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Europaisches Patentamt 0 372 560 J European Patent Office 00 Publication number: A2 Office europeen des brevets EUROPEAN PATENT APPLICATION C09K 11/02 © Application number: 89122598.9 <S) int. CIA © Date of filing: 07.12.89 LTD. © Priority: 08.1 2.88 JP 310648/88 © Applicant: KASEI OPTONIX, 12-7, Shibadaimon 2-chome Minato-ku © Date of publication of application: Tokyo 105(JP) 13.06.90 Bulletin 90/24 © Inventor: Tono, Hideo Naruda © Designated Contracting States: Kasei Optonix, Ltd 1060 DE GB IT NL Odawara-shi Kanagawa-ken(JP) Inventor: Miyazaki, Tomohiro Kasei Optonix, Ltd. 1060 Naruda Odawara-shi Kanagawa-ken(JP) © Representative: Wachtershauser, GUnter, Dr. Tal29 D-8000 Munchen 2(DE) © Phosphors and method for treating the surface thereof. of the and attached to © A phosphor comprising a phosphor and zinc oxide formed in a suspension phosphor the surface of the phosphor. CO m CM m LU Xerox Copy Centre EP 0 372 560 A2 PHOSPHORS AND METHOD FOR TREATING THE SURFACE THEREOF The present invention relates to phosphors for cathode ray tubes and a method for treating the surface thereof. More particularly, it relates to phosphors capable of forming excellent phosphor screens on face plates, and a method for treating the surface thereof. As is well known, phosphor screens for color television cathode ray (picture) tubes are composed of 5 blue, green, and red emitting phosphor dots or stripes of blue, green, and red emitting phosphor components disposed regularly on a face plate. The phosphor screens for color television picture tubes are prepared by photo-printing method. That is, a first light emitting phosphor component is dispersed in a solution of a light sensitive resin such as, for example, an aqueous solution of polyvinyl alcohol activated with a dichromate, to provide a phosphor slurry. The phosphor slurry obtained is applied over the whole 10 surface of a face plate by an appropriate coating method such as by rotary coating, etc. (slurry coating), and then the coated layer is irradiated by energy rays such as ultraviolet rays, etc., in conformity with a desired pattern, whereby the resin is hardened and insolubilized at the portions irradiated by the energy rays (light exposure). Thereafter, the resin at the non-irradiated portions (unhardened resin portions) is dissolved away by a solvent, etc. (development) to form dots or stripes composed of the first light emitting 75 phosphor component. Then, by successively repeating slurry coating, exposure and development in the same manner as described above using second and third light emitting phosphor components, dots or stripes composed of the second and third light emitting phosphor components are formed on the face plate. In this case, as matter of course, the energy ray irradiation must be so controlled that the dots or stripes composed of each of the first, second, and third light emitting phosphor components are repeatedly and 20 regularly disposed on the face plate without being overlapped with each other. Then, the fluorescent screen containing the resin component thus prepared is fired at a proper temperature to decompose and volatilize the resin component, whereby a desired phosphor screen is obtained. For making phosphor screens for color television picture tubes by a photo-printing method using the above-mentioned phosphor slurries, the following requirements must be met. 25 1 . The phosphor screen must be dense and have little pin holes or the like; 2. One light emitting phosphor component must not intermix with other light emitting component phosphors, i.e. color mixing must not occur; 3. The phosphor slurry must have high light exposure sensitivity and must be easy to work with; 4. Formation of the light emitting elements (dots or stripes) must be excellent, i.e. the edges must be 30 sharp, the dots must be circular, and the stripes must be linear; 5. The exposed phosphor screen must not fall off the face plate by high pressure aqueous development treatment during the development process, i.e. it must have a high adhesive strength. Heretofore, various studies and improvements have been made with respect to the surface treatment of phosphors, the compositions and the method for the preparation of phosphor slurries with an aim to satisfy 35 the above requirements. For example, Japanese Examined Patent Publication No. 21675/1985 discloses a phosphor having its surface coated with zinc hydroxide for the purpose of improving items 2 and 3 among the above requirements. With respect to the color television picture tubes, there has been an increasing demand for improving the image quality in recent years. For this purpose, it is necessary to form finer picture elements on a face 40 plate so that a highly fine image can be formed. To fulfill the above demand, it is firstly required to satisfy the requirement that the adhesive strength of the screen portion hardened by the exposure is high (above requirement 5) and the requirement that color mixing must not occur (above requirement 