JP7147582B2 - Method for producing conductive paste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a conductive paste, and more particularly to a method for producing a conductive paste suitable for use as internal electrodes of multilayer ceramic capacitors (MLCCs).

Conductive paste contains conductive metal powder, resin, solvent, and the like, and is widely used as a material for forming conductive parts such as electrodes of electronic parts. For example, after forming a printed film having a predetermined pattern shape from a conductive paste on the surface of a substrate such as a ceramic or a green sheet using a printing technique such as screen printing, the solvent is removed from the printed film by heating and drying. There is known a method of obtaining an electrode composed of a metal film by removing the dry film and firing the remaining dry film at a temperature at which the conductive metal powder contained therein is sintered and at a temperature at which the resin is combusted.

The conductive paste may be stored for a long period of time or screen-printed for a long period of time. Therefore, it is desirable that the conductive paste has a low rate of change in viscosity over time. For example, Patent Literature 1 discloses a technique for suppressing the rate of change in the viscosity of the conductive paste over time by improving the organic solvent added to the conductive paste.

JP 2012-226865 A

Rheology control agent, [online], [searched on November 29, 2018], Internet <URL: https://www.tetsutani.co.jp/wp-content/uploads/2015/12/06.pdf>

In addition to the problem of change over time, the initial viscosity of the conductive paste is also important. If the initial viscosity is too low, organic components such as solvents may float during long-term storage or transportation, and storage stability may not be satisfied. Defects may occur. On the other hand, if the initial viscosity is too high, although the storage stability is satisfied, there is a possibility that the printability may be deteriorated due to deterioration in handling, inability to print in a desired pattern, and the like.

The initial viscosity of the conductive paste can be adjusted within a predetermined range by adjusting the content of the solvent. However, when the content of the solvent is adjusted, the content of the conductive metal powder fluctuates, resulting in a change in the film thickness of the internal electrodes. As a result, it affects the performance of the MLCC, and it becomes necessary to reexamine the printing conditions of the conductive paste in order to maintain the performance of the MLCC. is not preferred.

In view of such circumstances, it is an object of the present invention to provide a method for producing a conductive paste that can satisfy the storage stability of the conductive paste during storage and transportation.

The inventors of the present invention conducted various studies on the above problem, and found that moisture in the conductive paste lowers the viscosity. Then, in order to increase the viscosity of the conductive paste, various studies were conducted to reduce the amount of water in the conductive paste, and the present invention was conceived.

In order to solve the above problems, the method for producing a conductive paste of the present invention includes a dehydration step of dehydrating water contained in an organic solvent, and a dispersion containing a resin, an organic solvent, and metal particles in which metal particles are dispersed, and a dilution step of diluting with an organic solvent dehydrated in the dehydration step.

According to the method for producing a conductive paste of the present invention, the storage stability can be satisfied by increasing the viscosity without changing the content of the conductive metal powder in the conductive paste.

It is the schematic which shows an example of the specific aspect of a dehydration process.

An example of the method for producing the conductive paste of the present invention will be described below. The manufacturing method of the conductive paste of the present invention includes a dehydration step and a dilution step.

[Dehydration process]
This step is a step of dehydrating water contained in the organic solvent.

(Organic solvent)
The organic solvent is one of the materials that constitute the conductive paste, and dissolves the resin, for example, and adjusts the viscosity of the conductive paste and the content of the metal particles. The organic solvent that can be used is not particularly limited, and conventionally known solvents can be appropriately selected and used. Preferred examples include saturated aliphatic hydrocarbon solvents, ethylene glycol monobutyl ether acetate, and the like. As the saturated aliphatic hydrocarbon solvent, a solvent containing saturated hydrocarbon as a main component can be preferably used, and a solvent containing tridecane, nonane, or cyclohexane can be particularly preferably used. Further, terpene solvents such as terpineol and dihydroterpineol, dihydroterpinyl acetate, isobornyl acetate, isobornyl propinate, isobornyl butyrate, isobornyl isobutyrate, and the like are included. Additionally, mixtures of hydrocarbons with 9 to 16 carbon chains can be used, including mineral spirits such as LAWS and HAWS. Only one type of these organic solvents may be used, or two or more types may be used.

