GB2203284A - Cathode ray tubes - Google Patents

Abstract

A method of making a phosphor pattern on a panel (1) of a colour cathode ray tube comprises forming a light absorptive layer (2) of a predetermined pattern, coating the entire inner surface with a photosensitive resin, exposing with light to form a protective layer (3), forming a resist layer (4a) on portions of the protective layer (3) other than the portion to be occupied by the first colour (Figs 2D and 2E), coating a phosphor slurry (6) containing a photosensitive agent and a phosphor of the first colour, the photosensitive agent being non-removable by an inverting agent which removes the resist layer (4a), exposing from the outer surface of the panel (1), developing the exposed surface, and removing the resist layer (4a) on the other portions using the inverting agent to give a phosphor stripe (6a Fig 2H), and repeating the steps of forming the phosphor strips (7,8 Fig 2I) for at least one further colour. The resin and the agent may be polyvinyl alcohol- stilbazolium resin. <IMAGE>

Description

CATHODE RAY TUBES This invention relates to methods of making a phosphor pattern on a panel of a colour cathode ray tube, and to colour cathode ray tubes including a panel having a phosphor pattern made by such a method.

For reproducing an ultra fine definition picture on a colour cathode ray tube, it is necessary that the respective phosphor stripes or dots of ultra fine definition of the three primary colours be clearly separated on the phosphor screen by a black light absorptive matrix. If the separation is not perfect, any misregistration of electron beams results in marked deterioration of the picture quality.

The most usual method of making colour cathode ray tube panels is the so-called inner surface exposure method, in which a phosphor slurry comprising a pigment dispersed in a light reactive resin is coated onto a glass panel on which carbon stripes of a predetermined pattern are formed, and is then exposed to light through an optical mask. The non-cured portions are removed by development. These operations are sequentially repeated for the red, green and blue colours in the production of a stripe type colour phosphor surface.

We have also proposed a so-called outer surface exposure method in which the admixture of colours between adjoining stripes is prevented by using two kinds of photosensitive agent having differential inversion capabilities, as disclosed in Japanese laidopen patent application no 60/119055. In this method, the phosphor surface is prepared by coating and curing in a predetermined sequence, on the glass panel on which carbon stripes have been previously formed, a resist layer using a first sensitizer which can be inverted by aqueous hydrogen peroxide, and a phosphor slurry obtained by dispersing a phosphor dyestuff in a second photosensitizer which is not inverted by hydrogen peroxide.

In the inner surface exposure method, the phosphor stripes are printed through an optical mask, which presents a problem because of a half shadow. In addition, due to the problem of insufficient adhesion between the phosphor stripes and the inner surface of the glass panel, ir is difficult to form phssDhcr~ stripes ..25JiF:s Pfir!el; def n~d, clear edges.

In the outer surface ligrt exposure method, the above defect of the inner surface light exposure method has been eliminated, but one problem remains to be solved. In the outer surface light exposure method, one inversion is necessarily caused to occur when forming the phosphor stripes of each colour, so that three inversions are required to form stripes of the three colours. However, with the repetition of the inversion of the resist layer, that is, solution and removal, the carbon stripe containing the resist layer is eroded little by little, until it may peel off, so lowering the quality of the phosphor screen surface.

According to the present invention there is provided a method of making a phosphor pattern on a panel of a colour cathode ray tube comprises: forming a light absorptive layer of a predetermined pattern on the inner surface of said panel; coating the entire inner surface of said panel with a photosensitive resin; exposing said entire inner surface to light to form a protective layer; forming a phosphor strip of a first colour by: (a) forming a resist layer on portions of said protective layer other than the portion to be occupied by said first colour; (b) coating a phosphor slurry containing a photosensitive agent and a phosphor of said first colour, said photosensitive agent being non-removable by an inverting agent which removes said resist layer; (c) exposing the overall surface from the outer surface of saic panel; (d) developing the exposed surface; and (e) removing the resist layer on said other portions through the use of said inverting agent; and repeating the steps of forming said phosphor strip for at least one further colour.

