JPH0878164A - Conductive paste, translucent conductive film, and dispersion type electroluminescent element using them - Google Patents

Abstract

PURPOSE: To provide a translucent conductive film which can provide a high emission luminance and an electroluminescent element using it by using a large needle indium-tin oxide particle having a long diameter of 30μm or more. CONSTITUTION: A conductive paste containing a needle indium-tin oxide powder having a long diameter of 30μm or more and an aspect ratio of 5 or more and a transparent conductive powder having a small particle size in a resin and its solvent is used to form a translucent conductive film on a base. Otherwise, a translucent conductive film consisting of the transparent conductive powder having a small particle size and the resin and a light translucent conductive film consisting of the needle indium-tin oxide powder having a long diameter of 30μm or more and the resin are alternately laminated on the base.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste and a transparent conductive film used for forming a transparent electrode such as an electroluminescent element, and an electroluminescent element using these.

[0002]

2. Description of the Related Art As a conductive paste used for forming a translucent electrode of a conventional electroluminescence (hereinafter abbreviated as "EL") light emitting element, an indium-tin oxide (hereinafter abbreviated as "ITO") is used as a conductive filler. There are those in which ultrafine powder is dispersed in a solvent in which a resin is dissolved, and those in which flaky ITO powder is dispersed in a solvent in which a resin is dissolved.

In the organic dispersion type EL device, a zinc sulfide (ZnS) layer which is a light emitting layer is formed on a substrate by screen printing or blade coating, and a conductive paste is applied thereon by screen printing or the like to transmit a transparent conductive film. Is formed.

In a conductive paste using ITO ultrafine powder as a conductive filler, it is necessary to use a large amount of conductive filler with respect to the resin in order to obtain conductivity. This transparent conductive film has a film thickness of 2 to 3 μm in order to obtain light transmittance.
It is said that it is preferable to make it thin.

In the zinc sulfide layer which is the light emitting layer, since the zinc sulfide particles have a size of several tens of μm, unevenness occurs on the printed surface. When the conductive paste is applied, the unevenness of the surface of the zinc sulfide layer causes the unevenness of the conductive paste. The film thickness becomes non-uniform, and a part of 1 μm or less or a part of 5 μm or more occurs, and the entire surface is 2-3 μm.
However, there is a problem in that the conductive film cannot be formed uniformly, and cracks occur in a thin portion to increase the resistance.

In the conductive paste in which the flaky ITO powder is dispersed in the solvent in which the resin is dissolved, the conductivity can be obtained by using a small amount of the conductive filler with respect to the resin. Also, sufficient light transmittance was obtained, and the unevenness on the surface of the zinc sulfide layer was not a serious problem, but the resistance of the film was not sufficient.

Therefore, the present inventor has made a conductive paste in which a needle-like ITO powder having a major axis of 5 μm or more and a major axis to minor axis ratio of 5 or more is dispersed in a solvent in which a resin is dissolved, and a light-transmitting property using the same. I first proposed a conductive film (Japanese Patent Application No. 5-12
0518).

This prior invention makes it possible to obtain a very low resistance film having excellent translucency by using acicular ITO powder as a conductive filler, and when using it for an EL device, it consumes less power. The effect is that it is useful for increasing the area.

[0009]

However, the above-mentioned conductive paste and the translucent conductive film using the same have the following problems. The dispersion-type EL element has a mechanism in which it is sandwiched between phosphor particles, a metal electrode and a translucent electrode, an AC voltage is applied to both electrodes, and a high electric field is applied to the phosphor particles to emit light. When acicular ITO particles are used for the translucent electrode of this dispersion type EL element, a net-shaped conductive path is formed by the acicular ITO filler on the translucent electrode surface. Therefore, the needle-shaped ITO having a large major axis
When the particles are used, a large mesh conductive path is formed, while when the acicular ITO particles having a small major axis are used, a small mesh conductive path is formed.

On the other hand, as described above, since the zinc sulfide particles in the light emitting layer have a size of several tens of μm, for example, the major axis is 30 μm.
When the above-mentioned translucent conductive film made of relatively large acicular ITO particles is used, the mesh of the conductive path is too large, and some of the zinc sulfide particles in the light emitting layer are not applied with an electric field or are applied with an electric field. Is also weak, resulting in a problem that the EL emission luminance is low.

Therefore, if needle-like ITO particles having a major axis smaller than the size of the phosphor particles, for example, 5 to 30 μm are used, the above problem does not occur, but in order to reduce the resistance of the conductive film, the major axis is required. It is more advantageous to use the needle-shaped ITO particles having a large diameter, and also in the production of the needle-shaped ITO powder, the ITO powder having a large major axis is easier to handle in solid-liquid separation in the manufacturing process.

