U.S. patent application number 11/155892 was filed with the patent office on 2006-01-05 for plasma display panel.
This patent application is currently assigned to FUJITSU HITACHI PLASMA DISPLAY LIMITED. Invention is credited to Ryouichi Mura, Minahiro Nonomura, Masayuki Seto, Yoshitaka Ukai, Naoto Yanagihara.
Application Number | 20060001373 11/155892 |
Document ID | / |
Family ID | 35513179 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060001373 |
Kind Code |
A1 |
Nonomura; Minahiro ; et
al. |
January 5, 2006 |
Plasma display panel
Abstract
A plasma display panel includes a front substrate and a rear
substrate that are opposed to each other with a discharge gas space
between them, and a sealing material for sealing the front
substrate and the rear substrate at their peripheral portions. The
sealing material contains an appropriate quantity of spacers so
that a thickness of the plasma display panel is uniform along the
entire perimeter of the sealing portion between the front substrate
and the rear substrate. The sealing material contains non-porous
beads as the spacers, preferably at a ratio within the range of
0.05-2.0 wt %.
Inventors: |
Nonomura; Minahiro;
(Kawasaki, JP) ; Yanagihara; Naoto; (Kawasaki,
JP) ; Seto; Masayuki; (Kawasaki, JP) ; Ukai;
Yoshitaka; (Kawasaki, JP) ; Mura; Ryouichi;
(Kawasaki, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
FUJITSU HITACHI PLASMA DISPLAY
LIMITED
Kawasaki
JP
|
Family ID: |
35513179 |
Appl. No.: |
11/155892 |
Filed: |
June 20, 2005 |
Current U.S.
Class: |
313/582 |
Current CPC
Class: |
H01J 11/48 20130101;
H01J 11/12 20130101; H01J 9/261 20130101 |
Class at
Publication: |
313/582 |
International
Class: |
H01J 17/49 20060101
H01J017/49 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2004 |
JP |
2004-194227 |
Dec 22, 2004 |
JP |
2004-372343 |
Claims
1. A plasma display panel comprising: a front substrate and a rear
substrate that are opposed to each other with a discharge gas space
between them; a structural member for defining a thickness of the
discharge gas space in a screen area; and a sealing material for
sealing the front substrate and the rear substrate at their
peripheral portions, wherein the sealing material contains
non-porous bead spacers.
2. A plasma display panel comprising: a front substrate and a rear
substrate that are opposed to each other with a discharge gas space
between them; a structural member for defining a thickness of the
discharge gas space in a screen area; and a sealing material for
sealing the front substrate and the rear substrate at their
peripheral portions, the sealing material containing spacers that
define a distance between the front substrate and the rear
substrate, wherein the spacers are non-porous bead spacers
contained in the sealing material at a ratio within the range of
0.05-2.0 wt %.
3. The plasma display panel according to claim 2, wherein the
sealing material is a burned material of low melting point glass
paste, and the bead spacers are non-porous glass beads having a
softening point higher than that of the sealing material.
4. The plasma display panel according to claim 3, wherein the
sealing material has strength as being not broken down even by a
pressure of 0.70 kgf/cm.sup.2 that is applied to the front
substrate or the rear substrate so as to compress the sealing
material.
5. The plasma display panel according to claim 4, wherein the
sealing material has a frame-like shape with a width within the
range of 8-12 millimeters.
6. The plasma display panel according to claim 1, wherein grain
sizes of the bead spacers contained in the sealing material have
values within the range of -1.5 times a design value of a distance
between the front substrate and the rear substrate.
7. The plasma display panel according to claim 2, wherein grain
sizes of the bead spacers contained in the sealing material have
values within the range of -1.5 times a design value of the
distance between the front substrate and the rear substrate.