Hereinafter, a specific example of the dehydration process will be described with reference to the schematic diagram showing an example of a specific mode of the dehydration process shown in FIG. For example, by placing the container 20 containing the organic solvent 10 to be dehydrated and the container 40 containing the dehydrating agent 30 in a sealed container 50 that can block the ingress and egress of fluid for a predetermined period of time, the organic Moisture contained in the solvent can be dehydrated. Here, the dehydrating agent 30 does not come into contact with the organic solvent 10, and dehydration is performed in a non-contact state. Since these are non-contact, it is possible to omit the process of separating the dehydrating agent 30 and the organic solvent 10 after the dehydration step, and the organic solvent 10 is not contaminated. In addition, since the dehydrating agent 30 can absorb the moisture volatilized in the closed container 50 because they are not in contact with each other in the closed state, a large decrease in the amount of the organic solvent 10 due to excessive volatilization of the organic solvent 10 can be prevented. can do.

In the dehydration process, there is no particular limitation as to how much the dehydrating agent 30 is used with respect to the organic solvent 10 . For example, the dehydrating agent 30 can have a mass ratio of 10 to 100 times the saturated water content of the organic solvent 10 . If the dehydrating agent 30 is 10 times or more the saturated water content of the organic solvent 10, a sufficient dehydrating effect can be obtained by standing still for 24 hours. For 24 hours, even if the dehydrating agent 30 is used in an amount exceeding 100 times the weight ratio, the dehydration effect does not change. If the mass ratio is less than 10 times, the dehydration effect may be insufficient, and the initial viscosity of the conductive paste may not be sufficiently increased.

As the sealed container 50, the material is not particularly limited as long as it has solvent resistance such as not being dissolved by the organic solvent 10 and can be sealed. . By sealing the organic solvent 10 and the dehydrating agent 30, the effect of dehydrating the water in the organic solvent 10 to the extent that the viscosity of the conductive paste can be sufficiently increased by dehydration for about 24 hours is exhibited. Sealing is not essential, but if it is not sealed, dehydration of the organic solvent 10 may take 24 hours or more.

In addition to the above, the dehydration step in the present invention may be a step of dehydrating by passing an organic solvent through a column filled with a dehydrating agent. However, considering the man-hours required for column washing and regeneration of the dehydrating agent, it is easier to regenerate the dehydrating agent if the organic solvent and the dehydrating agent do not come into contact with each other. good. In the dehydration process according to the present invention, it is effective to dehydrate other raw materials used in the conductive paste, such as metal particles, resins, and other additives, in the same manner as the organic solvent.

(dehydrating agent)
The dehydrating agent for dehydrating the water contained in the organic solvent is preferably one that can selectively remove water, and is not particularly limited as long as it satisfies this requirement. Calcium oxide and calcium chloride used can be mentioned. In addition, as a physical dehydrating agent, silica gel, activated carbon, aluminum oxide, zeolite (natural zeolite, synthetic zeolite (hereinafter also referred to as molecular sieve), aluminosilicate, which is a generic concept of zeolite, etc. ), layered substances such as allophane, and clay minerals. Among them, zeolite is more preferable because it can selectively adsorb only water by selecting a zeolite having a pore size of 0.3 nm or more and 0.5 nm or less. These dehydrating agents may be used alone or in combination of two or more.

In particular, if the dehydrating agent is at least one or more of silica gel, aluminum oxide, zeolite, allophane and clay minerals, these dehydrating agents can easily remove moisture, and the dehydrating agent can be repeatedly dehydrated by removing moisture. It is more preferable because it can be reused as

[Dilution process]
This step is a step of diluting the dispersion containing the resin, the organic solvent and the metal particles in which the metal particles are dispersed, with the organic solvent dehydrated in the dehydration step. This step allows the concentration of the metal particles in the conductive paste to be adjusted.

The dilution step is not particularly limited as long as it is a step capable of diluting the dispersion with a dehydrated organic solvent. For example, the dispersion can be diluted using a two-roll mill, three-roll mill, bead mill, ball mill, disper, planetary mixer, revolutionary stirrer, kneader, mix rotor, homogenizer, or the like.

