US3727525A

US3727525A - Device for making phosphor screen for color picture tubes

Info

Publication number: US3727525A
Application number: US00132331A
Authority: US
Inventors: J Degawa; O Takeuchi
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-06-29
Filing date: 1971-04-08
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17
Also published as: NL163670C; FR2011793A1; GB1270709A; JPS4810585B1; DE1932173A1; US3593056A; NL6908937A; NL163670B

Abstract

A novel mercury-arc lamp which is partly shielded so as to provide a point source of light for use with a make for producing color phosphor screens of color television picture tubes is disclosed. Various embodiments disclose different means for shielding the ends of the mercury-arc lamp. In addition, an apparatus for cooling the mercury-arc lamp is disclosed.

Description

United States Patent 1191 Degawa et al.

DEVICE FOR MAKING PHOSPHOR SCREEN FOR COLOR PICTURE TUBES Inventors: Jiro Degawa, 6-301 Makuhari-cho, Chiba; Osamu Takeuchi, 14-8 Tama-daira 2, Tokyo, both of Japan Filed: Apr. 8, 1971 Appl. N0.: 132,331

Related US. Application Data Continuation-impart of Ser. No. 836,871, June 26,

1969, Pat. No. 3,593,056.

Foreign Application Priority Data June 29, 1968 Japan ..43/45376 US. Cl ..95/1 R, 240/47, 313/204,

355/71 Int. Cl. ..G03

UNITED STATES PATENTS McKee ..95/ l R 1 Apr. 17, 1973 2,321,178 6/1943 Boume et a1. ..313/204 x 3,21 1,067 10/1965 Kaplan ..95/1 R 2,839,673 6 1958 Wilcoxon ..240/47 x 1,808,826 6/1931 Teasdale ..313/220 x 2,080,914 5 1937 Hagen et al.... .,...313/220 x 2,774,013 12 1956 Willoughby 13/220 x 2,241,968 5 1941 Suits .313/220 x 3,536,946 10/1970 Kopelman et al.. .....313 220 x 3,545,838 12 1970 Levin et a] ,.95/1 R 3,587,417 6/1971 Balder ..95/1 R Primary ExaminerRichard L. Moses Attorney-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT 1 l Claiim, 10 Drawing Figures PATENTEU P 1 7 1915 3'. 727, 525

SHEET 1 BF 5 (PRIOR ART) FIG.I

I40 k n5 K 62 0 62 'K us\ I40 I25 I00 I00 I25 JIRO DEGAWA OSAMU TAKEUCHI B) Qt/2W- Affy's PATENTEDAPR 1 11913 3'. 727, 525

SHEET 2 OF 5 (PRIOR ART) FIG. 3

INVENTORS Jl R0 DEGAWA OSAMU TAK EUCHI PATENTED H975 3. 727, 525

SHEET ll [1F 5 FIG.8

lA/VE/VTORS JIRO DEGAWA OSAMU TAKEUCHI Aflys PATENTED 1 71973 3.727. 525

SHEET 5 [IF 5 //V VE N TORS JIRO DEGAWA OSAMU TAKEUCHI we; wwh Affy's CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of the following application: Ser. No. 836,871, filed June 26, i969 and entitled MERCURY-ARC LAMP, now U.S.Pat.No.3,593,056.

BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates in general to mercury-arc lamps and in particular to a mercury-arc lamp which may be utilized as a point source of radiation for making color picture tubes.

2. Description of the Prior Art It has been conventional in the prior art to make color picture tubes by utilizing a shadow mask placed adjacent the color phosphor screen and illuminating the phosphor screen through the mask with a light source so as to produce a color screen with a red, blue and green phosphorus precisely located.

