Shadow mask having a slot structure that permits electron beams to enter at increased angles

In a shadow mask 1 of pressing type, a large number of slots are made in a mask body in the horizontal direction and in the vertical direction. Each slot has a roughly rectangular backside opening, a roughly rectangular front-side opening, and a through-hole that connects these two openings. Between each slot of the multiple slots made in the mask body that is situated at least on either of the two diagonal axes of the mask body but in such a position that the angle at which electron beams enter the slot is 20 degrees or more and another slot that is arranged adjacently to the above slot in the vertical direction, a connecting part connecting the peripheral-side vertical outer edges of the front-side openings of these slots is provided so that it runs through a horizontal bridge part formed between the front-side openings of the slots.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shadow mask for forming roughly rectangular beam spots on a fluorescent screen of a color cathode ray tube.

2. Background Art

As shown inFIG. 14, a shadow mask1is mounted in a color cathode ray tube101with its surface facing to a fluorescent screen102of the color cathode ray tube101. In the color cathode ray tube101, electron beams105emitted from electron guns103, deflected by the magnetic fields produced by a deflection yoke104, pass through the shadow mask1and then accurately strike predetermined points on the fluorescent screen102. Usually used for such a shadow mask1is a pressing-type shadow mask that is shaped by pressing, or a tension-type shadow mask that is stretched in the vertical direction (toward the upward and downward) before use.

The shadow mask1will be described in detail with reference toFIG. 1(that shows the present invention).FIG. 1is a diagrammatic plane view illustrating the positional relationship between the slots made in the shadow mask1. As shown in this figure, the shadow mask1comprises a mask body1athat is roughly rectangular in shape, and a large number of slots2(including slots2a,2b,2c, and2d) are arranged in the horizontal direction X and in the vertical direction Y on this mask body1aplane, each slot having a roughly rectangular through-hole that penetrates the mask body1ain the direction of thickness. In this Specification, a unit structure composed of a through-hole, and a front-side opening and a backside opening that form the through-hole is referred to as a “slot”. Further, inFIG. 1, reference numeral6denotes a center (also referred to as a “center point”) that is the intersection of two diagonal axes5,5connecting the opposite corners of the mask body1a, extending along the mask body1aplane; reference numeral3, a horizontal axis passing through the center6, extending in the horizontal direction X along the mask body1aplane; and reference numeral4, a vertical axis passing through the center6, extending in the vertical direction Y along the mask body1aplane. Furthermore, inFIG. 1, reference numeral2adenotes a slot situated in the center6of the mask body1a(see character a); reference numeral2b, slots situated in the outer end parts of the vertical axis4(see characters b, b′); reference numeral2c, slots situated in the outer end parts of the horizontal axis3(see characters c, c′); and reference numeral2d, slots situated in the outer end parts of the diagonal axes5(see characters d, d′, e, e′). Reference numeral1bdenotes a skirt part that surrounds the mask body1aand will be bent by pressing.FIG. 1is merely a diagrammatic view, and the slots shown in this figure are dimensionally exaggerated.

When such a shadow mask1is placed in the color cathode ray tube101shown inFIG. 14with the surface of the shadow mask1facing to the fluorescent screen102of the color cathode ray tube101, the electron beams105emitted from the electron guns103vertically enter the slot2asituated in the center of the shadow mask1but obliquely enter, at angles θ, the slots2b,2c, and2dthat are situated in the outer end parts of the respective axes (the horizontal axis3, the vertical axis4, and the diagonal axes5), that is, in the peripheral part of the shadow mask1. For this reason, in the shadow mask1, the positions of the front-side opening and the backside opening that form a slot are adjusted according to the position of the slot in the mask body.

FIGS. 11A,11B,11C and11D are diagrammatical plane views showing the shape of the slots2(slots2a,2b,2cand2d) made in the respective parts of the mask body1aof the shadow mask1. In these figures, reference numeral11denotes through-holes of the slots2. The through-holes11are made so that they connect the front-side openings12and the backside openings13that are etched in a thin metal sheet. The backside openings13are made on the side on which electron beams7are incident, and the front-side openings12are made on the side from which the electron beams7emerge. The backside openings13and the front-side openings12are made roughly rectangular in shape, and the front-side openings12are made large in area so that they do not obstruct the passage of the electron beams7.

Since electron beams enter, from the front, the slot2asituated in the center of the mask body1a, the through-hole11(the backside opening13) of this slot is made so that it is positioned almost in the center of the front-side opening12, as shown inFIG. 11A.FIG. 11Bshows the slot2bsituated in the outer end part of the vertical axis4;FIG. 11C, the slot2csituated in the outer end part of the horizontal axis3; andFIG. 11D, the slot2dsituated in the outer end part of the diagonal axis5. Electron beams7obliquely enter the slots2b,2c, and2dthat are situated in the peripheral part of the mask body1a. Therefore, in order not to obstruct the passage of the electron beams7that have passed through the through-hole11of each slot2, the front-side opening12is made so that its position is offset from the position of the through-hole11(the backside opening13) to the peripheral side in the mask body1aplane.

