JPH11189665A - Birefringent film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process whereby a birefringent film having the optical axis tilted relatively to the film surface is mass-produced at a low cost and to prepare a birefingent film produced thereby. SOLUTION: A photosensitive side-chaine-type polymer film 4 which has a main chain formed e.g. from a hydrocarbon, an acrylate, a methacrylate or a siloxane and has substituents (e.g. biphenyl, terphenyl, phenyl benzoate or azobenzene groups), side chains having a structure contg. photosensitive groups such as cinnamate groups, and side chains having no photosensitive group in a specified ratio is irradiated with linearly polarized ultraviolet rays 7 to conduct the dimerization of the photosensitive groups, thus giving a birefringent film having the optical axis tilted to a desired direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aligning molecules by irradiating a photosensitive side-chain type polymer liquid crystal film with a linearly polarized ultraviolet ray so as to align the optical axis and the light transmission direction. The present invention relates to a birefringent film having a structure for controlling a phase difference, and a method for manufacturing the same. In particular, 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 transmits a linearly polarized light component oscillating in a direction of a main axis perpendicular to each other, and gives a necessary phase difference between the two components. Birefringent films have also been utilized in the field of liquid crystal displays, and birefringent films having an inclined optical axis are particularly effective as optical compensation films for expanding the field of view of liquid crystal display devices. Compared to CRT display devices, liquid crystal display devices are `` flat and can be installed in small spaces, '' `` light and portable, '' `` adapted to high-speed video communication because they are digital images, '' It is driven by a low voltage and consumes little power, and is rapidly growing as a powerful means of generating video information. Many of the currently popular liquid crystal display devices use twisted nematic liquid crystals.

[0003] Liquid crystal molecules have different refractive indices in the major axis direction and the minor axis direction of the molecules, and exhibit birefringence. A phase difference occurs when light is vertically incident on such a birefringent body and when light is obliquely incident. According to FIG. 1, α
If a space having an axis, a β axis, and a γ axis is taken, its refractive index is represented by an anisotropic ellipsoid (110) as shown in the figure. In a liquid crystal display device having a structure in which a liquid crystal is sandwiched between two polarizers, if the liquid crystal has such optical anisotropy, a viewing angle characteristic in which a display color and a display contrast change depending on a viewing direction occurs. In other words, even with the same emitted light, the field of view (1) in the major axis (101) direction of the refractive index ellipsoid.
11) and the visual field (112) in a direction shifted from the long axis of the refractive index ellipsoid have different appearances. Since this kind of viewing angle characteristic lowers the visibility of the liquid crystal display device, development of a birefringent film (and a rational manufacturing method thereof) having an optional optical compensation action suitable for solving the problem has been an issue. I have.

[0004] This optical compensation function will be described with reference to FIG. Above the liquid crystal layer (100) including the inclined major axis (101) of the refractive index ellipsoid, the optical property for compensating the optical anisotropy of the refractive index ellipsoid (110), that is, the major axis (20)
By disposing a birefringent film (200) having an optical anisotropy represented by an index ellipsoid (210) having 1), the brightness sensed in the visual field (111) and the visual field (112). And the like. Since it is very unlikely that such a birefringent film having a specific optical anisotropy will be obtained by chance, a technique for producing a birefringent film having arbitrary optical characteristics (degree of inclination of the optical axis) is required. become.