8. A method for manufacturing a plasma display panel including a
front substrate and a rear substrate that are opposed to each other
with a discharge gas space between them, and a structural member
for defining a thickness of the discharge gas space in a screen
area, the method comprising the steps of: making the front
substrate and the rear substrate individually; applying low melting
point glass paste containing non-porous bead spacers at a ratio
within the range of 0.05-2.0 wt % to glass frit onto a peripheral
portion of the front substrate or the rear substrate so that the
low melting point glass paste forms a frame-like shape having a
height greater than that of the structural member; assembling the
front substrate and the rear substrate in face-to-face relation
with each other; and burning the low melting point glass paste
while vacuuming a discharge gas space between the front substrate
and the rear substrate so as to seal the front substrate and the
rear substrate at their peripheral portions.
9. The method according to claim 8, wherein the low melting point
glass paste is applied so that it forms a frame-like shape having a
height greater than that of the structural member and a width
within the range of 3.0-5.0 millimeters.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plasma display panel
(PDP), which is characterized in a structure of a sealing material
that is used for sealing a front substrate and a rear
substrate.
[0003] 2. Description of the Prior Art A plasma display panel
includes a front substrate and a rear substrate, which are both
larger than a screen. The front substrate and the rear substrate
are opposed to each other and sealed with a sealing material that
is arranged at the outer portion of the screen and has a frame-like
shape so that a closed discharge gas space is defined by them. The
front substrate and the rear substrate are glass substrates, while
the sealing material is a burned material of low melting point
glass.
[0004] Among plasma display panels having such a structure, a
surface discharge type plasma display panel for use as a color
display includes partitions that prevent discharge interference
between neighboring cells. The partitions divide the discharge gas
space into plural spaces and define a thickness of a portion of the
discharge gas space corresponding to the screen. Arrangement
patterns of the partitions include a stripe pattern and a mesh
pattern. According to the former arrangement pattern, the discharge
gas space is divided into plural columns of a matrix display.
According to the latter pattern, the discharge gas space is divided
into cells of plural columns and plural rows.
[0005] In a plasma display panel with partitions, there can be
generated a slight curvature of either the front substrate or the
rear substrate or the both of them after they are sealed. For
example, in a burning process for melting and hardening the sealing
material or in a vacuuming process for cleaning the inside prior to
filling discharge gas, the pair of glass substrates can be curved
by actions of temperature rise of the glass substrates and pressure
reduction inside so that the sealing material is compressed. As a
result, a thickness of the plasma display panel becomes smaller
than a design value at the sealing portion between the front
substrate and the rear substrate, while it becomes larger than the
design value at the peripheral portion of the screen inside the
sealing portion. There can be generated a gap of approximately 10
microns between the partition and the surface of the substrate that
are to contact each other inside the portion where the thickness of
the plasma display panel becomes larger than the design value. A
region with such malcontact may appear in a frame shape along the
edge of the screen with a width of approximately a few centimeters.
Hereinafter, the decrease of the thickness of the plasma display
panel at the sealing portion is referred to as "subsidence".
[0006] The malcontact between the front substrate and the rear
substrate inside the sealing portion may cause an abnormal noise
during a display operation. When a high frequency drive voltage is
applied for a display, periodical electrostatic attraction may
vibrate the glass substrates locally, so that a low level of noise
at an audible frequency is generated. This noise may deteriorate
quality of display operation.
[0007] Regarding a method of preventing the curvature of the front
substrate and the rear substrate, Japanese unexamined patent
publication No. 2001-236896 discloses a sealing material that
contains glass beads as spacers. The spacers have substantially the
same size of diameter as a height of the partition, so that the gap
between the front substrate and the rear substrate at the sealing
portion can be maintained at a desired value.
[0008] It is necessary that the sealing material contains a
sufficient quantity of spacers between the front substrate and the
rear substrate along the entire perimeter of the sealing portion in
order to make the thickness of the plasma display panel uniform. If
a quantity of the spacers is insufficient, the spacers may be
broken by an excessive pressure per spacer.
[0009] However, if a quantity of glass beads contained as the
spacers in the sealing material is increased, viscosity of glass
paste that is the sealing material before being burned increases.