However, even when the offset arrangement as shown inFIGS. 11A,11B,11C and11D (such an arrangement that the position of the front-side opening12of a slot2is offset from the position of the through-hole11(the backside opening13) of the slot2according to the position of the slot2in the mask body1a) is made, of the slots2b,2cand2dmade in the peripheral part of the mask body1a, especially the slots2dsituated in the outer end parts of the diagonal axes5have the shortcoming that, since electron beams7that have obliquely entered the slots2dare partially blocked by the front-side openings12and the backside openings13of these slots, the slots2dcannot let the electron beams7strike the fluorescent screen of the cathode ray tube to form thereon beam spots in the desired shape.

In order to overcome this problem, shadow masks having such a structure that, of the two long sides of a roughly rectangular through-hole of each slot made in a mask body, the long side situated on the side apart from the center of the mask body has a protrudent part protruding, in the direction opposite to the vertical axis of the mask body, from at least one of the upper and lower end parts of this long side, have been proposed in Japanese Laid-Open Patent Publications No. 320738/1989 and No. 6741/1993.

FIG. 12is a front view showing the shape of the slots in the conventional shadow mask described in Japanese Laid-Open Patent Publication No. 6741/1993. The shape of the slot2dshown in this figure corresponds to that of the slots situated in the upper-right outer end part of the diagonal axis5extending toward the upper right in the plane view of the mask body1a(FIG. 1). This slot2dhas the following features: the position of the front-side opening12is offset from the position of the through-hole11(the backside opening13) to the upper right, that is, to the peripheral side, and, at the same time, of the two long sides of the through-hole11, the long side situated on the right side, that is, on the peripheral side, has a protrudent part11aprotruding toward the peripheral side from the lower end part of this long side. The protrudent parts11aare provided for the purpose of forming roughly rectangular beam spots on a fluorescent screen of a cathode ray tube. Further, the front-side opening12of each slot2dis made so that it has a roughly rectangular outline composed of a pair of left- and right-hand long sides12a,12band a pair of upper and lower short sides12c,12d.

Incidentally, cathode ray tubes have came to be made flat in recent years, like the flat-type color cathode ray tube shown inFIG. 14. In such a flat-type color cathode ray tube, therefore, the angles θ at which electron beams7enter the slots2made in the shadow mask1, especially those slots2situated in the peripheral part of the shadow mask1, have come to be significantly great, and such a phenomenon that electron beams7that have passed through the through-holes11of the slots2are partially blocked by the sidewalls of the front-side openings12of the slots2occurs. For example, as shown inFIG. 12, although an electron beam7athat has passed through the lower part of the through-hole11of the slot2dsituated in the outer end part of the diagonal axis5emerges from the slot2dwithout striking the front-side opening12of this slot, electron beams7b,7cthat have passed through the upper part of the through-hole11of the slot2dare partially blocked by the sidewall of the front-side opening12of this slot at a site encircled by the dotted line8.

FIG. 13is a sectional view taken along line XIII-XIII inFIG. 12for explaining the above-described phenomenon. As shown in this figure, the front-side opening12of the slot2dis composed of sidewalls14,15, the backside opening13of the slot2dis composed of sidewalls16,17, and the through-hole11connects the front-side opening12and the backside opening13. As shown inFIG. 13, in such a slot2d, when electron beams7b,7cthat have passed through the upper part of the through-hole11pass through the front-side opening12, a part of these electron beams7b,7cstrikes the peripheral-side sidewall15of the front-side opening12and is thus blocked by this sidewall15at a site encircled by the dotted line8shown inFIG. 12. This phenomenon significantly occurs in the slots2dsituated, on the diagonal axes5passing through the center6of the mask body1a, in such positions that the angles at which electron beams enter the slots2dare 20 degrees or more, and causes the following problems: the electron beams7b,7cthat have passed through the slots2dget defective; the luminance is lowered; and the electron beams7cannot strike a fluorescent screen of a cathode ray tube to form thereon roughly rectangular beam spots in the desired size and shape.

SUMMARY OF THE INVENTION

The present invention was accomplished in the light of the aforementioned problems in the prior art. An object of the present invention is, therefore, to provide a shadow mask having a slot structure that can, as much as possible, prevent electron beams that have passed through the through-holes of slots from being blocked by the front-side openings of the slots even when the electron beams enter the slots at increased angles.

The present invention provides, as a first means of fulfilling the above-described object of the present invention, a shadow mask that comprises a mask body in which a large number of slots are made in the horizontal and vertical directions, and that allows electron beams to form roughly rectangular beam spots on a fluorescent screen of a cathode ray tube, each one of the slots made in the mask body having a roughly rectangular backside opening on the side on which electron beams are incident, a roughly rectangular front-side opening on the side from which electron beams emerge, and a through-hole that connects the backside opening and the front-side opening with each other, the mask body having a center point situated in the center of the mask body plane, a horizontal axis passing through the center of the mask body, horizontally extending along the mask body plane, a vertical axis passing through the center of the mask body, vertically extending along the mask body plane, and two diagonal axes passing through the center of the mask body, diagonally extending along the mask body plane, a horizontal bridge part extending in the horizontal direction being provided between the front-side openings of each two slots, of the multiple slots made in the mask body, that are arranged adjacently to each other in the vertical direction, and between each slot, of the multiple slots made in the mask body, that is situated at least on either of the diagonal axes of the mask body but in such a position that the angle at which electron beams enter the slot is 20 degrees or more and another slot that is arranged adjacently to the above slot in the vertical direction, a connecting part connecting the peripheral-side vertical outer edges of the front-side openings of these slots being provided so that it runs through the horizontal bridge part formed between the front-side openings of the slots, the connecting part being formed along and inward, to the center side, from the vertical line connecting the peripheral-side vertical outer edges of the front-side openings of the slots to be connected by the connecting part so that the relationship 0<D1<T is fulfilled, where T (μm) is the distance between the peripheral-side vertical outer edges of the front side openings and the peripheral-side vertical outer edges of the through-holes of the slots to be connected by the connecting part, and D1 (μm) is the horizontal width of the connecting part.