<Dispersion>
The dispersion contains a resin, an organic solvent and metal particles, and the metal particles are dispersed. If a dispersion is available, it is sufficient to use it, but when producing a dispersion, for example, powdered metal particles are added to a resin (binder resin) dissolved in an organic solvent and kneaded. Dispersions can thus be produced. The dispersion can also be produced by mixing a resin into a slurry in which metal particles are dispersed in a solvent or the like.

Here, when producing the dispersion, in addition to the resin, organic solvent and metal particles, a dispersant, a viscosity modifier, and other additives may be added. At this time, the order of adding these additives is not particularly limited, and for example, they can be added in an appropriate order, or all the materials can be added at the same time. Alternatively, these additives may be added after adding the metal powder to the binder resin.

The method for dispersing metal particles to obtain a dispersant is not particularly limited, but examples include a two-roll mill, a three-roll mill, a bead mill, a ball mill, a disper, a planetary mixer, a rotation-revolution stirring device, a kneader, a mix rotor, It can be dispersed using a stirrer or the like. For example, it is preferable to stir and mix the binder resin and the metal particles with a mixer, and then disperse them further with a three-roll mill. When a three-roll mill is used, aggregation of metal particles is loosened, so metal particles having finer particle diameters can be more uniformly dispersed in the dispersion.

(resin)
In the method for producing the conductive paste of the present invention, the content can be easily adjusted by using a binder resin obtained by previously dissolving the resin in an organic solvent. The organic solvent for dissolving the resin is preferably an organic solvent dehydrated by the dehydration step described above. However, even if an organic solvent that has not been dehydrated is used, the organic solvent is heated during the production of the binder resin, and this reduces the water content in the organic solvent, so that the effect of the present invention can be sufficiently obtained.

Examples of resins include cellulose resins such as ethyl cellulose and nitrocellulose, epoxy resins, and acrylic resins such as butyl methacrylate and methyl methacrylate. These can be used alone or in combination of two or more.

Specific conditions for preparing the binder resin are not particularly limited. It can be adjusted by heating with stirring until dissolved.

The concentration of the binder resin may be appropriately adjusted according to the purpose of use. Moreover, it is preferable to store the prepared binder resin in an airtight container.

(Organic solvent)
As for the organic solvent used for obtaining the dispersion, the one described in the dehydration step can be used. By using the organic solvent dehydrated by the dehydration step of the present invention, the water content in the conductive paste can be further reduced, so that the viscosity of the conductive paste can be increased. However, the effects of the present invention can be sufficiently obtained even if an organic solvent that is not dehydrated is used.

(metal particles)
As metal particles to be dispersed, particles of one or more kinds selected from Ni, Cu, Pd, Ag, and alloys thereof can be used. For example, if the metal particles are in the form of powder or slurry, the production of the conductive paste is facilitated.

The average particle diameter of the metal particles is not particularly limited, but in the case of the conductive paste, it is preferably 0.05 μm or more and 0.5 μm or less. The average particle size of the metal particles is a value obtained from a scanning electron microscope (SEM) photograph, and means the particle size at an integrated value of 50% in the particle size distribution.

(Other configurations)
Various additives can be added to the dispersion and the conductive paste as necessary within a range that does not impair their functions. Specifically, a dispersing agent for further improving the dispersibility of nickel particles, a rheology control agent for improving thixotropy, and the like can be contained in the dispersing step and the diluting step as described above. Moreover, as common materials, barium titanate, polyvinyl butyral (PVB), additives, and the like may be included for the purpose of adjusting the sintering temperature.

<Other processes>
In the present invention, the conductive paste can be produced by the dehydration step and the dilution step described above, but other steps may be included in addition to these steps. For example, in order to obtain the above-described dispersion, there are a dispersing step of dispersing metal particles in a resin or an organic solvent, and a step of dissolving a resin in an organic solvent to obtain a binder resin.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is by no means limited by these examples.

[Example 1]
A dehydration step, a dispersion step and a dilution step described below were performed to produce a conductive paste.

