Fluorescent film structure of color Braun tube

Abstract: The fluorescent film described improves color purity and brightness of a color Braun tube by constructing the fluorescent film of the red fluorescencer as a laminated structure. The fluorescent film of the red fluorescencer comprises fluorescencer layers having a laminate structure made of two different compositions of Y 2 O 2 S : Eu and Y 2 O 3 : Eu.

Description: FIELD OF THE INVENTION The present invention relates to a fluorescent film structure of a color Braun tube. More specifically, the present invention relates to a fluorescent film structure in which two or more multi-layer fluorescencers are constructed on a fluorescent film of a red fluorescencer, to enhance the white radiation brightness. BACKGROUND OF THE INVENTION Three-color fluorescencers are used in a color Braun tube, a fluorescent lamp, a projection type cathode-ray tube, or the like. A color Braun tube generally comprises as its essential component a fluorescent screen subsequently coated with three-color (green, blue, red) fluorescencers which radiates by an electronic ray on an inner surface of a panel with a whole surface of glass. The process for manufacturing such a fluorescent screen is largely divided into a coating of light-absorbing black material (BM) [FIG. 1] and a coating of three-color fluorescencer phosphor (PH) [FIG. 2]. As illustrated in FIG. 1, the process of coating of light-absorbing BM comprises washing and drying panel (1) and then injecting and coating a photoresist thereto; light-exposing and developing by the use of a mask which defines the portion to which three primary color fluorescent materials should be formed, to form a photoresist mask; coating graphite; and etching, developing and drying the said photoresist mask to form a graphite band (2) having a thickness of about 5 - 10 µm. Subsequently, as illustrated in FIG. 2, the panel to which a BM has been formed is washed, and then coated with a precoat and dried. A mixture of a green fluorescencer, photosensitizer, polyvinyl alcohol, light cross-linker and dispersing agent is coated thereto, dried, light-exposed and developed to form a green fluorescent film (3). Then a blue fluorescent film (4) and a red fluorescent film (5) are formed by the same procedure. Then, an emulsion film is formed and Al-deposited. In the three color fluorescent films, the green fluorescencer comprises ZnS : Cu,Al, ZnS : Au,Al, [(Zn,Cd)S : Cu,Al] etc.; the blue fluorescencer comprises ZnS : Ag, ZnS : Ag,Al, etc., and the red fluorescencer comprises Y 2 O 2 S : Eu, Y 2 O 3 : Eu, etc. These three color fluorescencers should have good radiation color purity as three primary color light, and high radiation efficiency to the electronic ray stimulating energy, i.e., high radiating brightness. At present, same colored pigment as the radiation color is adhered onto the surface of the fluorescencer core in order to improve the radiation color purity and contrast of the screen. Though such a pigment-adhered fluorescencer is advantageous for the color purity and contrast, it is disadvantageous for the radiation brightness. It is because pigment absorbs light (of whole wavelength range) by its essential characteristics, but the red pigment little absorbs the light of red wavelength range while it largely absorbs the light of other wavelength range to cause the above phenomenon. Documents GB2246361A and EP0529098A1 discuss ways in which the color purity and contrast of red cathode ray tube phosphors may be improved. SUMMARY OF THE INVENTION It would therefore be desirable to construct a red fluorescent film with a laminate structure having a first red fluorescent film layer and a second red fluorescent film layer, in order to enhance the red radiation and white brightness. Accordingly, the present invention provides a red fluorsecent film for a color Braun tube, the film comprising a laminate of at least a first fluorescencer layer comprising Y 2 O 2 S:EU and a second fluorescencer layer comprising Y 2 O 3 :EU. To this end embodiments of the present invention provide a fluorescent film for a color Braun tube comprising fluorescent films formed with three color fluorescencers of green, blue and red, wherein the fluorescent film of the red fluorescencer has fluorescencer layers having a laminate structure made of two or more different composition. