Panel for use in a cathode ray tube

FIELD OF THE INVENTION

The present invention relates to a cathode ray tube; and more particularly, to a cathode ray tube capable of effectively preventing the failure thereof by way of optimizing the location of a mold match line.

BACKGROUND OF THE INVENTION

As well known, a glass bulb in a cathode ray tube (CRT) used in a TV set or a computer monitor basically includes a panel for displaying picture images, a conical funnel sealed to the back of the panel and a cylindrical neck integrally connected to an apex portion of the conical funnel. The panel, the funnel and the neck are made of glass, wherein particularly the panel and the funnel are formed of predetermined dimensions and shapes by press forming a glass gob.

Referring to

FIG. 1

, there is illustrated a cross sectional view of a conventional glass bulb

10

. A panel

20

of the glass bulb

10

is provided with a face portion

21

whose inner surface is covered with an array of dots of fluorescent material (not shown) to display picture images; a skirt portion

23

extending backward from a perimeter of the face portion

21

and having a seal edge

22

on its back edge; and a blend round portion (or corner portion)

24

integrally joining the face portion

21

to the skirt portion

23

. A funnel

30

of the glass bulb

10

can be divided into a body portion

32

, i.e., a fore part thereof, having a seal edge

31

connected to the seal edge

22

of the skirt portion

23

; and a yoke portion

33

, i.e., a back part thereof, extending backward from the body portion

32

. And a neck

40

of the glass bulb

10

is connected to the yoke portion

33

of the funnel

30

. A tube axis

11

passes through the center of the face portion

21

and coincides with an axis of the neck

40

. Placed by way of the so-called “shrinkage fit” scheme around the outer periphery of the skirt portion

23

is a metallic implosion-proof band

50

, which strengthens the bulb

10

against tensile stress induced in the blend round portion

24

and the skirt portion

23

by evacuating the inner space of the bulb

10

, so that fragments of the glass can be prevented from flying away when the panel

20

is broken or exploded.

Referring to

FIG. 2

, there is illustrated a schematic cross-sectional view of a mold set

60

for forming the panel

20

. The mold set

60

is provided with a bottom mold

62

in which a cavity

61

is formed; a middle mold (or shell)

63

, for forming the skirt portion

23

and the seal edge

22

, which is fitted on top of the bottom mold

62

; and an upper mold

64

(or plunger) which presses a glass gob loaded in the cavity

61

of the bottom mold

62

to form the panel

20

. The upper mold

64

is connected to a press ram

65

, so that it can be lifted or lowered by the ram

65

so as to press the glass gob loaded in the cavity

61

of the bottom mold

62

to form the panel

20

. There exists a parting line

66

between the bottom mold

62

and the middle mold

63

. Therefore, when the panel

20

is formed in the mold set

60

as shown in

FIG. 1

, a mold match line

25

, which is a flash made by the parting line

66

, is formed on the outer periphery of the skirt portion

23

near the face portion

21

. The peripheral length of the mold match line

25

represents the maximum peripheral length of the panel

20

. And, in general, the position of the parting line

66

and thus the position of the mold match line

25

are set near the face portion

21

rather than the seal edge

22

in order to ease the extraction of the molded panel

20

from the bottom mold

62

.

Referring to

FIG. 3

, there is illustrated a schematic cross sectional view of the panel

20

of FIG.

1

. Formed on the outer periphery of the skirt portion

23

is a first tapered surface

26

, which extends from the mold match line

25

toward the seal edge

22

with an inward slant of a first slant angle θ

1

with respect to the tube axis

11

. And the first slant angle θ

1

is set less than 1.5° in order to prevent the band

50

from slipping. There is formed a second tapered surface

27

between the first tapered surface

26

and the seal edge

22

. The second tapered surface

27

has a second slant angle θ

2

ranging from, e.g., 3° to 4°. The border where the first tapered surface

26

meets with the second tapered surface

27

is referred to as a break line

28

, which is positioned away from a lower end of the implosion-proof band

50

.

