JP2000258781A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent display uniformity against in homogeneous heating as an external factor by specifying the relation between the gap thickness near peripheral seal and the gap thickness in the center of the panel. SOLUTION: The gap thickness d1 near the peripheral seal and the gap thickness d2 in the center of the panel satisfy the relation of d1>d2+(average film thickness of the color filter and the black matrix in the display pixel region-film thickness of the black matrix out of the display pixel region). A spacer is dispersed in the pixel region to maintain the gap thickness. In the peripheral part, a sealing resin in which a glass fiber or glass beads are dispersed and mixed is applied outside of the pixels, namely, in the frame region to seal the liquid crystal. Thus, the gap thickness near the peripheral seal is specified to be larger than the gap thickness in the center plus the difference between the sum of average film thickness of the color filter and the black matrix in the display pixel region and the film thickness of the black matrix outside the display pixel region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of converting the gap thickness in the vicinity of a peripheral seal portion into a gap thickness in a display pixel, a thickness of a black matrix outside the display pixel from an average thickness of a color filter and a black matrix in the display pixel. The external factor is set as a configuration that is larger than the product obtained by subtracting the above, and the configuration that the gap thickness distribution of the liquid crystal sealing seal part around the panel is smaller than the gap thickness distribution in the panel plane. The present invention relates to a liquid crystal display device which realizes excellent display uniformity against heat unevenness.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device, display uniformity has been regarded as important with the improvement of display characteristics. The display uniformity is evaluated by how uniform the threshold voltage change in the panel surface is. The change in the threshold voltage in the panel surface is caused by unevenness in the gap thickness, alignment processing, and the like in the panel surface. Therefore, conventionally, the gap thickness in the panel surface,
Configurations and methods for making the orientation treatment more uniform have been adopted.

[0003]

However, in the above-mentioned conventional configuration and method, there is a problem that a display defect such that the vicinity thereof is whitened due to heat generated from a backlight or a driving circuit as an external factor occurs. It has not been resolved.

In the STN (Super Twisted Nematic) display system, a liquid crystal panel is usually attached to an alignment state of a liquid crystal material having optical anisotropy sandwiched between glass substrates and a certain angle outside the glass. The phase difference information is read by using a phase plate and a polarizing plate having the obtained optical anisotropy to change the alignment state of the liquid crystal material between the glass substrates according to an applied voltage. Therefore, the accuracy of the in-plane uniformity of the birefringence Δn and the cell thickness d of the liquid crystal material constituting the phase difference is very strictly required.

The temperature dependence of the birefringence △ n of the liquid crystal material is as follows:
It tends to be smaller at higher temperatures. Since a part of the liquid crystal panel heated by an external factor becomes small as a phase difference, it is recognized as a blank state as if the rate of change was greatly expanded.

[0006] In general, in a color filter substrate of a printing system, the surface step structure is formed by an alternate arrangement of a color filter and a black matrix in a region inside a display pixel at a boundary between a region inside a display pixel and a region outside the display pixel. The superposition of the black matrix in the non-pixel area on the single layer of the black matrix has a width of several hundred microns or more, with the superimposed portion as a boundary, the average step distribution surface in the display pixel and the single layer surface of the black matrix outside the display pixel Has an average step of 1 micron.

[0007] However, since the boundary portion has a high portion of about one micron and several hundred microns, the step in this portion becomes dominant. Therefore, the black matrix portion outside the display pixel cannot maintain the cell thickness due to the plastic beads dispersed and dispersed in the center portion of the panel, the gap thickness is small outside the display pixel, and the region inside the display pixel near the boundary portion is not provided. Tends to have a large gap thickness.
It was very difficult to design the same gap thickness between the sealing portion and the panel central portion.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a liquid crystal display device which eliminates a color change near a backlight.

[0009]

In order to achieve this object, a liquid crystal display device according to the present invention has a relationship between a gap thickness d1 near a peripheral sealing portion and a gap thickness d2 at a panel central portion.
d1> d2 + (average film thickness of color filter and black matrix in display pixel−film thickness of black matrix outside display pixel).

Normally, in STN, the panel retardation value R1 is represented by the product of the anisotropy Δn of the birefringence of the liquid crystal and the cell thickness d. The optical compensation configuration is represented by a retardation value R2 represented by a retardation value of the retardation plate and a bonding angle with the polarizing plate.

