GB1588903A

GB1588903A - Method of manufacturing a phosphor screen for a colour television tube

Info

Publication number: GB1588903A
Application number: GB5403677A
Authority: GB
Original assignee: Toppan Printing Co Ltd
Current assignee: Toppan Inc
Priority date: 1976-12-27
Filing date: 1977-12-28
Publication date: 1981-04-29
Also published as: NL182761B; DE2758228A1; FR2375713B1; NL7714459A; FR2375713A1; DE2758228C2; NL182761C

Description

(54) METHOD OF MANUFACTURING A PHOSPHOR SCREEN FOR A COLOUR TELEVISION TUBE (71) We, TOPPAN PRINTING CO., LTD., a Japanese corporation, of 5 l-chome, Taito, Taito-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:- This invention is concerned with the manufacture of phosphor screens for colour television tubes.

Colour cathode ray tubes, which are widely used in colour television receiving sets, are designed to produce a colour picture upon selective irradiation by electron beams of a patterned phosphor layer in the form of dots, matrix or stripes on the inner wall of a face plate of a Braun tube. An ordinary colour television receiving set is provided with a phosphor layer capable of emitting light of the three primary colours of red, green and blue.

Hitherto, phosphor screens of colour television tubes have been made by photographic light exposure, in which the glass face plate to which a phosphor screen is to be deposited is first surface treated, after which a prescribed pattern is produced by imagewise exposure to light of a photosensitive film comprising polyvinyl alcohol treated with ammonium bichromate, scattering black lightabsorbing powder such as graphite on the photosensitive film and producing a light absorbing layer by selective photoetching. For example, the conventional slurry process comprises the complicated steps of preparing a slurry by dispersing a phosphor powder in a solution sensitized by.polyvinyl alcohol bichromate; applying the slurry on the inner wall of a face plate of a colour television tube, followed by drying, light exposure, development and again drying; and repeating these steps three times for red-, green- and blue-emitting phosphors. The slurry process involves many steps and is of the wet type, presenting difficulties in respect of stability, cost and disposal of waste liquids. A simpler process of manufacturing a phosphor screen for a colour television tube is therefore desirable. One proposal is a printing method in which ink is transferred to the face plate of a colour television tube from an engraved intaglio block. However, this method requires a high precision pattern in order to produce phosphor layers emitting red, green or blue light. Moreover, the ink-receiving surface is not a sheet of paper (as in ordinary printing), but often the face plate of the Braun tube, which is a plate of hard glass, and the face plate generally has a curved, concave surface. Such a glass face plate can not receive ink well.

Furthermore, the respective phosphor layers which have to emit sufficient luminance must be quite thick, for example, more than 15 microns thick, because the particle size distribution of colour television phosphors is concentrated at the range of 10 to 15 microns. Even a light-absorbing layer should have a thickness greater than 5 microns. If such layers are applied by printing, the printing ink should contain a far larger amount of phosphor particles (corresponding to pigments in the case of ordinary printing ink) or a ligh-absorbing material than customary printing ink. However, such a printing ink lacks fluidity and results in an irregular impression.

A further problem occurs when the phosphor layer contains a large amount of resin immediately after printing, then the excess resin remains even after subsequent baking, which tends to soil a Braun tube when it is put into operation.

In addition, gases evolved during baking (such gases being formed by decomposition of the resin) give rise to cracks or swells in a metal back layer (a light reflection layer) deposited on the phosphor layer, thus producing a phosphor layer of unacceptable quality.

From the above considerations, it can be seen that it is necessary to use an ink of low resin content, but such inks are difficult to apply by ordinary printing methods.

It has also been proposed to apply a phosphor-containing ink by a screen printing method; however, this necessitates ink being applied to the face plate through a mesh, which results in a printed pattern having irregular edges. Where a phosphor layer is formed of fine lines as narrow as 0.1 to 0.3 mm, the screen method has the drawback that the printed pattern is produced in broken lines. In the screen printing method, the mesh is forcefully rubbed by, for example, a squeegee which tends to stretch the mesh (whether it is made of synthetic fibres or stainless steel) and deform the phosphor layer pattern; the mesh also has iimited resistance to printing pressure. Therefore, the screen method is unsuitable for the multicolour printing of two or three colours or for the production of a phosphor layer pattern with high resolution.

