JPH06162817A - Conductive particulate and its manufacture - Google Patents

Abstract

PURPOSE:To provide a conductive particulate with excellence in particulate-diameter accuracy and without any electric defect by forming a coat layer, comprising partially deoxidized titanic oxide contained therein, on the surface of a spherical particulate made of a metallic oxide. CONSTITUTION:Spherical particulates (particulate diameter ranging from 0.5mu to 30mu) each made of a metallic oxide (silica or the like) are dispersed in an alcoholic group solvent consisting mainly of middle-class alcohol (butanol or the like), and then an aqueous solution of alkali (ammonium or the like) is added to the resultant solvent so as to activate the surface of each of the spherical particulates. A titanium compound (titanium tetrabutoxide) whereby titanic oxide can be formed is then added to the particulates-dispersed solution so as to be hydrolyzed, so that a titatic oxide coat layer(film thickness ranging from 0.01mu, to 1mu) may be formed on the surface of the spherical particulate. The coat layer is baked at a temperature ranging from 800 deg.C to 1,000 deg.C in a deoxidizing atmosphere (hydrogen gas) and/or in a nitriding atmosphere (nitrogen gas), so that a coat layer, comprising partially deoxidized titanic oxide of conductivity and/or titanium nitride contained therein, may be finally formed on the surface of the particulate. This process provides conductive particulate with highness in both strength and hardness, and also without any condensation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to conductive fine particles which can be used for anisotropic conductive films and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as conductive fine particles, there have been resin beads whose surface is plated with a metal such as nickel or gold. However, these have the following problems. Was there. That is, the particle size accuracy of the conductive fine particles is greatly affected by the particle size accuracy of the resin beads that are the mother particles, but the particle size accuracy of the resin beads is generally poor, and the particle size of the resulting conductive particles is Precision is also poor. Agglomeration of resin beads, which are the mother particles, often occurs during the plating process, so that when the conductive particles obtained after plating are used and the agglomerated parts are crushed, the agglomerated parts are incompletely plated. Therefore, conduction failure may occur. Since the hardness and strength of the resin beads are insufficient, conductive fine particles having resin beads as the mother particles cannot be used for applications requiring higher strength and hardness.

Although fine particles of metal such as nickel itself may be used as the conductive fine particles, they are easily aggregated and the insulation between terminals cannot be maintained in many cases. Further, conductive fine particles obtained by plating fine particles of metal oxide with nickel and / or gold have also been proposed, but these are also easily aggregated, and the adhesion between the mother particles and the coating metal is poor, so crushing In some cases, the coated metal part may fall off during the kneading process and the conductivity may be significantly reduced.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the conventional conductive fine particles and the method for producing the same, (a) excellent particle size accuracy, (b) no electrical defects, and (c) high strength. It is to provide a novel conductive fine particle having advantages such as high hardness, (d) no aggregation, and a method for producing the same.

[0005]

In order to achieve the above object, the conductive fine particles of the present invention are spherical particles composed of a metal oxide and partially reduced titanium oxide and / or spherical particles formed on the surface of the spherical particles. And a coating layer containing titanium nitride.

In order to achieve the above object, the method for producing conductive fine particles of the present invention is as follows: (1) Spherical particles made of a metal oxide are dispersed in an alcohol solvent mainly containing an intermediate alcohol to obtain spherical particles. A step of obtaining a dispersion liquid; (2) a step of activating the surface of the metal oxide spherical particles by adding an alkaline aqueous solution to the dispersion liquid; (3) forming titanium oxide in the dispersion liquid after the activation treatment A titanium compound capable of being added and hydrolyzed to form a titanium oxide coating layer on the surface of the spherical particles; and (4) firing the titanium oxide coating layer in a reducing and / or nitriding atmosphere. , And reduction and / or nitriding to form a coating layer containing partially reduced titanium oxide and / or titanium nitride having conductivity.

