US3873343A

US3873343A - Method of forming secondary electron emission preventing layer for post-deflection acceleration type color picture tube

Info

Publication number: US3873343A
Application number: US286948A
Authority: US
Inventors: Akira Misumi; Toshiaki Kasai; Kenji Fukuda; Hiromitu Nakai
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1971-09-08
Filing date: 1972-09-07
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: FR2152730B1; DE2243976A1; DE2243976B2; GB1405899A; CA974411A; DE2243976C3; FR2152730A1

Abstract

A method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube, wherein a layer made of a mixture consisting of particles of a secondary electron emission preventing material, an organic binder and fine metal grains is formed on those surfaces of constituting parts inside the tube, at least a shadow mask, on which primary electrons impinge, or an inorganic binder layer made of an inorganic compound is formed on the surfaces and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the inorganic binder layer, or the surfaces of the constituting parts are roughened and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the roughened surfaces, the organic binder being thereafter burnt away by heat treatment. Alternatively, a mixed layer of an inorganic binder consisting of an inorganic compound and particles of a secondary electron emission preventing material is formed on the surfaces and a surface layer made of the secondary electron emission preventing material is formed on the mixed layer.

Description

United States Patent [191 Misumi et a].

[ 1 Mar. 25, 1975 [75] Inventors: Akira Misumi; Toshiaki Kasai;

Kenji F ukuda; Hiromitu Nakai, all of Mobara, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Sept. 7, 1972 [21] Appl. No.: 286,948

[30] Foreign Application Priority Data Sept. 8, 1971 Japan 46-68891 Sept. 8, 1971 Japan 46-68892 Sept. 8, 1971 Japan 46-68893 Sept. 8, 1971 Japan 46-68895 [52] US. Cl. 117/46 CA, 117/70 S, 117/71 R, 117/71 M, ll7/2l6, 313/85 S, 313/92 B, 313/106 [51] Int. Cl. C230 1l/00, B44d H44 [58] Field of Search 117/46 CA, 46 CB, 71 R, 117/70 S, 71 M, 216; 313/106, 92 B, 85 S [56] References Cited UNITED STATES PATENTS 2,518,434 8/1950 Lubszynski 117/71 2,829,295 4/1958 Gast et al 2,942,130 6/1960 Sheldon 3,010,092 11/1961 Caddock.... 3,093,501 ll/1963 Clayton 3,475,639 10/1969 Driffort et a1 313/106 3,600,213 8/1971 Amdt 313/85 S 3,604,970 9/1971 Culberton et al 117/216 3,703,401 11/1972 Deal et al. 117/216 Primary Examiner-William D. Martin Assistant Examiner-Janyce A. Bell Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT A method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube, wherein a layer made of a mixture consisting of particles of a secondary electron emission preventing material, an organic binder and fine metal grains is formed on those surfaces of constituting parts inside the tube, at least a shadow mask, on which primary electrons impinge, or an inorganic binder layer made of an inorganic compound is formed on the surfaces and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the inorganic binder layer, or the surfaces of the constituting parts are roughened and a mixed layer of particles of a secondary electron emission preventing material and an organic binder is formed on the roughened surfaces, the organic binder being thereafter burnt away by heat treatment. Alternatively, a mixed layer of an inorganic binder consisting of an inorganic compound and particles ofa secondary electron emission preventing material is formed on the surfaces and a surface layer made of the secondary electron emission preventing material is formed on the mixed layer.

12 Claims, 10 Drawing Figures PATENTEDHAR25I975 3,873,343 sum 1 g5 g r 2 qoos goas aswo ACCELERATION VOLTAGE (V) .3 3 G o. h %m mmmmw. 2, F o .8 o

. 4 95m zommiw 58mm PATENTEDH 5 I975 snzileq g FIG FIG

FIG

, 05E zowwsm 58mm I000 ACCELERATION VOLTAGE (v) PATENTED MR2 5 I975 SHEET 3 0F 4 F'IG 5 OE. zgwgsm m 96uwm s oos oa a a ooo ACCELERATION VOLTAGE V PATENTED 3. 873 343 saw u p g SECONDARY EMISSION RA'HO (8) 2 5000 20000 ACCELERATION VOLTAGE (v) METHOD OF FORMING SECONDARY ELECTRON EMISSION PREVENTING LAYER FOR POST-DEFLECTION ACCELERATION TYPE COLOR PICTURE TUBE The present invention relates to a post-deflection acceleration type color picture tube, and more particularly to a method of forming a secondary electron emission preventing layer thereof.

