JP5178279B2 - Conductive paste for multilayer ceramic capacitors - Google Patents

Description

The present invention relates to a conductive paste that is excellent in adhesiveness and printability, is less prone to problems such as sheet attack and delamination, is excellent in surface smoothness after coating and drying, and has a small residual carbon content after firing.

In various fields, a method of preparing a precise conductive film or the like by applying a conductive paste in which an inorganic powder such as a conductive powder is dispersed and then baking is applied. A multilayer electronic component such as a multilayer ceramic capacitor using such a conductive paste is generally manufactured through the following steps as disclosed in Patent Document 1 or Patent Document 2.

First, after adding a plasticizer, a dispersing agent, etc. to a solution in which a binder resin such as polyvinyl butyral resin or poly (meth) acrylic ester resin is dissolved in an organic solvent, ceramic raw material powder is added and mixed uniformly by a ball mill or the like. A ceramic slurry composition having a constant viscosity after defoaming is obtained. This slurry composition is cast-molded on a support surface such as a polyethylene terephthalate film or a SUS plate which has been subjected to a release treatment using a doctor blade, a reverse roll coater or the like. This is heated to remove volatile components such as a solvent, and then peeled off from the support to obtain a ceramic green sheet.

Next, a plurality of sheets obtained by alternately applying a conductive paste serving as an internal electrode on the obtained ceramic green sheet by screen printing or the like, and thermocompression-bonded to obtain a laminate, the binder component contained in this laminate A multilayer ceramic capacitor is obtained through a process of thermally decomposing and removing a so-called degreasing process, and then sintering an external electrode on the end face of the fired ceramic product obtained by firing.

At this time, as the conductive paste used to form the internal electrode, a paste containing a metal material such as palladium or nickel, an organic solvent, or a binder resin such as ethyl cellulose is usually used as described in Patent Document 1. ing.

However, in recent years, multilayer ceramic capacitors have been required to have higher capacities, and further multilayering and thinning have been studied. In this way, when a multilayer ceramic capacitor with a very thin film is manufactured using a conventional conductive paste using ethyl cellulose as a binder resin, the adhesiveness with a ceramic green sheet using a polyvinyl acetal resin as a binder resin is poor. In other words, the delamination is likely to occur, so-called delamination, and the thermal decomposition of ethyl cellulose itself is inferior. Therefore, when the above laminate is degreased, the carbon component remains after firing, and the electrical characteristics are impaired. there were.

In addition, with the recent thinning of multilayer ceramic capacitors, a so-called sheet attack phenomenon in which the organic solvent of the conductive paste dissolves the ceramic green sheet has become a new major issue.

On the other hand, in recent years, a conductive paste using a polyvinyl acetal resin as a binder resin has been put into practical use, and by using such a conductive paste, occurrence of delamination can be effectively prevented. Patent Document 3 discloses a method of preventing sheet attack and improving adhesion by using a polyvinyl acetal resin modified with a specific solvent as a binder resin of a conductive paste.
However, such a method has a problem that unevenness is generated on the surface of the conductive paste layer obtained after coating and drying, so that the so-called leveling property is inferior, and a residual carbon content after sintering is increased.
Patent Document 4 discloses a conductive paste containing a predetermined organic solvent and an acrylic resin as a binder resin. However, such a conductive paste has a problem that since the binder resin used has a high molecular weight, stringing occurs during printing, and a predetermined shape cannot be printed.
Japanese Patent Publication No. 3-35762 Japanese Patent Publication No. 4-49766 JP 2007-116083 A JP 2005-158563 A

In view of the present situation, the present invention is excellent in adhesiveness and printability, hardly causes problems such as sheet attack and delamination, is excellent in surface smoothness after coating and drying, and has a residual carbon content after firing. An object is to provide a small amount of conductive paste.

As a result of intensive studies, the present inventors have found that when a (meth) acrylic resin having a weight average molecular weight of 5000 to 50000 is used as the binder resin and propylene carbonate or γ-butyrolactone is used as the organic solvent, It has been found that it has excellent printability, can effectively prevent the occurrence of sheet attack and delamination, can achieve high surface smoothness after coating and drying, and can reduce the residual carbon content after firing. It came to complete.