(Dehydration process)
30 g of zeolite (manufactured by Tosoh Corporation: A-3 type 585) as a dehydrating agent 30 was weighed into a polyethylene container 40 (capacity: 110 ml). Next, 100 g of terpineol (manufactured by Nippon Koryo Co., Ltd.) as the organic solvent 10 was weighed into another polyethylene container 20 (capacity: 110 ml). After that, put the weighed dehydrating agent 30 and the organic solvent 10 into the airtight container 50 (polypropylene resin container "Tight Box No. 2" (manufactured by Sunplatec Co., Ltd.)) without covering the polyethylene containers 20 and 40, sealed. In this state, the organic solvent 10 was allowed to stand at room temperature for 24 hours to dehydrate the organic solvent 10 . As a result of measuring the weight of the organic solvent 10 after the dehydration process, it was found that 0.4 g of the organic solvent 10 was reduced, and 0.4 g of water was removed from the organic solvent 10 .

(Dispersion process)
50 g of powdered nickel particles (average particle size: 0.3 μm) as a conductive powder, 30 g of a binder resin prepared in advance (ethyl cellulose: terpineol = 10:90 in mass ratio), and oleic acid (Kanto Kagaku Co., Ltd.) as a dispersant After rough kneading 0.5 g using a palette knife, a dispersion was prepared by passing a three-roll mill (manufactured by Buehler Co., Ltd.) 10 times at a roll temperature of 25°C ± 2°C.

(Dilution process)
Next, 20 g of terpineol dehydrated in the dehydration step was added to the dispersion to dilute it, and the mixture was stirred for 10 minutes with a stirring blade using a drilling machine at room temperature (18° C. to 24° C.) to prepare a conductive paste.

(Viscosity measurement)
The viscosity of the prepared paste was measured at room temperature (25° C.) using a rheometer (manufactured by PHYSICA: MCR501 CP25-0.5).

Table 1 shows the measurement results of the shear viscosity when the organic solvent to be dehydrated, the amount of water loss in the organic solvent during the dehydration process, and the shear rates of 0.01 s ^-1 , 0.315 s ^-1 and 1000 s ^-1 . . Examples 2 and 3 and Conventional Example 1 below are also shown in Table 1 in the same manner.

[Example 2]
The dehydration step was performed in the same manner as in Example 1, except that the organic solvent was changed to Mineral Spirit A (manufactured by JX Nikko Nisseki Energy Co., Ltd.), which is a mixed solvent of petroleum hydrocarbons. As a result of measuring the weight of the organic solvent 10 after the dehydration step, it was found that 2.8 g of water had been removed from the organic solvent 10 . Also, using this organic solvent 10, a conductive paste was prepared in the same manner as in Example 1, and the viscosity was measured.

[Example 3]
The same terpineol and mineral spirit as those used in Examples 1 and 2 were mixed at a mass ratio of 1:2.5, and 100 g of the mixed solvent was used as the organic solvent 10, and the amount of zeolite was changed to 150 g. The dehydration step was performed in the same manner as in 1. As a result of measuring the weight of the organic solvent 10 after the dehydration step, it was found that the organic solvent 10 had decreased by 2.4 g and that 2.4 g of water had been dehydrated from the organic solvent 10 . Also, using this organic solvent 10, a conductive paste was prepared in the same manner as in Example 1, and the viscosity was measured.

[Example 4]
The dehydration step was performed in the same manner as in Example 1, except that silica gel (manufactured by Toyoda Kako Co., Ltd.: model number QP (white) 10G) was used instead of zeolite. As a result of measuring the weight of the organic solvent 10 after the dehydration step, it was found that the organic solvent 10 had decreased by 1.0 g and that 1.0 g of water had been dehydrated from the organic solvent 10 . Also, using this organic solvent 10, a conductive paste was prepared in the same manner as in Example 1, and the viscosity was measured. The silica gel was used after being heat-treated at 120° C. for 2 hours in a constant temperature dryer (manufactured by ADVANTEC).

[Example 5]
The dehydration step was carried out in the same manner as in Example 2, except that silica gel heat-treated in the same manner as in Example 4 was used instead of zeolite. As a result of measuring the weight of the organic solvent 10 after the dehydration step, it was found that 3.2 g of water had been removed from the organic solvent 10 . Also, using this organic solvent 10, a conductive paste was prepared in the same manner as in Example 1, and the viscosity was measured.