Hitherto, several birefringent films (manufacturing methods) for improving the viewing angle characteristics of liquid crystal display devices have been proposed. For example, JP-A-3-3926, JP-A-3-29
No. 1601 describes a method for obtaining an optical compensation film in which liquid crystal molecules are aligned along an alignment film by applying a polymer liquid crystal to a substrate on which the alignment film is formed. In this method, molecules are uniformly oriented in a direction perpendicular to the substrate (alignment film), so that it is difficult to provide an arbitrary optical compensation characteristic, and it is not possible to sufficiently improve the viewing angle characteristic. Did not. Similarly, in the case of using a stretch-oriented polymer (polycarbonate) film, it is difficult to tilt the optical axis because the molecules are oriented in the stretching direction. Further, in this method, it is necessary to precisely control the degree of stretching and the thickness over the entire surface of the film, and it is difficult to accurately and uniformly maintain the retardation. On the other hand, a film (manufacturing method) for tilting the optical axis and optically compensating has been proposed. This is described, for example, in JP-A-4-113301 and JP-A-5-8032.
As described in Japanese Patent Publication No. 3 (1993), this is a method of slicing a polycarbonate plate having one optical axis (orientation) obliquely with respect to the optical axis. With this method, it is difficult to obtain a large-area birefringent film at a practical cost. As a birefringent element with an inclined optical axis, an inorganic crystal such as calcite that is cut out at an angle to the optical axis and whose surface is polished can be considered, but these inorganic crystals are expensive, low cost, and large. It is not possible to obtain a birefringent film in which the optical axis of the area is inclined. JP-A-5-5823 describes a method using a photoisomerizable substance. However, a birefringent film obtained by the method lacks heat and light stability and is suitable for applications. Does not. Further, Japanese Unexamined Patent Publication No.
287119, JP-A-7-287120,
A method of applying a discotic liquid crystal to a rubbing alignment film or a SiO oblique deposition alignment film, and heating and cooling the same is also described. However, it is necessary to obtain a birefringent film having a uniform orientation direction and uniform control over a large area at low cost. Is difficult.

[0006]

According to the present invention, there is provided a rational method for producing a birefringent film which solves the above problems.

[0007]

According to the present invention, there is provided a birefringent film having an arbitrary birefringent characteristic by irradiating a photosensitive side-chain type polymer film with linearly polarized ultraviolet rays. A method of producing a birefringent film, particularly a method of producing a birefringent film characterized in that the birefringence characteristic is controlled in the direction of the optical axis. A method for producing a birefringent film, wherein a side chain of the polymer includes at least a structure represented by Formula 1 and / or Formula 2 and has a structure represented by Formula 3 or Formula 4. In the method for producing a birefringent film, the temperature of the photosensitive side-chain type polymer film when irradiating linearly polarized ultraviolet light is adjusted to the transition temperature (T _{i) of the} side-chain type polymer to the isotropic phase. Difference from 10)
The method for producing a birefringent film, characterized in that the temperature is within the range of ° C. The method for producing a birefringent film comprises irradiating a photosensitive side-chain type polymer film or its support with linearly polarized ultraviolet rays at room temperature. And then a heating and / or cooling step, and a birefringent film obtained by these birefringent film manufacturing methods.

[0008]

The birefringent film according to the production method of the present invention
Has the following specific effects. The orientation of side chains can be controlled by irradiation with linearly polarized ultraviolet light and by the copolymer composition. As a result, a birefringent film whose optical axis is inclined with respect to the film surface can be obtained. The linearly polarized ultraviolet rays irradiated to the side chains of the polymer can be arranged in a direction parallel to the electric field oscillation direction and perpendicular to the irradiation light traveling direction. By irradiating the film from an oblique direction with respect to the film surface, the side chains of the polymer can be tilted and oriented, and this tilt can be set in any direction by changing the light irradiation direction and the vibration direction. . The degree of orientation of the side chain is controlled by the dose of linearly polarized ultraviolet light, and the phase difference can be controlled by the degree of orientation of the side chain.

[0009]

Embodiments of the present invention will be described below. The polymer as a raw material of the birefringent film of the present invention,
Side chain containing a structure in which a substituent such as biphenyl, terphenyl, phenylbenzoate, or azobenzene, which is frequently used as a mesogen component of a liquid crystalline polymer, and a photosensitive group such as a cinnamic acid group (or a derivative thereof) are bonded. Having a side chain containing a mesogen component to which a photosensitive group is not bound, in a certain ratio, a hydrocarbon, an acrylate,
It is a polymer having a structure such as methacrylate or siloxane in the main chain. The polymer solution is applied (spin-coated) on a substrate to form a polymer coating film. This polymer coating film is non-oriented at the time of film formation, and the photosensitive side chain portion represented by the chemical formula 1 does not face a specific direction. This state will be described with reference to FIG. 3. In the coating film (10), a photosensitive side chain () having a photosensitive group represented by a long ellipse and oriented in a direction corresponding to the vibration direction of the irradiation polarized ultraviolet light. 11) and the side chain (12) having poor photosensitivity exist without orientation. When this coating film is irradiated with linearly polarized ultraviolet light, the cinnamic acid group of the photosensitive side chain (11) (or, in the direction corresponding to the electrolytic oscillation direction of the irradiated linearly polarized light and the direction perpendicular to the irradiation light traveling direction) (or The dimerization of a photosensitive group such as a derivative group thereof occurs most sharply. In this dimerization reaction, a cyclopropane bond is formed as shown in the reaction formula 1.
In order to proceed with the quantification reaction, irradiation of linearly polarized light having a wavelength at which the cinnamate group of Formula 1 can react is performed, and the photoreactive portion is oriented in a direction perpendicular to the direction of the electric field of the irradiated linearly polarized light.
The wavelength of light that induces this reaction is represented by the following formula (1).
Although it varies depending on the type of R ₁ to -R ₅ , generally 200 to
It is 500 nm, and 250-400 nm is particularly effective in many cases.

