JPH10104614A - Formation of high polymer liquid crystal film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a uniaxial optical film having high quality by uniformly forming high-polymer liquid crystals. SOLUTION: A coating material having a desired viscosity is first prepd. by executing a compounding stage and dissolving the high-polymer liquid crystal having a prescribed phase transition point in a solvent. An orientation stage is next executed to orient the surface of a substrate 1 along a prescribed orientation direction. In succession, a coating stage is executed. The coating material 2 is deposited on a wire bar 4 wound with a fine wire 4b on a rotatable core bar 4a and this wire bar 4 is relatively moved in the state of bringing the bar into contact with the surface of the substrate 1 while the bar is rotated, by which the coating material 2 is applied on the surface of the substrate 1. A drying stage is thereafter, executed and the solvent is removed from the coating material 2 applied on the substrate is removed to form the thin film of the high-polymer liquid crystals 2a having a uniform thickness. Finally, an alignment stage is executed and the thin-film is heat treated once to the phase transition point or above and is then cooled down to the temp. below the phase transition point, by which the high-polymer liquid crystals 2a are aligned in the orientation direction and the uniaxial optical film 3 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a polymer liquid crystal film. More specifically, the present invention relates to a technique of forming a polymer liquid crystal as a uniaxial optical film and imparting a function of a quarter wavelength plate.

[0002]

2. Description of the Related Art In general, a wave plate is a birefringent plate (crystal plate) which gives a predetermined optical path difference (accordingly, a phase difference) between linearly polarized lights oscillating in mutually perpendicular directions when passing through the plate. . When the thickness of the birefringent plate is d, and the refractive indices of linearly polarized light vibrating in the direction of the electric principal axis perpendicular to each other are n1 and n2,
The optical path difference is given by | n1−n2 | d. This value is λ /
4, λ / 2, λ / 1 (λ is the wavelength of light used in vacuum)
Are called quarter-wave, half-wave and one-wavelength plates, respectively, which correspond to phase plates of π / 2, π and 2π. For example,
The quarter-wave plate is a birefringent plate whose thickness is determined so as to generate a quarter-wavelength optical path difference between linearly polarized lights vibrating in directions perpendicular to each other. A thin plate or the like obtained by cleaving muscovite to an appropriate thickness is used. Alternatively, a synthetic resin plate or the like having a molecular orientation in one direction is used. When linearly polarized light having an azimuth of 45 ° with respect to the principal axis direction is applied to this plate, the transmitted light becomes circularly polarized light.

The quarter-wave plate has various uses, and is used, for example, as a polarization control element of a reflection type guest-host liquid crystal display device. JP-A-6-222351 discloses a reflective guest-host liquid crystal display device having a quarter-wave plate incorporated therein. This conventional structure uses a quarter-wave plate in which a polymer film of polystyrene, polypropylene, polycarbonate, polyethylene terephthalate or the like is molecularly oriented in one direction. However, the optical anisotropy (birefringence) of the uniaxially stretched polymer film is not always sufficient, and a practically satisfactory level as a quarter-wave plate has not yet been obtained.

[0004]

The above-mentioned patent publication also discloses a quarter-wave plate layer made of a polymer liquid crystal. For example, a polymer liquid crystal is heated and adhered onto a separately heated or cooled substrate to form a quarter-wave plate layer. However, even with this method, it is difficult to molecularly align the polymer liquid crystal with high precision, and a practically satisfactory uniaxial anisotropic optical film has not been obtained. In particular, when a quarter-wave plate layer is formed, it is necessary to precisely and uniformly form a polymer liquid crystal with a constant thickness over the entire surface of the substrate. However, at the present stage, a uniform and high-precision film formation method of the polymer liquid crystal has not been established.

