JP2002202407A - Retardation film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a retardation film and a method for manufacturing the same by irradiation of ultraviolet rays, being a mixture of a completely polar ized component and an unpolarized component. SOLUTION: A mixture of a photosensitive polymer and a low molecular weight compound is applied (by spin coating or casting) on a substrate and film formed. Side chains in the photosensitive polymer and the low molecular weight compound are not oriented in the film, however, on irradiation of the ultraviolet rays, being a mixture of a completely polarized component and an unpolarized component, a photoreaction in a specified direction is suppressed, and at the same time with heating subsequent to the irradiation, orientation throughout the film takes place and birefringence is realized. Furthermore, as the inclination of the optical axis is freely set by the direction of the ultraviolet rays irradiation the film is useful as the retardation film enlarging a viewing angle of a liquid crystal display device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION A phase difference in which an optical axis is inclined by irradiating a film (film) of a mixture of a photosensitive polymer and a low-molecular compound with light in which a completely polarized component and a non-polarized component are mixed. And a method for producing the same. (Particularly, a retardation film in which the 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 retardation film is a film having a birefringence that 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.
Such a retardation film has been used in the field of liquid crystal display. In particular, a retardation film having an inclined optical axis is useful as an optical compensation film for expanding the viewing angle of a liquid crystal display device.
Several conventional techniques for producing such a retardation film have been reported. 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. Since the optical axis is oriented in the stretching direction, it is substantially impossible to tilt the optical axis.
In view of the above problems, as a method for producing a retardation film having an inclined optical axis, a method of arranging a liquid crystalline compound on a stretched film, rubbing, or a substrate that has been subjected to an alignment treatment by light irradiation has been proposed or put into practical use. For example, JP-A-7-287
No. 119 and JP-A-7-287120 describe a method of arranging discotic liquid crystals on a rubbing alignment film and 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 an 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 retardation 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. Japanese Patent Application Laid-Open No. 7-138308 discloses a method for developing a phase difference by light irradiation.
A method of irradiating (UV) light is described, but this method develops anisotropy in the vertical direction with the electric field vibration of the irradiated polarized UV light, and cannot tilt the optical axis, so that the viewing angle is increased. Difficult to do. Further, the present inventor also proposed in Japanese Patent Application Laid-Open No. 10-278123 a method for producing a retardation film having an inclined optical axis by irradiating linearly polarized ultraviolet rays to a photosensitive side chain type liquid crystalline polymer. . However, in the method of expressing a phase difference by light irradiation, it is necessary to convert non-polarized ultraviolet light into linearly polarized light before irradiation. As a general dichroic polarizer used for such polarization conversion, there is a sheet obtained by impregnating a sheet obtained by uniaxially stretching PVA (polyvinyl alcohol) with iodine by TAC (triacetyl cellulose). However, a dichroic polarizer impregnated with iodine in this way has a low transmittance of ultraviolet light and a low heat resistance, and thus cannot be used as a liquid crystal light alignment technique. For this reason, birefringent prisms are used to polarize ultraviolet light.However, birefringent prisms use a natural crystal of calcite as a prism, so that the entire surface of the substrate used for LCDs is illuminated. There is no large prism that can be made.

[0003]

The retardation of a retardation film produced by stretching orientation of a polymer film is as follows.
Since the molecules are oriented in the stretching direction, it is extremely difficult to tilt the optical axis. 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 retardation film with an inclined optical axis, but the process is complicated. Therefore, it is not easy to obtain a large-area retardation film having a large-area optical axis inclined at low cost. Further, in the method of manufacturing a retardation film by irradiating linearly polarized ultraviolet light, it is necessary to make the irradiation light linearly polarized through a polarizing element, but it is necessary to produce a practical polarizing element when irradiating a large area. It is difficult.

[0004]

