JP5975824B2 - Conductive composition - Google Patents

Description

  The present invention relates to a conductive composition comprising conductive particles, glass frit and a resin binder.

  Since copper or silver is a material having high electrical conductivity, it is useful as a conductive material for electrical conduction between electrodes. For example, it is used in the form of conductive powder or conductive paste formed by adding glass frit, resin binder, etc. to this, and is used for forming fine wiring by means of screen printing, dispensing, ink jet printing or the like. In order to form fine wiring, it is advantageous to reduce the particle size of these particles. However, since copper is a metal that is easily oxidized, if the particle size of the particles is reduced, the oxidation is more likely to proceed, and as a result, the electrical conductivity tends to decrease. On the other hand, silver has a problem that it tends to cause migration.

  In view of this, there has been proposed a particle in which a coating layer is provided on the surface of copper particles or silver particles to improve oxidation resistance and migration resistance. For example, Patent Document 1 proposes a composite copper fine powder in which at least one selected from the group consisting of an oxide containing at least one metal element and a composite oxide is fixed to the surface of the metal copper fine particles. . Examples of the oxide and composite oxide include alumina, silica, yttria, barium titanate, titania, magnesia and the like.

Apart from the above-described technology, Patent Document 2 discloses a zinc oxide particle having a specific surface area of 6 m ² / g or less in an electrode paste for a solar cell containing conductive particles, a lead-free glass frit, a resin binder, and zinc oxide particles. Is contained in an amount of 10% by weight or more based on the total amount of zinc oxide. This document describes that the paste has improved sintering characteristics at high temperatures by using zinc oxide particles having a small specific surface area, that is, a large particle size.

JP 2000-345201 A Special table 2011-501444 gazette

  When a conductive paste is produced using the composite copper particle powder described in Patent Document 1 as a raw material, when the conductive paste is applied to an object and then sintered, the molten glass frit becomes conductive particles. In some cases, the distance between the conductive particles increases and the electrical resistance increases. In addition, cracks may occur in the cooled state after sintering, which may reduce the conductivity. The problem of wetting and spreading of the glass frit melted at the time of sintering may also occur at the pace described in Patent Document 2.

  Therefore, the subject of this invention is providing the electroconductive composition which can eliminate the various fault which the prior art mentioned above has.

The present invention relates to a conductive composition comprising conductive particles, glass frit and a resin binder.
The conductive particles have core particles whose base material is a metal, and a coating layer composed of a plurality of inorganic oxide particles disposed on the surface of the core particles,
The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles is 0.1 to 20 μm , and the particle diameter of the inorganic oxide particles measured by microscopic observation is the volume cumulative of the conductive particles. 20% or less of the particle size D ₅₀ ,
Inorganic oxide constituting the inorganic oxide particles possess the glass frit compatible,
That the inorganic oxide particles are compatible with the glass frit means that the conductive composition is fired in an atmosphere of 1% by volume hydrogen and 99% by volume nitrogen at 1000 ° C. for 60 minutes. And providing a conductive composition in which no granular feeling derived from the glass frit is observed on the surface of the conductor when the conductor is observed with a microscope at a magnification of 5,000 to 10,000 times. It is.

  According to the present invention, since the coating layer of the inorganic oxide particles having good compatibility with the glass frit is formed on the surface of the conductive particles, the molten glass frit is formed during the sintering of the conductive composition. As a result, it becomes difficult to spread and spread on the surface of the conductive particles, and as a result, an increase in the electrical resistance of the conductor obtained by sintering is effectively suppressed without adversely affecting the heat shrinkage starting temperature of the conductive particles.

1 is a scanning electron microscope image of a conductor obtained using the conductive paste obtained in Example 1. FIG. 2A to 2D are scanning electron microscope images of conductors obtained using the conductive pastes obtained in Comparative Examples 1 to 4, respectively.