In the above-described first means of fulfilling the object of the present invention, it is preferable that a vertical bridge part extending in the vertical direction be provided between the front-side openings of each two slots, of the multiple slots made in the mask body, that are arranged adjacently to each other in the horizontal direction, and that the connecting part has an extended part extending in the horizontal direction toward the peripheral side so that the vertical bridge part recedes in the horizontal direction to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings of the slots to be connected by the connecting part. In this case, it is preferable that the connecting part fulfills the following relationship:
50 μm<[D1+D2]<[T+50] μm
where T and D1 are as defined above, and D2 (μm) is the horizontal width of the extended part.

Further, in the above-described first means of fulfilling the object of the invention, it is preferable that the shadow mask is a pressing-type shadow mask that is shaped by pressing.

The present invention provides, as a second means of fulfilling the above-described object of the present invention, a shadow mask that comprises a mask body in which a large number of slots are made in the horizontal and vertical directions, and that allows electron beams to form roughly rectangular beam spots on a fluorescent screen of a cathode ray tube, each one of the slots made in the mask body having a roughly rectangular backside opening made on the side on which electron beams are incident, a vertically-extending front-side opening in the shape of a groove made on the side from which electron beams emerge, and a through-hole that connects the backside opening and the front-side opening with each other, the mask body having a center point situated in the center of the mask body plane, a horizontal axis passing through the center of the mask body, horizontally extending along the mask body plane, a vertical axis passing through the center of the mask body, vertically extending along the mask body plane, and two diagonal axes passing through the center of the mask body, diagonally extending along the mask body plane, a vertical bridge part extending in the vertical direction being provided between the front-side openings of each two slots, of the multiple slots made in the mask body, that are arranged adjacently to each other in the horizontal direction, and between each slot, of the multiple slots made in the mask body, that is situated at least on either of the diagonal axes of the mask body but in such a position that the angle at which electron beams enter the slot is 20 degrees or more and another slot that is arranged adjacently to the above slot in the vertical direction, an extended part extending in the horizontal direction toward the peripheral side being provided so that the vertical bridge part recedes in the horizontal direction to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings of the slots.

In the above-described second means of fulfilling the object of the present invention, it is preferable that the extended part fulfills the following relationship:
0<D3<[T1−50] μm
where D3 (μm) is the horizontal width of the extended part, and T1 (μm) is the distance between the peripheral-side vertical outer edge of the front-side opening, and the center-side vertical outer edge of the front-side opening of the slot situated horizontally adjacently to the slot having the base front-side opening, on its peripheral side.

Further, in the above-described second means of fulfilling the object of the invention, it is preferable that the shadow mask is a tension-type shadow mask that is stretched in the vertical direction during use.

According to the shadow mask of the first means of fulfilling the object of the present invention, between each slot situated at least on either of the diagonal axes of the mask body but in such a position that the angle at which electron beams enter the slot is 20 degrees or more and another slot that is arranged adjacently to the above slot in the vertical direction, a connecting part connecting the peripheral-side vertical outer edges of the front-side openings of these slots is provided, and this connecting part is formed along and inward, to the center side, from the vertical line connecting the above-described vertical outer edges of the front-side openings so that the relationship 0<D1<T is fulfilled, where T (μm) is the distance between the peripheral-side vertical outer edges of the front side openings and the peripheral-side vertical outer edges of the through-holes of the slots to be connected by the connecting part, and D1 (μm) is the horizontal width of the connecting part. Therefore, the shadow mask can prevent, to the utmost, electron beams that have obliquely passed through the through-holes of the slots, from being partially blocked by the sidewalls of the slots at sites between the slots arranged adjacently to each other in the vertical direction. Consequently, the shadow mask can let the electron beams strike a fluorescent screen of a cathode ray tube to form thereon beam spots in the desired size and shape.

Further, according to the shadow mask of the first means of fulfilling the object of the invention, the horizontal width of the connecting part is smaller than the distance T between the peripheral-side vertical outer edges of the front-side openings and the peripheral-side vertical outer edges of the through-holes, so that a non-etched bridge part is present between the front-side openings (between the through-holes) of each two slots that are arranged adjacently to each other in the vertical direction. The shadow mask having such a structure can prevent, to the utmost, electron beams from being partially blocked, and, moreover, the mask body of such a shadow mask can maintain its strength. It is, therefore, possible to conduct pressing in the production process without causing any trouble, and produce a pressing-type shadow mask with certainty.