Generally the deposition of the color phosphorus is precisely obtained by a method utilizing a shadow mask which is mounted on a glass panel of the picture tube and a phosphor slurry mixed with a photosensitive binder is coated on the interior surface of the panel and is optically printed by exposure to light beams which pass through the shadow mask. The phosphors are exposed by utilizing a point source of light which passes light energy through the shadow mask. In prior art devices the point light source is produced by focusing the light from a mercury-arc lamp with a quartz focusing lens. The focusing lens absorbs a large amount of light which passes through it and thus intensity of the light leaving the lens is substantially decreased. Also the quartz lens absorbs nearly all of the light having a wave length below 3,000 Angstroms. The photosensitive binder which is mixed in the phosphor slurry and which is to be exposed by the light from the light source is relatively insensitive to light having a wave length above 3,000 Angstroms and thus the prior art method requires that exposure occur for a long time to obtain the necessary exposure. These two factors, one that the quartz focusing lens absorbs most of the energy below 3,000 Angstroms, and two the phosphor slurry is less sensitive to light above 3,000 Angstroms result in long printing times and decrease in production of color television tubes.

SUMMARY OF THE INVENTION In the present invention a novel mercury-arc lamp is utilized as a point source by covering the ends of the lamp with a suitable impervious coating or by placing cylindrical shields around the lamp so that a point source of light is obtained, which does not require a focusing lens and resulting loss oflight energy absorbed by such lens in the prior art. A novel mercury-arc lamp is disclosed which is capable of being suitably shielded to form a point source. Also means for mounting the lamp so it may be liquid cooled are disclosed.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view illustrating method and apparatus for optically printing color phosphorus screens according to the prior art,

FIG. 2 is a schematic view illustrating the invention,

FIG. 3 is a cross-sectional view of a prior art mercury-arc lamp,

FIG. 4 is an enlarged cross-sectional view illustrating one example of a mercury-arc lamp employed in this invention,

FIGS. 5, 6 and 7 are graphs illustrating the degree of devitrification of tube envelopes and are utilized for explaining the mercury-arc lamp used in this invention,

FIG. 8 is a side plan view, partially in section, show ing a modified form of the invention,

FIG. 9 is a graph illustrating illumination curves obtainable with the device of this invention, and with a prior art device, and

FIG. 10 is a side view, partly in cross-section, of a modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an example ofa prior art device and method for making a phosphor screen of color television tubes. The glass panel P comprises the end of the completed television tube, and is to be coated with a plurality of different colored phosphors. A shadow mask E is placed adjacent the inner surface of the panel P and a light source S comprising a point light source L which might be, for example, a mercury-arc lamp passes light through a collimating lens CL which focuses the light. The collimating lens internally reflects the light from a light source and passes it from its point to the panel P through the mask E. A reflector M is placed behind the light source L.

The lens CL absorbs a large portion of the light energy emitted from the light source because the columnar portion of the focusing lens CL might be as long as to millimeters. The light transmission of quartz glass which is generally used for constructing the focusing lens CL is extremely low for light having wave lengths below 3,000 Angstroms. Thus, large portions of the light energy from the light source L is absorbed by the lens CL and is not effective in exposing the phosphor slurry through the shadow mask E. On the other hand, the photosensitive binder mixed in the phosphor slurry which is to be printed is generally most sensitive to light having wave lengths in the vicinity or below 3,000 Angstroms. Thus the focusing lens CL appreciably attenuates light frequency which is most efficient in exposing the photosensitive phosphor.

Also the light transmission factor through the shadow mask is non-uniform and decreases with the distance from the center of the mask because the light emitted from the light source shines obliquely on the shadow mask at the edges and thus a smaller amount of light energy impinges upon the photosensitive material at the edges of the panel P. Thus the intensity of the light applied to the panel must be stronger at the edges of the panel than at the central portion of the panel. However, light sources of the prior art type such as shown in FIG. 1 cause the illumination on the panel P to decrease rather abruptly toward the edges of the panel and it is normally necessary to utilize optical filters such as the filter F between the light source device S and the panel P which allows more light to hit the edges of the panel P than at the center of the panel to compensate for the above described phenomena. As a result of these factors,the printing efficiency is low and the time for exposure for printing may be 20 to 40 minutes. This results in slow production of color television tubes and requires dissipation of great power. Also the long time exposure causes the light to blur and makes it difficult to obtain a sharp pattern from the exposure.

Also since the angle of diffusion of the light from the tip of a focusing lens C is relatively small, this lens cannot be used for printing phosphor screen of wide angle picture tubes.

The present invention a bro gates these defects and provides a light source and method of producing color television tubes which eliminate the problems of the prior art.