When the explosion-proof band

50

is installed around the outer periphery of the skirt portion

23

of the glass bulb

10

after the glass bulb being evacuated, the implosion-proof band

50

expanded by heating is pushed from the side of the face portion

21

, and then is fitted around the skirt portion

23

. At this time, the mold match line

25

is brought into contact with the implosion-proof band

50

, which may incur scratches or/and cracks in the mold match line

25

. Therefore, in a case where the mold match line

25

is formed near the face portion

23

, an area of the inner surface of the implosion-band

50

sweeping or scrubbing the mold match line

25

is comparatively greater and thus, the frequency of the contacts between the mold match line

25

and the implosion-proof band

50

increases. Consequently, a greater number of cracks and scratches are formed in the mold match line

25

. Further, additional cracks are developed in the mold match line

25

by a compressive stress generated by the shrinkage of the expanded implosion-proof band

50

.

Such cracks formed in the mold match line

25

of the skirt portion

23

are one of the major causes for rendering the breakage or failure of the cathode ray tube occurring when the cathode ray tube is subject to a heat treatment in an annealing lehr for removing remaining stress therefrom, resulting in an increase of the production cost and the deterioration of production yield.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a panel for use in a cathode ray tube (CRT) capable of effectively preventing the failure of the CRT, such as implosion or breakage, during a heat treatment process of the CRT by optimizing the location of the mold match line.

It has been found by the inventors of the present invention that the cracks and scratches can be effectively prevented from forming in the mold match line by locating the mold match line such that the inner surface area of the implosion-proof band sweeping the mold match line is comparatively less and the mold match line is subject to the comparatively less compressive force produced by the implosion-proof band.

In accordance with a preferred embodiment of the present invention, there is provided a panel for use in a cathode ray tube, including: a face portion for displaying picture images, whose mean outer radius of curvature is equal to or greater than 10,000 mm; a skirt portion extending from a periphery of the face portion and having a seal edge sealed to a funnel; and a blend round portion connecting the face portion and the skirt portion, wherein a mold match line is formed on the skirt portion in a manner that a mold match line height H1 satisfies a following equation: 0<H

1

≦H×0.47 where an overall height H is a distance between a first plane passing through the seal edge and a second plane passing through a center of the face portion, and the mold match line height H

1

is a distance between the first plane and a third plane passing through the mold match line.

In accordance with another preferred embodiment of the present invention, there is provided a panel for use in a cathode ray tube, including: a face portion for displaying picture images, whose mean outer radius of curvature is less than 10,000 mm; a skirt portion extending from a periphery of the face portion and having a seal edge sealed to a funnel; and a blend round portion connecting the face portion and the skirt portion, wherein a mold match line is formed on the skirt portion in a manner that a mold match line height H

1

satisfies a following equation: 0<H

1

≦H×0.37 where an overall height H is a distance between a first plane passing through the seal edge and a second plane passing through a center of the face portion, and the mold match line height H

1

is a distance between the first plane and a third plane passing through the mold match line.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

FIG. 1

illustrates a cross sectional view of a conventional glass bulb;

FIG. 2

presents a schematic cross-sectional view of a mold set for forming a panel;

FIG. 3

depicts a schematic cross sectional view of a panel of

FIG. 1

;

FIG. 4

offers a schematic cross sectional view of a flat panel in accordance with preferred embodiments of the present invention; and

FIG. 5

sets forth a schematic cross sectional view of a spherical panel (or regular type panel) in accordance with preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Panels for use in a cathode ray tube in accordance with preferred embodiments of the present invention will now be described with reference to accompanying drawings. And like parts will be represented with like reference numerals.

Referring to

FIGS. 4 and 5

, there are illustrated schematic cross sectional views of a flat panel

20

′ and a spherical panel (or regular type panel)

20

″ in accordance with preferred embodiments of the present invention, respectively. These panels are classified into the flat panel

20

′ and the spherical panel

20

″ on the basis of their mean outer radius of curvature R, which is an average of radii of curvature of an outside contour

21

a

passing through a center of a face portion

21

in predetermined radial directions. In addition, the center of the face portion

21

is a point where an axis of a neck

40

(shown in

FIG. 1

) passes through and is an intersection of the diagonals of the face portion

21

. The reference notation H represents an overall height of the panel

20

′ or

20

″, i.e., a distance between a first imaginary plane passing through a seal edge

22

and a second imaginary plane passing through the center of the face portion

21

on the outer contour

21

a

and being parallel to the first plane; H

1

, a height of a mold match line

25

, i.e., a distance between the first plane and a third imaginary plane passing through the mold match line

25

whose outer peripheral length represents a maximum length of the panel

20

′ and

20

″; and H

2

, a height of a break line

28

, i.e., a distance between the first plane and a fourth imaginary plane passing through the break line

28

.