In the field of the post-deflection acceleration type color picture tube, it has hitherto been suggested to form a secondary electron emission preventing layer on the inner wall of a glassenvelope of the color picture tube, the surface of a shadow mask or the surface of any other component on which primary electrons impinge, and to thereby prevent deterioration in color purity of a picture. A prior-art secondary electron emission preventing layer for the post-deflection acceleration type color picture tube has been formed in such a way that a mixed layer which consists of a secondary electron emission preventing material such as graphite particles and an inorganic binder, such as water glass, not being burnt away by heat treatment in the manufacture of the tube and having the function of the binder even after completion of the tube is provided on, e.g., the surface of the shadow mask.

With such a secondary electron emission preventing layer, since the inorganic binder covers the surfaces of the particles of the secondary electron emission preventing material and the surface of the secondary electron emission preventing layer in the form of a thin film, a film having a strong adhesive force is obtained. On the other hand, however, the seeondary'eleetron emission preventing effect decreases, and the function of the secondary electron emission preventing layer cannot be satisfactorily accomplished. This is attributable to the fact that, since the secondary emission ratio of the layer of the inorganic binder of water glass or the like covering the secondary electron emission preventing material is generally large, the number of secondary electrons generated on the inorganic binder layer becomes large, with the result that the number of secondary electrons emitted from the entire secondary electron emission preventing layer becomes large.

Accordingly, in order to reduce the ratio of the secondary emission from the secondary electron emission preventing layer, it has been tried to form a secondary electron emission preventing layer using as the binder, for example, only an organic binder which burns away by the heat treatment in the manufacture of the tube. In the trial, the secondary electron emission preventing layer has been formed in' such a manner that a suspension of the organic binder and particles of the secondary electron emission preventing material is sprayed by the conventional spraying method, and that the organic binder is burnt away by the heat treatment in the tube manufacturing process. The secondary electron emission preventing layer thus obtained, however. is not practical in being of a small adhesive force and being very liable to exfoliate.

An object of the present invention is to provide a method of forming a secondary electron emission preventing layer which is greatly effective to prevent the secondary emission.

Another object of the present invention is to provide a method of forming a secondary electron emission preventing layer according to which, not only the strength of the secondary electron emission preventing layer itself, but also the adhesive force of the secondary electron emission preventing layer with the surface of a member on which it is provided is increased.

The above and other objects, features and advantages of the invention will become more apparent from the following description having reference to the accompanying drawings, in which:

FIG. 1 is a sectional view for explaining a prior-art method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube;

FIG. 2 is a sectional view for explaining a method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube and according to the present invention;

FIG. 3 is a diagram showing secondary electron emission ratio for the secondary electron emission preventing layer formed by the method in FIG. 2, in comparison with that for the layer by the prior art method of FIG. 1;

FIGS. 4 and 5 are sectional views for explaining methods of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube and according to further embodiments of the present invention;

FIG. 6 is a diagram similar to FIG. 3 showing secondary electron emission ratio for the secondary electron emission preventing layers formed by the methods in FIGS. 4 and 5;

FIG. 7 is a sectional view for explaining a method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube and according to a still further embodiment of the present invention;

FIG. 8 is a diagram similar to FIG. 3 showing secondary electron emission ratio for the secondary electron emission preventing layer formed by the method in FIG. 7;

FIG. 9 is a sectional view for explaining a method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube and according to a yet further embodiment of the present invention; and

FIG. 10 is a diagram similar to FIG. 3 showing secondary electron emission ratio for the secondary electron emission preventing layer formed by the method in FIG. 9.

FIG. I illustrates a prior-art method of forming a secondary electron emission preventing layer for a postdeflection acceleration type color picture tube. Referring to the figure, numeral 1 designates a component or member, such as a shadow mask, on which the secondary electron emission preventing layer is formed. Shown at 2 is the secondary electron emission preventing layer which is composed of a mixed layer of a secondary electron emission preventing material 3 such as graphite particles and an inorganic binder 4. such as water glass, not being burnt off by heat treatment in the manufacture of the tube and keeping the function of the binder after completion of the tube. The secondary electron emission preventing layer 2 is formed on the surface of the member I.

