JP2012003992A - Conductive paste using inorganic material slurry and method of producing the paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste that has high dispersibility and can provide a smooth dry coating film even if fine particles are used.SOLUTION: A method of producing an inorganic material slurry comprises: a first step of agitating a rough slurry composition containing at least inorganic powder, a dispersant and an organic solvent while held under the reduced pressure atmosphere of -100 mmHg to -760 mmHg relative to normal pressure so as to perform dispersion processing while defoaming, thereby producing a preprocessed kneaded substance; a second step of performing further dispersion processing to the preprocessed kneaded substance with a high pressure homogenizer to produce a slurry; and a third step of filtrating the slurry using a filter.

Description

  The present invention relates to an electrically conductive paste that has a high dispersibility even when a fine powder is used and can provide a smooth dry coating film.

  As electronic devices such as cellular phones and digital devices become lighter, thinner, and smaller, multilayer ceramic capacitors (hereinafter referred to as MLCCs) that are chip parts are also desired to be reduced in size, increased in capacity, and improved in performance. The most effective means for realizing these is to reduce the thickness of the internal electrode layer and the dielectric layer to increase the number of layers.

This MLCC is generally manufactured as follows.
First, in order to form a conductor layer, a main component is barium titanate (BaTiO ₃ ), and a dielectric green sheet composed of this and an organic binder such as polyvinyl butyral. Then, a conductive paste serving as an internal electrode dispersed in a vehicle containing a solvent is printed in a predetermined pattern and dried to remove the solvent and form a dry film. Next, the dielectric green sheets on which the dry film is formed are integrated by thermocompression bonding in a state of being stacked in multiple layers, and then cut and debindered at 500 ° C. or lower in an oxidizing atmosphere or an inert atmosphere. Thereafter, heat and baking is performed at about 1300 ° C. in a reducing atmosphere so that the internal electrode is not oxidized, and then a fired chip is applied and fired, and then nickel plating is applied to the external electrode to produce an MLCC.

  However, in this firing step, the temperature at which the dielectric ceramic powder begins to sinter is about 1200 ° C., and a considerable mismatch occurs with the temperature at which sintering and shrinkage with conductive metal powder such as nickel starts. Structural defects such as delamination (delamination) and cracks were likely to occur. In particular, as the number of layers increases or the thickness of the ceramic dielectric layer decreases as the size and capacity increase, the occurrence of structural defects becomes more prominent.

  For example, the nickel paste for internal electrodes usually has a barium titanate system similar to the composition of the dielectric layer in order to control the sintering / shrinkage at least near the temperature at which the dielectric layer starts sintering / shrinking. Alternatively, ceramic powder containing a perovskite oxide such as strontium zirconate as a main component is added. This is because if the constituent elements of the main component of the dielectric layer and the constituent elements of the dielectric powder contained in the electrode paste are greatly different, the electrical characteristics are affected, for example, the dielectric loss increases.

In recent years, MLCCs have been required to further reduce the thickness of internal electrode layers using conductive metal powders such as nickel and dielectric layers using ceramic powders such as barium titanate in accordance with demands for further miniaturization and larger capacity. Progressing. Therefore, it is necessary to atomize and highly disperse conductive metal powder such as nickel and ceramic powder used for the conductive paste.
However, as the conductive metal powder and ceramic powder become finer, the ease of agglomeration increases, so that a sufficiently dispersed conductive paste can be produced with only the shear force of the conventional three-roll method. Therefore, it was difficult to obtain a smooth dry coating film and a high dry film density.

For this reason, a technique of mechanically dispersing and pulverizing the dried and agglomerated conductive metal powder and ceramic powder with a ball mill, a bead mill or the like has been proposed as a means for sufficiently dispersing in a vehicle and a solvent (for example, Patent Document 1). Etc.)
However, in the case of the above dispersion method, there has been a problem that sufficient dispersion cannot be obtained due to overgrinding and contamination with ceramic powder and deformation with conductive metal powder.

  Recently, regarding the production of conductive paste using a high-pressure homogenizer, a mixture containing at least dry agglomerated fine conductive metal powder and ceramic powder, vehicle, organic solvent, and dispersant is premixed, and the mixture is mixed with a high-pressure homogenizer. It has been shown that dispersion treatment of the contained powder is possible by using and processing (see, for example, Patent Documents 2 and 3).

By the way, the general dispersion process of inorganic powder is:
(1) “Wetting” of the inorganic powder, that is, a process in which air existing in the secondary particle surface and in the voids in the secondary particle is replaced by a solvent and a dispersant;
(2) A process in which secondary particles are dispersed and pulverized by a disperser,
(3) It includes three processes: a process in which a dispersant is adsorbed on the surface of dispersed and pulverized particles, and “re-aggregation prevention” of the particles is performed.
If these dispersion processes do not work well, it will greatly affect the dispersibility of the inorganic powder, resulting in a “filter increase in production time due to longer filter filtration time” and a smooth coating film of conductive paste and high drying. Since it becomes difficult to obtain the film density, disadvantages such as “degradation of paste coating quality” occur.