According to the present invention, a completely polarized component and a non-polarized component are mixed by a combination of a photosensitive polymer which exhibits anisotropy with ultraviolet light having a low degree of polarization and a low molecular compound. We have devised a method for manufacturing a retardation film that arbitrarily expresses a retardation and an optical axis obtained by irradiating light. In the production method (retardation film), a mixture of a photosensitive polymer and a low-molecular compound is formed and irradiated with light in which a completely polarized component and a non-polarized component coexist from a specific direction. And the low molecular weight compound molecules can be oriented in the direction of the electric field vibration of the completely polarized component. In addition, by irradiating the film surface obliquely,
It is possible to provide a retardation film in which the optical axis is arbitrarily inclined and oriented, and the optical axis is set in a desired direction.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. Examples of the aforementioned photosensitive polymer include substituents such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are frequently used as a mesogen component of a liquid crystalline polymer, and a cinnamoyl group, a chalcone group, a cinnamylidene group, and β- (2-furyl) has a side chain including a structure in which a photosensitive group such as an acryloyl group (or a derivative thereof) is bonded, and includes a hydrocarbon, an acrylate, a methacrylate,
Examples include polymers having a structure such as maleimide, N-phenylmaleimide, or siloxane in the main chain. The polymer may be a homopolymer composed of the same repeating unit or a copolymer of a unit having a side chain having a different structure, or a unit having a side chain containing no photosensitive group may be copolymerized. . Further, the low-molecular compound to be mixed also includes a compound having a crystalline or liquid crystalline property having a substituent such as biphenyl, terphenyl, phenylbenzoate, or azobenzene, which is frequently used as a mesogen component. In addition, not only a single compound but also a mixture of plural kinds of compounds is possible. Furthermore, to the extent that the liquid crystallinity is not impaired, an alignment aid for improving the alignment, a crosslinking agent for improving the heat resistance, or the like may be added. The monomer may be copolymerized with a photosensitive polymer. However, examples of the photosensitive polymer and the low-molecular compound are not limited to the above. The film of the mixture of the photosensitive polymer and the low-molecular compound is irradiated with ultraviolet light in which a completely polarized component and a non-polarized component are mixed, thereby anisotropically dimerizing the photosensitive group portion of the polymer. The desired retardation film can be formed without using a polarizing element for crosslinking and obtaining a highly linearly polarized ultraviolet ray. In addition, the ultraviolet light used in the present invention, in which a completely polarized component and a non-polarized component necessary to express a phase difference are mixed, is an ultraviolet lamp 13, a condenser mirror 15, a plane mirror 16, At least one quartz plate or the like is provided in the optical path of a normal light irradiation device including an integrator lens 17 and a collimator lens 18 or between the light emitting device and the polymer compound 12 (coated film, film) applied to the substrate 11. Transparent plate 1
4 can be obtained by a relatively easy means of tilting arrangement (more preferably, a transparent plate is coated with a dielectric or metal thin film), and there is no area limitation in the manufacturing method, and a large-area liquid crystal alignment film can be produced with high productivity. It can be manufactured by A preferred embodiment of a method of irradiating light in which a completely polarized component and a non-polarized component are mixed will be described. When a part of the non-polarized light passes through the interface between two media such as air and a quartz plate and partially reflects, there is a property that a completely polarized component and a non-polarized component are mixed in the transmitted light.
Now, assuming that the non-polarized light is incident on the quartz plate (refractive index: 1.4585), the P of the non-polarized light incident on the quartz plate is considered.
Transmittance of component and S component and degree of polarization of transmitted light: PS /
P + S (P and S are the intensities of the transmitted light of the P component and the S component, respectively, and the intensity of the completely polarized light component is indicated by P−S.
+ S is the intensity of the total transmitted light including the completely polarized component and the non-polarized component. ) Changes according to the incident angle of the non-polarized light on the quartz plate, and has a relationship shown in FIG. 4 (the incident angle θ is the angle between the perpendicular of the substrate and the incident direction of light, and the incident direction of light is Θ is 0 ° when vertical). In order to increase the utilization efficiency of the P component, it is desirable that the incident angle on the transparent plate is a Brewster's angle determined by the refractive index of the transparent plate at which the transmittance of the P component becomes 1.0.

The method for producing a retardation film of the present invention will be described with reference to FIG. First, a mixture of a photosensitive polymer and a low-molecular compound is applied (spin-coated or cast) on one surface of a substrate (not shown) to form a film (film) 20. Before being irradiated with light, the side chains (shown by ellipsoidal spheres 2a and 2b) and the low-molecular compounds (shown by cylinders 2c) of the photosensitive polymer in the film 20 do not turn in a specific direction. Coexist in orientation. Then, via the transparent plate 24 with respect to the film 20 is irradiated with non-polarized ultraviolet light L _n. In this case, tilt the transparent plate 24 with respect to the optical path axis of L _n (incident angle θ
When There is state) disposed not 0 °, a part of the incident light L _n is reflected in the transparent plate as reflected light L _s, The remaining component of the incident light L _n is a completely polarized component passes through the transparent plate non-polarized light component is irradiated obliquely to the film 20 become the light L _p of a mixture (state incident angle ψ is not 0 °). At this time, in the side chain portion of the photosensitive polymer randomly coexisting in the film 20, a side chain 2a having a high photosensitivity configuration and a side chain 2b having a low photosensitivity configuration are included. Occurs. Side chains 2a, relative to the major axis (the molecular chain direction) the optical path axis L _p (irradiation direction), also to the electric field vibration direction Q with L _p, are arranged both vertically. The side chain in such an arrangement is easily exposed, and the photoreactivity is maximized as compared with the side chain 2b in another arrangement. Selectively (2
As a result, the film 20 becomes anisotropic as a whole. In order to promote the photoreaction, it is necessary to irradiate light having a wavelength at which the portions of the photosensitive groups of Chemical Formulas 1 to 8 can react. This wavelength, -R ₁ ~-R from formula 1 shown in Formula 8
_Although it varies depending on the ₁₂ types, it is generally 200-500 nm, and in particular, the effectiveness of 250-400 nm is often high.