The present invention, (meth) acrylic resin, a conductive paste for a multilayer ceramic capacitor comprising an organic solvent and the conductive powder, the (meth) acrylic resin has a weight average molecular weight of 5,000 to 50,000, wherein (meth) The content of acrylic resin is 1 to 10% by weight, and the organic solvent is a conductive paste for a multilayer ceramic capacitor, which is propylene carbonate.
The present invention is described in detail below.

The conductive paste of the present invention contains a (meth) acrylic resin.

Examples of the (meth) acrylic resin include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, and isobutyl (meth) acrylate. (Meth) acrylic resin having segments derived from cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, n-stearyl (meth) acrylate, benzyl (meth) acrylate, polyoxyalkylene and the like Can be mentioned. Here, (meth) acrylate means acrylate or methacrylate. These may be used alone or in combination of two or more.
Of these, methyl methacrylate, which can obtain a high viscosity with a small amount and is excellent in low-temperature degreasing properties, is preferred.

As said (meth) acrylic resin, what has the segment derived from the monomer whose glass transition temperature of a homopolymer is 20 degreeC or more is preferable. “The glass transition temperature of the homopolymer is 20 ° C. or higher” means that when the glass transition temperature of the polymer obtained by polymerizing the monomer alone is measured, the measured value is 20 ° C. or higher. It means that. Examples of the monomer having a glass transition temperature of the homopolymer of 20 ° C. or higher include methyl methacrylate (glass transition temperature of the homopolymer 105 ° C.).

The said (meth) acrylic resin has a preferable lower limit of the weight average molecular weight of 5000 and a preferable upper limit of 50000. If the weight average molecular weight is less than 5,000, it may be difficult to obtain a sufficient viscosity for printing. On the other hand, when the weight average molecular weight exceeds 50000, the cohesive strength of the resin increases, and the yarn may be generated during coating, which may adversely affect handling properties. A more preferred lower limit is 10,000. A more preferable upper limit is 20000. When the weight average molecular weight is 10,000 to 20,000, the surface properties after printing and drying are excellent, and the stringiness is also good.
The weight average molecular weight can be measured by GPC measurement using, for example, a column LF-804 manufactured by SHOKO as a column and a polystyrene polymer as a standard substance.

The molecular weight distribution (weight average molecular weight / number average molecular weight = Mw / Mn) of the (meth) acrylic resin is not particularly limited, but the preferred upper limit is 3. When the molecular weight distribution exceeds 3, a low molecular weight component such as an oligomer in the polymerization solution becomes a plasticizer, and a sufficient viscosity may not be obtained in the conductive paste, or the high molecular weight component may deteriorate the stringiness. . A more preferred upper limit is 2.5.

The polymerization method of the (meth) acrylic resin is not particularly limited, and examples thereof include a method used for polymerization of a normal (meth) acrylate monomer. For example, a free radical polymerization method, a living radical polymerization method, an iniferter polymerization method, Examples thereof include an anionic polymerization method and a living anionic polymerization method.
When a polymerization initiator is used for the polymerization of the (meth) acrylic resin, the polymerization initiator is not particularly limited. The polymerization initiator may be added all at once during the polymerization of the (meth) acrylic resin, or may be added in several divided portions. When the polymerization initiator is added in several portions, the (meth) acrylic resin containing no low molecular weight components such as residual oligomers can be obtained.

The content of the (meth) acrylic resin in the conductive paste of the present invention is not particularly limited because it is determined by the type and specific gravity of the conductive powder to be used, the amount of the organic solvent used together, etc., but the preferred lower limit is 1% by weight and the preferred upper limit is 10 % By weight. When the amount is less than 1% by weight, the dispersibility of the conductive powder may be lowered. When the amount exceeds 10% by weight, the performance such as conductivity may be lowered.

