JPH0195172A - Graphite paste for fluorescent display tube - Google Patents

Abstract

PURPOSE:To obtain the title paste which can give a fluorescent display tube of an excellent luminous efficiency in good yields, by mixing a graphite powder with a binder aid comprising an Al2O3 powder, an SiO2 powder and a water glass in a specified weight ratio and a solvent. CONSTITUTION:1pts.wt. graphite powder (A) is mixed with a binder aid (B) comprising 1.0-2.0pts.wt. Al2O3 powder (a), 0.002-1.0pts.wt. SiO2 powder (b) and 0.01-0.25pts.wt. water glass (c), and a solvent (C) in an amount necessary to give a desired viscosity to the mixture to obtain the title paste having the lowest possible water glass content.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a graphite paste, and particularly to a graphite paste used in a fluorescent display tube. .

[Conventional technology]

Fluorescent display tubes are self-luminous display tubes that are characterized by high brightness, and demand for them has been increasing in recent years.

FIG. 3 is a sectional view of an example of a fluorescent display tube.

As shown in FIG. 3, in a fluorescent display tube, the inside of a glass envelope 1 is kept in a vacuum, the thermoelectrons emitted from a filament 2 are controlled by a grid 3, and the surface of a phosphor layer 4 is controlled. Excited light emission is performed by colliding with the The phosphor N34 is formed on the anode electrode layer 5 and is electrically connected to an external terminal (not shown) via the anode wiring 6. Further, adjacent anode layers 5 are electrically insulated by an insulating layer 7.

Each layer described above is formed on the glass substrate 8 by thick film or thin film wiring technology. For example, the anode wiring 6 is formed by sputtering, vapor deposition, or printing of a conductive paste, and the insulating layer 7, the anode electrode layer 5, and the phosphor layer 4 are formed thereon in this order by printing paste.

Here, as the anode electrode layer 5, a graphite paste whose conductor component is graphite powder is used for reasons such as low cost and ease of printing.

Conventional graphite paste for fluorescent display tubes (hereinafter referred to as graphite paste) uses alumina powder and water glass as auxiliaries from the viewpoint of printability and sinterability, and the mixing ratio is as follows: It is known that 1 part by weight of alumina powder contains 1.0 to 1.0 parts by weight of alumina powder and 0.5 to 1.0 parts by weight of water glass, and the influence of water glass is large in terms of sinterability. If the amount of water glass was less than 0.5 parts by weight, the sinterability would be extremely poor and the product could not be put to practical use.

[Problem that the invention seeks to solve]

However, the conventional graphite paste described above has the following drawbacks because the water glass contains alkali metals such as Na carbon.

(1) Alkali metals have a high tendency to ionize, easily migrate to silane, and are highly reactive, so when sintering graphite paste and phosphor paste, they may cause insulation deterioration of the insulating layer, contamination of the phosphor layer, or poor conductivity of the anode wiring. Problems such as these occur, resulting in poor yield.

(2) Especially with phosphors that are sensitive to contamination, the luminous efficiency of the product will be significantly lower.

(3) Furthermore, in order to improve product retention, it is necessary to increase the thickness of the insulating layer and the anode wiring, which requires a large number of man-hours.

An object of the present invention is to provide a graphite paste for fluorescent display tubes that has good luminous efficiency and a high product yield of fluorescent display tubes.

[Failure to solve the problem]

The graphite paste of the present invention is a graphite paste for fluorescent display tubes comprising graphite powder, an adjuvant for bonding the graphite powder, and a solvent for adjusting viscosity. 1.0 to 2.0 parts by weight of powder, 0.002 to 1.0 parts by weight of silica powder, 0.01 to 0.01 parts by weight of water glass
Contains 0.25 parts by weight.

〔Example〕

Table 1 shows the mixing ratio of the binder when graphite paste is made using silica powder with a maximum particle size of 30 μm, and graphite pastes that do not contain silica powder are also included as examples of the present invention and comparative examples. ing. We conducted an implementation evaluation of these.

