GB1600583A - Process for forming a powder image on a substrate - Google Patents

Description

(54) PROCESS FOR FORMING A POWDER IMAGE ON A SUBSTRATE (71) We, HITACHI LTD., a Corporation organised under the Laws of Japan, of 5-1, I-chome, Marunouchi, Chiyoda-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for forming a powder image on the face plate of a color picture tube. By this process it is possible to produce for example a phosphor screen of a color picture tube.

Previously, processes for forming powder images have generally involved using powder as a dispersion or mixture thereof, the powder being dispersed in a dispersion medium such as water. In such cases, a uniform dispersion has first been formed, the dispersion has then been stored in a uniform state and coated to form a powder image in complicated steps.

One example of these prior art processes will now be described with reference to Figures 1-A to 1-F of the accompanying drawings, which illustrates the formation of red, green and blue light-emitting phosphor layers on the inner surface of the face plate of a color picture tube.

As shown in Figure 1-A, the layer 2 is formed by coating the inner surface of the face plate 1 with a uniform mixture of a first color phosphor, for example, a green light-emitting phosphor and a photosensitive resin solution comprising a photosensitive resin, for example polyvinyl alcohol and ammonium bichromate and then drying the resulting coating. The layer 2 is then exposed to ultraviolet light through the apertures of a shadow mask. Here, the ultraviolet-light-irradiated areas correspond to an incident area of electron beams for exciting the phosphor, that is, the areas at which the phosphor is to be bound. The whole of the photosensitive resin layer at the exposed area becomes insoluble and the layer 2 is then washed with a solvent (usually water). Thus, as shown in Figure 1-B, only the layer 2' which has become insoluble by exposure to ultraviolet light remains on the inner surface of the face plate and the other layer is dissolved off.

Thereafter, a layer 3 of a mixture of a second color phosphor, for example, a blue lightemitting phosphor and a photosensitive resin is formed by the same operations as described above as shown in Figure 1-C. The layer 3 is then exposed to ultraviolet light and washed with water. Thus, as shown in Figure l-D, an insolubilized layer 3' remains on the inner surface of the face plate. Further, as shown in Figure l-E, a layer 4 of a mixture of a third color phosphor, that is, a red light-emitting phosphor and a photosensitive resin is formed by the same operations. The layer 4 is then exposed to ultraviolet light and washed with water. Thus, as shown in Figure 1-F, an insolubilized layer 4' remains on the inner surface of the face plate.

As is clear from the above explanation, the steps of producing the phosphor screen of a color picture tube are complicated. Further, many repetitions of wet coating, washing with water and drying are required, which give rise to various technical problems in each step and are disadvantageous from an economical point of view.

Alternatively, a simple process which comprises coating powder itself is known from Japanese Patent Laid-Open Publication No.

47-7,266 (1972). According to this process, a support for a phosphor screen is coated with a photosensitive lacquer layer, the surface of which is sticky before exposure but loses stickiness by exposure, the area of the photosensitive lacquer layer where the phosphor screen is to be formed is exposed, a light absorbing material powder which may be bound to the unexposed area is coated onto the layer, said exposed area is washed to remove the excess, unbound light-absorbing material, and finally phosphor screens which emit respectively different colored lights are provided.

However, the photosensitive lacquer layer used in this process loses stickiness at its once exposed area. Therefore, it is impossible to coat three phosphors onto the same photosensitive lacquer layer successively. Thus, this process is only a process for forming a light-absorbing material layer (a so-called black matrix), and it is not suitable for forming a phosphor screen.

The photosensitive lacquer used in this latter process, 'Kodak Mordant Cermitax' manufactured by Eastman Kodak Co., is known ('Kodak'is a Registered Trade Mark). However, this photosensitive lacquer has a low sensitivity and therefore, a long time is required for exposure which is disadvantageous from a commercial point of view. Further, the photosensitive lacquer is insoluble in water and is soluble only in organic solvents. However, the use of organic solvents on a commercial scale is disadvantageous since vapors of many organic solvents are toxic to human beings and are inflammable.

According to the present invention there is provided a process for forming a powder image on a face plate of a color picture tube which process comprises: (1) providing a layer of a photoresist on an inner surface of the color picture tube face plate, the photoresist being capable ofbecoming sticky on exposure to actinic radiation and development by washing with water.

(2) imagewise exposing the layer of photoresist to actinic radiation and developing the layer of photoresist by washing with water to remove the photoresist at areas other than the exposed area, (3) while the photoresist is still in a wet state following development, applying powder particles in a powdered form to the photoresist, and (4) developing the resulting powder-coated photoresist by washing with water to remove powder particles other than those adhering to the imagewise exposed area.

