US3768385A - Apparatus for producing a master dot pattern for photo-etching of a graded hole shadow mask - Google Patents

Abstract

Apparatus for the production of master dot patterns for photoetching a graded-hole shadow mask for use in a color picture tube comprising mounting a grading mask having its transparency concentrically, progressively decreasing from the center toward the periphery thereof between a light source and a photographic material and inserting a screen between the grading mask and the light source.

Description

United States Patent 1 [1 1 Noguchi APPARATUS FOR PRODUCING A MASTER DOT PATTERN FOR PHOTO-KITCHENS OF A GRADED HOLE SHADOW MASK [75] Inventor:

Kinichi Noguchi, Tokyo, Japan Assignee: Toppan Printing Co. Ltd., Tokyo,

Japan Filed: July 2, 1971 Appl. No.: 159,335

Related U.S. Application Data Continuation of Ser. No. 883,668, Dec. 22, 1969, which is a continuation of Ser. No. 387,724, Aug. 5, 1964, abandoned.

[52] US. Cl 95/1 R [51] Int. Cl. G03b 27/16 [58] Field of Search 95/1; 355/84 [56] References Cited UNITED STATES PATENTS 1,953,471 ,4/1934 Eich 96/27 Oct. 30, 1973 3,385,184 5/1968 Ramberg 95/1 2,717,545 9/1955 Engeler 355/84 3,109,117 10/1963 Kaplan 95/1 X Primary Examiner l0hn M. Horan Att0rney-Eric l-l. Waters et al.

[57] ABSTRACT Apparatus for the production of master dot patterns for photo-etching a graded-hole shadow mask for use in a color picture tube comprising mounting a grading mask having its transparency concentrically, progressively decreasing from the center toward the periphery thereof between a light source and a photographic material and inserting a screen between the grading mask and the light source.

9 Claims, 12 Drawing Figures PATENTEDucI 30 I973 SHEET 10F 3 FIG? F/GJ

PAIENIEDncwso ms M a; 768L385 SHEET 2 UF 3 FIG. 6

8 G H 0 T m 5 mwhmiio ,3 Ba

FIG. 7

DISTANCE FROM DISC CENTER PAIENTEDnmoms 3.768385 SHEET 3 UF 3 R Dm \7 Ir a U C) E 3 6 Q q 0 Dm 0 r DENSITY OF GRADING MASK DISTANCE FROM DISC CENTER F G. .9 Fl 6. /0

t g LLI Q 0 EXPOSE VALUE L065 APPARATUS FOR PRODUCING MASTER DOT PATTERN FOR PHOTO-ETCHING OF A GRADED HOLE SHADOW MASK CROSS-RELATED APPLICATION This is a Continuation Application of Application Ser. No. 883,668 filed Dec. 22, 1969 (issuedias U.S. Pat. No. 3,745,734 on- Feb. 29', 1972). which in turn is a Streamlined Continuation of Application Ser. No. 387,724 filed Aug. 5,1964 and now'abandoned.

' BRIEF SUMMARY or THE INVENTION This invention relates to apparatuszfor manufacturing a master dot pattern for photo-etching a graded-hole shadow mask used in'a color television picture tube and has particular reference to a grading mask used therein.

Existing shadow masksused' for color picture tube are, in most cases, made of aethinisheet of steel-orother metal which is provided with a. number of regularly aligned pores to permit the transmission of: an electron. beam therethrough. More recentimprovements in this type. of shadow mask comprise the provision of relatively large poresin the center-of the effective mask area and reduction of the size of concentrically aligned pores progressively toward the peripheral portion of the mask while eliminating amiss landing of electrons at the periphery of the screen of the tube. This. is termed a graded-hole shadow mask" whichis manufactured by a photo-etching process.-

Itis aprincipal objectof this invention to provide apparatus for preparing amaster dot'pattern'for photoetching of graded hole shadow maskswhich is provided with'a dot diameter larger at-the center of the effective surface and progressively smaller toward the peripheral portion of the mask.

It isanother object ofthe invention to provide apparatus 'formaking a; photo-etching master dot pattern with the use: of a-gradingmask adapted to'control the intensity of exposure light so that the brightness of a picture is greater at the center and smaller toward the periphery of the mask.

