U.S. patent application number 10/874355 was filed with the patent office on 2004-11-25 for liquid crystal display device.
Invention is credited to Aratani, Sukekazu, Kondo, Katsumi, Maekawa, Yasunari, Matsuyama, Shigeru, Tomioka, Yasushi, Utsumi, Yuka, Wakagi, Masatoshi.
Application Number | 20040233377 10/874355 |
Document ID | / |
Family ID | 26355211 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040233377 |
Kind Code |
A1 |
Utsumi, Yuka ; et
al. |
November 25, 2004 |
Liquid crystal display device
Abstract
A liquid crystal display device having a pair of substrates, a
liquid crystal layer, a group of electrodes for applying to the
liquid crystal layer an electric field substantially parallel to
the substrate surface, and a plurality of active elements connected
to the electrodes, the group of electrodes and active elements
being formed on one of the pair of substrates. An alignment control
film is formed between the liquid crystal layer and at least one of
the pair of substrates and is made from polyamic acid obtained by
reacting a diamine with an acid anhydride. The acid anhydride is at
least one member selected from the group consisting of
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride;
1,2,4,5-cyclehexanetetracarboxyic acid dianhydride;
3,3',4,4'-biscyclohexanetetracarboxylic acid dianhydride;
3,3',4,4'-benzophenonetetracarboxylic acid dianhydride;
1,2,3,4-butanetetracarboxylic acid dianhydride; and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride and
pyromellitic acid dianhydride.
Inventors: |
Utsumi, Yuka; (Hitachi-shi,
JP) ; Tomioka, Yasushi; (Hitachi-shi, JP) ;
Wakagi, Masatoshi; (Hitachi-shi, JP) ; Maekawa,
Yasunari; (Takasaki-shi, JP) ; Aratani, Sukekazu;
(Hitachiota-shi, JP) ; Kondo, Katsumi; (Mito-shi,
JP) ; Matsuyama, Shigeru; (Mobara-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
26355211 |
Appl. No.: |
10/874355 |
Filed: |
June 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10874355 |
Jun 24, 2004 |
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10189427 |
Jul 8, 2002 |
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6757044 |
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10189427 |
Jul 8, 2002 |
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09239521 |
Jan 29, 1999 |
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6441880 |
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Current U.S.
Class: |
349/155 |
Current CPC
Class: |
G02F 1/134363 20130101;
G02F 1/13392 20130101; G02F 1/133788 20130101 |
Class at
Publication: |
349/155 |
International
Class: |
G02F 001/1339 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 1998 |
JP |
10-018530 |
Feb 12, 1998 |
JP |
10-029504 |
Claims
What is claimed is:
1. A liquid crystal display device comprising: a pair of substrates
at least one of which is transparent; a liquid crystal layer
disposed between said pair of substrates; a group of electrodes for
applying to said liquid crystal layer an electric field
substantially parallel to a surface of at least one of said pair of
substrates, and a plurality of active elements connected to said
electrodes, said group of electrodes and active elements being
formed on one of said pair of substrates; and an alignment control
film formed between said liquid crystal layer and at least one of
said pair of substrates; wherein said alignment control film is
made from polyamic acid obtained by reacting a diamine with an acid
anhydride, said acid anhydride being at least one member selected
from the group consisting of: 1,2,3,4-cyclopentanetetracarboxylic
acid dianhydride; 1,2,4,5-cyclehexanetetracarboxyic acid
dianhydride; 3,3',4,4'-biscyclohexanetetracarboxylic acid
dianhydride; 3,3',4,4'-benzophenonetetracarboxylic acid
dianhydride; 1,2,3,4-butanetetracarboxylic acid dianhydride; and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride and
pyromellitic acid dianhydride.
2. A liquid crystal display device according to claim 1, wherein
said acid anhydride is 1,2,3,4-cyclobutanetetracarboxylic acid
dianhydride.
3. A liquid crystal display device according to claim 1, wherein
said acid anhydride is a mixture of 1,2,3,4-butanetetracarboxylic
acid dianhydride and 1,2,3,4-cyclobutanetetracarboxylic acid
dianhydride.
4. A liquid crystal display device according to claim 1, wherein
said alignment control film is aligned by irradiation with
polarized light.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a normally closed liquid
crystal display device, particularly to such a liquid crystal
display device incorporating an in-plane switching (IPS) mode which
is operated by applying an electric field to the liquid crystal
layer in the direction substantially parallel to the substrate
plane.
[0002] In liquid crystal display devices, the dark level of dark
display is a decisive factor for the contrast ratio. The principal
causes of worsening the dark level of dark display are the improper
conditions of pixel and electrode ends, low frame response and
light leakage at the periphery of the spacer.
[0003] Variations in thickness of the liquid crystal layer in these
liquid crystal display devices lead to serious deterioration of
display qualities such as reduction of contrast, nonuniformity of
luminance and color shading, so that the spacers are required for
keeping the uniform thickness of the liquid crystal layer.
[0004] Provision of such spacers, however, is causative of light
leakage as it disturbs alignment of the liquid crystal molecules
around the spacer surface. The higher the in-plane distribution
density of spacers, the more effective for suppressing variation of
thickness of the liquid crystal layer, but at the same time this
may invite a greater decrease of contrast ratio. Also, light
leakage at the periphery of the spacer tends to provoke a sense of
glaringness which hinders appearance of uniform blackness of the
picture when the display mode changes from dark to gray scale, and
may also cause nonuniformity of luminance due to localized
distribution of the spacers.
[0005] In the normally closed liquid crystal display devices of the
twisted nematic (TN) mode in which an electric field is applied
along the direction perpendicular to the substrates, a method for
minimizing light leakage at the spacer periphery by incorporating a
mechanism for vertically aligning the liquid crystal molecules in
the spacer surface has been proposed (JP-A-4-177324, etc.). This
method is indeed effective in the normally closed liquid crystal
display devices of the TN mode, but no disclosure is made on the
technique for reducing or eliminating light leakage which occurs
specifically in the IPS mode normally closed liquid crystal display
devices to which the conception of the present invention is
directed.
SHORT SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide an IPS mode
normally closed liquid crystal display device of high contrast
ratio, which is freed of the problem of light leakage caused by the
spacer beads in this type of liquid crystal display devices.
[0007] Accordingly, the present invention provides an IPS mode
normally closed liquid crystal display device comprising:
[0008] a pair of substrates at least one of which is
transparent,
[0009] a liquid crystal layer disposed between said pair of
substrates,
[0010] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and one or more active elements connected to said electrodes,
said group of electrodes and active elements being formed on one of
said pair of substrates,
[0011] an alignment control film formed on said pair of substrates,
and
[0012] an optical means for changing the optical properties
according to the state of molecular alignment of said liquid
crystal layer,
[0013] wherein the thickness of said liquid crystal layer is
controlled to be substantially uniform by the spacer beads
dispersed and held between said pair of substrates, a pretilt angle
between said alignment control film and liquid crystals is
4.degree. or less, and a contact angle between said liquid crystals
and said spacer is 0.degree. to 60.degree..
[0014] The present invention also provides a liquid crystal display
device of the type recited, which is freed of the problem of light
leakage due to the presence of the spacer beads by disposing
between said spacer and said liquid crystal layer a film provided
with a liquid crystal alignment controlling function by irradiation
with polarized light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other objects and features of the present
invention will be understood more clearly from the following
detailed description with reference to the accompanying drawings,
wherein:
[0016] FIG. 1 is a schematic illustration of 4-division alignment
of the liquid crystal molecules around a spacer bead in a liquid
crystal display device according to the present invention.
[0017] FIG. 2 is a schematic illustration of 2-division alignment
of the liquid crystal molecules around a spacer bead in a liquid
crystal display device according to the present invention.
[0018] FIG. 3 is a schematic sectional view of a panel in a liquid
crystal display device according to the present invention.
[0019] FIG. 4 illustrates the angles made by the long-axial
alignment direction of the liquid crystal molecules and the
polarized light transmission axis of the polarizer with the
direction of electric field.
[0020] FIGS. 5A to 5D illustrate the behavior of the liquid crystal
molecules in an IPS mode liquid crystal display device.
[0021] FIGS. 6A to 6C are a schematic plane view (6A) and schematic
sectional views (6B and 6C) showing a group of electrodes
(structure), an insulating film and an alignment control film in a
unitary pixel section in an embodiment of the present
invention.
[0022] FIG. 7 illustrates the circuit system in a liquid crystal
display device according to the present invention.
[0023] FIG. 8 illustrates the optical system in a liquid crystal
display device according to the present invention.
[0024] FIG. 9 is a schematic sectional illustration of a liquid
crystal display device according to an embodiment of the present
invention.
[0025] FIG. 10 is a fragmentary perspective view of a liquid
crystal display device of the present invention.
[0026] FIG. 11 is a graph explaining properties of a liquid crystal
display device of the present invention.
[0027] FIG. 12 is a schematic sectional illustration of a liquid
crystal display device according to another embodiment of the
present invention.
[0028] FIG. 13 illustrates setting of the alignment direction and
polarization direction of a liquid crystal display device in an
embodiment of the present invention.
[0029] FIGS. 14A to 14D illustrate the principle of switching
operation of a liquid crystal display device in an embodiment of
the present invention.
[0030] FIGS. 15A to 15C are schematic side sectional illustrations
of a liquid crystal display device in an embodiment of the present
invention.
[0031] FIG. 16 illustrates the circuit system in a liquid crystal
display device in an embodiment of the present invention.
[0032] FIG. 17 illustrates the optical system in a liquid crystal
display device in an embodiment of the present invention.
[0033] FIG. 18 a schematic frontal view of a spacer bead and its
circumferential area in a liquid crystal display device in an
embodiment of the present invention.
[0034] FIG. 19 illustrates the film structure around the group of
electrodes (electrode structure) in a liquid crystal display device
in an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] In the conventional TN mode normally open liquid crystal
display devices, dark display is obtained in a state where a high
voltage is applied. In this case, most of the liquid crystal
molecules are aligned in the direction of the electric field which
is normal to the substrate surface, and the black level is obtained
under a specific relationship between the alignment of liquid
crystal molecules and the disposition of polarizer. Therefore,
uniformity of the black level is, in principle, not much dependent
on the state of initial alignment under low voltage.
[0036] Further, the human eye recognizes the nonuniformity of
luminance as a relative ratio of luminance and shows a reaction
close to logarithmic scale, so that it is sensitive to the
variation of black level. In this connection, the conventional TN
mode normally open liquid crystal display devices, in which the
liquid crystal molecules are forcibly aligned in one direction
under high voltage, are insensitive to the state of initial
alignment and advantageous in this respect.
[0037] On the other hand, the IPS mode normally closed liquid
crystal display devices are very sensitive to disturbance of the
state of initial alignment as the black level is displayed at low
or zero voltage in these display devices. Particularly in the
configuration of birefrigent mode in which the liquid crystal
molecules take homogeneous alignment, i.e. they are aligned
parallel to each other on the upper and lower substrates, and
wherein one of the polarizers is arranged so that its light
transmission axis will be parallel to the direction of alignment of
the liquid crystal molecules while the other polarizer is arranged
orthogonal thereto, the polarized light incident on the liquid
crystal layer is allowed to propagate with little disturbance of
linear polarization. This is effective for darkening black the dark
level and allows ideal black display in principle.
[0038] Ideal black display in principle is indeed realized, but on
the other hand, only slight disturbance of initial alignment may
directly lead to the initiation of light leakage, causing
impediment of darkness in black display and degradation of the
black level.