  The conductive composition of the present invention contains conductive particles, glass frit and a resin binder as its constituent components. As a glass frit, the thing similar to what was conventionally used in the technical field of an electroconductive composition can be used. Glass frit is generally classified into leaded glass frit that does not contain lead and lead-free glass frit that does not contain lead. In the present invention, either leaded or lead-free glass frit may be used. Use of the leaded glass frit has an advantage that the sintering property of the conductive composition is improved. On the other hand, the lead-free glass frit has an advantage that the environmental load is reduced.

Examples of the leaded glass frit include PbO · SiO ₂ , PbO · B ₂ O ₃ , PbO · SiO ₂ · B ₂ O ₃ , ZnO · PbO, ZnO · PbO · B ₂ O _{3 and the} like. It is done. Meanwhile, as the lead-free glass frit, for example, _{SiO 2 · B 2 O 3 ·} Al 2 O 3, Bi 2 O 3 · B 2 O 3, Bi 2 O 3 · ZnO, Bi 2 O 3 · B 2 O 3 · ZnO SiO ₂ · ZnO · RO (R represents an alkaline earth metal), ZnO · B ₂ O ₃ · SiO ₂ (zinc borosilicate glass), and the like.

  The glass frit preferably has a softening point of 400 ° C to 600 ° C. Excessive sintering can be effectively suppressed because a softening point is 400 degreeC or more. On the other hand, when the softening point is 600 ° C. or lower, sufficient melt flow occurs during sintering, and thus sufficient adhesive strength is exhibited. The softening point is measured according to ASTM C338-57 fiber elongation method.

  As the resin binder which is another component of the conductive composition, the same resin binders conventionally used in the technical field of conductive compositions can be used. Epoxy resins are generally used as resin binders, but polyester resins, urethane resins, silicone resins, acrylic resins, methacrylic resins, polyimide resins, and other thermosetting resins and thermoplastic resins depending on the required properties and locations of use. Can also be used. As the resin binder, ethyl cellulose pine oil solution, ethylene glycol monobutyl ether monoacetate solution, ethyl cellulose terpineol solution, or the like can also be used.

  Conductive particles used with glass frit and resin binders are characterized by their structure. In detail, the electroconductive particle has the core particle which uses copper or silver as a base material, and the coating layer which consists of a some inorganic oxide particle arrange | positioned on the surface of this core particle.

  A core particle is a site | part which ensures the electroconductivity of electroconductive particle, and occupies most electroconductive particles. The core particles do not contain inorganic oxide particles described later. As the core particles, those obtained by a wet reduction method using a copper source compound or a silver source compound can be used. Or what was obtained by the atomizing method using the molten metal of copper or silver can be used. There is no restriction | limiting in particular in the shape of a core particle, What is necessary is just to select the thing of a suitable shape according to the specific use of an electroconductive composition. As the shape of the core particle, for example, a spherical shape or a polyhedral shape is common, but a flake shape may be used. As will be described later, since the thickness of the coating layer covering the surface of the core particle is sufficiently smaller than the particle size of the core particle, the shape of the core particle is considered to be substantially the same as the shape of the conductive particle. Can do.

  The particle size of the core particles is appropriately selected according to the specific use of the conductive composition. For example, when the electrode of a solar cell is formed using the conductive composition of the present invention, the core having an average primary particle diameter of preferably 0.1 to 20 μm, more preferably 0.2 to 7.0 μm. It is advantageous to use particles. The average particle diameter of the primary particles is obtained by observing the core particles under a microscope and measuring the maximum transverse length of 100 or more core particles in the observation field. And the average of the measured value is calculated | required and let this be the average particle diameter of a primary particle.

  The coating layer covering the surface of the core particle is composed of a plurality of inorganic oxide particles. The inorganic oxide particles may cover the surface of the core particle in a single layer state, or the core particle surface may be covered with another inorganic oxide particle arranged on the inorganic oxide particle. You may do it. In the state where the coating layer is formed on the surface of the core particle, the surface of the core particle may not be substantially exposed to the outside, or a part of the surface of the core particle may be exposed to the outside. . From the viewpoint of increasing the conductivity between the conductive particles, it is advantageous that a part of the surface of the core particle is exposed to the outside in a state where the coating layer is formed on the surface of the core particle.