For the above reasons, it has been desired to develop a light-transmissive conductive film and an EL element using the same, which can obtain high emission brightness even when large acicular ITO particles having a major axis of 30 μm or more are used.

The present invention has been made in view of the above circumstances, and has a large acicular ITO having a major axis of 30 μm or more.
An object of the present invention is to provide a light-transmissive conductive film which can obtain high emission brightness by using particles and an EL device using the same.

[0014]

As a means for solving the above problems, the present invention provides a resin and its solvent with a long diameter 30
Using a conductive paste containing acicular indium-tin oxide powder having a ratio of major axis to minor axis of 5 or more and a diameter of μm or more and transparent conductive powder having a small particle diameter, a metal electrode, a dielectric particle layer,
The major axis is 30 μm on the substrate in which the phosphor particle layers are laminated in this order.
A transparent conductive film comprising the above needle-shaped indium-tin oxide powder, a transparent conductive powder having a small particle size and a resin is formed, or a transparent conductive powder having a small particle size and a resin are formed on the substrate. The gist of the present invention is that the translucent conductive film made of (1) and the translucent conductive film made of acicular indium-tin oxide powder having a major axis of 30 μm or more and a resin are laminated on each other.

[0015]

The needle-like ITO powder used in the present invention is obtained by adding tin tetrachloride hydrate to a solution prepared by dissolving indium metal in nitric acid, concentrating it by heating with stirring, and then at a liquid temperature of 130 to 150 ° C.
Concentrate to form a thick slurry, add a large amount of water to this slurry, filter, wash the needle-like powder obtained by filtration, dry, and calcine at about 1200 ° C for about 30 to obtain .

This acicular ITO powder has a major axis of 5 μm or more,
Aspect ratios up to about 30 can be obtained depending on the tin compound added and the concentration conditions. The specific resistance (hereinafter referred to as “powder resistance”) of this powder when it is made into a pellet by applying a pressure of 100 kgf / cm ² is 0.0
It is about 3 Ω · cm.

In the present invention, the reason why the aspect ratio of the acicular ITO powder is 5 or more is that conductivity can be obtained by using a small amount of the resin in the resin. The higher the aspect ratio, the better, and preferably 10 or more.

The size of the acicular ITO powder obtained by the above method ranges from about 5 μm in major axis to 20 in major axis depending on the concentration conditions.
Although it is possible to obtain up to about 0 μm, when only a needle-like ITO powder having a major axis of 30 μm or more is used as a conductive filler to form a conductive film, the conductive path in the film is relatively large,
A cross section of a dispersion type EL element using such a conductive film is shown, for example, in FIG. In the figure, 1 is a metal electrode, 2 is a dielectric layer, 3 is phosphor particles, and 4 is a needle-like ITO powder having a major axis of 30 μm or more. That is, in the case of the conductive film using only the acicular ITO powder having a major axis of 30 μm or more as the conductive filler, the electric field is not uniformly applied to all the phosphors, so that the EL brightness cannot be sufficiently obtained. For example, the brightness is 1
It will decrease by about 50%. Of course, the major axis is small (30 μm or less)
If acicular ITO powder is used, the above drawbacks can be compensated, but in terms of the resistance of the conductive film, it is advantageous that the major axis has a large diameter.

According to the present invention, the resistance of the conductive film is reduced by using the acicular ITO powder having a large major diameter, and the resistance in the plane of the conductive film is made uniform by using the transparent conductive powder having a small particle size. It is a measure. Therefore, in the present invention, since the light-transmitting conductive film having a low resistance and the electric field is uniformly applied to the phosphor, an EL element having a low brightness and a high brightness can be obtained.

In the present invention, the size of the transparent conductive powder having a small particle size is several μm to several tens μ of the above-mentioned acicular ITO particles.
It is determined from the size of the mesh-shaped conductive path of m. If it is a granular transparent conductive powder, a particle size of 1 μm or less is preferable. When using a granular powder, if the particle size is 1 μm or more, the film thickness increases accordingly, which is not preferable. In contrast, the acicular or flaky powder can have a film thickness within 2 to 3 μm even if the particle diameter is about 10 μm, which is different from the granular powder.

Examples of the transparent conductive powder material having a small particle size include ITO, tin-antimony oxide (ATO), zinc-aluminum oxide, etc., but any material having both translucency and conductivity may be used. However, the present invention is not limited to these.

The resin used in the conductive paste of the present invention may be the same thermoplastic resin, thermosetting resin, ultraviolet curing resin, etc. as the resin used in the conventional translucent conductive film.