First, the conductive fine particles of the present invention will be described. The conductive fine particles of the present invention have spherical particles made of a metal oxide, and a coating layer formed on the surface of the spherical particles and containing partially reduced titanium oxide and / or titanium nitride. In the conductive fine particles of the present invention, the material forming the spherical particles that are the mother particles is a metal oxide. Examples of the metal oxide include silica, alumina, titania, zirconia, barium oxide, iron oxide, cobalt oxide, chromium oxide, vanadium oxide, hafnium oxide, magnesium oxide, and various ones such as strontium oxide, but silica is particularly preferable. . The reason is that silica fine particles are obtained by hydrolyzing silicon alkoxide in an aqueous ammonia solution and have a sharp particle size distribution.
In addition, it has characteristics such as high strength and hardness. The particle size of the spherical particles made of a metal oxide varies depending on the use of the conductive fine particles, but is generally in the range of 0.5 to 30 μm.

In the conductive particles of the present invention, a coating layer containing partially reduced titanium oxide and / or titanium nitride is formed on the surface of the spherical particles made of the above metal oxide.
The titanium oxide forming the coating layer is titanium dioxide (TiO 2
₂ ) is titanium oxide partially reduced, and TiO _n
(1.5 <n <2). The value of _n in TiO _n is preferably as small as possible in order to make the coating layer conductive, but as will be described later, a previously formed TiO ₂ layer is reduced and oxygen is stoichiometrically insufficient. In the case of forming a TiO _n layer having
The value of is usually about 1.6 to 1.9. The inventor
It has been confirmed that the TiO _n layer has sufficient conductivity even when the number of n is 1.6 to 1.9.

In the conductive fine particles of the present invention, the coating layer may be made of titanium nitride instead of partially reduced titanium oxide, or may be made of the partially reduced titanium oxide and titanium nitride. The film thickness of the coating layer is appropriately determined in consideration of the degree of conductivity required for the conductive fine particles, the adhesion of the mother particles to the spherical metal oxide particles, the strength, etc., but is usually 0.01 to 1 μm. Is.

The conductive fine particles of the present invention are composed of spherical particles made of a metal oxide as described above and a coating layer containing partially reduced titanium oxide and / or titanium nitride. As also demonstrated,
(A) excellent particle size accuracy, (b) no electrical defects,
It has advantages such as (c) high strength and high hardness, and (d) no aggregation.

The above-mentioned conductive fine particles of the present invention can be manufactured by various methods, but it is particularly preferable that the conductive fine particles of the present invention are manufactured by the method including the following steps. (1) A step of dispersing spherical particles made of a metal oxide in an alcoholic solvent mainly containing an intermediate alcohol to obtain a dispersion liquid of spherical particles; (2) An alkaline aqueous solution is added to the dispersion liquid to form spherical metal oxide particles. A step of activating the surface of the particles; (3) a titanium compound capable of forming titanium oxide is added to the dispersion liquid after the activation treatment and hydrolyzed to form a titanium oxide coating layer on the surface of the spherical particles. And (4) firing the titanium oxide coating layer in a reducing and / or nitriding atmosphere to reduce and / or nitride, thereby containing a partially reduced titanium oxide and / or titanium nitride having conductivity. A step of forming a coating layer.

Step (1) is a step in which spherical particles made of a metal oxide are dispersed in an alcohol solvent mainly containing an intermediate alcohol to obtain a dispersion liquid of spherical particles. The spherical particles used in this step (1) are generally 0.5 to
Those having a particle size in the range of 30 μm are preferred. Further, as the metal oxide fine particles constituting the spherical particles, silica,
Fine particles such as titania, zirconia, barium oxide, iron oxide, cobalt oxide, chromium oxide, vanadium oxide, hafnium oxide, magnesium oxide, and strontium oxide can be mentioned, but silica fine particles are used in terms of particle size accuracy, strength, and hardness. Is particularly preferable. Silica fine particles are produced by hydrolyzing and polycondensing a silicon alkoxide in a reaction liquid containing water, ammonia and alcohol. The uncalcined silica particles at this stage have many silanol groups, and organic substances, water, and ammonia are considerably left, and strength and hardness are low. When these unsintered silica particles are calcined at 500 to 1200 ° C, silanol groups, organic substances, water, and ammonia become almost no remaining silica particles, and the strength and hardness increase. In the method of the present invention, any of these two types of silica fine particles can be used, but when used for applications such as anisotropic conductive films, calcined silica is preferred because it has higher strength and hardness than uncalcined silica particles. Particular preference is given to using particles.