[0005]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, according to the present invention, a polymer liquid crystal is formed by the following steps. First, a blending step is performed, and a polymer liquid crystal is dissolved in a solvent to prepare a coating material having a desired viscosity. Next, a coating process is performed, the coating material is carried on a wire bar in which a thin wire is wound around a rotatable core rod, and the coating material is moved relative to the substrate by rotating the wire bar while in contact with the surface of the substrate. Is applied (transferred) to the surface of. Finally, a drying step is performed to remove the solvent from the applied coating material to form a polymer liquid crystal thin film having a uniform thickness.

The method of forming a polymer liquid crystal film according to the present invention is particularly suitable for forming a uniaxial optical film. In this case, first, a compounding step is performed, and a polymer liquid crystal having a predetermined phase transition point is dissolved in a solvent to prepare a coating material having a desired viscosity. Next, an alignment step is performed, and the surface of the substrate is aligned along a predetermined alignment direction. Subsequently, a coating process is performed, the coating material is carried on a wire bar in which a thin wire is wound around a rotatable core rod, and the coating material is moved relatively while rotating the wire bar in a state of being in contact with the surface of the substrate. Apply to the surface of. Further, a drying step is performed to remove the solvent from the applied coating material to form a thin film of polymer liquid crystal having a uniform thickness. Finally, an alignment step is performed. The thin film is once heated to a temperature equal to or higher than the phase transition point, then cooled to a temperature equal to or lower than the phase transition point, and the polymer liquid crystal is aligned in the alignment direction to form a uniaxial optical film.

The method of forming a polymer liquid crystal film according to the present invention is particularly applicable to a method of manufacturing a guest-host liquid crystal display device. In this case, first, a compounding step is performed, and a polymer liquid crystal having a predetermined phase transition point is dissolved in a solvent to prepare a coating material having a desired viscosity. Next, an alignment step is performed, and the surface of one of the substrates is aligned along a predetermined alignment direction. Subsequently, a coating process is performed, the coating material is carried on a wire bar in which a fine wire is wound around a rotatable core rod, and the coating material is relatively moved while rotating the wire bar while being in contact with the surface of the substrate. Apply to the surface of the substrate. Further, a drying step is performed to remove the solvent from the applied coating material to form a thin film of polymer liquid crystal having a uniform thickness. Subsequently, an alignment step is performed, and the thin film is once heated to a temperature equal to or higher than the phase transition point, and then cooled to a temperature equal to or lower than the phase transition point, and the polymer liquid crystal is aligned in the alignment direction to form a quarter-wave plate layer. . Thereafter, a bonding step is performed, and the other substrate is bonded to the one substrate via a predetermined gap. Finally, an injection step is performed, and a guest-host liquid crystal containing a dichroic dye is injected into the gap to complete a guest-host liquid crystal display.