It is afurtherobject of theinvention to provide a photo-etching master dot riatternwwhi'chhas a suitable pore size distribution by varying the densityv of the grad ing mask. I

It is still another object of the invention to .provide simple, economical means for obtaining the above grading mask'for use in the'manufacture of photoetching masterdot patterns.

These and other objects of theinventionwill become more apparent from thefollowingdescription taken in connection with the accompanying drawings illustrativeof the-manner of preparingamaster dot pattern'for photo-etching of graded-hole shadowzmasks according to the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is aperspective view ofagrading mask according to the present invention;

FIG. 2'is aperspective .view of-a grading. mask using an optical wedge according to thepresent invention;

FIG. 3' Ba perspective-view'of a gradingrnask using a plurality'of sheets accordingtothe present invention;

FIG. 4 is aperspective viewot' a gradingmask in the form of a platewith a conical.- recess thereinaccording; to the present invention;

FIG. 5 is a front view of a glass screen for photographing a shadow mask etching master dot pattern which has an angle of 60 cross-over of line groups;

FIG. 6 schematically illustrates the arrangement of a device for photographing a graded-hole shadow mask master pattern using a process camera;

FIG. 7 schematically illustrates the arrangement of a device for photographing a graded-hole shadow mask master pattern using a printing frame;

FIG. 8 is agraph illustrating the relation between the distance from the center of the effective area of the master dot pattern for photo-etching of graded-hole shadow masks to the periphery thereof and the dot diameter; I

FIG. 9 is a graph illustrating the relation between the grading mask density and the screen dot diameter where the photographic material, time of exposure and development conditions are all fixed for the screening of the gradingmask placed in front of a light source in the production of a shadow mask pattern;

FIG. 10 graphically illustrates the density distribution of the grading mask obtained from the graph of FIG. 9;

FIG. 11 graphically illustrates the characteristic curve of a dry'plate used in the manufacture of a grading mask; and

FIG-412 graphically illustrates an opening in a disc hereinafter referred-to as sector-disc which is used in the'manufacture of a grading mask.

DETAILED DESCRIPTION Generally, a master dot pattern required for photoetching of shadow masks may be obtained by passing thereto a light beam passed through a screen having a transparent spot at each comer of an'equilateral triangle. In such'instance, the pattern may be subjected to screening through a lithographic glass screen or contact screen 3. having a rhombic opening 2 with an angle of 60 for crossing of line groups 1, as illustrated in'FIG. 5,- thereby obtaining dots of uniform size over the entire surface of thepattern.

border to vary the dot size successively from the effective center area toward the periphery of the pattern, the present invention contemplates the use of a grading maskwhich may be placed in front of a light source to control the intensity of light therefrom.

The grading mask is based on an entirely new concept of the invention and comprises a suitable photographic material such as dryplate, film or the like which has alight transmittance which is high at the center and progressively lower toward the peripheral portionof the mask, such transmittance variation being determined. by the distribution of the pore size required for the performance of a desired shadow mask;

As a result of extensivesearch for the best mode of producing the afore-mentioned gradingmask, the present inventor has discovered the following:

l. Adisc member 11 having a transparent portion 11a and an opaqueportion 11b; which is similar to a sector-disc as used' in a sensitom'eter, such as for-example a I-Iurter-Driffield sensitometer anda Schiner sensitometer, is held in opposingrelation to arelatively lowlight transmittance.

the characteristic curve obtained from the tests conducted under the same conditions as .in the manufac-- ture of the grading mask. This process has the advan-- tagethat a density. distribution isobtained with accuracy as'desired, although the rotating center may be somewhat unstable.

2. As shown in FIG. 2,'an opaque disc 13 is provided with a transparent portion 13a having a suitable central angle and with an optical wedge 13b having a predete'r-' mined density distribution superimposed uponsaid transparent portion. The opaque disc 13 is positioned inopposing relation to a relatively low contrast photographic material 14. Light is passed through the disc member 13 to the photographic material member 14 while either of the two members is rotated about an axis coincident with the maximum density spot 15 of the optical wedge 13b; Density distribution of the opti-' cal wedge 13b may be determined by the characteristic curve'obtained from tests carried out under exactly the same conditions as provided forthe production of a grading mask. This process has the advantage that the central angle is easily fabricated and the'center of rota-. tion is established .with a reasonable degree of accuracy. r v