As a result, productivity in applying the glass paste may be
lowered, and height as well as width of a layer of the applied
paste tends to be nonuniform. In particular, if glass beads having
a broad distribution of granularity are used, viscosity of the
glass paste may increase largely.
[0010] It is desirable to use glass beads having uniform grain size
without smaller grains that do not work as spacers in order to
prevent the increase in viscosity. However, a classification work
for obtaining glass beads of a sharp distribution of granularity
causes increase of cost of the glass beads. It is difficult to
remove smaller particles compared with removal of larger particles
than a desired size.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to obtain a uniform
thickness of a plasma display panel along the entire perimeter of a
sealing portion between the front substrate and the rear substrate
by adding an appropriate quantity of spacers into a sealing
material for sealing the front substrate and the rear
substrate.
[0012] According to the present invention, a sealing material
containing non-porous bead spacers is used for sealing the front
substrate and the rear substrate that are opposed to each other
defining a discharge gas space. A "non-porous bead" in the present
invention means a bead having a small value of specific surface
area such that the viscosity of the sealing paste to be the sealing
material is not altered substantially when the beads are added into
the sealing material.
[0013] According to the present invention, the thickness of the
plasma display panel can be made uniform along the entire perimeter
of the sealing portion between the front substrate and the rear
substrate, so that an appropriate contact between the front
substrate and the rear substrate can be obtained along the entire
perimeter inside the sealing portion. Thus, generation of a noise
due to the malcontact can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a general structure of a plasma display
panel.
[0015] FIG. 2 is a schematic diagram of an electrode matrix.
[0016] FIG. 3 shows a cross sectional structure of the plasma
display panel.
[0017] FIG. 4 shows a cross sectional structure of the plasma
display panel at its peripheral portion with elements of a front
substrate and a rear substrate.
[0018] FIG. 5 shows an example of a method for applying sealing
paste.
[0019] FIG. 6 is a graph showing the relationship between content
of bead spacers and viscosity of seal paste.
[0020] FIG. 7 is a graph showing a result of a differential thermal
analysis of the glass beads.
[0021] FIG. 8 is a graph showing an effect of bead spacers.
[0022] FIG. 9 shows positions of measuring thickness values.
[0023] FIG. 10 shows positions of measuring thickness values along
the perimeter of the plasma display panel.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Hereinafter, the present invention will be explained more in
detail with reference to embodiments and drawings.
[0025] FIG. 1 shows a general structure of a plasma display panel.
The plasma display panel 1 includes a front substrate 10 and a rear
substrate 20, which constitutes a screen 60 made of plural
discharge cells arranged in a matrix. Each of the front substrate
10 and the rear substrate 20 has a structural body including a
glass substrate that is larger than the screen 60 and has a
thickness of approximately 3 millimeters, on which electrodes and
other elements are arranged. The front substrate 10 and the rear
substrate 20 are overlapped so as to be opposed to each other and
are sealed at their peripheral portions surrounding their
overlapped portions by using a sealing material 35 that has a
frame-like shape in a plan view. As shown in FIG. 1, the front
substrate 10 extends from right and left sides of the rear
substrate 20 by approximately 5 millimeters, while the rear
substrate 20 extends from upper and lower sides of the front
substrate 10 by approximately 5 millimeters. These extending ends
of the front substrate 10 and the rear substrate 20 are connected
to flexible printed circuit boards, which are connected to a drive
unit electrically. For example, if a size of the screen 60 is 41
inches diagonally, the plasma display panel 1 has dimensions of
approximately 994.times.585 millimeters.
[0026] FIG. 2 is a schematic diagram of an electrode matrix. There
are disposed display electrodes X and Y arranged in parallel on the
screen 60 for generating display discharge, and address electrodes
A are arranged so as to cross the display electrodes X and Y. The
display electrodes X and the display electrodes Y are arranged
alternately in the order like X, Y, X, Y, . . . , X, Y and X and
neighboring display electrodes X and Y constitute a pair of
electrodes. Each of the display electrodes X and Y has a lamination
structure of a transparent conductive film and a metal film that is
a bus conductor.
