JP2002082224A - Birefringent film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a birefringent film which is subjected to molecular orientation so as to arbitrarily exhibit retardation and an optic axis direction inside a polymer material, by making linearly polarized ultraviolet rays irradiate a film composed of a mixture of a photosensitive side chain polymer liquid crystal and a liquid crystalline compound and a method for manufacturing the same. SOLUTION: The mixture of the photosensitive side chain polymer liquid crystal and the liquid crystalline compound is applied on a substrate and is film formed. The linearly polarized ultraviolet rays are made to irradiate the film by using a device consisting of an ultraviolet ray lamp, a power supply, and an optical element converting natural light to polarized light (e.g. Glan-Taylor prism). By an anisotropic photoreaction of the side chain of the photosensitive side chain polymer liquid crystal, the side chain of the photosensitive side chain polymer liquid crystal and the liquid crystalline compound are aligned in a direction parallel to a filed vibration direction of the irradiating linearly polarized ultraviolet rays and perpendicular to an irradiating ray advancing direction. By making the rays irradiate the film from a direction inclined with respect to he film surface, the liquid crystalline compound is aligned with the optical axis arbitrary inclined. As a result, the berefringent film with the optic axis set to be in a desired direction is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a film of a mixture of a photosensitive side-chain polymer liquid crystal (photosensitive polymer) and a liquid crystal compound with linearly polarized ultraviolet rays (hereinafter referred to as "polarized light"). (Referred to as exposure) and a birefringent film in which the polymer is oriented so that the retardation and the optical axis direction are arbitrarily developed in the polymer material, and a method for producing the birefringent film. (Especially, a birefringent film whose optical axis is inclined with respect to the film surface is effective for expanding the viewing angle in a liquid crystal display device.)

[0002]

2. Description of the Related Art A birefringent film is a film having a birefringence that allows a linearly polarized light component oscillating in a direction of a principal axis perpendicular to each other to pass therethrough and gives a necessary phase difference between the two components.
Such birefringent films have been utilized in the field of liquid crystal displays. In particular, a birefringent film having an inclined optical axis is useful as an optical compensation film for expanding the viewing angle of a liquid crystal display device.
There are several prior art techniques for producing such birefringent films. One method is to stretch a polymer material such as polycarbonate, orient the polymer chains, and cause a difference between the refractive index in the stretching direction and the refractive index in the direction perpendicular to the stretching direction. Is that, because of the stretching step, molecules are oriented in the stretching direction, so that it is practically impossible to tilt the optical axis. In view of the above problems, as a method for producing a birefringent film having a tilted optical axis, a method of arranging a liquid crystalline compound on a stretched film or a substrate subjected to alignment treatment by rubbing or light irradiation has been proposed or put into practical use. For example, JP-A-7-287119 and JP-A-7-287120 describe a method of arranging discotic liquid crystals on a rubbing alignment film or a SiO oblique deposition alignment film. As a similar method, Japanese Patent Application Laid-Open No. 10-278123 describes a method in which a discotic liquid crystal containing a photopolymerization initiator is aligned on a photo-alignment film, and the alignment is fixed by light irradiation. The method using the alignment film as described above has problems such as complicated processes such as alignment treatment of the alignment film and alignment of the liquid crystal material.
Furthermore, as another method of manufacturing a birefringent film having an inclined optical axis, a method of obliquely vapor-depositing an inorganic dielectric has been proposed, but in order to form a vapor-deposited film continuously on a long sheet. However, there are problems such as an increase in the size of the apparatus and a complicated process. The present inventor has also disclosed in Japanese Patent Laid-Open No.
No. 23 proposes a method for producing a birefringent film having a tilted optical axis by polarizing exposure of a side chain type liquid crystalline polymer having photosensitivity. There is a problem that the degree increases.

[0003]

The retardation of a birefringent film produced by stretching and orientation of a polymer film is due to the stretching process, and the molecules are oriented in the stretching direction, so that it is extremely difficult to tilt the optical axis. It is. On the other hand, a method of arranging a liquid crystalline compound on an alignment-treated substrate or a method of obliquely depositing an inorganic dielectric can produce a birefringent film with an inclined optical axis, but the process is complicated. Therefore, there is a problem that a birefringent film having a large-area optical axis inclined at a low cost cannot be obtained. The present invention provides a birefringent film having a low haze and suitable for mass production by a simple process, and a method for producing the birefringent film.