  The inorganic oxide particles may be fixed to the surface of the core particles by intermolecular force. Alternatively, a part of each inorganic oxide particle may be embedded in the surface of the core particle and mechanically fixed. From the viewpoint of effectively suppressing the wetting and spreading of the molten glass frit on the surface of the conductive particles during sintering of the conductive composition, a part of each inorganic oxide particle is embedded in the surface of the core particle. It is preferable. In any fixed form, it is desirable that the inorganic oxide particles are not substantially present in the conductive composition by itself. “Substantially not present” is intended to exclude intentionally blending the inorganic oxide particles into the conductive composition in its own state, and is unavoidable in the process of manufacturing the conductive composition. In other words, it is acceptable that a very small amount of inorganic oxide particles are mixed in a single state.

  In order to fix the inorganic oxide particles to the surface of the core particles, for example, the following method can be employed. That is, the inorganic oxide particles are adhered to the surface of the core particles by means such as mechanochemical. Next, the core particles to which the inorganic oxide particles are adhered collide with each other or other objects to fix the inorganic oxide particles to the surface of the core particles. For fixing, for example, an ong mill, mechano-fusion (manufactured by Hosokawa Micron), a hybridizer, a coat mizer, a disperse coat, a jet mizer or the like can be used. By fixing using these apparatuses, the inorganic oxide particles can be easily embedded in the surfaces of the core particles.

  The present invention has one of the characteristics of the material of the inorganic oxide particles constituting the coating layer. Specifically, the inorganic oxide constituting the inorganic oxide particles has compatibility with the glass frit. By selecting the material of the inorganic oxide particles in relation to the material of the glass frit, the glass frit melted during sintering of the conductive composition is effectively suppressed from spreading on the surface of the conductive particles. be able to. Suppression of the spread of the molten glass frit leads to suppression of an increase in the distance between the conductive particles, and consequently, an increase in electrical resistance can be suppressed without adversely affecting the thermal shrinkage start temperature of the conductive particles. Moreover, the occurrence of short circuit can be suppressed. The suppression of the wet spread of the molten glass frit further leads to the suppression of cracks that are likely to occur after sintering.

  “Inorganic oxide particles are compatible with glass frit” means that a composition comprising conductive particles having a coating layer made of inorganic oxide particles on the surface of core particles, glass frit, and a resin binder is fired. Thus, when a conductor is formed and the conductor is observed with a microscope at a magnification of 5,000 to 10,000, no graininess derived from glass frit is observed on the surface of the conductor. On the contrary, when a granular feeling is recognized on the surface of the conductor, it is determined that the inorganic oxide particles are not compatible with the glass frit. Firing can be performed at 1000 ° C. for 60 minutes in an atmosphere of 1% by volume hydrogen and 99% by volume nitrogen, for example.

The kind of inorganic oxide particles having compatibility with glass frit depends on the composition of glass frit. For example, when the glass frit is mainly composed of SiO ₂ · B ₂ O ₃ · ZnO (for example, when the total amount of these three components is 50% by mass or more of the glass frit), the inorganic oxide particles are formed. As a result of the inventor's examination, it has been found that the substance to be used is preferably one or more selected from zinc oxide, magnesium oxide, tin oxide, and aluminum-doped tin oxide (ATO). Further, when at least one of the inorganic oxides constituting the glass frit is ZnO and the inorganic oxide particles are ZnO particles, the wet glass spreads effectively on the surface of the conductive particles of the molten glass frit. It has also been found as a result of the study of the present inventor that it is suppressed.

  As a result of the inventor's investigation, it has been found that the ratio of the inorganic oxide particles to the conductive particles is effective in suppressing the wetting and spreading of the molten glass frit even if the amount is small. Specifically, the desired effect can be achieved even when the proportion of the inorganic oxide particles in the conductive particles is as small as 0.1 to 10% by mass, more preferably 0.5 to 5.0% by mass. Is fully played. The proportion of the inorganic oxide particles in the conductive particles is measured by the following method. That is, after the powder having an oxide attached to the surface is completely dissolved with an acid or alkali solution, the ratio is measured by ICP emission spectroscopic analysis.

