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(11) | EP 0 445 298 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | COLOR CATHODE-RAY TUBE |
| (57) A color cathode-ray tube having a least a front panel, a funnel and an electron gun.
A luminescent film is provided on the front panel. The luminescent film is produced
in this manner. Red-light-emitting, green-light-emitting, and blue-light-emitting
phosphor layers are repetitively laminated with nonluminescent layers interleaved.
The laminate is cut along its thickness into films and baked. This makes it possible
to efficiently produce a cathode-ray tube having a color luminescent screen that features
very high accuracy and high resolution, and that can be adapted to small CRTs. |
BACKGROUND OF THE INVENTION
(Field of Application)
[0001] The present invention relates to a color cathode-ray tube and, in particular, to a color cathode-ray tube suitable for providing the higher fineness of the pattern that has recently come to be demanded of color cathode-ray tubes.
(Description of the Prior Art)
[0002] Recently, the electron guns that are widely used in color cathode-ray tubes have a form in which three electron guns are arranged in a straight line, to realize a method called an in-line method.
[0003] A stripe pattern that allows more efficient use of brightness than a dot pattern and enables the electron beams to correctly excite each of luminous color phosphor elements is mainly used for the phosphor layer on the front screen panel of the cathode-ray tube.
[0004] This stripe pattern is constructed of a repeating sequence of red phosphor layers, green phosphor layers, and blue phosphor layers, with layers of a non-luminous substance, such as carbon, between adjacent layers of differently colored phosphor.
[0005] With conventional technology, the stripe pattern is formed by either a slurry method, dusting method or an optical adhesion method using exposure technology, or a screen printing method using printing technology. The most common methods use slurries.
[0006] With these slurry methods, a liquid called a slurry formed by dispersing a phosphor in a mixture of polyvinyl alcohol and bichromate is coated onto the panel by spin-coater, then the required portions of the slurry are optically cured by exposure to ultraviolet light through an exposure mask such as a shadow mask, to fix the phosphor. Uncured portions of the slurry are washed away with hot distilled water, leaving the pattern of the phosphor layer. This process is repeated with the other phosphors and carbon to form the stripe-pattern phosphor layer.
[0007] With the screen printing method, differently colored phosphor pastes designed for printing are printed either directly or indirectly onto the panel, specific phosphor colors are fixed onto specific areas of the panel, then the stripe-pattern phosphor layer is formed by burning the binder resin component in the pastes.
[0008] The panel on which this phosphor layer is provided is then combined with a funnel and electron gun to form the color cathode-ray tube.
[0009] All of these conventional slurry, dusting, and optical adhesion methods have an exposure step, but in methods that use exposure technology an exposure mask that has a fine pattern is essential, and an even finer exposure mask would be required to make the cathode-ray tube smaller or increase the fineness of the pattern. Technical difficulties make this expensive from both the material and production points of view. In addition, the equipment, starting with the exposure device, is expensive, the manual labor required for steps such as recovering the phosphor is irksome, and losses are great.
[0010] With methods using exposure technology, ultraviolet light is reflected back unevenly by the phosphor when a thick layer such as a phosphor-containing slurry coated onto the panel surface is exposed, and the cross-sectional area of the ultraviolet light emitted from an entrance side toward the thick film widens as the light approaches the film, making it difficult to adjust the stripe width and also undesirably deteriorating the linearity of the stripes.
[0011] Screen printing methods using printing technology mainly use stainless-steel screens, but the minimum width of the slits that form the stripe pattern of these stainless-steel screens is 0.1 mm, so these methods cannot be used to make a smaller cathode-ray tube or a finer pattern.
SUMMARY OF THE INVENTION
[0012] The present invention is based on the above background and its object is to provide a color cathode-ray tube provided with a phosphor layer having the extremely fine pattern necessary for high resolution.
[0013] To summarize the present invention: A color cathode-ray tube comprises at least a front screen panel, a funnel, and an electron gun; a phosphor layer is provided on the panel, the phosphor layer being comprised of a multilayered material of a repeated sequence of red phosphor layers, green phosphor layers, blue phosphor layers, and non-luminous layers, and the laminate is sliced in the thickness direction thereof to form a thin layer and is burned; wherein the laminate has a construction such that non-luminous layers are interposed between adjacent phosphor layers.
