a hydroxyl group amount of 16 to 25 mol%, and acetyl. The group amount is 0.1 to 5 mol%, the acetal acetal group amount is 25 mol% or less, and
The polyvinyl acetal resin is an acetal product of two or more kinds 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 selected from the structural unit represented by the following formula (1-1) and the structural unit represented by the following formula (1-2). Have at least one species
The mixed polyvinyl alcohol resin contains a carboxylic acid-unmodified polyvinyl alcohol resin having neither a structural unit represented by the formula (1-1) nor a structural unit represented by the formula (1-2). A conductive paste characterized in that the difference in the degree of polymerization between the polyvinyl alcohol resin having the highest degree of polymerization and the carboxylic acid-unmodified polyvinyl alcohol resin is 1200 or more.

In the above formula (1-1), R ¹ and R ² are independent of each other, and an alkylene group having 0 to 10 carbon atoms and X ¹ and X ² are independent of each other and 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 independent of each other, and hydrogen atom or 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 conductive paste according to claim 1, wherein the conductive powder is made of nickel. The conductive paste according to claim 1 or 2, further comprising a ceramic powder. The conductive paste according to claim 1, 2 or 3, wherein the organic solvent has a solubility parameter of 8.0 to 11.0 (cal / cm ³ ) ^0.5. A monolithic ceramic capacitor produced by using the conductive paste according to claim 1, 2, 3 or 4.