JPH06309922A - Electroconductive paste and light transmissive electroconductive film - Google Patents

Abstract

PURPOSE:To provide a sufficient electroconductivity and light-beam transmissivity by using an electroconductive paste which contains needle-shaped indium-tin oxide fine powder having a short diameter/long diameter ratio as exceeding a specific value in a resin and a solvent for it in a certain specific weight ratio range. CONSTITUTION:In a resin and a solution for it which have been used as a photo-transmissive electroconductive film, needle-shaped indium-tin oxide(ITO) fine powder is included, whose long diameter is over 5mum and long-to-short diametric ratio is between 5 and 10. and thus an electroconductive paste is formed. The resultant electroconductive film should consist of ITO fine powder and resin, have a specific resistance of film under 1.0OMEGA.cm, and the ITO fine powder content by volume of the film being below 25 capacity %. The weight ratio of the ITO fine powder in the paste to the resin should preferably range between 60:40 thru 80:20. More resin content heightens the film resistance, and less resin sinks the film strength while heightens the resistance.

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 electroluminescence (EL) light emitting element.

[0002]

2. Description of the Related Art Conventional electroluminescence (E
L) As a conductive paste used for forming a light-transmitting electrode such as a light-emitting element, indium-tin oxide (ITO) ultrafine powder as a conductive filler is dispersed in a solvent in which a resin is dissolved, or phosphorus. There is one in which flaky ITO powder is dispersed in a solvent in which a resin is dissolved.

In an 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 material. A 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 that the thickness is about m.

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, and when the conductive paste is applied, the unevenness of the surface of the zinc sulfide layer causes the thickness of the conductive paste to be different. Is non-uniform, and a portion of 1 μm or less or a portion of 5 μm or more is generated, a conductive film of 2 to 3 μm cannot be uniformly formed on the entire surface, and there is a problem that cracks occur in a thin portion and resistance increases.

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

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a conductive paste and a light-transmitting conductive film which have sufficient conductivity and light transmittance.

[0008]

Means for Solving the Problems The means for solving the problems of the present invention is to provide acicular indium-tin oxide fine particles having a major axis of 5 μm or more and a major axis to minor axis ratio of 5 or more in a resin and its solvent. A conductive paste containing powder, and a translucent conductive film composed of acicular indium tin oxide fine powder and a resin, the specific resistance of the film being 1.0 Ω · cm or less, and the acicular indium in the film. Tin oxide fine powder volume content is 25% by volume
The following is in the transparent conductive film.

[0009]

The acicular indium-tin oxide fine powder used in the present invention is obtained, for example, by adding tin tetrachloride hydrous salt to a solution of indium metal dissolved in nitric acid, concentrating by heating with stirring, and 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-shaped powder obtained by filtration, dry, and calcinate at about 700 ° C. for about 30 minutes to obtain a slurry.

This acicular indium-tin oxide fine powder is
A major axis of 5 μm or more, an aspect ratio of 5 or more, and an aspect ratio of about 30 can be obtained depending on the tin compound to be added and the concentration conditions. When this powder is applied with a pressure of 100 kgf / cm ² to form a pellet, the specific resistance (hereinafter referred to as powder resistance) is about 0.03 Ω · cm.

In the present invention, the reason why the needle-like indium-tin oxide fine powder has an aspect ratio of 5 or more is that conductivity can be obtained by using a small amount of the resin in the resin. This is because if the aspect ratio is 5 or less, it is impossible to achieve the volume resistivity of the conductive filler of the translucent conductive film of 25% or less and the specific resistance of the film to 1.0 Ω · cm or less. A higher aspect ratio is better and preferably 10 or more.

In the present invention, the acicular indium-tin oxide fine powder has a major axis of 5 μm or more because the larger the major axis, the smaller the number of contact points between the particles and the low resistance film is obtained. For example, when used in a dispersion type EL, since the phosphor layer on the coated surface uses zinc sulfide particles having a diameter of 5 to 30 μm, the surface has irregularities of about several μm, but the major axis is 5
This is because when the thickness is at least μm, the needle-shaped particles are kept in contact with each other even if such irregularities are present, and required conductivity is obtained.

However, when the major axis is 100 μm or more,
Generally, it is difficult to pass through the screen mesh during screen printing, which may hinder printing.
A long diameter of 00 μm or less is preferable. However, this is not the case when using a coarse screen of 100 mesh or less. The conductive paste of the present invention uses a relatively large filler, but it is possible to screen-print a line having a width of about 200 μm.