FIG. 2 illustrates one example of the invention. A generally cylindrically shaped lamp housing LH supports the panel P of a tube envelope which has been coated on its inner surface with a suitable phosphor slurry which is to be exposed so as to produce the desired pattern of colored phosphors. A shadow mask E is mounted adjacent the panel P and receives light from a point source mercury-arc lamp ML which provides a point source of light with high radiation efficiency. The mercury lamp ML employed in this invention may have a luminous portion formed from an arc. The lamp. ML may have a diameter corresponding to the thickness ofthe panel P; however, it emits light as a point source because a shield member SH is formed about the mercury-arc lamp ML on either side of its center portion SL.

The mercury-arc lamp ML is mounted such that its center of its luminous portion is substantially at the position of the electron beam deflection center for the electron beam of the finished color tube on the central axis Z-Z' of the panel P. The longitudinal axis -0 of the mercury-arc lamp ML lies in a plane substantially parallel with the panel P and in the horizontal scanning direction H-H'.

The shield member SH on either end of the lamp ML is as close to the luminous portion as possible such that when the mercury-arc lamp ML is used from the front on the line Z-Z the size of the effective luminous portion seen through the slit SL will not vary with the viewers position due to parallax. The shield member SH may be formed by vapor deposition of metal coating of a light blocking paint directly on the outer wall of the mercury-arc lamp ML. Alternatively, a metal form may be deposited on the outer wall of the lamp. [t is also possible to cover the mercury lamp ML with a pair of tubular members adjacent the center light emitting slit SL. The width W of the slit SL in the direction of the 0-0 axis of the mercury-arc lamp is selected so that the slit limits the light directed toward the panel P from the mercury-arc lamp ML only in the direction of the axis 0-0 of the lamp. The slit does not limit the diameter of arc in the direction of the diameter of the lamp, thus the diameter of the luminous portion of the mercury-arc lamp ML does not vary due to parallax.

The shield member SH may be formed directly on the outer wall of the mercury-arc lamp ML by the following method. A carbon powder is mixed in a solution of aluminum phosphate and the mixture stirred. The mixture is coated onto the mercury-arc lamp at either side of the slit SL with a spray gun and is then dryed at 60 to C for 30 minutes. Then the coating is preheated by a burner to 800 C. for 3 minutes and is then heated up to 1,300C after which it is gradually cooled.

within the tube between the

electrodes

2A and 2B. The

inert gasses might be argon, xenon or the like, for example. It will be particularly noted that in prior art lamps the inside diameter of the tube 1 is small at the portion of the openings 4A and 4B adjacent the ends of the

electrodes

2A and 2B so as to prevent the mercury 3 from flowing out through these openings. The inner diameter of the tube 1 is substantially uniform between the ends of the

electrodes

2A and 2B. The diameter of the tube 1 is made small so as to render the luminous portion of the mercury-arc lamp linear and the plasma produced between the

electrodes

4A and 48 will have a small diameter. However, this causes devitrification of the tube 1 which results in a loss in the amount of light produced and also substantially shortens the service life of the mercury-arc lamp.

The devitrification of the tube 1 is caused by crystallization of the quartz glass and thermal decomposition of silicon dioxide into silicon and oxygen. The crystallization of the quartz glass occurs when it is heated or cooled to the vicinity of the transition point of the quartz glass. Once the devitrification of the tube 1 has started, it progresses rapidly and spreads. In some cases, heat distortion in the glass tube is introduced which decreases the pressure which the glass can withstand and explosions of the glass tube 1 result.

When the inner diameter of the tube 1 is small the inside surface of the tube 1 is very close to the electrodes 4A and 4B and this allows negative ions emanating from the electrodes to impinge upon the inner walls of the tube with great energy. The electrodes areheated to a temperature of 1,000" C or more and this intense heat causes the closely spaced glass tube to devitrify resulting in a short service life of the mercury-arc lamp. The creeping discharge is directed to the positive electrode but when the mercury-arc lamp is energized by an AC current, the current reverses in polarity and the creeping discharge is directed to the center between the

electrodes

2A and 2B of the tube 1. When the lamp is energized with AC current the creeping discharge is produced intensely and the loss of energy is as much as several times that which occurs when the tube is energized with a DC current. The effect is accumulative in that once the creeping discharge has occurred it forms a deposit which absorbs heat generated by the plasma and increases the devitrification of the tube and causes a local increase in the vapor pressure of the tube, thus lowering the luminous efficiency of the lamp and increasing the chance ofexplosion of the tube.