The so-called "octopus head" printing method has been proposed for printing a phosphor layer on the curved surface of the face plate. However, the "octopus head" press which transfers ink held in an intermediate position to the face plate is depressed by horizontally applied pressure thus causing ink to be transferred to the face plate with an uneven pressure and consequent failure to attain accurate and uniform transfer of the ink pattern over the whole area required. Further, the "octopus head" offset member is made of relatively soft material with a large thickness. Where, therefore, ink has to be applied over a large area, then the resultant ink pattern is deformed and the resolution of the pattern is impaired.

We have now devised an improved method of manufacturing a phosphor screen for a colour television tube, which method is simpler than the prior art photographic or printing methods and in which a phosphor pattern can be deformed with high resolution.

The method according to the invention comprises transferring an ink pattern from an intaglio surface, the ink-receiving portions of which are at least 10 microns deep, to a cylindrical offset roller having thereon a blanket of thickness 0.2 to 30 mm., the blanket having a durometer hardness (according to ASTM D-2240-75) not exceeding 52", and transferring the ink pattern from the offset roller to a face plate of a colour television tube, to a material which is subsequently attached to the inner surface of such a face plate, or to a transfer member from which the ink pattern is then transferred to such a face plate.

According to the present invention, the offset roller has a soft blanket of durometer hardness, measured as indicated above, of not more than 52". This durometer hardness, measured by an A or A2 type durometer using a test-piece more than 12 mm. thick, corresponds to that measured in International rubber hardness degrees (IRHD) based on the international specification (ISO).

The corresponding Japanese rubber hardness measurement, also measured with a test-piece more than 12 mm. thick, is JIS K6301, 1975. In This Japanese measurement, however, the numerical value assigned is two degrees lower than that obtained by the ASTM method. Thus a durometer hardness of 52" according to the ASTM method corresponds to a durometer hardness of 50 according to the JIS method. Preferred materials having the requisite durometer hardness are silicone rubbers and fluoroplasts.

The intaglio surface used in the method according to the invention has, as mentioned above, ink-receiving portions (hereinafter referred to as ink cells) at least 10 microns deep, for example, more than 30 microns deep. These ink cells may be in the form of dots, stripes or a matrix, all of which are suitable for the production of phosphor screen patterns for colour television tubes.

The phosphor screen is generally manufactured according to the invention by first forming light-absorbing layers in the selected portions of the phosphor screen, and then transferring red-, green- and blue-emitting phosphors in those portions of the phosphor screen which are not provided with light-absorbing layers, in the order mentioned in accurate positional alignment. The method according to the invention is analogous to ordinary multicolour printing. A metal back layer (or back plate) may then be spread over the whole of the phosphor screen by vacuum thermal deposition. Where a beam index type colour picture tube is used instead of the shadow mask type, a beam index layer is further deposited on the metal back layer. This beam index layer can be applied by the method of this invention as can the light-absorbing layers and phosphor layers.

In the method according to the invention, when the light-absorbing layer, the phosphor layer and the metal back plate are formed on a transfer member which is transferred to the face plate, the above layers are in the opposite order when on the transfer member, compared with the order of layers on the inner wall of the face plate after direct printing. Of course, the order of layers is reversed on transfer from the transfer member to the face plate. In both the direct printing method and the transfer printing method, excess resin is preferably removed from the face plate, after baking.

Preferred features of the present invention will be apparent from the following description, in which reference is made to the accompanying drawings, in which: Figure 1 is an oblique diagrammatic view of an example of a method of manufacturing a phosphor screen according to the present invention; Figure 2 is an enlarged sectional view of a phosphor screen of a colour television tube prepared by a prior art method; Figure 3 is an enlarged sectional view of a phosphor screen of a colour television tube manufactured by the method of the invention; Figure 4 is an enlarged sectional view of the condition of a phosphor screen of a colour television tube immediately after manufacture by the method of the invention; and Figure 5 is an enlarged sectional view of the condition of a phosphor screen of a colour television tube a considerable time after manufacture.

Referring to Figure 1, an intaglio block 1 having engraved ink cells which are formed with high precision by the photoetching process of gravure block-forming process is used (in Figure 1 are shown, in enlarged scale, striped ink cells).