A feature of the polymer liquid crystal film forming method according to the present invention is that a polymer liquid crystal is applied to the surface of a substrate using a coating method using a wire bar (hereinafter, a bar coating method). Conventionally, the bar coating method has been used, for example, for applying a photosensitive agent to a photographic film. However, this bar coating method has not been used in the field of liquid crystal technology. According to the present invention, it is possible to form a polymer liquid crystal with a uniform and constant thickness by coating the polymer liquid crystal by a bar coating method. In particular, in the field of liquid crystal devices, it is necessary to form a uniaxial optical film or a quarter-wave plate layer composed of a polymer liquid crystal with high precision and uniformity, and this point bar coating method is very effective.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a process chart showing a polymer liquid crystal film forming method according to the present invention. In this embodiment, a uniaxial optical film (quarter wavelength plate layer) is formed using a polymer liquid crystal. First, a preparation process is performed as a preparation step, and a polymer liquid crystal having a predetermined phase transition point is dissolved in a solvent to prepare a coating material having a desired viscosity. Next, an alignment step is performed as shown in FIG. That is, the surface of the substrate 1 is aligned along a predetermined alignment direction (indicated by an arrow). For example, polyimide (not shown) is applied to the surface of the substrate 1.
Is formed and then rubbed along the alignment direction. In some cases, the surface of the substrate 1 may be directly rubbed. Next, a coating step and a drying step are performed as shown in FIG. In the coating process, the coating material 2 is carried on a wire bar 4 in which a thin wire 4b is wound around a rotatable core bar 4a.
The coating material 2 is applied (transferred) to the surface of the substrate 1 by relatively moving while rotating the wire bar 4 in contact with the surface of the substrate 1. At this time, the thickness of the thin wire 4b and the viscosity of the coating material 2 are appropriately set so that the thickness of the formed coating film is λ / λ in the visible light region.
If a phase difference of 4 is generated, a desired quarter-wave plate layer can be obtained. A heat treatment is performed in a subsequent drying step to remove the solvent from the applied coating material 2 to form a thin film of the polymer liquid crystal 2a having a uniform thickness. For example, a low-temperature heat treatment is performed at a temperature lower than the boiling point to evaporate the solvent, thereby
Dry while keeping the (coating) uniform state. Thereby, pinholes and the like do not occur in the coating film. still,
In this drying step, a low-temperature heat treatment may be optionally performed under vacuum to promote the evaporation of the solvent. Finally, an alignment step is performed as shown in FIG. In this alignment step, the substrate 1 is once heated to a temperature equal to or higher than the phase transition point, then cooled to a temperature equal to or lower than the phase transition point, and the polymer liquid crystal 2a contained in the dried coating material 2 is aligned in the alignment direction to form a uniaxial optical film. Form 3 By using the bar coating method, the uniaxial optical film 3 can be formed over the entire surface of the large substrate with a thickness as designed, and the uniaxial optical film 3 can be used as it is as a quarter-wave plate layer. become. As shown in the drawing, in the coating and drying stages, the liquid crystal molecules of the polymer liquid crystal 2a contained in the coating material 2 are in a random state, but after the heat treatment, the liquid crystal molecules of the polymer liquid crystal 2a are aligned along the alignment direction. Align
A desired uniaxial optical anisotropy is obtained. Specifically, paint 2
The substrate 1 coated with and dried is put into an oven set to a nematic phase temperature or an isotropic phase temperature in advance and heated. Then, cool slowly and return to room temperature. As a result, the polymer liquid crystals 2a coated by the bar coating method are aligned in the alignment direction of the substrate 1 which has been rubbed in advance.

FIG. 2 is a schematic diagram showing a specific configuration of the wire bar. As shown in the drawing, the wire bar 4 has a structure in which a thin wire (wire) 4b having a diameter g is wound around a core bar 4a made of a metal having a diameter G without any gap.
When the coating material 2 in which the polymer liquid crystal is dissolved in the solvent is dropped on the wire bar 4, the coating material 2 is carried in the gaps between the fine wires 4b wound around the core rod 4a. In this state, the wire bar 4 relatively moves while rotating on the surface of the substrate 1 (see FIG. 1B), and a coating film is formed on the substrate 1. By setting the diameter g of the thin wire 4b to a desired value, the thickness of the coating film can be extremely uniformly and uniformly controlled over the entire surface of the substrate. Thereby, a high-precision quarter-wave plate layer can be formed on the substrate. In addition, by setting the winding width of the fine wire 4b around the core rod 4a to a desired size, it is possible to freely cope with a large-sized substrate. This bar coating method is optimal for saving the amount of coating material used. For example, 3
When a coating material is applied to a large substrate having a size of 00 mm × 350 mm, the use amount of about 2 cc is sufficient if a bar coating method is used. On the other hand, when applying by using a spinner, about 20 cc to 25 cc for a substrate of the same size.
cc paint is required. The spinner mounts a substrate on a rotary table, drops a coating material while rotating at a high speed, and performs coating using centrifugal force. Since a large amount of the coating material is shaken off by the centrifugal force, the used amount is wasted. On the other hand, in the bar coating method, the coating agent can be used for the coating treatment very efficiently. As described above, by using the bar coating method, a polymer liquid crystal can be formed on a substrate with a uniform thickness. Therefore, a uniaxial optical film having stable optical characteristics can be obtained. Also, the amount of material used can be greatly reduced. In this regard, since the polymer liquid crystal is an expensive material, it is practically effective in reducing the manufacturing cost.