  In addition, in the process of “wetting”, “dama” or “bubble” entrainment occurs when the mixture containing at least the conductive metal powder, the organic solvent, and the dispersant is simply stirred at high speed (premix). Even if the “wetting” of the particle surface occurs, the “wetting” of the primary particle surface inside the secondary particle becomes insufficient, and the above problem is not improved. Furthermore, even if power is applied more than necessary to suppress the generation of bubbles, it is difficult to remove submicron to several micron bubbles generated or present in the material. From the above, it is important to make full use of the high-pressure homogenizer in the pretreatment process and the post-dispersion process that can solve the “wetting” of the primary particle surface without generating “dama” and “bubbles”. .

  However, with regard to improving the "wetting" of the primary particle surface and improving the dispersion treatment efficiency and dispersibility of the mixture by the high-pressure homogenizer, the above-mentioned "Production cost reduction such as shortening of filter filtration time" and "Smooth conductive paste" No special ingenuity has been made for “quality improvement such as realizing a coating film”.

JP 2006-156204 A JP 1999-99514 A JP 2005-104070 A

The present inventor found from the following examination results that three points of “stirring atmosphere”, “stirring method”, and “defoaming” are important factors in the pretreatment process as measures for improving such problems. .
(A) In the “pretreatment dispersion method of degassing under reduced pressure after high-speed stirring under atmospheric pressure”, the bubbles in the processed product cannot be removed simply by high-speed stirring. As a result, problems such as an increase in filter processing time and a failure to obtain a smooth conductive paste coating film arise. Furthermore, even when the pretreated product is simply degassed under reduced pressure, there is a problem in that the paste must be left for a long time until the bubbles are removed, which does not lead to a reduction in production cost. For example, when a bubble is exposed to a vacuum pressure of 1/760 of atmospheric pressure, the bubble expands to about 760 times its volume under atmospheric pressure. Although it can be easily degassed, if the stirring operation is not performed simultaneously, a large convection does not occur in the mixture, so that the bubbles cannot be removed efficiently.

(B) In the “pretreatment dispersion method in which high-speed stirring is performed in a reduced-pressure atmosphere”, centrifugal force is small in high-speed stirring rotating only in one direction at a constant speed, and unevenness (residual portion) occurs in stirring of the processed material. In addition, these methods alone make it difficult to remove submicron to several micron bubbles generated or present in the material, so that wetting of the conductive metal powder and ceramic powder is insufficient, the processing time of the filter, Problems arise in the smoothness of the conductive paste coating film.

  In view of the above problems, the present invention holds in a pre-treatment step in which a mixture of at least an inorganic material powder, a dispersant, and an organic solvent is dispersed by a high-pressure homogenizer, and is held in a reduced-pressure atmosphere so that the rotation direction is in addition to the revolution direction By stirring while rotating, the centrifugal force increases, and the entire mixture is convected uniformly. Accordingly, no stagnation occurs and no bubbles are generated, so that the “wetting” process proceeds smoothly.

  By adding this pretreatment step, “nozzle clogging” is eliminated in the dispersion step in the high-pressure homogenizer, or “wetting” of the primary particle surface is improved, and the dispersant is adsorbed on the particle surface in the dispersion treatment step. Since the particles can be prevented from being “re-agglomerated”, the time for filtering the slurry with a filter can be shortened. In addition, it is expected to improve the smoothness of the dry coating film and the dry film density in order to give high dispersibility to conductive metal powders and ceramic powders miniaturized to make multilayer ceramic electronic parts smaller and thinner. It is possible to provide a conductive paste that can be produced.

  As described above, the present invention provides a conductive paste that is optimal for ceramic electronic components that can provide a smooth dry coating film because of its high dispersibility even when a fine powder is used.

1st invention of this invention is a manufacturing method of the inorganic material slurry characterized by having the following 1st process-3rd process.
First step: While performing defoaming by holding and stirring a crude slurry composition containing at least an inorganic material powder, a dispersant and an organic solvent in a reduced pressure atmosphere of −100 mmHg to −760 mmHg based on normal pressure The process of forming a pre-processed kneaded material by carrying out a dispersion process.
Second step: A step of preparing a slurry by further dispersing the pre-processed kneaded material prepared in the first step with a high-pressure homogenizer.
Third step: A step of filtering the slurry produced in the second step using a filter.