When the panel retardation value R1 and the retardation value R2 of the optical compensation structure are the same, FIG.
As shown in (a), the relationship of the transmittance to the static drive (rectangular wave application) voltage starts from zero when no voltage is applied, and increases near the threshold voltage. Looking at the change in on / off luminance in actual driving, as shown in FIG. 1B, the contrast ratio becomes maximum when the transmittance is considerably low.

When the panel retardation value R1 is slightly larger than the retardation value R2 of the optical compensation structure,
As shown in FIG. 2A, the relationship of the transmittance to the static drive (rectangular wave applied) voltage is such that the transmittance when no voltage is applied starts from a few percent and becomes minimum near the threshold voltage. When the applied voltage is further increased, the transmittance sharply increases. FIG. 2 shows the on / off luminance change in actual driving.
As shown in (b), the contrast ratio becomes maximum when the transmittance is sufficiently high. Usually, this configuration is used in the STN display system.

Here, the design is made such that the panel retardation R1 is larger than the retardation R2 of the optical compensation structure. As shown in FIG. 3A, the relationship of the transmittance with respect to the static drive (rectangular wave application) voltage is such that the transmittance when no voltage is applied starts from tens of percents and becomes minimum near the threshold voltage. When the applied voltage is further increased, the transmittance sharply increases. Looking at the change in on / off luminance in actual driving, the contrast ratio becomes maximum when the transmittance is sufficiently high, as shown in FIG. 3B. In this configuration, the off-brightness is small floating with respect to a temperature rise which is an external factor, so that there is a large margin for maintaining the contrast ratio.

If heat unevenness occurs in the panel surface, the portion has an optical configuration having no temperature margin as shown in FIG. Therefore, an R having a temperature margin as an optical compensation structure in a portion where heat unevenness occurs.
By adopting a configuration in which 1 is large, a liquid crystal panel configuration that is resistant to heat unevenness is realized.

Further, at the color filter surface step,
By increasing the gap thickness at the seal portion and reducing the influence of the projecting portion at the boundary portion, the gap thickness at the peripheral portion of the panel can be easily controlled.

According to the present invention, the cell thickness of a corresponding portion in the panel surface is slightly increased with respect to a portion of the liquid crystal panel whose temperature has increased due to an external factor.
With the configuration in which the gap thickness distribution of the liquid crystal sealing seal portion is smaller than the gap thickness distribution in the panel surface, white spots recognized as uneven temperature are eliminated.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) First, a description will be given of a surface step structure of a color filter which determines a cell thickness near a seal. In general, in a color filter manufacturing process, a black matrix (BM) and red, green and blue (RG
The film formation of B) is performed separately. In particular, a portion corresponding to the outside of the display area leaks light from the backlight if the light is not shielded, which affects recognition of information in the display area. For this reason, the BM used between each color RGB in the display pixel is usually extended outside the display area,
The light-shielding property of the peripheral part is maintained. FIG. 4A is an external view of the panel, and FIG. 4B is an enlarged view of the vicinity of the frame of RGB and BM for each color.

On the other hand, at the display pixel portion and at the boundary between the display pixel portion and the peripheral frame portion, the BM and the RG
Between B, an overlapping margin is set in a range of several microns to several tens of microns in order to prevent light leakage due to each deviation. FIG. 5 shows the overlapping margin of RGB and BM for each color.

However, the peripheral frame portion is only one layer of the BM, and the change in the film thickness of the frame portion is small. on the other hand,
Since RGB and BM are superimposed for each color up to the edge portion between the inside of the display pixel and the frame portion, there is a film thickness distribution of two layers in terms of an average step. The overlapping width of the film thickness in this part is important, and the BM in the display pixel overlaps with each color, that is, the film thickness distribution of two layers is extremely increased. Table 1 shows the film thickness of the substrate surface in this portion, and FIG. 6 shows a schematic diagram thereof. An example of the used color filter is a printing method.