[0004]

According to the present invention, a birefringent film having an optical axis direction arbitrarily developed by subjecting a film of a mixture of a photosensitive side-chain type liquid crystalline polymer and a liquid crystalline compound to polarized light exposure. provide. In the birefringent film and the method for producing the same (birefringent film according to the present invention), a mixture of a photosensitive side chain type liquid crystalline polymer and a liquid crystalline compound is formed and polarized light exposure is performed from a specific direction. The side chain of the photosensitive side-chain type polymer liquid crystal and the liquid crystal compound can be oriented in a direction parallel to the electric field vibration direction of the linearly polarized ultraviolet light irradiated with the liquid crystal compound and in a direction perpendicular to the traveling direction of the irradiation light. By performing this irradiation in an oblique direction with respect to the film surface, the optical axis can be arbitrarily inclined and oriented.
As a result, a birefringent film in which the optical axis is set in a desired direction can be provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. The photosensitive side-chain type liquid crystalline polymer described above includes a substituent such as biphenyl, terphenyl, phenylbenzoate, or azobenzene, which is frequently used as a mesogen component of the liquid crystalline polymer, and a cinnamic acid group (or a derivative group thereof). ) Has a side chain containing a structure to which a photosensitive group is bonded, such as a hydrocarbon,
It is a polymer having a main chain structure such as acrylate, methacrylate, maleimide, N-phenylmaleimide, and siloxane. A solution of the photosensitive side-chain type liquid crystalline polymer and the liquid crystalline compound is applied (spin-coated or cast) on a substrate to form a coating film. The film is isotropic at the time of film formation, and the side chain portion of the photosensitive side chain type liquid crystalline polymer and the liquid crystal compound are not oriented in a specific direction. This state will be described with reference to FIG. 2. In the coating film, the photosensitive side chain (2a) has a photosensitive group represented by a long ellipse and has a vibration direction (m) of irradiated polarized ultraviolet (L) and irradiation. In addition to being oriented in the direction perpendicular to the light traveling direction, the side chains (2b) having poor photosensitivity and the liquid crystal compound (2c) represented by a cylinder coexist randomly. When the film is subjected to polarized light exposure, the photoreaction of the side chain (2a) having high photosensitivity arranged in a direction corresponding to the electric field oscillation direction of the irradiation linearly polarized light and the direction perpendicular to the irradiation light traveling direction proceeds preferentially. In order to promote this photoreaction, it is necessary to irradiate linearly polarized light having a wavelength at which the portions of the photosensitive groups of Chemical Formulas 1 to 8 can react. This wavelength varies from Formula 1 according to the type of -R ₁ ~-R ₁₂ shown by the chemical formula 8, typically a 200-500 nm, among them is high is often the effectiveness of the 250-400Nm.

As shown in FIG. 3, the side chain (3b) which did not cause a photoreaction due to the molecular motion after the polarized light exposure was not in the direction corresponding to the direction of the electric field of the linearly polarized light and the direction perpendicular to the traveling direction of the irradiation light. And the liquid crystalline compound (3c) are oriented in the same direction as the photoreacted side chain (3a). As a result, in the entire coating film, the side chains of the side chain type liquid crystalline polymer and the liquid crystal compound molecules 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 birefringence is induced. .
The orientation by molecular motion after the polarized light exposure is promoted by heating the substrate. The heating temperature of the substrate is desirably lower than the softening point of the photoreacted portion and higher than the softening points of the unreacted side chains and the side chain portions having no photosensitive group. In addition, alignment can be promoted by performing polarized light exposure under heating (from room temperature to Ti + 5 ° C.). Here, Ti refers to a phase transition temperature when the photosensitive side chain type liquid crystalline polymer changes from a liquid crystal phase to an isotropic phase. When the film exposed to polarized light in this way is heated and the unreacted side chain is oriented or the film subjected to polarized light exposure and oriented under heating is cooled to a temperature equal to or lower than the softening point temperature of the polymer, the molecules are frozen, and the orientation of the present invention is reduced. A film is obtained. The liquid crystal compound improves the degree of freedom of molecular motion at the time of realignment, and promotes realignment by its own molecular alignment. The addition of an appropriate amount of this liquid crystal compound has the effect of suppressing the haze, but the excessive addition thereof causes an increase in the haze and a decrease in the alignment. From such a viewpoint, although depending on the type of the photosensitive polymer or the liquid crystal compound, a birefringent sheet can be produced by adding 0.1 wt% to 90 wt%, but preferably 3 wt% to 75 w%.
It is desirably t%. Further, the liquid crystal compound may or may not have reactivity, and if it has reactivity, the orientation is firmly fixed, so that improvement in heat resistance can be expected. In such a case, it is necessary to control the density of photoreactive points by suppressing the amount of polarized light exposure or adjusting the reactivity so as not to hinder the molecular motion during reorientation. Another method for improving heat resistance is to add a crosslinking agent such as a bifunctional compound. In this case, it is necessary to adjust the amount of addition so as not to hinder the molecular orientation.