[0014] In another preferred form of the present invention, each of the layers in the multilayered sheet is a red, green, or blue phosphor layer or a carbon layer that is a composite of red, green, or blue phosphor or carbon, respectively, uniformly dispersed in a burnable organic binder, and the laminate is composed of a repeating sequence of these layers stacked to a specific thickness, with carbon layers interposed between adjacent phosphor layers.
[0015] In yet another preferred form of the present invention, each of the layers in the multilayered sheet is a composite of red, green, or blue phosphor uniformly dispersed in a burnable organic binder, the composite being coated onto and dried on a film to obtain red, green, or blue phosphor-coated film, and the phosphor-coated films are stacked in a repeating sequence to a specific thickness.
[0016] In a preferred form of the color cathode-ray tube of the present invention, a black stripe layer is arranged between the burned slice of the laminate and the front screen panel, the black stripe layer being positioned to correspond to the non-luminous layers.
[0017] Since the phosphor layer of the present invention is obtained from a slice through a laminate, no exposure step such as that employed in a conventional photo-curing method is used, so there is no need to provide equipment such as an exposure device. In addition, since no expensive high-precision exposure mask is used, a cathode-ray tube with a phosphor screen of an extremely fine stripe pattern can be obtained at a low manufacturing cost.
[0018] Since the thickness of the phosphor layers can be easily controlled, the widths of the phosphor stripes and non-luminous stripes can be easily controlled to lie within a range from a fine width of about 10 µm to a comparatively thick width.
[0019] In addition, variations in stripe width are reduced, so a color cathode-ray tube with a color phosphor screen having a good linearity can be obtained.
[0020] Therefore, since the present invention can be used to efficiently construct a color phosphor panel having an extremely high precision and a high resolution, and can also form very fine RGB stripes, it can be applied to the construction of compact CRTs that is difficult with conventional techniques, and it thus has great industrial significance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 is a partially cutaway perspective view of an embodiment of the color cathode-ray tube of the present invention; Figure 2 is a detail of the state of a phosphor layer coated onto a film of an embodiment of the present invention; Figure 3 (A) is a detail of the state of alternately stacked phosphor layers and carbon layers according to one embodiment of the present invention; Figure 3 (B) is a detail of the state of repeatedly stacked phosphor-coated films according to one embodiment of the present invention; Figure 4 is a perspective view of a state in which a slice is being cut from a laminate; Figure 5 is a plane view of a state in which a slice is provided on a panel; Figure 6 is a plane view showing a color phosphor layer obtained by burning a panel; Figure 7 is a plane view of a state in which black stripes are formed on a panel; and Figure 8 is a cross-section through a slice pasted onto a panel on which black stripes are formed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The color cathode-ray tube of the present invention comprises at least a front screen panel, a funnel, and an electron gun. A phosphor layer that is used as a structural component thereof is formed as a thin slice through a laminate built up of alternate phosphor layers and non-luminous layers that is burned and arranged on the panel.
[0023] A partially cutaway perspective view of one embodiment of the color cathode-ray tube of the present invention is shown in Figure 1.
[0024] This embodiment comprises a front screen panel 5, a funnel 8, an electron gun 9, and a striped phosphor layer B applied to the surface of the front screen panel 5 on the electron gun 9 side. In addition, the phosphor layer B is covered by a metal back layer 6 formed by aluminum vapor deposition, and an index phosphor layer 7 is formed on this metal back layer 6.
[0025] The striped phosphor layer B of this embodiment comprises a repeating pattern of red phosphor layers 2, green phosphor layers 3, and blue phosphor layers 4, with non-luminous layers therebetween. In this case, the funnel 8 and the panel 5 are connected together by a frit seal 10, and an index signal read-out window 11 is provided in the cone part of the funnel.
[0026] The following gives a detailed description of the phosphor layer of the present invention, in other words, a description of how a laminate is formed and then the laminate is sliced and burned to form a burned slice.
[0027] In a first mode of the method of manufacturing the laminate, the method is such that red, green, and blue phosphor layers and carbon layers, each respectively formed of a composite of a red, green, or blue phosphor or carbon dispersed uniformly in a burnable organic binder, are stacked in a repeating pattern with carbon layers interposed between adjacent colored phosphor layers, to form a laminate of a specific thickness.
[0028] To be specific concerning the multilayering method of stacking layers of phosphors and carbon, the organic solvent diluent of the organic binder in which the phosphor is dispersed can be applied by a coating method using a roller-coater or by a screen-printing method, the organic solvent can be removed by drying, and the above process can be repeated on top of the dried layer.