[0010]

Embedded image The rectangle described in Reaction Formula 1 is a molecular chain connecting the main chain of the polymer and the photosensitive group in the side chain type polymer liquid crystal, and includes a liquid crystal component and a bending component.

FIG. 4 shows the orientation state of the coating film after irradiation with ultraviolet rays.
It will be explained by. Even if the coating film (10) does not have the photosensitive group represented by the chemical formula 2 or has the photosensitive group represented by the chemical formula 1 (since it is not oriented in the direction of the electric field of linearly polarized light), dimerization does not occur. The side chain (12) that has not occurred is dimerized by the molecular motion after the end of the light irradiation, and is dimerized.
1 ')). As a result, in the entire polymer coating film, the side chains are oriented perpendicular to the electric field oscillation direction D1 of the irradiated linearly polarized light and the irradiation light traveling direction D2.

The orientation by molecular motion is promoted by heating the polymer coating (substrate to be coated). The heating temperature is desirably lower than the softening point of the photoreacted portion (that is, the portion in which the orientation is fixed) and higher than the softening point of the side chain that has not been photoreacted and the side chain portion having no photosensitive group. Further, the polymer coating film is formed at T _i ± 10 ° C., preferably T _i ± 5 ° C., more preferably T _i ± 2 ° C. (where,
Ti can promote the alignment by irradiating polarized ultraviolet rays under heating at a temperature of a phase transition temperature when a liquid crystal phase changes to an isotropic phase. For example, in the chemical formulas 1 to 4, a: b
= 55: 45, n = 6, m = 2, k = 6, X, Y = no
ne, W = -COO -, - R 1 ~-R 5 = H, -R 6 =
In the example of -CN, 85 to 94C is suitable. Alternatively, a film in which unreacted side chains are oriented even when the polymer coating film (substrate to be coated) is heated after irradiating with linearly polarized ultraviolet light, or a film in which linearly polarized ultraviolet light is irradiated and aligned under heating Is cooled to a temperature equal to or lower than the softening point of the polymer to obtain an alignment film in which the molecular orientation is cooled. In addition, the side chain having no photosensitive group represented by the chemical formula 2 lowers the density of cross-linking points in the photodimerization reaction, improves the degree of freedom of molecular motion during alignment, and reorients itself due to its molecular orientation. To promote. From such a viewpoint, in the chemical formulas 3 and 4, a: b = 10
Although it can be prepared at 0: 0 to 0:99, a: b = 10
More preferably, it is 0: 0 to 30:70.

A method for synthesizing a raw material compound of a polymer material 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 ester represented by Chemical Formula 5.

Embedded image

(Monomer 2) 4-hydroxy-4'-cyanobiphenyl is reacted with 1,6-dibromohexane under alkaline conditions to give 4- (6-bromohexyloxy)-
4′-cyanobiphenyl was synthesized. Next, lithium methacrylate was reacted to obtain 4-cyano-4 ′-(6 ′).
-Biphenyloxyhexyl) methacrylate was synthesized. A methacrylic acid ester represented by Chemical Formula 6 was synthesized.

Embedded image

(Monomer 3) 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 methacrylate represented by the formula (7).