Furthermore, according to the shadow mask of the first means of fulfilling the object of the invention, when each connecting part is made so that it has an extended part extending in the horizontal direction toward the peripheral side so that the vertically-extending bridge part recedes in the horizontal direction to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings, the enlargement of the area through which electron beams that have obliquely passed through the through-holes of the slots can pass without being partially blocked is achieved not only for the sidewalls of the front-side openings at sites between two slots that are arranged adjacently to each other in the vertical direction, but also for the peripheral-side sidewalls of the front-side openings (the sidewalls of the bridge parts). Consequently, the shadow mask can let electron beams strike a fluorescent screen of a cathode ray tube to form thereon beam spots in the desired size and shape, while maintaining the luminance high. In this case, especially when the horizontal width of the connecting part with the extended part [D1+D2] (where D2 (μm) is the horizontal width of the extended part) is made so that the relationship 50 μm<[D1+D2]<[T+50] μm is fulfilled, it is possible to increase the area through which electron beams that have obliquely passed through the through-holes of the slots can pass without being partially blocked, while retaining the strength of the mask body.

According to the shadow mask of the second means of fulfilling the object of the present invention, between each slot situated at least on either of the diagonal axes of the mask body but in such a position that the angle at which electron beams enter the slot is 20 degrees or more and another slot that is arranged adjacently to the above slot in the vertical direction, an extended part extending in the horizontal direction toward the peripheral side is provided so that the vertical bridge part recedes in the horizontal direction to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings of the slots. Therefore, the shadow mask can prevent, to the utmost, electron beams that have obliquely passed through the through-holes of the slots. Consequently, the shadow mask can let the electron beams strike a fluorescent screen of a cathode ray tube to form thereon beam spots in the desired size and shape, while maintaining the luminance high.

The shadow masks according to the first and second means of fulfilling the object of the present invention have the above-described connecting parts and extended parts in the shape of grooves made by an etching process, so that they have increased surface areas. Consequently, these shadow masks can show the effect of reducing the occurrence of doming patterns (such a phenomenon that a shadow mask is deformed to be uneven in color due to heat generated by electron beams) and are, therefore, preferably used for flat-type cathode ray tubes of great deflection angle type, which are readily affected by doming patterns.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments and encompasses a variety of other embodiments that are within the technical concept of the present invention.

First Embodiment

First of all, the entire structure of a shadow mask according to the first embodiment of the present invention will be described with reference toFIG. 1. The shadow mask according to the first embodiment of the present invention is a pressing-type shadow mask that is shaped by pressing.

As shown inFIG. 1, a shadow mask1according to the first embodiment of the present invention comprises a mask body1athat is roughly rectangular in shape, and this mask body1ahas a large number of slots2(including slots2a,2b,2c, and2d) with roughly rectangular through-holes penetrating the mask body1ain the direction of thickness. The multiple slots2are arranged, in the above-described positional relationship, in the horizontal direction X and in the vertical direction Y on the mask body1aplane. When mounted in a cathode ray tube, such a shadow mask1acts not only to shield electromagnetic waves but also to let electron beams strike a fluorescent screen of the cathode ray tube to form thereon roughly rectangular beam spots. InFIG. 1, reference numeral6denotes a center (also referred to as a “center point”) that is the intersection of two diagonal axes5,5connecting the opposite corners of the mask body1a, extending along the mask body1aplane; reference numeral3, a horizontal axis passing through the center6, extending along the mask body1aplane; and reference numeral4, a vertical axis passing through the center6, extending along the mask body1aplane. Further, inFIG. 1, reference numeral2adenotes a slot situated at the center point6of the mask body1a(see character a); reference numeral2b, slots situated in the outer end parts of the vertical axis4(see characters b, b′); reference numeral2c, slots situated in the outer end parts of the horizontal axis3(see characters c, c′); and reference numeral2d, slots situated in the outer end parts of the diagonal axes5(see characters d, d′, e, e′). Reference numeral1adenotes a skirt part that surrounds the mask body1aand will be bent by pressing.

FIGS. 2 and 3are views showing a part of the structure of the slots that are made in the outer end part of the diagonal axis5of the shadow mask1shown inFIG. 1. As shown in these figures, the slots2are etched in a thin metal sheet made from Invar or the like, and through-holes31are made so that they connect front-side openings32and backside opening33that are etched in the metal sheet. The backside openings33of the slots2are made on the side on which electron beams7are incident, and the front-side openings32of the slots2are made on the side from which electron beams emerge. These backside openings33and front-side openings32are made roughly rectangular in shape. As shown inFIG. 4, the front-side opening32of each slot2is composed of sidewalls34,35, and is made to have a large area so that it does not obstruct the passage of electron beams that emerge from the slot2. Further, a narrow bridge part (horizontal bridge part)24remaining after the etching step is present between the front-side openings32of each two slots2,2that are arranged adjacently to each other in the vertical direction Y, that is, the slots2,2are arranged in the vertical direction Y with the bridge part24between them. Furthermore, a non-etched bridge part (vertical bride part)24′ remaining after the etching step is present between the front-side openings32of the slots2,2that are arranged adjacently to each other in the horizontal direction X.

The front-side openings32of the slots2vary in position relative to the through-hole31(the backside opening33), depending on the position of the slot2in the mask body1a. Namely, in the slot2asituated in the center6of the mask body1a, the front-side opening32is made so that the through-hole31(the backside opening33) is positioned in its center. On the other hand, the slots2csituated in the outer end parts of the horizontal axis3are made so that the position of the front-side opening32is gradually offset from the position of the through-hole31(the backside opening33) to the peripheral side as the position of the slot2cgets apart from the center6. Similarly, the slots2bsituated in the outer end parts of the vertical axis4are made so that the position of the front-side opening32is gradually offset from the position of the through-hole31(the backside opening33) to the peripheral side as the position of the slot2bgets apart from the center6.