As illustrated in FIG. 3, there are provided aplurality'of semitransparent sheets 16, 16, 16" 1 16 made of a synthetic resin film or paper having a uniform transmittance of light. They are provided with circular windows '17, 17, 17" 17, which are concentrically arranged but different in diameter, and are stacked together with the sheet 16 having the smallest 4. The arrangement illustrated in FIG. 4 involves a semitransparent block 18 of a synthetic'r'esin or the like which has uniform transmittance of light. The block is prevented with a conical recess andjis thinnest at the center 1 8a and becomes progressively thicker toward vthe periphery of the recess. Alternatively, such pattern may be printed on a'photographic material. According to this process, a good selection of transparent materials may be of matte form on the surface to act as a lens,

thereby allowing the gradingto vary as desired.

I follows.

A detailed description follows for the production of I the above grading masks according to the invention.

Process (1) Example v a. Determining the density distribution ofthe-grading mask. 1

, Density distribution of the grading mask required for the preparation of a graded-hole shadow mask pattern having a requisite screen dot size distribution may be obtained in the following manner. I I

In the phtographing of a shadow mask pattern, the grading mask is placed in front of a light source and screened where the'photographic material, time of exposure and development conditions are held invariable.

In this manner, there may be established a certain relation between the grading mask density and the screen dot diameter. This may begraphicallyillustrated as A dry plate is placed on a turn-table immediately un derneath an enlarging lens in a manner similar to the fabrication-0f a grading mask. ,To the dry-plate is adhered a step wedge whose density is known. It is exposed to .light for a suitable length of time and then subjected to development under certain conditions. By determining the density of the resulting dry-plate in view of the known density of the step wedge, it is possible to obtain a characteristiccurbe prevailing under such development conditions/See FIG. 11, from the exposure light intensity E required to obtain a desired density D maybe readily determined.

c. Determining the shape of the opening or transparent portion 11a in the sector-disc.

(See FIG. 12). v

From the definition of exposure light intensity, there maybe established the equation E=I-T where I is light intensityand T is exposure time. If light transmittance is uniform over the entire area of the transparent portion or opening in the sector-disc, the factor I remains constant, hence EaT. When light is applied while either of the sector-disc and the dry-plate is being rotated, the time of exposure Tr at point 7 away from the center of the disc is proportional to an arc length [r of the radius of the opening in the sector-disc. The arc length l r is further proportional to the angle Or from the center of the disc, so that, there may be established a relation defined by EaQ; that is, E=K-Q where K is an optional multiplier.

Accordingly, the sequenceof fabricating a grading mask may be given as followsm Y 1. The .value r is selected as often as required successively from the point 0.

2. The value D corresponding to each of the values is obtained from FIG. '10.

3.. T he value log E corresponding to each of the D values is obtained from FIG. 11.

4. The value E is derived from log E thereby obtaining Q from the equation of E=K'Q. In this inu n r stance, the value K determines the total .size of a With reference to a curve drawn by connecting the plotted dots, a base having a transparent portion and an opaque portionmay be prepared and subjected to photographing with a dry-plate thereby'producing a sectordisc. This disc is carried in a negative holder on an enlarger. A turn-table having a dry-plate holder mounted thereon and driven by a motor is placed immediately below the enlarger lens. With the image of the sectordisc projected onto the dry-plate, the center of the disc may be registered with the center of rotation of the turn-table.

i As a light source for theenlarger, there may be used a 100V, 150W enlarger light bulb. The lens may have a focal length of 135mm and a diaphragm opening of f 22. While the turntable is rotated at a speed of 78 rpm, a duplicating Olso dry-plate is exposed to light for 20 seconds. The dry-plate is developed with a specified developer to a low contrast.

Next. the manner in which photographing is made of a master dot pattern for photo-etching a graded-hole shadow mask according to the invention will be described in some detail as follows.

I. Photographing with process camera.

A. Equipment and material.

1. Camera.

A conventional camera with adjustable aperture is suitable for the purpose.

2. Light source.

A highly stable light source such as a 100V, 500W tungsten projection lamp used for an ordinary camera may besuccessfully used. A housing for the lamp may incorporate a cooling fan, a heat absorbing filter and a light diffusing plate (opal glass). In front of this diffusing plate, there is installed a photographically or mechanically fabricated grading mask having a brightness greater at the center and progressively diminishing away from the center of the mask.