In general, the mean outer radius of curvature R of the flat panel

20

′ is equal to or greater than 10,000 mm, and the mean outer radius of curvature R of the spherical panel

20

″ is less than 10,000 mm. And it is widely known that the flat panel

20

′ is more advantageous than the spherical panel

20

″ in that it causes less image distortion and less eye fatigue, and has wide range of visibility.

The flat panel

20

′ shown in

FIG. 4

satisfies a design guideline, such as the outer radius of the curvature R being equal to or greater than 10,000 mm and the mold match line height H

1

satisfying the following equation:

0<H

1

≦H×0.47 Eq. 1

In other words, the mold match line

25

is formed at or below a position whose height from the seal edge

22

is 47% of the overall height H.

Experiment 1

In Tables 1 and 2, band tensions measured at predetermined points of implosion-proof bands along its widthwise (or axial) direction are listed, wherein the implosion-proof bands were placed around glass panels for televisions of 29 and 32-inch models, respectively, each having a useful screen area of an aspect ratio of 4:3.

As shown in

FIG. 4

, Tables 1 and 2, a band zone Z

0

represents a reference height, i.e., the seal edge

22

; a band zone Z

1

, the height of the lower edge of the implosion-proof band

50

near the seal edge

22

; and a band zone Z

8

, the height of the upper edge of the explosion-proof band

50

near the face portion

21

. In addition, band zones Z

2

to Z

7

correspond to points arranged in the implosion-proof band

50

along the width thereof with predetermined distances therebetween. In Tables 1 and 2, ratios (%) represent percentages of the mold match line height H

1

, the break line height H

2

and heights of the band zones Z

1

to Z

8

to the overall height H of the panel

20

, respectively, wherein the heights of the band zones Z

1

to Z

8

are distances between the first plane and planes passing through the band zones Z

1

to Z

8

and being parallel with the first plane, respectively, and other height hereinafter will also be measured likewise.

TABLE 1

Flat Panel for

Band Tension

29-inch model

Height (mm)

Ratio (%)

(Mpa)

H

97.6

100

—

H1

69.6

71

—

H2

31.6

32

—

Band Zones

Z1

33.1

34

48.4

Z2

45.0

46

91.8

Z3

47.0

48

167.1

Z4

56.1

57

129.8

Z5

63.8

65

111.9

Z6

69.8

72

207.9

Z7

78.3

80

218.1

Z8

86.9

89

132.3

As indicated in Table 1, a lower edge of the implosion-proof band was positioned 33.1 mm high from the seal edge and 1.5 mm high from break line. Further, the upper edge of the implosion-proof band was positioned 86.9 mm high from the seal edge and 17.3 mm high from the mold match line.

The band tension at Z

3

of 167.1 MPa was dropped sharply to the band tension at Z

2

of 91.8 MPa, and the difference therebetween was as large as 75.3 MPa. From this and Table 1, it can be inferred that the band tension declines as the height from the seal edge is lowered below the band zone Z

2

whose ratio (%) of the height to the overall height H is 46% and hence, satisfies Eq. 1. Moreover, the height of a middle point between the band zones Z

2

and Z

3

, whose ratio of the height to the overall height H is 47%, satisfies Eq. 1. Accordingly, by forming the mold match line below the middle point, the mold match line will be subject to a comparatively less compressive force as a result of the band tension, and hence a comparatively less number of cracks will be formed therein. Consequently, breakage of glass bulbs made of panels whose mold match lines are formed below the middle point is reduced.