Embedded image

(Polymer 1) Polymer 1 is obtained by dissolving Monomer 1 in tetrahydrofuran, 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) Monomer 1 and Monomer 2 are dissolved in tetrahydrofuran at various ratios and polymerized by adding AIBN (azobisisobutyronitrile) as a reaction initiator and polymerizing. Merged 2 was obtained (a: b = 55: 4)
5). This polymer 2 exhibited liquid crystallinity in a temperature range of 44 to 95 ° C.

(Polymer 3) Monomer 1 and Monomer 2 are dissolved in tetrahydrofuran at various ratios, and polymerized by adding AIBN (azobisisobutyronitrile) as a reaction initiator and polymerizing. Merged 3 was obtained (a: b = 30: 7)
0). This polymer 3 exhibited liquid crystallinity in a temperature range of 45 to 101 ° C.

(Polymer 4) Polymer 4 is obtained by dissolving monomer 3 in tetrahydrofuran, adding AIBN (azobisisobutyronitrile) as a reaction initiator, and polymerizing.
I got This polymer 4 also exhibited liquid crystallinity.

[0020]

EXAMPLES The polymer material of the present invention exhibits a phase transition temperature by thermal analysis and a liquid crystal temperature range by observation with a polarizing microscope.
The birefringent optical pattern was confirmed to be a liquid crystal material. In Chemical Formulas 1 to 3, a: b =
55:45, n = 6, m = 2, k = 6, X, Y = none,
The thermal analysis curve of the polymer material of the present invention in which W = —COO—, R _{1 to} R ₅ = H, and R ₆ = —CN shows that 4
An endothermic peak was observed at 4 ° C, and an endothermic peak was also observed at 95 ° C.
It was a liquid crystalline material that exhibited a birefringent optical pattern in the temperature region when observed with a polarizing microscope. The orientation of the side chain by irradiation of the linearly polarized ultraviolet light of the polymer material is applied to the polymer coating film formed on the substrate by applying the linearly polarized light ultraviolet light,
It was verified by comparing polarized infrared spectra in the direction parallel to and perpendicular to the electric field oscillation direction of the irradiation light of the polymer coating film. FIG. 6 shows a difference spectrum ΔA of polarized infrared light in a direction parallel to and perpendicular to the direction of electric field oscillation of irradiation light 30 seconds after irradiation with polarized light. -CN, O in parallel direction by polarized light irradiation
It was confirmed that the absorption of -Ph and Ph was large, and the side chains were oriented in the direction of the electric field oscillation of the irradiation light. The magnitude of the birefringence of the polymer coating film depends on the irradiation amount of the linearly polarized ultraviolet light, and changes as shown in FIG. 7 depending on the irradiation time of the linearly polarized ultraviolet light. In the figure, the horizontal axis is the irradiation time of linearly polarized ultraviolet light, and the vertical axis is the value dN indicating birefringence. FIG.
Shows a method (apparatus) for producing an alignment film of the present invention. The disordered light (6) generated by the ultraviolet lamp (1) excited by the power supply (2) is converted into linearly polarized ultraviolet light (7) by the optical element (3) (for example, a Glan-Taylor prism) and the substrate (5). The resin film (4) applied (coated) is irradiated at an irradiation angle (η).

(Embodiments 1 to 6) In Embodiments 1 to 6, in particular, an optical compensation film for enlarging a viewing angle in a liquid crystal display device is assumed to obtain a film having a required optical axis inclination. It is each Example aiming at. Each polymer is dissolved in chloroform and placed on an optically isotropic substrate.
Spin coating was performed at a thickness of 600 μm. This substrate was arranged so as to be inclined by a required irradiation angle with respect to a horizontal plane, irradiated with ultraviolet rays converted to linearly polarized light using a Glan-Taylor prism (under each temperature condition), and then cooled (heat treated) to room temperature. The optical axis of the obtained birefringent film was measured for the optical axis inclination by a crystal rotation method.
It was confirmed that the target optical axis inclination was obtained. The results are summarized in Table 1.

(Embodiments 7 to 12) Embodiments 7 to 12
In each of the examples, a phase difference film in a liquid crystal display device is assumed, and the purpose is to obtain a film having a required phase difference. Each polymer was dissolved in chloroform and spin-coated on an optically isotropic substrate to a thickness of 10 μm. The ultraviolet light converted to linearly polarized light using the Glan-Taylor prism on the resin film adjusted in this way,
(Under each temperature condition) perpendicular to substrate (irradiation angle = 90
°). The retardation was measured as the optical property of the obtained film, and it was confirmed that the target retardation film was obtained. Table 2 summarizes the results.