The above description is applicable also to the slots2dthat are situated on or along the diagonal axes5,5; that is, these slots2dare made so that the position of the front-side opening32is gradually offset from the position of the through-hole31(the backside opening33) to the peripheral side as the position of the slot2dgets apart from the center6. For example, as shown in the plane view (FIG. 1) of the mask body1a, the slots2on the diagonal axis5extending toward the upper right are made so that the position of the front-side opening32is gradually offset from the position of the through-hole31(the backside opening33) to the right-hand side and upward (that is, to the upper right) as the position of the slot2gets apart from the center6toward the upper right, while that the position of the front-side opening32is gradually offset from the position of the through-hole31(the backside opening33) to the left-hand side and downward (that is, to the lower left) as the position of the slot2gets apart from the center6toward the lower left. The same is true for those slots2situated on the other diagonal axis5extending toward the lower right. The degree of the offset varies according to the angle θ at which electron beams7obliquely enter the slot2(seeFIG. 14), and is determined so that electron beams7that have passed through the through-holes31are not partially blocked by the sidewalls (see reference numeral35inFIG. 4) of the front-side openings32.

In the shadow mask1according to the first embodiment of the present invention, between each slot2d, of the multiple slots2made in the mask body1a, that is situated at least on either of the diagonal axes5of the mask body1abut in such a position that the angle θ at which electron beams7enter the slot2dis 20 degrees or more and another slot2dthat is situated adjacently to the above slot2din the vertical direction, a connecting part23connecting the peripheral-side vertical outer edges22a,22bof the front-side openings32,32of these slots2dis provided, as shown inFIGS. 2 and 3. This connecting part23is formed so that it runs through the bridge part24existing between the front-side openings32of each two slots2,2that are arranged adjacently to each other in the vertical direction Y.

The connecting part23is formed along and inward, to the center side, from the vertical line connecting the peripheral-side vertical outer edges22a,22bof the front-side openings32,32that are arranged adjacently to each other in the vertical direction, as shown inFIG. 3. InFIG. 3, character P denotes the slot center of the through-hole31of the slot2d; character Q, the intersection of the line horizontally drawn from the slot center P of the slot2dand the peripheral-side vertical outer edge of the front-side opening of the slot2d; and character R, the intersection of the line horizontally drawn from the slot center P of the slot2dand the peripheral-side vertical outer edge of the through-hole31. As shown in this figure, the connecting part23fulfills the relationship 0<D1<T, where T (μm) is the distance between the points Q and R, and D1 (μm) is the width, in the horizontal direction X, of the connecting part23. The horizontal width D1 (μm) of the connecting part23is the distance between the peripheral-side end S of the bridge part24present between the two slots2dthat are arranged adjacently to each other in the vertical direction and the peripheral-side vertical outer edge of the front-side opening32. This distance is given as the distance between the above-described peripheral-side end S and the intersection V of the line drawn in the horizontal direction from the peripheral-side end S and the peripheral-side vertical outer edge of the front-side opening32.

The connecting part23is formed by partially etching the peripheral part of the bridge part24remaining, after the etching step, between the front-side openings32of each two slots2dthat are arranged adjacently to each other in the vertical direction. The step of partially etching the bridge parts24is conducted simultaneously with the etching step for making the slots2.

Although the connecting parts23are formed in those slots2situated at least in such positions on the diagonal axes5that the angles θ at which electron beams7enter the slots2are 20 degrees or more, as mentioned above, they may be formed in the slots2situated in other positions. For example, the connecting parts23may be formed in the slots2situated in the vicinity of the above-described positions. Further, the connecting parts23may also be formed in the slots2situated outside the vertical lines passing through such points on the diagonal axes5that the angle θ at which electron beams enter the slots is 20 degrees, and, in an extreme case, the connecting parts23may be formed in all the slots2on the entire surface of the mask body1a. However, the most effective case is that the connecting parts23are formed in the slots2dthat are made in such positions that electron beams7pass through obliquely, as shown inFIG. 12. The reason why the connecting parts23are formed in the slots2situated in such positions that the angles θ at which electron beams enter the slots2are 20 degrees or more is that it is not necessary to form the connecting parts23in those slots2situated in such positions that the angles θ at which electron beams enter the slots2are less than 20 degrees.

As mentioned above, the width D1, in the horizontal direction X, of the connecting part23fulfills the relationship 0<D1<T. The shadow mask1having the connecting parts23fulfilling this relationship can prevent, to the utmost, electron beams7that have obliquely passed through the through-holes31of the slots2from being partially blocked by the sidewalls of the front-side openings32at sites between the slots2arranged adjacently to each other in the vertical direction. The reason why the width D1, in the horizontal direction X, of the connecting part23is made greater than 0 is that it is necessary to obtain the above-described actions and effects by forming at least the connecting parts23. On the other hand, the reason why the width D1, in the horizontal direction X, of the connecting part23is made smaller than the distance T is that it is necessary to make the non-etched bridge part24remain, with certainty, between the front-side openings32,32(between the through-holes31,31) of each two slots that are arranged adjacently to each other in the vertical direction Y. Since such bridge parts24are present even when the connecting parts23are formed, it is possible to retain the strength of the mask body1a. If the width D1, in the horizontal direction X, of the connecting part23is greater than the distance T, no bridge part24is present between the front-side openings32,32(between the through-holes31,31) of each two slots that are arranged adjacently to each other in the vertical direction Y. This is disadvantageous to a pressing-type shadow mask, which demands the maintenance of the strength of the mask body1a.