[0027] FIG. 3 shows a cross sectional structure of the plasma
display panel. The front substrate 10, the rear substrate 20 and
the sealing material 35 define a sealed inner space 30, which is
filled with discharge gas that is a mixture of neon and xenon.
[0028] FIG. 4 shows a cross sectional structure of the plasma
display panel at its peripheral portion with elements of the front
substrate and the rear substrate. For easy understanding, elements
between the glass substrates are drawn with their thickness
enlarged in FIG. 4.
[0029] The front substrate 10 includes a glass substrate 11, a
transparent conductive film 41 and a metal film 42 that are
patterned to constitute display electrodes, a dielectric layer 17
on which wall charge is accumulated, and a protection film 18 made
of magnesia. The metal film 42 is led to the outside of the sealing
material 35.
[0030] The rear substrate 20 includes a glass substrate 21, address
electrodes A that are column electrodes, a low melting point glass
layer 24, a plurality of partitions 29 that are structural members
according to the present invention, and fluorescent material layers
28R, 28G and 28B for a color display. The exemplified partitions 29
are arranged in a stripe pattern.
[0031] Each of the partitions 29 has a function of preventing
discharge interference between neighboring columns as well as a
function as a spacer. Namely, height (or depth) of the inner space
30 in the screen 60 is defined by the partitions 29, and it is
substantially the same as the height H of the partitions 29. The
height H is optimized in accordance with a cell size, and it is set
to a value within the range of 130-200 microns as a typical
value.
[0032] A distinctive element of the plasma display panel 1 is the
sealing material 35 for unifying the front substrate 10 and the
rear substrate 20. The sealing material 35 is a burned material of
low melting point glass paste, which contains a sufficient quantity
of bead spacers 71, 72, 73. . . . for preventing subsidence of the
plasma display panel 1 and for equalizing thickness at the
peripheral portion. The sealing material 35 has a width W within a
range of approximately 8-12 millimeters. A distance between the
inner end of the sealing material 35 and the partition 29 is
approximately 20 millimeters.
[0033] FIG. 5 shows an example of a method for applying sealing
paste. In a manufacturing process of the plasma display panel 1,
the front substrate 10 and the rear substrate 20 are made
individually. Then, the low melting point glass paste for sealing
(hereinafter referred to as seal paste) that contains bead spacers
is applied onto each or both of the front substrate 10 and the rear
substrate 20. In the example shown in FIG. 5, a dispenser is used
for applying seal paste 35A onto two rear substrates 20 that are
manufactured at a time on a mother glass 210 that is a material of
the glass substrate. The seal paste 35A is applied by moving two
nozzles 86 simultaneously with respect to the rear substrate 20 so
that each of them moves along a rectangular track. For example, the
nozzles 86 having inner diameter of 4 millimeters are used, and the
seal paste 35A having viscosity within the range of 40-50 Pa.s is
applied at movement speed of 100 mm/s and under discharge pressure
of 3.0 kgf/cm.sup.2, so as to obtain a paste layer having a width
within the range of 3-5 millimeters and a thickness within the
range of 450-550 microns.
[0034] After the seal paste 35A is applied, it is dried and burned
temporarily. After that, the mother glass 210 is divided into two
rear substrates 20. Then, one rear substrate 20 and one front
substrate 10 are overlapped with registration and are fixed
temporarily using clips at plural portions of the rim, which are
carried into a furnace. Then, the inner space defined by the front
substrate 10, the rear substrate 20 and the rectangular seal paste
layer is vacuumed through an air hole that is formed in the rear
substrate 20 and a tip tube communicating with the air hole. Thus,
the seal paste layer is burned while a pressure in the inner space
is reduced. The burning temperature is set to a temperature close
to a softening point of the glass frit.
