JP3294705B2 - High-temperature firing conductive paste and translucent conductive film - Google Patents

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 light-transmitting conductive film used for forming a light-transmitting electrode such as an electroluminescence (EL) light-emitting device.

[0002]

2. Description of the Related Art An electroluminescent (EL) light-emitting device emits light by applying a high electric field to a phosphor, and uses a phosphor of about 5 to 30 .mu.m and mixes it with an appropriate binder to form a film. This type is called a distributed EL. As the dispersion type EL, a type which uses a resin or a plastic as a binder and is manufactured at a relatively low temperature of about 100 to 200 ° C. is widely used.
Some types of EL are manufactured through a high temperature process of 500-600 ° C.

The light-transmitting electrodes of the former type of dispersion type EL element are formed by forming an ITO (indium-tin oxide) film on a plastic film by sputtering or the like, or a conductive filler in a solvent in which a resin is dissolved. What is formed of a conductive paste dispersed in a conductive paste is used.

In the latter type of dispersion type EL device, for example, a white enamel layer such as BaTiO ₃ or TiO is baked on a low carbon steel plate, and a mixture of a transparent glass having a low melting point and a high dielectric constant and a phosphor powder is formed thereon. Is used to bake the phosphor layer. As the translucent electrode, a Nesa film formed by a chloride CVD method or the like is used.

However, the use of the Nesa film has the following disadvantages. (1) Since a film is formed by the CVD method, a conductive film is formed on the entire surface, and patterning is difficult. (2) The white enamel layer, the phosphor layer, and the transparent protective layer (formed on the light-transmitting conductive film) are all formed by a printing method such as screen printing, but only the nesa film is a CVD method. This is inconvenient for simplifying the process.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a conductive paste and a light-transmitting conductive film that can form a light-transmitting conductive film by high-temperature firing using a printing method such as screen printing. It is intended to propose.

[0007]

The conductive paste according to the present invention comprises a transparent glass frit, a solvent, and a long diameter of 5 μm.
It is characterized in that it contains acicular indium-tin oxide fine powder having a ratio of a major axis to a minor axis of 5 or more, and this conductive paste has a volume ratio of acicular indium-tin oxide fine powder: transparent glass frit. Is 10:90 to 50:50
It is characterized by being. In addition, the light-transmitting conductive film according to the present invention is made of acicular indium-tin oxide fine powder and glass, and has a specific resistance of 5.0 Ω · cm or less.

[0008]

The acicular indium-tin oxide fine powder used in the present invention is acicular and has a characteristic of having a high aspect ratio of 5 or more and a low resistance value.
The following methods are known.

(A) An aqueous solution containing indium ions, nitrate ions, and a tin compound that becomes SnO ₂ by calcination is heated and concentrated to form a high-viscosity slurry. A method of separating the body and calcining the needle-like powder first intermediate.

(B) An aqueous solution containing indium ions, nitrate ions, indium hydroxide and / or indium oxide, and a tin compound which becomes SnO ₂ by calcination is heated and concentrated to form a high viscosity slurry. Separating the acicular powder first intermediate from the slurry and calcining the acicular powder first intermediate.

(C) An aqueous solution containing indium ions, nitrate ions, and indium-tin hydroxide is heated and concentrated to form a high-viscosity slurry, and a needle-like powder first intermediate is separated from the slurry. And calcining the first intermediate of the acicular powder.

(D) An aqueous solution containing indium ions and nitrate ions is concentrated by heating to form a high-viscosity slurry, and the first intermediate powder of the acicular powder is separated from the slurry. A method in which the intermediate is coated with a tin compound which becomes tin dioxide by calcination and calcined.

(E) An aqueous solution containing indium ions, nitrate ions, indium hydroxide and / or indium oxide is heated and concentrated to form a high-viscosity slurry, and the needle-like powder first intermediate is produced from the slurry. And calcinating the first intermediate of the acicular powder by coating with a tin compound which becomes tin dioxide by calcination.

In each of the above-mentioned production methods, as a method for separating the acicular powder first intermediate from the high-viscosity slurry produced by heat concentration, a method of adding a large amount of water to the slurry and filtering the slurry is used. The needle powder obtained by filtration is washed,
After drying, it is calcined at about 700 to 1200 ° C. for several tens minutes.

In each of the above-mentioned production methods, a method for reacting the first intermediate acicular powder with an aqueous alkali solution to obtain a second intermediate acicular powder, and calcining the second intermediate acicular powder. May be taken.