[0039] Transmittance T in the birefrigent mode in an IPS mode
liquid crystal display devices is generally given by the following
equation (1):
T=T0.multidot.sin 2{2.theta.(E)}.multidot.sin
2{(.pi..multidot.deff.multid- ot..DELTA.n)/.lambda.} (1)
[0040] wherein T0 is a factor, which is a numerical value decided
mainly by transmittance of the polarizer used in the liquid crystal
panel, .theta.(E) is the angle made by the effective optical axis
of the liquid crystal layer with the polarized light transmission
axis, .DELTA.n is liquid crystal refractive anisotropy, and
.lambda. is light wavelength. Here, the product of effective
thickness deff of the liquid crystal layer and liquid crystal
refractive anisotropy .DELTA.n, i.e. deff.multidot..DELTA.n, is
called retardation. Crystal layer thickness deff indicates the
thickness of only the liquid crystal layer which actually changes
its direction of alignment when an electric voltage is applied, and
does not express the thickness of the whole liquid crystal layer,
because the liquid crystal molecules around the interface of the
liquid crystal layer won't be changed in their direction of
alignment, under the influence of interfacial anchorage, even when
an electric voltage is applied. Therefore, when the thickness of
the whole liquid crystal layer held between a pair of substrates is
represented by dLC, there always exists the relation of
deff<dLC, and their difference can be estimated to be
approximately 20 to 40 nm though variable depending on certain
factors such as the material used for the liquid crystal panel and
the material forming the interface with the liquid crystal layer,
for example, the alignment film material.
[0041] As is seen from the above equation (1), what is dependent on
the strength of electric field is the member sin 2{2.theta.(E)} in
the above equation, and luminance can be adjusted by varying the
angle .theta. in accordance with the electric field strength. For
making a normally closed liquid crystal display device, the
polarizers are set such that .theta. will become 0.degree. (74=0)
when no electric voltage is applied, so that this display system is
designed to be sensitive to disturbance in the direction of initial
alignment.
[0042] Thus, in the IPS mode normally closed liquid crystal display
devices which are sensitively to the disturbance in the direction
of initial alignment, the main cause of retardation of darkness of
dark display is light leakage that occurs at the periphery of the
spacer, because such light leakage causes the liquid crystal
molecules in the spacer surface to get aligned contrary to the
action of the alignment control film which works to align the
liquid crystal molecules in the specified direction.
[0043] The above phenomenon--that the spacer interface functions
like an alignment control film to cause contrary alignment of the
liquid crystal molecules--is not the only case with the IPS mode.
However, as mentioned above, the TN mode normally closed liquid
crystal display devices are not much affected by light leakage
caused by disturbance in the direction of initial alignment. Also,
in the TN mode normally closed liquid crystal display devices,
means are incorporated for letting the liquid crystal molecules
align vertically on the spacer bead surface. This seems to be for
the following reason.
[0044] When the liquid crystal molecules are aligned parallel to
the spacer bead surface, this is an equal value as to whether they
are parallel or vertical to the substrate. In the TN mode normally
closed liquid crystal displays, an electric field is applied in the
direction vertical to the substrates to operate the display system
so that the liquid crystal molecules will be aligned parallel to
the direction of electric field, so that the disturbance of
alignment in the polar direction triggers a fatal increase of light
leakage. In other words, since in the TN mode the liquid crystal
molecules rise up in the polar direction when the system is
operated, such state of rise-up in the polar direction is equal to
parallel alignment when viewed from the spacer bead/liquid crystal
interface, and is stabilized as is. It is, therefore, almost
impossible to control the liquid crystal molecules to take parallel
alignment which can prevent them from rising up in the polar
direction. So, in the prior art, it has been tried to provide the
spacer beads with a vertically aligning function. This is designed
to instabilize the rise-up of the liquid crystal molecules in the
polar direction where light leakage is most likely to occur.
[0045] In the case of the IPS mode, however, although rise-up in
the polar direction gives no influence on light leakage,
disturbance of alignment in the azimuthal direction forces to cause
a fatal increase of light leakage. The spacer beads with
disposition to vertical alignment tend to cause deviation of
alignment in the azimuthal direction, so that when such vertical
alignment-oriented spacer beads used in the TN mode liquid crystal
displays are applied to the IPS mode liquid crystal displays, there
results in an increase of light leakage. It is thus impossible with
the conventional techniques to lessen light leakage around the
spacer beads in the IPS normally closed liquid crystal
displays.
[0046] This is the problem which is not encountered in the STN mode
where the same birefrigent mode is employed, so it is required to
contrive a means of solution peculiar to the liquid crystal display
devices employing the IPS mode in which an electric field is
generated in the transverse direction.
[0047] The present inventors have made further researches on the
cause of light leakage around the spacer beads and found that the
following factors are involved in the matter of light leakage
caused by the spacer beads.
[0048] One factor is that high light leakage around the spacer
beads impedes darkness of dark display to worsen the black level.
Another factor concerns the facts that the degree of light leakage
differs among the spacer beads, and that local concentration of the
spacer beads causing high light leakage induces nonuniformity or
irregularity of luminance.
[0049] Therefore, although it is of course a matter of concern to
lessen light leakage itself around the spacer beads, it is also an
important subject for study to device means for allowing their
uniform in-plane distribution.
[0050] Further, in the IPS mode liquid crystal display device, when
a pretilt angle between the alignment control film and the liquid
crystals becomes higher, there is a problem in that the wide
viewing angle of the IPS mode liquid crystal display, which is one
of characteristics, is damaged. Particularly when the pretilt angle
is more than 4.degree., the viewing angle properties are rapidly
narrowed, so that it is found that particularly the wide viewing
angle is preferable when the pretilt angle is made 3.degree. or
less (Ohe, et al: Liquid Crystals vol. 22, no. 4, p391, 1997).
[0051] It is an object of the present invention to provide a liquid
crystal display device of high contrast ratio, which is freed of
the said problem of light leakage associated with the spacer beads
in the IPS mode normally closed liquid crystal display devices.
[0052] More specifically, the present invention envisions to
provide a normally closed liquid crystal display device, especially
an active-matrix liquid crystal display device employing the
in-plane switching mode, and having a pretilt angle between an
alignment control film and liquid crystals of 4.degree. or less,
characterized in that light leakage centering around each spacer is
controlled to be divided into four shapes.
[0053] Embodiments of the present invention are described
below:
[0054] (1) A normally closed liquid crystal display device
comprising:
[0055] a pair of substrates at least one of which is
transparent,
[0056] a liquid crystal layer disposed between said pair of
substrates,
[0057] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and one or more active elements connected to said electrodes,
said group of electrodes and active elements being formed on one of
said pair of substrates,
[0058] an alignment control film formed on said pair of substrates,
and
[0059] an optical means for changing the optical properties
according to the state of molecular alignment of said liquid
crystal layers
[0060] wherein the thickness of said liquid crystal layer is
controlled to be substantially uniform by the spacer beads
dispersed and held between said pair of substrates, a pretilt angle
between said alignment control film and liquid crystals is
4.degree. or less, and a contact angle between said liquid crystals
and said spacer is 0.degree. to 60.degree..
[0061] (2) A normally closed liquid crystal display device
comprising:
[0062] a pair of substrates at least one of which is
transparent,
[0063] a liquid crystal layer disposed between said pair of
substrates,
[0064] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and one or more active elements connected to said electrodes,
said group of electrodes and active elements being formed on one of
said pair of substrates,
[0065] an alignment control film formed on said pair of substrates,
and
[0066] an optical means for changing the optical properties
according to the state of molecular alignment of said liquid
crystal layer,
[0067] wherein the thickness of said liquid crystal layer is
controlled to be substantially uniform by the spacer dispersed and
held between said pair of substrates, a pretilt angle between said
alignment control film and liquid crystals is 3.degree. or less,
and a contact angle between said liquid crystals and said spacer is
0.degree. to 60.degree..
[0068] (3) A normally closed liquid crystal display device
described in above (1) or (2), which further comprises a contact
angle between said liquid crystals and an alignment control
direction of said alignment control film and a contact angle
between said liquid crystals and a right-angle direction as to the
alignment control direction have anisotropy, and the former contact
angle is smaller than the latter contact angle.
[0069] (4) A normally closed liquid crystal display device
comprising:
[0070] a pair of substrates al least one of which is
transparent,
[0071] a liquid crystal layer disposed between said pair of
substrates,
[0072] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and one or more active elements connected to said electrodes,
said group of electrodes and active elements being formed on one of
said pair of substrates,
[0073] an alignment control film formed on said pair of substrates,
and
[0074] an optical means for changing the optical properties
according to the state of molecular alignment of said liquid
crystal layer,
[0075] wherein the thickness of said liquid crystal layer is
controlled to be substantially uniform by the spacer dispersed and
held between said pair of substrates, a pretilt angle between said
alignment control film and liquid crystals is 3.degree. or less,
and the contact angle between said liquid crystals and said spacer
is larger than that between the liquid crystal and the alignment
control direction of said alignment control film, and is smaller
than the contact angle between said liquid crystals and the right
angle direction as to the alignment control direction of said
alignment control film.
[0076] (5) A normally closed liquid crystal display device
described in above (4), wherein the contact angle between said
liquid crystals and said spacer is less than 10.degree..
[0077] (6) A normally closed liquid crystal display device
described in above (5) wherein the contact angle between the liquid
crystals and the alignment direction of said alignment control film
is 0.degree. to 5.degree..
[0078] (7) A normally closed liquid crystal display device
described in above (5) or (6), wherein the contact angle between
said liquid crystals and the right angle direction as to the
alignment control direction of said alignment control film is
10.degree. or more.
[0079] (8) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said spacer has a
roughened surface.
[0080] (9) A normally closed liquid crystal display device
described in above (8), wherein the spacer has a surface wherein
functional groups showing hydrophilic property and functional
groups showing hydrophobic property are introduced, and is
roughened by this surface layer.
[0081] (10) A normally closed liquid crystal display device
described in above (9), wherein the contact angle between a
material constituting said spacer and said liquid crystals is less
than 90.degree..
[0082] (11) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein the amount of adhesion
work between said liquid crystals and said spacer, said amount
being represented by a surface tension of said liquid crystals plus
a product obtained by multifying a cosine of the contact angle
between said liquid crystals and said spacer by said surface
tension of said liquid crystals, is 0.05 N/m or more.
[0083] (12) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said spacer has a
surface wherein functional groups having a function of a wetting
agent for said liquid crystals are introduced.
[0084] (13) A normally closed liquid crystal display device
described in above (12), wherein the functional groups having a
function of a wetting agent are selected from hydrocarbon groups
which may have at least one hydroxyl group such as a long-chain
alkyl group preferably having 8 to 15 carbon atoms, wherein
hydrogen atom(s) may be substituted with at least one hydroxyl
group.
[0085] (14) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said liquid crystals
contain a compound or functional groups having a function of a
wetting agent for a surface of said spacer.
[0086] (15) A normally closed liquid crystal display device
described in (14), wherein said liquid crystals contain a compound
having one or more cyano groups.
[0087] (16) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said liquid crystals
has a surface tension of 25 mN/m or less.
[0088] (17) A normally closed liquid crystal display device
described in above (16), wherein said liquid crystals contain a
compound having one or more fluorine atoms as a polar group.
[0089] (18) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said spacer causes
light leakage using said spacer as a center to form four-devided
shapes.
[0090] (19) A normally closed liquid crystal display device
described in above (1), (2) or (4), wherein said spacer causes
light leakage using said spacer as a center in an amount of
1.0.times.10.sup.-4%.multidot.mm/- piece or less, when one spacer
is present per mm.sup.2.
[0091] (20) A normally closed liquid crystal display device
described in above (17), wherein said spacer has a surface wherein
functional groups having a function as a wetting agent for said
liquid crystals are introduced.
[0092] (21) A liquid crystal display device comprising:
[0093] a pair of substrates at least one of which is
transparent;
[0094] a liquid crystal layer disposed between said pair of
substrates;
[0095] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
surface, and a plural number of active elements connected to said
electrodes, said group of electrodes and active elements being
formed on one of said pair of substrates; and
[0096] an alignment control film formed between said liquid crystal
layer and at least one of said pair of substrates,
[0097] wherein spacers are provided between said pair of
substrates, and a film made of a material that can be provided with
a liquid crystal aligning ability by irradiation with polarized
light is disposed between said liquid crystal layer and said
spacers.
[0098] (22) A liquid crystal display device described in above
(21), wherein said alignment control film comprises a film made of
a material which can be provided with a liquid crystal aligning
ability by irradiation with polarized light.
[0099] (23) A liquid crystal display device described in above
(22), wherein the film formed by irradiation with polarized light
between said spacers and said liquid crystal layer constitutes a
part of said alignment control film.