[0020]

[Table 1] Spacers are dispersed in the pixel to maintain the gap thickness. As shown in FIG. 6, in the peripheral portion, liquid crystal is sealed with a sealing resin in which glass fibers or glass beads are dispersed and mixed outside the pixel, that is, in the frame portion. From FIG. 6, it can be seen that in the frame portion where only one BM film is present, the spacer which should maintain the cell thickness does not contribute effectively. Further, the margin width of the overlapped portion existing at the boundary between the frame portion and the inside of the display pixel slightly differs depending on the color filter manufacturing method. Generally, the width is several hundred microns in the printing method, and several tens of microns in the spin coating method. In other words, for the stability of the gap thickness near the peripheral seal portion of the liquid crystal panel, it is important to control the cell thickness at the boundary between the frame portion and the inside of the display pixel.

Next, the panel configuration used for evaluating the display quality in the panel surface will be described. In the first embodiment,
A counter substrate and a color filter substrate as shown in Table 1 are used. On the counter substrate side, an indium tin oxide thin film (ITO) was formed on a glass substrate, and an ITO drawing pattern was formed from the inside of the display area to the outside. An insulating film is printed thereon to form a film. On the other hand, on the color filter substrate, after forming the BM and the color filter by printing, a smooth layer was formed, ITO was formed thereon, and an ITO drawing pattern was formed from the inside of the display area to the outside.
At this time, when the drawing patterns are combined with each other, they are orthogonal.

After that, when an alignment process is performed on the surfaces of both substrates under predetermined conditions, an alignment film having a pretilt angle of several degrees is printed, and after a predetermined temporary hardening heat treatment, a thermosetting process is performed to form a polyimide alignment film. did. The surface of the alignment film of each substrate was subjected to an alignment treatment by a normal rubbing method.

Next, a predetermined amount of glass beads having a diameter shown in Table 2 was mixed with the ultraviolet curable resin at a position outside the display pixel of the counter substrate, and a liquid crystal sealing seal was formed with a predetermined line width.

On the oriented surface of the color filter substrate, a considerable amount of plastic beads to which a fixing adhesive is adhered for ensuring a required gap thickness of 7.3 μm is sprayed, and a predetermined heat treatment is performed. Thus, the plastic beads were fixed on the alignment film surface. Thereafter, a necessary and substantial amount of liquid crystal material was dropped on the alignment-treated surface of the color filter substrate, and bonded to the counter substrate in a vacuum. After the liquid crystal material is sufficiently spread on the liquid crystal sealing seal, only the liquid crystal sealing seal is irradiated with ultraviolet rays to temporarily cure the ultraviolet curable resin. Further, heat treatment was sufficiently performed, and after cooling, the display uniformity in the panel surface was evaluated.

Next, the results of evaluating the display uniformity within the panel surface are shown in Table 2 below. From Table 1, the surface step in the display pixel is 0.72 microns when the seal portion is used as a reference. However, in practice, the cell thickness at the time of normal sealing can be reduced unless the step difference of 1.20 microns or more is corrected. We cannot guarantee. Further, when the color filter is manufactured by the spin coating method, it is necessary to further correct a step difference of 1.40 μm or more.
Therefore, because the cell thickness is thin due to the step of the frame part,
It can be understood that the cell thickness at the time of sealing becomes thin.

[0026]

[Table 2] (Embodiment 2) By the same liquid crystal panel manufacturing method as that used in Embodiment 1 described above, in order to make the gap thickness distribution around the panel and the liquid crystal sealing seal portion uniform, the sheet pressure at the time of assembling the panel is used. By increasing the time, the thickness of the gap around the panel was made uniform. Table 3 shows the changes in the sheet pressing time, the gap thickness around the panel, and the uniformity in the panel surface. Further, the numerical evaluation of the display uniformity is based on the luminance change amount in the panel surface as an index in the halftone display.
It was shown to. By increasing the sheet pressing time by 2.5 times, the variation in luminance in the panel surface was reduced by half. Further, the change in luminance at the left side of the panel is sufficiently smaller than the change in luminance at the center. The amount of change in luminance as an evaluation parameter substantially correlates with the gap thickness distribution σ. With a conventional sheet pressurization time of 4 seconds, gap variations during sealing are conspicuous and in-plane uniformity is insufficient.
In addition, heat unevenness also occurred. However, as the sheet pressurizing time was increased, the uniformity at the time of sealing and in-plane increased, and the occurrence of heat unevenness was eliminated.

