TWI663614B - Conductive paste for internal electrode of multi-layer capacitor and production method thereof, and multi-layer ceramic capacitor - Google Patents

Abstract

An object of the present invention is to provide a conductive paste at a low cost, which can prevent the occurrence of structural defects such as interlayer peeling in the debonding step and the subsequent calcination step, and the viscosity change during long-term storage Fewer internal electrodes suitable for forming multilayer ceramic capacitors. To a conductive paste containing a conductive powder, a medium solution, and a viscosity modifier containing a petroleum-based hydrocarbon, 0.1 to 1 part by mass of a modified polyurethane, 100 parts by mass of the conductive powder, One or more compounds of modified polyamide and ammonium phosphate are used as thermal decomposition inhibitor additives.

Description

Conductive paste for internal electrodes of multilayer ceramic capacitor, manufacturing method thereof, and multilayer ceramic capacitor

The present invention relates to a conductive paste for forming an internal electrode of a multilayer ceramic capacitor and a manufacturing method thereof. The present invention also relates to a multilayer ceramic capacitor using the conductive paste.

A multi-layer ceramic capacitor (MLCC) has a structure in which ceramic dielectric layers and internal electrode layers are alternately overlapped and integrated. As a conductive powder for forming an internal electrode of the multilayer ceramic capacitor, a powder of a noble metal such as palladium has been conventionally used. However, from the viewpoint of cost reduction, currently, a technology using nickel powder or an alloy powder containing nickel as a main component instead of a powder of a precious metal has become mainstream.

Generally speaking, such a multilayer ceramic capacitor can be obtained by printing a conductive paste in which a conductive powder is dispersed in a medium on a ceramic green sheet, and heating and crimping it by stacking it into multiple layers. After integration, calcination is performed in an oxidizing environment or an inert environment at a temperature of 500 ° C or lower. Thereby, the binder is removed (debonding step), and then, the internal electrode is calcined in a reducing environment such that the internal electrode is not oxidized (calcination step).

However, in recent years, with the miniaturization of electronic devices, the miniaturization of various electronic components has rapidly progressed. In multilayer ceramic capacitors, miniaturization and higher capacity have also been promoted. Specifically, multilayered ceramic capacitors and thinner internal electrode layers have been promoted. However, when a nickel powder is used as the conductive powder, with the multilayering and thinning, the following problems arise: structural defects such as interlayer peeling or cracking when the internal electrode layer and the ceramic dielectric layer are peeled off.

As a cause of such a problem, it is thought that it is the influence of the catalyst action of nickel in a debonding step. That is, on the surface of the nickel powder and its vicinity, due to the catalyst action of nickel, the thermal decomposition temperature of the resin component (binder) contained in the medium solution is lowered, and in the debonding step, decomposition and generation of gas are rapidly generated. For example, when ethyl cellulose is used as a binder, the thermal decomposition that is originally performed at around 355 ° C is lowered to a temperature of about 290 ° C, and a decomposition gas is rapidly generated. On the other hand, since the resin component of the ceramic dielectric layer is not affected by the action of the catalyst, thermal decomposition is not performed at this point. As a result, it is considered that the decomposition generated gas is blocked near the surface of the nickel powder, and a gap is generated between the internal electrode layer and the ceramic dielectric layer. After subsequent calcination steps, structural defects such as interlayer peeling or cracking are caused. In particular, in order to reduce the thickness of the internal electrode layer, it is necessary to use a nickel powder with a small diameter as the nickel powder. However, the catalyst action of nickel is thereby activated, and structural defects are more likely to occur.

In order to solve such problems, conventionally, attempts have been made to add to the conductive paste a component that suppresses the catalyst action of nickel in the debonding step or a component that delays the sintering of nickel.

For example, Japanese Patent Laid-Open No. 2011-18898 describes a technique in which, in addition to nickel powder, a binder, and a solvent, a nickel paste used for an internal electrode of a laminated ceramic capacitor is mixed with sulfur. Barium titanate containing barium titanate powder is used as an additive. It is considered that according to this technology, the effect of sulfur in suppressing the catalyst action of nickel and the sintering effect of barium titanate can be used to suppress the rapid generation of decomposition gas, and therefore, the occurrence of structural defects during firing can be sufficiently suppressed. However, in this technique, a step of containing sulfur in barium titanate is required before kneading the constituent components. Therefore, an increase in cost due to an increase in the number of steps cannot be avoided. In addition, the presence of inorganic components other than nickel powder in the nickel paste may adversely affect the reliability of electronic components.