The conductive paste of the present invention contains propylene carbonate or γ-butyrolactone as the organic solvent. By using the propylene carbonate or γ-butyrolactone, sheet attack can be effectively prevented. The propylene carbonate or γ-butyrolactone has low toxicity and can be dried at 200 ° C. or lower. In addition, as said organic solvent, you may contain organic solvents other than a propylene carbonate or (gamma) -butyrolactone.

The organic solvent other than propylene carbonate or γ-butyrolactone is not particularly limited as long as it can prevent sheet attack and dissolves the binder resin, but preferably has a boiling point of 150 ° C. or higher and lower than 300 ° C. When the boiling point is less than 150 ° C., the organic solvent volatilizes when the conductive paste of the present invention is applied, so that the viscosity changes, so that stable coating may not be performed. If so, a great amount of time and heat energy may be required in the stage of drying the organic solvent in the conductive paste after coating. More preferably, it is 160-280 degreeC.

The organic solvent other than the propylene carbonate or γ-butyrolactone preferably has a specific gravity of 0.95 or more and less than 1.35. When the specific gravity is less than 0.95 and 1.35 or more, a sheet attack may occur or coating properties may be deteriorated. In the present specification, the specific gravity means the ratio of the density of water at 4 ° C. to the density of the organic solvent at 20 ° C.

Examples of organic solvents other than propylene carbonate or γ-butyrolactone include diols such as ethylene glycol diacetate, cyclohexanol, diethylene glycol, propanediol, butanediol, pentanediol, 2-butene-1,4-diol, and cyclohexane. Hexanol, diethylene glycol monobutyl acetate, diethylene glycol monobutyl ether acetate, phenoxy acetate, 2-butoxyethyl acetate, 2-ethoxyethyl acetate, 2-methoxyethyl acetate, dimethyl sulfoxide, N-methylpyrrolidone, N-methylacetamide, acetamide, N, N-dimethylformamide, N-methylformamide, formamide and the like can be mentioned.
Among them, the dielectric constant is preferably 25 or more because it is particularly difficult to cause sheet attack. Examples of the solvent having a dielectric constant of 25 or more include diethylene glycol, dimethyl sulfoxide, N-methylpyrrolidone, N-methylacetamide, acetamide, N , N-dimethylformamide, N-methylformamide, formamide.
In addition, these organic solvents may be used independently and may use 2 or more types together.

The conductive paste of the present invention contains a conductive powder.
The material of the conductive powder is not particularly limited as long as it exhibits conductivity, and examples thereof include powder made of nickel, palladium, platinum, gold, silver, copper, and alloys thereof. These metal powders may be used alone or in combination of two or more.

The content of the conductive powder in the conductive paste of the present invention is not particularly limited because it is determined by the type / specific gravity of the conductive powder to be used and the printing process, but the preferred lower limit is 30% by weight and the preferred upper limit is 80% by weight. is there. If the content of the conductive powder is less than 30% by weight, problems such as insufficient viscosity being obtained and printability being reduced, and residual organic content being increased due to a large amount of organic components may occur. There is. If it exceeds 80% by weight, it may be difficult to disperse the conductive powder.

Moreover, the electrically conductive paste of this invention may contain additives, such as surfactant. The surfactant is not particularly limited, and examples thereof include a cationic surfactant, an anionic surfactant, and a nonionic surfactant.

The viscosity of the conductive paste of the present invention is not particularly limited, but the preferred lower limit of the viscosity is 0.1 Pa · s, and the preferred upper limit when measured at 20 ° C. using a B-type viscometer and setting the probe rotation speed to 5 rpm. 100 Pa · s. When the viscosity is less than 0.1 Pa · s, it may be difficult to maintain the predetermined shape of the conductive paste after coating by a die coating method or the like. The printability may be inferior.

It does not specifically limit as a coating method of the electrically conductive paste of this invention, For example, screen printing, die coating printing, offset printing, gravure printing, inkjet printing etc. are mentioned.

It does not specifically limit as a manufacturing method of the electrically conductive paste of this invention, The said (meth) acrylic resin, an organic solvent, electrically conductive powder, and various additives are conventionally well-known stirring methods, Specifically, for example, 3 rolls etc. Kneading may be performed.

