AU463511B2

AU463511B2 - A luminescent alphanumeric display tube

Info

Publication number: AU463511B2
Application number: AU36985/71A
Authority: AU
Inventors: HIROSHI IVANO and HIDEYUKI NARAOKA MITSUO TAKEDA
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1970-12-17
Filing date: 1971-12-16
Publication date: 1975-07-31
Also published as: DE2162558A1; US3737705A; NL7117234A; GB1340010A; AU3698571A; FR2118792A5; SE366426B

Description

36,985/71 This invention relates to a luminescent display

tube, and more particularly to a luminescent alphanumeric

display tube comprising means for emitting electrons

or ion particles and fluorescent means including an

insulating substrate and an array of fluorescent segments

disposed on one surface of the substrate, each segment

being insulated from the other and selectively

activated by impingement of emitted electrons or ion

particles to present a desired pattern of luminescence.

The above-mentioned type of fluorescent alphanumeric

display tube is disclosed in U.S. Patent 3,508,101 and

an American engineering journal "Electronics", May 29,

1967, pp. 212 to 213, and is generally used with rela-

tively low voltage (say, about 20 volts). The conventional

fluorescent segment of such a fluorescent alphanumeric

display tube is usually formed in the following manner.

First, a conductive layer is deposited on one surface-

of the insulating substrate in a suitable known manner.

This substrate is then placed at the bottom of a vessel

filled with a suspension of fluorescent particles and

metal ions of potassium or lithium as a binder, and the

fluorescent particles and metal ions are deposited onto

the surface of the substrate to form a fluorescent layer

on the conductive layer. The metal ions included in the

deposited fluorescent layer prepared in this way undesirably

reduce the luminescence of the fluorescent layer, when

it is impinged on by electrons or ions of low energy.

The prior art display tube, therefore, contains as small

an amount as possible of ions of metals acting as a binder

for the fluorescent materials, and consequently has the

4635,1 1

36 985/7 drawback that due to the reduced amount of binder,

the fluorescent segment of the conventional display tube

is bonded to the conductive layer with extremely low

strength.

The present invention provides a fluorescent

alphanumeric display tube wherein the fluorescent

layer is firmly bonded to the conductive layer, and

provided with a fluorescent segment capable of becoming

brightly luminescent even when impinged on by electrons

or ions of relatively low energy.

According to this invention, there is provided a

luminescent alphanumeric display tube comprising a

sealed transparent envelope containing means for

emitting electrons or ion particles and fluorescent means

including an insulating substrate and an array of

fluorescent segments disposed on one surface of said

substrate, each of said segments being insulated from

the others and being selectively activated by impingement

thereon of emitted electrons or ion particles so as to

present a desired luminescent pattern each of said

segments comprising a carbon layer deposited on the

surface of the substrate; a first fluorescent layer

superposed on said carbon layer and comprising

particles of fluorescent material, having a diameter

smaller than the diameter of the particles constituting

said carbon layer; and a second fluorescent layer

superposed on said first fluorescent layer and comprising

particles of fluorescent material having a diameter larger

than the diameter of the particles constituting said

first fluorescent layer. 3 46

36,98517 The present invention may be more readily understood

from the following detailed description in conjunction

with reference to the appended drawings, in which:

Fig. 1 is a sectional view of a fluorescent display

tube according to this invention;

Fig. 2 is a perspective view of the luminescent

anode of the fluorescent display tube of Fig. 1; A-A of Fig. 3 is a cross sectional view on line

the luminescent anode of Fig. 2 as taken in thp direction

of the indicated arrows; and

Fig. 4 schematically illustrates the method of

manufacturing the luminescent segments of Fig. 2.