If desired, the coated photoresist in the wet state achieved at the end of the process of the invention may be completely dried after development.

As the photoresist, all known photoresists capable of becoming sticky on exposure to actinic radiation and development by washing with water may be used, though preferably water-soluble photoresists as illustrated in the Example are used.

As the powder to be bound onto the photoresist layer, examples are the phosphors and light-absorbing substances e.g. graphite.

The powder used in the present invention may have any particle size of a normal powder.

In general, powder having a particle size of 0.01 to 100,us, preferably 4 to 10,us, is used.

In order to produce a so-called stripe-type black matrix color picture tube, a matrix pattern having a plurality of light-absorbing parallel stripes can be formed by exposure to actinic radiation, in accordance with the present invention, through a shadow mask for a color picture tube so that light maybe thrown on the areas at which a light-absorbing layer is to be formed, followed by development and adhering powder of a light-absorbing substance to the areas of the photosensitive layer left after development.

In order to improve the coating property, various surface active agents may further be added. It is known to add a surface active agent to a composition in order to improve the coating property of the composition. All the surfaceactive agents known for such a purpose may be used in the present invention.

A further embodiment according to the present invention includes binding the powder firmly onto the photo resist layer by physical means. For example, in producing a phosphor screen for a color picture tube, the screen may be coated with an organic polymer film after forming the powder image. The object of applying such a film is to give metallic luster to an aluminum film as a light-reflecting film when that aluminum film is formed on the surface of the phosphor screen by vacuum evaporation.

It is desirable that the phosphor screen is mechanically firm in the step of applying this coating.

A method for making a coated powder layer mechanically firm is to keep the coated powder layer in a more humid atmosphere and then dry the layer. The most practical process for carrying out this process is to contact air saturated with moisture with the powder image for several seconds and then dry the layer.

The following Example illustrates the present invention. In this example, all parts and % are expressed by weight unless otherwise indicated.

EXAMPLE Referring to Figures 2-A to 2-E, this Example is explained below. Onto the inner surface of a face plate 1, is coated to a film thickness of 0.5 to 1.2 m a photosensitive agent consisting of: Polyvinyl alcohol (degree of polymerization 2400, degree of saponification 88%) 3% Ammonium bichromate 0.15% Ethylene glycol 0.85% Deionized water 96% A shadow mask (not shown) is installed onto the resulting coating and exposure for 40 seconds through this stripe-type shadow mask is carried out, with the position of a light source being shifted from the positions of green, blue and red electron guns by Bp P (1 +mm 6Q wherein P is the distance from a light source (not shown) to the shadow mask, Q is the distance from the shadow mask to the photosensitive layer and Bp is the lateral pitch of the stripe-type shadow mask. The distance P is 230 mm, the distance Q is 12.10 mm, and the lateral pitch Bp is 0.77 mm. The effective size of the light source is 2.2 mm f dnd light intensity is 0.3 mW/cm2 at the central part while the effective size of the light source is 1.2 mmf and light intensity is 0.24 mW/cm2 at the peripheral part. Thus, as is shown in Figure 2-B, after exposure the photosensitive layer 1 0a is formed. After exposure, the shadow mask is removed and development is carried out with warm deionized water at 35-40 OC for 120 seconds. Only the above-mentioned photosensitive layer 1 0a remains and after development the photosensitive layer 1 0a is as shown in Figure 2-C. When the inner surface of the face plate is in a wet state, graphite powder 9 having a particle size of 0.5 to 0.9 ,um as a light absorbing substance is sprayed and then dried.

After drying, development is again carried out with warm water at 35-40 OC for 60 seconds.

Thus, as is shown in Figure 2-E, graphite powder is bound onto only the exposed area, that is, the above-mentioned photosensitive layer 10a and a black stripe pattern 9' is formed. On the surface of the resulting black striped face plate I, a phosphor screen can be formed by the dusting method or slurry method to complete a black stripe-type phosphor screen.

As described above, the process for forming a phosphor screen according to the Example, a black stripe image of a light-absorbing substance can easily be formed by simple steps. Also, since a black stripe pattern is formed prior to the formation ofa phosphor screen, it is possible to achieve sharp edges to the phosphor screen pattern.

WHAT WE CLAIM IS: 1. A process for forming a powder image on a face plate of a color picture tube, which process comprises: ( I ) providing a layer of a photoresist on an inner surface of the color picture tube face plate, the photoresist being capable of becoming sticky on exposure to actinic radiation and development by washing with water, (2) imagewise exposing the layer of photoresist to actinic radiation and developing the layer of photoresist by washing with water to remove the photoresist at areas other than the exposed area (3) while the photoresist is still in a wet state following development, applying powder particles in a powdered form to the photoresist, and (4) developing the resulting powder-coated photo resist by washing with water to remove powder particles other than those adhering to the imagewise exposed area.