[Example 6]
The dehydration step was carried out in the same manner as in Example 3, except that silica gel heat-treated in the same manner as in Example 4 was used instead of zeolite. As a result of measuring the weight of the organic solvent 10 after the dehydration step, it was found that the organic solvent 10 had decreased by 3.0 g, and that 3.0 g of water had been dehydrated from the organic solvent 10 . Also, using this organic solvent 10, a conductive paste was prepared in the same manner as in Example 1, and the viscosity was measured.

[Conventional example 1]
A paste was prepared in the same manner as in Example 3, except that a mixed solvent (terpineol and mineral spirit at a mass ratio of 1:2.5) that had not been dehydrated was used.

From the results in Table 1, the water content of the organic solvent could be dehydrated by the dehydration step using zeolite or silica gel in any of the organic solvents of Examples 1 to 6 (Examples 1 to 6). . Since the dehydration step was not performed in Conventional Example 1, the mixed solvent used in the dilution step was recognized to contain at least 2.4% by mass of water when the results of Examples 3 and 6 were developed. can.

In addition, the evaluation of the shear viscosity is based on the shear rate during storage of the conductive paste (0.001 to 0.01 s ^-1 ), the shear rate during transportation (0.01 to 1 s ^-1 ), handling, screen printing, etc. The shear rate (10 to 100000 s ^-1 ) during use is assumed (for example, Non-Patent Document 1), and representative values of each are 0.01 s ^-1 , 0.315 s ^-1 , and 1000 s ^-1 shear The shear viscosity at speed was measured.

As a result, there was no significant difference between Examples 1 to 6 and Conventional Example 1 in the shear viscosities at shear rates of 0.01 s ^-1 and 1000 s ^-1 . From this result, it was found that no significant change in viscosity due to moisture in the organic solvent was observed during storage and use, and that the conductive pastes of Examples 1 to 6 exhibited properties equivalent to conventional ones.

On the other hand, with respect to the shear viscosity at a shear rate of 0.315 s ⁻¹ , a significant difference due to the dehydration of the water content of the organic solvent was observed. That is, the conductive pastes of Examples 1 to 6 all exhibited higher shear viscosities than the conductive paste of Conventional Example 1. From this result, during transportation, the conductive paste of Conventional Example 1 floats organic components such as organic solvents, and even under conditions that require re-stirring of the conductive paste after transportation, it is possible to carry out the operation. With the conductive pastes of Examples 1 to 6, it was expected that re-stirring was not required or that re-stirring that was milder than in the past would suffice.

In addition, the content of the metal particles in the conductive pastes of Examples 1 to 6 was the same as in Conventional Example 1, and the content was not changed. and as a result does not affect the performance of the MLCC. Moreover, there is no need to review the printing conditions of the conductive paste again, and the existing conditions can be used as they are.

[summary]
As described above, according to the present invention, it is possible to easily improve the storage stability during transportation and the like without requiring expensive equipment or scale-resistant equipment and without reducing the performance of conventional conductive pastes. can be done.

10 organic solvent 20 container 30 dehydrating agent 40 container 50 airtight container

Claims (3)

A dehydration step of dehydrating water contained in the organic solvent;
a dilution step of diluting the dispersion containing the resin, the organic solvent and the metal particles in which the metal particles are dispersed, with the organic solvent dehydrated in the dehydration step;
including
The dehydration step includes a step of dehydrating the water contained in the organic solvent to be dehydrated with a dehydrating agent, the dehydration target is only the organic solvent containing water, and the dehydrating agent does not come into contact with the organic solvent.
A method for producing a conductive paste. 2. The method for producing a conductive paste according to claim 1 , wherein said dehydrating agent is at least one of calcium oxide, calcium chloride, silica gel, activated carbon, aluminum oxide, zeolite, allophane and clay minerals. 3. The method for producing a conductive paste according to claim 1, wherein said dehydrating agent is at least one of silica gel, aluminum oxide, zeolite, allophane and clay minerals.

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