It was also found that the inorganic oxide particles are advantageously fine particles from the viewpoint of effectively suppressing the wetting and spreading of the molten glass frit on the surface of the conductive particles. Specifically, the particle diameter of the inorganic oxide particles measured by microscopic observation (for example, a transmission electron microscope or a scanning electron microscope) is preferably 20% or less of the volume cumulative particle diameter D ₅₀ of the conductive particles. More preferably, it is 10% or less, More preferably, it is 5% or less. The particle size of the inorganic oxide particles are preferably of a volume cumulative particle diameter D ₅₀ of the conductive particles is 0.001% or more, still more preferably 0.002% or more, more preferably 0.1% Or more, and more preferably 0.5% or more. The particle size of this range, the core particles having a volume cumulative particle diameter D ₅₀ as described above, it is also advantageous to securely fix the inorganic oxide particles.

  The particle size of the inorganic oxide particles is obtained by observing the conductive particles under a microscope and measuring the maximum transverse length of 100 or more inorganic oxide particles in the observation field. And the average of the measured value is calculated | required and this is made into the particle size of inorganic oxide particle.

As for the particle size of the conductive particles themselves, the volume cumulative particle size D _{50 at} a cumulative volume of 50% by volume is preferably 0.1 to 20 μm, and more preferably 0.2 to 10 μm. By using conductive particles having a particle size in this range, wetting and spreading on the surface of the conductive particles of the molten glass frit can be effectively suppressed. Moreover, desired electroconductivity can be expressed.

Cumulative volume particle diameter D ₅₀ of the conductive particles is measured by, for example, the following method. That is, 0.1 g of a sample is mixed with a 0.1% by mass aqueous solution of SN Dispersant 5468 (manufactured by San Nopco), and then dispersed for 5 minutes with an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho). Then, the particle size distribution is measured using a laser diffraction / scattering particle size distribution measuring device Micro Trac HRA 9320-X100 (Leeds + Northrup).

  Regarding the glass frit, the resin binder, and the conductive particles that are the constituent components of the conductive composition described so far, it is preferable that the blending ratio in the conductive composition is as follows. That is, the blending ratio of the glass frit is preferably 1 to 30 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the conductive particles. The blending ratio of the resin binder is preferably 5 to 25 parts by mass, more preferably 10 to 20 parts by mass with respect to 100 parts by mass of the conductive particles.

  In addition to the above-described components, various components can be blended in the conductive composition of the present invention as needed, depending on the specific form of the conductive composition. When the conductive composition is, for example, a conductive paste, a thickener, a stabilizer, a dispersant, a viscosity modifier, and the like can be blended. When the conductive composition is, for example, a conductive ink, a solvent, a surface tension adjusting agent, a viscosity adjusting agent, a coupling agent, and the like can be blended. These components can be used individually by 1 type or in combination of 2 or more types. The blending ratio of these components is appropriately determined according to the specific application of the conductive composition.

  When the conductive composition of the present invention is, for example, a conductive paste, it can be produced by mixing the above-described components with a three-roll kneader. At this time, the viscosity of the conductive paste obtained can be adjusted by adjusting the blending ratio of each component or blending a viscosity modifier.

  The conductive composition of the present invention can be used, for example, in the form of a conductive paste or conductive ink as a fine wiring material for electric circuits and electronic elements. Or it can also be used for electrode formation of a solar cell panel or a plasma display panel. For example, when used in the form of a conductive paste, after applying the paste to an object to form a coating film, it is preferably 400 to 1100 ° C., more preferably 400 to 1000 ° C. in a reducing atmosphere or an air atmosphere. Sintering is performed under the following conditions. Thereby, a conductor can be formed. At the time of sintering, the molten glass frit is difficult to spread on the surface of the conductive particles, so that it is difficult to increase the distance between the conductive particles. As a result, the conductivity of the conductor is difficult to decrease, and a short circuit between adjacent conductors is difficult to occur.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” and “part” mean “% by mass” and “part by mass”, respectively.