[0100] (24) A liquid crystal display device described in above (22)
or (23), wherein a transparent organic polymer layer is provided
between said alignment control film and at least one of said pair
of substrates, and said spacers are disposed between said
transparent organic polymer layer and said alignment control
film.
[0101] (25) A liquid crystal display device comprising:
[0102] a pair of substrates at least one of which is
transparent;
[0103] a liquid crystal layer disposed between said pair of
substrates;
[0104] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and a plural number of active elements connected to said
electrodes, said group of electrodes and active elements being
formed on one of said pair of substrates; and
[0105] an alignment control film formed between said liquid crystal
layer and at least one of said pair of substrates,
[0106] wherein spacers are provided between said pair of
substrates, and a film made of a chemically treated material which
can be provided with a liquid crystal aligning ability by
irradiation with polarized light is disposed between said liquid
crystal layer and said spacers.
[0107] (26) A liquid crystal display device comprising:
[0108] a pair of substrates at least one of which is
transparent;
[0109] a liquid crystal layer disposed between said pair of
substrates;
[0110] a group of electrodes for applying to said liquid crystal
layer an electric field substantially parallel to the substrate
plane and a plural number of active elements connected to said
electrodes, said group of electrodes and active elements being
formed on one of said pair of substrates; and
[0111] an alignment control film formed between said liquid crystal
layer and at least one of said pair of substrates,
[0112] wherein spacer surface is coated with a material which can
be provided with a liquid crystal aligning ability by irradiation
with polarized light.
[0113] (27) A liquid crystal display device described in any one of
above (21) to (26), wherein the material which can be provided with
a liquid crystal aligning ability by irradiation with polarized
light is a material having photoisomerization reactivity.
[0114] (28) A liquid crystal display device described in above
(27), wherein the structural segment contributing to the
photoisomerization reaction by polarized light irradiation of the
material which can be provided with a liquid crystal aligning
ability by irradiation with polarized light is identical with the
structural segment contributing to the photoisomerization reaction
by polarized light irradiation of said alignment control film.
[0115] (29) A liquid crystal display device described in above
(27), wherein the wavelength region where the photoisomerization
reaction of said material capable of being provided with a liquid
crystal aligning ability by irradiation with polarized light and
disposed between said liquid crystal layer and said spacers is
induced substantially coincides with the wavelength region where
the photoisomerization reaction by polarized light irradiation of
said alignment control film is induced.
[0116] (30) A liquid crystal display device described in above
(27), wherein said alignment control film is made of a material
which does not absorb light in the wavelength region where the
photoisomerization reaction of the material capable of being
provided with a liquid crystal aligning ability by irradiation with
polarized light is induced.
[0117] The present inventors have studied earnestly and found that
by making the contact angle between the spacer and the liquid
crystals 60.degree. or less, the liquid crystal molecules on the
spacer surface aligned substantially uniform, and the spacer having
a four-devided shape can appear predominantly.
[0118] FIG. 1 is a cross-sectional view of one layer in the liquid
crystal display device. Since the parallel alignment direction of
the spacer beads surface and the alignment direction of the
alignment control film make an angle of substantially 90.degree. in
the region 48 in FIG. 1, the liquid crystal molecules are subjected
to the liquid crystal molecules are subjected to the greatest
stress. Thus, in order to make the region 48 stabler, it is
preferable to impart wettability against the sight angle direction
to the alignment control direction of the alignment control film,
that is to impart anisotropy to the contact angle, and to make the
contact angle against the alignment control direction small.
[0119] Particularly, even in a liquid crystal display device
wherein a wide viewing angle is provided by making the pretilt
angle very low, it is possible to make the 4-divided type very
stable by making the contact angle between the liquid crystals and
the spacer larger than the contact angle between the alignment
control direction of alignment control film and the liquid
crystals, and smaller than the contact angle between the liquid
crystals and the right-angle direction as to the alignment control
direction.
[0120] Further, when the contact angle between the liquid crystals
and the spacer beads is 90.degree. or less, it is possible to make
the contact angle smaller by roughening the spacer beads
surfaces.
[0121] The roughening of the spacer beads surfaces is important,
and even very fine roughened surfaces produced by introducing
surface layers can provide expected effects.
[0122] In order to make the contact angle between the spacer and
the liquid crystals 60.degree. or less, one method is to introduce
a functional group which becomes a wetting agent for the liquid
crystals into the spacer surface. The introduction of such a
functional group can be carried out by using a silane coupling
agent, or by chemical modification using a surface modifying agent
having an acryl group, while applying vinyl groups or hydroxyl
groups of the spacer beads by themselves.
[0123] For example, a long-chain alkyl group having one or more
multi-valent hydroxyl groups, an alkyl group having a terminal
amino group, etc. can be introduced into the spacer beads surfaces
via a silane coupling agent, etc. Alternatively, a long-chain alkyl
group having one or more multi-valent hydroxyl groups and one or
more acryl groups or vinyl groups at another end, an alkyl group
having a terminal amino group, etc. can be introduced by chemical
modification. When a silane coupling agent is used, the spacer
beads can be an inorganic material such as silica.
[0124] On the other hand, it is possible to introduce a functional
group into the liquid crystals, said functional group being able to
make wetting properties with the spacer surface better. For
example, a fluorine group remakably reduces its critical surface
tension. To obtain a solid surface tension directly is not
established yet. But, when the spacer is made from a polymeric
compound which has a surface tension of about 30 mN/m or more, the
contact angle can be effectively lowered by making the surface
tension of liquid crystals 25 mN/m or less.
[0125] The anisopropy of the contact angle between the alignment
control film and the liquid crystals can be imparted by increasing
the rubbing strength, taking a rigid molecular structure in the
alignment control direction, taking a molecular structure which
strengthens intermolecular attaction with the liquid crystals,
etc.
[0126] As another embodiment for eliminating light leakage
associated with the spacer beads, there is offered a liquid crystal
display device of a structure comprising a pair of substrates at
least one of which is transparent, a liquid crystal layer disposed
between said pair of substrates, a group of electrodes for applying
to said liquid crystal layer an electric field substantially
parallel to the substrate plane and a plural number of active
elements connected to said electrodes, said group of electrodes and
active elements being formed on one of said pair of substrates, and
an alignment control film formed between said liquid crystal layer
and at least one of said pair of substrates, wherein spacer beads
are provided between said pair of substrates, and a film is
disposed between said spacer beads and the liquid crystal layer,
said film having been made of a material that can be provided with
a liquid crystal aligning ability by irradiation with polarized
light.
[0127] Thus, when the spacer bead surface is provided with an
alignment controlling function by irradiation with poralized light,
there takes place no division of alignment such as described above,
with consequent elimination of light leakage attributable to the
spacer beads themselves. Also, as a result of affording a liquid
crystal aligning ability to the spacer bead surface by polarized
light irradiation, it becomes possible to control alignment of the
liquid crystal molecules in the same direction as the alignment
film, regardless of the shape of the spacer beads, with no concern
on whether the liquid crystal molecules are aligned horizontally or
vertically.
[0128] Further, when a film formed by exposing to polarized light a
material capable of being provided with a liquid crystal aligning
ability by poralized light irradiation is used as said alignment
control film, there is eliminated any need of conducting a rubbing
treatment, and it is possible to provide an alignment controlling
function with a substantially same degree of alignment regulating
force as possessed by the alignment control film.
[0129] Furthermore, when the film formed by polarized light
irradiation between the spacer and the liquid crystal layer is
adapted to constitutes a part of the alignment control film, it
becomes possible to afford the same alignment regulating force to
the alignment control film and to unnecessitate polarized light
irradiation for the spacer bead surface.
[0130] Still further, when a transparent organic polymer layer is
formed between said alignment control film and at least one of a
pair of substrates, and a spacer is disposed between this
transparent organic polymer layer and the alignment control film,
adhesion between the alignment control film and the substrate is
strengthened and also the substrate surface is more flattened,
resulting in remarkable improvement of the image quality.
[0131] According to still another embodiment of the present
invention, a liquid crystal display device is provided which
comprises a pair of substrates at least one of which is
transparent, a liquid crystal layer disposed between said pair of
substrates, a group of electrodes for applying to said liquid
crystal layer an electric field substantially parallel to the
substrate plane and a plural number of active elements connected to
said electrodes, said group of electrodes and active elements being
formed on one of said pair of substrates, and an alignment control
film formed between said liquid crystal layer and at least one of
said pair of substrates, wherein a spacer is provided between said
pair of substrates, and a film obtained by chemically treating a
material that can be provided with a liquid crystal aligning
ability by polarized light irradiation is disposed between said
spacer and liquid crystal layer.
[0132] It is also preferable to coat the spacer surface with a
material that can be provided with a liquid crystal aligning
ability by polarized light irradiation.
[0133] The material that can be provided with a liquid crystal
aligning ability by polarized light irradiation and is used for the
said purpose in this invention is preferably the one having
photo-isomerization reactivity.
[0134] When the structural section contributing to
photo-isomerization reaction by polarized light irradiation of the
specified material is equalized to the structural section
contributing to similar photo-isomerization reaction of the
alignment control film, the alignment treatments can be
accomplished simultaneously using the same light.
[0135] Also, when the long wavelength region which causes the
photo-isomerization reaction of the specified material formed
between the spacer and the liquid crystal layer is arranged to
substantially coincide with the long wavelength region which
induces the photo-isomerization reaction of the alignment control
film by polarized light irradiation, it becomes possible to perform
the alignment treatments in the same direction simultaneously using
the same light.
[0136] Conversely, when the alignment control film is made of a
material which is incapable of inducing photo-isomerization
reaction with light in the long wavelength region causing
photo-isomerization reaction of the specified material or which is
incapable of absorbing light in said long wavelength region, it
becomes possible to freely conduct the alignment treatment of the
spacer bead surface.
[0137] In the present invention, as explained above, since a liquid
crystal aligning ability is afforded to the spacer bead surface by
polarized light irradiation, control of alignment of the liquid
crystal molecules in the same direction as the alignment film, not
alignment in either horizontal or vertical direction, is enabled
regardless of the shape of the spacer beads.
[0138] Further, according to the present invention, it becomes
possible to lessen light leakage due to disturbance of initial
alignment of the liquid crystal layer around the spacer bead
surface and to provide a high-contrast liquid crystal display
device.
[0139] As described above, in an in-plane switching mode liquid
crystal display device, the light leakage amount can be reduced by
making the light leakage taking a 4-devided shapes by placing the
spacer heads in the center.
[0140] The present invention is further illustrated by the
following embodiments.
EXAMPLE 1
[0141] Referring to FIG. 3, there is shown a schematic sectional
view of a panel in a liquid crystal display device according to the
present invention. It will be seen that a liquid crystal layer 30
comprising a composition of plural compounds is disposed between a
pair of transparent substrates 1,1'. In FIG. 3, the liquid crystal
molecules are schematically shown as rod-like bodies 6. Polarizers
9, 9' are disposed on the outside of said pair of substrates 1, 1'.
Strip electrodes 2, 3 are provided on the surface of one of the
substrates 1 on the inside of the cell, and an alignment control
film 8 is overlaid thereon. Electrode 2 is a common electrode which
supplies an electric voltage of a fixed waveform independently of
the picture signal, and electrode 3 is a pixel electrode providing
a voltage whose wavelength varies according to the picture signal.
An image signal electrode 10 is provided at the same altitude as
the pixel electrode 3. There are provided two insulating layers 4
each of which is made of silicon nitride. On the opposite substrate
1' is provided a color filter 5 for making color display.
[0142] A 3% solution of polyamic acid, which is precursor of the
alignment control film 8, is applied to the substrate and calcined
at 200.degree. C. for 30 minutes for imidization. Specifically,
polyamic acid is prepared using 1,2,3,4-cyclopentenetetracarboxylic
acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid
dianhydride, 3,3',4,4'-biscyclohexanetetracarboxylic acid
dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride
or the like as acid anhydride and 4,4'-diaminodiphenyl sulfide,
3,3'-diaminodiphenyl sulfide, 1,4-diaminocyclohexane,
3,3'-diaminodiphenyl sulfone or the like as diamine, and its
solution is applied to the substrate, dried and calcined to form an
alignment control film 8, followed by rubbing thereof for aligning
the liquid crystal molecules. The long axis direction of the liquid
crystal molecules in the produced state of alignment, i.e. the
initial alignment direction 11, is adjusted so that the angle
.phi.LC defined in FIG. 4 becomes 75.degree.. The acid anhydrides
and diamine compounds such as mentioned above can be used either
singly or by mixing two or more of them as desired.