Such a secondary electron emission preventing layer 2 is advantageous in becoming a film with a strong adhesive force, since the inorganic binder 4 fully covers the surfaces of the particles 3 of the secondary electron emission preventing material and the surface of the secondary electron emission preventing layer 2 in the form of the thin film. On the other hand, the secondary electron emission preventing effect exhibits a tendency as illustrated at a curve in FIG. 3, and the function as the secondary electron emission preventing layer is not sufficiently attained. This is considered to come from the fact that, since the secondary emission ratio (8) of the layer of the inorganic binder, such as water glass, covering the secondary electron emission preventing material 3 is generally large, the number of secondary electrons created by the inorganic binder layer becomes large, resulting in a large number of secondary electrons ejected from the whole secondary electron emission preventing layer 2.

Accordingly, to the end of diminishing the secondary emission ratio of the secondary electron emission preventing layer, it has been tried to form a secondary electron emission preventing layer using as the binder, for example, only an organic binder which burns off by the heat treatment in the manufacture of the tube. More specifically, the secondary electron emission preventing layer has been formed in such a way that a suspension of the organic binder and the particles of the secondary electron emission preventing material is sprayed by the conventional spraying method, and that the organic binder is burnt off by the heat treatment in the tube producing process. The secondary electron emission preventing layer formed in this way, however, has been weak in the bonding power among the particles of the secondary electron emission preventing material, and has been very easily exfoliated.

When, herein, the secondary electron emission preventing material has been made of fine particles being less than several microns in the particle size, there has been obtained the film of a secondary electron emission preventing layer which is increased in the bonding power among the particles and which has a sufficient bonding strength even after the baking. With a film thickness enough to prevent the secondary emission, however, although the film is strong in the bonding power among the particles of the secondary electron emission preventing material, it is weak in the adhesive force between the particles of the secondary electron emission preventing material and the substrate or member on which the film is formed. A phenomenon in which the film exfoliates from the substrate has therefore occurred.

The present invention will be described hereunder with reference to FIGS. 2 to 10. In these figures, the same numerals are assigned to the same elements of the construction of the invention or necessary for explaining the invention.

FIG. 2 is a sectional view for explaining a method according to an embodiment of the present invention, for forming a secondary electron emission preventing layer for use in a post-deflection acceleration type color picture tube. In the figure, numeral I designates a member inside the tube, such as a shadow mask, on which the secondary electron emission preventing layer is formed. Numeral 7 indicates a mixed layer of particles 3 ofa secondary electron emission preventing material, fine grains 5 of a metal, and an organic binder 6. The mixed layer 7 is provided on that surface of the member inside the tube on which primary electrons impinge, for example, on the surface of the shadow mask on the electron gun side. The secondary electron emission preventing layer is formed, by way of example, as below.

In order to increase the adhesive force of the secondary electron emission preventing layer to-be-formed, the fine metal grains 5, such as silver powder, being 1 ,u. or less in the grain diameter are added to a suspension of the organic binder 6 and the secondary electron emission preventing material 3 such as graphite to the amount of several percent by weight with respect to the secondary electron emission preventing material in the suspension. Using the suspension added with the metal powder, the mixed layer 7 is made on, e.g., the surface of the shadow mask on the electron gun side by a suitable method such as spraying, coating with a brush, and immersion. Thereafter, the organic binder is burnt away by baking in the production of the tube. Thus, a secondary electron emission preventing layer consisting of the secondary electron emission preventing material and the fine grains of the metal is formed. In consideration of a satisfactory secondary emission preventing effect of the secondary electron emission preventing layer to-be-formed, a value of at least 3 t suffices for the thickness of the mixed layer 7. In consideration of the working property etc., a thickness of approximately 5 u to IO ,u is the most effective. The upper limit is approximately 30 p. in practical use.