The weight ratio of the acicular ITO powder having a major axis of 30 μm or more and the resin in this conductive paste is such that the acicular ITO powder:
Resin = 50: 50 to 80:20 is preferable. The reason is that if the amount of resin is more than 50:50, the resistance of the light-transmitting conductive film becomes too high, and if the amount of resin is less than 80:20, the strength of the light-transmitting conductive film decreases and at the same time the resistance also increases. is there.

Further, in this conductive paste, the major axis 3
The weight ratio of the acicular ITO powder having a particle diameter of 0 μm or more and the transparent conductive powder having a small particle diameter is preferably 95: 5 to 60:40. The reason is that if the amount of the transparent conductive powder having a particle size smaller than 95: 5 is small, the effect of making the film resistance uniform cannot be obtained, while
When it is more than 0:40, the membrane resistance increases, which is not preferable. In addition, it is more preferably 90:10 to 70:30.

As the solvent used for the conductive paste, an organic solvent or water used for general paints / pastes can be used. For example, as an organic solvent, cyclohexanone, isophorone, a ketone solvent such as diacetone alcohol, an alcohol solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol, terpineol, an ester solvent such as ethyl acetate or butyl acetate, cellosolve, butyl cellosolve. , Butyl carbitol, N,
Examples thereof include, but are not limited to, N-dimethylformamide and the like.

The conductive paste of the present invention is applied to a substrate by a method such as screen printing, blade coating, wire bar coating, etc., and then dried and cured, heat cured, and ultraviolet cured to form a film, depending on the type of paste.

[0027]

EXAMPLE FIG. 1 is a schematic view showing a cross section of an EL device of the present invention, in which 5 is a transparent conductive powder having a small particle size, and 6 is a transparent conductive powder layer having a small particle size.

That is, FIG. 1 (a) is an EL device using the acicular ITO powder 4 having a major axis of 30 μm or more and the transparent conductive powder 5 having a small particle size in the same film, and (b) and (c) are the major axis 30.
This is an EL element in which the needle-like ITO powder 4 having a size of μm or more and the transparent conductive powder layer 6 having a small particle size are used in different films, and the films have low resistance and uniform resistance.

The uniform resistance is obtained by acicular ITO having a large major axis.
Since it may be performed in a mesh-shaped conductive path of several μm to several tens of μm formed by the powder 4, the conductivity of the transparent conductive powder 5 having a small particle size to be used may not be so high. The specific resistance is preferably several hundred Ω · cm or less, more preferably several Ω · cm or less.

In the case of FIGS. 1B and 1C, the surface resistance of the transparent conductive powder layer 6 having a small particle size is several hundreds k.
Since even Ω / □ is sufficiently effective, the layer thickness is, for example, 1μ.
Even if it is as thin as m or less, it has almost no effect on the light transmittance of the entire transparent conductive film. This transparent conductive powder layer 6 is
Similar to the conductive paste, it is obtained by applying a paste in which a transparent conductive powder having a small particle size is dispersed in a solution in which a resin is dissolved, and then performing dry curing, heat curing, and ultraviolet curing.

Example 1 To a solution of indium metal dissolved in nitric acid was added tin tetrachloride hydrate, and the mixture was heated and concentrated with stirring to a liquid temperature of 130 to 15
It was obtained by concentrating to 0 ° C. to form a thick slurry, adding a large amount of water to this slurry, filtering, washing the needle-shaped powder obtained by filtration, drying and calcining at 1200 ° C. for 30 minutes. In addition, the average value of the major axis is 42 μm, the aspect ratio is 5 or more, the dust resistance is 0.01 Ω · cm, and the tin content is 2.
6% by weight of ITO powder (the crystal structure of which is shown in FIG. 2 in an electron micrograph) and granular IT having an average particle size of 0.04 μm, a dust resistance of 0.28 Ω · cm, and a tin content of 4.4% by weight.
O powder was mixed with the composition of paste 1 in Table 1, mixed, stirred, and then filtered through a 200-mesh stainless steel wire net, and the obtained conductive paste was a PET film having a thickness of 100 μm (Lumirror T type manufactured by Toray Industries, Inc.) A 150 mesh screen plate was screen-printed on the top to a size of 4 × 5 cm, and dried at 120 ° C. for 20 minutes to obtain a translucent conductive film. The surface resistance and the total light transmittance of the obtained conductive film (38
0 to 780 mm) and haze values are shown in Table 2. Surface resistance is Loresta MCP-T400 manufactured by Mitsubishi Petrochemical Co., Ltd.
It was measured by (trade name). The total light transmittance and the haze value were measured together with the PET film of the substrate by a direct reading haze computer HGM-ZDP (trade name) manufactured by Suga Test Machine Co., Ltd.