On the other hand, in Japanese Patent Laid-Open No. 2008-223068, nickel powder is described as a conductive powder having a surface oxide layer, containing nickel particles containing sulfur, and having an average particle diameter of 0.05 μm to 1.0 μm. The nickel powder is characterized in that the sulfur content is 100 ppm to 2000 ppm with respect to the total weight of the powder, and the nickel particles are subjected to Electron Spectroscopy for Chemical Analysis (ESCA) (X-ray photoelectron spectroscopy). In the analysis of the surface, the intensity of the peak of the sulfur atom attributed to the nickel atom changes from the particle surface toward the center, and its intensity reaches a maximum at a position 3 nm deep from the particle surface. In addition, Japanese Patent Laid-Open No. 2008-223068 describes the following: The sulfur-containing nickel powder dispersed in a non-oxidizing gas environment is exposed to an oxidizing gas in a temperature range of 300 ° C to 800 ° C. In contact, such a nickel powder can be obtained.

Furthermore, Japanese Patent Laid-Open No. 2013-87355 describes: As the conductive powder, sulfur-containing nickel fine particles containing sulfur in a range of 0.05% by mass to 1.0% by mass can be used. The sulfur-containing nickel fine particles can exceed 100 in the presence of sulfur compounds such as sodium thiosulfate or thiourea. It is obtained by performing a hydrothermal treatment in a temperature range of ℃ to 300 ° C.

In these technologies, since the inorganic components other than nickel powder are not present in the conductive paste, it is considered that the reliability of electronic components will not be adversely affected. However, in any technique, it is necessary to contain sulfur in the nickel powder, and it is inevitable to increase costs due to an increase in the number of steps.

In this regard, Japanese Patent Laid-Open No. 2006-24539 describes a technique of suppressing the catalyst action of nickel by adding a sulfur-containing organic compound to a conductive paste. Specifically, a technique is described in which nickel powder is dispersed in a vehicle liquid obtained by dissolving a binder in a solvent, and contains a triazinethiol or a sulfate-containing compound. According to this technology, sulfur can be used to suppress the catalyst action of nickel without increasing the number of steps. Therefore, it is considered that the problem can be solved at a low cost.

However, the triazine thiols or sulfate-containing compounds exemplified in Japanese Patent Laid-Open No. 2006-24539 have a significantly low solubility in petroleum-based solvents and tend to swell when pasted. Therefore, the viscosity of the conductive paste may change over time and gel. In particular, when the conductive paste is stored for a long time, the viscosity is remarkably increased, and it is extremely difficult to form a required internal electrode layer.

As a means for improving the stability of the viscosity of a conductive paste, Japanese Patent Laid-Open No. 2001-6434 describes the addition of an amine-based surfactant to a conductive paste containing a conductive powder and an organic vehicle, and an anionic property. Polymer Dispersant Technology Surgery. However, amine-based surfactants or anionic polymer dispersants do not have the effect of suppressing the catalyst action of nickel or the effect of delaying sintering, and cannot suppress the occurrence of structural defects in the debonding step and the calcining step.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2011-18898

[Patent Document 2] Japanese Patent Laid-Open No. 2008-223068

[Patent Document 3] Japanese Patent Laid-Open No. 2013-87355

[Patent Document 4] Japanese Patent Laid-Open No. 2006-24539

[Patent Document 5] Japanese Patent Laid-Open No. 2001-6436

An object of the present invention is to provide a conductive paste which can prevent the occurrence of structural defects such as interlayer peeling during the debonding step and the subsequent calcining step, and has a small change in viscosity during long-term storage, and is suitable for forming a laminate. Internal electrode of ceramic capacitor. An object of the present invention is to provide a manufacturing method capable of manufacturing such a conductive paste at low cost. A further object of the present invention is to provide a multilayer ceramic capacitor including an internal electrode layer formed using the conductive paste.