According to a second aspect of the present invention, there is provided a conductive paste comprising the inorganic material slurry, vehicle and organic solvent according to the first aspect.
Furthermore, the conductive metal powder in the inorganic powder constituting the inorganic material slurry has a content of 30 to 70% by mass with respect to the total amount of the conductive paste.

  According to the present invention, even a slurry using a fine powder has an effect of improving the dispersibility of the fine powder. Therefore, a smooth dry coating film can be easily obtained, and a conductive paste suitable for a multilayer ceramic electronic component that is required to be small and thin can be provided.

  The conductive paste for forming internal electrodes of a multilayer ceramic capacitor according to the present invention is characterized by a paste in which conductive metal powder and ceramic powder are dispersed in a vehicle in which a binder is dissolved in a solvent. For that purpose, it is necessary to be a paste in which fine conductive powder and ceramic powder are sufficiently dispersed. Therefore, in the present invention, the conductive component of the conductive paste is supplied by the slurry in which the conductive component is sufficiently dispersed, and the manufacturing process of the slurry requires the following three steps.

[First step]
In the first step of slurry production in the present invention, a crude slurry composition containing an inorganic material powder, a dispersant and an organic solvent is held in a reduced-pressure atmosphere, and defoamed by stirring while rotating in the rotation and revolution directions. While being dispersed, a pretreated kneaded product is formed.

By rotating and revolving in this reduced pressure atmosphere, fluidity is generated in the material itself, and a large centrifugal force is applied to cause vertical convection in the kneaded material inside the container. By efficiently using this force, the kneaded product is stirred, and by adding a reduced-pressure atmosphere, bubbles on the bottom surface and wall surface of the container rise to the top surface due to strong fluidity, thereby removing submicron bubbles. Moreover, since rotation of rotation and revolution can be controlled separately according to the viscosity of the kneaded material, it is also effective as a measure for raising the temperature.
As such a rotation and revolution stirring device, for example, a dispersion / kneading device such as “TK Hibis Disper Mix” manufactured by PRIMIX Corporation is used.

As the rotation speed in the rotation and revolution directions in the present invention, the rotation speed in the rotation direction is preferably 1000 rpm / min or more, and the rotation speed in the revolution direction is preferably 10 rpm / min or more.
If the rotation speed in the rotation direction is less than 1000 rpm / min, the force that creates the flow in the vertical direction (height) in the container becomes weak, and the bubbles may not be able to move to the upper surface. Moreover, when the rotation speed in the revolution direction is less than 10 rpm / minute, the fluidity is lowered and only a small centrifugal force can be obtained, so that sufficient stirring cannot be performed.

The pressure in a reduced-pressure atmosphere for performing the kneading treatment is preferably −760 mmHg or more and −100 mmHg or less. The value of the pressure is displayed on the basis of the normal pressure with the atmospheric pressure set to 0 mmHg.
Bubbles are released from the solvent and the solvent components are evaporated at the same time. However, when it is -100 mmHg or less, the bubbles can be effectively expanded and discharged while suppressing the evaporation of the solvent. On the other hand, when kneading without a reduced pressure environment, bubbles separated from the material may be crushed and become smaller and cannot be removed from the solvent.

[Second step]
The second step of slurry production in the present invention is a step of further dispersing the pretreated kneaded product obtained in the first step with a high-pressure homogenizer. The high-pressure homogenizer generally pressurizes a raw material to a high pressure or an ultrahigh pressure, and performs pulverization, dispersion, and emulsification using a shearing force when exiting an orifice.
This high-pressure homogenizer includes a dispersion method in which a jet flow ejected from an orifice collides with a wall, a dispersion method in which jet flows ejected from an orifice collide with each other, and a jet flow (processed product) ejected from an orifice is the next orifice By colliding with a back-pressure treated material that has accumulated due to subsequent resistance, a speed change is generated, force is applied, and the process proceeds to the next orifice. can give. Examples thereof include a microfluidizer (manufactured by Microfluidics), a nanomizer (manufactured by Yoshida Kikai Kogyo Co., Ltd.), an optimizer (manufactured by Sugino Machine Co., Ltd.), and Nano3000 (manufactured by Miebu Co., Ltd.).

  As for the processing conditions by the high-pressure homogenizer in the present invention, the processing pressure is preferably 50 to 300 MPa, and more preferably 100 to 250 MPa. When the processing pressure is less than 50 MPa, the speed of the jet flow ejected from the orifice is insufficient, and the energy applied to the processed material is weak, resulting in poor dispersion. The reason why the pressure is 300 MPa or less is that it is preferable from the viewpoint of suppressing wear of the members of the disperser and withstanding long-term use.