According to each of the above manufacturing methods, the major axis is 5 μm or more,
With an aspect ratio of 5 or more, an aspect ratio of about 30 can be obtained depending on the tin compound to be added and the concentration conditions. The specific resistance (hereinafter referred to as the powder resistance) when the powder is formed into a pellet by applying a pressure of 100 kgf / cm ² is 0.0
It is about 3Ω · cm. The aspect ratio is set to 5 or more so that conductivity can be obtained by using a small amount of glass. If the aspect ratio is less than 5, the specific resistance of the film cannot be reduced to 5.0 Ω · cm or less. The aspect ratio is preferably higher, more preferably 10 or more.

Further, the major axis of the acicular indium-tin oxide fine powder to be used is set to 5 μm or more because the larger the major axis, the smaller the number of contact points between the particles and a lower resistance film is obtained. When used for a mold EL, since the phosphor layer on the coating surface uses zinc sulfide particles having a diameter of 5 to 30 μm, the surface has irregularities of about several μm, but the long diameter is 5 μm.
This is because if the number is not less than m, the contact between the acicular particles is maintained and the necessary conductivity can be obtained even if such irregularities are present. However, if the major axis is 100 μm or more, it is difficult to pass through the screen mesh at the time of screen printing, which may hinder printing.
The following major diameter is preferred. However, this does not apply when a coarse screen having a mesh size of 100 mesh or less is used. In the conductive paste of the present invention, a relatively large filler is used, but a line having a width of about 200 μm can be screen-printed.

As the glass frit used in the present invention, a glass frit that has passed through a sieve of 300 to 500 mesh can be used. The type is not particularly limited, but is selected according to the firing temperature. 500-600 ° C
Is, for example, PbO-B having a relatively low melting point.
₂ O ₃ —SiO ₂ glass can be used. However, when formed on the phosphor of the EL element, it is necessary to select a glass that does not react with zinc sulfide (ZnS) of the phosphor. _{PbO-B 2} O 3 -SiO ₂ based glass, Pb
This is not preferred because O reacts with ZnS.
When used for an EL element, for example, Na containing no PbO
_{2 O-B 2} O 3 -ZnO based glass can be used.

In the present invention, the volume ratio of the acicular indium-tin oxide fine powder in the paste to the glass frit is limited to 10:90 to 50:50.
If the amount of glass is more than 90, the resistance of the light-transmitting conductive film becomes too high, and if the amount of glass is less than 50:50, the strength of the light-transmitting conductive film is reduced and the resistance is also increased.

The reason why the volume ratio is used as the ratio between the acicular indium-tin oxide fine powder and the glass frit is that the specific gravity of the glass frit varies greatly from 2 to 6 depending on the frit used. For example, when a resin is used as the binder, the specific gravity of the resin is usually 1.1 to 1.3, so that using either the weight ratio or the volume ratio does not cause a serious problem.

On the other hand, the paste is usually adjusted to an appropriate viscosity by using a thickener for printing by screen printing. As the thickener, a cellulose-based material such as methylcellulose or ethylcellulose, or a resin such as acryl can be used. Any of these may be used as long as they are burned and removed during the firing process.

As the solvent used for the paste, an organic solvent or water used for general paints and pastes can be used. For example, as the organic solvent, cyclohexanone,
Ketone solvents such as isophorone and diacetone alcohol;
Alcohol solvents such as methyl alcohol, ethyl alcohol and isopropyl alcohol; ester solvents such as ethyl acetate and butyl acetate; cellosolve, butyl cellosolve, butyl carbitol; Examples include, but are not limited to, N-dimethylformamide.

The baking temperature of the coating film is preferably higher than the softening point of the glass frit used. If it is lower than the softening point, the flow of the glass frit as a binder is insufficient and a film having sufficient strength cannot be obtained.

The firing of the coating film can be performed in the air.
In addition, although it can also be performed in an inert gas or weakly reducing atmosphere, in this case, since holes are introduced into the ITO particles, the resistance can be reduced as compared with firing in the air. . However, combustion of celluloses and resins, which are commonly used thickener components, requires oxygen, and after completion of combustion of these thickener components, an inert gas atmosphere or a weak reducing atmosphere is required.

[0025]

【Example】

Example 1 Tin tetrachloride hydrate was added to a solution in which indium metal was dissolved in nitric acid, and the mixture was heated and concentrated with stirring, and the solution temperature was 130 to 15%.
The solution is concentrated to 0 ° C. to form a thick slurry, a large amount of water is added to the slurry, and the slurry is filtered. The acicular powder obtained by the filtration is washed, dried, and calcined at about 1200 ° C. for 30 minutes. In addition, the major axis is 5 μm or more, the aspect ratio is 5 or more, the dust resistance is 0.02Ω · cm, and the tin content is 2.5% by weight.
Needle-like indium-tin oxide fine powder shown in FIG.
An ITO powder) and a glass frit were blended into the composition of paste 1 in Table 1, mixed and stirred well, filtered through a 200-mesh stainless steel wire mesh, and the obtained conductive paste was soaked in 75 × 75 × 1.1 mm soda. 2 on lime glass plate
A screen printing plate having a size of 4 × 5 cm was printed on a 00 mesh screen plate, dried at 120 ° C. for 20 minutes, and then baked at 540 ° C. in the air for 10 minutes.
FIG. 2 shows a 000-fold micrograph, and Table 2 shows the film thickness, surface resistance, total light transmittance (380 to 780 mm), haze value, and specific resistance.