In the step (1), the spherical particles are dispersed in an alcohol solvent to obtain a dispersion of spherical particles. The alcohol solvent used is butanol, pentanol, hexanol, heptanol, octanol, nonanol, Limited to medium-grade alcohols having 4 to 10 carbon atoms such as decanol. The reason is that it has been clarified that the use of these intermediate alcohols increases the thickness of the titanium oxide coating layer formed in the step (3) described later. These middle alcohols may be linear or branched. However, with the above-mentioned intermediate alcohol, methanol, ethanol,
Lower alcohols such as propanol or hydrophilic organic solvents such as acetonitrile, THF, DMF, DM
A small amount of SO, etc. for all alcohols (eg 20 vol)
%)).

Next, step (2) is a step of activating the surface of the metal oxide spherical particles by adding an alkaline aqueous solution to the dispersion of the spherical particles obtained in step (1).
This activation treatment is a treatment for promoting the proton desorption from the silanol groups on the surface of the metal oxide spherical particles by the action of alkali, and the activation treatment will be described later. Adhesion between the titanium oxide coating layer formed in step (3) and the spherical metal oxide particles, and thus the coating layer and metal containing partially reduced titanium oxide and / or titanium nitride formed in step (4) described later Adhesion with spherical oxide particles is improved, and peeling or cracking of the coating layer is prevented. In particular, when silica is used as the spherical particles, the silica spherical particles and the titanium oxide layer formed on the surface have a large difference in shrinkage between silica and titanium oxide. Although there were concerns about cracking, it is noteworthy that these problems were solved by the activation treatment in the method of the present invention.

As the alkaline aqueous solution used for this activation treatment, an alkaline aqueous solution such as ammonia, alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal salt or alkaline earth metal salt is used. It is particularly preferable to use an aqueous ammonia solution.

Next, in the step (3), a titanium compound capable of forming titanium oxide is added to the dispersion liquid obtained in the step (2), and the mixture is hydrolyzed so that the surface of the spherical particles is represented by the formula TiO ₂ . Is a step of forming a coating layer of titanium oxide (titanium oxide composed of stoichiometric amount of titanium and oxygen). The titanium compound capable of forming titanium oxide used in this step (3) is represented by the general formula Ti (OR) ₄ or Ti (R ′) _n (OR) _4-n (wherein R and R ′ are alkyl groups). Group, especially 1 to 5 carbon atoms
Is an alkyl group, and n is an integer of 1 to 3), or a partial hydrolyzate thereof. Specific examples of R and R'are a methyl group, an ethyl group, a linear or branched propyl group, a linear or branched butyl group, and a linear or branched pentyl group. These titanium compounds added to the dispersion are hydrolyzed by the so-called sol-gel method to form a titanium oxide layer on the surface of the spherical particles. The film thickness of the formed titanium oxide layer is appropriately determined according to the film thickness of the conductive coating layer required for the conductive particles of the target, but is usually 0.01 to 1 μm.
According to the method of the present invention, as described above, by using a medium alcohol having 4 to 10 carbon atoms as the alcohol solvent in the step (1), it is possible to increase the thickness of the titanium oxide layer. .