A method for synthesizing a raw material compound of a photosensitive side chain type liquid crystalline polymer and a reactive liquid crystal compound will be described below. (Monomer 1) 4,4′-biphenyldiol and 2-chloroethanol were heated under alkaline conditions to synthesize 4-hydroxy-4′-hydroxyethoxybiphenyl. This product is added under alkaline conditions with 1,
6-Dibromohexane was reacted to synthesize 4- (6-bromohexyloxy) -4′-hydroxyethoxybiphenyl. Next, lithium methacrylate was reacted to synthesize 4-hydroxyethoxy-4 ′-(6′-biphenyloxyhexyl) methacrylate. Finally, cinnamoyl chloride was added under basic conditions to synthesize a methacrylic acid ester represented by Chemical Formula 11.

Embedded image

(Monomer 2) 4-Hydroxy-4'-hydroxyethoxybiphenyl was synthesized by heating 4,4'-biphenyldiol and 2-chlorohexanol under alkaline conditions. This product was reacted with 1,6-dibromohexane under alkaline conditions to obtain 4-
(6-Bromohexyloxy) -4′-hydroxyethoxybiphenyl was synthesized. Next, lithium methacrylate was reacted to give 4-hydroxyethoxy-4′-
(6′-biphenyloxyhexyl) methacrylate was synthesized. Finally, under basic conditions, 4-methoxycinnamoyl chloride was added to synthesize a methacrylic ester represented by Chemical Formula 12.

Embedded image

(Polymer 1) Monomer 1 is dissolved in tetrahydrofuran, and polymerized by adding AIBN (azobisisobutyronitrile) as a reaction initiator and polymerizing.
I got This polymer 1 exhibited liquid crystallinity in a temperature range of 47 to 75 ° C.

(Polymer 2) Polymer 2 is dissolved by dissolving monomer 2 in tetrahydrofuran and adding AIBN (azobisisobutyronitrile) as a reaction initiator to carry out polymerization.
I got This polymer 2 also exhibited liquid crystallinity.

(Reactive liquid crystal compound 1) Methyl 4-octenyloxybenzoate was synthesized by heating methyl p-hydroxybenzoate and bromooctene under alkaline conditions. This product was heated under alkaline conditions to synthesize 4-octenyloxybenzoic acid. Next, 4-octenyloxybenzoic acid chloride was synthesized by reacting with thionyl chloride, and reacted with methylhydroquinone to synthesize a reactive liquid crystal compound 1 represented by Chemical Formula 13.

Embedded image

[0012]

EXAMPLES The photosensitive side-chain type liquid crystalline polymer used in the present invention exhibits a phase transition temperature by thermal analysis and a birefringent optical pattern in a polarizing microscope observation image in a liquid crystal temperature range. It was confirmed that the material was a liquid crystal material. In Chemical Formula 9, n = 6, m = 2, X = none, W ₁ = Chemical Formula 1, -R ₁ to -R ₇ = H, and a photosensitive side-chain type liquid crystalline polymer in which a main chain is methacrylate. Is a liquid crystal material which shows endothermic peaks at 47 ° C. and 75 ° C. in the course of temperature rise, and exhibits a birefringent optical pattern in the temperature range when observed with a polarizing microscope. FIG. 1 shows a method (apparatus) for producing an alignment film of the present invention. Disordered light (1) generated by an ultraviolet lamp (11) excited by a power supply (12)
6) is a photosensitive side-chain liquid crystal liquid which is converted into linearly polarized ultraviolet light (17) by an optical element (13) (for example, a Glan-Taylor prism) and applied (coated) on a substrate (15). The film (14) of the polymer and the liquid crystal compound is irradiated. Examples 1 to 6 are examples in which a birefringent film having an inclined optical axis was produced by the production method of the present invention.

