JPH10293311A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective type color liquid crystal display device having high contrast with a uniform cell gap, as well as high color purity by providing the first spacer beads for keeping a gap between a pair of a substrate and a thin film separator, and the second spacer beads for clamping the substrates as a pair. SOLUTION: Fastened type beads 60 are dispersed where the first and the second substrates 11 and 12 are stacked, and then heated, thereby being fastened to the substrate 11 and 12. A sealant is printed on the substrate 11 for use as a seal part 10. Also, the sealant is mixed with beads. In this case, the diameter of each bead is taken at a sum of the thickness of the first and the second liquid crystal layers 21 and 22, the thickness of a thin film separator 45 and the thickness of a color filter 15. Also, the thin film separator 45 is stacked on the fastened beads on the second substrate 12, thereby assembling the first and the second substrates 11 and 12 with each other. In order words, the thin film separator 45 made of a vertical directivity polymeric film is used for separating the two liquid crystal layers 21 and 22, and held with one layer of the spacer beads of the seal part 10 of the first and the second substrates 11 and 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-layer type liquid crystal display device having two liquid crystal layers, and more particularly to an optimum structure of a guest-host type two-layer type color liquid crystal display device having a dichroic dye in the liquid crystal layer. About.

[0002]

2. Description of the Related Art Conventionally, there have been liquid crystal display devices using two pairs of substrates, but these have caused parallax. Also,
In particular, there has been a problem in a reflective color liquid crystal display device in which a color filter is combined with a two-layer orthogonally stacked liquid crystal display device. Parallax is a phenomenon in which light observed by a user enters a liquid crystal display device, is reflected by a reflection plate, exits the liquid crystal display device, and enters a pixel different from the incident light in a process of reaching the user. When the parallax occurs, the contrast ratio and the saturation of the display color decrease. In order to eliminate this parallax, in Japanese Patent Laid-Open No. 7-159805, a dielectric layer is provided between liquid crystal layers to divide the liquid crystal layer.

[0003]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 7-159
In the liquid crystal display device having the constitution of No. 805, when the dielectric layer and the substrate are bonded with a sealant, the gap between the substrates does not become a predetermined gap, and there is a problem that the light transmission characteristic changes. This is because in a liquid crystal display device having no thin film separator, a gap can be controlled because a liquid crystal layer and a single layer of spacer beads are sandwiched between a pair of substrates. When a pressure is applied to the substrate when bonding the substrate and the thin film separator when the substrate and the thin film separator are bonded to each other, the respective substrates and the thin film separator are held only through the spacer beads. As described above, where spacer beads are not formed symmetrically with respect to the center of the thin film separator, the thin film separator is very liable to be distorted and the gap between the substrates is not uniform. Similarly, the substrate was sandwiched between two layers of spacer beads, so that the strength of the substrate itself was reduced, and the adhesive strength was reduced by the amount of bonding between the substrate and the thin film separator, and the yield was reduced due to easy peeling. .

An object of the present invention is to realize a two-layered liquid crystal display device having a constant cell transmission and a constant light transmission characteristic and a high cell strength, in particular, a two-layer orthogonally stacked liquid crystal display device. .

Further, since the dielectric layer (hereinafter referred to as a thin film separator) between the liquid crystal layers disclosed in Japanese Patent Application Laid-Open No. 7-159805 is very thin, it is impossible to use an alignment treatment method by mechanical stress such as rubbing. There's a problem. It is also possible to use a thick dielectric so that it can be rubbed,
Then, the advantage of using a dielectric material is lost. Therefore, a further object of the present invention is to use a thin film separator capable of aligning liquid crystal molecules in various alignment directions by a method other than rubbing in a liquid crystal display device in which the thin film separator is not distorted.
In particular, it is an object of the present invention to realize a two-layer orthogonally stacked liquid crystal display device which can sufficiently absorb both of two specific polarized lights and can realize a high contrast ratio, a high luminance, and a high color purity.

