1. Field of the Invention
The present invention relates to a cathode-ray tube and a method for manufacturing a cathode-ray tube suitable for use in a projection-type display, for example.
2. Description of the Related Art
For cathode-ray tubes for use in projectors and the like, what is called deposition-type glass (deposited bulbs), in which the panel and funnel sections of the body of the cathode-ray tube are integrally formed, is used.
By reason of glass formation, the inner wall of the funnel section and the side of the panel section generally constitute mirror finished surfaces in cathode-ray tubes of this type.
When an electron beam is irradiated upon the fluorescent surface created on the inner surface of the panel section, part of it is reflected off in the form of reflected electrons.
Since the inner wall of the funnel section and the sides of the panel section constitute mirror-like surfaces, as described above, the reflected electrons are reflected back off the inner wall and are again incident upon the fluorescent surface. This has a marked deteriorating effect on the contrast of the projected image.
In the case where a plurality of cathode-ray tubes are located next to each other, such as cathode-ray tubes in a television receiver using a projector, light leaking from the funnel section and the sides of the panel section of a cathode-ray tube affects each other and causes deterioration of the contrast.
When an excellent quality of displayed image is to be achieved in a monochrome cathode-ray tube like those used in projectors, an especially high degree of intensity and contrast is required.
In order to counteract factors which cause the contrast to deteriorate, one measure that has conventionally been adopted involves coating the inner wall of the funnel and the sides of the panel with a black material, such as carbon, thereby reducing and absorbing the reflection of light as much as possible.
When the measure is employed for a cathode-ray tube using deposition-type glass in which the panel and funnel sections are integrally formed, coating the inner surface is performed by inserting a brush or other coating implement through the neck section and rotating the glass.
Accordingly, it has hitherto been possible to coat only that part of the inner surface of the funnel which has a circular cross-section. It also has been difficult to ensure that the funnel section and the sides of the panel section are coated evenly with the black material.
Meanwhile, if a thick coating is applied to the inner wall in such a manner as to avoid missing anywhere, the black material tends to peel off, thereby causing the withstand voltage properties of the cathode-ray tube to deteriorate.
The inner surface of the funnel section needs a furnished conductive film in order to ensure that high voltage supplied from the anode button is fed to the fluorescent surface and the inner surface of the funnel section of the body of the cathode-ray tube has the same potential.
Since it is possible to coat only that part of the inner surface of the funnel which has a circular cross-section in a cathode-ray tube using deposition-type glass, it has been necessary instead to deposit aluminum over a wide area as a metal backing layer in order to form an inner conductive film.
However, depositing a metal backing layer over a wide area in this manner, in order to form the conductive film, results in the fact that the contrast of the image deteriorates by reason of reflected electrons and stray light caused by not being absorbed sufficiently and reflected off the metal-backing layer.
Examples of stray light which causes the contrast of the image to deteriorate include stray light caused by light reflected off the inner surface of the body of the cathode-ray tube being subject to multiple reflection within the glass thereof and returning to the front surface of the panel and stray light caused by light reflected off the inner surface of the funnel section of the body of the cathode-ray tube returning directly to the front surface of the panel.
In order to solve the abovementioned disadvantages, the present invention proposes a cathode-ray tube having an excellent quality of image with a highly enhanced contrast and a method of manufacturing such a high-contrast cathode-ray tube by reducing stray light and the re-entering of reflected electrons through the fluorescent surface thereof.