As the resin used in the present invention, a thermoplastic resin, a thermosetting resin, an ultraviolet curable resin or the like similar to the resin used in the conventional transparent conductive film is used. The weight ratio of acicular indium-tin oxide fine powder and resin in the paste is
Needle-shaped indium-tin oxide fine powder: resin = 60: 40-
80:20 is good. This is because if the amount of resin is more than 60:40, the resistance of the transparent conductive film becomes too high, and if the amount of resin is less than 80:20, the strength of the transparent conductive film is lowered and at the same time the resistance is increased.

The resistance of the obtained transparent conductive film is slightly different depending on the substrate to which the conductive paste is applied. For example, a film applied to a polyester film generally has a lower resistance than a film applied to glass.

Comparing the light-transmitting conductive film of the present invention with a conventional conductive film using ITO ultrafine powder as a conductive filler, in the present invention, acicular indium-tin oxide fine powder having a high aspect ratio is obtained. Since it is used as a conductive filler, the optimum weight ratio of acicular indium-tin oxide fine powder to resin is 60:40 to 80:20, preferably 65:40.
35 to 70:30, while conventional ITO
In the case of using ultrafine powder, the weight ratio of ITO: resin is 8
It is about 5:15 to 90:10. Therefore, in the present invention, the volume content of the acicular indium-tin oxide fine powder in the film of the transparent conductive film is set to 25% or less and 1.0 Ω · cm.
The following specific resistance can be obtained. In the present invention, since the conductive film can be made thicker than before, the surface resistance can be lowered.

Comparing the optical characteristics of the translucent conductive film of the present invention with that of a conventional film using ITO ultrafine powder, the film of the present invention has a very high haze value of about 90%, so that light scattering occurs. It is large and therefore the total light transmittance measured is 50-80.
% Is low. However, when it is used as a translucent conductive film of an EL element, the light transmittance thereof does not simply reflect on the brightness of the EL. In the translucent conductive film of the present invention, the light transmittance is low because a large amount of incident light is scattered due to high haze rather than large light absorption.
When considering the brightness of the device, the absorption of light from the ITO particles is more important than the scattered light.

It is considered that the smaller the amount of acicular indium-tin oxide fine powder present in the film, the smaller the amount of light absorption. Therefore, the light-transmitting conductive film of the present invention capable of forming a low-resistance light-transmitting conductive film with a small amount of acicular indium-tin oxide fine powder can obtain high brightness despite the low measured light transmittance. You can

[0019]

【Example】

Example 1 As shown in FIG. 1, the major axis manufactured by the applicant is 5 μm or more, the aspect ratio is 5 or more, the dust resistance is 0.03 Ω · cm, and the tin content is 2.
6% by weight of acicular indium-tin oxide fine powder (hereinafter referred to as IT
O powder) and the resin liquid were mixed in the composition of paste 1 in Table 1 and mixed and stirred well, and then filtered through a 200-mesh stainless wire mesh to obtain a conductive paste.

The obtained conductive paste is 75 × 75 ×
A 1.1 mm soda lime glass plate and a 100 μm thick polyester film of the same size (made by Toray Industries, Inc., trade name Lumirror T type) are screened to a size of 4 × 5 cm with a 200 mesh screen plate. Printing was performed, followed by drying at 120 ° C. for 20 minutes and curing to obtain a translucent conductive film. FIG. 2 shows a 2000-times micrograph of the translucent conductive film obtained on the polyester film.

The film thickness, surface resistance, total light transmittance, haze value, and film weight (glass plate only) of the obtained film were measured.
Since the surface of the film has irregularities, the film thickness was read from the measurement chart in units of 0.5 μm. The weight of the polyester film was not measured because the weight changes due to moisture absorption and the like. The specific resistance of the film was determined from the film thickness and the surface resistance, and the ITO powder volume content of the film was determined from the weight of the conductive film, the film thickness, and the paste composition.