An example of the shadow mask1of pressing type is specifically as follows: the slots2are arranged in the horizontal direction X with a pitch P1 of approximately 700 μm and in the vertical direction Y with a pitch P2 of approximately 650 μm, and the distance T is approximately 150 to 250 μm. The slot pitch P1 gradually becomes greater as the position of the slot2gets apart, in the horizontal direction X, from the center to the peripheral side and the angle θ (seeFIG. 14) at which electron beams7enter the slot2becomes greater.

FIGS. 4 and 5are sectional views taken along line IV-IV and line V-V inFIG. 3, respectively. As is clear from these figures, the connecting part23with a width D1 is formed inward, to the center side, from the peripheral-side vertical outer edge Q of the front-side opening. The connecting part23has a cross section in the shape of a groove that connects two front-side openings32arranged in the vertical direction Y, and is made by partially etching the peripheral part of the bridge part24. Electron beams7can pass through the connecting part23without being blocked by the sidewall35of the front-side opening32.

Next, a modification of the shadow mask1according to the first embodiment shown inFIGS. 1 to 5will be described hereinafter with reference toFIGS. 6 to 8.

As shown inFIG. 6, in a shadow mask1′ of this embodiment, each connecting part23has an extended part41extending in the horizontal direction X toward the peripheral side so that a bridge part24′ extending in the vertical direction recedes in the horizontal direction X to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings of the slots connected by the connecting part23.

It is preferable that the width [D1+D2] (where D2 (μm) is the width, in the horizontal direction X, of the extended part41), in the horizontal direction X, of the connecting part23with the extended parts41fulfill the relationship50μm<[D1+D2]<[T+50] μm. The width [D1+D2], in the horizontal direction X, of the connecting part23is made more than 50 μm in order to prevent, as much as possible, electron beams7from being blocked by the side wall of the bridge part24′, by making the bottom of the connecting part23lower (i.e., by forming a deeper groove for the connecting part23). On the other hand, the width [D1+D2], in the horizontal direction X, of the connecting part23is made less than [T+50 μm] in order to maintain the molding characteristics. Therefore, when the width [D1+D2], in the horizontal direction X, of the connecting part23is less than 50 μm, the passage of electron beams7can be imperfect at the connecting part23, while when this width [D1+D2] is [T+50] μm or more, the shadow mask cannot have sufficiently high strength, which makes the molding characteristics and the results of drop test poor.

The extended part41with a width D2, extending in the horizontal direction X toward the peripheral side, is formed so that it extends from the peripheral-side vertical outer edge of the front-side opening, as shown inFIG. 6. The width D2 of the extended part41is the distance, in the horizontal direction X, between the peripheral-side vertical outer edge Q of the front-side opening and the peripheral-side outer edge W of the connecting part23, and is made approximately 50 to 150 μm. On the other hand, the extended part41is formed so that it has a vertical width Z of approximately 150-400 μm.

Thus, according to the shadow masks1,1′ of the first embodiment of the present invention, between each slot2dsituated at least on either of the diagonal axes5of the mask body1abut in such a position that the angle θ at which electron beams7enter the slot2dis 20 degrees or more and another slot2dthat is situated adjacently to the above slot2din the vertical direction Y, the connecting part23connecting the peripheral-side vertical outer edges22a,22bof the front-side openings32,32of these slots2dis provided; and this connecting part23is formed along and inward, to the center side, from the vertical line connecting the peripheral-side vertical outer edges22a,22bof the front side openings32,32of the slots2dto be connected by the connecting part23so that the relationship 0<D1<T is fulfilled, where T (μm) is the distance between the peripheral-side vertical outer edges of the front-side openings and the peripheral-side vertical outer edges of the through-holes of the slots2d, and D1 (μm) is the width, in the horizontal direction X, of the connecting part23. Therefore, the shadow masks1,1′ can prevent, to the utmost, electron beams7that have obliquely passed through the through-holes31of the slots2dfrom being partially blocked by the sidewalls of the front-side openings32at sites between the slots2dthat are arranged adjacently to each other in the vertical direction Y. Consequently, the shadow masks1,1′ can let the electron beams strike on a fluorescent screen of a cathode ray tube to form thereon beam spots in the desired size and shape, while maintaining the luminance high.

Further, according to the shadow masks1,1′ of the first embodiment of the present invention, since the width D1, in the horizontal direction X, of the connecting part23is smaller than the distance T between the peripheral-side vertical outer edges of the front-side openings32and the peripheral-side vertical outer edges of the through-holes31, a non-etched bridge part24is present between the front-side openings32,32(between the through-holes31,31) of each two slots2,2that are arranged adjacently to each other in the vertical direction Y. The shadow masks1,1′ having such a structure can therefore prevent, to the utmost, electron beams7from being partially blocked, and, moreover, the mask bodies1aof these shadow masks1,1′ can maintain their strength. It is, therefore, possible to conduct pressing in the production process without causing any trouble and produce a pressing-type shadow mask with certainty.