  Further, the high-pressure homogenizer is characterized in that a fine orifice is used to generate a high-speed jet flow. Therefore, the orifice diameter is preferably about 0.03 to 0.5 mm in view of productivity and the efficiency of the apparatus, and the shape is preferably a straight line that does not have a curved portion or a bent portion and is difficult to wear. Furthermore, examples of the material for forming the orifice include diamond such as sintered diamond and single crystal diamond, ceramic materials such as alumina, zirconia, and carborundum, and metals such as stainless steel, iron, and titanium. A material excellent in abrasion is preferred.

Here, the faster the passage speed in the orifice of the slurry, the greater the shearing force, and the particle size of the particles can be made finer, but if the particle size of the particles becomes too small, aggregation tends to occur. In order to maintain the particles at an appropriate particle size, it is necessary to adjust the speed of the slurry passing through the orifice so that the stress applied to the slurry is optimal in the orifice and in the space after passing through the orifice.
This passage speed can be adjusted by selecting conditions such as orifice diameter and processing pressure. The passage speed of the slurry orifice is set in the range of 100 to 1000 m / sec, more preferably in the range of 400 to 800 m / sec. By adjusting, the particles can be maintained at an appropriate fine particle size.

  In addition, the slurry can be manufactured while applying back pressure in order to prevent collision of the slurry with the inner wall of the space after passing through the orifice and generation of bubbles that cause uneven shearing force. Further, when the slurry temperature is increased, the stability of the particles is lowered and problems such as re-aggregation occur, which is not preferable. Therefore, it is preferable to equip a cooling device in order to prevent an increase in the slurry temperature. Furthermore, the number of dispersion passes in the high-pressure homogenizer can be appropriately selected depending on the required particle size, particle size distribution, and the like. In addition, it is preferable to perform the number of times of the dispersion pass by a device configuration that circulates slurry.

[Third step]
Next, the slurry obtained by dispersing with a high-pressure homogenizer is filtered.
As the condition, it is desirable to filter with a filter having 99% cut filtration accuracy and an opening of 5 μm or less. When a filter with an opening exceeding 5 μm is used, inorganic non-dispersed materials and coarse particles cannot be removed, and if a substance larger than the thickness of the dielectric layer is mixed, protrusions are generated on the paste coating surface. Therefore, the smoothness decreases. Therefore, a conductive paste excellent in smoothness cannot be obtained.

  In particular, the conductive metal slurry having a high concentration and high specific gravity in the present invention has a problem that clogging occurs earlier when the filter is filtered after a long time after the dispersion treatment by the high-pressure homogenizer. In the process, filter filtration is performed immediately after the dispersion treatment with a high-pressure homogenizer and immediately before the removal.

  In addition, filtering with a filter having a 99% cut filtration accuracy and an opening of 5 μm or less means that 99% or more of particles having a size of 5 μm or more are captured. For example, a single pass test based on seven kinds of JIS z 8901 regulation test powder (5 mg / L dispersion, 10 L / min) can be mentioned. Further, examples of the filter medium include metals, PTFE, and polypropylene, but are not limited thereto. Furthermore, examples of the filter structure used here include a membrane type, a pleat type, and a depth type, but are not limited thereto.

[Conductive paste]
In the present invention, in order to obtain a conductive paste that improves the smoothness of the dry coating film and the dry film density, it is preferable to use a fine powder having a nickel particle size of 0.5 μm or less.
Coarse particles may be formed by aggregation in the nickel powder. When the particle size of the nickel powder exceeds 0.5 μm, the film formability when the paste layer is thinned is deteriorated, and a predetermined capacitance is obtained. In addition to the absence, the probability of inclusion of coarse particles increases, and a failure in which the breakdown voltage (BDV) decreases is likely to occur. Further, if an electrode film that can be used for thinning is formed, the dry film has insufficient smoothness and is insufficiently filled with nickel powder particles, and a desired dry film density cannot be ensured.

On the other hand, the reason why the particle size of the nickel powder is 0.5 μm or less is that it is essential for forming an electrode film having excellent continuity in thinning the multilayer capacitor. Furthermore, when the particle size is less than 0.03 μm, the specific surface area of the particles becomes too large, the surface activity of the metal particles becomes too high, and not only adversely affects drying and debinding properties, but also proper viscosity characteristics are obtained. Otherwise, there is a risk of deterioration during long-term storage of the conductive paste.
In the present invention, the particle size of the nickel powder is a particle size obtained by calculating the specific surface area based on the BET method unless otherwise specified. The calculation formula is shown in Equation 1.

  The ratio of the conductive metal particles in the conductive paste of the present invention is preferably 30 to 70% by mass. If the conductive metal particles are less than 30% by mass, the thickness of the electrode after firing becomes extremely thin and the resistance value increases, or the electrode film is insufficiently formed and loses conductivity, and the desired capacitance cannot be obtained. There is a case. If it exceeds 70% by mass, it is difficult to make the electrode film thinner. The conductive metal powder is more preferably 40 to 60% by mass with respect to the entire paste.