Referring to Fig. 1i, reference numeral 1 represents comprises a fluorescent alphanumeric display tube which thermonic a vacuum envelope 2 made of transparent glass, electrode electron emitting filament 3, an acceleration indicating 4 in a form of a mesh, mask 5 for distinctly anode patterns, (for example letters), and luminescent within 6, all these elements being hermetically sealed

said envelope. The electrode elements are connected to by inner outer leads 8 (consisting of conductive rods)

leads 7 formed of conductive wires. shown The luminescent anode electrode 6 consists, as of, in Figs. 2 and 3, of an insulating substrate 10 made

for example, ceramic material and a plurality of

fluorescent segments 14 arranged on a surface of said

substrate in a suitable mosaic pattern. Each fluorescent

of segment 14 comprises a conductive layer 12 formed

graphite or carbon, a first fluorescent layer which consisting substantially of fluorescent particles 4 6 3 5.1

36,985/71 have a diameter smaller than that of the particles

constituting said conductive layer 12 and a second

fluorescent layer 16 substantially consisting of

fluorescent particles which have a diameter larger

than that of the particles constituting said first

fluorescent layer 15. Said fluorescent segments are

deposited in grooves 11 formed in one surface of the

insulating substrate 10. The conductive layers 12

contact the inner leads 7 penetrating the insulating

substrate

The display tube 1 as described above operates

when the outer leads 8 have the prescribed voltage applied,

causing electrons to be emitted from the filament 3.

These electrons are directed to the fluorescent anode

6 by the acceleration electrode 4. When the particular

fluorescent segments 14 are selectively applied with

positive voltage through the outer leads 8, the segments

impinged on by electrons luminesce and produce a

luminous pattern, (for example numerals).

The fluorescent' segments are prepared in the

following manner. Powdered carbon or graphite consisting

of extremely fine particles with average diameter ranges

from 3 to 5 microns are mixed with an aqueous suspension

of a vitreous binder material composed mainly of

potassium oxide. This mixture is applied by known

techniques, for example, by spraying, to the side of the

insulating substrate of the ceramic material on which

there are the grooves 11. After being coated with this

mixture, the substrate 10 is baked in air heated to a 0 temperature of 400 to 500 C. Carbon deposited on parts

of the surface of the substrate 10 other than the bottom

of the grooves 11 is removed thus obtaining the required

conductive carbon layer 12 at the bottom of each grooye, 1 1 q63

36,985 /71 A first fluorescent layer is superposed over

each of the carbon layers in the following steps.

First, one of the known fluorescent mateiials (zinc

oxide according to this embodiment) is poured into

deionized water. The zinc oxide in the deionized

water is stirred and milled with glass beads of 1 added to this to 5 millimeters in diameter which are

water, to obtain a suspension of zinc oxide particles.

The particle size distribution of this zinc oxide

suspension falls within a certain range. In this

embodiment, the fluorescent zinc oxide has an average

particle size of about 4 microns. Finer particles are

in the selected from the suspension by water screening

following manner. The suspension is poured into a in a place vessel and left to settle for several minutes

which is not subject to vibration. As is well known,

ones. larger particles settle more quickly than smaller second This suspension is then skimmed to obtain a

suspension containing finer particles. The size of

controlled particles of this second suspension is easily suspension is by the length of time for which the former

left to settle. In this latter embodiment, the water- have a size of screened fluorescent particles generally

less than 2 microns. above manner The second suspension obtained in the 24 is poured which contains the finer fluorescent particles in a vessel 21, from a beaker 23 into deionized water 22

as shown in Fig. 4. At the bottom of the vessel 21, there

the conductive is placed the ceramic substrate 10 having each groove 11. carbon layer 12 formed at the bottom of

46B I

36,985 /71 The fluorescent particles 24 gravitationally settle

down on the ceramic substrate 10 to form a first

fluorescent layer 15 on the surface of said substrate

as well as on the conductive carbon layer 12.

According to this embodiment, said first fluorescent

layer 15 is about 10 microns thick.

A second fluorescent layer 16 is deposited

over the first fluorescent layer 15 in the same manner

as the first layer. To this end, a suspension containing

larger fluorescent particles is prepared by the water

screening process. These larger particles suspended

in the deionized water are deposited on the first

fluorescent layer 15 by settling to form the second

fluorescent layer 16. According to this embodiment,

this second fluorescent layer 16 is about 40 microns

thick and consists of particles having a size of more

than 2 microns.