3. Lens.

An ordinary lens (such as for example Aponicol F60cm) may be used with a controlled round aperture or an iris diaphragm.

4. Screen. 7

A 60 cross angle glass screen provided with a rhornbic opening and having a width ratio of transparent portion to opaque portion of 1:1 1:2 is suitable. Alternatively, a white dot screen having a circular or regular polygonal transparent dotat each comer of a equilateral triangle may be fabricated from a dry-plate or film. The screen is secured to a screen holder.

5. Photographic material.

This may be a dimensionally stable base lith type film or dry-plate. I

B. Process of preparing a pattern.

The apparatus required for the production of a master dot pattern comprises a light source 9, a heat absorbing filter 20 and a light diffusing plate 21 which are journalled in a-lamp housing (not shown) with a grading mask 22 placed in front of the diffusing plate 21, as shown in FIG. 6. Designated at 23 is a camera which is mounted before the grading mask.

Designated at 24 is the camera lens and at 25 is an iris diaphragm. A screen mounted in a screen holder is placed in front of the camera.

Designated at 26 is a photographic material'(dryplate or film).

An example of the above equipment, the camera lens is located about 300 centimeters from a ground glass 24' the camera lens 24 having a focal distance of 60 centimeters and mounted to 70 centimeters from the light source 9 and the diffusing plate 21. The diffusing plate 21 has mounted thereon the grading mask 22 with a diameter of about 10 centimeters, the periphery of which is covered with a sheet of black paper to prevent the permeation of light. The screenl0 is a 60 cross angle glass screen having a transparent-opaque ratio of 1:2 and a line pitch of 0.5 lm/m and the screen is placed 35 millimeters from the ground glass 24 of the camera 23. The light source 9 may be a 100V, 500W projection lamp which gives 90 seconds of exposure oflight to a lith type film 26 in a vacuum bag while the lens iris is set at f: 64. The film thereby exposed may be developed using Kodaris Super developer with care not to cause irregularities in the development.

II. Photographing with printing frame. A. Equipment and material.

1. Printing frame. This may be an ordinary vacuum suction type printer.

2. Light source.

As a light source, there may be used a tungsten lamp which may be located centrally at the bottom of the printing frame. Inserted between the lamp and the top glass of the printer is an opal glass or suitable synthetic resin, upon which is placed a photographically or mechanically fabricated grading mask having a greater transparency at the center and progressively diminishing away from the center of the mask. In this manner, theintensity of light is reduced progressively from the center toward the periphery of the pattern. f

3. Screen.

A 60 cross angle screen or a white dot screen prepared therefrom with use of a dry-plate or film which has a transparent portion of any suitable configuration at each of an equilateral triangle may be used.

4. Photographic material.

A lith type or dry-plate may be used as in the-case of Process I above.

B. Process of preparing a pattern.

The apparatus required for the production of a master dot pattern in this embodiment of the invention comprises a printing frame 27 having a top glass 28 upon which is placed a screen 29 with emulsified face up and a spacer of transparent sheet 30 placed on the screen. Alternatively, the screen 29 may be placed so that the emulsified surface thereof firmly contacts the top glass 28 of the printing frame thereby spacing the screen 29 uniformly from the emulsified face of the photographic material 31 and thereby enabling the adjustment of screen dot printing. The distance between the light source 32 and the printer top glass 28 is about 50 to 100 centimeters. A diffusing plate 33 made of opal glass or synthetic resin is inserted in such a manner as to permit the distance (height) to be adjusted, and thus the grading of screen dots may be varied at will. Placed on the opal diffusing plate 33 is a grading mask 35 which is covered at the periphery with a sheet of blackpaper 34. The grading mask 35 may preferably be of disc form which has a diameter sufficiently large to cover the area required for exposure. The rest of the process involved in the printing of a master dot pattern is the same as described in Process I hereinabove.

III. Photographing with graded-hole contact screen.

photographed. In this instance, the size of these ob scure screen dots is reduced progressively from the center toward the peripheral portion of the screen by the effect of the grading mask. This-contact screen is adhered to a lith type film and exposed to light uniformly overv the entire surface, thereby obtaining a negative pattern having a clear-cut edge.

. The screen dot pa'ttern obtained from either of the aboveprocesses may be provided with suitable symbols including a display line, a cutting line, codes, numbers, etc., before it is finished asa photo-etching master pattern.