Next, in the step (4), the titanium oxide coating layer formed in the step (3) is fired in a reducing and / or nitriding atmosphere to reduce and / or nitride, thereby partially reducing titanium oxide and / or Alternatively, it is a step of forming a coating layer containing titanium nitride. In this step (4), the reducing atmosphere is achieved by using a reducing gas such as hydrogen gas, and the nitriding atmosphere is achieved by using a nitriding gas such as nitrogen gas. The reducing and nitriding atmosphere is also a reducing gas and can be achieved by using ammonia gas which is also a nitriding gas or by using hydrogen gas and nitrogen gas in combination. Firing is usually performed in a high temperature furnace, and the temperature is usually in the range of 800 to 1,000 ° C. By this firing treatment in a reducing and / or nitriding atmosphere, the titanium oxide coating layer is converted into partially reduced titanium oxide and / or titanium nitride represented by the formula TiO _n (1.5 <n <2),
Conductive fine particles having a conductive coating layer on the surface of the metal oxide spherical particles can be obtained. The preferable value of n is 1.6 to 1.9 as described above.

The conductive fine particles obtained by the method of the present invention have (i) metal oxide fine particles having a sharp particle size distribution as mother particles, on which a uniform conductive coating layer is provided. Excellent particle size accuracy, (ii) Since the coating layer contains partially reduced titanium oxide and titanium nitride, which have excellent conductivity, the conductive fine particles are also excellent in conductivity and have no electrical defects.
ii) Metal oxide spherical particles and partially reduced titanium oxide and / or
Alternatively, since the coating layer containing titanium nitride has high strength and high hardness, the conductive fine particles also have high strength and high hardness.
(Iv) on the surface of the metal oxide spherical particles having excellent monodispersity,
Since the conductive coating layer can be formed without causing aggregation, the obtained conductive fine particles are not aggregated,
(V) Excellent adhesion between the metal oxide spherical particles and the coating layer,
It has remarkable advantages such as no peeling or cracking of the coating layer.

[0019]

The present invention will be further described with reference to the following examples.

Example 1 Step (1) The spherical particles made of a metal oxide have an average particle size of 6.
Silica fine particles using monodispersed silica fine particles of 07 μm and n-butanol as an alcohol solvent.
46 g was added to 140 ml of n-butanol, and ultrasonic irradiation was performed for 30 minutes to obtain a dispersion liquid of silica fine particles.

Step (2) 0.5 g of 25% ammonia water was added dropwise to the obtained dispersion liquid of silica fine particles, and the surface of the silica fine particles was activated by stirring at 30 ° C. for 30 minutes.

Step (3) Titanium tetrabutoxide is used as a titanium compound capable of forming titanium oxide, and a solution prepared by dissolving 5.45 g of this titanium tetrabutoxide in 20 ml of n-butanol is added to the dispersion liquid obtained through the above step (2). The mixture was added dropwise over 10 minutes and stirred at 30 ° C. for 1 hour. Then, after adding a solution prepared by dissolving 8.14 g of 0.5% aqueous ammonia in 20 ml of 2-propanol over 30 minutes, the reaction system was heated to 60 ° C. and stirred for 12 hours to dissolve titanium tetrabutoxide. The decomposition reaction was terminated. After the completion of the reaction, the reaction solution was allowed to stand and the particles were allowed to settle, and then the supernatant was removed by decantation. Further, decantation was repeated in the order of methanol and water, followed by freeze-drying to obtain silica fine particles having a titanium oxide (TiO ₂ ) coating layer.

Step (4) The freeze-dried silica fine particles with a titanium oxide coating layer are put into a boat made of quartz glass and placed in a furnace core tube consisting of a quartz tube, and oxygen in the furnace core tube is purged with nitrogen gas. did. Then, the temperature was raised at a heating rate of 200 ° C./hr, and when it reached 500 ° C., the temperature was raised to 850 ° C. while introducing ammonia gas from the liquefied ammonia cylinder at a flow rate of 250 ml / min, and kept at this temperature for 6 hours. Then, the reduction and nitriding treatments were completed, and a coating layer made of partially reduced titanium oxide and titanium nitride was formed to obtain the target conductive fine particles.

The obtained conductive fine particles maintained the monodispersity of the silica fine particles as the mother particles. The conductivity of the obtained conductive fine particles was measured and found to be 50.0 S / c.
m shows almost the same conductivity as that of metal. When an anisotropic conductive film was prepared using the conductive fine particles, excellent anisotropic conductivity was exhibited.