The present invention relates to a conductive paste containing a conductive powder, a medium, a viscosity adjuster containing petroleum-based hydrocarbons, and a thermal decomposition inhibitor additive.

In particular, the conductive paste of the present invention is characterized in that, as the thermal component, Decomposition inhibiting additive contains one or more compounds selected from modified polyurethane and modified polyamide, and the content of the thermal decomposition inhibiting additive is 0.1 part by mass relative to 100 parts by mass of the conductive powder. 1 part by mass.

The thermal decomposition suppressing additive is preferably modified polyamide.

The boiling point of the viscosity adjusting agent is preferably 150 ° C to 260 ° C.

The average particle diameter of the conductive powder is preferably 1 μm or less.

The conductive powder is preferably at least one selected from the group consisting of Ni powder, Pd powder, Ni-containing alloy powder, and Pd-containing alloy powder. Among them, Ni powder is more preferred.

The conductive paste of the present invention can be produced by adding the conductive powder, the viscosity adjusting agent, and the thermal decomposition suppressing additive to the vehicle, and kneading the mixture thereof.

Furthermore, the conductive paste of the present invention can be suitably used when forming an internal electrode layer of a multilayer ceramic capacitor.

According to the present invention, by adding a specific thermal decomposition suppressing additive, it is possible to suppress the thermal decomposition of the binder from occurring on the surface of the nickel powder in the conductive paste during the debonding step when manufacturing the multilayer ceramic capacitor, and the accompanying The rapid generation of gas generated can effectively prevent the occurrence of structural defects such as interlayer peeling in the subsequent calcination step. In addition, according to the present invention, it is possible to improve the stability of the viscosity of the conductive paste without adding additional additives other than the thermal decomposition suppressing additive. Therefore, even after a long period of time after the conductive paste is manufactured, the laminate can be stably formed. pottery The inner electrode layer of a ceramic capacitor. Furthermore, according to the present invention, it is not necessary to control the shape or particle diameter of the conductive powder, and a conductive paste having such characteristics can be realized by adding a small amount of a specific thermal decomposition suppressing additive. Therefore, it is also simple to manufacture and hardly requires The cost increases due to the addition of thermal decomposition inhibitor additives. Therefore, the industrial significance of the present invention is extremely great.

1‧‧‧Conductive paste containing thermal decomposition inhibitor additive

2‧‧‧ conductive paste without thermal decomposition inhibitor

3‧‧‧ Medium

T _1a 、 T _1b 、 T ₂ 、 T ₃ ‧‧‧Thermal decomposition peak temperature

△ TG, △ TG _1a , △ TG _1b , △ TG ₂ and △ TG ₃ ‧‧‧ peak thermal decomposition intensity

FIG. 1 is a diagram for explaining an effect obtained by adding a thermal decomposition suppressing additive to a vehicle liquid.

The present inventors have conducted intensive studies on conductive pastes for forming multilayer ceramic capacitors. As a result, they have discovered that by adding modified polyurethanes, modified polyamines, ammonium phosphates, and the like to the conductive pastes, As a thermal decomposition inhibitor additive, the compound can solve the problems described above. The present invention has been completed based on this knowledge.

Composition

Hereinafter, each of the constituent components of the conductive paste of the present invention will be described.

(1) Conductive powder

As the conductive powder constituting the conductive paste of the present invention, at least one selected from the group consisting of nickel (Ni) powder, palladium (Pd) powder, Ni-containing alloy powder, and Pd-containing alloy powder can be used as in the prior art. Among them, it is preferable to use low-cost Ni powder.

In addition, as the alloy powder containing Ni, for example, a metal containing alloy powder containing Ni and at least one selected from chromium (Cr), cobalt (Co), copper (Cu), and the like is suitably used as the alloy containing Pd. The powder is preferably a metal-containing alloy powder containing Pd and at least one selected from silver (Ag), platinum (Pt), and the like. The content of Ni or Pd in these alloy powders is preferably 50% by mass or more, and more preferably 80% by mass or more.