The ceramic powder contained in the conductive paste can be selected because BaTiO ₃ which is usually a perovskite type oxide and various additives are added thereto. Moreover, the same composition as the ceramic powder used as a main component of the dielectric layer green sheet for MLCC, or a similar composition is also preferable.

There are various methods for producing ceramic powder, such as solid phase method, hydrothermal synthesis method, alkoxide method, sol-gel method, etc. Especially, hydrothermal synthesis method can be used in the present invention because a fine and sharp particle size distribution can be obtained. The ceramic powder is preferable.
If necessary, the ceramic powder can be added as a sintering inhibitor to a ceramic paste that has been dispersed and pulverized by a device such as a bead mill or a high-pressure homogenizer.

  The ceramic powder preferably has a particle size in the range of 0.01 to 0.2 μm. When the particle size of the ceramic powder exceeds 0.2 μm, the dry film density decreases. In the dry film, since the ceramic powder is filled in the gap formed by stacking the substantially spherical nickel powder particles, when the particle size of the ceramic powder exceeds 0.2 μm, the contact point between the substantially spherical nickel powder particles is between Since it becomes difficult to enter, the desired dry film density cannot be obtained, and the effect of delaying the sintering start temperature of the conductive paste to the sintering start temperature of the ceramic layer is limited.

  On the other hand, when the particle size of the ceramic powder is less than 0.01 μm, the sintering delay effect of the conductive paste becomes difficult, and structural defects such as delamination and cracks occur. Furthermore, it is difficult to reduce the thickness of the dielectric layer due to the decrease in the dry film density and the agglomerated powder of the ceramic powder described above, and the reliability of the capacitor (such as a decrease in insulation resistance and an increase in the short-circuit rate) deteriorates. A problem occurs.

  In the present invention, the particle size of the ceramic powder is a particle size obtained by calculating the specific surface area based on the BET method unless otherwise specified. The calculation formula is shown in Equation 2.

  As the organic solvent used in the present invention, terpineol (α, β, γ and a mixture thereof), dihydroterpineol, octanol, decanol, tridecanol, butyl carbitol, butyl carbitol acetate, dipropylene glycol monomethyl ether, or the like may be used. it can. In order to adjust the viscosity, aromatic hydrocarbons or aliphatic hydrocarbons are used as a diluent for the paste. Such diluents are used to control the drying rate after paste printing and to impart moderate viscosity characteristics to the paste.

Furthermore, examples of the binder resin for the conductive paste include organic resins such as ethyl cellulose, nitrocellulose, acrylic, and polyvinyl butyral, and one or more of these are selected. The molecular weight is based on the premise that the molecular weight is soluble in the solvent, but a resin having a molecular weight of 20,000 to 200,000 is preferably used.
The amount of the binder resin in the paste is desirably 1.0 to 5.0 wt%, and more preferably 2.0 to 4.0 wt%. If it is less than 1.0 wt%, it is difficult to obtain a viscosity suitable for screen printing, and if it exceeds 5.0 wt%, the amount of residual carbon increases at the time of binder removal, which causes delamination of the laminated chip, which is not preferable.

  The dispersant in the present invention is not particularly limited, and conductive metal powders and ceramic powders such as cationic dispersants, anionic dispersants, nonionic dispersants, amphoteric surfactants, and polymeric dispersants can be used. Any dispersing agent that can be stably dispersed in a finely divided state in a binder and an organic solvent may be used, and a known dispersing agent can be used. Among these, anionic dispersants are preferable, and examples thereof include carboxylic acid dispersants, phosphoric acid dispersants, and phosphate dispersants. These dispersants may be used alone or in combination of two or more. Anionic dispersants have a high adsorptive power to inorganic surfaces, and thus contribute to increasing the dispersibility of inorganic components by their surface modification action, resulting in improved coating smoothness and dry film density. is there.

The average molecular weight of the anionic dispersant is preferably 200 to 20000. More preferably, it is 300-10000. If this average molecular weight is less than 200, the particles may not have sufficient electrostatic repulsion, and the dispersibility and storage stability of the particles may be reduced. Usually, a dispersing agent is adsorbed on the particle surface to form an adsorbing layer of the dispersing agent, and an electrostatic repulsive force or a three-dimensional repulsive force is imparted to the particles, whereby a paste having excellent dispersibility can be obtained.
However, the average molecular weight is preferably 200 or more because it is considered that particles collide with each other over the electrostatic repulsion force of the adsorption layer due to the collision of the particles with time. On the other hand, if the molecular weight is larger than 20000, the compatibility with the vehicle and the solvent may be reduced, the particles may be aggregated, and the dispersibility and storage stability may be reduced. Furthermore, the problem that a paste viscosity becomes high also arises.