[0027]

[Table 3]

As described above, according to the present invention, the gap thickness in the vicinity of the peripheral seal portion is converted into the gap thickness in the display pixel by using the average thickness of the color filter and the black matrix in the display pixel. By adopting a configuration that is larger than the one obtained by adding the value obtained by subtracting the film thickness, and a configuration in which the gap thickness distribution of the liquid crystal sealing seal portion around the panel is smaller than the gap thickness distribution in the panel plane, There is an effect that excellent display uniformity can be obtained with respect to thermal unevenness, which is a main factor.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a rectangular wave applied voltage and transmittance when a rectangular wave voltage is zero and a transmittance is zero, and a transmittance by applying an actual driving waveform.

FIG. 2 is a diagram showing the relationship between a rectangular wave applied voltage and transmittance when the rectangular wave voltage is zero and the transmittance is several percent, and the transmittance by applying an actual driving waveform.

FIG. 3 is a diagram showing the relationship between a rectangular wave applied voltage and transmittance when the transmittance is tens of percents when the rectangular wave voltage is zero and the transmittance by applying an actual driving waveform.

FIG. 4 is a schematic diagram showing a frame portion and a display pixel portion near a peripheral seal portion of the liquid crystal panel.

FIG. 5 is a schematic view showing a cross section of the surface of a color filter substrate.

FIG. 6 is a schematic cross-sectional view of a frame portion near a peripheral seal portion of a liquid crystal panel and a part of a display pixel portion.

FIG. 7 is a diagram showing a variation in luminance from the center to the periphery of the panel due to a difference in pressing time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Peripheral black matrix 2 Sealing seal 3a-3c Color filter (RGB) 4 In-pixel black matrix 5 Color filter substrate 6 Counter substrate 7 Liquid crystal 8 Smoothing layer 9 Transparent electrode (ITO) 10 Alignment film 11 Insulating layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H089 HA07 KA15 LA12 LA15 LA19 MA01X MA04X NA22 NA44 NA45 NA51 PA06 QA06 QA11 QA14 QA16 RA05 SA03 SA10 SA18 TA04 TA09 TA12 TA13 2H091 FA02Y FA35Y FD04 FD12 FD22 GA08 KA02 KA05

Claims (3)

[Claims] 1. A liquid crystal display element comprising two substrates each having an alignment treatment layer and an electrode film on the inner surface thereof, and filling a gap between the substrates with liquid crystal. A cell using a color filter substrate having a superposition of a width of several hundred microns or more from an alternate arrangement of the color filter and the black matrix in the region inside the display pixel to a single layer of the black matrix in the region outside the display pixel at the boundary of the region. In the configuration, the relationship between the gap thickness d1 in the vicinity of the peripheral seal portion and the gap thickness d2 in the center portion of the panel is d1> d2 + (average film thickness of color filter and black matrix in display pixel−
(A film thickness of a black matrix outside a display pixel). 2. A liquid crystal display device in which two substrates each having an alignment layer and an electrode film on the inner surface thereof are opposed to each other, and a liquid crystal is filled in a gap between the substrates. A cell using a color filter substrate having a superposition of a width of several hundred microns or more from an alternate arrangement of the color filter and the black matrix in the region inside the display pixel to a single layer of the black matrix in the region outside the display pixel at the boundary of the region. In the configuration, the gap thickness distribution σ1 of the sealing portion around the panel is
A liquid crystal display device characterized by being smaller than a gap thickness distribution σ2 of a display pixel portion. However, the gap thickness distribution σ1 of the sealing seal portion and the gap thickness distribution σ2 of the display pixel portion
Is represented by the following equation. σ1 = (δdseal) / (δSseal) Change in seal gap thickness per unit seal area, dseal: seal gap thickness Sseal: seal area σ2 = (δd1) / (δScell) or (δd2) /
(ΔScell) Change in cell gap thickness per unit area of the display pixel portion, d1: gap thickness in the vicinity of the peripheral seal portion d2: gap thickness in the center of the panel Scell: area of the display pixel portion 3. A liquid crystal having both the cell thickness configuration of the peripheral portion and the central portion according to claim 1, and the liquid crystal sealing portion and the gap thickness distribution configuration within the panel surface according to claim 2. Display device.