Specific resistance of film (Ω · cm) = surface resistance (Ω /
□) × Film thickness (10 ⁻⁴ cm) ITO powder volume content (%) = Film weight (g) × {ITO
(G) / [ITO (g) + resin (g)]} × {1/7.
2 (specific gravity of ITO g / cm ³ )} × {1 / [4 × 5 (area cm ² ) × film thickness (10 ⁻⁴ cm)]} × 100

The film thickness is measured by a surface roughness measuring device manufactured by Tokyo Seimitsu Co., Ltd.
The surface resistance was measured with a product name Surfcom 900A, and the surface resistance was measured with a product name Loresta MCP-T400 manufactured by Mitsubishi Petrochemical Co., Ltd., respectively. The total light transmittance and the haze value were measured by a direct reading haze computer HGM-ZDP manufactured by Suga Test Machine Co., Ltd. together with the glass plate of the substrate and the polyester film.

Example 2 A conductive paste and a translucent conductive film were obtained in the same manner as in Example 1 except that the same ITO powder as in Example 1 was used except that the composition of the paste was Paste 2 in Table 1. FIG. 3 shows a 2000 × micrograph of the translucent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 3 A conductive paste and a light-transmissive conductive film were obtained in the same manner as in Example 1 except that the same ITO powder as in Example 1 was used except that the composition of the paste was Paste 3 in Table 1. FIG. 4 shows a 2000 × photomicrograph of the translucent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 4 A conductive paste and a transparent conductive film were obtained in the same manner as in Example 1 except that the same ITO powder as in Example 1 was used except that the composition of the paste was paste 4 in Table 1. FIG. 5 shows a 2000 × photomicrograph of the translucent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 5 A conductive paste and a translucent conductive film were obtained in the same manner as in Example 1, except that the same ITO powder as in Example 1 was used except that the composition of the paste was Paste 5 in Table 1. FIG. 6 shows a 2000-times micrograph of the transparent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 6 FIG. 7 with a tin content of 2.6% by weight and a dust resistance of 0.03 Ω · cm.
A conductive paste and a translucent conductive film were obtained in the same manner as in Example 1 except that the ITO powder shown in 1 was used and the paste composition was changed to that of paste 6 in Table 1. FIG. 8 shows a 2000 × photomicrograph of the translucent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 7 A conductive paste and a translucent conductive film were obtained in the same manner as in Example 1 except that the ITO powder used in Example 6 was used and the paste composition was changed to that of paste 7 in Table 1. . Example 1
Measurements similar to those described above were performed, and the obtained results are shown in Table 2.

Example 8 The same procedure as in Example 1 was carried out except that the ultraviolet curable resin shown in Table 1 was used as the resin, the ITO powder used in Example 6 was used, and the paste composition was the paste 8 shown in Table 1. Thus, a conductive paste and a transparent conductive film were obtained. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2. The curing of the film
Metal highland lamp M01 made by Eyegraftik Inc.
-L212, illuminator (cold mirror type) UE011-
201C, power supply device UB01.51-3A / BM-E
2. Using a heat ray cut filter, illuminance 150m
It was performed in nitrogen gas at W / cm ² for 20 seconds.

Example 9 Using the ITO powder used in Example 1, the paste 9 in Table 1 was used.
A conductive paste and a translucent conductive film were obtained in the same manner as in Example 1 except that the above composition was used. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Example 10 The conductive paste obtained in Example 3 was used for 3.3 lines / m.
FIG. 9 shows a 100 × micrograph of the line pattern of the translucent conductive film obtained by screen-printing the line m in the same manner as in Example 1.

Example 11 Using the conductive paste obtained in Example 6, organic dispersion type E
L was prototyped. First, a barium titanate paste (TU-made by Tohoku Kako Co., Ltd. as an insulating layer (dielectric layer) was formed on the aluminum vapor-deposited surface of a polyester film having a thickness of 100 μm, an area of 4 × 5 cm, and an area of 0.95 Ω / □, which was vapor-deposited on one surface. 217) was printed in a size of 4 × 5 cm using a 200 mesh screen and dried.

On the insulating layer, zinc sulfide paste (TU-219 manufactured by Tohoku Kako Co., Ltd.) was printed twice in a size of 4 × 5 cm using a 200 mesh screen and dried. Then, the conductive paste of Example 6 was printed on a size of 3 × 4 cm with a 200 mesh screen, and 120 ° C., 1
It was dried for 0 minutes to form a transparent conductive film.

A voltage-carrying lead wire was connected to one end of the translucent conductive film, a resistance-measuring lead wire was connected to the other end, and the voltage-carrying lead wire was connected to one end of the aluminum deposition surface of the polyester film. And 4x5c on both sides of these laminates
m water-absorbing films were stacked, the ends of the lead wires were exposed to the outside from both sides of the film, and the film was wrapped with a 5 × 6 cm fluorine film for moisture-proof lamination to produce an EL device.