When a protective film of a transparent light-curable resin which does not undergo depolymerization by aqueous hydrogen peroxide is previously provided for a glass panel on which carbon stripe are formed, these striped are completely isolated by the protective fil; from the resist ayer or phosphor stripes to be formed in the subsequent steps, so that there is no risk of peeling even afte.

repetition of the inversion steps. Also, the protective film is optically transparent and does not obstruct light irradiation to be performed in the subsequent step.

The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Figure 1 is a spectrum diagram showing the absorption and sensitivity of a polyvinyl alcohol-stilbazolium photosensitive resin as a material for a protective film; Figures 2A to 21 are sectional views on an enlarged scale showing a typical example of a method for the step-by-step preparation of a colour cathode ray tube screen using a method according to the present invention; Figure 2A shows the step of forming carbon stripes; Figure 2B shows the step of forming a protective film; Figure 2C shows the step of applying a polyvinyl alcohol-ammonium dichromate photosensitive liquid; Figure 2D shows the step of light exposure of the inner surface; Figure 2E shows the step of forming a PVA-ADC resist layer;; Figure 2F shows the step of applying a green phosphor slurry and the step of light exposure of the outer surface; Figure 2G shows a development step; Figure 2H shows the step of forming green phosphor stripes by inversion development; and Figure 21 shows the arrangement of green, red and blue phosphor stripes after their formation; Figures 3A to 3C are diagrams showing the reduction in luminance in the case of immersing the respective phosphors in aqueous hydrogen peroxide; Figure 3A shows the luminance characteristics of the green phosphors; Figure 3B shows the luminance characteristics of the blue phosphors; and Figure 3C shows the luminance characteristics of the red phosp!#:r#; Figures 4A and 4B are X-Y chromaticity diagrams showing the colour purity of phosphor stripes observed on the colour cathode ray tubes; Figure 4A shows the colour purity of the green phosphor stripes; and Figure 4B shows the colour purity of the blue phosphor stripes.

The first step in forming the phosphor surface of the colour cathode ray tube involves forming the carbon stripes. A photosensitizing liquid of polyvinyl alcohol (PVA) is coated and dried on the inner surface of a glass panel for a colour cathode ray tube.

Then, an ultraviolet exposure is performed using an apertured grill as an optical mask. The ultraviolet light source is precisely positioned at the deflection centre of each of the red, green and blue light sources, and the light exposure is repeated three times. Upon developing the panel, resist layers including numerous stripes are formed at the positions corresponding to the phosphor stripes of the respective colours. The overall surface of the panel is then coated with a carbon slurry and dried, after which the process of inversion is carried out whereby the carbon on the resist is peeled off along with the resist layer, thus forming a plurality of carbon stripes 2 about 1 m in thickness on a glass panel 1 as shown in Figure 2A.

The protective layer is then formed. The materials used for the protective layer should have properties such as good adhesion to the black matrix or the carbon stripes, adhesion to the glass panel, good wettability, and the capacity to be thinly and uniformly coated on the black matrix and the glass panel, optical transparency, sufficient film coating strength, and the capacity of not being dissolved in the inverting developing agent. Materials satisfying these requirements include polyvinylpyrrolidone-azide type photosensitive resins, diazotype photosensitive resins, and polyvinyl alcohol-stilbazolium type photosensitive resins, hereinafter referred to as PVA-SBQ photosensitive resins. The PVA-SBQ photosensitive resins are the most preferred in that they satisfy all of the above conditions.The structural formula of the PVA-SBQ photosensitive resin is expressed as follows:

This photosensitive resin is one in which the side chain of the stilbazolium group is bonded to the main chain of polyvinyl alcohol through an acetal structure. Since the side chain is a quaternary ammonium salt, the resin itself is sufficiently hydrophilic for practical purposes.

The PVA-SBQ photosensitive resin is prepared as an aqueous solution with a 1.5; concentration and is coated on the entire surface of the glass panel 1 on which the carbon stripes 2 have been formed.