FIG. 3 is a schematic diagram showing a chemical structure showing an example of a polymer liquid crystal. As shown in the figure, this polymer liquid crystal has a side chain branched from an alkyl main chain. Methoxyphenylbenzoate is connected as a pendant to the tip of the side chain. Side chain spacer length is carbon number n
And two and six are arranged. In this example, the side chains of n = 2 and n = 6 are copolymerized with the main chain at a ratio of 1: 1. For example, this polymer is dissolved in a solvent obtained by mixing cyclohexanone and methyl ethyl ketone (MEK) at a ratio of 8 to 2 to prepare a coating material. This coating material is applied to a substrate by a bar coating method to form a uniaxial optical film. That is,
This coating agent is applied by a bar coating method on a substrate that has been previously rubbed.

FIG. 4 is a graph showing a temperature profile when the above-mentioned coating material is subjected to a drying process and an alignment process.
First, in the drying step, heat treatment is performed at a low temperature of about 80 ° C. for about 2 hours to sufficiently evaporate the solvent. The evaporation may be further promoted by performing this under vacuum during the low-temperature firing. Next, heating and slow cooling are performed in the alignment step. The polymer liquid crystal shown in FIG. 3 has a phase transition point TP between a nematic phase and a liquid phase of 110 ° C. Therefore, the substrate is once subjected to a high-temperature heat treatment at a temperature higher than the phase transition point TP (for example, 120 ° C.), and then gradually cooled to a temperature lower than the phase transition point TP to align the polymer liquid crystal contained in the coating material in the alignment direction. A uniaxial optical film is formed. Good uniaxial orientation (good orientation) by performing the alignment process at 120 ° C. that exceeds the phase transition point TP
Can be stably formed.

Finally, a method of manufacturing a guest-host liquid crystal display device using the polymer liquid crystal film forming method according to the present invention will be described with reference to FIGS. First, in the step (A) of FIG. 5, a thin film transistor 12 is formed on an insulating substrate 11 made of glass or quartz. Specifically, the gate electrode 13 made of a high melting point metal or the like is
After patterning is formed on the surface of the substrate 1, a gate insulating film 14 made of a silicon oxide film or a silicon nitride film is formed thereon by CVD or the like. A semiconductor thin film 15 made of polycrystalline silicon or the like is formed thereon, and is patterned in an island shape according to the element region of the thin film transistor 12. A stopper 16 made of a silicon oxide film or the like aligned with the gate electrode 13 is formed thereon by patterning. Impurities are implanted into the semiconductor thin film 15 by ion doping or ion implantation using the stopper 16 as a mask to form the bottom gate thin film transistor 12. An interlayer insulating film 17 made of silicon oxide or the like is formed by CVD or the like so as to cover the thin film transistor 12.

In step (B), after opening a contact hole in the interlayer insulating film 17, aluminum or the like is deposited by sputtering, and is patterned into a predetermined shape to form a source electrode 18 and a drain electrode 19. At this time, the light reflection layer 20 is simultaneously formed using aluminum. This light reflection layer 20 is connected to the same potential as the drain electrode 19. The light reflection layer 20 is formed of a resin film 20a having unevenness.
And an aluminum film 20b formed on the surface thereof. The resin film 20a is a photosensitive resin film whose unevenness is patterned by photolithography. The photosensitive resin film 20 a is made of, for example, a photoresist, and is entirely applied to the surface of the substrate 11. This is exposed through a predetermined mask, and is patterned into, for example, a cylindrical shape. Then, by heating and performing reflow, the uneven shape can be formed stably. An aluminum film 20b having a desired film thickness and good light reflectivity is formed on the surface of the thus formed uneven shape.
To form If the depth dimension of the unevenness is set to several μm, good light scattering characteristics can be obtained, and the light reflection layer 20 exhibits white.