[0035] In the burning process, the front substrate 10 and the rear
substrate 20 are attracted to each other due to the decreasing
pressure inside. In the area of the screen the front substrate 10
contacts the upper surface of the partitions of the rear substrate
20, while in the area of the sealing portion the distance between
the front substrate 10 and the rear substrate 20 decreases as the
sealing material is softened. As a result, the width of the seal
paste layer is enlarged along the surface of the substrate from
approximately 3-5 millimeters to approximately 8-12 millimeters. On
this occasion, the bead spacers contained in the seal paste layer
prevent the subsidence, i.e., they prevent the gap between the
front substrate 10 and the rear substrate 20 from becoming smaller
than the height of the partition 29.
[0036] When the temperature inside the furnace is decreased so that
the sealing material is hardened, the front substrate 10 and the
rear substrate 20 are sealed completely. After that, the discharge
gas is filled in the space, and the tip tube is melted so that the
discharge gas space 30 is sealed completely.
[0037] Hereinafter, composition of the sealing material 35 will be
explained in more detail.
[0038] As the bead spacers 71, 72, 73, . . . , glass beads are
selected, which contain Na.sub.2O, CaO and SiO.sub.2 as major
components and have a center grain size of 135 microns (made by
Nippon Electric Glass Co., Ltd., product number GS/135LR, softening
point 730.degree. C.). The grain size of 135 microns is equal to
the design value d of the thickness of the sealing material 35 in
this embodiment. These glass beads satisfy the following conditions
(1), (2) and (3).
[0039] (1) The softening point of them is higher than that of the
glass frit (the sealing material) of the major component of the low
melting point glass paste. Therefore the shape of them is
maintained when the sealing material is burned.
[0040] (2) Thermal expansion coefficient of them is close to that
of the sealing material.
[0041] (3) Increase of viscosity of the seal paste is very
little.
[0042] As the condition (2) is satisfied, generation of crack due
to the thermal stress can be prevented as much as possible. The
thermal expansion coefficient of the above-mentioned glass beads is
80.times.10.sup.-7/.degree. C., which is close to the thermal
expansion coefficient 74.times.10.sup.-7/.degree. C. of the sealing
material that is used in this example.
[0043] The condition (3) is important for obtaining a good sealing
structure of the plasma display panel without reducing
productivity. If the increase of the viscosity due to addition of
the glass beads is little, the seal paste can be applied in the
same manner as the case without glass beads so that workability in
applying the seal paste is not impaired. In addition, a sufficient
quantity of glass beads for obtaining sufficient mechanical
strength can be added into the seal paste. Furthermore, if the
increase of the viscosity is little, it is not necessary to remove
particles having sizes smaller than the desired value so as to
suppress the increase of the viscosity. Namely, tolerance of the
distribution of granularity of the glass beads can be enlarged, so
that a cost necessary for the classification can be eliminated.
[0044] FIG. 6 is a graph showing the relationship between content
of bead spacers and viscosity of seal paste. As viscosity measuring
means a rotating viscometer was used, and its rotation speed was 10
rpm.
[0045] The glass beads that are added into the low melting point
glass paste as the bead spacers have relatively broad distribution
of granularity including grain sizes of approximately times the
above-mentioned design value d and approximately 1.5 times the
same, and despite that the viscosity of the seal paste is scarcely
altered within the range of content 0.05-2.0 wt % as shown by the
thick solid line in FIG. 6.
[0046] On the contrary, when glass beads of a comparison example
are added into the low melting point glass paste, the viscosity
increases along with increase of the content as shown by the broken
line in FIG. 6.
[0047] The low melting point glass paste that was used contains
glass frit having a softening point of 410.degree. C. (made by
Nippon Electric Glass Co., Ltd.) dispersed in a vehicle that is a
solvent in which a binder such as ethyl cellulose or acrylic is
dissolved at a ratio of approximately 5 wt %. The content (wt %) of
bead spacers in the present invention is expressed as a weight
ratio to the glass frit.
[0048] FIG. 7 is a graph showing a result of a differential thermal
analysis of the glass beads.