The ink cells of the intaglio block 1 are filled with ink by first spreading excess ink 2 over the surface of the intaglio block 1 and then scraping off surplus ink 2 using a doctor 3. A cylindrical offset roller 4 comprising a cylindrical body 5 coated with a soft blanket 6 having a rubber hardness smaller than 50 as measured by the JIS A spring type hardness tester (according to JIS K 6301, 1975). The provision of this soft blanket 6 on the peripheral surface of the offset roller 4 enables sand-like coarse-grained ink containing a large amount of powder to be taken up on the offset roller 4 without decreasing the thickness of the deposited ink. Consequently, an ink pattern can be transferred, without loss of this thickness, to a receiving surface 7 (even if the latter is made of hard material like glass as when the receiving surface is the face plate of a colour television tube). The ink pattern of the intaglio block is transferred first to offset roller 4, to form a pattern 9 which is dried by drier 8, and thence to the receiving surface 7.

If the blanket 6 were to have a hardness of JIS K 6301, 1975 of greater than 50 (that is, if the method of manufacturing a phosphor screen using such an offset member is outside the scope of the present invention), then the resulting transferred ink pattern tends to be thinner, even if a thicker blanket were to be used.

As mentioned above, in the method according to the invention, the blanket 6 is between 0.2 mm. and 30 mm. thick. If the blanket 6 is greater than 30 mm. thick, then the resulting transferred ink pattern tends to be displaced even if the blanket has a hardness according to JIS K 6301, 1975 of 50 , while if the blanket is less than 0.2 mm. thick, the properties of the cylindrical body 5 may affect the thickness of the transferred ink pattern, even if the blanket has a hardness according to JIS K 6301, 1975 of less than 20 . The provision of the blanket 6 in the method according to the invention enables the ink pattern to be transferred without damage to the receiving surface 7, even if the latter surface has some irregularities.

In order to prevent ink accumulating on the offset roller during operation, the surface of the blanket is preferably of a silicone rubber or a fluoroplast as release material. This release material may be in the form of a coating on the blanket 6 or the blanket 6 itself may be formed of the release material. The use of such a release material enables not only thin films of ink but also, advantageously, thicker films of ink, for example 10 to 30 microns thick, to be transferred. Such a release material does not allow the ink pattern to be easily transferred from the intaglio block 1 to the offset roller 4, but it does allow the ink to be easily transferred from the offset roller 4 to the receiving surface 7, so that little ink remains on offset roller 4 after each cycle.

The transfer of the ink pattern 9 from the offset roller 4 to the receiving surface 7 is promoted in the embodiment shown in Figure 1 by drying the surface of the ink pattern 9 after each cycle of printing using a suitable drier 8, or forcefully drying the surface of the ink pattern 9 after a certain length of time, before transfer to the receiving surface 7. Such drying increases the viscosity of the ink 2 and slightly promotes its coagulation. The viscosity of the ink 2 increased by drying causes that plane of the ink 2 which faces the receiving surface 7 to be rendered more sticky than that plane of the ink 2 which faces the soft blanket 6 of the offset roller 4. The deepest portion of the ink pattern 9 on the soft blanket 6 of the offset roller 4 is least affected by drying and retains the original low viscosity of the ink 2.

Peeling of the ink pattern 9 starts at this deepest portion, enabling easy transfer of 60 to 80% of the ink 2 (80 to 100% when the blanket 6 is of release material) to the receiving surface 7.

The drying conditions used depend on the ink 2 used, the velocity of transfer and the materials of the offset roller 4 and receiving surface 7.

The drier 8 may be of the hot air, far infra-red, or infra-ied type or a combination thereof, or microwave type, while an ultraviolet ray hardenable ink can be quickly and efficiently dried by an ultra-violet ray source or electron irradiator. Many other types of drying can be achieved by combining the abovementioned driers with, for example moisture-setting ink or thermosetting ink.

This optional drying in the method according to the invention is very effective where a pattern phosphor screen is to be applied to the inner wall of a face plate of a colour picture tube with an appreciable thickness by means of ink containing more than 30% by volume of pigment or inorganic filler, or where it is necessary to provide a phosphor screen by transferring an ink pattern which is so soft as readily to crumble and has as large a thickness as 20 to 30 microns, because the ink pattern transferred to the receiving surface 7 is unlikely to be distorted during transfer from the transfer member to the receiving surface. Moreover, since the ink pattern 9 can be substantially fully transferred to the receiving surface 7, it is possible to omit cleaning the surface of the offset roller, as is generally required for the ordinary intaglio offset printing for each cycle of printing.