Proceeding to step (C), the thin film transistor 12
Then, the planarization layer 21 is formed so as to fill the irregularities of the light reflection layer 20. The flattening layer 21 is preferably made of a transparent organic material such as an acrylic resin. The surface of the flattening layer 21 is subjected to an alignment process along a predetermined alignment direction. For example, a base alignment layer 22 made of polyimide is formed on the surface of the flattening layer 21 and then rubbed along a predetermined alignment direction. With the planarization layer 21 interposed, the film formation and the rubbing treatment of the base alignment layer 22 can be stably performed.

Proceeding to step (D), a coating comprising a polymer liquid crystal having a predetermined phase transition point and a solvent having a predetermined boiling point is uniformly coated on the surface of the base alignment layer 22 with a predetermined thickness by a bar coating method. Coating in the condition. In this example, the coating treatment was performed by a bar coating method using a high precision coater (HPC) manufactured by Fuji Film Co., Ltd. Thereafter, a low-temperature heat treatment is performed at a temperature lower than the boiling point to evaporate the solvent, and the coating film is dried while maintaining a uniform state. The substrate 11 is once subjected to a high-temperature heat treatment above the phase transition point, then gradually cooled to a temperature below the phase transition point, and the polymer liquid crystal contained in the dried coating material is aligned in the rubbing direction of the base alignment layer 22 to form a quarter. One wavelength plate layer 2
Process into 3.

Proceeding to step (E) in FIG. 6, a contact hole 24 is formed through the quarter-wave plate layer 23, the underlying alignment layer 22, and the planarizing layer 21 to communicate with the drain electrode 19 of the thin film transistor 12. . For example, the above-described lamination (21,
22 and 23) are patterned to form contact holes 24.

Proceeding to step (F), the quarter-wave plate layer 23
A transparent conductive film made of ITO or the like is formed thereon, and is patterned into a predetermined shape to obtain the pixel electrode 25. This pixel electrode 2
5 is a thin film transistor 1 through a contact hole 24.
2 is electrically connected to the drain electrode 19. The alignment layer 26 is formed so as to cover the surface of the pixel electrode 25. For example,
An alignment solvent in which polyimide is dissolved is applied and then dried to form an alignment layer 26.

Finally, the process proceeds to step (G), where the incident-side substrate 31 is joined to the reflective-side substrate 11 via a predetermined gap. A counter electrode 32 and an alignment layer 33 are previously formed on the inner surface of the incident side substrate 31. When the guest host liquid crystal 40 is injected into this gap, a reflection type guest host liquid crystal display device is completed. The guest host liquid crystal 40 includes nematic liquid crystal molecules 41 and, for example, a black dichroic dye 42. In the illustrated example, the liquid crystal molecules 41 are controlled to be vertically aligned by a pair of alignment layers 33 and 26 located above and below. Following this, the dichroic dye 42 is also vertically aligned.

Next, a description will be given of an operation in the case of performing monochrome display using the reflection type guest-host liquid crystal display device shown in FIG. When no voltage is applied, the liquid crystal molecules 4
1 is oriented vertically, and the dichroic dye 42 is similarly oriented. Light incident from the upper substrate 31 passes through the liquid crystal layer 40 without being absorbed by the dichroic dye 42, and is reflected by the light reflection layer 20 without being polarized by the quarter-wave plate layer 23. The reflected light passes through the quarter-wave plate layer 23 again, and
At 0, light is emitted without being absorbed. Therefore, white display is obtained. On the other hand, when a voltage is applied, the liquid crystal molecules 41 shift to horizontal alignment in response to an electric field generated between the pixel electrode 25 and the counter electrode 32. The dichroic dye 42 is similarly oriented. Upper substrate 31
When light incident from the side passes through the liquid crystal layer 40, components of the incident light having a vibration plane parallel to the major axis direction of the molecules of the dichroic dye 42 are absorbed by the dichroic dye 42. The component of the dichroic dye 42 having a vibration plane perpendicular to the major axis direction of the molecule passes through the liquid crystal layer 40 and is reflected by the quarter-wave plate layer 23 formed on the reflective side substrate 11. The light is polarized and reflected by the light reflection layer 20. At this time, the polarization of the reflected light is reversed and passes through the quarter-wave plate layer 23 again, and the dichroic dye 4
A component having a vibration plane parallel to the major axis direction of the second molecule. Since this component is absorbed by the dichroic dye 42, a complete black display is obtained.