A concentration of the PVA-SBQ photosensitive resin of 0.5 to 3% is sufficient. With a concentration lower than the stated range, the coating tends to be thin with uneven coating and peeling of the carbon stripes cannot be completely prevented. With a concentration higher than the above range, the coating tends to be so thick that light cross-linking tends to occur, while the coating film strength tends to be insufficient, so that the coating tends to be peeled off at the time of inversion.

The PVA-SBQ photosensitive resin is then polyrerizec by light irradiation. For this step, it is necessary to know the opto-chemical properties of the photosensitive resin. Figure 1 shows an absorption curve I for the PVA-SBQ photosensitive resin and a sensitivity curve II for the light polymerization. It can be seen from this figure that the PVA-SBQ photosensitive resin has an absorption maximum at 340 nm with the sensitivity being good from the ultraviolet range to the vicinity of 450 nm in the visible range. Thus, ultra-high voltage mercury lamps, ultraviolet fluorescent lamps or blue lamps safe to the eyes may be employed. The volume of light exposure should be not less than 50 mJ to assure sufficient coating film strength.With such light exposure, the PVA-SBQ photosensitive resin undergoes photopolymerization and cures to form a protective film 3 having a thickness of 0.2 to 1ssm as shown in Figure 2B.

Next, a photosensitive liquid 4 of polyvinyl alcohol containing a minor amount of ammonium dichromate, referred to as PVA-ADC, is coated and dried on the protective film 3 as shown in Figure 2C.

Then, as shown in Figure 2D, a light exposure is performed by the usual method, using an apertured grill 5 as an optical mask. When forming green phosphor stripes, for example, the positions corresponding to the red and blue stripes are covered with the apertured grill 5 and the exposure is made from the directions of R (red) and B (blue) in the drawing. The portions thus exposed to light are curved by photopolymerization to form a PVA-ADC resist layer 4a, while the unexposed portions are removed by washing with water to produce the structures shown in Figure 2E. The PVA-ADC resist layer 4a may be inverted (that is, dissolved and removed) by aqueous hydrogen peroxide.

Then, as shown in Figure 2F, the green phosphor slurry 6 in which the green phosphor is dispersed in the PVA-SBQ photosensitive resin is coated on the entire inner surface of the panel, as shown in Figure 2F and the total light exposure is performed from the outer surface of the panel.

The PVA-SBQ photosensitive resin is not inverted by aqueous hydrogen peroxide. When the panel is developed, the green phosphor slurry is removed, with the green phosphor cured portion 6b and the green phosphor strips 6a cured by the photopo3ymerizatior remaining, so that the structure shown in Figure 2G is now achieved. The green phosphor cured portion 6b also remains on the PVA-ADC resist layer 4a This is because the irradiated light reaches the PVA-ADC resist layer Lia, which is transparent, to cause photopolymerization.

The product in this state is immersed in aqueous hydrogen peroxide as the inverter liquid to effect inversion development whereby the PVA-ADC resist layer Lia is dissolved and removed while simultaneously, the green phosphor cured portion 6b formed on the resist layer 4a is also removed. As a result, only the green phosphor stripes 6a, 15 to 29#rn thick, are left, as shown in Figure 2H.

The steps shown in Figures 2C to 2H are similarly repeated for the remaining colours, whereby the red phosphor stripes 7 and the blue phosphor stripes 8 are ultimately removed as shown in Figure 21 to complete the phosphor screen surface.

In the present embodiment, no peeling of the carbon stripes is observed, and a good phosphor screen surface is obtained.

From the foregoing it will be seen that when the PVA-SBQ photosensitive resin is previously coated before formation of the phosphor stripes, peeling of the carbon stripes that presented problems in the earlier method may be effectively prevented, so that a colour cathode ray tube having high picture quality may be obtained.

Since the protective film and the phosphor stripes formed thereon are made of the same material, adhesiveness of the phosphor stripes to the panel is improved and a colour cathode ray tube having a highly reliable phosphor screen may be provided without substantially altering the conventional manufacturing process.