[0143] Then the polymeric spacer beads 40 having a particle size of
4 .mu.m are dispersed on the substrates by dry scatter method. "Dry
scatter method" is a method in which a negative pressure is
generated at the nozzle section by discharging an inert gas from a
compressed gas supply pipe to suck up and scatter the spacer beads
from a spacer beads supply pipe. No solvent is used as a dispersing
medium for the spacer beads. The spacer beads are made of
divinylbenzene and have a C.sub.5 alkyl group and a hydroxyl group
introduced to the surfaces with the aid of a silane coupling agent.
Each bead is coated with an alignment control film 42 which
functions to have the liquid crystal molecules aligned in the
parallel direction. Then the upper and lower substrates are placed
in position and the peripheral parts are sealed to constitute an
empty cell-like structure. A schematic sectional illustration of
this liquid crystal display device is shown in FIG. 9. The
reference numerals used in FIG. 9 correspond to those in FIG.
3.
[0144] Nematic liquid crystal with positive dielectric anisotropy
is used as the liquid crystal composition. Dielectric anisotropy
.DELTA..epsilon. of the liquid crystal is 10.2 and its refractive
anisotropy .DELTA.n is 0.073. FIGS. 5A to 5D illustrate the
switching behavior of the liquid crystal molecules in the liquid
crystal panel obtained in the manner described above. In this
Example, the liquid crystal molecules 6 are aligned to have the
angle .PHI.LC of 75.degree. against the direction vertical to the
longitudinal direction of the strip electrodes when no electric
field is applied. In case dielectric anisotropy of the liquid
crystal is positive, alignment would be made to satisfy the
condition of
45.degree..ltoreq..vertline..PHI.LC.vertline.<90.degree.. In the
case of the liquid crystal composition illustrated in FIGS. 5A to
5D, dielectric anisotropy of the liquid crystal may be negative. In
this case, it is recommended to initially align the liquid crystal
molecules to the angle of
0.degree..ltoreq..vertline..PHI.LC.vertline.<45.degree- . from
the direction vertical to the strip electrodes. In FIGS. 5A to 5D,
the direction of alignment is indicated by an arrow 11. When an
electric field 13 is applied across the electrodes 2, 3, alignment
of the liquid crystal molecules 6 is shifted so that their long
axis direction will become parallel to the direction of electric
field 13 as shown in FIGS. 5B and 5D. As a result of this
operation, .theta. in the formula (1) varies in accordance with
electric field strength E, causing a corresponding variation of
transmittance.
[0145] In the instant embodiment of the present invention, the
liquid crystal is sandwiched between a pair of polarizers arranged
normal to each other since a birefrigent mode display system is
employed. Further, in order to provide the characteristics of the
normally closed system which gives dark display at low voltage, the
arrangement of FIG. 4, .phi.P=.phi.LC=75.degree., was made, i.e.
the polarized light transmission axis 12 of one of the polarizers
is paralleled to the direction of initial alignment while the
polaraized light transmission axis 12' of the other polarizer is
set perpendicular to the initial alignment. The observed
transmitted light strength is determined by the formula (1).
[0146] FIGS. 6A to 6C illustrate the layout of a group of
electrodes comprising common electrode 2, pixel electrode 3,
picture signal electrode 10 and scanning electrode 14, amorphous
silicon 16, thin-film transistor 15, insulating film 4 and
alignment control film 8 in a unitary pixel section in the instant
embodiment of the present invention. FIG. 6A is a frontal view
taken from the direction vertical to the panel surface, and FIGS.
6B and 6C are lateral sectional views. FIG. 7 illustrates the
circuit system in the liquid crystal display device in the instant
embodiment of the present invention. The circuit system comprises
vertical scanning signal circuit 17, picture signal circuit 18,
common electrode driving circuit 19, power circuit and controller
20, but the circuit arrangement available in the present invention
is not limited to the shown system.
[0147] One example of constitution of the optical system in the
liquid crystal display device formed as mentioned above is shown in
FIG. 8. It will be seen that a back light unit 26 comprising a
power source 21, a light cover 22, a photoconductor 23 and a
diffuser 24 is provided on the backside of a liquid crystal panel
27. A prism sheet 25 for increasing luminance at the normal angle
is shown in the drawing, but there is no problem when no prism
sheet is used. A fragmentary perspective view of such a liquid
crystal display device, for example, is shown in FIG. 10.
[0148] In this case, the surface tension of the liquid crystal
material is 28 mN/m, and the contact angle between the liquid
crystal and the spacer beads is 48.6.degree.. Since the contact
angle between the liquid crystal and the alignment direction of the
alignment film is 10.degree., a 4-division type shown in FIG. 1 can
be obtained, wherein light leakage due to the spacer beads is shown
almost over the whole bead surface. The volume of light leakage per
piece of spacer bead is
8.2.times.10.sup.-5%.multidot.mm.sup.2/piece.
[0149] In FIG. 10, numeral 23 denotes a photoconductor, numeral 24
denotes a diffuser, numeral 21 denotes a light source, numeral 27
denotes a liquid crystal panel, numeral 31 denotes a shield case,
numeral 32 denotes an aperture, numeral 33 denotes a reflector,
numeral 34 denotes an invertor circuit, and numeral 35 denotes a
lower case.
[0150] The light leakage can be measured as follows. First a
luminance of dark display in a region containing no spacer heads in
a liquid crystal panel is measured. Then, a luminance in a region
containing spacer beads and having the same area as the region
previously measured is measured. Next, the difference between both
luminances measured is divided by the density of spacer beads and
the resulting value is defined as a light leakage per spacer bead.
By measuring as mentioned above, the light leakage can be measured
quantitatively.
[0151] A transmittance used herein can be defined as a
transmittance in a display picture element (pixel) region. That is,
a transmittance (luminance) in a practical liquid crystal display
is results of aperture ratio of a color filer and a display region,
and influences of light leakage caused by factors other than the
spacer beads, for example, edge portions of picture element, etc.
Therefore, these influences are removed and the transmittance is
shown in a state wherein only the influence of spacer is
quantitatively evaluated.
[0152] FIG. 11 shows a relationship between a spacer dispersing
density and a light leakage of the spacer of this Example, and
influences of spacers of Comparative Examples mentioned below on
lowering in contrast ratio. As shown in FIG. 11, the lowering of
the contrast ratio can be inhibited remarkably. The maximum value
of the spacer dispersing density is 500 pieces/mm.sup.2. The
dispersing density necessary for maintaining the thickness of
liquid crystal layer at constant depends on the margin of
production process of a liquid crystal display device but is not
preferable practically above 500 pieces/mm.sup.2 due to bad
influences on the picture quality.
[0153] From FIG. 11, it is possible to estimate an allowable value
against the light leakage of spacer. That is, when the light
leakage is above 1.0.times.10.sup.-4 (%.multidot.mm.sup.2/piece),
the contrast ratio is reduced to a half by only the influence of a
spacer. Since there are many factors for lowering the contrast
ratio other than the spacer, it is not preferable to further lower
the contrast ratio only by the influence of light leakage of
spacer. Therefore, in order to realize an in-plane switching mode
liquid crystal display device having a good picture quality, which
is an object of the present invention, it is necessary to make the
light leakage of spacer 1.0.times.10.sup.-4
(%.multidot.mm.sup.2/piece) or lower.
[0154] When the above layout is applied to a prototype model of IPS
mode TFT liquid crystal display device having a diagonal of 13.3
inches, a pixel count of 1,024.times.RGB.times.768 and a spacer
bead dispersion density of about 120 pieces/mm.sup.2, the black
display with very good level is shown. This device has a high
contrast ratio of 300.
[0155] Contrast ratio can be determined by measuring transmittance
(luminance) of bright display, or luminance and transmittance
(luminance) of dark display, and dividing the measured value of the
former by the measured value of the latter. Transmittance can be
determined by a photomultiplier with brightness of the light source
being supposed to be 100. Luminance can be determined by measuring
brightness of the display device by a luminance meter.
EXAMPLE 2
[0156] 10 g of polymeric spacer beads having a particle size of 4.0
.mu.m and composed of divinylbenzene-styrene copolymer resin is
immersed in a mixed solution of 70 g of 20% hydrochloric acid and
30 g of isopropyl alcohol, to which a solution of 3 g of
7-hydroxyoctylcarboxyaldehyde in 10 g of isopropyl alcohol is added
dropwise with stirring. After 2-hour reaction at 50.degree. C., the
reaction solution is filtered and the thus treated spacer beads are
immersed in a solution of 70 g of pure water and 30 g of isopropyl
alcohol and filtered. After repeating the above operation 10 times,
the the beads are immersed in 70 g of toluene and filtered, this
operation being repeated 5 times, followed by drying.
[0157] For forming an alignment film, polyamic acid is prepared by
using 1:4 mixture (by molar ratio) of
4-octadecyloxy-1,3-diaminocyclohexane and p-phenylenediamine as
diamine segment and an equimolar mixture of
1,2,3,4-butanetetracarboxylic acid dianhydride and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride as acid
anhydrides, and this solution is applied to the substrate, dried
and calcined to form an alignment control film 8 and rubbed for
aligning the liquid crystal molecules. These acid anhydrides and
diamine compounds need not be used singly; they may be used by
mixing two or more of them as desired.
[0158] When the thus treated spacer beads are applied to a
prototype of IPS mode TFT liquid crystal display device having a
diagonal of 13.3 inches, a pixel count of 1,024.times.RGB.times.768
and an average spacer bead dispersion density of 100
pieces/mm.sup.2 for the manufacture in the same way as in Example
1, there can be obtained spacer beads with light leakage of the
4-division type shown in FIG. 1 and the volume of light leakage of
7.8.times.10.sup.-5 (%.multidot.mm.sup.2/piece of spacer bead)
almost over the whole surface. The contact angle between the liquid
crystal and the spacer beads in this Example is 38.2.degree. and
that between the liquid crystal and the alignment direction of
alignment film is 8.degree.. The obtained liquid crystal display
device shows fine-level black display and a contrast ratio of
320.
COMPARATIVE EXAMPLE 1
[0159] A polyamic acid solution of PIQ-1800 (an amorphous film
produced by Hitachi Chemical Co., Ltd.), diluted to 4%
concentration, is applied to the substrate, calcined and imidized
at 200.degree. C. for 30 minutes to form an alignment control film
8, and rubbed. Then the silica spacer beads, 4 .mu.m in particle
size and having a strong action to urge horizontal alignment of
liquid crystal, are dispersed on the substrate by the dry scatter
method.
[0160] A prototype of liquid crystal display device is manufactured
in the same way as in Example 1. The spacer beads inducing the
2-division type alignment of liquid crystal shown in FIG. 2 and
offering a light leakage contribution of 28.times.10.sup.-5
(%.multidot.mm.sup.2/piece) develope in an existence ratio of
approximately 60%. In this Comparative Example, the contact angle
between the liquid crystal and the spacer is 7.8.degree., and that
between the liquid crystal and the alignment direction of alignment
film is 8.9.degree. and the contrast ratio of the display device is
200.
COMPARATIVE EXAMPLE 2
[0161] A polyamic acid solution of PIQ-1800, diluted to 4%
concentration, is applied to the substrate, calcined and imidized
at 200.degree. C. for 30 minutes to form an alignment control film
8, and rubbed.
[0162] The polymeric spacer beads having a particle size of 4 .mu.m
and modified so as to be covered with a C.sub.18 long-chain alkyl
group on the surface for expediting vertical alignment of liquid
crystal are dispersed on the substrate by a dry scatter method.
Then the upper and lower substrates are placed in position and the
peripheral parts are sealed to make an empty cell-like structure.
With this construction, a prototype of liquid crystal display
device is manufactured in the same way as in Example 1.