[0006]

Means for solving the above problems include a pair of substrates, a thin film separator sandwiched between the pair of substrates, and a liquid crystal layer sandwiched between each of the pair of substrates and the thin film separator. A first spacer bead formed on the liquid crystal layer and maintaining a distance between the pair of substrates and the thin film separator; a sealing portion formed at an end of a facing surface of the pair of substrates; and a sealing member formed on the sealing portion. And a second spacer bead for sandwiching the pair of substrates.

[0007] In addition to the above configuration, the length of the second spacer beads in the normal direction to the pair of substrates is made longer than the length of the first spacer beads in the normal direction of the pair of substrates. You may.

[0008] The configuration of the liquid crystal display device that produces the same effect includes a pair of substrates, a thin film separator sandwiched between the pair of substrates, a liquid crystal layer sandwiched between each of the pair of substrates and the thin film separator, and A first spacer bead formed on the liquid crystal layer and maintaining a distance between the pair of substrates and the thin film separator; a seal formed on an end of the opposing surface of the substrate; and a second spacer bead formed on the seal. It is conceivable that the thin film separator has a smaller area than the opposing surfaces of the pair of substrates, and the seal portion is formed outside the thin film separator.

The liquid crystal molecules in the vicinity of the thin film separator are aligned perpendicular to the thin film separator, and the liquid crystal molecules in the vicinity of each of the pair of substrates are aligned substantially parallel to each of the substrates. It is preferable that the liquid crystal molecules at the interface between the first substrate and the second substrate are aligned so as to be orthogonal to each other when viewed from the normal direction to the substrate plane. Further, the liquid crystal molecules near the thin film separator are horizontally aligned with respect to the thin film separator, and the liquid crystal molecules are aligned so that the liquid crystal alignment directions on both surfaces of the thin film separator are orthogonal to each other when viewed from the normal direction of the first substrate plane. Is preferred.

Further, the thin film separator may be a transparent thin film in which a vertical alignment film, which is a polymer film of vertical alignment, is coated on both sides.

The thin film separator is a laminate of two polymer films stretched and formed into a film, and the two polymer films may be laminated so that the stretching directions are orthogonal to each other. .

[0012]

FIG. 2 (e) is a sectional view of a liquid crystal display device according to the present invention. The thin film separator 45 has a smaller area than the substrate, is distributed inside the seal part 70, and is distributed so as to cover the entire display part. Into the sealing portion, spacer beads having a diameter larger than the diameter of the spacer beads disposed inside the sealing portion and desirably approximately equal to the sum of the thickness of the two liquid crystal layers and the thickness of the thin film separator are mixed. Since the two opposing substrates are held directly by the seal without passing through the thin film separator, the strength of the liquid crystal cell is improved to the same level as that of the conventional single-layer liquid crystal cell, and the cell gap is made uniform in the same manner. Can be. Further, since the number of bonding surfaces is the same as that of the conventional single-layer liquid crystal cell, the occurrence of peeling is as low as that of the conventional single-layer liquid crystal cell.

Next, means for making the orientation directions of the two liquid crystal layers separated by the thin film separator orthogonal to each other will be described.

Many of the polymer films produced by the stretching method have an action of horizontally orienting liquid crystal molecules in the vicinity of both surfaces in the stretching direction. However, some polymer films made of an organic polymer having a bulky group such as a long-chain alkyl group in the side chain show vertical orientation.

The thin film separator is formed of a vertically oriented polymer film. A horizontal alignment film having a pretilt angle of 45 degrees or less is applied to the two opposing substrates on the side close to the liquid crystal layer. An alignment process is performed on these two layers of alignment films by a rubbing method, and the alignment process direction is set to be orthogonal to the substrate normal direction.

Alternatively, the same liquid crystal alignment can be realized by using a thin film separator in which a vertically oriented polyimide film is coated on both sides of a horizontally oriented polymer film.

Further, a laminate of two polymer films having horizontal orientation on a thin film separator is used, and the two polymer films are laminated so that the stretching directions are orthogonal to each other. The alignment film of the counter substrate may be a vertical alignment film or a horizontal alignment film.

According to the above method, the orientation directions of the two liquid crystal layers separated by the thin film separator can be made orthogonal.

The specific embodiments of the present invention will be described below.

Embodiment 1 FIG. 1 is a perspective view showing the structure of a liquid crystal cell of a liquid crystal display device according to the present invention.