  Here, the addition amount of the anionic dispersant is, for example, preferably 0.01 to 2.00 parts by mass, and 0.30 to 1.00 with respect to 100 parts by mass of the inorganic content, relative to the conductive metal powder. Part by mass is more preferable. If the surfactant is less than 0.01 parts by mass, sufficient dispersibility tends to be difficult to obtain. On the other hand, when it exceeds 2.00 parts by mass, the drying property is deteriorated, and the problem that the density of the dried film is lowered is caused.

The content of the ceramic powder is desirably 3 to 25 parts by mass with respect to 100 parts by mass of the conductive metal powder. More desirably, it is 5 to 15 parts by mass with respect to 100 parts by mass of the conductive metal powder.
When the content of the ceramic powder is less than 3 parts by mass, for example, the sintering of the nickel powder cannot be controlled, the mismatch of the sintering shrinkage behavior of the internal electrode layer and the dielectric layer becomes significant, and the internal electrode is sintered. Since it starts from a low temperature and the difference in sintering temperature between the internal electrode layer and the dielectric layer becomes large, firing cracks are generated. On the other hand, when the content of the ceramic powder exceeds 25 parts by mass, the thickness of the dielectric layer expands due to, for example, sintering from the internal electrode layer to the ceramic particles in the dielectric layer, resulting in a composition shift. It adversely affects electrical characteristics such as rate reduction.

  Hereinafter, the present invention will be described in detail based on more specific examples. The scope of the present invention is not limited by the examples.

1. Production of inorganic material slurry (production of nickel slurry)
A crude slurry composition in which nickel powder (particle size: 0.3 μm) is 85 wt%, an organic solvent is 14.5 wt%, and an anionic dispersant is 0.5 wt% is held in a reduced-pressure atmosphere having a pressure of −650 mmHg. A pretreatment dispersion was carried out by stirring and defoaming while rotating at 2500 rpm / min in the rotation direction and 25 rpm / min in the revolution direction to form a pretreatment kneaded product. Next, the obtained pre-processed kneaded product was subjected to a high-pressure homogenizer with a processing pressure of 200 MPa, a diamond orifice diameter of 0.1 mm, and a processing frequency of 5 times to prepare a nickel slurry. This nickel slurry was filtered through a depth type filter having an opening of 2.0 μm to obtain a final nickel slurry.

2. Production of conductive paste The nickel content contained in the nickel slurry produced by the production of the inorganic material slurry is 50 wt%, the vehicle is 3.5 wt%, the anionic dispersant is 0.5 wt%, and the terpineol is 46 wt%. Each component was mixed so as to be kneaded with three rolls to prepare a conductive paste. The vehicle consisted of 9% by weight of ethyl cellulose as a resin component and 91% of terpineol as an organic solvent, and was prepared by heating. The particle size distribution of the produced conductive paste and the surface roughness Rz of the dried film by the conductive paste were measured by the following measuring method. The results are shown in Table 1.

[Evaluation characteristics and evaluation method]
(A) Particle size distribution In order to compare the final dispersibility of nickel slurries with different pretreatment methods, the particle size distribution D50 of the slurry immediately before the above-mentioned filter treatment was measured.
The particle size distribution was measured with a Microtrack manufactured by Nikkiso Co., Ltd.
The reason why the particle size distributions are compared before the filter treatment is to prevent the influence of the difference in the pretreatment stirring conditions on the dispersibility of the nickel powder from being discriminated by the filter treatment. The difference in particle size distribution before the filter treatment affects the filtration efficiency of the filter and the degree of clogging. That is, the larger the particle size distribution, the longer the filtration time and the more clogging occurs.

(B) Dry film surface roughness: Rz
A nickel paste manufactured using a nickel slurry with a different pretreatment method is applied onto a glass substrate using an applicator (gap thickness 10 μm), and then dried in air at 120 ° C. for 5 minutes to produce a dry film. Then, the dry film was measured using a surface roughness meter (device name: SURFCOM 551A, pickup: stylus 10 μmR, diamond 90 ° cone), Cut-off: 1.6 mm, measurement range 3.0 mm, measurement speed: 0.6 mm 10-point average roughness (Rz) was measured under the conditions of / sec.