The film thickness was measured with a surface roughness measuring device (trade name: Surfcom 900A) manufactured by Tokyo Seimitsu Co., Ltd. At this time, the measurement chart shows 0.5
Read in μm units. The surface resistance was measured with a LORESTA MCP-T400 (trade name) manufactured by Mitsubishi Yuka Corporation. The total light transmittance and the haze value were measured using the HGM-ZDP direct reading haze computer manufactured by Suga Test Machine Co., Ltd.
(Trade name). The specific resistance of the film was determined by the following equation. Specific resistance of the film (Ω · cm) = surface resistance (kΩ / □) × film thickness (10 ⁻⁴ cm)

Example 2 A conductive paste and a light-transmitting conductive film were obtained in the same manner as in Example 1 except that the composition of the paste was Paste 2 shown in Table 1. FIG. 3 is a photomicrograph (magnification: 2000) of the obtained light-transmitting conductive film. FIG. 3 shows the film thickness, surface resistance, and total light transmittance (38
Table 2 shows the haze value and the specific resistance.

Example 3 A conductive paste and a light-transmitting conductive film were obtained in the same manner as in Example 2, except that the screen plate used for screen printing was 150 mesh. The thickness, surface resistance, and total light transmittance (3%) of the obtained translucent conductive film obtained by the same means as in Example 1.
Table 2 shows the haze value and the specific resistance.

Example 4 The composition of the paste was the paste 3 shown in Table 1, and the baking was performed in the atmosphere 5
The same ITO as in Example 1 except that it was performed at 60 ° C. for 10 minutes.
A conductive paste and a light-transmitting conductive film were obtained in the same manner as in Example 1 using the powder. Table 2 shows the film thickness, surface resistance, total light transmittance (380 to 780 mm), haze value, and specific resistance of the obtained translucent conductive film obtained by the same means as in Example 1.

Example 5 A conductive paste and a light-transmitting conductive film were obtained in the same manner as in Example 4, except that the screen plate used for screen printing was 150 mesh. The thickness, surface resistance, and total light transmittance (3%) of the obtained translucent conductive film obtained by the same means as in Example 1.
Table 2 shows the haze value and the specific resistance.

Example 6 A conductive paste and a light-transmitting conductive material were prepared in the same manner as in Example 5, except that a low alkali glass of 75 × 75 × 1.1 mm was used for the substrate and sintering was performed at 600 ° C. in the air for 10 minutes. A membrane was obtained. The film thickness, surface resistance, and total light transmittance (380 to 78) of the obtained light-transmitting conductive film obtained by the same means as in Example 1.
0 mm), haze value, and specific resistance are shown in Table 2.

[0032]

Comparative Example A conductive paste and a light-transmitting conductive film were obtained in the same manner as in Example 1 except that the composition of the paste was Paste 4 shown in Table 1 and the same ITO powder was used. The film thickness, surface resistance, total light transmittance (380 to 780 mm) of the obtained translucent conductive film obtained by the same means as in Example 1,
Table 2 shows the haze value and the specific resistance.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

As described above, the conductive paste and the light-transmitting conductive film of the present invention have sufficient conductivity and light transmittance, and can form a light-transmitting electrode such as an electroluminescent (EL) light-emitting element. Greatly contributes to

[Brief description of the drawings]

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

FIG. 2 is a micrograph of a light-transmitting conductive film obtained in Example 2 of the above.

FIG. 3 is a micrograph of a light-transmitting conductive film obtained in Example 3 of the above.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-80591 (JP, A) JP-A-3-24188 (JP, A) JP-A-3-62433 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01B 1/16 H01B 1/00 H01B 5/14 C01G 19/00

Claims (3)

(57) [Claims] 1. A conductive paste for high-temperature firing containing a transparent glass frit, a solvent, and a fine powder of acicular indium-tin oxide having a major axis of 5 μm or more and a ratio of the major axis to the minor axis of 5 or more. 2. The conductive paste according to claim 1, wherein the volume ratio of the acicular indium-tin oxide fine powder to the transparent glass frit is from 10:90 to 50:50. 3. A light-transmitting conductive film comprising acicular indium-tin oxide fine powder and glass, wherein the specific resistance of the film is 5.
A light-transmitting conductive film having a resistivity of 0 Ω · cm or less.