JPH1031206A - Formation of macromolecule liquid crystal film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly form a macromolecule liquid crystal film and to stably form a uniaxial optical film having high quality. SOLUTION: The surface of a substrate 1 is first subjected to an orientation treatment along a prescribed orientation direction by executing an orientation stage. Next, the surface of the substrate 1 is coated with a coating material 2 consisting of macromolecule liquid crystals 2a having a prescribed phase transition point and a prescribed b. p. at a prescribed thickness in a uniform state by executing a coating stage. In succession, a drying state is executed to dry the applied coating material 2 subjected to a low-temp. heat treatment at the b. p. or below to evaporate the solvent while maintaining the uniform state of the coating material. Finally, an aligning stage is executed. The uniaxial film 3 is formed by once subjecting the substrate 1 to the high-temp. heat treatment to the phase transition point or above, then slowly cooling the substrate down to the temp. below the phase transition point and aligning the macromolecule liquid crystals 2a included in the dried coating material 2 in the orientation direction.

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 directions perpendicular to each other 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, for example, used as a polarization control element of a reflective 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. In this conventional structure, a quarter-wave plate layer in which a polymer film of polystyrene, polypropylene, polycarbonate, polyethylene terephthalate or the like is molecularly oriented in one direction is used. However, the optical anisotropy of the uniaxially stretched polymer film is not always sufficient, and a practically satisfactory level as a quarter-wave plate layer has not yet been obtained. Also, in this conventional structure,
A quarter-wave plate layer composed of a polymer liquid crystal is also disclosed.
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 a high degree of order, and a practically satisfactory uniaxially anisotropic optical film has not been obtained.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, an object of the present invention is to form a uniform and highly ordered uniaxial optical film using a polymer liquid crystal. The following measures were taken to achieve this purpose. That is, in the method of forming a polymer liquid crystal film according to the present invention, first, an alignment step of aligning the surface of the substrate along a predetermined alignment direction is performed.
Next, a coating process is performed, and a coating material composed of a polymer liquid crystal having a predetermined phase transition point and a solvent having a predetermined boiling point is applied in a uniform state on the surface of the substrate with a predetermined thickness. Subsequently, a drying step is performed, and a low-temperature heat treatment is performed at a temperature lower than the boiling point to evaporate the solvent, thereby drying the applied coating material while maintaining a uniform state. Lastly, an alignment step is performed, and after the substrate 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 alignment direction. A uniaxial optical film is formed. Preferably, the drying step is a low-temperature heat treatment under vacuum to promote the evaporation of the solvent. In the coating step, the coating is applied by spin coating, dipping or printing. Further, in the alignment step, a polyimide film is formed on the surface of the substrate, and then rubbed along the alignment direction.

The polymer liquid crystal film forming method according to the present invention can be applied to a method for manufacturing a guest-host liquid crystal display device. In this case, first, an alignment step of aligning the surface of one substrate along a predetermined alignment direction is performed. Next, perform the coating process,
A coating material consisting of a polymer liquid crystal having a predetermined phase transition point and a solvent having a predetermined boiling point is applied to the surface of the substrate with a predetermined thickness in a uniform state. In the subsequent drying step, a low-temperature heat treatment is performed at a temperature lower than the boiling point, and the solvent is evaporated to dry the coated material while maintaining a uniform state. Further, an alignment step is performed. The substrate is once subjected to a high-temperature heat treatment at a temperature higher than 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 alignment direction to form the liquid crystal. Process into a one-half wavelength plate layer. Thereafter, a bonding step of bonding the one substrate to the other substrate via a predetermined gap is performed. 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.

