Methods of making fluorescent surfaces in beam index type colour cathode ray tubes

Abstract

 A method of manufacturing a fluorescent surface of a beam index type colour cathode ray tube comprises successively forming a photosensitive resin layer (1) and an index fluorescent material layer (11) on a metal backing layer (2), and effecting exposure, development and removal of undeveloped resin (10) to form clearly spaced index fluorescent material stripes (ID).

Description

[0001] This invention relates to methods of making fluorescent surfaces in beam index type colour cathode ray tubes, and to beam index type colour CRTs having a fluorescent surface so made.

[0002] The fluorescent surface of a beam index type colour CRT generally has a cross-section as, for example, shown in Figure 2 of the accompanying drawings. A face plate 1 is made of a flat glass plate and black matrixes b are formed thereon, with a respective fluorescent stripe R, G or B for red, green and blue successively formed between each adjacent pair of the black matrixes b. A metal backing layer 2 made, for example, of aluminium film is formed on the colour fluorescent stripes R, G and B, and index fluorescent stripes ID are further formed thereover. A funnel portion 3 of the CRT is sealed with frit 4 to the periphery of the face plate 1.

[0003] In the beam index CRT, optical output signals obtained by scanning the index fluorescent stripes ID by the electron beam are detected, for example, by a photo-receiving element disposed in the funnel portion, to produce index signals, by which the positions for the three primary colour fluorescent stripes R, G and B are forecast to effect colour synchronization.

[0004] The fluorescent surface of the beam index colour CRT of this kind has usually been manufactured as follows. As shown in Figure 3A, as in the manner for the conventional fluorescent surface of a shadow mask type colour CRT, the black matrixes b, the colour fluorescent stripes R, G and B, an organic base layer 5 made for example of an acrylic resin, and a metal backing layer 2 made of aluminium by vacuum deposition, are formed. Thereafter a suspension of the index fluorescent material including a photosensitive agent such as polyvinyl alcohol (PVA) and ammonium dichromatic (ADC) is centrifugally-coated over the metal backing layer 2 and dried to form a photosensitive fluorescent resin layer 6. Then, as shown in Figure 3B, the portions to be formed with the index fluorescent stripes ID are exposed to, for example, ultraviolet rays 8 by way of a photomask 7 to cure the exposed portions, and are then developed with water to obtain the index fluorescent stripes ID as shown in Figure 3C.

[0005] However, in the conventional method described above, since the suspension of the index fluorescent material containing PVA and ADC is directly coated on the metal backing layer 2 to form the photosensitive fluorescent resin layer 6, followed by ultraviolet exposure and development, fluorescent material 9 remains on the entire surface of the metal backing layer 2, so clearly delineated index fluorescent stripes ID are not obtained. Accordingly, indistinctive and noisy index signals may be obtained and, moreover, if the pressure with which the developing solution is applied is raised or the developing time is increased in order to eliminate uncovered residual fluorescent material 9, it may possibly damage the metal backing layer 2.

[0006] According to the present invention there is provided a method of making a fluorescent surface in a beam index type colour cathode ray tube having fluorescent colour elements secured to a face plate and a metal backing layer covering said elements, characterised by:

forming a photosensitive resin layer on said metal backing layer;

then forming an index fluorescent material layer on said photosensitive resin layer;

then exposing said photosensitive resin layer through a mask, followed by development to form cured index fluorescent material stripes secured on said metal backing layer; and

then washing away the photosensitive resin layer where uncured, with the fluorescent material layer thereon.

[0007] In embodiments of the method according to the present invention, the index fluorescent material is kept from direct contact with the metal backing layer due to the presence of the photosensitive resin layer, and the unwanted portions of the index fluorescent layer can be washed away together with the uncured portion of the previously coated photosensitive resin layer following exposure and development. Accordingly, deposition of the fluorescent material on the uncovered portion can be avoided.

[0008] The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which:

Figures 1A to 1D show steps in a method according to the present invention;

Figure 2 is a cross-sectional view showing the fluorescent surface of a prior beam index type colour CRT; and

Figures 3A to 3C show steps in a prior method.

[0009] A method according to the present invention will now be described. As shown in Figure 1A, there are first formed black matrixes b, colour fluorescent stripes R, G and B, an organic base layer 5 for example of an acrylic resin, and a metal backing layer 2 of aluminium by successive vacuum deposition on a face plate 1. A photosensitive material such as of polyvinyl alcohol (PVA) and ammonium dichromate (ADC) is coated thereover by using a printing process and dried to form a photosensitive resin layer 10 of, for example, about 0.5 to 1 _Jlm thickness.

[0010] Then, as shown in Figure 1B, a suspension containing index fluorescent material is coated on the photosensitive resin layer 10 by a printing process, so as not to damage the photosensitive resin layer 10, and dried, thereby to form an index fluorescent layer 11 of, for example, about 10 µm thickness, on the photosensitive resin layer 10.

[0011] Then, as shown in Figure 1C, the portion of the photosensitive resin layer 10 to be formed with index fluorescent stripes 1D, is exposed to irradiation by, for example, ultraviolet rays 8 through a photomask 7 so as to be cured. The photosensitive resin layer 10 is immediately developed in water and the uncured portions of the photosensitive resin layer 10 are washed away together with the corresponding portions of the index fluorescent layer 11, to obtain the index fluorescent stripes ID as shown in Figure 1D.

[0012] In this method, since the index fluorescent material 11 is kept from direct contact with the metal backing layer 2 by the presence of the photosensitive resin layer 10 and, moreover, since the unwanted portions of the index fluorescent layer 11 are washed away along with the uncured portion of the photosensitive resin layer 10, unwanted deposition of the fluorescent material can be avoided. In this way, clearly defined or delineated, index fluorescent stripes ID, and thus satisfactory index signals, can be obtained. It is also unnecessary in this method to increase the developing time, or the hydrostatic pressure during the development, so damage to the metal backing layer 2 can be avoided.

Claims

1 A method of making a fluorescent surface in a beam index type colour cathode ray tube having fluorescent colour elements (R,G,B) secured to a face plate (1) and a metal backing layer (2) covering said elements (R,G,B), characterised by:

forming a photosensitive resin layer (10) on said metal backing layer (2);

then forming an index fluorescent material layer (11) on said photosensitive resin layer (10);

then exposing said photosensitive resin layer (10) through a mask (7), followed by development to form cured index fluorescent material stripes (ID) secured on said metal backing layer (2); and

then washing away the photosensitive resin layer (10) where uncured, with the fluorescent material layer (11) thereon.

2. A method according to claim 1 wherein a black matrix (b) is applied to said face plate (1) prior to application of said metal backing layer (2).

3. A method according to claim 1 or claim 2 wherein said metal backing layer (2) is vacuum deposited.

4. A beam index type colour cathode ray tube including a fluorescent surface made by a method according to claim 1, claim 2 or claim 3.

Drawing