According to the present invention, the conductive paste is excellent in adhesiveness and printability, hardly causes problems such as sheet attack and delamination, has excellent surface smoothness after coating and drying, and has a small residual carbon content after firing. Can be provided.

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

Example 1
(Synthesis of (meth) acrylic resin)
In a 2 L separable flask equipped with a stirrer, cooler, thermometer, hot water bath and nitrogen gas inlet, 100 parts by weight of methyl methacrylate (MMA), 0.9 part by weight of dodecyl mercaptan as a chain transfer agent, and propylene carbonate as an organic solvent 100 parts by weight was mixed to obtain a monomer mixture.

The obtained monomer mixture was bubbled with nitrogen gas for 20 minutes to remove dissolved oxygen, and then the inside of the separable flask system was replaced with nitrogen gas, and the temperature was raised until the hot water bath boiled with stirring. . As a polymerization initiator, a solution obtained by diluting 0.02 part by weight of perbutyl PV manufactured by NOF Corporation with ethyl acetate was added. Further, an ethyl acetate solution containing a polymerization initiator was added several times during the polymerization.

Seven hours after the start of polymerization, the polymerization was terminated by cooling to room temperature. Thereby, a propylene carbonate solution of a (meth) acrylic resin was obtained. When the obtained (meth) acrylic resin was analyzed by gel permeation chromatography using a column LF-804 manufactured by SHOKO as a column, the weight average molecular weight in terms of polystyrene was 50,000.

(Preparation of conductive paste)
The obtained propylene carbonate solution of (meth) acrylic resin was mixed with nickel powder (“NFP201”, manufactured by JFE Mineral Co., Ltd.), and passed through three rolls several times to produce a conductive paste.
The composition ratio in the conductive paste was adjusted to 55% by weight of nickel powder and 6% by weight of (meth) acrylic resin.

(Production of ceramic green sheets)
10 parts by weight of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., ESREC B “BM-2”, degree of polymerization 850) is added to a mixed solvent of 30 parts by weight of toluene and 15 parts by weight of ethanol, and dissolved by stirring. As an agent, 3 parts by weight of dibutyl phthalate was added and dissolved by stirring. To the obtained resin solution, 100 parts by weight of barium titanate (“BT-02 (average particle size: 0.2 μm)” manufactured by Sakai Chemical Industry Co., Ltd.) as ceramic powder was added and mixed with a ball mill for 48 hours to obtain a ceramic slurry composition. Got. The obtained slurry composition was applied onto a release-treated polyester film so that the thickness after drying was about 1 μm, air-dried at room temperature for 1 hour, a hot-air dryer at 80 ° C. for 3 hours, then A ceramic green sheet was obtained by drying at 120 ° C. for 2 hours.

(Printing of conductive paste)
On one side of the obtained green sheet, the prepared conductive paste was printed by screen printing so that the thickness after drying was about 1.5 μm, and dried to form a conductive layer.

(Production of laminate)
The green sheets were cut into 5 cm square, 100 sheets were stacked, and thermocompression bonded at a temperature of 70 ° C. and a pressure of 150 kg / cm ² for 10 minutes to obtain a green sheet laminate.
The obtained green sheet laminate was heated to 400 ° C. at a rate of temperature increase of 3 ° C./min and held for 5 hours in a nitrogen atmosphere, then again heated to 1350 ° C. at a rate of 5 ° C./min to 10 The laminate was obtained by sintering for a period of time.

( Reference Example 2)
(Synthesis of (meth) acrylic resin)
Polymerization was carried out in the same manner as in Example 1 except that the amount of dodecyl mercaptan added was changed to 1.5 parts by weight. About the obtained (meth) acrylic resin, it was 30,000 when the weight average molecular weight by polystyrene conversion was measured like Example 1. FIG.
A conductive paste and a laminate were produced in the same manner as in Example 1 except that the obtained (meth) acrylic resin γ-butyrolactone solution was used.
The composition ratio in the conductive paste was adjusted to 55% by weight of nickel powder and 8% by weight of (meth) acrylic resin.