In the present invention, a high-molecular liquid crystal (liquid crystal polymer) is dissolved in a suitable solvent and applied to a substrate by spin coating or printing. When the solvent is evaporated, by performing this at a sufficiently low temperature, the occurrence of defects such as pinholes is suppressed. At this time, by performing a low-temperature heat treatment under vacuum,
Further, evaporation may be promoted. For example, when a quarter-wave plate layer is formed on a guest-host liquid crystal display device, a liquid crystal polymer as a material is dissolved in an appropriate solvent such as cyclohexanone, and then applied by spin coating, printing, or the like. Further, after performing a heat treatment at a relatively low temperature to evaporate the solvent, a heat treatment at a relatively high temperature is performed to align the liquid crystal polymers. When evaporating the solvent contained in the coating agent, for example, if a heat treatment at a relatively high temperature exceeding the boiling point of the solvent is performed, pinholes (repelling) are generated on the coating film surface and the uniformity of the coating film is impaired. In order to prevent this, heat treatment is performed at a temperature sufficiently lower than the boiling point of the solvent to evaporate the solvent and then align the polymer liquid crystal.

[0006]

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. First (A)
The alignment process 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, after a polyimide (not shown) is formed on the surface of the substrate 1, rubbing is performed 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 step, a coating material 2 composed of a polymer liquid crystal 2a having a predetermined phase transition point and a solvent having a predetermined boiling point is applied to the substrate 1 with a predetermined thickness.
Is applied uniformly on the surface of. For example, the coating material 2 is applied by spin coating, dipping, or printing. In the case of performing spin coating, it is desirable to appropriately set conditions such as the concentration of the coating agent and the number of spin rotations so that the thickness of the formed coating film causes a phase difference of λ / 4 in the visible light region. Is obtained. In the subsequent drying step, the solvent is evaporated at a temperature lower than the boiling point, and the solvent is evaporated to dry the coated coating material 2 (coating film) while maintaining a uniform state.
Thereby, pinholes and the like do not occur in the coating film.
In this drying step, a low-temperature heat treatment may be performed in some cases 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 higher than the phase transition point, then gradually cooled to a temperature 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 be uniaxial optically. The film 3 is formed. By setting the thickness appropriately, the uniaxial optical film 3 can be used as it is as a quarter-wave plate layer. As shown in the drawing, the liquid crystal molecules of the polymer liquid crystal 2a contained in the coating material 2 are in a random alignment state in the coating and drying stages, whereas the liquid crystal molecules of the polymer liquid crystal 2a are in the alignment direction after the high-temperature heat treatment. And the desired uniaxial optical anisotropy is obtained. Specifically, the substrate 1 on which the coating material 2 has been applied 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 applied polymer liquid crystal 2a is aligned in the alignment direction of the substrate 1 which has been rubbed in advance. As can be understood from the above description,
In the present invention, 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.
On the other hand, when the heat treatment is performed at a high temperature which is higher than or close to the boiling point, defects such as pinholes are generated in the coating film, and a uniaxial optical film having good film quality cannot be stably obtained.

FIG. 2 is a schematic view showing a chemical structure of an example of a polymer liquid crystal. As shown, 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. The length of the side chain spacer is 2 with carbon number n.
And six are alternately arranged. That is, n =
2 and n = 6 side chains are copolymerized to the main chain at a ratio of 1: 1. This polymer liquid crystal is dissolved in a solvent obtained by mixing cyclohexanone and methyl ethyl ketone (MEK) at a ratio of 8 to 2 to form a coating material. This coating material is applied to a substrate to form a uniaxial optical film. That is, this coating agent is applied by spin coating, printing, or the like on a substrate that has been previously rubbed.

FIG. 3 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. On the other hand, about 10%
Experiments have shown that when heated at a temperature of 0 ° C. or more, pinholes are generated and a good coating film cannot be obtained. Next, heating and slow cooling are performed in the alignment step. The polymer liquid crystal shown in FIG. 2 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 equal to or higher than the phase transition point TP (for example, 120 ° C.), and then gradually cooled to a temperature equal to or lower than the phase transition point TP so that the polymer liquid crystal contained in the dried coating material is oriented in the alignment direction. Align to form a uniaxial optical film. By performing the alignment step at 120 ° C. exceeding the phase transition point TP, an optical film having good uniaxial orientation (good orientation) can be stably formed.