[0029] The phosphors used in the manufacture of the phosphor layer can be commercially available products, but, in order to obtain an extremely fine stripe pattern, phosphors of a fine particle size are preferable. Specific examples of these phosphors include Y₂O₂S:Eu for red, (ZnCd)S:Cu, Al for green, and ZnS:Ag for blue, all of a particle size of about 3 to 10 µm.
[0030] The organic binder in which the phosphors are dispersed is not specifically limited, so long as it is a resin with excellent burning properties, the phosphors and carbon can be uniformly dispersed therein, and it can layers of a uniform thickness can be formed. Calcination residues are not preferable because they can cause the generation of black spots during the manufacture of the CRT, and can greatly shorten the life of the CRT.
[0031] Specific examples of the organic binder include cellulose resins, vinyl alcohols, and (meth)-acrylic resins, but (meth)-acrylic resins are preferable from the calcination property point of view.
[0032] In the same way as with the phosphors described above, the carbon can be a commercially available product, but, in order to obtain an extremely fine stripe pattern, carbon of a fine particle size is preferable. A specific example of the carbon is highly pure graphite, used in a particle size of about 3 to 10 µm.
[0033] An actual example of the method of the first mode of the manufacture of the laminate is to screen-print each layer of phosphor to a thickness of 20 µm, and each carbon layer to a thickness of 10 µm, then repeat coating and drying steps to obtain a laminate.
[0034] A part of a laminate obtained by the above mode is shown in Figure 3 (A). This laminate A is a stack of layers formed in the repeated sequence of a red phosphor layer 2, a carbon layer (non-luminous layer 1), a green phosphor layer 3, a carbon layer (non-luminous layer 1), a blue phosphor layer 4, and a carbon layer (non-luminous layer 1).
[0035] The laminate is then sliced through the thickness direction thereof to a thickness of 0.02 mm by some means such as a microtome or a high-precision band-saw.
[0036] In accordance with the present invention, approximately 10 to 60 µm is normally used as the thickness of each phosphor layer.
[0037] Figure 4 shows a state in which the laminate A is being sliced by a microtome through the thickness direction thereof to obtain a slice thereof.
[0038] The thus-obtained phosphor slice has 220 triplets, where 1 triplet is defined as a group of three phosphor lines.
[0039] In a second mode of manufacture of the laminate, composites of red, green, and blue phosphors dispersed uniformly in a burnable organic binder are coated onto film, these composites are dried to obtain films coated with each of the red, green, and blue phosphors, and the phosphor-coated films are stacked in a repeating sequence to obtain a laminate of a specific thickness.
[0040] To be specific concerning the method of stacking layers of phosphor-coated film, the composite of the organic binder in which the phosphor is dispersed can applied to the film by a coating method using a roller-coater or by a screen-printing method, the organic solvent can be removed by drying, and the above process can be repeated.
[0042] A film with good calcination properties, such as a polyvinyl alcohol or acrylic film, is preferable as the film used in this mode of the present invention; in particular, an acrylic film is preferable because of its good balance between calcination properties and flexibility. The film thickness can be determined by the desired layer thickness.
[0043] If a plastic type of film is used, a composite in which carbon or graphite is uniformly dispersed in a resin can be used.
[0044] A specific example of the method of the second mode of the manufacture of the laminate is to screen-print each layer of phosphor to a thickness of 20 µm onto 20-µm thick film, then repeat coating and drying steps to obtain a laminate.
[0045] A part of a laminate obtained by the above mode is shown in Figure 3 (B). This laminate A is a stack of layers formed in the repeated sequence of a red phosphor layer 2, a film layer (non-luminous layer 1), a green phosphor layer 3, a film layer (non-luminous layer 1), a blue phosphor layer 4, and a film layer (non-luminous layer 1).
[0046] In the manufacture of the phosphor layer, the laminate is then thinly sliced through the thickness direction thereof. In this case, the slicing means could be, for example, a microtome or an extremely fine band-saw.
[0047] Normally about 10 to 60 µm is used as the thickness of the phosphor layers, but this can be varied as required. In the above example of the second mode, the laminate is sliced to a thickness of 20 µm.
[0048] Figure 4 shows the state in which the laminate A is being sliced by a microtome through the thickness direction thereof to obtain a slice thereof.
[0049] The thus-obtained phosphor slice has 220 triplets, where 1 triplet is defined as a group of three phosphors.
[0050] The thus-obtained phosphor film is either affixed or pressure-bonded to a front screen panel of a color cathode-ray tube.