Using the conductive paste obtained in this example,
An organic dispersion type EL was prototyped. First, aluminum was vapor-deposited on one surface to have a thickness of 100 μm, an area of 4 × 5 cm, and 0.95.
An insulating layer (dielectric layer) was formed on the aluminum deposition surface of the Ω / □ polyester film. The insulating layer was obtained by printing a barium titanate paste having barium titanate particles dispersed in a cyanoethyl cellulose resin solution in a size of 4 × 5 cm using a 200 mesh screen and drying.

On this insulating layer, zinc sulfide paste in which phosphorous zinc sulfide particles were dispersed in a cyanoethyl cellulose resin solution was printed twice in a size of 4 × 5 cm using a 200 mesh screen and dried. did. further,
On top of that, add a conductive paste having the composition of paste 1 in Table 1
Printing was performed with a 0 mesh screen in a size of 3 × 4 cm and dried at 120 ° C. for 10 minutes to form a translucent conductive film.

A voltage applying lead wire is connected to one end of the translucent conductive film, and a resistance measuring lead wire is connected to the other end thereof.
A voltage application lead wire was connected to one end of the aluminum deposition surface of the polyester film. Then, 4 × 5 cm water catching films were superposed on both surfaces of these laminates, and the end portions of the lead wires were exposed to the outside from both sides thereof to form 5 ×.
An EL device was prepared by wrapping with a 6 cm fluorine film and subjecting it to moisture-proof lamination.

The resistance between the voltage applying lead wire and the resistance measuring lead wire connected to both ends of the transparent conductive film of this EL element was measured to measure the surface resistance of the transparent conductive film. A pseudo trapezoidal wave voltage of 106 V and 800 Hz is applied between the voltage applying lead wire connected to one end of the translucent conductive film and the voltage applying lead wire connected to one end of the vapor deposition surface of the polyester film. The device was made to emit light, and its brightness was measured. Luminance is measured by a luminance meter (product name: B manufactured by Topcon)
It was measured by M-8). The results are shown in Table 2.

Example 2 As a transparent conductive powder having a small particle size, an average particle size of 4 μm,
A translucent conductive film, EL was prepared in the same manner as in Example 1 except that the flaky ITO powder having a dust resistance of 26 Ω · cm and a tin content of 4.1% by weight was used and the composition of the paste 2 in Table 1 was used. The device was obtained. Example 1 was applied to the obtained translucent conductive film and EL device.
Table 2 also shows the result of the same measurement.

Example 3 As a transparent conductive powder having a small particle diameter, the average value of the major axis was 20.
Using a needle-shaped ITO powder having a particle size of μm, a powder resistance of 0.05 Ω · cm, and a tin content of 2.6 wt% (the crystal structure of which is shown in FIG. 3 by an electron micrograph), and the composition of paste 3 in Table 1 is used. A transparent conductive film was formed in the same manner as in Example 1 except that
An EL device was obtained. The results of the same measurements as in Example 1 are also shown in Table 2.

Example 4 The granular ITO powder used in Example 1 was used as the paste 5 in Table 1.
The paste made to have the composition of 100 μm thick
4 × 5 cm with a 200 mesh screen plate on a PET film (Lumirror T type manufactured by Toray Industries, Inc.)
Was screen-printed to a size of 100 μm and dried at 120 ° C. for 20 minutes to obtain a conductive film having a thickness of 0.8 μm and a surface resistance of 113 kΩ / □. Next, a paste prepared by making the needle-like ITO powder used in Example 1 so as to have the composition of paste 4 in Table 1 on the conductive film was 4 × with a 150 mesh screen plate.
An EL device was obtained in the same manner as in Example 1 while screen-printing to a size of 5 cm and drying at 120 ° C. for 20 minutes to obtain a translucent conductive film. Table 2 also shows the results obtained by performing the same measurement as in Example 1 on the obtained transparent conductive film and EL device.

Example 5 A paste prepared by using the flaky ITO powder used in Example 2 so as to have the composition of paste 6 in Table 1 had a thickness of 100 μm.
4 x 5 cm with 200 mesh screen plate on m PET film (Lumirror T type manufactured by Toray Industries, Inc.)
Was screen printed and dried at 120 ° C. for 20 minutes to obtain a conductive film having a film thickness of 0.8 μm and a surface resistance of 135 kΩ / □. Next, a paste prepared by making the needle-like ITO powder used in Example 1 so as to have the composition of paste 4 in Table 1 on the conductive film was 4 × with a 150 mesh screen plate.
An EL device was obtained in the same manner as in Example 1 while screen-printing to a size of 5 cm and drying at 120 ° C. for 20 minutes to obtain a translucent conductive film. Table 2 also shows the results obtained by performing the same measurement as in Example 1 on the obtained transparent conductive film and EL device.

