Photography – Exposing multicolor cathode-ray tube targets
Reexamination Certificate
2000-04-14
2002-07-16
Gray, David M. (Department: 2851)
Photography
Exposing multicolor cathode-ray tube targets
C396S548000, C430S023000
Reexamination Certificate
active
06421507
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of producing a screen on a panel for a color display device, which screen comprises a dotted structure of apertures in a black matrix and electroluminescent material in said apertures in which method a photosensitive material on the panel is exposed to light emitted by a point source and passed through a segmented lens and a mask, the segmented lens comprising an array of facets with boundaries between them, at least two of the facets having a top surface which is inclined at different angles and simultaneously changes the relative position of the segmented lens and the panel in a direction oblique to the boundaries of the facets during exposure of the photosensitive material, the extent and direction of changing the relative position of the segmented lens and the panel being such that, in moving from one extreme position to another extreme position, an image of a first facet on the panel occupies substantially an extreme position previously occupied by an image of a second facet obliquely adjacent to the first facet.
The invention also relates to a screen produced by using such a method and to a color display device provided with such a screen.
BACKGROUND AND SUMMARY OF THE INVENTION
A method of producing a screen for a color display device as described above is disclosed in U.S. Pat. No. 4,866,466. The method according to this specification describes an exposure process for manufacturing screens for color display devices, like cathode ray tubes.
On the inside of the panel, which is the glass faceplate, cathode ray tubes (CRTs) are provided with the so-called screen. This screen has a black matrix structure and electroluminescent material in the apertures left free by the black matrix. The structure of the black matrix in most common CRTs is either a dotted structure or a line structure. This structure is produced by exposing a photosensitive material that is deposited on the inside of the panel and by using an exposure system and the shadow mask serving as the color selection means in CRTs. For exposing line-type CRTs, an exposure system with a continuous exposure lens can be used. However, for dotted-type CRTs, it is common practice to apply a segmented exposure lens in order to have enough degrees of freedom to obtain a dotted structure on the screen that fulfills the requirements regarding good landing properties. Landing in a CRT is the quality that defines how well the electron beams hitting the screen coincide with the corresponding electroluminescent material.
After the black matrix layer has been applied on the inside of the panel, another photosensitive process is used for applying the electroluminescent material—for instance, three colors of phosphor like red, green and blue—to the areas of the panel that were left free by the black matrix structure.
In producing a screen with a dotted structure, light from a point source is directed through the segmented lens and the shadow mask. This segmented lens comprises a rectangular array of differently inclined facets If the screen is illuminated through a stationary segmented lens, the images of consecutive facets will not fit as consecutive areas on the screen. This will cause dark and light lines, during the exposure process, in the areas where the images of two consecutive facets are disjunct or overlap, respectively. This phenomenon is normally referred to as facet marking. In order to obtain a substantially uniform illumination across the entire screen, the segmented lens is wobbled and drifted in oblique directions with respect to the rectangular array of facets. The wobble and drift directions are mutually nearly orthogonal, In this method the image of one facet is spread across a larger area so that the light and dark lines are faded to such an extent that facet marking is considerably reduced and even prevented.
In the currently used method of producing screens by exposure, the use of a point source for illuminating the screen daring exposure leads to a screen structure that closely resembles the mask structure. If, for instance, the mask has a structure of round apertures, the apertures in the black matrix will also be substantially round. For new designs of dotted-type tubes, it is often recognized that the currently used method has its drawbacks.
The structure of a dotted-type screen is, amongst others, determined by the horizontal and by the vertical pitch. In this context pitch means the distance between phosphor dots of the same color. In general, a small pitch is desired in order to obtain a good resolution of the screen. On the other hand the vertical pitch should be chosen to be such that the scan-moiré phenomenon is suppressed as much as possible. In order to fulfill these two requirements it appears that it is generally not possible to use a purely hexagonal screen structure. For instance, if the desired vertical pitch is increased with respect to the pitch corresponding to a hexagonal structure, the circular apertures in the black matrix lead to less electroluminescent material on the screen. As a consequence, the display device will have a lower luminance (light output).
In most commonly used CRTs, the screen is scanned in two directions. The line scan, being the higher frequency, is usually in the horizontal direction, while the frame scan, being the lower frequency and perpendicular to the line scan, is in the vertical direction. It is remarked that the frame direction is not per se the vertical direction. The frame direction in the vertical direction is not to be considered limitative.
The interaction between the mask and the consecutive lines causes the scan-moiré phenomenon. It is a disadvantage of the screens produced by means of the method mentioned in of the opening paragraph that a good moiré performance is mostly at the expense of the luminance.
It is an object of the invention to provide an improved method as compared with the method described in the opening paragraph, of producing a screen with a dotted structure for a color display device.
According to the invention, this object is realized with a method which is characterized in that said facets comprise light-refracting means having a base surface coinciding with the top surface of the facet and at least a first and a second light-refracting surface disposed at predetermined angles with respect to the base surface, thereby creating a number of virtual light sources corresponding to the number of light-refracting surfaces.
The invention is based on the recognition that, by providing each facet with light-refracting means having at least two light-refracting surfaces, the real point source viewed from the screen—is subdivided in to a number of virtual light sources equal to the number of light-refracting surfaces. The light-refracting means may be, for example, a prism structure.
It is to be noted that, for instance, British Patent Specification 1 577 503 discloses a rectangular structure of small prisms with two light-refracting surfaces. The purpose thereof is to create two virtual line-shaped light sources in order to be able to control the phosphor line width across the entire screen of a CRT. In contrast to the present invention, which is meant for CRTs with a dotted screen and a black matrix structure, the CRT described in said British Patent Specification is a tube with a line structure on the screen, originating. from a striped shadow mask and without a black matrix. By changing the distance between the two virtual light sources across the screen, a compromise can be achieved in this case between the phosphor line width and the phosphor adhesion on the screen. Although the use of prisms creating virtual light sources is known per se, the present invention describes a totally different measure compared to said British Patent Specification 1 577 503.
A preferred embodiment of the method according to the present invention is characterized in that the light-refracting surfaces are inclined in the frame direction in such a way that the virtual light sources are separated in sai
LandOfFree
Method of producing a screen for a display device, screen... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing a screen for a display device, screen..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing a screen for a display device, screen... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2861181