2. A process according to claim 1, wherein the exposure is carried out at the position at which a stripe-type black matrix of the color picture tube is to be formed, the powder is a light absorbing substance, and the powder image is a stripe-type black matrix pattern.

3. A process according to claim 2, wherein the color picture tube is adapted to have a plurality of electron guns, therein, and the photoresist layer is exposed to light through a stripe-type shadow mask, the light source being at a position shifted from the positions where the plurality of electron guns for the color picture tube are placed by Bp ' P (l+Q/P)mm 6Q wherein P is a distance from the light source to the shadow mask, Q is a distance from the shadow mask to the inner surface of the face plate, and Bp is a lateral pitch of the stripe-type shadow mask.

4. A process according to any one of the preceding claims wherein, after completion of formation of the powder image, the powder particles rebound firmly to the layer of photoresist by physical means.

5. A process according to claim 4, wherein the powder image is kept in a humid atmosphere and is then dried.

6. A process according to claim 1 substantially as described in the Example.

7. A process according to claim 1 substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

8. A substrate bearing a powder image when prepared by a process as claimed in claim 1, 4 or5.

9. A substrate bearing a powder image when prepared by a process as claimed in any one of claims 2, 3,6 or 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. effective size of the light source is 1.2 mmf and light intensity is 0.24 mW/cm2 at the peripheral part. Thus, as is shown in Figure 2-B, after exposure the photosensitive layer 1 0a is formed. After exposure, the shadow mask is removed and development is carried out with warm deionized water at 35-40 OC for 120 seconds. Only the above-mentioned photosensitive layer 1 0a remains and after development the photosensitive layer 1 0a is as shown in Figure 2-C. When the inner surface of the face plate is in a wet state, graphite powder 9 having a particle size of 0.5 to 0.9 ,um as a light absorbing substance is sprayed and then dried. After drying, development is again carried out with warm water at 35-40 OC for 60 seconds. Thus, as is shown in Figure 2-E, graphite powder is bound onto only the exposed area, that is, the above-mentioned photosensitive layer 10a and a black stripe pattern 9' is formed. On the surface of the resulting black striped face plate I, a phosphor screen can be formed by the dusting method or slurry method to complete a black stripe-type phosphor screen. As described above, the process for forming a phosphor screen according to the Example, a black stripe image of a light-absorbing substance can easily be formed by simple steps. Also, since a black stripe pattern is formed prior to the formation ofa phosphor screen, it is possible to achieve sharp edges to the phosphor screen pattern. WHAT WE CLAIM IS:

1. A process for forming a powder image on a face plate of a color picture tube, which process comprises: ( I ) providing a layer of a photoresist on an inner surface of the color picture tube face plate, the photoresist being capable of becoming sticky on exposure to actinic radiation and development by washing with water, (2) imagewise exposing the layer of photoresist to actinic radiation and developing the layer of photoresist by washing with water to remove the photoresist at areas other than the exposed area (3) while the photoresist is still in a wet state following development, applying powder particles in a powdered form to the photoresist, and (4) developing the resulting powder-coated photo resist by washing with water to remove powder particles other than those adhering to the imagewise exposed area.

2. A process according to claim 1, wherein the exposure is carried out at the position at which a stripe-type black matrix of the color picture tube is to be formed, the powder is a light absorbing substance, and the powder image is a stripe-type black matrix pattern.

3. A process according to claim 2, wherein the color picture tube is adapted to have a plurality of electron guns, therein, and the photoresist layer is exposed to light through a stripe-type shadow mask, the light source being at a position shifted from the positions where the plurality of electron guns for the color picture tube are placed by Bp ' P (l+Q/P)mm 6Q wherein P is a distance from the light source to the shadow mask, Q is a distance from the shadow mask to the inner surface of the face plate, and Bp is a lateral pitch of the stripe-type shadow mask.

4. A process according to any one of the preceding claims wherein, after completion of formation of the powder image, the powder particles rebound firmly to the layer of photoresist by physical means.

5. A process according to claim 4, wherein the powder image is kept in a humid atmosphere and is then dried.

6. A process according to claim 1 substantially as described in the Example.

7. A process according to claim 1 substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

8. A substrate bearing a powder image when prepared by a process as claimed in claim 1, 4 or5.

9. A substrate bearing a powder image when prepared by a process as claimed in any one of claims 2, 3,6 or 7.