With such a process, the fine metal grains 5 included within the secondary electron emission preventing layer are somewhat sintered during the baking. For this reason, the bonding force among the particles 3 of the secondary electron emission preventing material is increased, and the strength of the whole secondary electron emission preventing layer as well as the adhesive force of the same with the substrate I is increased. The film of a strength sufficiently enduring practical use can accordingly be formed. Besides, in the film of the embodiment, the added fine metal grains 5 amount to several percent or less with respect to the secondary electron emission preventing material 3, and are uniformly distributed in the film. For this reason, little increase in the secondary electron emission ratio is brought about, and the film can be satisfactorily put into practical use as the secondary electron emission preventing film. In this case, the fine metal grains are desirably those which are difficult to oxidize in the air and which are small in the secondary emission ratio. In addition, a smaller grain size is better. It has been made sure that, when the grain size exceeds 1 u, the adhesive force lowers. Yet in addition, the quantity of addition of the fine metal grains is determined in consideration of the secondary emission ratio of the fine metal grains, and generally amounts to several percent or less by weight.

EXAMPLE I To a graphite suspension containing 6.6% by weight of flake graphite having a particle size of l p. and an organic binder in a dispersion medium such as water, 0.04% by weight of silver powder having a grain size of 0.1 p, is added. The suspension thus prepared is sprayed on the surface of a shadow mask to a thickness of approximately lO p.. Thereafter, the organic binder is burnt off by heat treatment in the conventional manufacturing process of the color picture tube. In a mixed layer obtained in this way as comprises the graphite and the silver powder, the fine silver powder is interposed among the graphite particles to increase the bonding power among the graphite particles. A very solid film of the secondary electron emission preventing layer is accordingly formed. In this case, the silver powder increases also the adhesive force between the shadow mask and the graphite particles, to prevent the film of the secondary electron emission preventing layer from being exfoliated from the shadow mask.

The secondary emission ratio of the mixed layer of the graphite and silver powder as constitutes the secondary electron emission preventing layer thus formed, is shown by a curve 21 in FIG. 3. In comparison with the secondary emission ratio (at a curve 22) of a secondary electron emission preventing layer employing no fine metal grain, the secondary emission ratio of the mixed layer is increased only very slightly, and hence, the mixed layer is satisfactorily practicable as the secondary electron emission preventing layer. The silver power can also be I p. or below in the grain size, and range from 0.01 to 0.5% by weight in the amount of addition. In FIG. 3, the axis of abscissa represents the acceleration voltage (in volts) of primary electrons, while the axis of ordinate the secondary emission ratio (6). The same applies to FIGS. 6, 8 and 10.

In the foregoing embodiment, the fine metal grains are directly used as the metal powder mixed into the particles 3 of the secondary electron emission preventing material. The present invention, however, is not restricted to such aspect, but fine metal grains may of course be employed which are obtained in such way that a metallic salt dissolved in a suitable solvent is added to the graphite suspension, and that the fine metal grains are precipitated from the metallic salt during the baking in the production of the tube.

FIG. 4 is a sectional view for explaining a method according to another embodiment of the present invention, for forming a secondary electron emission preventing layer for use in a post-deflection acceleration type color picture tube. In the figure, numeral 8 indicates an inorganic binder layer formed on the member 1 inside the tube and made of an inorganic compound, such as water glass, which does not burn away by the heat treatment. Shown at 9 is a mixed layer which is formed on the inorganic binder layer 8 and in which the particles 3 of the secondary electron emission preventing material and the organic binder 6 are mixed. The secondary electron emission preventing layer is formed, by way of example, as stated below.

In order to prevent the exfoliation phenomenon of the secondary electron emission preventing layer, an inorganic binder consisting of the inorganic compound, such as water glass, which does not burn off even by the heat treatment is very thinly coated on that surface of the member 1 on which primary electrons impinge, for example, the surface of a shadow mask on the electron gun side. Thus, the inorganic binder layer 8 being I to 2 [L thick is formed. A suspension of the organic binder 6 and the particles 3 of the secondary electron emission preventing material such as graphite and not exceeding several microns in the particle size is sprayed on the inorganic binder layer 8 by the conventional spraying method, to thereby form the mixed layer 9. Thereafter, the organic binder 6 is burnt away by the heat treatment, to thereby form a secondary electron emission preventing layer which consists of the inorganic binder layer 8 and the secondary electron emission preventing material.

With such method, even after the organic binder 6 burns away by the baking in the manufacture of the tube, the secondary electron emission preventing layer is sufficiently strong in the bonding among the particles and in the bonding between the particles and the substrate or member, and can sufficiently endure practical use. In addition, the inorganic binder having a large secondary emission ratio exists only in the vicinity of the surface of the member I, so that the secondary emission ratio of the secondary electron emission preventing layer can be suppressed to a sufficiently small value by thickly forming the mixed layer 9.

