JP2003014927A - Method for manufacturing optically anisotropic element, optically anisotropic element and liquid crystal display device using the optically anisotropic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optically anisotropic element making phase difference and its angular dependence arbitrarily emerge in a polymer material by irradiating a film of a mixture of a photosensitive polymer and a low molecular weight compound with light resulting in molecular orientation and a method for manufacturing the same. SOLUTION: The mixture of the photosensitive polymer and the low molecular weight compound is applied to a substrate and is film-formed. The film is irradiated with linearly polarized light from a direction inclined with respect to the film by using an apparatus composed of an ultraviolet lamp and a power source or an optical element to convert natural light into polarized light (i.e., a Glan-Taylor prism). Subsequently the film is irradiated with linearly polarized light having a vibration plane of an electric field in the identical plane from a direction vertical to the film. Thereby the phase difference is induced in the film and the optically anisotropic element effective in widening a viewing angle of a liquid crystal display device is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a phase difference and its angle dependence by irradiating a film of a mixture of a photosensitive polymer and a low molecular weight compound with linearly polarized light (polarized light exposure). The present invention relates to a method for producing an optically anisotropic element in which

[0002]

2. Description of the Related Art A retardation film is an optical anisotropic element having a birefringence that allows linearly polarized light components vibrating in mutually perpendicular principal axis directions to pass therethrough and gives a necessary retardation between the two components. Such an optical anisotropic element has been utilized in the liquid crystal display field. In particular, an optically anisotropic element with an inclined optical axis is useful as an optical compensation film for expanding the viewing angle of a liquid crystal display device. In a liquid crystal display device, liquid crystal molecules, which are positive index ellipsoids, are slanted near the substrate of the liquid crystal cell. Because of the orientation, it is effective to incline a positive refractive index ellipsoid and a negative refractive index ellipsoid having the opposite birefringence angle dependence.

Conventional techniques for manufacturing such an optical anisotropic element have been reported. For example, patent registration 2640083
JP-A No. 2003-242242 describes an optical anisotropic element in which discotic liquid crystal is inclinedly arranged by a rubbing alignment film and an SiO oblique vapor deposition alignment film. Further, in Japanese Patent Laid-Open No. 10-332933, a liquid crystal polymer having a positive birefringence is formed by a rubbing alignment film, a film in which a diagonal alignment is formed on a SiO oblique vapor deposition alignment film, and a negative birefringence layer. An optical anisotropic element is described.

However, in the method using the alignment film as described above, the manufacturing process such as the alignment film application process, the alignment treatment process, and the liquid crystal material alignment process becomes complicated, and the optical anisotropy in which the optical axis of a large area is tilted is complicated. The manufacturing cost of the device is high. Also,
When the alignment film has an unfavorable influence on the display characteristics of the liquid crystal display device, it is necessary to remove the alignment film by a method such as peeling or melting. As another method for producing an optically anisotropic element with an inclined optical axis, a method of obliquely vapor-depositing an inorganic dielectric has been proposed, but in order to continuously form a vapor-deposited film on a long sheet, There are problems such as large scale of the device and complicated process. Further, in order to fully realize the effect of enlarging the viewing angle of the liquid crystal display device, such a layer in which the liquid crystal component is tilt-aligned and a uniaxial refractive index ellipsoid layer and / or a biaxial refractive index ellipsoid layer are used. Must be combined,
There is a problem that the steps become complicated because the two layers are bonded together by an adhesive layer or the like that has no optical influence.

[0005]

In an optically anisotropic element produced by stretch orientation of a polymer film, it is extremely difficult to tilt the optical axis because the orientation of molecules is limited to the stretching direction. On the other hand, although it is possible to produce an optically anisotropic element with an inclined optical axis by a method of arranging a liquid crystalline compound on an alignment-treated substrate or a method of obliquely vapor-depositing an inorganic dielectric, it is possible to produce it at low cost. It is not possible to obtain an optical anisotropic element having a large area with a tilted optical axis, and in order to sufficiently realize the effect of enlarging the viewing angle of a liquid crystal display device, a uniaxial refractive index ellipsoid layer or /
And the process becomes complicated because the biaxial refractive index ellipsoidal layer is attached by an adhesive layer or the like. In the present invention, in a simple process,
An optical anisotropic element suitable for mass production and a manufacturing method thereof are provided.