As described above, the conductive paste of the present invention is not limited by the average particle diameter and the like of the conductive powder. However, in order to reduce the thickness of the internal electrode layer, it is important to use a conductive powder having a smaller diameter than its thickness. Specifically, as the conductive powder, a powder of 1 μm or less is preferably used, and a powder of 0.4 μm or less is more preferably used. In such a small-diameter conductive powder, the catalyst action described above is activated, so the effect obtained by the present invention becomes more significant. For this reason, in conductive powders with an average particle size of more than 1 μm, the proportion of coarse particles increases, which is not only detrimental to the thinning of laminated ceramic capacitors, but also the coarse particles in the internal electrode layer penetrate through the ceramic dielectric layer and cause electrical Short circuit, which sometimes leads to insufficient capacity.

(2) Medium

The vehicle constituting the conductive paste of the present invention is not particularly limited. As in the prior art, a vehicle obtained by uniformly mixing a solvent and a binder can be used. For example, as the solvent, terpineol, butylcarbitol acetate, butylcarbitol, dihydroxyterpineol, dihydroxyterpineol acetate, and the like can be used. As the binder, celluloses such as ethyl cellulose, polyvinyl butyral, and the like can be used.

Moreover, the content of the binder in the vehicle is not particularly limited, and it should be based on its content. The use or required characteristics are appropriately selected, and it is preferably adjusted to 1 to 7 parts by mass, and more preferably 1.5 to 6 parts by mass relative to 100 parts by mass of the conductive powder described above.

(3) viscosity adjuster

The viscosity adjusting agent is a component added to adjust the viscosity of the conductive paste to print well on an object such as a ceramic green sheet.

As such a viscosity adjusting agent, from the viewpoint of imparting appropriate dryness and solubility to the conductive paste, the main component must be a component using a petroleum-based hydrocarbon. In particular, the boiling point is preferably in a range of 150 ° C to 260 ° C, and more preferably in a range of 160 ° C to 200 ° C. When the boiling point of the viscosity modifier is lower than 150 ° C., the drying time is very short, and the viscosity of the conductive paste during printing increases sharply, so that it becomes difficult to form the required internal electrode layer. On the other hand, when the boiling point exceeds 260 ° C, drying properties are significantly deteriorated, drying after printing takes a long time, and productivity is significantly deteriorated.

Examples of the viscosity adjuster that satisfies the above conditions include, for example, a viscosity adjuster containing methyl ethylbenzene, trimethylbenzene, tridecane, nonane, cyclohexane as a main component, and specifically, JX A solvent (trade name, boiling point: 160 ° C ~ 200 ° C) manufactured by Nippon Nissei Energy Co., Ltd .; dry solvent high soft (trade name, Boiling point: 160 ° C ~ 195 ° C), LS solvent (trade name, boiling point: 200 ° C ~ 260 ° C), etc.

The content of the viscosity modifier in the conductive paste is preferably 10 to 50 parts by mass, and more preferably 10 to 40 parts by mass based on 100 parts by mass of the conductive powder. When the content of the viscosity modifier is less than 10 parts by mass, it may not be sufficiently obtained The effect described above. On the other hand, if the content of the viscosity modifier exceeds 50 parts by mass, the viscosity will be significantly reduced, the conductive paste will penetrate during printing, or it will be difficult to control the thickness of the internal electrode layer within a desired range.

(4) Thermal decomposition inhibitor additives

The conductive paste of the present invention is characterized in that, in addition to the components described above, the conductive paste contains 0.1 to 1 part by mass of 100 parts by mass of the conductive powder and is selected from the group consisting of modified polyurethane, modified One or more compounds of polyamine and ammonium phosphate are used as thermal decomposition inhibitor additives.

In the conductive paste of the present invention, the effects of suppressing the catalyst function of the conductive powder in the debonding step and preventing the rapid generation of the resulting decomposition gas are obtained by adding the thermal decomposition suppressing additives. The reason why such an effect can be obtained is not clear, but it is thought that the reason is that, in the case of modified polyurethane or modified polyamine, although S is not contained in the structure, it is because it constitutes a thermal decomposition inhibitor additive. The functional group of the molecule is adsorbed on the surface of the conductive powder, so it will hinder the contact between the conductive powder particles and the binder, and inhibit the rapid thermal decomposition. On the other hand, it is thought that the reason is that the phosphoric acid-containing functional group decomposes when heated, thereby becoming a film. Similarly, the contact between the adhesive and the conductive powder is inhibited, and the part of the adhesive is inhibited. Thermal decomposition.