One of the pair of substrates (hereinafter, referred to as a first substrate) is made of borosilicate glass and has a thickness of 0.7 mm.
An alignment film, a common electrode, a planarizing layer, and a color filter are sequentially laminated. The alignment film is a polyimide polymer, has a layer thickness of 1000 °, is subjected to an alignment treatment by a rubbing method, and has a pretilt angle of 10 °. The common electrode is made of ITO and has a thickness of 1000 °. The flattening layer is made of epoxy resin and has a thickness of 2 μm. The color filter is prepared by a dyeing method, and the transmittance at the wavelength at which the transmittance is minimum is about 5 for any of the R, G, and B color filters.
0%.

The other of the pair of substrates (hereinafter, referred to as a second substrate) has the same material and thickness as the first substrate, and has an alignment film,
A reflective electrode, an insulating layer, and an active element are sequentially stacked. The alignment film is the same as that on the first substrate. The reflective electrode is made of Al and has a layer thickness of 2000 °. The insulating layer is made of SINx and has a thickness of 1 μm. The active element is an inverted staggered thin film transistor. The reflective electrode forms one pixel, has a substantially rectangular shape, and a size of about 100 μm × 900 μm. The reflection electrode and the active element are connected by a through hole.

The thin film separator is a thin film of a polyimide polymer and has a thickness of 2 μm. As the polyimide polymer of the thin film separator, a polymer having a long-chain alkyl group in a side chain was used. It is considered that the surface of the thin film separator is covered with a long-chain alkyl group of a side chain, and the long-chain alkyl group extends in the normal direction of the alignment film plane. It is considered that the liquid crystal molecules are aligned along the long-chain alkyl group, resulting in vertical alignment.

FIG. 2 shows the subsequent processing and assembly of the first and second substrates. Fixed beads having a diameter of 5 μm were dispersed at a density of 200 per cm ² on the side of the first substrate and the second substrate on which the respective layers were laminated (FIG. 2).
(A)). Thereafter, the substrate was heated to fix the fixed beads on the substrate (FIG. 2B). Next, a sealant was printed on the first substrate to form a seal portion (FIG. 2C). Beads having a diameter of 13 μm were mixed in the sealing agent. The diameters of the beads in the sealant are the first liquid crystal layer, the second liquid crystal layer (each 5 μm, the normal direction to the substrate of the fixed beads is equal), the thickness of the thin film separator (2 μm), and the color. The sum of the filter thicknesses (1 μm) was used. A thin film separator was laminated on the fixed beads of the second substrate (FIG. 2 (d)), and then the first substrate and the second substrate were assembled to form a liquid crystal display device (FIG. 2 (e)).

FIG. 3 shows the distribution of the seal portion, the thin film separator, and the display portion on the liquid crystal display element of the present invention as viewed from the normal direction of the substrate plane. The thin film separator covers the entire display section and is distributed inside the seal section. A first substrate,
2 is also shown in FIG. The orientation directions of the first substrate 2 and the second substrate 2 are both at 45 ° with the four sides of the substrate. First
The orientation processing directions of the first substrate and the second substrate are orthogonal to each other when viewed from the normal direction of the substrate plane.

A liquid crystal layer containing a dichroic dye at 3% by weight and having a positive dielectric anisotropy was sealed in the liquid crystal layer by a vacuum sealing method. The time required for encapsulation is affected by the angle between the moving direction of the liquid crystal and the orientation processing direction, and the smaller the angle, the shorter the encapsulation time. Since the angle formed by the alignment processing direction and the four sides of the substrate was 45 °, the angle formed by the main liquid crystal movement direction and the alignment processing direction when the liquid crystal was sealed was approximately 45 ° on both the first substrate side and the second substrate side. °. Therefore, the liquid crystal was injected at substantially the same speed on both the first substrate side and the second substrate side.

Since there is a gap between the thin film separator and the sealing portion, the liquid crystal moves between the first liquid crystal layer and the second liquid crystal layer. However, since the layer thickness and the alignment state of the first liquid crystal layer and the second liquid crystal layer are maintained, the display is not affected.