(Example 3)
(Synthesis of (meth) acrylic resin)
Polymerization was carried out in the same manner as in Example 1 except that the amount of dodecyl mercaptan added was changed to 2.1 parts by weight. About the obtained (meth) acrylic resin, when the weight average molecular weight by polystyrene conversion was measured like Example 1, it was 10,000.
A conductive paste and a laminate were prepared in the same manner as in Example 1 except that the propylene carbonate solution of the obtained (meth) acrylic resin was used.
The composition ratio in the conductive paste was adjusted to 60% by weight of nickel powder and 10% by weight of (meth) acrylic resin.

Example 4
(Synthesis of (meth) acrylic resin) In the same manner as in Example 1 except that 100 parts by weight of isobutyl methacrylate (IBMA) was used instead of 100 parts by weight of methyl methacrylate (MMA), (meth) acrylic resin, A conductive paste and a laminate were prepared.

(Example 5)
(Synthesis of (meth) acrylic resin) In the same manner as in Example 1 except that 100 parts by weight of cyclohexyl methacrylate (CHMA) was used instead of 100 parts by weight of methyl methacrylate (MMA), (meth) acrylic resin, A conductive paste and a laminate were prepared.

(Example 6)
(Synthesis of (meth) acrylic resin) In the same manner as in Example 1 except that instead of 100 parts by weight of methyl methacrylate (MMA), a mixture of 80 parts by weight of MMA and 20 parts by weight of lauryl methacrylate (LMA) was used. A (meth) acrylic resin, a conductive paste and a laminate were produced.

(Example 7)
In (Synthesis of (meth) acrylic resin), instead of 100 parts by weight of methyl methacrylate (MMA), acrylic monomer (polypropylene glycol monomethacrylate: PPGMA) having 80 parts by weight of MMA and a propylene oxide unit (manufactured by NOF Corporation, BLEMMER PP1000) ) A (meth) acrylic resin, a conductive paste and a laminate were prepared in the same manner as in Example 1 except that 20 parts by weight of the mixture was used.

(Comparative Example 1)
In (Preparation of conductive paste), in place of the propylene carbonate solution of (meth) acrylic resin, a terpineol solution of ethyl cellulose in which 85 parts by weight of terpineol was added to 15 parts by weight of ethyl cellulose (manufactured by Dow, STD100) was used. Produced a conductive paste and a laminate in the same manner as in Example 1.
The composition ratio in the conductive paste was adjusted to 55% by weight of nickel powder and 2.5% by weight of ethyl cellulose resin.

(Comparative Example 2)
(Synthesis of (meth) acrylic resin)
Polymerization was carried out in the same manner as in Example 1 except that the amount of dodecyl mercaptan added was changed to 0.4 parts by weight. About the obtained (meth) acrylic resin, when the weight average molecular weight by polystyrene conversion was measured like Example 1, it was 100,000.
A conductive paste and a laminate were produced in the same manner as in Example 1 except that the terpineol solution of the obtained (meth) acrylic resin was used.

(Comparative Example 3)
In (Preparation of conductive paste), instead of the propylene carbonate solution of (meth) acrylic resin, a propylene carbonate solution of ethyl cellulose in which 85 parts by weight of propylene carbonate was added to 15 parts by weight of ethyl cellulose (manufactured by Dow, STD100) was used. It was.
In this case, ethyl cellulose was not sufficiently dissolved in propylene carbonate, and a conductive paste and a laminate could not be obtained.

(Comparative Example 4)
In (Preparation of conductive paste), instead of propylene carbonate solution of (meth) acrylic resin, γ-butyrolactone solution of ethyl cellulose in which 85 parts by weight of γ-butyrolactone is added to 15 parts by weight of ethyl cellulose (manufactured by Dow, STD100). Was used.
In this case, ethyl cellulose was not sufficiently dissolved in γ-butyrolactone, and a conductive paste and a laminate could not be obtained.