Further, although skirt portion's configuration of panels whose match mold line is formed at or below the middle point is different from that of the panel used in this Experiment 1, the difference can be neglected since the first slant angle θ

1

is small and therefore, the distribution of the band tension of the implosion-proof band used in such panels is similar to that of the panel used in this Experiment 1.

The heights of the band zones Z

3

to Z

8

do not satisfy Eq. 1. And if the mold match line is formed at one position between the band zones Z

3

and Z

8

, it will be subject to a greater compressive force as a result of the greater band tension, thereby having a higher potential to be scratched and/or crack during and after the installation of the implosion-proof band. Consequently, the glass bulb made of such panel also will have a higher potential to be broken.

TABLE 2

Flat panel for

band tension

32-inch model

height (mm)

ratio (%)

(Mpa)

H

113.0

100

—

H1

82.5

73

—

H2

33.0

29

—

Band Zones

Z1

34.5

31

94.7

Z2

49.0

43

72.9

Z3

54.1

48

218.8

Z4

60.9

54

132.0

Z5

69.7

62

115.7

Z6

82.8

73

309.6

Z7

91.3

81

231.0

Z8

99.8

88

100.0

As indicated in Table 2, a lower edge of the implosion-proof band surrounding a flat panel for 32-inch model was positioned 34.5 mm high from the seal edge and the upper end thereof was positioned 99.8 mm high from the seal edge. The band tension at the band zone

3

of 218.8 MPa was dropped sharply to the band tension at the band zone

2

of 72.9 MPa, and the difference therebetween was as large as 145.9 MPa. From this and Table 2, it can be inferred that band tension declines as a measuring height is lowered below the band zone Z

2

whose ratio of the height to the overall height H is 43% and hence, satisfies Eq. 1. Accordingly, by forming the mold match line below the middle point, the mold match line will be subject to a comparatively less compressive force as a result of the band tension, and hence a comparatively less number of cracks will be formed therein. Consequently, breakage of glass bulbs made of panels whose mold match lines are formed below the middle point will be reduced.

The band zones Z

3

to Z

8

do not satisfy Eq. 1. And if the mold match line is formed at one position between the band zones Z

3

and Z

8

, it will be subject to a greater compressive force as a result of the greater band tension and therefore, comparatively more scratches and/or cracks will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z

3

and Z

8

also will have a higher potential to be broken.

Further, in Tables 1 and 2, although band stress of the band zone

8

was close to that of the position whose ratio (%) was 47%, it was so near to the face portion that the mold match line could not be formed thereon. And although band stresses of the band zones Z

4

and Z

5

were also close to that of the position whose ratio was 47%, more cracks and/or scratches were formed during the implosion-proof band installation since the face portion was first entered into the implosion-proof band. In other words, the area of the implosion-proof band sweeping or scrubbing the mold match line was comparatively greater and thus the frequency of contacts between the mold match line and the inner surface of the implosion-proof band.

The spherical panel

20

″ shown in

FIG. 5

satisfies design guideline, such as outer radius of curvature R being less than 10,000 mm and the height of the mold match line H

1

satisfying the following Eq. 2:

0<H

1

≦H×0.37 Eq. 2

In other words, the mold match line is formed on the spherical panel in a manner that the ratio of the mold match line height H

1

to the overall height H is equal to or less than 37%.

Experiment 2

Two spherical glass panels for televisions of 28 and 29-inch models, each having a useful screen area of an aspect ratio of 4:3, were prepared. Then, explosion-proof bands were placed around the outer periphery of the skirt portions thereof. Afterwards, band tensions were measured at band zones Z

1

to Z

8

and listed in Tables 3 and 4. The ratios and heights in Tables 3 and 4 were defined with a same method as in Experiment 1, and therefore, the explanation therefor will be omitted for simplicity.