[0006]

In the method for producing an optical anisotropic element according to the present invention (the optical anisotropic element according to the present invention), a film of a photosensitive polymer or a mixture of a photosensitive polymer and a low molecular compound is formed on a substrate. ), Irradiate linearly polarized light obliquely with respect to the normal direction of the film, and then irradiate linearly polarized light whose electric field vibration plane is in the same plane from the normal direction of the film. This makes it possible to form an optical anisotropic element in which a refractive index ellipsoidal layer having an arbitrary optical axis inclination and an index ellipsoidal layer having no optical axis inclination are formed, which is effective for expanding the viewing angle of a liquid crystal display device. A method for manufacturing an optically anisotropic element by a simple process is realized.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below. The above-mentioned photosensitive polymer is biphenyl, terphenyl, which is often used as a mesogenic component of liquid crystalline polymers,
Substituents such as phenylbenzoate and azobenzene,
It has a side chain containing a structure in which a photosensitive group such as cinnamic acid group (or its derivative group) is bonded, and has a structure such as hydrocarbon, acrylate, methacrylate, maleimide, N-phenylmaleimide, siloxane in the main chain. It is a polymer. The polymer may be a homopolymer of the same repeating unit or a copolymer of units having side chains with different structures, or it is also possible to copolymerize units having side chains containing no photosensitive group. . Further, the low-molecular compound to be mixed also has a substituent such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are often used as mesogenic components, and the mesogenic component and allyl, acrylate, methacrylate, cinnamic acid groups (or their A functional group such as a derivative group) via a flexible component, or
It is a compound having crystallinity or liquid crystallinity that is bonded without being interposed. When mixing these low molecular weight compounds, not only a single compound but also a plurality of types of compounds can be mixed.

2 and 3, linearly polarized light L (vibration indicated by arrow m) is applied to a coating film 20 formed by coating a mixture of a photosensitive polymer of this kind and a low molecular weight compound on a substrate. 3 shows the changes that occur in the coating film when irradiated with (having a direction) (or subjected to orientation treatment such as heating) (before irradiation = FIG. 2, after irradiation and orientation treatment = FIG. 3).

The coating film 20 is isotropic during film formation,
The side chains (indicated by a long ellipse) and low molecular weight compounds (indicated by a cylinder) of the photosensitive polymer do not face a specific direction. When the linearly polarized light L (having a vibration direction indicated by an arrow m) is irradiated (polarized light exposure) from a specific direction on the coating film 20, the vibration direction m of the irradiation light and the irradiation light traveling direction are present in the film. On the other hand, there is a side chain 2a having a highly photosensitive arrangement and a side chain 2b having a poor photosensitivity in the direction corresponding to the vertical direction. In addition, the low molecular weight compound 2c coexists randomly. When this film is exposed to polarized light, the photoreaction of the side chain 2a arranged parallel to the electric field oscillation direction of the irradiation light and oriented in the direction corresponding to the direction perpendicular to the traveling direction of the irradiation light preferentially proceeds.

FIG. 3 shows the film 30 after the reaction has proceeded by irradiating the film 20 of FIG. 2 with light. The side chain 3b (2b) of the polymer that did not cause a photoreaction due to molecular motion after exposure to polarized light
And the low molecular weight compound 3c (2c) also photoreacted with the side chain 3a (2
Orient in the same direction as a). As a result, in the entire coating film, the side chains of the polymer and the molecules of the low molecular weight compound are oriented in the direction of the electric field oscillation of the irradiated linearly polarized light and in the direction perpendicular to the direction of the irradiation light, and the phase difference is induced to induce an optical anisotropic element. Becomes In order to promote the photoreaction, irradiation with light having a wavelength with which the photosensitive group moiety can react is required. This wavelength is generally 200-500 nm, although it depends on the type of photosensitive group,
The effectiveness of 50-400 nm is often high.

The inventor has paid attention to the above-mentioned properties of the coating film formed of a photosensitive polymer or a mixture of a photosensitive polymer and a low molecular weight compound, and as shown in FIG. The linearly polarized light (L ₁ ) is obliquely applied to the film normal direction, and the linearly polarized light (L ₁ ) whose electric field vibration plane is in the same plane as (L ₁ ) The inventors have found that a completely new optical anisotropic element in which the angle dependence of the phase difference is arbitrarily controlled can be prepared by irradiating the film with ₂ ) from the normal direction to the present invention. In the optically anisotropic element obtained by the present invention, as shown in FIG. 4, the obliquely oriented refractive index ellipsoid 41 and the horizontally oriented refractive index ellipsoid 42 are mixed. Thus, when light passes through the layer 40 in which the refractive index ellipsoids are mixed, the phase difference given between the linearly polarized light components vibrating in the mutually perpendicular principal axis directions is the phase difference given by the refractive index ellipsoids. Is a composite of.