(Comparative Example 1A)
A crude slurry composition in which nickel powder (particle size: 0.3 μm) is 85 wt%, organic solvent is 14.5 wt%, anionic dispersant is 0.5 wt%, and the pressure in a reduced-pressure atmosphere is maintained at −80 mmHg. A pretreatment dispersion was performed by stirring and defoaming while rotating at 2500 rpm / min in the rotation direction and 25 rpm / min in the revolution direction to form a pretreatment kneaded product. Next, a nickel slurry was prepared by performing a high-pressure homogenizer on the pre-processed kneaded material obtained under the conditions of a processing pressure of 200 MPa, a diamond orifice diameter of 0.1 mm, and a processing frequency of 5 times. This nickel slurry was filtered through a depth type filter having an opening of 2.0 μm to obtain a final nickel slurry.
Next, a conductive paste was produced in the same manner as in Example 1.
The characteristics were evaluated using the conductive paste, and the results are shown in Table 1 as in Example 1.

(Comparative Example 1B)
A rough slurry composition in which nickel powder (particle size: 0.3 μm) was 85 wt%, terpineol was 14.5 wt%, and an anionic dispersant was 0.5 wt% was subjected to pretreatment dispersion by stirring at high speed under normal pressure. .
Next, a conductive paste was produced in the same manner as in Example 1.
The characteristics were evaluated using the conductive paste, and the results are shown in Table 1 as in Example 1.

As shown in Table 1, after stirring in the direction of rotation and revolution in a reduced-pressure atmosphere as pretreatment conditions, the nickel slurry produced by the high-pressure homogenizer (see Example 1) was produced through pretreatment conditions of only high-speed stirring. Compared to nickel slurry (see Comparative Example 1B), the D50 value is about 13% smaller. This shows that the difference in pretreatment conditions improves the wetting of the nickel surface, and the dispersion efficiency by the high-pressure homogenizer in the post-process improves, resulting in a difference in the dispersibility of the Ni powder.
Furthermore, even when the pretreatment kneading conditions are the same under reduced pressure, the D50 value is about 11 even when compared with nickel slurry (see Comparative Example 1A) produced under conditions where the amount of reduced pressure is small and out of the scope of the present invention. % Is smaller.

Furthermore, by stirring in the direction of rotation and revolution in a reduced pressure atmosphere as a pretreatment condition, the Rz value of the nickel paste dry film is improved by about 38% compared to the pretreatment condition of only high-speed stirring (see Comparative Example 1B). It can be seen that a smooth dry film is obtained. This is because the wettability of the particles is improved during the pretreatment and the dispersibility is improved.
Also, the Rz value of the dried film is lower than that of nickel slurry (see Comparative Example 1A) prepared under the same pretreatment kneading conditions under the same reduced pressure but with a reduced amount of reduced pressure and out of the scope of the present invention. It can be seen that is improved by about 32%.

1. Preparation of Ceramic Slurry A crude slurry composition containing 40 wt% ceramic powder (particle size: 0.03 μm), 59 wt% organic solvent, and 1.0 wt% anionic dispersant is maintained at -650 mmHg under reduced pressure. Then, pretreatment dispersion is performed by stirring and degassing while rotating at 2000 rpm / min in the rotation direction and 20 rpm / min in the revolution direction to form a pretreatment kneaded product. Subsequently, the obtained pre-processed kneaded material was processed using the above-described high-pressure homogenizer under the conditions of a processing pressure of 200 MPa, a diamond orifice diameter of 0.1 mm, and a processing frequency of 10 times to obtain a ceramic slurry. The obtained ceramic slurry was filtered through a membrane filter having an opening of 0.8 μm to obtain a final ceramic slurry.

2. Preparation of nickel paste Ceramic slurry in an amount of 4.7 wt% of ceramic powder (particle size: 0.03 μm) contained in the prepared ceramic slurry and 47 wt% of nickel powder (particle size: 0.2 μm) %, Vehicle 2.8 wt%, anionic dispersant 0.5 wt%, and terpineol 45 wt%, and kneaded with three rolls. The vehicle was a vehicle made of 9% by weight of ethyl cellulose as a resin component and 91% of terpineol as an organic solvent and heated.
The nickel slurry was filtered through a depth type filter having an opening of 1.0 μm to produce a final nickel slurry, and a nickel paste as a conductive paste was produced in the same manner as in Example 1.
The surface roughness Ra and dry film density (DFD) of the dry film by the nickel paste were measured by the following measurement method, and the results are shown in Table 2.

  A nickel paste was prepared under the same conditions as in Example 2 except that the orifice diameter was 0.01 mm and the number of treatments was 20 in the ceramic slurry production, except that the orifice diameter was 0.01 mm and the number of treatments was 20. The surface roughness Ra and the dry film density ( DFD) was measured and the results are shown in Table 2.

  A nickel paste was prepared under the same conditions as in Example 2 except that the orifice diameter was 0.06 mm and the number of treatments was 20 in the ceramic slurry production, except that the orifice diameter was 0.06 mm and the number of treatments was 20. The surface roughness Ra and the dry film density ( DFD) was measured and the results are shown in Table 2.