Example 1 3.75% by weight of polymer 1 and 1.25% by weight of liquid crystal material E7 (Merck Japan)
Was dissolved in dichloroethane and applied to an optically isotropic substrate in a thickness of about 3 μm. Place the substrate 4
Ultraviolet rays, which were arranged so as to be inclined by 5 degrees and converted into linearly polarized light using a Glan-Taylor prism, were irradiated at 120 mJ / cm ² at room temperature from a direction perpendicular to the horizontal plane. Then, 10
After heating to 0 ° C., it was cooled to room temperature. The substrate thus obtained had an optical axis inclined by 22 ° from the normal direction of the substrate, had a phase difference of 76.5 nm in the substrate plane, had little haze, and was sufficiently durable for practical use. .

Example 2 3.75% by weight of polymer 1 and 1.25% by weight of liquid crystal material E7 (Merck Japan)
Was dissolved in dichloroethane and applied to an optically isotropic substrate in a thickness of about 3 μm. Place the substrate 2
Ultraviolet rays, which were arranged so as to be inclined at 0 degrees and converted into linearly polarized light using a Glan-Taylor prism, were irradiated at 120 mJ / cm ² at room temperature from a direction perpendicular to the horizontal plane. Then, 10
After heating to 0 ° C., it was cooled to room temperature. The optical axis of the substrate thus obtained was inclined by 9.5 ° from the normal direction of the substrate, and the in-plane phase difference of the substrate was 94.8 nm.

Example 3 2.5% by weight of Polymer 1 and 2.5% by weight of a liquid crystal material E7 (Merck Japan) were dissolved in dichloroethane and placed on an optically isotropic substrate at about 3%.
It was applied in a thickness of μm. The substrate was arranged so as to be inclined at 45 degrees with respect to the horizontal plane, and irradiated with ultraviolet rays converted to linearly polarized light using a Glan-Taylor prism at room temperature from the vertical direction at room temperature at 120 mJ / cm ² . Subsequently, at 100 ° C
And then cooled to room temperature. In the substrate thus obtained, the optical axis was inclined by 20.5 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 72.3 nm.

Example 4 2.5% by weight of polymer 2 and 2.5% by weight of a liquid crystal material E7 (Merck Japan) were dissolved in dichloroethane and placed on an optically isotropic substrate at about 3%.
It was applied in a thickness of μm. The substrate was arranged so as to be inclined at 45 degrees with respect to the horizontal plane, and irradiated with ultraviolet rays converted to linearly polarized light using a Glan-Taylor prism from the vertical direction at room temperature at 60 mJ / cm ² . Subsequently, after heating to 100 ° C., it was cooled to room temperature. The optical axis of the substrate thus obtained was inclined by 18 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 69.0 nm.

Example 5 3.75% by weight of Polymer 1 and 1.25% by weight of Reactive Liquid Crystal Compound 1 are dissolved in dichloroethane, and a thickness of about 3 μm is formed on an optically isotropic substrate. Was applied. The substrate was arranged at an angle of 45 degrees with respect to the horizontal plane, and the ultraviolet light converted to linearly polarized light using a Glan-Taylor prism was applied at room temperature from a direction perpendicular to the horizontal plane at room temperature.
Irradiation was performed at 0 mJ / cm ² . Subsequently, after heating to 100 ° C., it was cooled to room temperature. Further, the substrate was irradiated with unpolarized ultraviolet light at 1 J / cm ² at room temperature. In the substrate thus obtained, the optical axis was inclined by 20.5 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 38.0 nm.