It should be noted that, in the aforementioned method, at least one inversion process with aqueous hydrogen peroxide must be carried out for forming a phosphor stripe of one colour, so that three inversion processes need to be carried out to form the three phosphor colour stripes. However, when the inversion, that is, the removal by dissolution of the resist layer is performed repeatedly, the phosphors in the phosphor stripes and, above all, the green and blue phosphors, are gradually eluted by the aqueous hydrogen peroxide, resulting in lowering of the colour purity or brilliance of the phosphor screen.

In view of this difficulty, the phosphor for the colour cathode ray tube may be coated' with an acid resistant film.

Any type of phosphor normally employed in a colour cathode ray tube may be employed, such as zinc sulphide, zinc sulphide cadmium, zinc sulphide selenide, zinc oxide, zinc silicate, gadlinium oxysulphide, lanthanum oxysulphide, yttrium aluminate, yttrium aluminate-gadlinium, strontium thiosulphate-gallium, yttrium oxysulphide or yttrium silicate, these being activated by metal elements such as copper, aluminium, gold, silver, manganese, arsenic, terbium, cerium or europium, depending on the colour desired. The best effect may be obtained with a phosphor of the zinc sulphide type.

The coating material employed for forming the coating film for the phosphor must be insoluble in the inverting -agents, such as aqueous hydrogen peroxide, and must show affinity to the phosphor while not obstructing the colouring effect on the phosphor, and should have sufficient film forming properties. These coating materials include acrylic resins (polymethylmethacrylate, polymethacrylate), acrylic monomers, polystyrene, polyvinyl acetate, polyvinyl alcohol, and a mixture of gelatine and gum arabic. The first named four materials are suitable for practical purposes, while the latter two, namely polyvinyl alcohol and the mixture of gelatine and gum arabic are slightly poorer in coating film strength although they have sufficient water resistance.

In the coating procedure, the phosphor is suspended in water and the suspension is mixed with an emulsion of the above coating material with water as the dispersion medium, after which the pH is adjusted to a predetermined value and the resulting phosphor is washed with water and dried.

The coated phosphor thus obtained may be coated with silicon dioxide to improve dispersibility in the photosensitive resin.

The above coating material, applied in the form of a watersoluble emulsion, forms a uniform coating on the phosphor surface.

Thus the phosphor and the inverting agent such as aqueous hydrogen peroxide are separated by the acid-resistant coating even during the inversion development for effectively preventing phosphor elusion and deterioration.

An example of a coated phosphor is hereinafter given.

A coating is first applied to the phosphor. 500 g of the phosphor were suspended in 11 of water and the resulting suspension was mixed with 1 to 15 ml of an anionic acrylic emulsion witn a concentration of 110%. A small amount of the pigment was added to adjust the chromaticity in accordance with various standards concerning the cathode ray tube. The amount of addition of green phosphor was 0.5 to 1 weight %, that for the blue phosphor was 1 to 1.5 weight % and that for the red phosphor was 0.05 to 0.1 weight %.

The above-described mixture was stirred for five to ten minutes at room temperature until a thorough dispersion was obtained. Then, 0.3 to 2 ml of a cationic acrylic emulsion with a 110% concentration was added to improve the adhesivity and the pH was adjusted to 11 to 7 using ammonia and hydrochloric acid. The coated phosphors were washed with water and dried after removal of the washing water by decantation. In this manner, an acid-resistant phosphor was obtained in which the pigment was retained on the surface and which was coated in its entirety by an acrylic resin.

In the present example, europium activated yttrium oxysulphide, copper activated zinc sulphide and aluminium activated zinc sulphide were used as a red, green and blue phosphors, respectively.

The above described acid-resistant phosphors were further coated with silicon dioxide to improve their coatability.