Finally, a driving device was connected to produce a two-layer orthogonal type liquid crystal display device having the structure shown in FIG. The liquid crystal layer has a hybrid orientation in which the liquid crystal layer is vertically aligned near the thin film separator and horizontally aligned near the substrate. In the process of manufacturing the liquid crystal display device described above, the cell gap was not reduced more than a predetermined amount, and the substrate was not peeled off.

FIG. 5 shows the dependence of the reflectance on the applied voltage. It is a normally closed type applied voltage dependency. At a driving voltage of 7 V, the reflectance for white display is 18.8%, the reflectance for black display is 2.8%, and the contrast ratio is 7.8: 1. Met. FIG. 4 shows the results of measuring the chromaticities of red, blue, green, yellow, cyan, and magenta. Practically enough vivid color display was obtained.

As described above, the two liquid crystal layers are separated by using a thin film separator composed of a vertically oriented polymer film.
A structure in which the first substrate having a built-in color filter and the second substrate having a built-in reflective electrode are held by a single layer of spacer beads in a sealing portion, thereby providing a two-layer layer having a high contrast ratio and excellent optical characteristics. A multilayer liquid crystal display device was obtained.

Example 2 In the liquid crystal display device of Example 1, the thin film separator was changed to the one prepared as follows.

A polyethylene terephthalate polymer film having a thickness of 2 μm was fixed on a glass plate with a tape, and a vertically oriented alignment film was applied by spin coating. After the heat treatment, the organic polymer film was turned upside down and fixed again on a glass plate with a tape, and a vertically oriented alignment film was applied by a spin coating method, followed by heat treatment. The alignment film was a polyimide polymer having a long-chain alkyl group in the side chain.

Also in this case, a two-layer orthogonal type liquid crystal display device having no parallax and made of a low-molecular liquid crystal can be produced, and a reflection type color liquid crystal display device having high reflectance, high contrast ratio and high color purity can be obtained. Was.

Example 3 In the liquid crystal display device of Example 1, the thin film separator was changed to one prepared as follows.

A polymer film made of polyethylene terephthalate having a thickness of 2 μm is laminated so that the stretching directions are orthogonal to each other.
This was arranged such that the orientation direction of the adjacent substrate was perpendicular to the stretching direction. Since the thickness of the thin film separator became 4 μm, the diameter of the beads in the sealant was changed to 15 μm. Since the liquid crystal is horizontally aligned near the thin film separator,
The first liquid crystal layer and the second liquid crystal layer were in a homogeneous alignment, and the alignment directions were perpendicular to the upper and lower sides of the thin film separator.

Also in this case, a two-layer orthogonal liquid crystal display device having no parallax and made of a low-molecular liquid crystal can be manufactured, and a reflection type color liquid crystal display device having high reflectance, high contrast ratio and high color purity can be obtained. Was.

Example 4 In the liquid crystal display device of Example 3, the thin film separator was arranged so that the direction of orientation and the direction of stretching of the adjacent substrate were orthogonal to each other. Accordingly, the liquid crystal layer contains 3% by weight of a dichroic dye and a chiral agent S manufactured by Merck.
811 was replaced with a mixture of 0.2% by weight. The first liquid crystal layer and the second liquid crystal layer were in a twisted orientation, and the orientation directions were perpendicular to the top and bottom of the thin film separator.

Also in this case, a two-layer laminated orthogonal type liquid crystal display device made of a low-molecular liquid crystal can be produced, and a reflection type color liquid crystal display device having high reflectance, high contrast ratio and high color purity can be obtained.

Example 5 In the liquid crystal display device of Example 3, the thin film separator was arranged such that the orientation direction and the stretching direction of the adjacent substrate were 250 degrees. Along with this,
The liquid crystal layer was replaced with a mixture containing 1.0% by weight of a chiral agent S811 manufactured by Merck in addition to 3% by weight of a dichroic dye. Further, the electrodes of the first and second substrates were matrix electrodes. The first liquid crystal layer 2 was twist-aligned, and the alignment directions were perpendicular to the top and bottom of the thin film separator.