[0051] One method of affixing the phosphor film to the front screen panel could be such that a water-soluble adhesive, for example water glass or polyvinyl alcohol, is coated onto the front screen panel, the phosphor layer is affixed thereto, and the layer is dried and fixed. Alternatively, one method of pressure-bonding the phosphor film could be such that, for example, a rubber roller or the like is used to press the phosphor film onto a glass baseplate in such a manner that no bubbles remain between the phosphor film and the baseplate, to fix the phosphor layer to the baseplate.
[0052] Figure 5 shows a slice formed of a stripe pattern of a repeated sequence of a red phosphor layer 2, a film (non-luminous layer 1), a green phosphor layer 3, a film (non-luminous layer 1), a blue phosphor layer 4, and a film (non-luminous layer 1) on a panel 5.
[0054] Figure 6 is a plane view of one example of a color phosphor layer provided by a phosphor layer B comprising stripes of red phosphor 2, green phosphor 3, and blue phosphor 4 on a front screen panel 5 of a color cathode-ray tube.
[0055] In accordance with the present invention, the interposing of non-luminous layers between layers of differently colored phosphors is intended to prevent color mixing at the boundaries between red, green, and blue, ensure separation of each color, and improve contrast in the image generated on the screen.
[0056] To prevent deterioration of the contrast in the image generated on the screen, black stripe layers could be added to the phosphor screen in addition to providing non-luminous layers as described above.
[0057] The method used to form these black stripe layers is not specifically limited--any known method could be used. For example, black stripe layers can be formed by a vapor deposition method by which a non-luminous material with a low light-transmissivity, such as aluminum, is applied to a baseplate using a striped metal mask of a specific width. The preferred material in accordance with the present invention is aluminum. Carbon or graphite could also be used, but individual particles of a substance such as carbon could condense, deteriorating the linearity of the stripes.
[0058] If aluminum is the vapor deposition metal used for this example, the stripe width is 20 µm and the thickness of the stripe layer is 0.05 to 0.06 µm.
[0060] One method of stacking phosphor screen and black stripe layers could be such that, for example, black stripe layers are formed on the front screen panel, then a phosphor layer is superimposed thereon in such a manner that the black stripes coincide with either boundary portions between the red, green, and blue phosphor layers or non-luminous layers.
[0061] Figure 8 shows the state of a phosphor layer B superimposed onto the panel 5 in such a manner that non-luminous layers 1 and black stripe layers 12 coincide.
[0062] The thus-obtained panel is used in the assembly shown in Figure 1 to form a color cathode-ray tube having a resolution of 220 TV lines with a panel size of 35 mm × 25 mm.
INDUSTRIAL APPLICABILITY OF THE PRESENT INVENTION
1. A color cathode-ray tube comprising at least a front screen panel, a funnel, and an
electron gun;
wherein a phosphor film is provided on said panel, said phosphor layer being comprised of a laminate of a repeated sequence of red phosphor layers, green phosphor layers, blue phosphor layers, and non-luminous layers, and said laminate being sliced in the thickness direction thereof to form a thin layer which is burned; and
wherein said laminate has a construction such that non-luminous layers are interposed between adjacent phosphor layers.
wherein a phosphor film is provided on said panel, said phosphor layer being comprised of a laminate of a repeated sequence of red phosphor layers, green phosphor layers, blue phosphor layers, and non-luminous layers, and said laminate being sliced in the thickness direction thereof to form a thin layer which is burned; and
wherein said laminate has a construction such that non-luminous layers are interposed between adjacent phosphor layers.
2. A color cathode-ray tube according to claim 1, wherein each of said layers in said
laminate is a red, green, or blue phosphor layer or a carbon layer that is a composite
of red, green, or blue phosphor or carbon, respectively, uniformly dispersed in a
burnable organic binder, and said laminate is composed of a repeating sequence of
said layers stacked to a specific thickness, with carbon layers interposed between
adjacent phosphor layers.
3. A color cathode-ray tube according to claim 1, wherein each of said layers in said
laminate is a composite of red, green, or blue phosphor uniformly dispersed in a burnable
organic binder, said composite being coated onto and dried on a film to obtain red,
green, or blue phosphor-coated film, and said phosphor-coated films being stacked
in a repeating sequence to a specific thickness.
4. A color cathode-ray tube according to claim 1, wherein a black stripe layer is arranged
between said burned slice of said laminate and said front screen panel, said black
stripe layer being positioned to correspond to said non-luminous layers.