In addition, these thermal decomposition inhibitor additives are difficult to swell even when mixed with the viscosity-adjusting agent mainly composed of petroleum-based hydrocarbons as described above, so that the mixed state can be maintained for a long period of time. Therefore, even when the conductive paste of the present invention is stored for a long period of time after production, the viscosity changes are small, and a desired internal electrode layer can be easily formed.

As a modified polyurethane in the thermal decomposition inhibitor additive described above Examples of the acid ester include urea-modified polycarbamate in which a diamine skeleton is introduced into a urethane bond via a urea bond, but may be a fluorene imine bond, a fluorene bond, and a fluorene imine Bonds and other modified polyurethane. Specifically, Efka (EFKA) 4046 (trade name), EFKA 4047 (trade name), etc. manufactured by Ciba Specialty Chemicals are suitably used.

Examples of the modified polyfluorene include those obtained by substituting at least a part of a hydrogen atom of a fluorene bond with a functional group such as a methoxymethyl group. Specifically, DISPARLON DA-1401 (trade name) manufactured by Nanben Chemical Co., Ltd. is suitably used.

Examples of the ammonium phosphate include diammonium hydrogen phosphate, type I ammonium polyphosphate, type II ammonium polyphosphate, and specifically, TAIEN K (trade name) and TAIEN manufactured by Taiping Chemical Industry Co., Ltd. are suitably used. C = II (trade name), etc.

The content of the thermal decomposition suppressing additive is 0.1 to 1 part by mass, preferably 0.2 to 0.8 part by mass, and more preferably 0.4 to 0.6 part by mass with respect to 100 parts by mass of the conductive powder. When the content of the thermal decomposition suppressing additive is less than 0.1 parts by mass, the effect of suppressing the thermal decomposition of the adhesive cannot be sufficiently obtained. On the other hand, if the content of the thermal decomposition suppressing additive exceeds 1 part by mass, the effect of suppressing the thermal decomposition of the adhesive can be obtained, but the characteristics of the electronic component may be adversely affected. In addition, when stored for a long period of time, in addition to deteriorating the viscosity stability of the conductive paste, it may also lead to an increase in cost.

(5) Other additives

In the conductive paste of the present invention, in addition to the additives described above, For its use, additives such as dispersant, flame retardant, and anti-settling agent (hereinafter referred to as "other additives") are added. These other additives preferably have a decomposition temperature in the range of 150 ° C to 350 ° C. When the decomposition temperature is lower than 150 ° C, it is easy to decompose during mixing or kneading, and the effect of adding other additives may not be obtained in some cases. On the other hand, if the decomposition temperature exceeds 350 ° C, these other additives will remain after the debonding step, and a gas will be generated due to thermal decomposition in the calcination step, so that the above-mentioned gas may be generated due to the gas. Structural defects such as cracks or interlayer peeling.

The content of other additives is preferably 1.0 part by mass or less, more preferably 0.5 part by mass or less, based on 100 parts by mass of the conductive powder in total. When the content of other additives exceeds 1.0 parts by mass, the effects of the present invention may not be obtained depending on the relationship with other constituent components.

2. Conductive paste

(1) Manufacturing method of conductive paste

The conductive paste of the present invention can be produced by the same method as the conventional technology, as long as the constituent components described above can be uniformly dispersed. For example, it can manufacture by kneading each component mentioned above uniformly using a 3-roll mill etc.

In addition, the timing for adding the thermal decomposition suppressing additive described above is not particularly limited and may be dispersed in the vehicle liquid in advance, but it is desirable to mix in the step of dispersing the conductive powder in the vehicle liquid.

In addition, the timing of adding the other additives described above is not particularly limited, and can be added at any timing. However, it is also considered that depending on the type of other additives, high affinity with conductive powder may occur, and thermal decomposition may be inhibited due to this. When the agent is adsorbed on the surface of the conductive powder. In this case, the order of addition of the thermal decomposition suppressing additive and other additives must be appropriately adjusted.