The two optically anisotropic elements 50 and 50 'of the present invention can be used in a liquid crystal display device by arranging them on the upper and lower sides of a liquid crystal cell 55 with their optical anisotropic axes orthogonal to each other. Will be described with reference to FIG. When light passes through a plurality of optical elements (a plurality of refractive index ellipsoids), it can be considered that these refractive index ellipsoids are combined. In FIG. 5, the obliquely oriented refractive index ellipsoid 51 of the upper optical anisotropic element 50 and the horizontally oriented refractive index ellipsoid 54 of the lower optical anisotropic element 50 'are combined, and conversely, the upper optical anisotropic element When the horizontally oriented refractive index ellipsoid 52 and the obliquely oriented refractive index ellipsoid 53 of the lower optical anisotropic element are combined, two negative refractive index ellipses effective for expanding the viewing angle of the liquid crystal display device are obtained. The bodies 5a and 5b are inclined, and the optical characteristics equivalent to the arrangement in which the directions are orthogonal to each other are exhibited. Further, by enhancing the horizontally oriented index ellipsoid component, a layer having a tilted negative index ellipsoid and a uniaxial index ellipsoid layer and / or a biaxial index ellipsoid layer are combined. The optical characteristics equivalent to The optical characteristics of such an optical anisotropic element are designed according to the optical characteristics of the liquid crystal display device in which the optical anisotropic element is mounted. Further, for optical compensation of the liquid crystal display device, it is necessary to adjust the phase difference of the optical anisotropic element in consideration of the phase difference of all the optical systems constituting the device including the polarizing plate.

A photosensitive polymer or a mixture of a photosensitive polymer and a low molecular weight compound is coated on a substrate to form a film.
It is also possible to use a uniaxial index ellipsoidal layer and / or a biaxial index ellipsoidal layer on the substrate. As the uniaxial refractive index ellipsoid layer and / or the biaxial refractive index ellipsoid layer, a uniaxially or biaxially stretched polymer material such as polycarbonate or triacetyl cellulose, or a photosensitive material such as the present invention can be used. Examples thereof include those that are irradiated with light to exhibit a phase difference. However, it is not limited to these as long as it has desired optical characteristics.

The above-mentioned orientation by molecular motion after polarized light exposure is promoted by heating the substrate (via the film). The heating temperature of the substrate is preferably lower than the softening point of the photoreacted portion and higher than the softening points of the side chains and the low molecular weight compound which are not photoreacted. When the film thus polarized and exposed to light and oriented with unreacted side chains or the film exposed to polarized light and heated under heating is cooled to a temperature not higher than the softening point of the polymer, the molecule is frozen and the oriented film of the present invention. Is obtained. When the low molecular weight compounds have heat and / or photoreactivity with each other or with respect to the polymer, the orientation is firmly fixed, and thus the heat resistance is expected to be improved. In such a case, it is necessary to control the density of photoreactive points by suppressing the exposure dose or adjusting the reactivity so as not to hinder the molecular movement during reorientation.

Further, mixing a low molecular weight compound has the effect of suppressing the haze when an appropriate amount is added, but when added in an excessive amount, it causes an increase in haze and a decrease in orientation. From such a point of view, depending on the kind of the photosensitive polymer or the low molecular weight compound, the low molecular weight compound is 0.1 wt% to 80 w.
Although the optical anisotropic element can be manufactured even if t% is added, it is preferably 5 wt% to 50 wt%. Here, when the compatibility between the photosensitive polymer and the low molecular weight compound is not sufficient, a crystal having a size capable of inducing phase separation or visible light scattering by heating the substrate during film formation or after exposure to polarized light is used. It forms and causes an increase in haze. In order to suppress this phase separation and formation of fine crystals, it is necessary to adjust the compatibility between the polymer and the low molecular weight compound. As a measure of this compatibility, Polymer Engineering and
Science, Vol. 7, No. 2,147 (19
74), the evaporation energy (ΔE
The solubility parameter (σ) calculated by the calculation formula (1) from v) and the molecular volume (V) can be conveniently used, and the ratio of the solubility parameter (σ) of the polymer and the low molecular weight compound: z
However, it has been found from experiments that phase separation and formation of fine crystals can be effectively suppressed when 0.93 <z <1.06. σ = (ΔEv / V) ^1/2 Calculation formula (1)