The ink used in the method according to the invention may have various degrees of viscosity. However, when the ink pattern contains a large amount of, for example, pigment (solid components other than resin and solvent) and is of coarsegrained sandy form, there may be difficulties in uniform transfer.

Where the cylindrical offset roller 4 is rotated more slowly than is usual, at a circumferential velocity of less than 100 mm/sec, (even an ordinary offset proof press has a transfer velocity higher than 200 mm/sec) in order to deposit the pattern form of such a coarse-grained ink 2 in a larger amount on the rubber blanket 6 of the offset roller 4 having a high ink-releasing property, then even such an ink pattern can be clearly transferred from the intaglio block I to the surface of the rubber blanket 6. However, soft ink admitting of doctoring which is used in gravure offset printing tends to take a raised form when deposited on the surface of a rubber blanket. When the ink pattern is transferred to the receiving surface, the ink pattern may be distorted. It is therefore preferred that the offset roller be rotated on the receiving surface 7 at a speed twice the above-mentioned speed of 100 mm/sec.

In more detail, the offset roller 4 is rotated over the inked intaglio block at a velocity v1, causing the ink paltern 9 to be deposited on the soft rubber blanket 6. The surface of the ink pattern 9 is dried by the drier 8, and the offset roller 4 is rotated at a velocity v2 (which is higher than v1) to transfer the ink pattern 9 to the receiving surface 7. Thus, the offset roller 4 is rotated slowly on the intaglio block 1, thereby causing a larger amount of ink 2 to be transferred from the engraved portions of the intaglio block 1 to the surface of the soft rubber blanket 6, and rotated more quickly on the receiving surface 7, so that the pattern 9 of the ink 2 is quickly transferred without distortion.

The circumferential velocity of the offset member when the ink is transferred from the intaglio block 1 to the offset roller 4 is preferably less than 150 mm/sec, more preferably less than 100 mm/sec. In any case, it is advised to select an appropriate transfer velocity depending on the particular ink used.

Where the ink pattern 9 takes the form of a stripe as in the embodiment illustrated in Figure 1, it has been discovered that when the intaglio block I, offset roller 4 and receiving surface 7 have such relative positions as ensure coincidence between the direction in which the stripe is to be formed on the receiving surface 7 and the direction in which the offset roller 4 is rotated, then the precision with which the ink pattern 9 can be transferred to the receiving surface 7 is considerably elevated. Coincidence in the above-mentioned directions most effectively restricts the bleeding and deformation of the ink pattern 9 in a direction perpendicular to that in which the stripe extends, thereby ensuring transfer with high precision.

As previously indicated, the method of this invention makes it possible to use even such inks as would be unsuitable for ordinary printing. Thus, the invention allows the use of an ink which contains, for example, more than 30% by volume (or 65% by weight) of solids, such as phosphor powder having a higher specific gravity than 4, or graphite. Since such dense ink has low fluidity and tends to plug meshes, the prior art screen printing method is unable to print a phosphor screen pattern with so high precision as is attainable by the method of this invention. According to the present invention (referring to the embodiment of Figure 1), the ink can be easily transferred to the receiving surface 7 within the deformation limit of rubber blanket 6, regardless of whether the receiving surface 7 is flat or slightly curved.

Where the receiving surface is of round cylindrical form, the ink pattern 9 can be transferred thereto by rotating the offset roller 4 along the curved peripheral surface of the receiving surface.

The ink pattern can be transferred by the method of this invention to a receiving surface of pliable paper, plastics material, hard rigid metal, or hard and brittle materials of low impact strength, such as glass, ceramics or porcelain.

When the receiving surface is not itself the face plate of a colour television tube (and some of the materials listed above are, of course, inherently unsuitable for this purpose), the receiving surface is a material (such as heat-resistant plastics or glass) which is subsequently attached to the inner surface of such a face plate, or a transfer member (such as paper) from which the ink is then transferred to such a face plate.

The structure of a prior art phosphor screen and a phosphor screen manufactured by the method according to the invention will now be described with reference to Figures 2 to 5 of the accompanying drawings.