The resistance between the voltage-carrying lead wire and the resistance measuring lead wire connected to both ends of the transparent conductive film is measured to measure the surface resistance of the transparent conductive film. A voltage of a pseudo trapezoidal wave of 106 V and 800 Hz is applied between the voltage-carrying lead wire connected to one end of the conductive film and the voltage-carrying 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. The brightness was measured with a brightness meter (trade name: BM-8, manufactured by Topcon). The results are shown in Table 3.

Example 12 An EL device was prepared in the same manner as in Example 11 except that the paste of Example 9 was used, and the same measurement was carried out. The results are shown in Table 3.

Comparative Example 1 The same ITO powder as in Example 1 was used, and the paste 10 in Table 1 was used.
A conductive paste was prepared in the same manner as in Example 1 except that the above composition was used to obtain a translucent conductive film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Comparative Example 2 The conductive paste of Example 3 was subjected to a strong dispersion treatment using a three-roll mill, and the ITO powder was broken and the aspect ratio was 5
A paste containing a large amount of the following ITO powder was made. Using this paste, a transparent conductive film was obtained in the same manner as in Example 1. FIG. 10 shows a 2000 × photomicrograph of the translucent conductive film obtained on the polyester film. The same measurement as in Example 1 was performed, and the obtained results are shown in Table 2.

Comparative Example 3 A conductive paste having a composition of paste 11 shown in Table 1 obtained by dispersing ITO ultrafine powder having an average particle size of 0.03 μm as a conductive filler in an acrylic resin and a solvent (trade name X- manufactured by Tohoku Kako Co., Ltd.). 101) is a 75 × 75 × 1.1 mm thick soda lime glass and a thickness of 100 μm and a size of 75 × 75.
mm polyester film (Lumirror T type, manufactured by Toray Industries, Inc.) was printed with a 300 mesh screen plate having a size of 4 × 5 cm, and then dried with infrared rays at 50 ° C. for 10 minutes, then 120 ° C. for 5 minutes, and then transparent A photoconductive film was obtained. 10000 of the translucent conductive film on the obtained polyester film
A magnified micrograph is shown in FIG. The same measurement as in Example 1 was performed. The results are shown in Table 2.

[0041]

[Table 1] Paste composition Ingredients% by weight ITO powder / resin weight ratio ──────────────────────────────────── Paste 1 ITO powder 40.0 Acrylic resin A 10.0 80:20 (Soken Chemical Co., Ltd., trade name Thermolac M-45C) Solvent A Isophorone 50.0 ─────────────── ───────────────────── Paste 2 ITO powder 30.5 Acrylic resin A 13.0 70:30 Solvent A 56.5 ──────── ─────────────────────────── Paste 3 ITO powder 29.0 Acrylic resin A 14.0 67.5: 32.5 Solvent A 57 .0 ─────────────────────────────────── Paste 4 ITO powder 27.7 Acrylic resin A 14.9 65:35 Solvent A 57.4 ─────────────────────────────────── Paste 5 ITO Powder 27.0 Acrylic resin A 18.0 60:40 Solvent A 55.0 ───────────────────────────────── ─── Paste 6 ITO powder 29.4 Acrylic resin B 14.1 67.5: 32.5 (Mitsubishi Rayon Co., Ltd. Dynal BR-80) Solvent A 56.5 ──────────── ──────────────────────── Paste 7 ITO powder 39.8 Acrylic thermosetting resin 19.1 67.5: 32.5 (Kansai Paint Company name Magicron No.1000) Solvent A 41.1 ─────────────────────────────────── Paste 8 IT Powder 34.2 Vinyl ester resin 13.7 (trade name Lipoxy VR-77 manufactured by Showa High Polymer Co., Ltd.) Trimethylolpropane triacrylate 8.0 2-Hydroxy-2-methyl-1-phenyl-propanone-1 1.1 60 : 40 Solvent A 43.0 ─────────────────────────────────── Paste 9 ITO powder 30.5 High Dielectric thermoplastic resin 15.5 67:33 (trade name Cyanoresin CR-S manufactured by Shin-Etsu Chemical Co., Ltd.) Solvent γ-butyrolactone 53.0 ───────────────────── ─────────────── Paste 10 ITO powder 21.5 Resin A 21.5 50:50 Solvent A 57.0 ─────────────── ──────────────────── Paste 11 ITO ultrafine powder 29.0 Resin A 6. 88:12 solvent A 42.7 ───────────────────────────────────