(2) Characteristics of conductive paste

As described above, according to the conductive paste of the present invention, the catalyst action of the conductive powder in the debonding step can be suppressed, and therefore, the thermal decomposition temperature of the binder in the paste can be prevented from being excessively lowered. Therefore, when the conductive paste of the present invention is used to constitute the internal electrode layer of a multilayer ceramic capacitor, it is possible to effectively prevent the occurrence of structural defects such as interlayer peeling or cracking.

The thermal decomposition suppressing effect of the adhesive can be judged by measuring the thermal decomposition peak strength of the adhesive in the medium and the thermal decomposition peak strength of the adhesive contained in the conductive paste using a differential thermal gravimetric analyzer.

FIG. 1 schematically shows a change amount ΔTG (thermal decomposition peak intensity) of the thermal weight TG of the medium and the conductive paste with respect to temperature. In the conductive paste (2) containing no thermal decomposition suppressing additive, the thermal decomposition peak temperature T ₂ of the adhesive is higher than that of the adhesive in the vehicle (3) due to the catalyst action of the conductive powder in the conductive paste. The thermal decomposition peak temperature T ₃ is shifted further toward the low temperature side.

On the other hand, in the electrically conductive paste (1) containing a thermal decomposition inhibitor additive, the thermal decomposition peak intensity becomes two steps. Specifically, if a thermal decomposition suppressing additive is added to the conductive paste (2) containing no thermal decomposition suppressing additive, the thermal decomposition peak intensity ΔTG ₂ will decrease as the amount of addition increases, and the thermal decomposition peak temperature will decrease. T ₂ also shifts toward the high temperature side. That is, at the thermal decomposition peak temperature T _1a on the low temperature side, the first-stage thermal decomposition peak intensity ΔTG _{1a is formed} . At the same time, on the high-temperature side, the second-stage thermal decomposition peak intensity △ TG _1b appears, and its intensity increases. This phenomenon means that the use of the thermal decomposition suppressing additive can relax the catalyst action of the conductive powder, and thus can suppress the thermal decomposition of the adhesive.

Thus, measuring a thermal decomposition peak temperature of the liquid medium (3) of the adhesive T _3, and a conductive paste containing the additives inhibit the thermal decomposition of binder (1) of the thermal decomposition peak temperature T _1, according to the liquid medium (3 The thermal decomposition peak intensity △ TG ₃ of the adhesive in) and the thermal decomposition peak intensity ΔTG _1a of the low temperature side of the adhesive in the conductive paste (1) are calculated based on the following formula (a), If the thermal decomposition intensity ratio α is less than 1, it means that thermal decomposition is suppressed.

Thermal decomposition intensity ratio: α = △ TG _1a / △ TG ₃ (a)

Moreover, the viscosity stability of the conductive paste of the present invention is also excellent, and even when stored for a long time after production, the viscosity hardly rises. Specifically, when the viscosity at the point of 24 hours after the production of the conductive paste is η ₁ , the conductive paste is stored at a constant temperature of 25 ° C. for 20 days, and the viscosity after the period is η ₂ , The increase rate of the viscosity, that is, the increase rate β of the viscosity calculated based on the following formula (b) can be made less than 20%, preferably less than 15%.

Rise rate of viscosity: β = (η ₂ -η ₁ ) / η ₁ × 100 (b)

Such a conductive paste of the present invention is suitable for forming a multilayer ceramic capacitor. Internal electrode. In addition, the manufacturing method of the multilayer ceramic capacitor of the present invention is the same as that of the prior art except that the conductive paste of the present invention is used. Therefore, the description is omitted here.

[Example]

Hereinafter, the present invention will be described in more detail using examples and comparative examples. Furthermore, in the following examples and comparative examples, the present invention will be described by taking as an example a case where Ni powder having a particularly large catalyst effect is used in all of the conductive powders described above. However, the present invention is not limited to this, and is also applicable to the case where Pd powder, Ni-containing alloy powder, and Pd-containing alloy powder are used.

Further, in the following examples and comparative examples, as the vehicle liquid, a vehicle liquid obtained by mixing ethyl cellulose and terpineol at a mass ratio of 1:19 was used. The thermal decomposition temperature of ethylcellulose in this vehicle, that is, the peak temperature of thermal decomposition of ethylcellulose when no conductive powder is used as a catalyst, is measured by the following method.