Referring to Figure 2, there is shown a conventional colour television screen comprising a face plate 11 having thereon a layer 12 of red-, green- and blueemitting phosphors. A metal back plate 14 is provided by vacuum thermal deposition of a metal film having high reflectivity on layer 12. This metal back plate 14 has the very important effect of elevating by its reflecting property the luminance of light rays emitted from the phosphors and preventing the phosphors from being negatively charged by electron beams and burnt by ions.

Direct thermal deposition of the metal back plate 14 on the phosphor screen 12 would give rise to noticeable irregularities on the surface of the phosphor layer 12 (which would mean that metal back plate 14 would not have a mirror-like plane, with resultant loss of desired reflected luminance); a flat smooth resin intermediate layer 13 is therefore provided, the metal back plate 14 being thermal deposited on this intermediate resin layer 13.

Such intermediate resin layers 13 are generally thermally deposited by dripping, spraying, emulsion application or fluidization, all of which require advanced technique and present considerable difficulties in operation control leading to production of a high percentage of reject television receiving sets.

According to this invention, an ink is transferred to a face plate or to a material which is subsequently attached to the inner surface of a face plate; such an ink can contain, in addition to phosphor, as much resin as 25 to 85% by volume.

This enables a metal back plate to be directly thermally deposited on a phosphor screen, the metal back plate being prevented from penetrating the phosphor screen, and the surface of the phosphor screen is smooth due to a large content of resin, ensuring a satisfactory reflected luminance. However, a large content of resin in the phosphor screen has the drawback that in the subsequent baking process for evaporating organic ingredients from the resin, an overlying metal back plate tends to swell or be cracked by vapours evolved from the resin. We have shown that swells or cracks of the metal back plate take place in varying degrees according to the kind of the resin; thus, with respect to polyester resin or acrylic resin, a metal back plate is not generally subject to swells or cracks, even when the resin content of the phosphor screen is as high as 85% by volume (41% by weight in the case of a colour television phosphor screen).

The application of a metal back plate directly on the phosphor screen formed on the inner wall of the face plate, without the necessity of providing the intermediate resin layer, is shown in Figure 3, in which 11 represents the face plate, 15 the phosphor screen and 16 the back plate. Numeral 17 shows a light-absorbing layer, and numeral 18 shows a beam index pattern which emits ultraviolet-rays when irradiated by electron beams.

The phosphor screen 15 contains a larger proportion of phosphor than the ink, since the latter also contains evaporizable solvent. For this reason a UV-hardenable ink is preferred, such an ink being more adaptable for preparation of a phosphor screen.

As illustrated in Figure 4, a phosphor screen 19 comprising phosphors 21 and binder 20 manufactured by the method according to the invention has an uneven surface immediately after production. When it is desired to thermally deposit a metal back plate (such as a layer of aluminium) to the phosphor screen (as described above with reference to Figures 2 and 3), the transferred phosphor screen 19 (present on face plate 11) is preferably smoothened after being allowed to stand for a certain period. The resulting smoothened layer may be as illustrated in Figure 5. This procedure enables a mirror-like light-reflecting plane to be obtained.

The phosphor ink used in the method according to the invention preferably contains 15 to 95 (more preferably, 15 to 90) % by volume of a phosphor powder and, optionally, 7 to 25% by volume of a black (light-absorbing) powder.

The phosphor ink preferably contains 25 to 85% by volume of a resin, which is preferably ultraviolet-settable, such as a polyester or acrylic resin. The resin preferably comprises acryloyl or methacryloyl radicals in an amount of, for example, 0.04 to 1.50 moles per 100 g. of ink, more particularly 0.1 to 0.7 moles of such radicals, and optionally, at least one pdlyester (saturated or unsaturated, or an alkyd). Such a polyester may be, for example, a polycondensate of tere- or isophthalic acid and ethylene oxide, a polycondensate of polyhydric alcohol such as ethylene glycol and a saturated dibasic acid such as maleic anhydride, or, as an alkyd, a partly oil-denatured polycondensate of polyhydric alcohol such as pentaerythritol and a polybasic acid such as phthalic anhydride such a polyester being reacted with acrylic or methacrylic acid.