[0163] In this case, 4-division type light leakage placing the
spacer in the center is about 70% and the 2-division type light
leakage is about 30%. The amount of light leakage in the 4-division
type region in this Comparative Example is 42.times.10.sup.-5
(%.multidot.mm.sup.2/piece), and that in the 2-division type region
is 94.times.10.sup.-5 (%.multidot.mm.sup.2/piece). The contact
angle between the liquid crystal and the spacer beads is
83.degree., which shows almost vertical alignment. In the case of
vertically aligned spacer beads, both the 4-divided type and the
2-divided type (shown in FIGS. 1 and 2) show disturbance in
alignment in the azimuthal direction against the aligning direction
of the alignment control film and increase the light leakage rate
remarkably. Consequently, float of the black level was prominent,
and the contrast ratio is as low as 150.
EXAMPLE 3
[0164] 100 g of the polymeric spacer beads having a particle size
of 3.8 .mu.m and otherwise the same as used in Example 2, are
immersed in 100 g of a THF solution containing equimolar amounts of
3-aminopropyldiethoxyme- thylsilane, 7-hydroxyoctylcarbonyl
chloride and triethylamine, and the solution is stirred at
50.degree. C. for 2 hours, then filtered, washed with THF and
dried.
[0165] For forming an alignment film, polyamic acid is prepared
using p-phenylenediamine as a diamine moiety and pyromellitic acid
dianhydride as an acid anhydride moiety, and this solution is
coated on the substrate, dried and calcined to form an alignment
control film 8, and rubbed for aligning the liquid crystal
molecules so as to make the pretilt angle 3.3.degree..
[0166] A prototype of IPS mode TFT liquid crystal display device
having a diagonal of 13.3 inches, a pixel count of
1,024.times.RGB.times.768 and an average spacer bead dispersion
density of 120 pieces/mm.sup.2 is manufactured in the same way as
in Example 1. The contact angle between the liquid crystal and the
spacer beads is 41.degree. and that between the liquid crystal and
the alignment direction of alignment film is 6.7.degree.. The
spacer beads of the 4-division type shown in FIG. 1 with a light
leakage contribution of 7.8.times.10.sup.-5
(%.multidot.mm.sup.2/piece) appeare almost over the whole surface.
This liquid crystal display device shows very fine black level and
a contrast ratio of 295.
EXAMPLE 4
[0167] 10 g of the polymeric spacer beads having a particle size of
3.8 .mu.m and otherwise the same as used in Example 2, are immersed
in 100 g of THF solution containing equimolar amounts of
3-aminopropydiethoxymethy- lsilane, trifluoromethoxyoctylcarbonyl
chloride and triethylamine, and the solution is stirred at
50.degree. C. for 2 hours, filtered, washed with THF and dried.
[0168] For forming an alignment film, polyamic acid is prepared
using 4,4'-diaminodiphenylmethane as a diamine moiety and
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride as an acid
anhydride moiety, and this solution is coated on the substrate,
then dried and calcined to form an alignment control film 8, and
rubbed for aligning the liquid crystals.
[0169] A prototype of IPS mode TFT liquid crystal display device
having a diagonal of 13.3 inches, a pixel count of
1,024.times.RGB.times.768 and an average spacer bead dispersion
density of 90 pieces/mm.sup.2 is manufactured in the same way as in
Example 1. The contact angle between the liquid crystal and the
spacer beads is 28.9.degree. and that between the liquid crystal
and the alignment direction of alignment film is 9.8.degree.. The
spacer beads of the 4-division type shown in FIG. 1 with a light
leakage contribution of 7.1.times.10.sup.-5
(%.multidot.mm.sup.2/piece) appeare almost over the whole bead
surface. A liquid crystal display device showing very fine black
level and a contrast ratio of 310 is obtained.
EXAMPLE 5
[0170] Equimolar amounts of diethoxy-3-glycidoxypropylmethylsilane
and dihydroxyoctylamine are mixed, stirred and evaporated, and the
produced compound is dissolved in ethanol. The polymeric spacer
beads as used in Example 2 are immersed in this solution, stirred
at 50.degree. C. for 2 hours, filtered, washed with ethanol and
dried.
[0171] For forming an alignment film, polyamic acid is prepared
using a 1:4 mixture (by molar ratio) of
4-octadecyloxy-1,3-diaminocyclohexane and p-phenyldiamine as a
diamine moiety and an equimolar mixture of
1,2,3,4-butanetetracarboxylic acid dianhydride and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride as acid
anhydrides, and its solution is coated on the substrate, dried and
calcined to form an alignment control film 8, and rubbed for
aligning the liquid crystal molecules so as to make the pretilt
angle 2.8.degree.. The acid anhydrides and diamine compounds such
as mentioned above need not be used singly; they may be used by
mixing two or more of them as desired.
[0172] A prototype model of IPS mode TFT liquid crystal display
device having a diagonal of 13.3 inches, a pixel count of
1,024.times.RGB.times.768 and an average spacer bead dispersion
density of 100 pieces/mm.sup.2 is manufactured in the same way as
in Example 1. The contact angle between the liquid crystal and the
spacer beads is 18.degree. and that between the liquid crystal and
the alignment direction of the alignment film is 9.3.degree.. The
spacer beads of the 4-division type shown in FIG. 1 with a light
leakage contribution of 8.0.times.10.sup.-5
(%.multidot.mm.sup.2/piece) appeare almost over the whole bead
surface. The obtained liquid crystal display device shows very fine
black level and a contrast ratio of 310.
EXAMPLE 6
[0173] 10 g of the polymeric spacer beads having a particle size of
3.8 .mu.m and otherwise the same as used in Example 2, are immersed
in 100 g of a THF solution containing equimolar amounts of
3-aminopropyldiethoxyme- thylsilane, 4-hydroxypentylbenzoyl
chloride and triethylamine, stirred at 50.degree. C. for 2 hours,
filtered, washed with THF and dried.
[0174] For forming an alignment film, polyamic acid is prepared
using 1:4 mixture (by molar ratio) of
4-octadecyloxy-1,3-diaminocyclohexane and p-phenylenediamine as a
diamine moiety and an equimolar mixture of
1,2,3,4-butanetetracarboxylic acid dianhydride and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride as acid
anhydrides, and its solution is coated on the substrate, dried and
calcined to form an alignment control film 8, and rubbed for
aligning the liquid crystal molecules. The acid anhydrides and
diamine compounds such as mentioned above need not be used singly;
they may be used by mixing two or more of them as desired.
[0175] A prototype model of IPS mode TFT liquid crystal display
device having a diagonal of 13.3 inches, a pixel count of
1,024.times.RGB.times.768 and an average spacer bead dispersion
density of 80 pieces/mm.sup.2 is manufactured in the same way as in
Example 1. The contact angle between the liquid crystal and the
spacer beads is 32.degree., and that between the liquid crystal and
the alignment directin of alignment film is 10.degree.. The spacer
beads of the 4-division type shown in FIG. 1 with a light leakage
rate of 7.1.times.10.sup.-5 (%.multidot.mm.sup.2/piece) appeare
almost over the whole surface. It is possible to obtain a liquid
crystal display device showing very fine dark level and a contrast
ratio of 290.
EXAMPLE 7
[0176] Equimolar amounts of diethoxy-3-glycidoxypropylmethylsilane
and dihydroxypentylamine are mixed, stirred and evaporated, and the
resulting compound is dissolved in ethanol. The polymeric spacer
beads having a particle size of 4.0 .mu.m are immersed in this
solution, stirred at 50.degree. C. for 2 hours, filtered, washed
with ethanol and dried.
[0177] As the monomer component of the alignment film, a 1:4
mixture (in molar ratio) of 4-octadecyloxy-1,3-diaminocyclohexane
and p-phenylenediamine is used as diamine moiety and an equimolar
mixture of 1,2,3,4-butanetetetracarboxylic acid dianhydride and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride is used as acid
anhydride to prepare polyamic acid. This solution is coated on the
substrates, dried and calcined to form an alignment control film 8,
and the film is rubbed for aligning the liquid crystal molecules.
The rubbing density is adjusted to provide a pretilt angle of
1.degree.. These acid anhydrides and diamine compounds may not be
used singly; they may be used by mixing two or more of them as
required.
[0178] An IPS mode TFT liquid crystal display device with a
diagonal of 13.3 inches, a pixel count of 1,024.times.RGB.times.768
and an average spacer bead dispersion density of 100
pieces/mm.sup.2 is made in the same way as in Example 1. In the
device of this embodiment, the liquid crystal/spacer bead contact
angle is 8.degree., the contact angle between the liquid crystal
and the alignment film in its aligning direction is 6.degree. and
the contact angle in the direction orthogonal to the aligning
direction is 9.8.degree.. In the liquid display of this
construction, the spacer beads of the 4-division type shown in FIG.
1 with a light leakage contribution of 7.9.times.10.sup.-5
(%.multidot.mm.sup.2/piece) appeare almost over the whole surface.
Thereby a liquid crystal display device showing a very good dark
level with a contrast ratio of 310 can be obtained.
[0179] The liquid display device of the instant embodiment has a
particularly wide viewing angle because of very small pretilt
angle. In case the pretilt angle is small as in the instant
embodiment, the liquid crystal molecules in the region 48 shown in
FIG. 1 must be aligned vertically to the spacer fairly strictly.
This is for the reason that if the liquid crystal molecules are
aligned horizontally to the azimuthal direction, no 4-division type
alignment is provided nor can be effected molecular alignment
horizontal to the polar direction. In this case, if the contact
angle with the alignment control film in its alignment controlling
direction is smaller than the liquid crystal/spacer contact angle,
it is possible to afford an easy-to-wet property to the molecules
in the alignment controlling direction, and if the contact angle in
the direction orthogonal to the alignment controlling direction is
smaller than the liquid crystal/spacer contact angle, the liquid
crystal molecules become hard to wet in this direction, i.e. they
become easy to control in the alignment controlling direction. This
has the effect of realizing preferential emergence of the
4-division type even in case the pretilt angle is low and the
liquid crystal/spacer contact angle is small. Particularly when the
liquid crystal/spacer contact angle is smaller than 10.degree., the
horizontal aligning tendency becomes very strong, so that it is
desirable to make use of the above effect of the instant
embodiment.
EXAMPLE 8
[0180] 10 g of polymeric spacer beads having a particle size of 4.0
.mu.m are immersed in 100 g of a THF solution containing equimolar
amounts of 3-aminopropyldiethoxymethylsilane,
7-hydroxyoctylcarbonyl chloride and triethylamine, and the solution
is stirred at 50.degree. C. for 2 hours, then filtered, washed with
THF and dried. Then glass fibers of 4 .mu.m in diameter are mixed
in a ratio of 20%, and the mixture is dispersed in a 1:1 mixed
solvent of 2-propanol and water by an ultrasonic cleaner for 10
minutes and then centrifuged to separate the spacer beads. This
treatment produce a small cavity on the spacer surface.
[0181] As the monomer component of the alignment film,
p-phenylenediamine is used as diamine moiety and pyromellitic acid
dianhydride is used as acid anhydride moiety to prepare polyamic
acid, and this solution is coated on the substrates, dried and
calcined to form an alignment control film 8, which is then rubbed
for aligning the liquid crystal molecules. The rubbing density is
adjusted to provide a pretilt angle of 3.3.degree..
[0182] An IPS mode TFT liquid crystal display device with a
diagonal of 13.3 inches, a pixel count of 1.024.times.RGB.times.768
and an average spacer bead dispersion density of 120
pieces/mm.sup.2 is made in the same way as in Example 3. In this
Example, the liquid crystal/spacer bead contact angle is 20.degree.
and the contact angle with the alignment film in its aligning
direction is 6.7.degree.. In the thus composed liquid crystal
display device, the spacer beads of the 4-division type shown in
FIG. 1 with a light leakage contribution of 7.3.times.10.sup.-5
(%.multidot.mm.sup.2/piece) emerge almost over the whole surface.
Thereby a liquid crystal display device showing very good dark
level and a contrast of 305 can be obtained.