First, using an applicator (manufactured by Kodaira Manufacturing Co., Ltd., YBA-2), this vehicle was applied to a PET film so as to have a thickness of 100 μm, and dried at 90 ° C. for 6 hours. After confirming that the vehicle liquid was completely dried, only the dried film of the vehicle liquid was peeled from the PET film, pulverized in a mortar, and spread on a sieve having a mesh size of 100 μm, thereby obtaining a vehicle liquid dried powder.

Next, the obtained vehicle liquid dry powder was subjected to a differential thermal gravimetric analyzer (manufactured by Bruker BioSpin Co., Ltd., TG-DTA2000SA) in a nitrogen flow of 200 ml / min, and the temperature rising rate was set to The analysis was performed at 10 ° C / min, and the amount of change in thermal weight with respect to temperature ΔTG _{3 was} calculated according to the following formula (c). From this result, the thermal decomposition peak temperature T _{3 of} ethyl cellulose was determined, and it was confirmed that it was 355 ° C.

△ TG = (Amount of change in thermal weight TG) / (Heating time) (c)

(Example 1)

As the conductive powder, Ni powder (manufactured by Sumitomo Metal Mining Co., Ltd.) having an average particle diameter of 0.2 μm was prepared, and 60 parts by mass of the above-mentioned medium solution (ethyl cellulose: 3 parts by mass), 40 parts by mass of a viscosity modifier (manufactured by Idemitsu Kosan Co., Ltd., A solvent), and 0.1 parts by mass of DISPARLON DA-1401 (manufactured by Kusumoto Chemical Co., Ltd.) as a thermal decomposition inhibitor additive. Then, the constituent components were mixed at the same time and kneaded using a 3-roll mill (Inoue Seisakusho Co., Ltd., 43/4 × 11S roll mill) until the particle size measured by a FOG meter (fineness meter) reached 10 μm Hereinbelow, a conductive paste was produced.

[Evaluation of Thermal Decomposability]

The thermal decomposition peak temperature of the ethyl cellulose contained in the conductive paste was measured in the same manner as the thermal decomposition peak temperature of the ethyl cellulose in the vehicle solution described above, thereby specifying the thermal decomposition For the peak temperature T _1a , the thermal decomposition intensity ratio α was calculated from the formula (a). Based on the results, the thermal decomposition properties of ethyl cellulose in the conductive paste of Example 1 and the degree of gas generation that followed were evaluated.

[Evaluation of viscosity stability]

First, after the conductive paste was prepared, the viscosity η ₁ at a point in time after 24 hours was measured using a viscometer (manufactured by Brookfield, HBT type viscometer). Then, the conductive paste was stored at a constant temperature of 25 ° C. for 20 days, and the viscosity η ₂ after this period was measured in the same manner. Then, the rate of increase in viscosity β is calculated from the formula (b). Based on the results, when the viscosity increase rate β is less than 15%, it is evaluated as "good (◎)", when it is 15% or more and less than 20%, it is evaluated as "OK (○)", and when it is 20% or more, it is evaluated as "Impossible (×)". The results are shown in Table 2.

(Examples 2 to 5, Reference Example 6, Examples 7 to 8)

The types and contents of the thermal decomposition inhibitor additives were set as shown in Tables 1 and 2. A conductive paste was produced in the same manner as in Example 1, and the thermal decomposition peak temperature T _1a and the thermal decomposition strength were measured. The ratio α evaluates the thermal decomposability of ethyl cellulose in these conductive pastes and the degree of gas generation that follows. Further, the rate of increase in viscosity β was measured in the same manner as in Example 1, and the stability of the viscosity was evaluated. The results are shown in Table 2.

(Examples 9 and 10)

As the viscosity modifier, except that the types shown in Tables 1 and 2 were used, a conductive paste was prepared in the same manner as in Example 2 and the thermal decomposition peak temperature T _1a and the thermal decomposition intensity ratio α were measured. The thermal decomposition properties of ethyl cellulose in these conductive pastes and the degree of gas generation that followed were evaluated. Further, the rate of increase in viscosity β was measured in the same manner as in Example 1, and the stability of the viscosity was evaluated. The results are shown in Table 2.