Having thus described the principal concepts of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without limit to such specific embodiments as herein described and illustrated and without departing from the spirit and scope of the invention defined in the following claims. For example, the pore distribution may be concentrically elliptical instead of concentrically circular. Or, some pores may be larger or smaller than the others. 1

What is claimed is:

1. Apparatus for the production of a master dot pattern for photo-etching of graded hole shadow masks in color television picture tubes comprising a light source, a photographic material spaced from said light source and adapted to be formed as said master dot pattern, a screen with a regular arrangement of openings therein positioned between said light source and said photographic material, a grading mask adjacent said screen and between said source and photographic material, said grading mask comprising a flat plate of photographic material having a progressively decreasing transparency from the center thereof to its periphery to control the exposure intensity in the central and peripheral portions of the master dot pattern without substantial deflection of the light rays from said light source and a lens and diaphragm between said mask and said'screen. v

2. Apparatus as claimed in claim 1 wherein said plate has a light transmittance characteristic arranged in concentric circular fashion, the transmittance decreasing from the center to the periphery.

SQApparatus as claimed in claim 2 wherein said plate comprises a succession of stacked elements having uniform light transmittance and provided with concentric openings which successively increase in diameter.

4. Apparatus as claimed in claim 2 wherein said plate is semitransparent and has uniform light transmittance, said plate having a conical recess therein.

5. Apparatus as claimed in claim 1 comprising a circular disc having a transparent portion and an opaque portion, and comprising means to provide relative rotation between said disc and said flat plate of photographic material, said transparent portion providing said progressively decreasing transparency.

' 6. Apparatus as claimed in claim 5 wherein said transparent portion has one radial edge and one curved edge intersecting atthe center of the disc, the curved edge being progressively further from the radial edge with increasing radial distance. 1...; 7. Apparatus as claimed in claim 5 wherein said transparent portion is an angular sector, and comprising an optical wedge in said transparent portion with a density varying radially in said wedge.

8. Apparatus as claimed in claim 1 comprising a printing frame, said light source being within said frame, a glass member on said frame, said screen being mounted on said glass member, said photographic material having an emulsified surface and being mounted on said screen, said mask being in said frame between said source and said glass member.

9. Apparatus as claimed in claim 8 comprising a diffusing plate supporting said grading mask and adjustable in distance relative to said source and glass member.

Claims (9)

1. Apparatus for the production of a master dot pattern for photo-etching of graded hole shadow masks in color television picture tubes comprising a light source, a photographic material spaced from said light source and adapted to be formed as said master dot pattern, a screen with a regular arrangement of openings therein positioned between said light source and said photographic material, a grading mask adjacent said screen and between said source and photographic material, said grading mask comprising a flat plate of photographic material having a progressively decreasing transparency from the center thereof to its periphery to control the exposure intensity in the central and peripheral portions of the master dot pattern without substantial deflection of the light rays from said light source and a lens and diaphragm between said mask and said screen.

2. Apparatus as claimed in claim 1 wherein said plate has a light transmittance characteristic arranged in concentric circular fashion, the transmittance decreasing from the center to the periphery.

3. Apparatus as claimed in claim 2 wherein said plate comprises a succession of stacked elements having uniform light transmittance and provided with concentric openings which successively increase in diameter.

4. Apparatus as claimed in claim 2 wherein said plate is semitransparent and has uniform light transmittance, said plate hAving a conical recess therein.

5. Apparatus as claimed in claim 1 comprising a circular disc having a transparent portion and an opaque portion, and comprising means to provide relative rotation between said disc and said flat plate of photographic material, said transparent portion providing said progressively decreasing transparency.

6. Apparatus as claimed in claim 5 wherein said transparent portion has one radial edge and one curved edge intersecting at the center of the disc, the curved edge being progressively further from the radial edge with increasing radial distance.

7. Apparatus as claimed in claim 5 wherein said transparent portion is an angular sector, and comprising an optical wedge in said transparent portion with a density varying radially in said wedge.

8. Apparatus as claimed in claim 1 comprising a printing frame, said light source being within said frame, a glass member on said frame, said screen being mounted on said glass member, said photographic material having an emulsified surface and being mounted on said screen, said mask being in said frame between said source and said glass member.

9. Apparatus as claimed in claim 8 comprising a diffusing plate supporting said grading mask and adjustable in distance relative to said source and glass member.

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