[0049] Using a differential thermal analysis device,
thermogravimetric change of the glass beads was measured. As shown
by the thick solid line in FIG. 7, there was no outstanding change
of thermogravimetric value of the glass beads according to this
example. In contrast, thermogravimetric value of the glass beads
according to the comparison example showed substantial decrease at
temperature around 100.degree. C. as shown by the broken line in
FIG. 7. This substantial decrease is considered to be caused by
evaporation of moisture adsorbed on the surface of the glass beads.
In addition, there is also decrease of thermogravimetric value at
temperature above 300.degree. C., which is considered to be caused
by degassing. As shown in FIG. 7 as results, the glass beads
according to the comparison example are porous, while the glass
beads according to this example are non-porous.
[0050] FIG. 8 is a graph showing an effect of bead spacers. FIG. 8
shows differences (=Ts--Tr) between thickness Tr and thickness Ts
shown in FIG. 9 at different content values of bead spacers in the
sealing material in plural plasma display panels. The thickness Tr
means a thickness of the plasma display panel at the position where
an outermost partition 29 is disposed, while the thickness Ts is a
thickness of the plasma display panel at the position where the
sealing material 35 is disposed. The thickness Tr and the thickness
Ts were measured for each plasma display panel at twelve positions
P01-P12 as shown in FIG. 10, and variations of the measured values
are shown by vertical bars in FIG. 8. Each of circles on the bars
in FIG. 8 indicates the average value of the twelve measured
values.
[0051] As shown in FIG. 8, in the case where the content of the
bead spacers is zero the measured value of the difference between
the thickness Tr and the thickness TS (hereinafter referred to as a
thickness difference) varies substantially from -15 to 15 including
negative values. A negative value of the thickness difference means
that the glass substrate 11 and the glass substrate 21 are
abnormally close to each other at the sealing portion. Namely,
there is generated a subsidence that makes the glass substrate 11
convex toward the front, which may cause malcontact between the
glass substrate 11 and the partition 29. The malcontact may cause
generation of a noise.
[0052] On the contrary, in the case where the content of the bead
spacers is 0.1 wt %, 0.9 wt % or 1.8 wt %, the thickness difference
has positive values with small variation. However, the variation in
the case where the content is 0.1 wt % is a little larger than that
in the case where the content is 0.9 wt % or 1.8 wt %. In the case
where the content of the bead spacers is 0.06 wt %, an average
value of the thickness differences has a positive value although
the thickness differences have a variation from -5 to 10.
Therefore, the subsidence can be reduced by adding the bead spacers
also in the case where the content is 0.06 wt %.
[0053] There is a tendency that the thickness difference increases
along with increase of the content. The reason of this is
considered to be a large number of particles having a grain size
larger than the design value d of the glass beads. If
classification is performed more precisely, this tendency can be
decreased.
[0054] It is desirable that the content is larger in order to
prevent mechanical breakdown of the bead spacers. However,
considering bonding power of the sealing material 35 or increase of
cost due to addition of the bead spacers, content of 0.05-1.5 wt %
is preferable, and 1.0 wt % is more preferable. In the case of 1.0
wt %, 15 bead spacers are contained per 3.6 mm.sup.2 of the sealing
material 35 by calculation. In this case, the sealing material 35
has strength as being not broken down even by the pressure of 0.70
kgf/cm.sup.2 that is applied to the front substrate 10 or the rear
substrate 20 so as to compress the sealing material 35.
[0055] In the above-explained embodiment, the pattern of the
partition 29 is not limited to the stripe pattern, but it can be a
mesh pattern.
[0056] The present invention can be applied to a display device
having a structural member for defining a gap between a pair of
substrates that are sealed at an outer position away from the
structural member, and it can contribute to improvement of
reliability of the sealing structure.
[0057] While example embodiments of the present invention have been
shown and described, it will be understood that the present
invention is not limited thereto, and that various changes and
modifications may be made by those skilled in the art without
departing from the scope of the invention as set forth in the
appended claims and their equivalents.
* * * * *