Example 6 In Example 4, the paste 5 of Table 1 containing granular ITO powder and the PE of paste 4 of Table 1 containing acicular ITO powder.
A translucent conductive film obtained in the same manner as in Example 4 except that the film formation on the T film and the EL substrate was performed in the reverse order.
The same measurement results as in Example 1 of the EL element are also shown in Table 2.

Comparative Example 1 Translucency obtained in the same manner as in Example 1 except that the conductive paste prepared by making the acicular ITO powder used in Example 1 to have the composition of paste 4 in Table 1 was used. Conductive film and EL
The same measurement results as in Example 1 of the device are also shown in Table 2.

Comparative Example 2 The average value of the major axis used in Example 3 was 20 μm, and the powder resistance was 0.
Obtained in the same manner as in Example 1 except that a needle-like ITO powder having a content of 05 Ω · cm and a tin content of 2.6 wt% was used and a conductive paste prepared so as to have the composition of paste 7 in Table 1 was used. The same measurement results as in Example 1 for the transparent conductive film and the EL element are also shown in Table 2.

As is clear from the results shown in Table 2, all of the transparent conductive film and EL element of the present invention showed a low resistance almost equal to that of the conventional one, and a brightness superior to that of the conventional one was obtained.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

As described above, since the transparent conductive film and the EL element of the present invention use large acicular ITO powder having a major axis of 30 μm or more, a low resistance conductive film can be obtained, and at the same time, particles can be obtained. Since the transparent conductive powder having a small diameter is used, it has an excellent effect that the resistance in the plane of the conductive film can be made uniform and a higher brightness than the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of an EL element of the present invention,
(A) is an EL element using acicular ITO powder having a major axis of 30 μm or more and transparent conductive powder having a small particle size in the same film,
In (b) and (c), needle-like ITO powder having a major axis of 30 μm or more and a transparent conductive powder layer having a small particle size are used in different films, and the films are made to have low resistance and uniform resistance. EL
It is an element.

FIG. 2 is an electron micrograph showing a crystal structure of acicular ITO powder in Example 1 of the present invention.

FIG. 3 is an electron micrograph showing the crystal structure of acicular ITO powder in Example 3 above.

FIG. 4 is a schematic view showing a cross section of a dispersion-type EL device using a conductive film formed by using only acicular ITO powder having a major axis of 30 μm or more as a conductive filler.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal electrode 2 Dielectric layer 3 Phosphor particles 4 Needle-like ITO powder with a major axis of 30 μm or more 5 Transparent conductive powder with small particle size 6 Transparent conductive powder layer with small particle size

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Usoba 7-9-4 Nishigotanda, Shinagawa-ku, Tokyo Tohoku Kako Co., Ltd.

Claims (6)

[Claims] 1. A major axis of 30 μm in a resin and its solvent.
A conductive paste containing acicular indium-tin oxide powder having a ratio of major axis to minor axis of 5 or more and transparent conductive powder having a small particle diameter. 2. A transparent conductive film comprising acicular indium-tin oxide powder having a major axis of 30 μm or more, transparent conductive powder having a small particle size, and resin. 3. A transparent conductive film made of a transparent conductive powder having a small particle size and a resin, and a transparent conductive film made of acicular indium-tin oxide powder having a major axis of 30 μm or more and a resin. A transparent conductive film in which the two types of transparent conductive films are laminated on each other. 4. A needle-shaped indium-tin oxide powder having a major axis of 30 μm or more, a transparent conductive powder having a small particle size, and a resin are formed on a substrate in which a metal electrode, a dielectric particle layer, and a phosphor particle layer are laminated in this order. Dispersive electroluminescent element having a transparent conductive film formed thereon. 5. A transparent conductive film composed of a transparent conductive powder and a resin having a small particle size, and a long diameter of 30 μm or more on a substrate in which a metal electrode, a dielectric particle layer and a phosphor particle layer are laminated in this order. A dispersion-type electroluminescence device in which translucent conductive films made of acicular indium-tin oxide powder and resin are laminated on each other. 6. A transparent conductive powder having a small particle size has a major axis of 3
6. At least one of acicular indium-tin oxide powder having a particle size of 0 μm or less, scaly indium tin oxide powder having a particle size of 30 μm or less, or granular conductive oxide powder having a particle size of 1 μm or less. Conductive paste, translucent conductive film, and dispersion type electroluminescent device.