[0021]

As described above, according to the present invention,
A polymer liquid crystal is applied by a bar coating method to form a film. That is, the coating material is carried on a wire bar formed by winding a fine wire around a rotatable core rod, and the coating material is applied to the surface of the substrate by relatively moving while rotating the wire bar in contact with the surface of the substrate. As a result, a polymer liquid crystal can be formed with a uniform and uniform thickness over the entire surface of a large-area substrate. By using the formed polymer liquid crystal as a uniaxial optical film, a quarter-wave plate layer having stable optical characteristics can be obtained. Also, by using the wire bar method, it is possible to greatly reduce the amount of expensive polymer liquid crystal used.

[Brief description of the drawings]

FIG. 1 is a process chart showing a polymer liquid crystal film forming method according to the present invention.

FIG. 2 is a schematic view showing the structure of a wire bar used in the method for forming a polymer liquid crystal film according to the present invention.

FIG. 3 is a schematic diagram illustrating an example of a polymer liquid crystal.

FIG. 4 is a graph showing a temperature profile of a polymer liquid crystal film forming method.

FIG. 5 is a process chart showing a method for manufacturing a guest-host liquid crystal display device to which the polymer liquid crystal film forming method according to the present invention is applied.

FIG. 6 is a process drawing showing the same manufacturing method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Coating agent, 2a ... Polymer liquid crystal, 3 ... Uniaxial optical film, 4 ... Wire bar, 4a ... Core rod, 4b ... Fine wire

Claims (3)

[Claims] 1. A compounding step of preparing a coating material having a desired viscosity by dissolving a polymer liquid crystal in a solvent; and carrying the coating material on a wire bar in which a fine wire is wound around a rotatable core rod, and applying the coating material on the surface of the substrate. A coating process in which the wire bar is rotated while moving in contact with each other to apply the coating material on the surface of the substrate, and a solvent is removed from the applied coating material to form a polymer liquid crystal having a uniform thickness. And a drying step of forming a thin film. 2. A compounding step of dissolving a polymer liquid crystal having a predetermined phase transition point in a solvent to prepare a coating material having a desired viscosity, and an alignment step of performing an alignment treatment on a surface of a substrate along a predetermined alignment direction. A coating is carried on a wire bar in which a thin wire is wound around a rotatable core rod, and the wire bar is rotated and relatively moved to apply the coating to the surface of the substrate while being in contact with the surface of the substrate. And a drying step of removing a solvent from the applied coating material to form a thin film of a polymer liquid crystal having a uniform thickness. And a step of aligning the polymer liquid crystal in the alignment direction to form a uniaxial optical film. 3. A compounding step of dissolving a polymer liquid crystal having a predetermined phase transition point in a solvent to prepare a coating material having a desired viscosity, and performing an alignment treatment on a surface of one of the substrates along a predetermined alignment direction. Orientation step, the coating material is carried on a wire bar in which a fine wire is wound around a rotatable core rod, and relatively moved while rotating the wire bar in a state of being in contact with the surface of the substrate to apply the coating material to the surface of the substrate. A coating step of applying, a drying step of removing a solvent from the applied coating agent to form a thin film of a polymer liquid crystal having a uniform thickness, and a step of heating the thin film once to a phase transition point or higher. An alignment step of cooling the polymer liquid crystal to a temperature below the transition point and aligning the polymer liquid crystal in the alignment direction to form a quarter-wave plate layer, and joining the other substrate to the one substrate via a predetermined gap Bonding step, and a guest-host liquid crystal containing a dichroic dye A method of manufacturing a guest-host liquid crystal display device, which performs an injection step of injecting into a gap.