[0183] If the liquid crystal/spacer contact angle is 90.degree. or
less, the liquid crystal can fill up the cavity on the spacer bead
surface, so that a smooth surface is provided in which a certain
portion is the solid of the space bead surface and another portion
is composed of the liquid crystal. Since the liquid crystal/liquid
crystal contact angle is 0.degree., the apparent contact angle
decreases. This accounts for the effect of reducing the contact
angle from 41.degree. to 20.degree. in the instant embodiment.
Therefore, when the liquid crystal/spacer contact angle is
70.degree. to 90.degree., the spacer beads composed of a
high-molecular weight compound may be used by mixing therewith the
ceramic particles, glass fibers or the like, stirring the mixture
and separating the beads. It is to be noted that when the liquid
crystal/spacer contact angle exceeds 90.degree., the liquid crystal
is incapable of filling up the cavity on the spacer surface, so
that a certain portion becomes the solid of the spacer bead surface
while another portion is turned into air, resulting in an increase
of apparent contact angle. Therefore, the liquid crystal/spacer
contact angle exceeding 90.degree. is impracticable.
EXAMPLE 9
[0184] In order to investigate the liquid crystal/spacer contact
angle and the liquid crystal/alignment control film contact angle,
a model experiment is carried out using the unit cells. The unit
cells are constructed by washing the glass substrates, coating the
substrates with the polyimide-based alignment films produced by
Nissan Chemical Co., Ltd., Hitachi Chemical Co., Ltd., Chisso
Corp., etc., changing wettability of the alignment control film in
its alignment controlling direction and in the direction orthogonal
thereto, scattering the spacers on the film-coated substrates and
sealing the peripheral portions to make the empty cells. After the
sealant is cured, the liquid crystal is encapsulated and the
deflectors are set in position to construct the unit cells.
[0185] As the liquid crystal, the liquid crystal compositions
produced by Merck & Co., Ltd., Chisso Corp. and Lodic Co., Ltd.
were used. As the spacers, those employed in Examples 1 to 8 and
the commercial products available from Sekisui Chemical Co., Ltd.,
Kao Corp. and Natoco Paint Co., Ltd. were used. Light leakage is
determined by a method in which the contact angles are measured in
the manner described above and a combination of the unit cells that
provides the desired contact angles are assembled. In the IPS mode
normally closed liquid crystal display devices, light leakage can
be determined at the dark level where no electric field is applied,
so that the amount of light leakage determined by this method is
equal to the value obtained from the measurement on a full-fledged
IPS mode liquid crystal display device. Therefore, the contrast
ratio of the IPS mode liquid crystal display devices can be
predicted from this method. Since this method is designed for the
model experiments, it is possible to carry out an experiment using
model liquid crystal for close investigation of the liquid
crystal/spacer contact angle.
[0186] In this way, various types of unit cells are manufactured
and investigated. As a result, it is found that when the liquid
crystal/spacer contact angle is made smaller than 60.degree., the
liquid crystal molecules on the spacer surface substantially assume
parallel alignment and it is possible to let the 4-division type
spacers emerge preferentially. On the other hand, when the liquid
crystal/spacer contact angle exceeds 80.degree., the liquid crystal
molecules on the spacer surface assume vertical alignment
regardless of anchoring of the alignment control film and other
conditions, and consequently, as noted in Comparative Example 2,
light leakage centering around each spacer is increased. When the
said contact angle is within the range of 60.degree. to 80.degree.,
the liquid crystal molecules on the spacer surface can take either
horizontal or vertical alignment depending on the other factors
such as anchoring and pretilt angle of the alignment control film.
In this case, the latter of the above-mentioned two phenomena
relating to the spacers, viz. degradation of image quality due to
the presence of the spacers with large and small light leakage, is
called in question. It is also a matter of concern that alignment
around the spacer is unstable and subject to change with time.
[0187] Thus, in order to provide parallel alignment of the liquid
crystal molecules on the spacer surface, it is necessary to make
the liquid crystal/spacer contact angle not greater than
60.degree..
[0188] The results of the instant embodiment are shown in Table 1.
In this way, there were acquired means for obtaining the objective
high-image-quality IPS mode liquid crystal displays.
1 TABLE 1 Contact angle with liquid crystal (.degree.) Alignment
Run controlling Orthogonal Light Features of liquid No. Spacer
direction direction leakage crystals and spacers Evaluation 1 85 7
15 97 .times. 10.sup.-4 *2 X 2 15 5 10 0.7 .times. 10.sup.-4 *3
23.8 mN/m .largecircle. 3 70 3 8 *1 *4 X 4 58 3 8 0.92 .times.
10.sup.-4 *5 .largecircle. 5 8 5 10 0.85 .times. 10.sup.-4 *6
.largecircle. 6 8 3 5 *1 *7 X Note) *1: Emergence of 2-division
type *2: Neutral liquid crystals *3: Cyano + fluorine liquid
crystals *4: Divinylbenzene spacer *5: Liquid crystal of Run No.
and spacer of Example 1 *6: Cyano + fluorine liquid crystals;
Spacer of Example 1 *7: Same liquid crystals and spacers as used in
Example 1; Change of alignment film rubbing conditions
[0189] The following facts are clarified from the above
results.
[0190] The neutral liquid crystal having no polar group has a
stronger inclination to assume vertical alignment. This is
considered attributable to the wetting agent-like action of the
functional group having polarity on the spacer surface. Also, by
introducing a functional group such as alkyl group or hydroxyl
group to the spacer surface as in Run Nos. 3 and 4, it is possible
to improve wettability and to obtain a positive effect in reducing
light leakage due to the spacers. This owes to the fact that the
functional group on the spacer surface has the function of a
wetting agent. It can thus be learned that it is effective to
introduce to the liquid crystal or spacer surface a functional
group acting like a wetting agent which betters wettability of both
the liquid crystal and the spacer surface. These effects are
attributable to the difference between them in intermolecular
attraction and individual cohesive force, so that the desired
result can be obtained by offering a combination that strengthens
intermolecular attraction. These features are not limited to the
compounds in the instant embodiment of the present invention.
[0191] The pretilt angle of Run No. 6 is almost 0.degree.. It is
noted that if the liquid crystal/spacer contact angle is reduced
excessively to induce a strong tendency to assume horizontal
alignment and also the liquid crystal/alignment control film
contact angle is reduced radically, the liquid crystal molecules in
the region indicated by numeral 48 in FIG. 1 are stabilized in
their horizontal alignment on the spacer surface and consequently
the 2-division type prevails. It is thus seen that it is important
to control the value of liquid-crystal/alignment control film
contact angle, especially in case the liquid crystal/spacer contact
angle is extremely small.
EXAMPLE 10
[0192] A schematic sectional illustration of a liquid crystal
display device embodying the present invention is shown in FIG.
12.
[0193] In this liquid crystal display device, common electrodes 2
adapted to apply a voltage of a fixed waveform independently of the
picture signal and scanning wiring electrodes are provided on the
lower one (numeral 1) of a pair of substrates 1, 1'. Overlaid on
these electrodes is an insulating film 4' made of silicon nitride,
and on this insulating film 4' are provided pixel electrodes 3
which are varied in waveform according to the picture signal and
signal distributor 10 which issues picture signal to the pixel
electrodes. Overlaid on these electrodes are another insulating
film 4 made of silicon nitride and a transparent organic polymer
film 7 in this order. On said organic polymer film 7 are provided
an alignment control film 8 and spacer beads 40, said alignment
control film 8 being partly disposed between each spacer bead 40
and a liquid crystal layer 30. Also, this alignment control film 8
is made of a material which can be provided with a liquid crystal
aligning function by irradiation with polarized light. A polarizer
9 is provided on the underside of the substrate 1.
[0194] On the lower side of the other substrate 1' is provided a
color filter 5 for making color display, and an organic polymer
film 7' and an alignment control film 8' are laid underneath said
color filter 5. A polarizer 9' is provided on the upper side of
this substrate 1'.
[0195] FIG. 13 shows the aligning direction of the alignment
control film and the polarization axis of the polarizer.
[0196] In this figure, the angles made by the polarizers with the
direction of electric field 13 are indicated by .PHI.p1 and .PHI.p2
and the angle made by the alignment direction with the direction of
electric field is indicated by .PHI.LC. In this Example, the above
angles are set to be .PHI.LC=75.degree., .PHI.p1=30.degree. and
.PHI.p2=120.degree.. That is, the angular setting is made to
provide the normally open display characteristics. In FIG. 13,
reference numeral 11 indicates the alignment direction, 12 the
polarized light transmission axis of one of the polarizers, 12' the
polarized light transmission axis of another polarizer which
crosses the transmission axis 12 at right angles, and 28 is a strip
electrode.
[0197] FIG. 18 shows a frontal view taken from the direction
vertical to the panel plane, which schematically illustrates the
alignment direction of the liquid crystal molecules around a spacer
bead in the liquid crystal display device according to the instant
embodiment of the invention.
[0198] No alignment control film is shown in this figure, but since
a liquid crystal aligning force is provided between each spacer
bead 40 and the liquid crystal layer by polarized light
irradiation, the liquid crystal layer around each spacer bead won't
be disturbed in its alignment and the liquid crystal molecules are
aligned in the same direction as the aligning direction of the
alignment control film. This greatly contributes to the reduction
of light leakage around the spacer beads and the consequent
improvement of contrast.
[0199] A process for producing this liquid crystal display device
is shown below.
[0200] The procedure till formation of the pixel electrodes 3,
common electrodes 2 and insulating film 4 is the same as in the
conventional process for producing an IPS mode liquid crystal
display device, but the process of the present invention is
different in that a transparent organic polymer film 7, alignment
control film 8 and spacer beads 40 are produced in the following
way.
[0201] The organic polymer film 7 is formed by applying on the
insulating film 4 a polyamic acid solution of PIQ-1800 (an
amorphous film produced by Hitachi Chemical Co., Ltd.) diluted to a
8.5% concentration, and heating it at 150.degree. C. for 10 minutes
to evaporate the solvent. This organic polymer film 7 is provided
for securing adhesion of the alignment control film to the
insulating film or the electrodes, but it may not be provided when
secure adhesion can be provided by merely imidizing the alignment
control film. Provision of said film 7 also proves useful for
flattening the assembly structure.
[0202] Spacer beads 40 are provided after forming the organic
polymer film by dispersing the polymeric spacer beads of 4 .mu.m in
particle size on the substrate by the dry scatter method. The "dry
scatter method" used in the present invention is a method in which
a negative pressure is produced in the nozzle section by
discharging an inert gas from a compressed gas supply pipe to suck
up and scatter the spacer beads for liquid crystal display devices
from a spacer bead supply pipe. In this method, no solvent is used
as spacer beads dispersing medium.
[0203] Alignment control film 8 is formed after dispersion of the
spacer beads 40 by applying a 3% solution of polyamic acid, and
calcining the coating at 200.degree. C. for 30 minutes for
imidization. The precursor of the alignment control film 8 is
polyamic acid which is a polyimide precursor. Polymeric acid is
synthesized using an equimolar mixture of 4,4'-diaminoazobenzene
containing diazobenzene groups and 4,4'-diaminophenylmethane as
diamine moiety and pyromellitic acid dianhydride and
1,2,3,4-cyclobutanetetracarboxylic acid dianhydride as acid
anhydrides. In the instant embodiment of the present invention,
azobenzene groups such as described in U.S. Pat. No. 4,974,941,
which is herein fully incorporated by reference, are introduced
into the composition to afford photo-isomerization reactivity, but
other groups, preferably stilbene group or the like, may be applied
if they have photo-isomerization reactivity and an ability to
control liquid crystal alignment.
[0204] After formation of said polyimde precursor film (organic
polymer layer), dispersion of the spacer beads and formation of
another polyimide precursor film (alignment control layer) have
been completed, imidization was effected by calcination.
[0205] Imidization after coating of the spacer bead surfaces with
the alignment control film 8 makes it possible to prevent transfer
of the spacer beads.
[0206] The substrate on the lower side is placed in registration
with the upper side substrate and the peripheral parts are sealed
to form a liquid crystal cell.