The present invention utilizes a special mercury-arc lamp which is free from the above defects, has long life, is high in brightness and is capable of producing an extremely fine and linear luminous portion.

FIG. 4 illustrates such a mercury-arc lamp which is designated generally by the numeral 10. A substantially cylindrical tube 11 constructed of quartz glass has a pair of rod-like electrodes 12A and 128 which partially extend into the tube from both ends in the longitudinal direction of the tube. The ends 12a and 12b of the

electrodes

12A and 12B are formed into the form of truncated cones with the base of the cones which forms the main portion of the electrodes having a diameter of about 0.5 millimeters and the truncated point of the electrodes are tapered to a diameter of about 0.3 millimeters. The distance between the ends of the electrodes 12A and 128 may be approximately millimeters.

The tube of this invention is formed such that the inner diameter of the tube 11 is within the range from 0.5 to 1.4 millimeters which is much smaller than that of convention mercury-arc lamps.

The inner walls of the tube adjacent the

end portions

120 and 12b of

electrodes

12A and 12B are formed with enlarged spherical cavities 14A and 148 as shown. The inner diameters of the cavities 14A and 148 may be selected such that the distance between the inner wall of the cavity and the end of the electrode is greater than the diameter of the tube in the central portion and may be about four times the diameter of the small end ofthe electrode as, for example, between 2 to 2.5 millimeters.

Portions of the tube adjacent the cavity 14A and 148 between the ends of the electrodes 12a and 12b are reduced in size and are filled with mercury 15. The ends of the tube are formed of quartz glass and a gradient glass seal material 11A is attached to the end of the tube. Tungsten glass 11B is attached to the gradient glass 11A at either end and the

electrodes

12A and 12B pass therethrough as shown.

FIGS. 5, 6 and 7 are graphs illustrating the degree of devitrification of the glass tube of mercury-arc lamps. These particular curves were obtained with the tube which had an outer diameter of 4 millimeters and an inner diameter of l millimeter. The spacing between the ends olthe electrodes 12A and 128 was l5 millimeters. The diameters of the electrodes 12A and 128 were 0.5 at the main body portion with the ends tapered in the form of truncated cones toO.3 mm.

The degree of devitrification is plotted on a scale where l0 indicates that the tube is opaque to such a degree that an electrode in each cavity cannot be seen from outside the tube.

In FIG. 5 the inner diameter dof the cavities 14A and 14B is used as a parameter. The curves illustrate the plot of the lighted time in hours versus devitrification degree of the cavities with various diameters d of the cavities 14A and 14B. A pressure P of cooling air fed to the lamp was 1.5 kg./cm For example, it is to be noted that the top curve which is labeled d 1.0 mm. has a devitrification degree which is much higher than those curves wherein the d diameter is equal to 1.5 mm, 2.0mm and 2.5 mm, respectively.

Thus the larger spherical cavities 14A and 14B result in substantial increase in the usable time ofthe lamps.

FIGS. 6 and 7 illustrate respectively the devitrification degree of the cavities 14A and 148 relative to their diameters d of the cavities 14A and 14B of tube 11 with the pressure P used as a parameter. Curve of FIG. 6 is for a lighted time of 1 hour and illustrates that the devitriftcation becomes substantially lower as the diameter of the cavities 14A and 14B is increased. However, when the inner diameter of the cavities becomes 2.5 mm. or more, the improvement in devitrification does not substantially increase with an increase of the distance D. An increase in the diameter of the cavities results in an increase in the pressure within the cavities resulting in loss of mechanical strength of the tube when D is equal to or less than 2 mm., the devitrification degree is large. Therefore, it is desirable that the cavities 14A and 148 have diameters in the range of between about 2 to 2.5 mm.