EXAMPLE 2 Potash water glass at a concentration of 10% by weight is sprayed onto the surface of a shadow mask, to form an inorganic binder layer made of the water glass, having a strong adhesive force, being in the semidried state and being I to 2 ,u. thick. A suspension of graphite and an organic binder in water as contains 6.6% by weight of flake graphite of a particle size of l ,u. is sprayed onto the inorganic binder layer by means of a spray gun, to form a mixed layer of the graphite and organic binder and having a thickness of I0 s. Thereafter, the mixed layer is heated by the step of heat treatment in the process of producing the color picture tube, to burn off the organic binder. Then, a secondary electron emission preventing layer consisting of the inorganic binder layer and the graphite layer is formed.

The secondary electron emission preventing layer thus formed, has a sufficient strength. In addition, as illustrated at a curve 23 in FIG. 6, the secondary electron emission preventing effect of the layer of the embodiment is excellent as compared with that of the prior-art mixed layer which consists of the inorganic binder and the secondary electron emission preventing material and whose secondary emission preventing characteristics are shown at the curve 20. Besides, the curve 23 is quite similar to a characteristic curve in the case of graphite alone with no inorganic binder layer, although the latter curve is not illustrated. Therefore, the layer of the invention exhibits an excellent effect of preventing the secondary electron emission.

FIG. 5 is a sectional view for explaining a method of forming a secondary electron emission preventing layer, according to a further embodiment of the present invention. In the figure, reference numeral 10 represents an inorganic binder layer which is formed on the member 1 and which is made of an inorganic binder, such as water glass, not burning off by heat treatment and fine powder 11 of a material, such as graphite and silver, not exerting any adverse effect on the picture tube. Reference numeral 9 indicates the mixed layer which is formed on the inorganic binder layer 10 and which consists of the particles 3 of the secondary electron emission preventing material and the organic binder 6. The addition of the fine powder 11 results in a roughened surface of the binder layer 10, and thus a stronger adhesion between the member 11 and the layer 10 and between the mixed layer 9 and the same can be obtained. Also, the roughened surface lowers secondary electron emission from the inorganic binder layer so that the secondary electron emission preventing effect is increased. The secondary electron emission preventing layer is formed, by way of example, as below.

In order to prevent the exfoliation phenomenon of the secondary electron emission preventing layer, a mixture consisting of the inorganic binder solution which does not burn away even by the heat treatment and the fine powder of the material which exercises no evil influence on the picture tube is previously coated thinly on the member 1 by, e.g., the spraying method, to form the binder layer 10. Thereafter, a suspension of the particles 3 of the secondary electron emission preventing material such as graphite and of a particle size of several microns or below, the suspension containing the organic binder 6, is sprayed by the conventional spraying method, to form the mixed layer 9. Thereafter, the organic binder is burnt away by the heat treatment, to form a secondary electron emission preventing layer.

In accordance with the forming method, even after the organic binder 6 is burnt off by the baking in the manufacture of the tube, the secondary electron emission preventing layer is sufficient in the bonding among the particles and in the bonding between the particles and the substrate, and can satisfactorily endure practical use. Since the inorganic binder of a large secondary emission ratio is present only in the vicinity of the member 1, the secondary emission ratio of the secondary electron emission preventing layer can be restrained to a sufficiently small one if the layer is thickly formed.

EXAMPLE 3 A liquid consisting of potash water glass at a concentration of 10% by weight and 5% by weight of flake graphite of a particle size of 0.3 u in water is sprayed on the surface of the substrate of a shadow mask by means ofa spray gun. An inorganic binder layer having a strong adhesive force, being in the scmidried state and being l to 2 a thick is thus formed. A suspension of graphite and an organic binder in water as contains 6.6% by weight of flake graphite having a particle size of l p, is sprayed on the inorganic binder layer by means of a spray gun. A mixed layer consisting of the graphite and the organic binder and being 7 a thick is thus formed. Thereafter, the mixed layer is heated by the step of heat treatment in the process of manufacturing the color picture tube, to burn away the organic binder. A secondary electron emission preventing layer is thus formed.

The secondary electron emission preventing layer formed in this way, has a sufficient strength. The secondary emission ratio of the layer is shown by the curve 23 in FIG. 6 as in the secondary electron emission preventing layer according to the embodiment in FIG. 4.