The haze tends to increase as the film thickness increases and the molecular orientation is disturbed. To suppress the haze, it is effective to reduce the film thickness. Although reducing the film thickness leads to a decrease in the phase difference, by coating the material solution on both sides of the substrate and decreasing the film thickness per layer, the haze can be reduced without decreasing the phase difference of the entire optical anisotropic element. Can be suppressed. Further, as a method of obtaining a large retardation, a method of laminating films can be mentioned. In this case, the film is formed first, and the material solution is applied and laminated on the film that has been subjected to polarized light exposure. It is effective to dissolve and use. Also, polarized exposure from both sides from the film side of the mixture of the photosensitive polymer on the front surface and the low molecular compound and the substrate on the back surface (or the film side of the mixture of the photosensitive polymer on the low molecular compound on the back surface). By doing so, the phase difference can be efficiently expressed. The substrate to be used may be any material as long as it has a property of transmitting light having a wavelength capable of reacting with a photosensitive polymer, but the higher the light transmittance, the less the exposure amount is, which is advantageous in the manufacturing process. Becomes

The synthetic method for the examples of the raw material compounds in the present invention is shown below. (Monomer 1) 4,4′-biphenyldiol and 2-chloroethanol were heated under alkaline conditions to synthesize 4-hydroxy-4′-hydroxyethoxybiphenyl. This product is
6-Dibromohexane was reacted to synthesize 4- (6-bromohexyloxy) -4′-hydroxyethoxybiphenyl. Then, lithium methacrylate was reacted to synthesize 4- (2-hydroxyethoxy) -4 ′-(6-methacryloyloxyhexyloxy) biphenyl. Finally, under basic conditions, cinnamoyl chloride was added to synthesize the methacrylic acid ester represented by Chemical Formula 1.

[Chemical 1]

(Polymer 1) Polymer 1 is prepared by dissolving Monomer 1 in tetrahydrofuran and adding AIBN (azobisisobutyronitrile) as a reaction initiator to polymerize.
Got This polymer 1 exhibited liquid crystallinity in the temperature range of 47 to 75 ° C.

(Low molecular weight compound 1) 4,4'-biphenyldiol and 1,6-dibromohexane were reacted under alkaline conditions to synthesize 4,4'-bis (6-bromohexyloxy) biphenyl. Next, the low molecular compound 1 represented by the chemical formula 2 was synthesized by reacting with lithium methacrylate and purifying the product with a column.

[Chemical 2]

[0020]

EXAMPLE FIG. 8 shows an example of a manufacturing method (apparatus) for manufacturing the optically anisotropic element of the present invention by polarization exposure of linearly polarized ultraviolet light. However, the manufacturing method of the optical anisotropic element of the present invention is not limited to this. Power supply 8
The disordered light 86 generated by the ultraviolet lamp 81 excited by 2 is converted into linearly polarized ultraviolet light 87 by an optical element 83 (for example, a Glan-Taylor prism),
A film 84 of a photosensitive material coated (coated) on a substrate 85
Irradiate. Examples of the optically anisotropic element manufactured by the manufacturing method of the present invention are shown below. The angle dependence of the phase difference of the optically anisotropic element is measured by the Senarmont method using a polarizer, a quarter-wave plate and an analyzer while measuring the extinction angle of the analyzer while rotating the measurement sample with a predetermined optical system. Was obtained by doing.

3.75% by weight of Polymer 1 and 1.25
A low molecular weight compound 1 (wt%) was dissolved in dichloroethane, and the solution was applied onto a substrate to a thickness of about 4 μm to form a film. The substrate is arranged so as to be tilted at 45 degrees with respect to the horizontal plane, and ultraviolet rays converted into linearly polarized light by using a Glan-Taylor prism are respectively applied from the front and back sides of the substrate at a room temperature in a direction perpendicular to the horizontal plane at room temperature.
Irradiation was performed with each of 00 mJ / cm ² and 200 mJ / cm ² . Then, each of the ultraviolet converted just as the linearly polarized light in a horizontal substrate, from front and back surfaces of the substrate at room temperature from a vertical direction with respect to the horizontal plane ^{150mJ / cm 2, 300mJ / cm} 2
Irradiate each. Then, after heating at 100 degreeC, it cooled to room temperature. The angle dependence of the phase difference of the optical anisotropic element thus manufactured was as shown in FIG.