The acid-resistant phosphors for the respective colours were dispersed in the polyvinyl alcohol-stilbazolium type photosensitive resin to produce to produce a slurry which was coated on the glass panels for the cathode ray tube, dried and cured by irradiation with light. Only one half of the respective glass panels was immersed in aqueous hydrogen peroxide at a concentration of 15% and a temperature of 40 C, removed after a certain time, washed with water, and dried.

the entire panel surface was coated with aluminium by evaporation and irradiated with electron beams in vacuum and the luminance was measured. Figures 3A to 3C show the result of a comparison of the portions immersed and not immersed in aqueous hydrogen peroxide. In these figures, the immersion time in minutes in aqueous hydrogen peroxide was plotted on the abscissae, and the relative luminance (8: of the immersed portion relative to the luminance (100) of the portion not treated with aqueous hydrogen peroxide was plotted as the ordinate. The broken line indicates the luminance properties of the usual phosphor not having an acid-resistant coating, and the solid line indicates the luminance properties of a phosphor provided with the acid-resistant film.It is seen that while there is not any marked difference between the red phosphor having an acid-resistant film and that not having he film as shown in Figure 3C, there is a marked improvement in the luminance achieved with the green phosphor shown in Figure 3A and the blue phosphor shown in Figure 3B.

In order to check the effect of the acid-resistant coating on the colour purity for each colour, stripe type phosphor surfaces were prepared in accordance with the aforementioned procedure by using a phosphor provided with an acid-resistant coating and another not provided with the acid resistant coating.

The phosphor screen thus formed was incorporated into a cathode ray tube, and the chromaticity was measured with the single green and blue light raster in connected with green and blue phosphors that underwent considerable lowering in the luminance in the above described immersion tests in aqueous hydrogen peroxide. Figures 11A and 4B show the result of an X-Y chromaticity diagram. In these drawings, the portions surrounded by the solid line square represents the permissible range of colour purity under the European Broadcasting Union, while the mark 0 represents the chromaticity of the phosphor stripes provided with an acid-resistant coating or film, and the mark X represents the chromaticity of the phosphor stripes employing the usual phosphor not having the acid-resistant coating or film. It can be seen that colour purity was not lowered in the green phosphor stripes shown in Figure 11A and in the blue phosphor stripes shown in Figure 4B, but actually showed an improvement.

It will be seen from the foregoing that when the acid-resistant coating is applied to the phosphors used in the phosphor screen prepared by outer surface light exposure, elusion or deterioration of the phosphors by an inverting agent such as aqueous hydrogen peroxide is markedly lowered, so preventing colour admixture between the adjacent colour stripes, and preventing lowering in luminance with improvement in colour purity.

Claims (7)

1. A method of making a phosphor pattern on a panel of a colour cathode ray tube comprises: forming a light absorptive layer of a predetermined pattern on the inner surface of said panel; coating the entire inner surface of said panel with a photosensitive resin; exposing said entire inner surface to light to form a protective layer; forming a phosphor strip of a first colour by: (a) forming a resist layer on portions of said protective layer other than the portion to be occupied by said first colour; (b) coating a phosphor slurry containing a photosensitive agent and a phosphor of said first colour, said photosensitive agent being non-removable by an inverting agent which removes said resist layer; (c) exposing the overall surface from the outer surface of said panel; (d) developing the exposed surface; and (e) removing the resist layer on said other portions through the use of said inverting agent; and repeating the steps of forming said phosphor strip for at least one further colour.

2. A method according to claim 1 wherein said photosensitive resin is a polyvinyl alcohol-stilbazolium resin in which a side chain of the stilbazolium group is bonded to a main chain of polyvinyl alcohol through an acetal structure.

3. A method according to claim 1 or claim 2 wherein the thickness of said protective layer is from 0.2 to fm.

4. A method according to claim 1, claim 2 or claim 3 wherein the surface of said phosphor is coated with an acid-resistant flit.

5. A method according to claim 4 wherein said acid-resistant film contains an acrylic resin.

6. A method according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

7. A cathode ray tube including a panel having a phosphor pattern made by a method according to any one of the preceding claims.