That is, after forming the anode wiring 6 and the insulating layer 7 on the glass substrate 8 shown in FIG. 3 by sputtering and screen printing, respectively, the anode electrode 1@5 is formed by screen printing using the graphite paster shown in Table 1. did. Each graphite paste was adjusted to have a viscosity of 600 to 800 voids using diethylene glycol during screen printing. Further, sintering was performed at 590°C for 10 minutes.

After forming the anode electrode layer 5, the phosphor layer 4 was formed on the anode electrode layer 5 by screen printing. After that, the grid 3 and the filament 2 are placed in a predetermined position,
A glass surrounding atmosphere 1 was formed and vacuum sealing was performed.

The incidence of brightness defects and the incidence of failures in the anode electrode layer of the fluorescent display tubes manufactured in this manner were investigated, and the results shown in FIGS. 1 and 2, respectively, were obtained.

FIG. 1 is a characteristic diagram showing the relationship between the water glass content and the brightness defect occurrence rate of a graphite paste containing 0.002 parts by weight of silicon powder. From this figure, it can be seen that when the water glass content is 0.25 parts by weight or less, the incidence of brightness defects can be suppressed to 10% or less. Note that no correlation was observed between the silica powder content and the incidence of poor brightness, and the same tendency as shown in FIG. 1 was observed in other graphite pastes with different silica powder contents.

FIG. 2 is a characteristic diagram showing the relationship between the water glass content of the graphite paste and the rate of failure of the anode electrode layer, using the silica powder content as a parameter. If the sinterability of the graphite paste is weak, poor application of the anode electrode layer will occur during printing of the phosphor paste in the next step.

As can be seen from FIG. 2, a graphite paste containing no silica powder has a high defect rate when the water glass content is 0.25 parts by weight or less, and is not suitable for practical use. On the other hand, with graphite paste containing silica powder, even if the water glass content is 0.25 parts by weight or less, the incidence of coating defects is low and the final yield is 3% or less, making it suitable for practical use. At the same time, as can be seen from FIG. 1, the incidence of brightness defects also decreases.

If the amount of silica powder added is less than 0.002 parts by weight, the effect of improving the sinterability of graphite paste will be small;
Also, 1. If there are too many OM placement parts, the specific resistance of the graphite paste will become high, making it impractical and 0.002 to 1.0.
The parts by weight fall within an appropriate range.

Note that the smaller the particle size of the silica powder to be added, the larger the surface area9, and the better the sinterability, so the maximum particle size is 100.
Silica powder of micrometer or less is practical.

〔Effect of the invention〕

As explained above, the present invention improves the film strength of the anode electrode layer by minimizing the content of water glass containing alkali metals, which degrades the product characteristics and manufacturing yield of fluorescent display tubes, and by adding silica powder. This has the effect of increasing the luminous efficiency and manufacturing yield of the fluorescent display tube.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the water glass content of graphite paste containing 0.002 parts by weight of silica powder and the incidence of poor brightness. Characteristic diagram showing the relationship between the glass content and the occurrence rate of failure of the anode electrode layer, Part 3
The figure is a cross-sectional view of an example of a fluorescent display tube. DESCRIPTION OF SYMBOLS 1... Glass envelope, 2... Filament, 3... Grid, 4... Phosphor layer, 5... Anode electrode Layer, 6...adjacent wiring, 7...absolute layer, 8...glass substrate. Agent Patent Attorney Uchihara Backwater D゛fusu 1 shoulder angle 11 (ri"fushifu 1to / 1su 4 nahito 1choshima) gata l Figure J', 77" Busa 7 angle measurement (ri') h I F-1 heavy! MoP
Figure 2

Claims (1)

[Claims] In a graphite paste for fluorescent display tubes, which includes graphite powder, an adjuvant for binding the graphite powder, and a solvent for adjusting viscosity, 1.0 to 2 parts of alumina powder is added as an adjuvant to 1 part by weight of graphite powder.
．． 0 parts by weight, 0.002 to 1.0 parts by weight of silica powder,
Graphite paste for fluorescent display tubes, characterized in that it contains 0.01 to 0.25 parts by weight of water glass.