Example 6 2.5% by weight of polymer 1,
2.5% by weight of liquid crystal material E7 (Merck Japan) and 0.0375% by weight of difunctional monomer HX-620
(Nippon Kayaku) was dissolved in dichloroethane and applied to an optically isotropic substrate at a thickness of about 3 μm. The substrate was arranged so as to be inclined at 45 degrees with respect to the horizontal plane, and irradiated with ultraviolet rays converted to linearly polarized light using a Glan-Taylor prism from the vertical direction at room temperature at 60 mJ / cm ² . Subsequently, after heating to 100 ° C., it was cooled to room temperature. Further, the substrate was irradiated with unpolarized ultraviolet light at 1 J / cm ² at room temperature.
In the substrate thus obtained, the optical axis was inclined by 20 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 55.0 nm.

From these examples, it is possible to produce a film whose optical axis direction is controlled by polarized light exposure, and to manufacture a birefringent film whose optical axis direction is controlled by a relatively simple method called polarized light exposure. I was able to prove it. In the birefringent film of the present invention and the method for producing the same, the film that has caused birefringence by polarized light exposure is further irradiated with ultraviolet light to promote the photoreaction of unreacted photosensitive groups, thereby firmly orienting the orientation in the film. Can be fixed. Such a birefringent film was excellent in heat resistance and light stability and was sufficient for practical use.

[0020]

According to the simple operation of irradiating linearly polarized light,
A birefringent film can be obtained without using a stretching step as in the prior art. Furthermore, by changing the irradiation direction of the linearly polarized ultraviolet light, regions having different optical axes can be formed on the same substrate, and it is expected to be used for various optical elements. Further, the birefringent film having an inclined optical axis can be used as an optical compensation film for expanding a viewing angle in a liquid crystal display device using a twisted nematic liquid crystal utilizing an optical rotation mode and a birefringence mode. Conventionally,
Although the birefringent film with an inclined optical axis could not be produced at a low cost in a large area, according to the present invention,
A large area can be manufactured by a simple operation of performing polarized light exposure from an oblique direction.

[0021]

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for producing a birefringent film of the present invention.

FIG. 2 is a schematic view of a side chain exposed by polarized light exposure.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Ultraviolet lamp 12 ... Power supply 14 ... Film 15 ... Base material 16 ... Disordered light 17 ... Linearly polarized ultraviolet light

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 13, 2000 (2009.1)
3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Birefringent film and method for producing the same

Claims (8)

[Claims] 1. A birefringent film and a method for producing the birefringent film, which are produced by a process including an operation of irradiating a mixture of a photosensitive polymer and a liquid crystalline compound with light. 2. The birefringent film according to claim 1, wherein the photosensitive polymer has liquid crystallinity, and a method for producing the same. 3. The birefringent film according to claim 1, wherein the liquid crystalline compound has reactivity, and a method for producing the birefringent film. 4. The birefringent film according to claim 1, wherein the photosensitive polymer has at least one of the structures represented by Chemical Formulas 1 to 8, and a method for producing the same. Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image _{However, -R 1 ~-R 11 =} -H, halogen, -CN, alkyl such as an alkyl group or their fluoride and groups, -R ₁₂ = methyl group, an ethyl group, such as an alkyl group or a methoxy group Or a fluorinated group thereof. 5. The photosensitive polymer according to claim 1, 2, 3 or 4, wherein at least
Or a birefringent film having a structure represented by Chemical Formula 10 and a method for producing the same. Embedded image Embedded image However, n = 1 to 12, m = 1 to 12, X, Y = non
e, -COO, -OCO-, -N = N-, -C = C-or
—C ₆ H ₄ —, W ₁ , W ₂ = Chemical Formula 1 or Chemical Formula 2 or Chemical Formula 3 or Chemical Formula 4 or Chemical Formula 5 or Chemical Formula 6
Or, it is a structure represented by Chemical Formula 7 or Chemical Formula 8. 6. A birefringent film according to claim 1, wherein the light applied is linearly polarized light or partially polarized light, and a method for producing the birefringent film. 7. A birefringent film and a method for producing the same according to claim 1, further comprising a step of heating and / or cooling. 8. The birefringent film and the method for producing the birefringent film according to claim 1, further comprising a cross-linking step.