The phosphor ink preferably also contains a suitable amount of one or more of the following materials: (1) a slow-drying (non-volatile) solvent capable of preventing the ink film from being solidified while the phosphor screen is smoothed (as described above with reference to Figure 5), such as benzyl alcohol, octyl alcohol, or diethylene glycol phenyl methyl ether; (2) a surfactant, such as a precipitation promoter, (for example, dimethyl silicone oil, which causes phosphors having a high specific gravity (more than 4 in the case of colour television phosphor) to precipitate while uniformly dispersed in the phosphor ink, thereby forming a smooth-surfaced phosphor screen); and (3) a plasticizer, such as dibutyl phthalate or diethyl phthalate, which keeps the ink layer itself fluidized.

The phosphor powder contained in the ink may be of the same type as used conventionally in the photographic light exposure process. Generally, a red lightemitting phosphor is formed of a compound of an yttrium series metal, while a green or blue light-emitting phosphor is prepared from a zinc sulphide-type compounds. These phosphors, producing light rays having the three primary colours should be of the types, which, when made to emit light rays jointly, provide a white light. Where one or two of the three phosphors 21 happen to have an improportionately higher luminance than the pother, then it is preferred to add an inorganic material which has little effect on the light-emitting property of the phosphor powder but which obstructs the penetration of electron beams through the phosphor. Suitable such inorganic materials include calcium salts such as calcium carbonate and calcium sulphate; oxides such as silica, alumina and titanium white; barium salts such as barium sulphate and barium carbonate; and magnesium salts such as magnesium carbonate. Such an inorganic material is preferably added to the ink while the ink is prepared. The use of such a material enables the unduly high luminance of a given phosphor to be balanced with that of any other phosphor, thereby ensuring the easy adjustment of all the light ravs issued from the three phosphors to an apparent white colour.

In order that the present invention may be more fully understood, the following Examples are given by way of illustration only. In the Examples, the hardness values are as measured according to ASTM D--22400-75. As indicated above, these values are two degrees higher than the values obtained by the corresponding JIS method.

Example 1.

A light-absorbing film was formed on a face plate (flat) by gravure-offset printing according to the following procedure.

Ink composition: Weight % Volume % Graphite powder 30 16 Ultraviolet-ray setting varnish (see NOTE) 70 84 NOTE: Composition of ultraviolet-ray setting varnish: NK Ester A-TMM-3* 93 Benzophenone 5 Triethanolamine 3 *) NK Ester A-TMM-3 is an oligoester polyhydric acrylate prepolymer from Shin-Nakamura Kagaku Kogyo Co., Ltd., Japan which contains approximately 1.07% of methacryloyl group as compared with the total weight of vehicle.

With this ink, offset printing was carried out on a gravure-offset printing machine. On the gravure plate was formed a striped line pattern with recessed portions 30y deep and line width 150,u. The circumferential speed of the offset roller was 200 mm/sec both on the plate and on the printed material (face plate).

The following results were obtained with the following offset rollers:

Rubber layer Rubber hardness thick The gravure-offset printing performance of these cylindrical rollers are givenas follows:

F Stripe reproducibility after 100 Accuracy in Transferring Ink continuous cycles transferring cylinder transferability of transcription location A Good Good Good B Good Very good Good When the aforesaid ink was used with a conventional gravure-offset blanket (e.g., gravure-offset blanket from Kinyo-sha Co., Ltd., Japan -- rubber hardness: 620 to 720) in printing in accordance with the same printing method, the film thickness was 2 to 3,u, and the ink pattern had poor reproduction (it had some blots). According to this example, however, there was obtained a black stripe pattern very high in light-sheiding property whose reproducibility was stabilized during continuous operation especially on the roller B. Further, the accuracy in transferring location proved highly satisfactory as a whole, being free from such deformation as is characteristic of octopus head printing.

Example 2.

There was obtained a sharp picture subject to hardly any blots by setting the gravure plate with the longitudinal direction of the stripe pattern in alignment with the rotating direction of the roller according to the printing specifications of Example 1.

Example 3.

By using the roller B with the following circumferential speeds in the same manner as in Example 1, the results were given as follows:

Circumferential speed Stripe (mm /sec) Transferability reproducibility I (On plate) I (On printed I material) 80 1 200 Very good Good 200 g 200 Good Good Further, the resultant film thickness could attain 8,u and above with each transferring speed, while a light-shielding stripe pattern with satisfactory impression was obtained with varying transferring speed.