X-ray photoelectric spectroscopy (XPS or ESC
The composition of the coating layer was determined according to A). The conditions of the X-ray photoelectric spectroscopic analysis are as follows. Model name: ESCA- manufactured by ULVAC-PHI, Inc.
5400 Degree of vacuum: 3 to 5 × 10 ⁻⁹ Pa X-ray source: MgKα (1253.6 eV) Analysis area: 1.1 mmφ Photoelectron uptake time: 1.0 to 10.0 min / element Sputtering treatment: None Path energy: 178. As a result, the average value of _n in partially reduced titanium oxide TiO _n was 1.75, and TiO _1.75 and TiN were about 70.
% And about 30%.
The film thickness of the coating layer was found to be 0.05 μm as a result of measuring the particle size before and after coating with an electron microscope.

Further, as a result of observing the conductive fine particles obtained in this example with a microscope (2500 times), no peeling or cracking of the coating layer was observed.

Example 2 This example is an example in which t-amyl alcohol (2-methyl-2-butanol) was used as a medium alcohol solvent instead of n-butanol used in Example 1, The details are shown below.

Step (1) The spherical particles made of a metal oxide have an average particle size of 6.
Using 77 μm of monodisperse silica fine particles and t-amyl alcohol as a medium alcohol solvent, 6.31 g of silica fine particles was added to 140 ml of t-amyl alcohol, and ultrasonic irradiation was performed for 30 minutes to obtain a dispersion liquid of silica fine particles. Got

Step (2) 0.30 g of 25% aqueous ammonia was added dropwise to the obtained dispersion liquid of silica fine particles, and the surface of the silica fine particles was activated by stirring at 30 ° C. for 30 minutes.

Step (3) As a titanium compound capable of forming titanium oxide, titanium tetrabutoxide is used, and a solution prepared by dissolving 5.45 g of this titanium tetrabutoxide in 20 ml of t-amyl alcohol is subjected to the above step (2). The mixture was added dropwise over 10 minutes and stirred at 30 ° C. for 1 hour. Thereafter, 8.34 g of 0.5% aqueous ammonia was added to 20 m of 2-propyl alcohol.
After adding the solution dissolved in 1 over 30 minutes, the reaction system was added to 6
The temperature was raised to 0 ° C. and the mixture was stirred for 12 hours to complete the hydrolysis reaction of titanium tetrabutoxide. After the completion of the reaction, the reaction solution was allowed to stand and the particles were allowed to settle, and then the supernatant was removed by decantation. Further, decantation was repeated in the order of methanol and water, followed by freeze-drying to obtain silica fine particles having a titanium oxide (TiO ₂ ) coating layer.

Step (4) The freeze-dried silica fine particles with a titanium oxide coating layer are put in a boat made of quartz glass and placed in a furnace core tube made of a quartz tube, and oxygen in the furnace core tube is purged with nitrogen gas. did. Next, the temperature is raised at a heating rate of 200 ° C./hr, and when it reaches 500 ° C., the temperature is raised to 850 ° C. while introducing ammonia gas from the liquefied ammonia cylinder at a flow rate of 250 ml / min, and this temperature is maintained for 4 hours. Then, the reduction and nitriding treatments were completed, and a coating layer made of partially reduced titanium oxide and titanium nitride was formed to obtain the target conductive fine particles.

The obtained conductive fine particles maintained the monodispersity of silica fine particles as the mother particles. The conductivity of the obtained conductive fine particles was measured and found to be 50.0 S / c.
m shows almost the same conductivity as that of metal. When an anisotropic conductive film was prepared using the conductive fine particles, excellent anisotropic conductivity was exhibited.

X-ray photoelectric spectroscopy (XPS or ESC
When the composition of the coating layer was determined according to A), almost the same results as in Example 1 were obtained. The film thickness of the coating layer is 0.
It was 05 μm. Furthermore, as a result of observing the conductive fine particles obtained in this example with a microscope (2500 times), no peeling or cracking of the coating layer was observed.