The substrate thus obtained was peeled off from the polarizing sheet of the Casio liquid crystal color television EV-510,
One each on the top and bottom of the liquid crystal cell, or two on the top or bottom
The sheets were laminated and laminated, and then polarizing sheets (HEG1425DU manufactured by Nitto Denko) were laminated one on top of the other.
The axial arrangement of each optical element was as shown in FIG. In FIG. 7, reference numerals 71 and 71 'denote substrates, a and a'represent tilt directions of respective refractive index ellipsoids, 72 denotes a liquid crystal cell, and b and b'represent pretilt directions of upper and lower substrates. 7
Reference numerals 3 and 73 'denote polarizing sheets, and c and c'represent respective light absorption axis directions. When the liquid crystal color television was driven with such a configuration and the contrast ratio when white display and black display was 5 was defined as the viewing angle, the viewing angle in the vertical and horizontal directions was measured. BM-5A manufactured by Topcon was used for measuring the contrast ratio. The results are shown in Table 1. As shown in Table 1, it was confirmed that the viewing angle was increased in the examples of the present invention (downward and leftward and rightward).

[Table 1]

[0023]

INDUSTRIAL APPLICABILITY In the optical anisotropic element and the method for producing the same of the present invention, the element having a phase difference caused by the polarized light exposure is further irradiated with ultraviolet rays to promote the photoreaction of the unreacted photosensitive group, The orientation inside can be firmly fixed.
Such an optically anisotropic element was excellent in heat resistance and light stability and was sufficient for practical use. Conventionally, a complicated process was required to manufacture an optical element with an inclined optical axis that can be utilized as an optical anisotropic element for enlarging a viewing angle in a liquid crystal display device. Alternatively, it is possible to manufacture an optically anisotropic element that can obtain a viewing angle expansion effect of a liquid crystal display device by a simple process of exposing a film of a mixture of a photosensitive polymer and a low molecular weight compound to polarized light.

[0024]

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing polarized light exposure directions in a method for manufacturing an optical anisotropic element of the present invention.

FIG. 2 is a schematic diagram of side chains exposed by polarized light exposure.

FIG. 3 is a schematic diagram of side chains arranged by molecular motion after polarized light exposure.

FIG. 4 is a schematic view of an index ellipsoid of the optically anisotropic element of the present invention.

FIG. 5 is a schematic diagram of a refractive index ellipsoid when the optical anisotropic element of the present invention is made orthogonal to each other.

FIG. 6 is a graph showing measurement results of phase difference angle dependency of the optical anisotropic element of the example.

FIG. 7 is a schematic diagram showing an optical system when evaluating viewing angle characteristics.

FIG. 8 is a conceptual diagram showing a method for manufacturing an optical anisotropic element of the present invention.

[Explanation of symbols]

11 ... Coating films L ₁ , L ₂ ... Linearly polarized light 81 ... UV lamp 82 ... Power source 83 ... Optical element (Glan-Taylor prism) 84 ... Film (film) 85 ... Substrate 86 ... Chaotic light 87 ... Linearly polarized ultraviolet light

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Claims (8)

[Claims] 1. A film made of a photosensitive polymer or a mixture of a photosensitive polymer and a low-molecular compound is irradiated with linearly polarized light (L ₁ ) in an oblique direction with respect to the normal direction of the film. And an operation of irradiating (L ₁ ) and linearly polarized light (L ₂ ) having an electric field vibration plane in the same plane from the normal direction to the film. , Method for manufacturing optical anisotropic element. 2. Irradiation of linearly polarized light to a film formed of a mixture of the photosensitive polymer and a low molecular weight compound,
The method for producing an optical anisotropic element according to claim 1, wherein the film is formed from a mixture of the photosensitive polymer and a low molecular weight compound from both front and back sides. 3. The method according to claim 1, further comprising a step of heating and / or cooling a film formed of a mixture of the photosensitive polymer and the low molecular weight compound. Manufacturing method of optically anisotropic element. 4. The method according to claim 1, comprising a step of crosslinking a mixture of the photosensitive polymer and a low molecular weight compound.
~ The method for manufacturing an optical anisotropic element according to claim 3. 5. An optical anisotropic element manufactured by the manufacturing method according to any one of claims 1 to 4. 6. The optical anisotropic element according to claim 5, wherein the photosensitive polymer has liquid crystallinity. 7. A structure in which a uniaxial refractive index ellipsoidal layer and / or a biaxial refractive index ellipsoidal layer are added to the optical anisotropic element manufactured by the manufacturing method according to any one of claims 1 to 4. An optical anisotropic element characterized by being processed. 8. A liquid crystal display device, characterized in that at least two layers or more of the optically anisotropic element according to any one of claims 5 to 7 are laminated in a configuration in which their optical anisotropic axes are orthogonal to each other. .