Example 4.

A hot blast at some 1500C was applied for 30 seconds by means of a hot-air drier to the graphite ink layer transferred on to the roller B at a reduced on-plate speed as in Example 3 immediately before transferring the layer on to a face plate.

Thereafter, when the roller was rotated with a proper printing pressure on the face plate, the ink film on the roller was transferred on to the face plate at nearly 100%, no portions of the in layer remaining on the cylinder. This complete cycle of printing and drying processes was continuously repeated approximately 200 times; 100% transference was reproduced on each occasion by adjusting the drying degree.

Example 5.

A green phosphor film was prepared by printing between the light-shielding stripes on a face plate with light-absorbing stripes formed thereon as prepared according to the method of Example 1, with the ink composition changed as follows: Ink composition: Volume % (Weight %) Zinc Sulfite Green Phospho Pigment P-22 (from Dai-Nippon Paint Co., Ltd., Japan) 35 (70) Ultraviolet-ray setting varnish (see NOTE) 65 (30) NOTE: Same as that of Example 1.

The plate used had stripe-shaped recesses 30,u deep deeper than the forming depth of the light-shielding graphite stripe picture.

In the printing-process, there was recognized a quality tendency similar to that with the graphite ink, while the ink film was relatively thick. Further, also according to the methods as described in Examples 3 and 4, there was noticed the same tendency; no ink remained on the roller and the thickness of the ink film on the face plate was 17,u or more. Transfer was made on to a face plate with a lightshielding stripe pattern already formed thereon, exhibiting satisfactory ink transferability and accuracy in transferring location.

Moreover, the spaces between the light-shielding stripes could be filled up with three-colour (red, green and blue) phosphor ink layers by repeating the aforesaid cycle of processes three times with the phosphor pigment replaced by blue and red phosphor pigments (P-22 from Dai-Nippon Paint Co., Ltd., Japan), with the same quantitative composition. When layer one colour on top of another, the surface layer of the previously printed ink film was irradiated for 20 seconds by means of an ultraviolet radiator for setting before the subsequent printing process.

Example 6.

When an aluminium film was formed to a thickness of 2,000A directly on a phosphor screen prepared according to the method of Example 5 under a pressure of 4 x 10-5 Torr by the vacuum-evaporation method at a film speed of 25 A/sec, and calcined at 450"C for an hour, the resin contained in the ink was turned into an incinerated gas without destroying the aluminium surface, thus producing a satisfactory phosphor screen.

The aluminium surface (metal-back) exhibited a moderate smoothness, requiring no suich intermediate film formation as is the case with the phosphor screens prepared by the photographic exposure method. The phosphor screen was white and bright on exposure to electron beams.

Example 7.

The phosphor film printed according to Example 5 was left for approximately 6 hours with every printing of a colour; when the film surface was rendered smooth, it was exposed to ultraviolet-rays, and ink was set for a subsequent phosphor-ink printing. At this point, there was noticed a distinct difference in gloss as compared with those films which were exposed to ultraviolet-rays immediately after printing.

When thus obtained phosphor screen was aluminium-evaporated and calcined. On exposure to a prescribed dose of electron beams, the brightness was improved by approximately 20% as compared with those screens which had not been left for 6 hours, and the whiteness degree varied a little.

Example 8.

3% of dibutyl phthalate (as compared with the total quantity) was added to the ink of the composition of Example 5, and a resultant phosphor screen was left for an hour after printing, aluminium-evaporated and burnt. On exposure to a prescribed dose of electron beams, the brightness was improved by approximately 20% as compared with the screens with no such addition.

Example 9.

When 6% of calcium carbonate (as compared with the total quantity) was added to the red phosphor ink of the composition of Example 5, the whiteness degree could be changed from the original reddish tone to a pale-bluish tone without constituting any hindrance to the subsequent processes including aluminium-evaporation and burning. Effective chromaticity adjustment was achieved without involving red-coloured turbidity (which might be expected to be caused by the calcium carbonate). Further, the variation in whiteness degree was very small, which ensured that the correct colour resulted.

Example 10.

Printing over a prescribed area was achieved by using as the offset roller a silicone-rubber-coated cylinder (with the same rubber composition as that of Example 1, the silicone rubber having a hardness of 3 and a thickness of 20 mm), the ink being applied to the inner surface of a cylindrical glass face plate.