Furthermore, according to the shadow mask1′ of the first embodiment of the present invention, each connecting part23has the extended part41extending in the horizontal direction X toward the peripheral side so that the bridge part24′ extending in the vertical direction recedes in the horizontal direction X to the peripheral side relative to the peripheral-side vertical outer edges of the front-side openings of the slots connected by the connecting part23. Therefore, not only for the sidewalls of the front-side openings32at sites between two slots2d,2dthat are arranged adjacently to each other in the vertical direction Y, but also for the peripheral-side sidewalls of the front-side openings32(the sidewalls of the bridge parts24′), the enlargement of the area through which electron beams7that have obliquely passed through the through-holes31of the slots2dcan pass without being partially blocked can be achieved. Consequently, the shadow mask1′ can let the electron beams7strike a fluorescent screen of a cathode ray tube to form thereon electron beams in the desired size and shape, while maintaining the luminance high. In the shadow mask1′ according to the first embodiment of the present invention, especially the width, in the horizontal direction X, of the connecting part23having the extended part41with a horizontal width D2 (μm) is made to fulfill the relationship 50 μm<[D1+D2]<[T+50] μm, so that it is possible to increase the area through which electron beams7that have obliquely passed through the through-holes31of the slots2dcan pass without being partially blocked, while retaining the strength of the mask body1a.

Since the shadow masks1,1′ according to the first embodiment of the present invention have the above-described connecting parts23and extended parts41in the shape of grooves that are made by an etching process, they have increased surface areas. Consequently, the shadow masks1,1′ can show the effect of reducing the occurrence of doming patterns that takes place due to heat generated when electron beams strike the shadow mask, and are, therefore, preferably used for flat-type cathode ray tubes of great deflection angle type, which are readily affected by doming patterns.

Second Embodiment

Next, a shadow mask according to the second embodiment of the present invention will be described with reference toFIGS. 9,10A and10B. The shadow mask according to the second embodiment of the present invention is a so-called tension type shadow mask that is stretched in the vertical direction Y during use.

As shown inFIG. 9, the entire structure of a shadow mask50according to the second embodiment of the present invention is similar to that of the shadow mask1shown inFIG. 1. Namely, in the shadow mask50, a large number of slots2are arranged in the horizontal direction X and in the vertical direction Y on the mask body plane, each slot2having a roughly rectangular through-hole penetrating the mask body in the direction of thickness. The positional relationship between the slots2on the mask body plane is as mentioned previously, and the detailed description for this relationship will be omitted.

The slots2are etched in a thin metal sheet made from Invar or the like, as shown inFIG. 9, and through-holes51are made so that they connect front-side openings52and backside openings53that are made by an etching process. The backside openings53of the slots2are made on the side on which electron beams7are incident, and the front-side openings52of the slots2are made on the side from which the electron beams7emerge. Further, between the front-side openings52of each two slots, of the multiple slots, that are arranged adjacently to each other in the horizontal direction X, a non-etched bridge part (vertical bridge part)57remaining after the etching step is present. The backside openings53are made roughly rectangular. On the other hand, the front-side openings52are made in the shape of grooves extending in the vertical direction Y, and the peripheral-side vertical outer edges of the grooves correspond to the peripheral-side vertical outer edges55of the front-side openings52.

In such a shadow mask50according to the second embodiment, between each slot2d, of the multiple slots2made in the mask body, that is situated at least on either of the diagonal axes of the mask body but in such a position that the angle at which electron beams7enter the slot2dis 20 degrees or more and another slot2dthat is arranged adjacently to the above slot2din the vertical direction Y, an extended part54extending in the horizontal direction X toward the peripheral side is formed so that the bridge part57extending in the vertical direction Y recedes in the horizontal direction X to the peripheral side relative to the peripheral-side vertical outer edge55of the front-side opening52(the outer edge Q1 of the front-side opening52), as shown inFIGS. 9 and 10A. The extended parts54are formed simultaneously with the formation, by an etching process, of the front-side openings52in the shape of grooves extending in the vertical direction Y.

Although the extended parts54are formed in those slots2situated at least in such positions on the diagonal axes that the angles θ at which electron beams7enter the slots2are 20 degrees or more, as in the shadow mask1′ according to the aforementioned first embodiment, they may also be formed in the slots2situated in other positions. For example, the extended parts54may be formed in the slots2situated in the vicinity of the above-described positions. Further, the extended parts54may also be formed in the slots2situated outside the vertical lines passing through such points on the diagonal axes5that the angle θ at which electron beams enter the slots is 20 degrees, and, in an extreme case, the extended parts54may be formed in all the slots2on the entire surface of the mask body1a. However, the most effective case is that the extended parts54are formed in those slots2dthat are made in such positions that electron beams7obliquely pass through the slots2d, as shown inFIG. 12. The reason why the extended parts54are formed in the slots2situated in such positions that the angles θ at which electron beams enter the slots2are 20 degrees or more is that it is not necessary to form the extended parts54in those slots2situated in such positions that the angles θ at which electron beams enter the slots2are less than 20 degrees.