[Example 1]
(1) Production of conductive particles Copper particles (Mitsui Metal Mining Co., Ltd. 1100Y) were used as core particles. The copper particles had an average primary particle size of 1.0 μm. As the inorganic oxide particles, ZnO ultrafine particles (Mitsui Metal Mining Co., Ltd., particle size 10 nm) were used. Copper particles and ZnO ultrafine particles were mixed at a mass ratio of 9: 1, and ZnO ultrafine particles were adhered to the surfaces of the copper particles. Next, using Mechanofusion (manufactured by Hosokawa Micron Corporation), the mixture was circulated for 5 minutes under the condition of 8000 rpm to fix ZnO ultrafine particles on the surface of the copper particles. In this way, conductive particles were obtained. When the conductive particles were observed with a microscope, ZnO ultrafine particles were embedded in the surfaces of the copper particles. Moreover, a part of the surface of the copper particles was exposed to the outside. The proportion of the ultrafine ZnO particles in the conductive particles was 1.0%. The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles was 1.1 μm.

(2) Production of Conductive Composition As the glass frit, zinc borosilicate glass frit (ASF-1981F manufactured by Asahi Glass Co., Ltd.) was used. This glass frit contained 30 to 50% by mass of zinc oxide, 23% by mass of boron oxide, and 2 to 15% by mass of silicon dioxide. An acrylic resin was used as the resin binder. A glass frit and a resin binder were mixed with the conductive particles obtained above and kneaded with a three-roll kneader to obtain a conductive paste. The blending amount of the glass frit was 17 parts with respect to 100 parts of the conductive particles. The compounding quantity of the resin binder was 15 parts with respect to 100 parts of conductive particles.

[Example 2]
Instead of the ZnO ultrafine particles used in Example 1, conductive particles were obtained in the same manner as in Example 1 except that ATO (aluminum-doped tin oxide) ultrafine particles (Mitsui Metal Mining Co., Ltd., particle size 10 nm) were used. It was. The proportion of ATO ultrafine particles in the conductive particles was 1.0%. The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles was 0.9 μm. Using the conductive particles, a conductive paste was produced in the same manner as in Example 1.

Example 3
Copper particles (Mitsui Metal Mining Co., Ltd. 1400Y) were used as the core particles. The copper particles had an average primary particle size of 4.5 μm. Further, in place of the ZnO ultrafine particles used in Example 1, MgO ultrafine particles (manufactured by Sakai Chemical Industry Co., Ltd., particle size 100 nm) were used. Except these, it carried out similarly to Example 1, and obtained electroconductive particle. The proportion of the ultrafine MgO particles in the conductive particles was 1.0%. The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles was 4.8 μm. Using the conductive particles, a conductive paste was produced in the same manner as in Example 1.

[Comparative Examples 1 to 3]
In place of the ZnO ultrafine particles used in Example 1, Al ₂ O ₃ ultrafine particles (Comparative Example 1, aluminum oxide C manufactured by Nippon Aerosil Co., Ltd., particle size 13 nm), SiO ₂ ultrafine particles (Comparative Example 2, manufactured by Nippon Aerosil Co., Ltd.) Conductive particles were obtained in the same manner as in Example 1 except that AEROSIL 300, particle size 7 nm) and TiO ₂ ultrafine particles (Comparative Example 3, TITON A-110 manufactured by Sakai Chemical Industry Co., Ltd., particle size 15 nm) were used. The proportion of Al ₂ O ₃ ultrafine particles in the conductive particles was 1.0%, the proportion of SiO ₂ ultrafine particles was 1.0%, and the proportion of TiO ₂ ultrafine particles was 1.0%. The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of these conductive particles was 1.1 μm in Comparative Example 1, 1.1 μm in Comparative Example 2, and 1.1 m in Comparative Example 3. Using these conductive particles, a conductive paste was produced in the same manner as in Example 1.