[0207] The liquid crystal cell is irradiated externally with
polarized light from a high pressure mercury lamp through a
polarizing film at an irradiation dose of 2 J/cm.sup.2. Then the
liquid crystal composition is encapsulated at room temperature and
annealed at 100.degree. C. for 10 minutes to obtain liquid crystal
alignment of the direction substantially vertical to the polarized
light direction. The long axial direction of the liquid crystal
molecules in the produced state of alignment was set so that the
angle .PHI.LC defined in FIG. 13 becomes 75.degree.. In this way, a
liquid crystal display device with a liquid crystal layer thickness
d of 4.0 .mu.m is obtained. Nematic liquid crystal with positive
dielectric anisotropy is used for the liquid crystal composition of
the liquid crystal layer. Dielectric anisotropy .DELTA..epsilon. of
the liquid crystal is 10.2 and its refractive anisotropy .DELTA.n
is 0.073.
[0208] FIGS. 14A to 14D illustrate the switching behavior of the
liquid crystal molecules in the thus obtained liquid crystal panel.
In the instant embodiment of the invention, the liquid crystal
molecules are aligned with the angle .PHI.LC of 75.degree. against
the direction vertical to the longitudinal direction of the strip
electrodes when no electric field is applied, but in case
dielectric anisotropy of the liquid crystal is positive, it is
advised to develop alignment with
45.degree..ltoreq..vertline..PHI.LC.vertline.<90.degree.. The
liquid crystal composition of the liquid crystal layer may be of
negative dielectric anisotropy. In this case, it is preferable to
adjust initial alignment to
0.degree..ltoreq..vertline..PHI.LC.vertline.<45.degree. from the
direction vertical to the strip electrodes. In FIGS. 14A to 14D,
the long axial direction of the liquid crystal molecules is shown
by an arrow 11. When an electric field is applied in the direction
13 between a common electrode 2 and a pixel electrode 3, the liquid
crystal molecules 6 are shifted so that the long axes of the
molecules will become parallel to the direction of electric field
13 as shown in FIGS. 14B and 14D. Consequently, .theta. in the
formula (1) changes in accordance with electric field strength E,
causing corresponding change of transmittance. In this Example,
since birefrigent mode display system is employed, liquid crystal
is held between a pair of crossed polarizers.
[0209] Further, in order to produce a normally closed system where
dark display is given at low voltage, the polarized light
transmission axis 12 of one of the polarizers is set parallel to
the initial alignment direction 11 while the polarized light
transmission axis 12' of the other polarizer is set to cross the
initial alignment direction 11 at right angles as shown by arrows
in FIG. 14C. The observed transmitted light strength is given by
the formula (1).
[0210] FIGS. 15A to 15C show the layout of a unitary pixel section
in the instant embodiment of the present invention, said unitary
pixel section comprising a group of electrodes including a common
electrode 2, a pixel electrode 3, a picture signal electrode 10 and
a scanning electrode 14, amorphous silicon 16, a thin-film
transistor 15, an insulating film 4, an alignment control film 8,
an organic polymer film 7, and a display zone 31 where display is
made on application of an electric field from the common and pixel
electrodes 2, 3. FIG. 15A is a frontal view taken from the
direction vertical to the panel plane, and FIGS. 15B and 15C are
the side sectional views.
[0211] FIG. 16 shows the circuit system in the liquid crystal
display device according to the instant embodiment of the
invention, said circuit system comprising vertical scanning signal
circuit 17, picture signal circuit 18, common electrode driving
circuit 19, power circuit and controller 20.
[0212] FIG. 17 shows the optical system in the liquid crystal
display device.
[0213] A back light unit 26 comprising a light source 21, a light
cover 22, a photoconductor 23 and a diffuser 24 is provided on the
back side of a liquid crystal panel 27. In this embodiment, a prism
sheet 25 is provided for increasing frontal luminance. In case no
such prism sheet is provided, it is possible to lessen viewing
angle dependency of luminance.
[0214] FIG. 18 is a frontal view taken from the direction vertical
to the panel plane, which schematically illustrates the alignment
direction of the liquid crystal molecules around a spacer bead in
the liquid crystal display device according to the instant
embodiment of the invention. Since the alignment control film is
formed after dispersion of the spacer beads and its alignment
controlling ability is provided by irradiation with polarized light
from a high pressure mercury lamp, the surface of the portion of
each spacer bead contacted with liquid crystal is covered with the
alignment control film as shown in FIG. 12. Consequently, the
liquid crystal layer around each spacer bead is not disturbed in
its alignment and the liquid crystal molecules are aligned in the
same direction as the aligning direction of the alignment control
film. This greatly contributes to the reduction of light leakage
around the spacer beads.
[0215] Light leakage contribution in the instant embodiment is
1.0.times.10.sup.-5 (%.multidot.mm.sup.2/piece). At this level,
even if the spacer bead dispersion density is supposed to be as
high as 1,000 pieces/mm.sup.2, the increase of transmittance is
only 0.01%. It is noted that in the liquid crystal display device
of this Example the influence of the spacer beads on dark display
is very small. "Trasmittance" referred to herein is defined to be
transmittance of the display pixel region. Actual transmittance of
a liquid crystal display device is subject to the influence of
light leakage due to the factors other than the spacer beads,
aperture ratio of color filter or display zone, pixel edge, etc.
Therefore, transmittance shown herein is that in a state free of
such influence.
[0216] Under the above conception, a prototype of IPS mode TFT
liquid crystal display device with a diagonal of 13.3 inches, a
pixel count of 1,024.times.RGB.times.768 and a spacer bead
dispersion density of about 120 (pieces/mm.sup.2) is manufactured.
There is obtained a liquid crystal display device showing
fine-level black display and a contrast ratio of 300.
EXAMPLE 11
[0217] 10 g of the polymeric spacer beads having a particle size of
4.0 .mu.m and composed of divinylbenzene-styrene copolymer resin is
immersed in a solution of 30 g of 2% hydrochloric acid and 30 g of
isopropyl alcohol, to which a solution of 3 g of
4-stilbenzenecarboxyaldehyde in 10 g of isopropyl alcohol is added
dropwise with stirring. After 2-hour reaction at 50.degree. C. and
successive filtration, the treated spacer beads are immersed in a
solution of 70 g of pure water and 30 g of isopropyl alcohol and
filtered. The above operation is repeated 10 times and the
resulting beads are immersed in 70 g of toluene and filtered, this
operation being repeated 5 times followed by drying. Thereby an
organic film 42 which can be provided with a liquid crystal
aligning ability by irradiation of polarized light is formed on the
surface of each spacer bead 40.
[0218] A prototype of liquid crystal display device is manufactured
using these spacer beads. This prototype is different from that of
Example 10 in the following points.
[0219] For forming a transparent organic polymer layer, a 8.5%
polyamic acid solution of PIQ-1800 (an amorphous film produced by
Hitachi Chemical Co., Ltd.) is applied to the substrate and heated
at 150.degree. C. for 10 minutes to evaporate the solvent, and then
a 3% solution of polyamic acid is applied thereto. The precursor of
the alignment control film 8 is polyamic acid which is a polyimide
precursor, and the polyamic acid is synthesized using an equimolar
mixture of 4,4'-diaminostilbene containing stilbene groups and
4-phenylmethane as diamine compounds and pyromellitic acid
dianhydride and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride
as acid anhydrides. The coating is then calcined at 200.degree. C.
for 30 minutes for imidization.
[0220] Then the spacer beads treated as described above are
dispersed on the substrate by the half-dry scatter method.
"Half-dry scatter method" is a method in which the spacer beads are
dispersed in an alcohol or a water/alcohol mixed solvent and
scattered as a mist with a jet of an inert gas. In this operation,
the inside of the disperser from the nozzle to the substrate is
heated so that the solvent is evaporated before reaching the
substrate, allowing the spacer beads alone to deposit on the
substrate.
[0221] In this Example, imidization by calcination and dispersion
of the spacer beads are performed after formation of a polyimide
precursor film constituting a transparent organic polymer layer and
a polyimide precursor film constituting an alignment control film.
Then the upper and lower substrates are placed in registration with
each other and the peripheral parts are sealed to make an empty
cell-like structure.
[0222] Thereafter, the cell is irradiated externally with polarized
light through a polarizing film using as light source xenon
chloride eximer laser having a peak at 308 nm.
[0223] FIG. 19 is an emphasized schematic illustration of the film
structure around the group of electrodes in the instant embodiment
of the invention. It will be seen that a transparent organic
polymer film 7 is laid on an insulating film 4 covering the
electrodes 3, 10, and overlaid on said film 7 is an alignment
control film 8, on which are disposed the spacer beads 40 each
having on its surface a coating film 42 provided with a liquid
crystal aligning ability by irradiation with polarized light.
[0224] Light leakage contribution L of this unit determined in the
same way as in Example 10 is 1.1.times.10.sup.-5
(%.multidot.mm.sup.2/piece).
[0225] Incorporating the above construction, a prototype of IPS
mode TFT liquid crystal display device having a diagonal of 13.3
inches, a pixel count of 1,024.times.RGB.times.768 and an average
spacer bead distribution density of 100 pieces/mm.sup.2 is
manufactured in the same way as in Example 10. In this prototype,
light leakage due to the spacer beads in dark display is markedly
reduced and good uniformity of display with excellent black level
is obtained. Contrast ratio is about 300.
[0226] Similar treatments can be applied to the spacer beads if
they have a hydroxyl group in the surface. When a hydrophilic group
is present in abundance in the surface, there exist plenty of
binding water and hydroxyl groups derived from this binding water,
so that the materials usable for these spacer beads are not limited
to the specific types; it is possible to use inorganic materials,
for instance, synthetic glass, borosilicate glass, alumina, alumina
silicate glass, etc; or organic materials such as epoxy resins,
phenol resins, melamine resins, unsaturated polyester resins,
divinylbenzene polystyrene resins, divinylbenzene polyester resins,
divinylbenzene-acryl ester resins, and diacryl phthalate
resins.
COMPARATIVE EXAMPLE 3
[0227] For forming a transparent organic polymer layer, a 8.5%
polyamic acid solution of PIQ-1800 (an amorphous film produced by
Hitachi Chemical Co., Ltd.) is applied to a substrate and heated at
150.degree. C. for 10 minutes to evaporate the solvent, and then a
3% solution of polyamic acid (precursor of the alignment control
film 8) is applied, followed by 30-minute calcination at
200.degree. C. for imidization.
[0228] Then the silica spacer beads having a particle size of 4
.mu.m and provided with a strong urging force to let the liquid
crystal molecules align horizontally are dispersed on the
substrate.
[0229] In this Comparative Example, imidization by calcination and
dispersion of the spacer beads are conducted after formation of a
polyimide precursor film constituting a transparent organic polymer
layer and a polyimide precursor film constituting an alignment
control layer. Then the upper and lower substrates are placed in
position and the peripheral parts are sealed to constitute an empty
cell-like structure. With this construction, a prototype of liquid
crystal display device is manufactured in the same way as in
Example 10. The light leakage contribution is 28.0.times.10.sup.-5
(%.multidot.mm.sup.2/piece).
[0230] In the liquid crystal display device of this Comparative
Example, there takes place heavy light leakage around each spacer
bead as typically illustrated in the light leakage zone 41 in FIG.
2, and the contrast ratio is 200.
COMPARATIVE EXAMPLE 4
[0231] For forming a transparent organic polymer layer, a 8.5%
polyamic acid solution of PIQ-1800 is applied to a substrate and
heated at 150.degree. C. for 10 minutes to evaporate the solvent,
and then a 3% solution of polyamic acid (precursor of the alignment
control film 8) is applied, followed by 30-minute calcination at
200.degree. C. for imidization.
[0232] Then, the polymeric spacer beads 4 .mu.m in particle size
and having their surfaces chemically modified for expediting
vertical alignment of the liquid crystal molecules are dispersed on
the substrate by the dry scatter method.
[0233] In this Comparative Example, imidization by calcination and
dispersion of the spacer beads are conducted after formation of a
polyimide precursor film constituting a transparent organic polymer
layer and a polyimide precursor film constituting an alignment
control layer. Then the upper and lower substrates are placed in
registration with each other and the peripheral parts are sealed to
constitute an empty cell-like structure. With this construction, a
prototype of liquid crystal display device is manufactured in the
same way as in Example 10. This model shows a light leakage
contribution of 95.0.times.10.sup.-5
(%.multidot.mm.sup.2/piece).