The diameter of the main portion of the tube 11 is selected to be in the range between 0.5 to 1.4 mm. because tubes having diameters of less than 0.5 mm. are low in efficiency, whereas tubes with diameters which exceed 2.5 mm. are undesirable because the diameter of the plasma is increased to the point where the lamp becomes an inadequate line source of light, and also the surface tension of the mercury 15 is exceeded which allows the mercury to flow from the mercury cavities when the lamp is mounted in a vertical position. The tube of this invention is selected so there is small and linear radiation can be produced. Therefore, the mercury-arc lamp ofthis invention when used as the light source for optical printing of the color phosphor screen does not require optical systems such as illustrated in the prior art of FIG. 1. It has been discovered that the mercury-arc lamp of this invention increases the brightness five to 20 times over that of conventional mercury-arc lamps such as illustrated in FIG. 3 when used with conventional optional systems.

Since the electrodes are spaced a substantial distance from the inside wall of the tube within the cavities 14A and 14B surrounding them, the probability of negative ions from the

electrodes

12A and 12B impinging upon the inner walls of the tube will be decreased. Any ions which do impinge upon the wall of the tube will be substantially reduced.

Also due to the spacing of the electrodes a substantial distance from the inner wall, the so-called thermal layer will exist which will reduce the transmission of heat from the electrode to the wall of the tube so that devitrification of the tube will be effectively prevented and thus the service life of the lamp will be substantially increased.

By tapering the ends of the electrodes as illustrated at 12a and 12b the transmission of heat from the heated electrodes will be reduced. Also the heat radiation will be low. Therefore the electrodes can be maintained at high temperature for long periods of time. Also an electric charge will concentrate on the electrodes to insure efficient discharge between the electrodes.

When using mercury-arc lamp ML it is necessaryto provide means for cooling it and it is generally preferable to utilize a water cooling system.

FIG. 8 illustrates a cooling device designated generally as 19. The cooling device 19 has a water-tight liquid tank 20 in which the mercury-arc lamp ML is mounted. An inlet port 21 provides coolant as, for example, water into the tank 20 about the lamp ML. A transparent window 23 is mounted adjacent the lamp ML and light from the mercury-arc lamp ML passes from the tank through the window 23. An exhaust or outlet port 22 is provided at the end of the lamp ML away from the inlet port 21 and allows the cooling water to be discharged from the tank 20. A pair of shield members 24A and 24B are mounted around the mercury-arc lamp ML and are separated leaving an opening which forms a slit SL from which the light of the lamp is emitted. The shield members 24A and 24B may be formed of metal sleeves placed around the lamp ML, for example.

FIG. 9 has a curve 30 which shows the distribution of illumination on the panel P of the television tube as measured by photocell illuminometer when the mercury-arc lamp of this invention was installed in the water cooling device illustrated in FIG. 8 and disposed relative to thepanel P as shown in FIG. 2. The particular curve was made without the shadow mask E in place. The origin of the curve indicated as Oat the bottom of the graph corresponds to the center line Z-Z of the panel P and the distance from the center line in the direction of H-H' indicated on the abscissa of the graph. The particular mercury-arc lamp according to this invention had adiameter of l .2 mm. and the slit SL had a width of 1.2 mm., and the mercury-arc lamp was energized with 900 volts at 1.1 l amperes. No reflector was used.

The curve 31 is a similar illumination curve for a conventional light source S employing a focusing lens CL. This type of light source S is illustrated in FIG. 1, and in this example the reflector M was used and the light source was cooled by air cooling. The mercury-arc lamp ML was two mm. in diameter and 24 mm. in length and was operated at a power'of l kilowatt. The diameter of the focusing lens CL adjacent the mercuryarc lamp ML was 16 mm. and the length of the columnar portion of the focusing lens was 80 mm. and the diameter of the light diffusion tip was 4 mm. It may be observed from curve 31 that the conventional light source S, according to the prior art,'results in great decrease in illumination as the distance from the center of the panel P increases. To prevent this undesirable effect, the correction filter F is used in the prior art devices for decreasing the illumination at the center of the panel relative to the peripheral area so as to obtain substantially uniform illumination over the entire area of the panel. Curve 32 illustrates the illumination on the panel with the filter F in place with a conventional device according to FIG. 1. It is to be noted that the light actually utilized, as shown by curve 32, is a small portion of the total light emitted from the light switch L and that the exposure efficiency is very low. Further, since the focusing lens CL and the filter F greatly increase the amount oflight energy absorbed below wave length of 3,000 Angstroms, the printing efficiency of the phosphor is poor, and the time for printing will be to 50 minutes.