(Comparative example 1)

A conductive paste was prepared in the same manner as in Example 1 except that no thermal decomposition inhibitor additive was added, and the thermal decomposition peak temperature T _1b and the thermal decomposition intensity ratio α were measured. For ethyl groups in these conductive pastes, The thermal decomposition properties of cellulose and the degree of gas generation that followed were evaluated. Further, the rate of increase in viscosity β was measured in the same manner as in Example 1, and the stability of the viscosity was evaluated. The results are shown in Table 2.

(Comparative Example 2 and Comparative Example 3)

The types and contents of the thermal decomposition inhibitor additives were set as shown in Tables 1 and 2. A conductive paste was produced in the same manner as in Example 1, and the thermal decomposition peak temperature T _1a and the thermal decomposition strength were measured. The ratio α evaluates the thermal decomposability of ethyl cellulose in these conductive pastes and the degree of gas generation that follows. Further, the rate of increase in viscosity β was measured in the same manner as in Example 1, and the stability of the viscosity was evaluated. The results are shown in Table 2.

(Overview)

From Tables 1 and 2, it was confirmed that the thermal decomposition peaks of ethylcellulose for the conductive pastes of Examples 1 to 5 and Examples 7 to 10 and Reference Example 6 included in the technical scope of the present invention. The temperature is in the range of 300 ° C to 315 ° C, and the thermal decomposition intensity ratio α is less than 1, which can suppress the thermal decomposition of the adhesive. Moreover, the evaluation of the stability of viscosity was also confirmed to be favorable. Therefore, it is considered that a multilayer ceramic capacitor having an internal electrode layer formed using these conductive pastes can significantly reduce the occurrence of structural defects in the debonding step or the firing step. In addition, it is considered that after the conductive paste is manufactured and after a long period of time, the internal electrode layer can be formed without failure. Moreover, in Example 10 which used the viscosity modifier with a boiling point exceeding 200 degreeC, compared with other Examples, the viscosity increase rate (beta) was high, but there was no problem in actual use.

In contrast, in the conductive pastes of Comparative Examples 1 and 2, it was confirmed that the thermal decomposition peak temperature of ethylene cellulose was lowered to 290 ° C, and the thermal decomposition intensity ratio α was also 1 or more. In addition, it was confirmed that the conductive paste of Comparative Example 3 had a large amount of thermal decomposition inhibitor additives, and no decrease in thermal decomposition peak temperature was observed. However, the viscosity increase rate β reached 20% or more, and the viscosity stability was low.

Claims (8)

A conductive paste containing a conductive powder, a medium, a viscosity modifier containing petroleum-based hydrocarbons, and a thermal decomposition inhibitor additive, and containing one or more selected from the group consisting of modified polyurethane and modified polyamide. The compound is used as a thermal decomposition inhibitor additive, and the content of the thermal decomposition inhibitor additive is 0.1 to 1 part by mass relative to 100 parts by mass of the conductive powder. The conductive paste according to item 1 of the scope of patent application, wherein the thermal decomposition inhibiting additive is modified polyamide. The conductive paste according to item 1 or item 2 of the scope of patent application, wherein the viscosity adjusting agent has a boiling point of 150 ° C to 260 ° C. The conductive paste according to item 1 or 2 of the scope of patent application, wherein the average particle diameter of the conductive powder is 1 μm or less. The conductive paste according to item 1 or item 2 of the patent application scope, wherein the conductive powder is at least one selected from the group consisting of Ni powder, Pd powder, Ni-containing alloy powder, and Pd-containing alloy powder. The conductive paste according to item 5 of the scope of patent application, wherein the conductive powder is Ni powder. A method for manufacturing a conductive paste, which is a method for manufacturing the conductive paste according to item 1 or 2 of the scope of patent application, and the method for manufacturing the conductive paste is to add the conductive paste to the medium. The powder, the viscosity adjusting agent, and the thermal decomposition suppressing additive are kneaded. A multilayer ceramic capacitor includes an internal electrode layer formed using the conductive paste described in item 1 or 2 of the patent application scope.