TABLE 3

Spherical Panel

Band Tension

for 32-inch model

Height (mm)

Ratio (%)

(Mpa)

H

99.6

100

—

H1

53.1

53

—

H2

25.1

25

—

Band Zones

Z1

15.0

15

110.5

Z2

36.8

37

150.2

Z3

40.0

40

364.5

Z4

44.5

45

394.1

Z5

48.5

49

387.3

Z6

51.0

51

336.3

Z7

55.0

55

250.0

Z8

60.0

60

157.6

As indicated in Table 3, a lower edge of the explosion-proof band placed around the glass panel for TV of 28-inch model was positioned 15 mm high from the seal edge and an upper edge of the explosion-proof band was positioned 60 mm high from the seal edge. The band tension at the band zone

3

of 364.5 MPa was dropped to the band tension at the band zone

2

of 150.2, and the difference therebetween was as large as 214.3 MPa. From this and Table 3, it can be inferred that band tension declines phenomenally below the band zone Z

2

whose the ratio of the height to the overall height H is 37%, thereby satisfying Eq. 2.

Accordingly, by forming the mold match line below the band zone Z

2

, the mold match line will be subject to a less compressive force as a result of the less band tension, hence comparatively less number of cracks will be formed therein. Consequently, breakage of the bulb made of a panel whose mold match line is formed below the middle point can be reduced.

The band zones Z

3

to Z

8

do not satisfy Eq. 2. And if the mold match line is formed at one position between the band zones Z

3

and Z

8

, it will be subject to a comparatively greater compressive force as a result of the comparatively greater band tension and therefore, more cracks and scratches will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z

3

and Z

8

will have a higher potential to be broken.

Further, although the band tension of the band zone Z

8

was close to that of the band zone Z

2

whose ratio was 37%, the band zone Z

8

was so near to the face portion that the mold match line was formed thereon.

TABLE 4

Spherical Panel

Band Tension

for 32-inch model

Height (mm)

Ratio (%)

(Mpa)

H

113.7

100

—

H1

50.7

45

—

H2

25.7

23

—

Band Zones

Z1

10.0

9

100.6

Z2

20.0

18

125.5

Z3

41.0

36

150.8

Z4

43.0

38

322.9

Z5

45.0

40

260.9

Z6

48.7

43

214.8

Z7

52.6

46

150.0

Z8

55.3

49

110.0

As indicated in Table 4, a lower edge of the implosion-proof band surrounding the spherical glass panel for a TV of 32-inch model was positioned 10 mm high from the seal edge and an upper edge thereof was positioned 55.3 mm high from the seal edge. The band tension at the band zone

4

of 322.9 MPa was sharply dropped to the band tension at the band zone

3

of 150.8 MPa, and the difference therebetween was as large as 172.1 MPa. From this and Table 4, it can be inferred that band tension declines phenomenally as a measuring height is reduced below the band zone Z

3

whose ratio of the height to the overall height H is 36%, thereby satisfying Eq. 2. Accordingly, by forming the mold match line at or below the band zone Z

3

, the mold match line will be subject to a comparatively less compressive force as a result of the comparatively less band tension, and hence comparatively less number of cracks will be formed therein. Consequently, breakage of the bulb made of a panel whose mold match line is formed below the band zone Z

3

can be reduced.

The band zones Z

4

to Z

8

do not satisfy Eq. 2. And if the mold match line is formed at one position between the band zones Z

4

and Z

8

, it will be subject to a comparatively greater compressive force as a result of the comparatively greater band tension and therefore, comparatively more cracks and scratches will be formed therein during and after the installation of the implosion-proof band. Consequently, the glass bulb made of a panel whose mold match line is formed between the band zones Z

4

and Z

8

also will have a higher potential to be broken.

Further, in Table 4, although the band stresses of the band zone Z

7

and Z

8

were close to that of the band zone Z

3

, the band zones Z

7

and Z

8

were so near to the face portion that the mold match line could not be formed therein.

As described above, if the mold match line is formed at a position near the seal edge where the band tension is comparatively less, the mold match line will be subject to the comparatively less compressive force and will not contact with the implosion-proof band as many times as the mold match line formed near the face portion during the implosion-proof band installation. Accordingly, the formation of scratches and cracks in the mold match line of the flat or spherical glass panels for a cathode ray tube in accordance with the preferred embodiments of the present invention can be effectively reduced, and therefore, the glass bulb made of the panel of the present invention will have a less potential to be broken in the annealing lehr or other process, resulting in an improvement in productivity thereof and reduction in the economic loss.

While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Panel for use in a cathode ray tube

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (1)