WHAT WE CLAIM IS: 1. A method of manufacturing a phosphor screen for a colour television tube, which comprises transferring an ink pattern from an intaglio surface, the inkreceiving portions of which are at least 10 microns deep, to a cylindrical offset roller having thereon a blanket of thickness 0.2 to 30 mm., the blanket having a durometer hardness (according to ASTM D--22400-75) not exceeding 52", and transferring the ink pattern from the offset roller to a face plate of a colour television tube, to a material which is subsequently attached to the inner surface of such a face plate, or to a transfer member from which the ink pattern is then transferred to such a face plate.

2. A method according to claim 1, in which at least the surface of the blanket is of silicone rubber or a fluoroplast.

3. A method according to claim I or 2, in which the ink pattern is transferred to and from the offset roller with rotation of the latter, the circumferential velocity of the offset roller relative to the intaglio surface being lower than the circumferential velocity of the offset roller relative to said face plate, material or transfer member.

4. A method according to claim 3, in which the circumferential velocity relative to the intaglio surface is not more than 100 mm/second.

5. A method according to any of claims I to 4, in which the ink is part dried while on the offset member.

6. A method according to any of claims I to 5, in which the ink pattern is in the form of parallel stripes and the offset roller is rotated about an axis perpendicular to the stripes.

7. A method according to any of claims I to 6, in which the ink pattern is transferred from the offset roller to the face plate.

8. A method according to any of claims I to 6, in which the ink pattern is transferred from the offset roller to a screen glass which is subsequently attached to the inner surface of the face plate.

9. A method according to any of claims 1 to 6, in which the ink pattern is transferred from the offset roller to a heat-resistant plastics film which is subsequently attached to the inner surface of the face plate.

10. A method according to any of claims I to 6, in which the ink pattern is transferred from the offset roller to a paper transfer sheet from which the ink pattern is transferred to the inner surface of the face plate.

II. A method according to any of claims I to 10, in which the ink contains 15 to 90% by volume of a phosphor powder.

12. A method according to claim 11, in which the ink contains an inorganic, electron-beam-absorbing material which has substantially no effect on the luminous properties of said ink.

13. A method according to claim 11 or 12, in which the face to which the ink pattern is transferred has a light-absorbing pattern thereon.

14. A method according to any of claims I to 10, in which the ink contains 7 to 25% by volume of a black powder.

15. A method according to any of claims I to 14, in which the ink contains 25 to 85% by volume of a resin.

16. A method according to claim 15, in which the resin is a polyester or acrylic o;n

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 9. When 6% of calcium carbonate (as compared with the total quantity) was added to the red phosphor ink of the composition of Example 5, the whiteness degree could be changed from the original reddish tone to a pale-bluish tone without constituting any hindrance to the subsequent processes including aluminium-evaporation and burning. Effective chromaticity adjustment was achieved without involving red-coloured turbidity (which might be expected to be caused by the calcium carbonate). Further, the variation in whiteness degree was very small, which ensured that the correct colour resulted. Example 10. Printing over a prescribed area was achieved by using as the offset roller a silicone-rubber-coated cylinder (with the same rubber composition as that of Example 1, the silicone rubber having a hardness of 3 and a thickness of 20 mm), the ink being applied to the inner surface of a cylindrical glass face plate. WHAT WE CLAIM IS:

1. A method of manufacturing a phosphor screen for a colour television tube, which comprises transferring an ink pattern from an intaglio surface, the inkreceiving portions of which are at least 10 microns deep, to a cylindrical offset roller having thereon a blanket of thickness 0.2 to 30 mm., the blanket having a durometer hardness (according to ASTM D--22400-75) not exceeding 52", and transferring the ink pattern from the offset roller to a face plate of a colour television tube, to a material which is subsequently attached to the inner surface of such a face plate, or to a transfer member from which the ink pattern is then transferred to such a face plate.

17. A method according to claim 15 or 16, in which the resin is ultravioletsettable.

18. A method according to claim 17, in which the resin comprises acryloyl or methacryloyl radicals.

19. A method according to any of claims I to 18, in which the ink contains a non-volatile solvent, a plasticiser and/or a surface active agent.

20. A method according to claim 1, substantially as herein described in any of Examples 1 to 10.