Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
2001-06-25
2003-05-13
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C264S001270
Reexamination Certificate
active
06563645
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of producing a segmented lens which is used in the manufacturing process of colour display tubes.
The invention also relates to the segmented lens itself and to the mould which is used for producing the segmented lens.
Further, the invention relates to a method of producing a screen, having a dotted pattern of apertures in a black matrix and electroluminescent material in said apertures, on a display window of a colour display tube, which method comprises, exposing a photosensitive material on the display window to light which has been emitted by a point source and has passed through the segmented lens and a mask, the segmented lens comprising facets having a diagonal, with bounderies between them, and changing the relative position of the segmented lens with respect to the display window over a first distance and in a first direction oblique to the boundaries of the facets during exposure of the photosensitive material.
The invention further relates to a screen of a colour display tube and a colour display tube provided with a screen that is produced by using said segmented lens.
BACKGROUND OF THE INVENTION
A method of producing a screen for a colour display tube as mentioned in the opening paragraph is disclosed in U.S. Pat. No. 4,866,466. The method according to this specification describes an exposure process for manufacturing screens for colour display tubes. In this exposure process a segmented lens is used. The presently used segmented lens is manufactured by using a mould which contains a two-dimensional array of metal poles. The segmented lens comprises a glass carrier which—in the manufacturing process of the segmented lens—is brought together with the metal mould, while keeping a well-defined distance to this mould. The space between the segmented lens and the mould is filled with a fluid plastic that hardens after it has been applied, for instance by exposing it to UV light. The segmented lens consisting of a glass carrier provided with a plastic layer which contains the facets, being the inclined top faces of the segments of the lens, is then removed from the mould.
The metal poles of this mould are stacked by just placing them next to each other, starting in one corner of the two dimensional array which typically consists of 21 by 17 metal poles each having a bottom surface of 8*8 mm
2
. This way of stacking has the disadvantage that tolerance errors in the parallellism of opposite sides—which are in contact with a side of an adjacent metal pole—of the metal poles add up, leading to obliquely positioned metal poles. As a result the facets of these metal poles will have a wrong inclination, causing landing errors. These misregistrations lead to a deteriorating performance with respect to colour purity. In this way of stacking, it is important that the metal poles are firmly pressed together, so that the friction between adjacent metal poles prevents that the metal poles can become detached from the mould when the segmented lens is removed
On the inner side of the display window, a colour display tube is provided with a screen. This screen has in general a black matrix structure having a pattern of apertures, in which apertures the electroluminescent material is provided. The structure of the black matrix in most common colour display tubes is either a dotted pattern or a line pattern. This pattern is produced by exposing a photosensitive material that is deposited on the inner side of the display window and by using an exposure system and the shadow mask, which serves as the colour selection means in colour display tubes. For exposing colour display tubes with a line pattern an exposure system with a continuous lens can be used. However, for colour display tubes with a dotted pattern, it is common use to apply a segmented lens in order to have enough degrees of freedom to obtain a dotted pattern on the screen that fulfils the requirements regarding good landing properties. Landing in a colour display tube is the quality that defines how well the electron beams that hit the screen coincide with the corresponding electroluminescent material.
After the black matrix layer has been applied on the inner side of the display window, another photosensitive process is used for applying the electroluminescent material—for instance, three colours of phosphor like red, green and blue—to the areas of the display window that were left free by the black matrix structure.
In producing a screen with a dotted pattern, light from a point source is directed through the segmented lens and the shadow mask. This segmented lens comprises a two dimensional array of differently inclined facets. In case 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 over the entire screen, the segmented lens is moved during the exposure process. These movements are in general in oblique directions, called the wobble and drift direction, with respect to the rectangular array of facets. The wobble and drift directions are mutually nearly orthogonal. By this method, the image of one facet is by this method spread over a larger area, so that the light and dark lines are smeared out to such an extent that facet marking is reduced.
The ever-increasing demand for improved image quality in colour display tubes also leads to higher requirements with respect to the colour purity. This colour purity is directly related to the landing properties of the colour display tube and so, also to the quality of the segmented lens.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of producing a segmented lens for the exposure system used in the manufacturing process of colour display tubes that leads to a colour display tube with an improved behaviour with respect to landing and colour purity.
According to the present invention, this object is achieved by means of a method of producing a segmented lens, in which a fluid plastic is applied between a glass carrier and a mould comprising a two-dimensional array of metal poles, each metal pole having a top section which is rectangular in shape, a top surface with a chosen inclination and a bottom section which is cylindrical in shape for engaging a corresponding two-dimensional array of round apertures in a carrier plate, which fluid plastic is hardened after which the segmented lens, being the assembly of the glass carrier and the plastic top layer having a two dimensional array of facets, is removed from the mould.
The invention is based on the recognition that the tolerances that occur in stacking the two-dimensional array of metal poles can be strongly diminished when the metal poles are supported by a carrier plate only and do not lean against adjacent metal poles. The invention is realized by making a mould which has a carrier plate that serves as the bottom. In this carrier plate a two dimensional array of round apertures is provided. The metal poles have a bottom section that is round in shape to engage the apertures in the carrier plate. By inserting the metal poles in the round apertures of the carrier plate, a two-dimensional array of metal poles is formed which are freely positioned without leading to wrong inclinations of the facets due to adding the errors in parallellism of the metal poles. In order to be able to remove the segmented lens from the mould after the plastic has hardened, it is required to fix the metal poles firmly to the carrier plate, for instance by locking them with a screw at the bottom side. Application of this invention in the production process of colour display tubes leads to a strongly improved landing performance, and so, to a better colour purity.
In EP-0737996-A1 a mould is disclosed that i
Heemstra Tewe Hiepke
Poorter Tiemen
Epps Georgia
Hindi Omar
LandOfFree
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