[0042]

[Table 2] Example Hoast Substrate Coating film Physical composition Composition Thickness ITO surface resistance Membrane specific resistance Total ray haze value (μm) Volume included (Ω / □) (Ω · cm) Transmittance (%) Rate (%) (%) ) 1 1 glass 7.5 19.7 630 0.47 40.1 92.8 PET 6.5 405 0.26 44.3 92.6 2 2 glass 6.0 17.5 383 0.23 58.7 92.8 PET 6.0 342 0.21 59.4 92.8 3 3 glass 6.0 17.6 410 0.25 62.5 92.6 PET 6.0 405 0.24 64.3 92.7 4 4 glass 5.0 16.5 486 0.24 64.2 92.8 PET 5.0 468 0.23 65.8 92.7 55 Glass 5.5 15.0 1500 0.83 70.3 92.6 PET 5.5 1100 0.61 72.1 92.5 6 6 Glass 5.0 15.8 347 0.17 77.1 82.2 PET 7.0 147 0.10 73.0 90.7 7 7 Glass 9.0 19.8 189 0.17 63.7 91.2 PET 14.0 176 0.25 61.6 92.0 8 8 Glass 8.0 16.9 140 0.11 50.5 92.2 PET 8.0 145 0.12 52.0 92.0 9 9 Glass 6.0 16.2 490 0.29 60.4 92.7 PET 6.0 410 0.25 65.3 92.6 ────────────── ───────────── ──────── Comparative Example 1 10 Glass ^{5.0 12.3 1.5 × 10 4 7.5 78.0} 91.5 PET 6.0 1.1 × 10 4 6.6 79.0 91.6 2 3 Glass 4.0 21.1 4820 1.93 70.5 92.5 PET 4.5 3870 1.74 70.0 92.7 3 11 Glass 1.9 43.4 630 0.12 80.7 9.3 PET 2.5 520 0.13 78.5 10.6 ─────────────────────────────────── Glass is a glass plate And PET indicates a polyester film.

[0043]

[Table 3] Translucent conductive film Surface resistance (Ω / □) EL brightness (conductive paste) (Cd / m ² ) Example 11 ITO powder film 188 198 (Paste 6) Example 12 ITO powder film 720 212 (Paste) 9)

[0044]

According to the present invention, it is possible to provide a conductive paste and a light-transmissive conductive film which have sufficient conductivity and light transmittance.

[Brief description of drawings]

FIG. 1 is a micrograph showing a crystal structure of acicular indium-tin oxide fine powder used in Example 1.

FIG. 2 is a micrograph of a translucent conductive film obtained in Example 1.

FIG. 3 is a micrograph of a translucent conductive film obtained in Example 2.

FIG. 4 is a micrograph of the translucent conductive film obtained in Example 3.

5 is a micrograph of a translucent conductive film obtained in Example 4. FIG.

FIG. 6 is a micrograph of a translucent conductive film obtained in Example 5.

7 is a micrograph showing a crystal structure of needle-shaped indium-tin oxide fine powder used in Example 6. FIG.

8 is a micrograph of a translucent conductive film obtained in Example 6. FIG.

9 is a micrograph of a line pattern of the transparent conductive film obtained in Example 10. FIG.

10 is a micrograph of a transparent conductive film obtained in Comparative Example 2. FIG.

11 is a micrograph of a transparent conductive film obtained in Comparative Example 3. FIG.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location H01L 23/31 33/00 N 7376-4M H05K 1/09 A 6921-4E

Claims (3)

[Claims] 1. A conductive paste comprising a resin and a solvent thereof containing acicular indium-tin oxide fine powder having a major axis of 5 μm or more and a major axis to minor axis ratio of 5 or more. 2. The conductive paste according to claim 1, wherein a weight ratio of acicular indium-tin oxide fine powder: resin is 60:40 to 80:20. 3. A translucent conductive film comprising acicular indium-tin oxide fine powder and a resin, the specific resistance of which is 1.0.
A translucent conductive film having an Ω · cm or less and a volume content of fine acicular indium-tin oxide powder in the film of 25% by volume or less.