The present invention, however, gives substantially uniform distribution of illumination over the entire surface of the panel P as shown by the curve 30 and a correction filter is not required and the light emitted from the lamp can be efficiently utilized.

Thus the present invention allows a linear source of light to be employed and the provision of the slit SL provides an apparent point source of light. This eliminates the necessity of a focusing lens and avoids the disadvantages and defects which result in the use of a focusing lens.

The use of the shield members SH with the mercuryarc lamp I0 allow a very small point source of light to be obtained by limiting the width of the slit and thus to provide for enhanced sharpness in the printing of the phosphor.

The invention insures that sufficient light having a wave length to which the photosensitive binder mixed in the phosphor slurry to be printed is sensitiye impinges on the panel P without being absorbed by a focusing lens and thus the light emitted from the light source irradiates the panel P very efficiently. The greatly enhanced efficiency of exposure allows the time for printing to be as short as l to 2 minutes which is less than one tenth of the time required with conventional light sources. This allows color television tubes to be made much faster and increases the total production of tubes. Power consumption is also substantially reduced since much shorter periods are required for making the exposures.

The apparatus illustrated in FIG. 8 can maintain the mercury-arc lamp ML fixed but at times it is, desirable to rotate the lamp during the printing process to minimize dispersion of the illumination.

This may be accomplished by mounting the cooling device illustrated in FIG. 8 on a shaft 25 which is rotatably mounted on the axis Z-Z as shown in FIG. 8. The shaft 25 is mounted in a suitable bearing and is driven by motor 28 which has an output shaft 27. A pair of pulleys are respectively mounted on the

shafts

25 and 27 and are connected by belt 26, such that the motor 28 drives the shaft 25 to rotate the mercury-arc lamp ML and its water-cooled housing. The shaft 25 may be driven at a speed of 40 to 100 rpm, for example.

With such an arrangement, the apparent luminosity of the slit SL of the mercury-arc lamp ML, when viewed from the front, through the window 23 appears to be circular in shape. Also the light source approximates a point source more accurately than if it were not rotated.

In FIG. 8 the cooling device is mounted with the axis of the mercury-arc lamp ML designated as 0-0 perpendicular to the central axis Z-Z of the panel P and is rotated about the axis Z-Z'. It is also possible to rotate the light source with the mercury-arc lamp ML mounted obliquely to the central axis Z-Z' of the panel P as illustrated in FIG. 10.

In FIG. 10 the elements similar to those in FIG. 8 are identified by the same reference numerals and characters and their description will not be repeated. The mercury-arc lamp ML is mounted on the rotating shaft 25 at an angle such that the luminous portion of the slit SL lies on the central axis Z-Z' of the panel P and aligned with the center of the rotary supporting axis 25, but the longitudinal axis through the tube ML corresponding to QQ' does not make a angle with the axis 2-2, but makes an angle of approximately 45, as shown. Thus, when the shaft 25 is driven to rotate the mercury-arc lamp ML assembly on the axis 2-2 the apparent luminous portion of the mercury-arc lamp ML appears substantially spherical when viewed from the panel P and therefore the changing of the effective size of the luminous portion is decreased to eliminate parallax effects.

In such an arrangement the light of the greatest intensity is directed toward the peripheral area of the panel P away from the center of the panel P and a uniform illumination can be obtained over a wide area. Thus an arrangement according to FIGv proves to be very effective when exposing panels of wide angle picture tubes. Generally the device of FIG. 10 does not require a correction filter, due to the even distribution ofthe illumination.

When the mercury-arc lamp ML rotates as shown the change in size of the luminous portion due to parallax is decreased and the shield member SH can be spaced from the mercury lamp ML to some extent. Thus, when the mercury lamp is mounted in the cooling device 19 the shield member SH can be mounted on the window 23 of the cooling device 19, thus assuring efficient cooling ofthe lamp.

it will be apparent that many modifications and variations may be effected without departing from the scope ofthe novel concepts of this invention.