[Comparative Example 4]
Copper particles (Mitsui Metal Mining Co., Ltd. 1400Y) were used as the core particles. The copper particles had an average primary particle size of 4.5 μm. As the ultrafine particles, Al ₂ O ₃ particles (aluminum oxide C manufactured by Nippon Aerosil Co., Ltd., particle size 13 nm) used in Comparative Example 1 were used. Except these, it carried out similarly to Example 1, and obtained electroconductive particle. The ratio of Al ₂ O ₃ ultrafine particles to the conductive particles was 1.0%. The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles was 4.5 μm. Using the conductive particles, a conductive paste was produced in the same manner as in Example 1.

[Evaluation]
For the conductive pastes obtained in Examples 1 to 3 and Comparative Examples 1 to 4, the resistance value of the fired film was evaluated by the following method. The results are shown in Table 1 below. Further, these conductive pastes were applied to an alumina substrate to form a coating film, and the coating film was baked at 1000 ° C. for 60 minutes in an atmosphere of 1% hydrogen and 99% nitrogen to form a conductor. Scanning electron microscope images of this conductor are shown in FIGS. 1 (a) to 1 (c) and FIGS. 2 (a) to 2 (c).

[Measurement method of fired film resistance]
The resistance value of the fired film was measured using a Loresta GP manufactured by Mitsubishi Chemical Analic Co., Ltd., and evaluated for ◯ ×. As an evaluation method, the one having a high resistance value and exceeding the measurement range (10 ⁻³ -10 ⁻⁷ Ω) was evaluated as “x”, and the one having a low resistance could be measured as “◯”.

As is clear from the comparison between FIGS. 1A to 1C and FIGS. 2A to 2D, the conductors obtained by firing the conductive pastes of Examples 1 to 3 have a smooth surface. It can be seen that while there is no graininess, the conductors obtained by firing the conductive pastes of Comparative Examples 1 to 4 have graininess on the surface. From these facts, the inorganic oxide particles used in Examples 1 to 3 are compatible with glass frit, whereas the inorganic oxide particles used in Comparative Examples 1 to 4 are glass frit and It can be seen that they are not compatible.
Further, as is clear from the results shown in Table 1, the conductive pastes of Examples 1 to 3 can produce a low resistance film compared to the conductive pastes of Comparative Examples 1 to 4. I understand.

Claims (4)

In a conductive composition comprising conductive particles, glass frit and a resin binder,
The conductive particles have core particles whose base material is a metal, and a coating layer composed of a plurality of inorganic oxide particles disposed on the surface of the core particles,
The volume cumulative particle diameter D _{50 at} a cumulative volume of 50% by volume of the conductive particles is 0.1 to 20 μm , and the particle diameter of the inorganic oxide particles measured by microscopic observation is the volume cumulative of the conductive particles. 20% or less of the particle size D ₅₀ ,
Inorganic oxide constituting the inorganic oxide particles possess the glass frit compatible,
That the inorganic oxide particles are compatible with the glass frit means that the conductive composition is fired in an atmosphere of 1% by volume hydrogen and 99% by volume nitrogen at 1000 ° C. for 60 minutes. When the conductor is observed under a microscope at a magnification of 5,000 to 10,000 times, the conductive composition is such that no granular feeling derived from the glass frit is observed on the surface of the conductor.   The conductive composition according to claim 1, wherein a ratio of the inorganic oxide particles in the conductive particles is 0.1 to 10% by mass. The blending ratio of the glass frit is 1 to 30 parts by mass with respect to 100 parts by mass of the conductive particles,
The conductive composition according to claim 1 or 2 , wherein a blending ratio of the resin binder is 5 to 25 parts by mass with respect to 100 parts by mass of the conductive particles . The electroconductivity as described in any one of Claims 1 thru | or 3 with which the substance which comprises the said inorganic oxide particle is 1 type, or 2 or more types chosen from zinc oxide, magnesium oxide, a tin oxide, and aluminum dope tin oxide. Composition.