Also in this case, a two-layer orthogonal liquid crystal display device having no parallax and made of a low-molecular liquid crystal can be produced, and a reflection type color liquid crystal display device having high reflectance, high contrast ratio and high color purity can be obtained. Was.

The thin film separator is arranged so that the orientation direction and the stretching direction of the adjacent substrate are at 250 degrees, but if the angle is within 180 to 270 degrees, a similar two-layer liquid crystal display device is used. Can be realized.

Example 6 As shown in FIG. 8, in the two-layer liquid crystal display device of Example 1, a thin film separator was sandwiched between seal portions.

As described above, since the end portion of the substrate is not sandwiched between the two layers of spacer beads via the thin film separator by forming it so as to be sandwiched by the sealant, the distortion of the sealant is further prevented. Can be. Further, since the thin film separator is pulled by the seal portion, the entire thin film separator can be further flattened. "Comparative Example 1" In the liquid crystal display device of Example 1 in FIG.
A two-layered liquid crystal display device in which spacer beads are formed in two layers via a thin film separator like a conventional two-layered liquid crystal display device is shown. However, the thin film separator was distorted by the spacer beads in the seal portion, the cell gap became non-uniform, and the display characteristics deteriorated.

Further, the cell gaps could not be made uniform depending on the degree of dispersion of the spacer beads at the ends.

Comparative Example 2 In the liquid crystal display device of Example 1, the thin film separator was changed and made of stretched polyethylene terephthalate. Both the first liquid crystal layer and the liquid crystal layer 2 were oriented in the stretching direction of the separator at the interface with the separator. As a result, the orientation directions of the two liquid crystal layers did not become orthogonal.

Comparative Example 3 In the liquid crystal display device of Example 1, the thin film separator was changed and made of stretched polyethylene terephthalate. First liquid crystal layer, second liquid crystal layer
Both liquid crystal layers were oriented in the stretching direction of the thin film separator at the interface with the thin film separator. As a result, the orientation directions of the two liquid crystal layers did not become orthogonal.

When the display characteristics were measured by connecting a driving device, the reflectance of white display was slightly higher at 25.5%.
The black display has a reflectivity of 9.4% and a contrast ratio of 2.
It was greatly reduced to 7: 1. As a result, the color purity of the color display has also been significantly reduced.

Since a thin film separator cannot be subjected to an orientation treatment by a rubbing method or the like, a polymer film having horizontal orientation is used.
When a layer was used and the surface treatment was not performed, the orientation directions of the two liquid crystal layers could not be made orthogonal.

[Comparative Example 4] In the liquid crystal display device of Example 1, the distribution of the thin film separators was expanded to extend to the spacer bead region of the seal portion formed at the end. FIG. 6 shows a cross-sectional view of this liquid crystal display device. With the expansion of the distribution of the thin film separators, the manufacturing method of the liquid crystal display element was also changed as follows. Seal portions were formed on both the first substrate and the second substrate. The diameter of the spacer beads mixed with the sealant of the first substrate having the color filter is the total thickness of the color filter (1 μm) assuming the layer thickness of the first liquid crystal layer (5 μm, which is equal to the diameter of the fixed beads). There was a certain 6 μm.
The length of the spacer beads mixed with the sealant of the second substrate in the direction perpendicular to the substrate was equal to the layer thickness of the second liquid crystal layer (5 μm, equal to the diameter of the fixed beads). After laminating the thin film separator on the second substrate, the first substrate was laminated thereon.

FIG. 7 shows a cross section of the liquid crystal display device thus manufactured. Since the two substrates are held via the two seal portions and the thin film separator, stress is applied to the thin film separator sandwiched between the two seal portions, and the specified cell gap cannot be realized. In addition, since the bonding surface was increased, it was easy to peel off.

In the manufacturing process, a crack was found in a portion of the thin film separator close to the seal portion. In addition, peeling from the bonding surface occurred.

[0052]

As described above, a reflection type color liquid crystal display device having a uniform cell gap, a high contrast ratio and a high color purity can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a liquid crystal cell of a liquid crystal display device of the present invention.

FIG. 2 is a view showing a method of assembling the liquid crystal display device of the present invention.