As regards the thickness of the mixed layer in the embodiments in FIGS. 4 and 5, a value of approximately 3 ,u. is sufficient in view ofa satisfactory secondary electron emission preventing effect, and a value of approximately 5 to p. is effective in view of the working property, etc. The upper limit of the thickness is approximately 30 u in practical use.

FIG. 7 is a sectional view for explaining a method according to a still further embodiment of the present invention, for forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube. In the figure, the surface of the member 1 is roughened. The mixed layer 9 of the secondary electron emission preventing material 3 and the organic binder 6 is formed on the uneven surface of the member 1.

The secondary electron emission preventing layer is formed, by way of example, as stated below.

The surface of the member 1, e.g., the surface of a shadow mask on the electron gun side is roughened by such method as chemical etching and sand blasting, to make unevenness of the surface ofthc member 1 large. A suspension of the organic binder 6 and fine powder of the secondary electron emission preventing material 3 such as graphite of less than several microns in the particle size is sprayed onto the uneven surface, thereby to coat the suspension on the member 1. Thus, the mixed layer 9 is formed. Thereafter, the organic binder is burnt off by heat treatment, to form a secondary electron emission preventing layer on the member 1.

With such a method, even after the organic binder is burnt away by the heat treatment in the process of producing the tube, the secondary electron emission preventing layer is strong in its adhesive force with the member 1. The layer does not exfoliate from the member 1, and can be put into practical use. In addition, since the surface of the member 1 is made uneven, the secondary emission preventing effect of the film of the secondary electron emission preventing layer formed on the surface of the member 1 can be enhanced more.

EXAMPLE 4 The surface of a shadow mask is roughened by sand blasting. A suspension of an organic binder and 6.6% by weight of flake graphite having a particle size of approximately 0.2 p. in water is sprayed on the roughened surface by a spray gun. Thus, a mixed layer consisting of the graphite and organic binder and having a thickness of 10 u is formed. Thereafter, the mixed layer is heated by the step of heat treatment in the process of manufacturing the color picture tube, to burn away the organic binder. A secondary electron emission preventing layer is thus formed. A curve 24 in FIG. 8 represents the secondary emission ratio of the secondary electron emission preventing layer according to this embodiment, a curve 25 represents the secondary emission ratio of the prior-art secondary electron emission preventing layer which is formed similarly to the embodiment but without roughening the surface of the substrate, and the curve 20 represents, as in FIGS. 3 and 6, the secondary emission ratio of the prior-art secondary electron emission preventing layer formed of the mixed layer of the inorganic binder and the secondary electron emission preventing material. The secondary electron emission preventing layer formed in accordance with the embodiment in FIG. 7 has a sufficient mechanical strength, and as apparent from the graph, it has a sufficient secondary emission preventing effect as compared with the prior-art secondary electron emission preventing layers.

FIG. 9 is a view for explaining a method according to a still further embodiment of the present invention, for forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube. Referring to the figure, the mixed layer 2 which contains the inorganic binder 4 consisting of an inorganie compound, such as water glass, not burning away by heat treatment and the particles 3 of the secondary electron emission preventing material is formed on the member 1. Numeral l2 designates a surface layer formed on the mixed layer 2 and made of the particles 3 of the secondary electron emission preventing material. The addition of the particles of the secondary electron emission preventing material in the layer 2 is for decreasing secondary electron emission from this layer by roughing the surface of the layer 2 as well as by its particular property. The roughened surface of the mixed layer also provides a stronger adhesion between the mixed layer and the surface layer.

The secondary electron emission preventing layer is formed, by way of example, as follows. In order to prevent the exfoliation phenomenon of the secondary electron emission preventing layer, a mixture which consists of the inorganic binder 4 of water glass or the like, not burning away even by the heat treatment, and the particles 3 of the secondary electron emission preventing material such as graphite is very thinly coated on the surface of the member 1, for example, the surface of a shadow mask on the electron gun side. The thickness of the coating is l 2 microns. In this case, an organic binder burning away by the heat treatment may be mixed in order to raise the coating efficiency.