EXAMPLE 12
[0234] This Example differs from Example 10 in the following
points.
[0235] For forming a transparent organic polymer layer, a 8.5%
polyamic acid solution of PIQ-1800 is applied and heated at
150.degree. C. for 10 minutes to evaporate the solvent, and then a
3% solution of polyamic acid, which is the alignment control film
precursor having the 4 .mu.m polymeric spacer beads dispersed
therein, is applied. The polyamic acid is the same as used in
Example 10. Thereafter, the coating is calcined at 200.degree. C.
for 30 minutes for imidization.
[0236] In this Example, imidization by calcination is conducted
after formation of a polyamide precursor film constituting a
transparent organic polymer layer and an alignment control film by
application of a spacer beads-dispersed polyimide precursor. Then
the upper and lower substrates are set in position and the
peripheral parts are sealed to constitute an empty cell-like
structure. Light leakage contribution of this unit is
1.0.times.10.sup.-5 (%.multidot.mm.sup.2/piece).
[0237] With the above construction, a prototype of IPS mode TFT
liquid crystal display device having a diagonal of 13.3 inches and
a pixel count of 1,024.times.RGB.times.768 is manufactured in the
same way as in Example 10. Light leakage due to the spacer beads in
dark display reduces remarkably, and the display device shows
excellent black level and a contrast ratio of 300.
EXAMPLE 13
[0238] 10 g of the polymeric spacer beads having a particle size of
4.0 .mu.m are immersed in 100 g of a THF solution containing
equimolar amounts of 3-aminopropyldiethoxysilane,
4'-propylstilbene-4-carbonyl chloride and triethylamine, and the
solution is stirred at 50.degree. C. for 2 hours, filtered, washed
with THF and dried. The thus obtained spacer beads show a light
leakage contribution of 1.2.times.10.sup.-5
(%.multidot.mm.sup.2/piece).
[0239] Using these space beads, a trial model of liquid crystal
display device is manufactured in the same way as in Example
11.
[0240] With the above construction, a prototype of IPS mode TFT
liquid crystal display device having a diagonal of 13.3 inches and
a pixel count of 1,024.times.RGB.times.768 is manufactured. Light
leakage due to the spacer beads in dark display reduces remarkably,
and the display device shows excellent black level, good uniformity
of display and a contrast ratio of 295.
[0241] The above treatment can be applied to the spacer beads if
they have hydroxyl groups on the surface. When hydrophilic groups
are present in abundance on the surface, there exist plenty of
binding water and hydroxyl groups derived from this binding water,
so that the materials usable for the spacer beads are not limited
to the specific types; it is possible to use, for instance,
inorganic materials such as synthetic glass, borosilicate glass,
alumina, alumina silicate glass, etc.; and organic materials such
as epoxy resins, phenol resins, melamine resins, unsaturated
polyester resins, divinylbenzene polystyrene resins, divinylbenzene
polyester resins, divinylbenzene-acryl ester resins, diacryl
phthalate resins, etc.
EXAMPLE 14
[0242] 10 g of the polymeric spacer beads, 4.0 .mu.m in particle
size, are immersed in 100 g of a THF solution containing equimolar
amounts of 3-aminopropyldiethoxy-methylsilane,
4-(4-pentylphenylazo)benzoyl chloride and triethylamine, stirred at
50.degree. C. for 2 hours, filtered, washed with THF and dried.
[0243] Using these spacer beads, a prototype of liquid crystal
display device is manufactured in the same way as in Example
12.
[0244] For forming a transparent organic polymer layer, a 8.5%
polyamic acid solution of PIQ-1800 is applied to a substrate and
heated at 150.degree. C. for 10 minutes to evaporate the solvent,
and then a 3% solution of polyamic acid, the precursor of the
alignment control film 8, is coated. The precursor of the alignment
control film 8 is polyamic acid which is the polyimide precursor.
This polyamic acid is synthesized using an equimolar mixture of
4,4'-diaminoazobenzene containing azobenzene groups and
4,4'-diaminophenylmethane as diamine compounds and pyromellitic
acid dianhydride and 1,2,3,4-cyclobutanetetracarboxylic acid
dianhydride as acid anhydrides. The coating is calcined at
200.degree. C. for 30 minutes for imidization.
[0245] The spacer beads treated as described above are dispersed on
the substrate by the half-dry scatter method. "Half-dry scatter
method" is a method in which the spacer beads are dispersed in an
alcohol or a water/alcohol mixed solvent and scattered in the form
of a mist with a jet of an inert gas. In this operation, since the
inside of the dispenser from its nozzle through the distance to the
substrate is heated, the solvent is evaporated before reaching the
substrate, allowing the spacer beads alone to deposit on the
substrate.
[0246] In this Example, imidization by calcination and dispersion
of the spacer beads are conducted after formation of a polyimide
precursor film constituting a transparent organic polymer layer and
a polyimide precursor film constituting an alignment control layer.
Then the upper and lower substrates are placed in position and the
peripheral part is sealed to constitute an empty cell-like
structure. Light leakage contribution of the cell is
0.9.times.10.sup.-5 (%.multidot.mm.sup.2/piec- e).
[0247] With the above construction, a prototype of IPS mode TFT
liquid crystal display device having a diagonal of 13.3 inches and
pixel count of 1,024.times.RGB.times.768 is manufactured in the
same way as in Example 10. This prototype is markedly reduced in
light leakage due to the spacer beads in dark display and shows
excellent black level and a contrast ratio of 320.
[0248] The same treatment can be applied to the spacer beads if
they have hydroxyl groups on the surface. When hydrophilic groups
are present in abundance on the surface, there exist plenty of
binding water and hydroxyl groups derived therefrom, so that the
materials usable for the spacer beads are not limited to the
specific types; it is possible to use, for instance, inorganic
materials such as synthetic glass, borosilicate glass, alumina,
alumina silicate glass, etc.; and organic materials such as epoxy
resins, phenol resins, melamine resins, unsaturated polyester
resins, divinylbenzene polystyrene resins, divinylbenzene polyester
resins, divinylbenzene-acryl ester resins, diacryl phthalate
resins, etc.
EXAMPLE 15
[0249] Equimolar amounts of diethoxy-3-glycidoxypropylmethylsilane
and 4-(4-propylphenylazo)aniline are mixed, stirred and evaporated,
and the produced compound is dissolved in ethanol. The polymeric
spacer beads of 4.0 .mu.m in particle size are immersed in the
solution, stirred at 50.degree. C. for 2 hours, filtered, washed
with ethanol and dried. Light leakage contribution is
1.3.times.10.sup.-5 (%.multidot.mm.sup.2/piece).
[0250] Using these beads, a prototype of IPS mode TFT liquid
crystal display device with a diagonal of 13.3 inches and a pixel
count of 1,024.times.RGB.times.768 is manufactured in the same way
as in Example 5. Light leakage due to the spacer beads in dark
display markedly reduces, and the prototype shows excellent black
level and a contrast ratio of 280.
[0251] The same treatment can be applied to the spacer beads if
they have the hydroxyl groups on the surface. When the hydrophilic
groups are present in abundance on the surface, there exist plenty
of binding water and the hydroxyl groups derived therefrom, so that
the materials usable for the spacer beads are not limited to the
specific types; it is possible to use, for instance, inorganic
materials such as synthetic glass, borosilicate glass, alumina,
alumina silicate glass, etc.; and organic materials such as epoxy
resins, phenol resins, melamine resins, unsaturated polyester
resins, divinylbenzene polystyrene resins, divinylbenzene polyester
resins, divinylbenzene-acryl ester resins, diacryl phthalate
resins, etc.
EXAMPLE 16
[0252] 10 g of the polymeric spacer beads, 3.8 .mu.m in particle
size, are immersed in 100 g of a THF solution containing equimolar
amounts of 3-aminopropyldiethoxymethylsilane,
4-(4-pentylphenylazo)benzoyl chloride and triethylamine, stirred at
50.degree. C. for 2 hours, filtered, washed with THF and dried.
[0253] Using these spacer beads, a prototype of liquid crystal
display device is manufactured.
[0254] A distinctive feature of this embodiment is that the
alignment control film 8 has no light aligning ability and does not
absorb light used for light alignment. In this embodiment, polyamic
acid is prepared using 1,2,3,4-cyclopentenetetracarboxylic acid
dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride,
3,3',4,4'-biscyclohexanetetracarboxylic acid dianhydride,
3,3',4,4'-benzophenonetetracarboxylic acid dianhydride or the like
as acid anhydride and 4,4'-diaminodiphenyl sulfide,
3,3'-diaminodiphenyl sulfide, 1,4-diaminocyclohexane,
3,3'-diaminodiphenyl sulfone or the like as diamine, and this
solution is applied to a substrate, dried and calcined to form an
alignment control film 8, and rubbed for aligning the liquid
crystal molecules. These acid anhydrides and diamine compounds may
be used either singly or by mixing two or more of them as
desired.
[0255] The spacer beads treated as described above are dispersed on
the substrate by the half-dry scatter method. "Half-dry scatter
method" is a method in which the spacer beads are dispersed in an
alcohol or a water/alcohol mixed solvent and scattered in the form
of a mist with a jet of an inert gas. In this operation, since the
inside of the disperser from the nozzle through the distance to the
substrate is heated, the solvent is evaporated before reaching the
substrate, allowing the spacer beads alone to deposit on the
substrate.
[0256] In this Example, imidization by calcination and dispersion
of the spacer beads are conducted after formation of a polyimide
precursor film constituting a transparent organic polymer layer and
a polyimdie precursor film constituting an alignment control film.
Then the upper and lower substrates are placed in position and the
peripheral part is closed by a sealant to constitute an empty
cell-like structure.
[0257] Then the cell is irradiated externally with polarized light
from a high-pressure mercury lamp through a polarizing film.
Thereby the modified film on the spacer bead surface is provided
with a liquid crystal aligning ability and the liquid crystal
molecules on the spacer bead surface are aligned in the same
direction as the rubbing direction. Light leakage contribution of
the cell is 0.9.times.10.sup.-5 (%.multidot.mm.sup.2/piece).
[0258] With the above construction, a prototype of IPS mode TFT
liquid crystal display device with a diagonal of 13.3 inches and a
pixel count of 1,024.times.RGB.times.768 is manufactured in the
same way as in Example 10. Light leakage due to the spacer beads in
dark display markedly reduces, and this prototype also shows
excellent black level and good uniformity of display with a
contrast ratio of 320.
EXAMPLE 17
[0259] In this Example, the polymeric spacer beads 40 with a
particle size of 4 .mu.m are dispersed on the substrate by the dry
scatter method without forming an organic polymer film 7.
[0260] Then a 3% solution of polyamic acid (precursor of the
alignment control film 8) is applied, followed by 30-minute
calcination at 200.degree. C. for imidization. The precursor of the
alignment control film 8 is polyamic acid which is a polyimide
precursor, and it is synthesized using an equimolar mixture of
4,4'-diaminobenzene containing diazobenzene groups and
4,4'-diaminophenylmethane as diamine compounds and pyromellitic
acid dianhydride and 1,2,3,4-cyclobutanetetracarboxylic acid
dianhydride as acid anhydrides.
[0261] In this Example, imidization by calcination is conducted
after dispersion of the spacer beads and formation of a polyimide
precursor film constituting an alignment control layer, and a trial
model of liquid crystal display device is manufactured in the same
way as in Example 10. Light leakage contribution is
1.1.times.10.sup.-5 (%.multidot.mm.sup.2/pi- ece).
[0262] With the above construction, a prototype of IPS mode TFT
liquid crystal display device with a diagonal of 13.3 inches and a
pixel count of 1,024.times.RGB.times.768 is manufactured. Light
leakage due to the spacer beads in dark display reduces remarkably,
and this prototype also shows excellent black level and a contrast
ratio of 300.
[0263] According to the present invention, as described above, a
high-contrast normally closed type in-plane switching mode liquid
crystal display device which is operated by applying to the liquid
crystal layer an electric field in the direction substantially
parallel to the substrates is realized.
* * * * *