FIG. 3 is a diagram showing the relationship between the distribution of the display section, the thin film separator, and the seal section and the orientation direction of the liquid crystal display device of the present invention.

FIG. 4 is a diagram showing the chromaticity of the color display of the reflectance of the liquid crystal display device of the present invention.

FIG. 5 is a diagram showing the applied voltage dependence of the reflectance of the liquid crystal display device of the present invention.

FIG. 6 is a cross-sectional view illustrating a structure of a liquid crystal cell of a liquid crystal display device according to Comparative Example 4.

FIG. 7 is a cross-sectional view at an end of a liquid crystal cell of a liquid crystal display device according to Comparative Example 4.

FIG. 8 is a sectional view showing a structure of a liquid crystal cell of the liquid crystal display device according to the present invention.

[Explanation of symbols]

Reference numeral 10: substrate, 11: first substrate, 12: second substrate, 1
5: color filter, 16: flattening layer, 21: first liquid crystal layer, 22: second liquid crystal layer, 31, 32: alignment film, 35
... common electrode, 40 ... reflective electrode, 45 ... thin film separator,
Reference numeral 50 denotes a TFT, 60 denotes a spacer bead, 70 denotes a sealing portion, 75 denotes a sealing port, 80 denotes a display portion, 91 denotes an orientation direction of the first liquid crystal layer near the first substrate, and 92 denotes a direction near the second substrate. , 93... Liquid crystal injection direction.

Claims (9)

[Claims] A pair of substrates; a thin film separator sandwiched between the pair of substrates; a liquid crystal layer sandwiched between each of the pair of substrates and the thin film separator; A first spacer bead disposed so as to maintain an interval between each of the substrates and the thin film separator; a seal portion formed at an end of an opposing surface of the pair of substrates; and a pair of the pair formed at the seal portion. And a second spacer bead disposed so as to sandwich the substrate. 2. A pair of substrates, a thin film separator sandwiched between the pair of substrates, a liquid crystal layer sandwiched between each of the pair of substrates and the thin film separator, and a pair of substrates formed on the liquid crystal layer. A first spacer bead for maintaining a distance between the thin film separators, a seal portion formed at an end of the pair of substrates facing each other, and a second spacer bead formed on the seal portion; The liquid crystal display device, wherein the separator has a smaller area than the opposing surfaces of the pair of substrates, and at least a part of the seal portion is formed outside the thin film separator. 3. The length of the second spacer beads in the direction normal to the pair of substrates according to claim 1 or 2, wherein the length of the first spacer beads in the direction of normal of the pair of substrates is larger than the length of the first spacer beads. A liquid crystal display device characterized by being long. 4. A liquid crystal display according to claim 1, wherein the liquid crystal molecules in the vicinity of the thin film separator are vertically aligned with respect to the thin film separator, and the liquid crystal molecules in the vicinity of each of the pair of substrates are attached to each of the substrates. A liquid crystal display device, wherein the liquid crystal molecules are aligned substantially parallel to each other, and the liquid crystal molecules at the interface between the first substrate and the second substrate are aligned so as to be orthogonal to each other when viewed from the normal direction of the substrate plane. 5. The thin film separator according to claim 1, wherein liquid crystal molecules in the vicinity of the thin film separator are horizontally oriented with respect to the thin film separator, and both surfaces of the thin film separator are viewed from a direction normal to a plane of the first substrate. The liquid crystal display device is formed so that the liquid crystal alignment directions are orthogonal to each other. 6. The liquid crystal display device according to claim 1, wherein said thin film separator is a vertically oriented polymer film. 7. A liquid crystal display device according to claim 1, wherein said thin film separator is a transparent thin film having a vertical alignment film applied on both sides. 8. The thin film separator according to claim 1, wherein the thin film separator is a laminate of two polymer films stretched and formed into a film, and the stretching directions of the two polymer films are orthogonal to each other. A liquid crystal display device characterized by being laminated on a substrate. 9. The method according to claim 1, wherein a length of the second spacer bead in a direction normal to the pair of substrates is two times a length of the first spacer bead in a direction normal to the pair of substrates. A two-layered liquid crystal display device characterized by at least twice as large.