We claim as our invention:

1. A device for making a phosphor screen on a panel ofa color picture tube comprising:

mounting means supporting said panel;

a light source of fine-line radiation supported at a predetermined position relative to said panel; said light source comprising a mercury-arc lamp consisting of a tube made of glass, two electrodes sealed in the tube at opposite ends thereof, mercury contained in the tube at the both ends thereof, an inert gas sealed in said lamp, enlarged spherical cavities formed in the tube about the ends of said two electrodes, the inner diameter of the main portion of the tube being in the range of 0.5 to 1.4 mm., the inner diameter of said spherical cavities being greater than 1.5 mm., said two electrodes being circular in cross-section and having diameters of about 0.5 mm.;

shield means for said glass tube forming a slit perpendicular to the longitudinal direction of said tube and comprising a light impervious coating formed on said tube with said slit formed adjacent the central portion of said tube;

means for mounting said light source; and

means for rotating said mounting means for said light source.

2. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 1 wherein said light source rotates about an axis perpendicular to the longitudinal direction of said mercury-arc lamp.

3. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 1 wherein the central axis of beams of light emitted from said light source is inclined relative to the center of said panel.

4. A device for making a phosphor screen on panel of a color picture tube as claimed in claim 1 including a liquid tank enclosing said mercury-arc lamp and said mounting supporting said tank, an inlet port for mtroducing cooling water into said tank, and an outlet port for discharging the cooling water from said tank.

5. A device according to claim 1 wherein said coating comprises a mixture of carbon and a metal in solution.

6. A device according to claim 5 wherein said metal is aluminum.

7. A device for making a phosphor screen on a panel of a color picture tube comprising:

a light source of fine-line radiation;

shielding means for said light source having a slit perpendicular to the longitudinal direction of said fine-line light source and comprising a light impervious coating formed on said light source with said slit formed adjacent the central portion of said light source;

means for mounting said light source for rotational movement; and

means for rotating said mounting means.

8. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 7 wherein said light source rotates about an axis perpendicular to the longitudinal direction of said light source.

9. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 7 which includes means for mounting said panel relative to said light source.

10. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 9 wherein the central axis of beams of light emitted from said light source is inclined relative to the center, of the panel to provide substantially uniform irradiation over the entire area of the panel.

11. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 7 wherein a liquid tank is supported by said mounting means and said light source mounted in said tank, an inlet port for introducing cooling water into said tank, and an outlet port for discharging the cooling water from said tank.

Claims

1. A device for making a phosphor screen on a panel of a color picture tube comprising: mounting means supporting said panel; a light source of fine-line radiation supported at a predetermined position relative to said panel; said light source comprising a mercury-arc lamp consisting of a tube made of glass, two electrodes sealed in the tube at opposite ends thereof, mercury contained in the tube at the both ends thereof, an inert gas sealed in said lamp, enlarged spherical cavities formed in the tube about the ends of said two electrodes, the inner diameter of the main portion of the tube being in the range of 0.5 to 1.4 mm., the inner diameter of said spherical cavities being greater than 1.5 mm., said two electrodes being circular in cross-section and having diameters of about 0.5 mm.; shield means for said glass tube forming a slit perpendicular to the longitudinal direction of said tube and comprising a light impervious coating formed on said tube with said slit formed adjacent the central portion of said tube; means for mounting said light source; and means for rotating said mounting means for said light source.

4. A device for making a phosphor screen on panel of a color picture tube as claimed in claim 1 including a liquid tank enclosing said mercury-arc lamp and said mounting supporting saiD tank, an inlet port for introducing cooling water into said tank, and an outlet port for discharging the cooling water from said tank.

6. A device according to claim 5 wherein said metal is aluminum.

7. A device for making a phosphor screen on a panel of a color picture tube comprising: a light source of fine-line radiation; shielding means for said light source having a slit perpendicular to the longitudinal direction of said fine-line light source and comprising a light impervious coating formed on said light source with said slit formed adjacent the central portion of said light source; means for mounting said light source for rotational movement; and means for rotating said mounting means.

10. A device for making a phosphor screen on a panel of a color picture tube as claimed in claim 9 wherein the central axis of beams of light emitted from said light source is inclined relative to the center of the panel to provide substantially uniform irradiation over the entire area of the panel.