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart of a conventional process for graphite coating. FIG. 2 is a flow chart of a conventional process for fluorescencer coating. FIG. 3 is a structural view of a conventional fluorescent film. FIG. 4 is structural view of a fluorescent film embodying the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 4, illustrating the structure of the fluorescent film embodying the present invention, the fluorescent film is different from the conventional fluorescent film [FIG. 3] in that the former comprises multi-layer structure of the red fluorescent film. On the inner surface of a face plate of panel (1) to which BM has been formed, a green fluorescent film (3) and a blue fluorescent film is formed, and the red fluorescent film comprises the first red fluorescencer layer (6) and the second red fluorescencer layer (7). In the above-mentioned structure, the multi-layer fluorescent film is prepared by injecting a composition for the first red fluorescencer layer (6) comprising Y 2 O 2 S : Eu adhered with a pigment by rotary coating method, drying and light-exposing thereof (the layer is not developed); injecting a composition for the second red fluorescencer layer (7) comprising Y 2 O 3 : Eu which is not adhered with a pigment, drying, light-exposing and developing thereof; and coating with acrylic emulsion. The X-coordinate of a powder color coordinate system of Y 2 O 2 S : Eu fluorescencer used in the present invention is 0.645 ± 0.005, and the Y-coordinate thereof is 0.635 ± 0.005. The fluorescencer has powder reflexibility [with reference to MgO] of 30 - 70 %. It has advantages of excellent color purity and contrast due to the reduction of reflection of external light by the adhesion of the pigment, while it has a disadvantage of low brightness. On the other hand, the Y 2 O 3 : Eu fluorescencer has X-coordinate of 0.635 ± 0.005, and Y-coordinate of 0.655 ± 0.005 in the powder color coordinate system, and powder reflexibility of 70% or more. It has a lower color purity than the former, while it has a relatively advantageous brightness. Therefore, every characteristics cannot be satisfied if the fluorescencer is comprised of mono-layer. However, according to the described embodiment, both color purity and brightness can be improved by constructing these two fluorescencers as a multi-layer. The film thickness of the first red fluorescencer layer (6) is preferable 10 - 50% of the second red fluorescencer layer (7). If the thickness of the first red fluorescencer layer (6) is less than 10% of the second red fluorescencer layer (7), contrast may be lowered owing to the direct contact of a part of the second red fluorescencer layer onto the face plate. If the thickness is more than 50%, the radiation intensity of the second red fluorescencer layer is relatively weakened, so that the brightness cannot be improved. Though, in the example of the described embodiment, the first fluorescencer layer comprises Y 2 O 2 S : Eu, and the second layer comprises Y 2 O 3 : Eu, the composition of each layer can be exchanged, and each layer is not limited to a composition. According to the described embodiment a fluorescent film having high radiation efficiency without lowering overall color purity, by passing the light radiated from the second fluorescencer layer (7) having excellent radiation efficiency through the first fluorescencer layer (6) having excellent color purity. As described above, according to the described embodiment a red fluorescent film is formed to overcome the inherent disadvantages of fluorescencers, and the characteristics of laminated fluorescencers having different compositions are complemented each other, to obtain a fluorescent film having improved color purity, brightness, and so on. It provides an excellent fluorescent screen of a fluorescent lamp or a projection type cathode-ray tube as well as a color Braun tube.

Claims: A red fluorescent film for a color Braun tube, the film comprising a laminate of at least a first fluorescencer layer comprising Y 2 O 2 S:EU and a second fluorescencer layer comprising Y 2 O 3 :EU. A film as claimed in claim 1 wherein the first fluorescencer layer is adhered with a pigment and the second fluorescencer layer is not adhered with a pigment. A film as claimed in any preceding claim wherein the thickness of the first fluorescencer layer is between 10% and 50% of the thickness of the second fluorescencer layer. A fluorescent film structure for a color Braun tube comprising green, blue and red fluorescent films, wherein the red fluorescent film or films accord to any preceding claim.

Inventors: KANG SEOUG WAN, KANG, SEOUG WAN
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1996
Main classification: H01J29
IPC codes: H01J29, C03C17