(Comparative Example 2)
A crude slurry composition containing 40 wt% ceramic powder (particle size: 0.03 μm), 59 wt% organic solvent, and 1.0 wt% anionic dispersant was stirred at high speed under normal pressure, and then the same conditions as in Example 2 A ceramic slurry was prepared by pre-dispersing with.
Next, in the same manner as in Example 2, a nickel paste was prepared, and the surface roughness Ra and the dry film density (DFD) were measured. The results are shown in Table 2.

(Comparative Example 3)
The coarse slurry composition of Comparative Example 2 was stirred at high speed under normal pressure, and then without pretreatment dispersion, the nickel powder (particle size: 0.2 μm) was 47 wt% and the ceramic powder (particle size: 0.03 μm). A ceramic slurry was prepared so as to have a component composition of 4.7 wt%, vehicle A 2.8 wt%, anionic dispersant 0.5 wt%, and terpineol 45 wt%, and kneaded with three rolls. Vehicle A was a vehicle made of 9% by weight of ethyl cellulose as a resin component and 91% of terpineol as an organic solvent and heated.

[Evaluation characteristics and evaluation method]
(C) Measurement of non-contact type surface roughness Ra The measuring method of the average surface roughness in this invention used the following method.
A nickel paste is applied onto a glass substrate using an applicator (gap thickness 5 μm), and then dried in air at 120 ° C. for 5 minutes to obtain a dry film having a thickness of about 3 μm. Next, the protrusion on the surface of the dried film is measured by an optical method, that is, a phase shift interference method.
Specifically, the sample and the reference mirror are irradiated with light from a light source limited to a specific wavelength region, and the surface state is observed by interference fringes of the light irradiated on the sample and the reference mirror. Furthermore, the surface state is observed from the interference fringes of the light by moving the sample in the direction in which the light is irradiated every quarter wavelength. For example, the average roughness of the dried film can be measured using an optical interference type surface shape measuring device (NT-1100 manufactured by WYCO). The number of measurements is three.

(D) Measurement of dry film density (DFD) The dry film density is measured by printing the paste on a PET film so as to have a film thickness of 30 μm in an area of 5 cm × 10 cm, and then drying in air at 120 ° C. for 40 minutes. The dried nickel paste dry film was cut into 1 × 1 cm, the thickness and mass were measured, and the dry film density was calculated according to the following equation (3). The number of measurements was 15 places, and the average value of the obtained film densities was taken as the film density of the conductive paste.

The dry film density is measured by printing a conductive paste on a PET film, but it goes without saying that the same characteristics are exhibited even when the conductive paste of the present invention is printed on a dielectric layer green sheet.
Here, the dry film density is the density after the conductive paste is dried.

  In Comparative Example 3 dispersed with a conventional three roll, the dry film density is as low as 5.1 and fine ceramic powder cannot be dispersed, but in Comparative Example 2 dispersed by a high-pressure homogenizer, the dry film density is 5.4. Improved. In Example 2, which incorporated a rotation and revolution vacuum stirring step as a pretreatment of the dispersion step shown in Comparative Example 2, the Ra value was reduced by about 15% due to improved wettability of the particles, and the dry film density was It showed a high value of 5.6. Further, in Example 3 in which the number of passes through the orifice was 20, the Ra value and the dry film density were further improved. Furthermore, as shown in Example 4, when the orifice diameter was reduced to 0.06 mm, the dry film density showed a higher value of 5.9, 15% for Comparative Example 3 and 15% for Comparative Example 2. 10% improvement.

  From the above results, after adding the pretreatment step by rotation and revolution vacuum stirring, the number of passes, orifice diameter, etc. are examined and dispersed with a high pressure homogenizer, so that treatment with a conventional three-roll or normal high pressure homogenizer In this case, the smoothness of the paste coating film and the filling property of the particles were improved due to the improvement of the dispersibility that could not be realized in the above.

Claims (3)

A method of manufacturing an inorganic material slurry,
It has the following 3rd process from the 1st process.
[First step]
A crude slurry composition containing at least an inorganic powder, a dispersant, and an organic solvent is dispersed and treated while degassing by holding and stirring in a reduced pressure atmosphere of −100 mmHg to −760 mmHg based on normal pressure. A step of forming a processed kneaded product.
[Second step]
A step of further dispersing the pre-processed kneaded product with a high-pressure homogenizer to produce a slurry.
[Third step]
Filtering the slurry using a filter. A conductive paste containing an inorganic material slurry, vehicle, organic solvent,
The inorganic material slurry is formed by the inorganic material slurry manufacturing method according to claim 1.   The conductive paste according to claim 2, wherein the conductive metal powder in the inorganic powder constituting the inorganic material slurry has a content of 30 to 70 mass% with respect to the total amount of the conductive paste.