[0023]

As described above, according to the present invention, a birefringent film can be obtained by photoreaction. This birefringent film can be applied to a retardation film of a liquid crystal display device and the like to improve viewing angle characteristics and the like. It is obtained by a simple operation, and it is possible to form regions having different phase differences in the same plane. A birefringent film having an inclined optical axis can be used as an optical compensator 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, there has been no method for manufacturing such a birefringent film having an inclined optical axis at a large area and at low cost. However, the present invention has made it possible to manufacture a birefringent film for a large-screen liquid crystal display device. In the birefringent film of the polymer material of the present invention, the side-chain-oriented film is irradiated with linearly polarized ultraviolet light, and the UV-irradiation further promotes the dimerization reaction of the photosensitive group to irradiate the side chain. Can be fixed firmly. Such a birefringent film is excellent in heat resistance and light resistance and has high practicality.

[0024]

[Brief description of the drawings]

FIG. 1 shows a refractive index ellipsoid showing the optical characteristics of the liquid crystal.
FIG. 2 is a conceptual diagram illustrating an operation of arranging a birefringent film on the liquid crystal of FIG. 1 to optically compensate. FIG. 3 shows the state of molecules (side chains) in the polymer coating film before irradiation with ultraviolet light, and FIG. 4 shows the state of orientation of side chains after irradiation with linearly polarized ultraviolet light. FIG. 5 is a conceptual diagram showing a method for producing a birefringent film of the present invention. FIG. 6 is a graph showing the infrared difference spectrum ΔA between the direction parallel to the electric field and the direction perpendicular to the electric field oscillation direction of the irradiation light after the irradiation of the linearly polarized ultraviolet light, and FIG. 7 shows the change in the birefringence with the irradiation time of the linearly polarized ultraviolet light. It is a graph.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultraviolet lamp 2 ... Power supply 3 ... Optical element (Glan-Taylor prism) 4 ... Resin film 5 ... Substrate 6 ... Disordered light 7 ... Linearly polarized ultraviolet light η・ Irradiation angle

[Table 1]

[Table 2]

Claims (6)

[Claims] 1. A method for producing a birefringent film, comprising irradiating a photosensitive side-chain polymer film with linearly polarized ultraviolet light to obtain a birefringent film having any birefringent characteristics. 2. The method for producing a birefringent film according to claim 1, wherein the optional birefringence characteristic is control in an optical axis direction. 3. The method for producing a birefringent film according to claim 1, wherein the structure of the photosensitive side-chain type polymer is represented by at least chemical formula 1 and / or chemical formula 2 on the side chain. Formula 3 or 4 including the structure
The manufacturing method of the birefringent film characterized by having the structure represented by these. Embedded image Embedded image Embedded image Embedded image However, in the chemical formulas 1 to 4, n, m, k = 1 to 12, a: b = 100: 0 to 1:99 R _{1 to} R ₆ = -H, -CN, -C = C-, -C = C (C
N) ₂ , —C ＝ CH—CN, an alkyloxy group such as a halogen group or a methoxy group, X, Y = none, —COO,
-OCO -, - N = N - , - C = C -, - C 6 H 4 -,
_{Z = -H, -CH 3, -C} 2 H 5, -C 3 H 7, halogen, W = none, -COO, -OCO -, - (O-
CH ₂₎ -. 4. The method for producing a birefringent film according to claim 1, wherein the temperature of the photosensitive side-chain type polymer film when irradiating linearly polarized ultraviolet light is adjusted to the side-chain type polymer film. A difference from the transition temperature (T _i ) to the isotropic phase within 10 ° C. 5. The method for producing a birefringent film according to claim 1, wherein the photosensitive side-chain type polymer film or its support is irradiated with linearly polarized ultraviolet rays at room temperature, and thereafter, the high-refractive-index film is irradiated with the ultraviolet light. Heating the molecular membrane or its support,
And / or a method for producing a birefringent film, comprising a step of cooling. 6. A birefringent film obtained by the method for producing a birefringent film according to claim 1.