US2289978A - Television picture tube screen - Google Patents

Description

July 14, 1942. L. MALTER TELEVISION PIVCTURE TUBE SCREEN Filed Nov. 50, 1940 Fifa. 1.

DIRECT] 0N OF' .BE/7M JJ/RL'C "flo/v :Smoentor L0 ,LL L6 Mal t e r 0F' BE/7M f (Ittorneg particularly to Patented July 14, 1942 TELEVISION PICTURE TUBE SCREEN Louis Malter, Newark, N. I., assignor to Radio` Corporation of America, a corporation of Dela- Ware application November so, 1940, seriaiNo. 361,877 y (ci. 25o- 164) h Claims.

i This invention relates to television systems of the type employing cathode ray tubes and more picture screens for kinescope tubes. I

In television receiving picture tubes a decrease in detail f is encountered due to the halation caused by the electron beam striking the screen l of fluorescent material. Halation involves -the spreading of light beyond its proper boundaries. One of the principal causes of halation in a `kinescope screen is `the reflection of the vlight from the fluorescent material between the surfaces of the member supporting the fluorescent material. When .the fluorescent material is coated on the supporting member, light from the fluorescent material is permitted to enter the supporting member at the inner surface over awide angle and hence be reflected from both surfaces to a `comparatively high degree.

Thisreilection can be reduced considerably by decreasing the optical contact between the sup porting member and the screen material. I Ifno optical contact existed between the screen material and the transparent supporting member, none of the light which enters the supporting member on the surface of the supporting member adjacent the fluorescent material can experience total reflection at the opposite surface of the supporting member.

It is practically impossible to reduce the optical contact between the supporting ymember and screen material sutllciently without experiencing the trouble from the screen material dropping on? the supporting member.

According to this invention, the optical contact between the screen material and the supporting member can be effectively reduced without decreasing the mechanical support of the screen material. A layer of small transparent particles of glass or quartz is interposed between the screen material and the supporting member. Therefore, the only eifective contact between the fluorescent material and the supporting member is that comparatively small area of contact between the layer of particles and the supporting member.

The primary object of this invention is to provide a picture screen for'a kinescope.

Another object of this invention is to provide a means for reducing halation in kineseopes.

Other and incidental objects of the invention will beapparent to'those skilled in the art `from the following specication considered in connection with the accompanying drawing, in which Figure 1 is a sectional view of a kinescope.

vvention, and

Figure 2 isl a greatly enlarged cross section of a screen in accordance with one Hform of this inkFigure 3 is anenlarged cross section of another v form of this invention.

Referring inmore detail to Fig. l, there is an envelope I containing an electron gun with an indirectly 4heatedv cathode :3,1 a control. electrode 5, av first anode l, and asecondanode 9. The electron gun is adapted to produce an electron Vbeam which is deflected by the horizontal vdefiecting coils II aridy the' vertical deilecting coils I3 across the image screen I5, the detailv of which is shownmore fully in 'Figs. 2 and 3.

Fig. 2 shows a supporting member I 'I which may be the end of the envelope I of Fig. 1 or it may be a supporting member positioned inside the envelope I'of Fig. `l upon which there vis a layer of small transparent particle'sj I 9 which may be of small polished spheroidal glass or quartz beads. The spheroidalfparticles may be, made adherent to the supporting member I'I by the use of a suitable binder orby actually bringing about a' slight sintering action at the points of contact between the particles I 9 andthe supporting member I1 under the inilu'ence of heat.

It will be 'noticed that only asmall fraction of the supporting member I1 is in actual physical contact with the spheroidal particles i9. The particles are brought into as close physicalvconvtact with each other as is practically possible.

A coating of fluorescent material 2i is then spread over the surface 'of the p/articles.

@In operation, light from the screen material 2| enters the spheroidal particles from the back side. Due to the close physical or optical contact between the fluorescent material 2l and the particles Il, light travels in all directions within the particles I! and is either transmitted through the particles Il after suifering refraction, or is rei'lected until either scattered at the surface of contact between the fluorescent material 2i and the spheroidal particles I9 or transmitted into the supporting member at the point of contact between it and the spheroidal particles I9.

The light which is transmitted through the spheroidal particles I9 in an upward direction will enter the supporting member I'I and will be transmitted without experiencing total reflection, because of the relatively small angle from perpendicular that the light intersects the surtween the spheroidal particles I9 and that light which intersects the supporting member I'I at angles greater than the critical angle. Since the area of the point of contact between the particles I9 and the supporting member I'l is only a small fraction of the total surface of the supporting member II, a marked diminution of the amount of light suffering total reflection in the supporting member I'I is brought about.

Halation will be further reduced by reason of the fact that light which experiences total reflection at the outer surface of the supporting member II would normally suer total reflection again at the lower surface unless it impinges upon a region of optical contact with some other particle or object. In the conventional structure, the optical points of contact between the iluorescent material particles and the bulb serve as points for diiiused reflection of the totally reiiected rays. It is the upwardly directed portion of the diffused reflected rays which result in halation with its consequent reduction of detail and contrast.

Since, in accordance with this invention, only a small fraction of the supporting member I1 is in contact with the spheroidal particles I9, most of the light totally reected from the upper surface of the supporting member I1 will be totally reilected again from the lower surface. This process of reflection will repeat itself with ultimate absorption of the totally reilected rays.

Fig. 3 shows another form of this invention in which the supporting member 23 has thereon a layer of irregularly shaped particles 25 whose optical contact with the supporting member 23 covers a very small relative part of the lower surface of the supporting member 23. The layer of fluorescent material 21 covers the lower surface of the mosaic particles 25. The operation of this form of the invention is similar to that given above for the form of the invention shown in Fig. 2. The light caused by the impinging of the electron beam upon the iluorescent material 21 is caused to reect in the particles 25 until it is projected into the supporting member 23 through its point of contact with the particles 25.

While several systems for carrying this invention into effect have been indicated in this drawing, it will be apparent to one skilled in the art that this invention is by no means limited to the particular organization shown and described but that many modifications may be made without departing from the scope of this invention as set forth in the appended claims.

I claim as my invention:

1. In a picture-reproducing system including an envelope and means positioned in said envelope for producing an electron beam, a mosaic positioned in the path of said electron beam and comprising spheroidal transparent particles having a coating of fluorescent material on the surface adjacent said electron gun.

2. In a picture-reproducing system including an envelope and means positioned in said envel lope for producing an electron beam, an image screen positioned in the path of said electron beam and comprising a mosaic of transparent particles having a coating thereon of fluorescent material, a transparent member mounted in one end of said envelope upon which said particles are supported with substantiallly none of said fluorescent material in contact therewith.

3. In a picture-reproducing system including an envelope and means positioned in said envelope for producing an electron beam, an image screen positioned in the path of said electron beam and comprising a mosaic of spheroidal transparent particles on one end of said envelope and said particles having a coating thereon of iluorescent material.

4. In a picture-reproducing system including an envelope and means positioned in said envelope for producing an electron beam, an image screen positioned in the path of said electron beam and comprising a mosaic of transparent particles having a coating thereon of fluorescent material, a transparent member mounted in one end of said envelope upon which said particles are adapted to be supported, the total of the area of contact between the particles and said member being substantially less than the area of said mosaic. 5. In a picture-reproducing system including an envelope and means positioned in said envelope for producing an electron beam, an image screen positioned in the path of said electron beam and comprising a mosaic of spheroidal transparent particles on one end of said envelope and said particles having a coating thereon of fluorescent material, the total of the area of contact between the particles and envelope being substantially less than the area of said mosaic.

LOUIS MALTER..Y

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