Subsequently, a liquid in which the particles 3 of the secondary electron emission preventing material of less than several microns in the particle size are dispersed in water or ethyl alcohol is sprayed on the coating by the conventional spraying method, for example, with a spray gun. Thus, the surface layer 12 is formed. A secondary electron emission preventing layer is composed of the surface layer 12 and the mixed layer 2. The thickness of the surface layer 12 may suffice with several microns or more, and the upper limit is approximately 20 a.

In accordance with the forming method, the seeondary electron emission preventing layer is sufficiently strong in the bonding among the particles and the bonding between the particles and the substrate, and can satisfactorily endure practical use. Moreover, the secondary emission ratio of the layer can be suppressed to a sufficiently small value, since the inorganic binder of a large secondary emission ratio exists only in the vi einity of the member 1.

EXAMPLE 5 A mixed liquid containing potash water glass at a concentration of %by weight and 6.6% by weight of flake graphite of a particle size of l ,u. is sprayed on the surface of a shadow mask to a thickness of approximately 1 to 2 by means of a spray gun, to form a mixed layer 2. Subsequently, a liquid in which flake graphite particles are dispersed in water or ethyl alcohol at a concentration of l to 10% by weight, practicaily 6 to 8% by weight, is sprayed on the mixed layer using, for example, a spray gun, to form the surface layer. A secondary electron emission preventing layer is formed of the surface layer and the mixed layer.

The secondary electron emission preventing layer thus formed, has a sufficient strength. The secondary emission ratio is shown at a curve 26 in FIG. 10, which is quite similar to the case of graphite alone with no mixed layer 2, and hence, an excellent secondary emission preventing effect is exhibited.

The secondary electron emission preventing layer of the present invention has a great effect in improving a picture of the post-deflection acceleration type color picture tube by applying it not only to the shadow mask, but also to other components on which primary electrons impinge, for example, the inner wall of a glass bulb, a mask support, a shield electrode and so forth.

As described above, the method of forming a secondary electron emission preventing layer for a postdeflection acceleration type color picture tube according to the present invention is very greatly effective in practical use in that the bonding force of the particles of the secondary electron emission preventing material is increased, that the strength of the whole secondary electron emission preventing layer and the adhesive force of the layer with the substrate can be increased, and that the secondary emission ratio can be reduced as compared with that of the prior-art secondary electron emission preventing layer employing the inorganic binder.

What we claim is:

1. A method of forming a secondary electron emission preventing layer for a post-deflection acceleration type color picture tube, comprising: forming a first layer of water glass at least on a surface at which the formation of secondary electron emissions is to be prevented in a color picture tube on an electron gun side, forming a second layer of an organic binder containing graphite particles on said first layer, and thereafter burning away said organic binder in said second layer by a heat treatment, to form a secondary electron emission preventing layer on said surface.

2. The method according to claim 1, wherein said first layer is formed to a thickness of l to 2 [.L.

3. The method according to claim 1, wherein said second layer is formed to a thickness of 3 to 30 [.L.

4. The method according to claim 1, wherein said second layer is formed to a thickness of 5 to 10 a.

5. The method according to claim 1, wherein said graphite particles have a particle size of at most several microns.

6. The method according to claim 1, wherein fine powder of a material which exerts no adverse influence on the picture tube is added to said water glass of said first layer.

7. The method according to claim 6, wherein said material exerting no adverse influence on the picture tube is one selected from the group consisting of graph ite and silver.

8. The method according to claim 1, wherein said first layer is of a potash water glass material which does not burn away by heat treatment.

9. The method according to claim 1, wherein said surface at which the formation of secondary electron emission is prevented in a color picture tube on the electron gun side is a surface of at least one of a shadow mask, the inner wall of the glass bulb, a mask support, or a shield electrode.

10. The method according to claim 1, wherein said surface is the surface of the shadow mask on the electron gun side.

11. The method according to claim 1, wherein said second layer contains 6.6 percent by weight of flake graphite.

12. The method according to claim 1, wherein said flake graphite has a particle size of 1 micron.

Claims

2. The method according to claim 1, wherein said first layer is formed to a thickness of 1 to 2 Mu .

3. The method according to claim 1, wherein said second layer is formed to a thickness of 3 to 30 Mu .

4. The method according to claim 1, wherein said second layer is formed to a thickness of 5 to 10 Mu .

7. The method according to claim 6, wherein said material exerting no adverse influence on the picture tube is one selected from the group consisting of graphite and silver.