Further, a method for manufacturing a guest-host liquid crystal display device to which the method for forming a polymer liquid crystal film according to the present invention is applied will be described with reference to FIGS. First, in step (A) of FIG. 4, an insulating substrate 11 made of glass, quartz, or the like is used.
The thin film transistor 12 is integratedly formed thereon. 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 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 irregularities are 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 reflectance on the surface of the uneven shape formed in this manner.
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.

In step (C), the thin film transistor 12
Then, the flattening layer 21 is formed so as to fill the unevenness 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, the planarization layer 21
Is formed on the surface of the substrate, and then rubbed along the alignment direction. By interposing the flattening layer 21, the formation and the rubbing treatment of the base alignment layer 22 can be performed stably.

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 coated in a uniform state on the surface of the base alignment layer 22 with a predetermined thickness. Work. A low-temperature heat treatment is performed at a temperature below the boiling point to evaporate the solvent, and the coating film is dried while maintaining a uniform state. Substrate 1
1 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 by a quarter. The wave plate layer 23 is processed.

Proceeding to the step (E) of FIG. 5, a contact hole 24 penetrating through the quarter-wave plate layer 23, the base alignment layer 22, and the planarizing layer 21 and communicating with the drain electrode 19 of the thin film transistor 12 is opened. . 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 positioned 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, an almost complete black display is obtained.

[0017]

As described above, according to the present invention, after applying a coating material composed of a liquid crystal polymer and a solvent, a low-temperature heat treatment is performed at a temperature lower than the boiling point to evaporate the solvent, thereby evaporating the solvent. It is dry while maintaining such a state. Thereafter, the film is heated at a temperature higher than the phase transition point and then gradually cooled to a temperature lower than the phase transition point, thereby aligning the polymer liquid crystals contained in the coating film to form a uniaxial optical film. With this method, defects such as pinholes do not occur in the coating film, and an optical film having good uniaxial orientation can be stably formed. It is suitable for applications such as plate layers.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram illustrating an example of a polymer liquid crystal.

FIG. 3 is a graph showing a temperature profile of a polymer liquid crystal film forming method.

FIG. 4 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. 5 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

Claims (5)

[Claims] An alignment step of aligning a surface of a substrate along a predetermined alignment direction, and applying a coating material comprising a liquid crystal polymer having a predetermined phase transition point and a solvent having a predetermined boiling point to a predetermined thickness. A coating step of coating the surface of the substrate in a uniform state, a drying step of performing low-temperature heat treatment at a temperature below the boiling point, evaporating the solvent, and drying the coated coating while maintaining the coated coating in a uniform state; After the substrate 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 orientation direction to form a uniaxial optical film. A polymer liquid crystal film forming method for performing an alignment step. 2. The polymer liquid crystal film forming method according to claim 1, wherein in the drying step, low-temperature heating is performed under vacuum to promote evaporation of the solvent. 3. The polymer liquid crystal film forming method according to claim 1, wherein said applying step applies said coating agent by spin coating, dipping or printing. 4. The method according to claim 1, wherein in the alignment step, a polyimide film is formed on the surface of the substrate and then rubbed along the alignment direction.
The method for forming a polymer liquid crystal according to the above. 5. An alignment step of aligning the surface of one of the substrates along a predetermined alignment direction, and applying a coating material comprising a polymer liquid crystal having a predetermined phase transition point and a solvent having a predetermined boiling point to a predetermined direction. A coating step of coating the surface of the substrate in a uniform state with a thickness, and a drying step of performing a low-temperature heat treatment at a temperature below the boiling point, evaporating the solvent, and drying the coated coating while maintaining a uniform state. And heating the substrate once at a high temperature above the phase transition point, then gradually cooling the substrate to a temperature below the phase transition point, and aligning the polymer liquid crystal contained in the dried coating material in the alignment direction with a quarter. An alignment step of processing into a wavelength plate layer; a bonding step of bonding the other substrate to the one substrate via a predetermined gap; and an injection step of injecting a guest-host liquid crystal containing a dichroic dye into the gap. Of manufacturing a guest-host liquid crystal display device.