Comparative Example 1 This comparative example is a comparative example in which methanol, which is not contained in the intermediate alcohol specified in the present invention, is used as the alcohol solvent, and the details will be described below. As spherical particles made of a metal oxide, monodispersed silica fine particles having an average particle diameter of 3.04 μm were used, and methanol was used as an alcohol-based solvent.
It was added to g and was irradiated with ultrasonic waves for 10 minutes to obtain a dispersion liquid of silica fine particles. 2 in the resulting dispersion of silica particles
20 g of 8% ammonia water was added and mixed.

Titanium tetraisopropoxide was used as a titanium compound capable of forming titanium oxide, and a solution prepared by dissolving 2.4 g of this titanium tetraisopropoxide in 70 g of methanol was added to the above dispersion liquid kept at 30 ° C. Mix and stir. After stirring for several hours, the reaction solution was allowed to stand to settle the particles, and the supernatant was removed by decantation. Further, decantation was repeated in the order of methanol and water, followed by freeze-drying to obtain silica fine particles having a titanium oxide (TiO ₂ ) coating layer.

The freeze-dried silica fine particles with a titanium oxide coating layer were put in a boat made of quartz glass, placed in a furnace core tube made of a quartz tube, and oxygen in the furnace core tube was purged with nitrogen gas. Then, the temperature was raised at a heating rate of 200 ° C./hr, and when it reached 500 ° C., the temperature was raised to 850 ° C. while introducing ammonia gas from the liquefied ammonia cylinder at a flow rate of 250 ml / min, and kept at this temperature for 6 hours. Then, the reduction and nitriding treatments were completed, a coating layer made of partially reduced titanium oxide and titanium nitride was formed, and conductive fine particles were obtained.

The obtained conductive fine particles maintained the monodispersity of silica fine particles as the mother particles. The conductivity of the obtained conductive fine particles was measured and found to be 0.12 S / c.
When the anisotropic conductive film was produced using this conductive fine particle, it showed anisotropic conductivity, but the performance was insufficient. The thickness of the coating layer was 0.0018 μm, which was extremely thin.

Comparative Example 2 Dried silica fine particles with a titanium oxide (TiO ₂ ) coating layer obtained through the steps (1), (2) and (3) of Example 1 were fired in an oxygen atmosphere. That is, put the silica particles with a titanium oxide coating layer in a boat made of quartz glass,
This was placed in a furnace core tube made of a quartz tube, heated to 800 ° C. at a temperature rising rate of 200 ° C./hour in an oxygen atmosphere, held at this temperature for 4 hours, and fired. The conductivity of the obtained silica fine particles with a coating layer was measured to be 5.6.
It was impossible to produce an anisotropic conductive film which showed an insulating property of 9 × 10 ⁻¹² S / cm.

[0039]

According to the present invention, there are advantages such as (a) excellent particle size accuracy, (b) no electrical defects, (c) high strength and hardness, and (d) no aggregation. There is provided a novel conductive fine particle having the above and a method for producing the same.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Sakai 2-1-1 Yabuta Nishi, Gifu City, Gifu Ube Nitto Kasei Co., Ltd.

Claims (2)

[Claims] 1. Conductive fine particles comprising spherical particles made of a metal oxide, and a coating layer formed on the surface of the spherical particles and containing partially reduced titanium oxide and / or titanium nitride. 2. A step of (1) dispersing spherical particles made of a metal oxide in an alcohol solvent mainly containing an intermediate alcohol to obtain a dispersion of spherical particles; (2) adding an alkaline aqueous solution to the dispersion. And (3) a titanium compound capable of forming titanium oxide is added to the dispersion liquid after the activation treatment and hydrolyzed to the surface of the spherical particles. And (4) firing the titanium oxide coating layer in a reducing and / or nitriding atmosphere to reduce and / or nitride the titanium oxide coating layer, and to provide partially reduced titanium oxide having conductivity and / or Alternatively, the method for producing conductive fine particles comprises a step of forming a coating layer containing titanium nitride.