(Comparative Example 5)
In (Preparation of conductive paste), instead of the propylene carbonate solution of (meth) acrylic resin, a polyvinyl butyral propylene carbonate solution in which 85 parts by weight of propylene carbonate is added to 15 parts by weight of polyvinyl butyral (manufactured by Sekisui Chemical, BHS). Was used.
In this case, polyvinyl butyral was not sufficiently dissolved in propylene carbonate, and a conductive paste and a laminate could not be obtained.

(Comparative Example 6)
In (Preparation of conductive paste), instead of propylene carbonate solution of (meth) acrylic resin, γ- of polyvinyl butyral obtained by adding 85 parts by weight of γ-butyrolactone to 15 parts by weight of polyvinyl butyral (manufactured by Sekisui Chemical, BHS) A butyrolactone solution was used.
In this case, polyvinyl butyral was not sufficiently dissolved in γ-butyrolactone, and a conductive paste and a laminate could not be obtained.

(Evaluation)
The following evaluation was performed about the (meth) acrylic resin, electrically conductive paste, and laminated body which were obtained by the Example and the comparative example. The results are shown in Table 1. Table 1 also shows the glass transition temperature (Tg) of the homopolymer in the constituent monomer of the resin used in each Example and Comparative Example, and the specific gravity and boiling point of the organic solvent used in each Example and Comparative Example. It was shown to.

(Sheet attack)
The surface (printing surface) and the back surface (polyester film surface) of the ceramic green sheet on which the conductive paste was printed were observed visually and with a magnified microscope, and evaluated according to the following criteria.
A sample in which no wrinkles or cracks were observed was marked with “◯”, and a sample in which wrinkles or cracks were observed was marked with “X”.

(Measurement of surface roughness)
About the conductive layer formed in the Example and the comparative example, the centerline average roughness (Ra) of the surface was measured by the method based on JISB0601. Note that a stylus roughness meter (manufactured by Tokyo Seimitsu Co., Ltd., Surfcom 1400D) was used for the measurement.
As a result of the measurement, the case where Ra was 0.07 μm or less was rated as “◯”, the case where it was larger than 0.07 μm and 0.1 μm or less, “Δ”, and the case where it exceeded 0.1 μm as “X”. If Ra exceeds 0.1 μm, it will break through the dielectric during lamination, resulting in deterioration of product yield, and quality failure due to piezoelectric breakdown of the dielectric layer pressed by the protrusion during use.

(Sinterability evaluation)
The laminates obtained in Examples and Comparative Examples were cooled to room temperature, the center part was cut in the direction perpendicular to the laminate surface, and the sheet state in the vicinity of the 50th layer was observed with an electron microscope. The presence or absence of cracks was confirmed.
The case where there was no crack and the black dot-like material was not confirmed was evaluated as “◯”, and the case where there was a crack or black dot-like material was shown as “X”.

(Evaluation of adhesion (delamination confirmation))
The laminates obtained in the examples and comparative examples were cooled to room temperature, the center part was cut in the direction perpendicular to the laminate surface, and the sheet state in the vicinity of the 50th layer was observed with an electron microscope. The presence or absence of delamination with the conductive layer was observed.
The case where delamination could not be confirmed was marked with ◯, and the case where delamination could be confirmed was marked with X.

According to the present invention, the conductive paste is excellent in adhesiveness and printability, hardly causes problems such as sheet attack and delamination, has excellent surface smoothness after coating and drying, and has a small residual carbon content after firing. Can be provided.

Claims (2)

A conductive paste for a multilayer ceramic capacitor containing a (meth) acrylic resin, an organic solvent and a conductive powder,
The (meth) acrylic resin has a weight average molecular weight of 5000 to 50000,
The content of the (meth) acrylic resin is 1 to 10% by weight, and
The organic solvent, a conductive paste for a multilayer ceramic capacitor, which is a propylene carbonate. The conductive paste for a multilayer ceramic capacitor according to claim 1, wherein the (meth) acrylic resin has a segment derived from a monomer having a glass transition temperature of a homopolymer of 20 ° C or higher.