Further, it is preferable that the extended part54fulfills the relationship 0<D3<[T1−50] μm, where D3 is the width, in the horizontal direction X, of the extended part54, and T1 is the distance between the peripheral-side vertical outer edge Q1 of the front-side opening52, and the center-side vertical outer edge Q2 of the front-side opening52of the slot2that is situated horizontally adjacently to the slot having the base front-side opening52, on its peripheral side.

The shadow mask50having the extended parts54that fulfill the above-described relationship can prevent, to the utmost, electron beams7that have obliquely passed through the through-holes51of the slots2from being partially blocked by the sidewalls of the front-side openings52(see reference numeral56inFIG. 10B). The reason why the width D3, in the horizontal direction X, of the extended part54is made greater than 0 is that it is necessary to obtain the above-described actions and effects by forming at least the extended parts54. On the other hand, the reason why the width D3, in the horizontal direction X, of the extended part54is made less than [T1−50] μm is that the shadow mask50cannot have sufficiently high strength when the width D3 is made equal to or more than [T1−50] μm.

An example of the shadow mask50of tension type is specifically as follows: the slots2are arranged in the horizontal direction X with a pitch P3 of approximately 700 μm and in the vertical direction Y with a pitch P4 of approximately 650 μm, and the distance T1 is approximately 50 to 300 μm. The slot pitch P3 gradually becomes greater as the position of the slot2gets apart, in the horizontal direction X, from the center to the peripheral side and the angle θ (seeFIG. 14) at which electron beams7enter the slot2becomes greater. On the other hand, the extended parts54are formed so that they have a vertical width Z1 of approximately 150-400 μm.

FIG. 10Bis a sectional view taken along line XB-XB inFIG. 10A. As shown in this figure, the front-side openings52of the slots2are in the shape of grooves connecting the front-side openings52that are arranged adjacently to each other in the vertical direction Y. As is clear fromFIG. 10B, each extended part54has the width D3 that is the distance between the peripheral-side vertical outer edge Q1 of the front-side opening and the peripheral-side outer edge W1 of the front-side opening and is made so that it protrudes in the horizontal direction X toward the peripheral side. The extended parts54are formed by partially etching the peripheral parts of the bridge parts24. Electron beams7can pass through the extended parts54without being blocked by the sidewalls56of the front-side openings52.

Thus, according to the shadow mask50of the second embodiment of the present invention, between each slot2dsituated at least on either of the diagonal axes5of the mask body1abut in such a position that the angle θ at which electron beams7enter the slot2dis 20 degrees or more and another slot2dthat is arranged adjacently to the above slot2din the vertical direction Y, the extended part54extending in the horizontal direction X toward the peripheral side is formed so that the bridge part57extending in the vertical direction Y recedes in the horizontal direction X to the peripheral side relative to the peripheral-side vertical outer edges55(the outer edges Q1) of the front-side openings52of the slots2d. For this reason, the shadow mask50can prevent, to the utmost, electron beams7that have obliquely passed through the through-holes51of the slots2dfrom being partially blocked by the sidewalls of the front-side openings52. Consequently, the shadow mask50can let the electron beams7strike a fluorescent screen of a cathode ray tube to form thereon electron beams in the desired size and shape, while maintaining the luminance high.

Further, since the shadow mask50of the second embodiment of the present invention has the above-described extended parts54in the shape of grooves made by an etching process, it can show the effect of reducing the occurrence of doming patterns, like the shadow masks1,1′ according to the above-described first embodiment, and is, therefore, preferably used for a flat-type cathode ray tube of great deflection angle type, which is readily affected by doming patterns.

(Process for Producing Shadow Masks According to First and Second Embodiments)

A typical process for producing the shadow masks1,1′,50according to the above-described first and second embodiments will be described hereinafter. It is needless to say that the shadow masks of the present invention are not limited to ones produced by the following manufacturing process.

It is possible to produce the shadow masks1,1′,50according to the aforementioned first and second embodiments by the following conventionally known process.

Namely, to produce the shadow masks1,1′,50, a photo-etching process using a continuous in-line system is usually employed. Specifically, for example, an aqueous colloidal photoresist or the like is applied to both surfaces of a thin metal sheet and dried. Thereafter, a photomask with a pattern of the aforementioned front-side openings32,52is brought into close contact with the front surface of the metal sheet, and a photomask with a pattern of the above-described backside openings33,53is brought into close contact with the back surface of the metal sheet. This one is exposed to ultraviolet light emitted from a high mercury vapor pressure lamp or the like and then developed with water. The positional relationship between the photomask with a pattern of the front-side openings32,52and the photomask with a pattern of the backside openings33,53, and the shape of these photomasks are designed with consideration for the positional relationship between the front-side openings32,52and the backside openings33,53of the slots2in the resulting shadow masks1,1′,50, and the size of the openings.

The bare-metal portions of the thin metal sheet, surrounded by the resist film after development, are made into the above-described shapes by changing the etching speed. After conducting heat treatment, etc., the etching step is effected by spraying a ferric chloride solution over both surfaces of the metal sheet, for example.

Thereafter, the post-treatment steps such as rinsing with water and stripping are successively conducted. Thus, there are finally obtained the shadow masks1,1′,50according to the above-described first and second embodiments.