2), simultaneously. However, in order to increase the adhesive strength of phosphor screens by conventional methods for forming phosphor screens, a method is usually 45 employed wherein the drying is strengthened at the time of coating, whereby there will be a difficulty such that the higher the adhesive strength of the phosphor screen, the more the unnecessary phosphors tend to remain on other position, thus leading to color mixing. With the above-mentioned phosphor coated with zinc hydroxide, it is hardly possible to satisfy such mutually opposing requirements at the same time. It is conceivable to increase the amount of zinc hydroxide coated in order to adequately prevent color mixing in so the above-mentioned phosphor coated with zinc hydroxide. However, if the amount of the coated zinc hydroxide increases, the action for aggregation of zinc hydroxide colloid increases in the phosphor slurry, whereby the dispersibility of the phosphor in the slurry deteriorates, which in turn tends to lead to a decrease of the adhesive strength, formation of pin holes or a deterioration in the sharpness of the edge. The present invention has been made in view of the above problems, and it is an object of the present invention to provide a phosphor which is capable of preventing the occurrence of color mixing of the EP 0 372 560 A2 the time and which phosphor screen and increasing the adhesive strength of the phosphor screen at same is excellent in the dispersibility in the slurry, and a method for treating the surface thereof. and as a The present inventors have conducted extensive researches to accomplish the above object obtained by result, have found that among phosphors having zinc oxide attached in their surface, those of have the above- 5 forming and attaching zinc oxide on the phosphor surface in a suspension a phosphor, mentioned desired properties for forming phosphor screens. oxide formed in a Namely, the phosphor of the present invention comprises a phosphor and zinc "zinc oxide is formed in a suspension of the phosphor and attached to the surface of the phosphor. Here, alkaline solution in the suspension" means that zinc oxide is formed by reacting zinc ions and an w suspension. embodiments. Now, the present invention will be described in detailed with reference to the preferred In the companying drawings: zinc oxide Figures 1(a) and (b) are microscopic enlarged photographs of phosphor particles having formed in a suspension attached on their surface. having zinc oxide 75 Figures 2(a) and (b) are microscopic enlarged photographs of phosphor particles attached merely by mixing phosphor and ready made zinc oxide on their surface. having zinc Figures 3(a) and (b) are microscopic enlarged photographs of phosphor particles hydroxide attached on their surface.. particle having Figures 4(a), (b) and (c) are diagrammatical views of the above-mentioned phosphor oxide on its surface and the 20 zinc oxide attached on its surface, the phosphor particle having zinc deposited phosphor particle having zinc hydroxide attached on its surface. is formed. Figure 5 is a graph showing the temperature and pH ranges in which zinc oxide zinc oxide attached Figures 6 and 7 are graphs showing cross-contamination of the phosphor having and the phosphor having zinc on its surface, the phosphor having zinc oxide deposited on its surface 25 hydroxide attached on its surface. invention enlarged 5,000 and Figures 1(a) and (b) show photographs of the phosphor of the present and show, for the purpose 20,000 magnifications, respectively, by an electron microscope. Figures 2(a) (b) with 5,000 and 20,000 of comparison with the phosphor of the present invention, electroscopic photographs its surface by adding a magnifications, respectively, of a phosphor having zinc oxide deposited on of the phosphor, followed by stirring and 30 dispersion of commercially available zinc oxide to a suspension with 5,000 and 20,000 mixing. Further, Figures 3(a) and (b) are electron microscopic photographs in of the phosphor magnifications, respectively, of a phosphor having zinc hydroxide formed a suspension 1 corresponding to attached on its surface. Figures 4(a), (b) and (c) are diagrammatical views of a phosphor 1 corresponding to the phosphor of Figure 1 and having zinc oxide 2 attached on its surface, a phosphor its surface, and a phosphor 1 35 the phosphor of Figure 2 and having zinc oxide 2 deposited on attached its surface. These corresponding to the phosphor of Figure 3 and having zinc hydroxide 3 on followed dehydration and drying. phosphors were taken out from the respective suspensions by filtration, by invention has zinc oxide It is evident from the above Figures that the phosphor of the present zinc oxide directly consistently firmly attached thereto as compared with the phosphor having particles invention is different in the shape of 40 deposited Further, zinc oxide attached to the phosphor of the present surface in a relatively attachment from the conventional zinc hydroxide and is attached to the phosphor uniformly distributed state.