After deposition of the first fluorescent layer

the deionized water 22 is removed and the substrate

is thermally dried. After drying, fluorescent material

attached to parts of the substrate surface other than

that on which the conductive carbon layer 12 has been

formed is brushed off to obtain the first fluorescent

layer 15 over the conductive carbon layer 12. The

second fluorescent layer 16 is formed in the same way

as the first fluorescent layer

The fluorescent segment 14 thus prepared is very

firmly bonded to the substrate 10. It is believed that the

reason for this is that in the interface between the

conductive carbon layer and the first fluorescent layer

the relatively finer particles of the fluorescent

4635.11

36, 985 /7 larger material are intermeshed with the relatively

carbon particles.

Moreover, the fluorescent segments 14 display

extremely high luminescence. It is believed that the

reason for this is that the second fluorescent layer

14 16 which constitutes the top surface of segment

consists of relatively large particles. Additionally,

free from the first and second fluorescent layers are

metal ions which give rise to low luminescence.

The foregoing description refers to a display characters tube which displays any one of a group of

or numerals. However, this invention is also applicable a plurality to a display tube of the type which displays as a of numerals or characters simultaneously, such

number comprising a plurality of digits. Such a

sealed fluorescent display tube includes a hermetically the vacuum envelope and a filament disposed within

envelope. An alignment of a plurality of fluorescent

anodes is placed within the single envelope, each

an array of anode comprising an insulating substrate and manner. fluorescent segments prepared in the aforementioned vacuum The above-mentioned embodiment refers to a Where, fluorescent display tube utilizing electrons.

however, this invention is applied to a discharge sealed fluorescent display tube, the tube comprises a

glass envelope containing ionizable gases, (for example

arranged neon), an anode and fluorescent cathode segments

within the envelope. The display is produced by

impingement luminescensce from the fluorescent cathode by

thereon of ions during discharge. In this embodiment,

46 3, L

36,985 17 there is used as a cathodea luminescensce electrode

6 comprising an insulating substrate on which the

aforesaid fluorescent segments 14 are formed in the

manner described above.

4635, 11

Claims

36, 985 /71 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A luminescent alphanumeric display tube comprising

a sealed transparent envelope containing means for

emitting electrons or ion particles and fluorescent

means including an insulating substrate and an array

of fluorescent segments disposed on one surface of

said substrate, each of said segments being insulated

from the others and being selectively activated by

impingement of emitted electrons or ion particles so

as to present a desired luminescent pattern, each of

said segments comprising: a layer of carbon particles

deposited on the surface of said substrate; a first

fluorescent layer superposed on said carbon layer

comprising particles of fluorescent material having a

diameter smaller than the particles constituting said

carbon layer; and a second fluorescent layer

superposed on said first fluorescent layer comprising

particles of fluorescent materials having substantially a

diameter larger than the diameter of the particles

constituting said first fluorescent layer.

2. A luminescent alphanumeric display tube according

to claim 1 wherein said fluorescent material is zinc oxide.

3. A luminescent alphanumeric display tube according

to claim 1 or claim 2 wherein said first fluorescent layer

and said second fluorescent layer are substantially free

from potassium and lithium ions.

4. A luminescent alphanumeric display tube according to

any one of claims 1 to 3 wherein said first fluorescent

36.985 17 materials layer comprises particles of fluorescent said having a diameter less than two microns, and

second fluorescent layer substantially comprises a larger particles of fluorescent materials having

diameter than two microns. substantially A luminescent alphanumeric display tube, the as hereinbefore described with reference to

accompanying drawing.

DATED this 25th day of JUNE, 1975.

TOKYO SHIBAURA ELECTRIC CO. LTD. By its Patent Attorneys:

CLEMENT HACK CO. Fellows Institute of Patent Attorneys of Australia.

11 4635,11