FIG. 3 shows a state of the film 30 after the film 20 of FIG. 2 has been irradiated with light and the reaction has proceeded. Side chain 3 of a photosensitive polymer that did not cause photoreaction by molecular motion after light irradiation
b (2b) and the low molecular compound 3c (2c) are oriented in the same direction as the side chain 3a (2a) that has undergone photoreaction. This is due to the interaction between side chains and with low molecular weight compounds. As a result, in the entire film, the side chains of the photosensitive polymer and the low-molecular compound molecules are oriented parallel or inclined to the electric field vibration direction Q of the completely polarized component of the irradiated ultraviolet light and the direction of the irradiation light, and the birefringence is reduced. Induced. By performing this irradiation in an oblique direction with respect to the film surface, the optical axis can be arbitrarily tilted and oriented, so that a retardation film in which the optical axis is set in a desired direction is produced. For measuring the tilt of the optical axis, Japan Journal Applied
Physics, Vol. 19, 2013 (1980)
The crystal rotation method for measuring the transmission intensity of polarized light while rotating the measurement sample, described in the above section, was used. In this measuring method, the stereoscopic birefringence of the measurement sample can be measured from the angle dependence of the transmittance of polarized light. The orientation by molecular motion after irradiation with ultraviolet light in which a completely polarized component and a non-polarized component are mixed is promoted by heating the film. The heating temperature of the film is desirably lower than the softening point of the photoreacted portion and higher than the softening points of the unreacted side chains and the low molecular weight compounds. Also,
In order to promote the orientation of the film, it is effective to irradiate ultraviolet light in which a completely polarized component and a non-polarized component are mixed under heating (from room temperature to Ti + 5 ° C.). Here, Ti indicates a phase transition temperature when the phase changes from a liquid crystal phase to an isotropic phase. Preferably T
Irradiating around i is effective. As described above, a film heated after irradiating the ultraviolet ray in which the completely polarized component and the non-polarized component are mixed or a film irradiated with the ultraviolet ray in which the completely polarized component and the non-polarized component are mixed under heating to the softening point temperature of the polymer or lower. Upon cooling, the molecules are frozen, and the retardation film of the present invention is obtained.

In the present invention, when the low-molecular compound mixed with the photosensitive polymer has heat and / or photoreactivity with each other or with the low-molecular compound, the orientation becomes strong. Since it is fixed, improvement in heat resistance is expected. In such a case, it is necessary to control the density of the photoreaction points by suppressing the irradiation dose or adjusting the reactivity so as not to hinder the molecular movement at the time of reorientation. Low molecular compounds are
An appropriate amount has the effect of suppressing the haze, but if added in excess, causes an increase in haze and a decrease in orientation. From such a viewpoint, depending on the type of the photosensitive polymer or the low-molecular compound, the low-molecular compound is contained in an amount of 0.1 wt% to 80 wt%.
Although the retardation sheet can be manufactured even if it is added by wt%, it is preferably 5 wt% to 50 wt%.
Here, if the compatibility between the photosensitive polymer and the low molecular weight compound is not sufficient, the film is heated when the film is heated or after the film is irradiated with ultraviolet light in which a completely polarized component and a non-polarized component are mixed, and phase separation or visible light is visible. Crystals of a size capable of inducing light scattering are formed, causing an increase in haze.

As a method of increasing the film thickness and obtaining a larger phase difference, there is a method of laminating films. In this case, in the process of applying the material solution again on the film that has been formed and irradiated with ultraviolet rays and then laminating, in order to prevent the destruction of the previously formed film, the polymer is added to a solvent having reduced solubility. It is effective to dissolve and use the low molecular weight compound. In addition, when a mixed film of a photosensitive polymer and a low-molecular compound is irradiated with ultraviolet light in which a completely polarized component and a non-polarized component are mixed from the front and back surfaces,
Birefringence appears more efficiently. Irradiation with ultraviolet light in which a completely polarized component and a non-polarized component are mixed may be applied to the compound directly or via a support. When the support is interposed, the support may be made of any material as long as it has light transmittance of a wavelength at which the photosensitive polymer can react, but the higher the light transmittance, the more the irradiation amount. Less is required, which is advantageous in the manufacturing process. Alternatively, a mixture of a photosensitive polymer and a low-molecular compound may be formed on a peelable support, and after peeling, ultraviolet light containing a mixture of a completely polarized component and a non-polarized component may be irradiated from the front and back surfaces of the film. it can.

The synthesis method for the starting compound and the low molecular weight compound of the photosensitive polymer 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 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-methacryloylhexyloxy) biphenyl. Finally,
Under basic conditions, cinnamoyl chloride was added to synthesize Monomer 1 represented by Chemical Formula 10.

Embedded image

(Polymer 1) Polymer 1 was obtained by dissolving this monomer 1 in tetrahydrofuran and adding AIBN (azobisisobutyronitrile) as a reaction initiator to carry out polymerization. This polymer 1 exhibited liquid crystallinity in a 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, lithium methacrylate was reacted, and the product was purified by column to synthesize a low molecular compound 1 represented by Chemical Formula 11.

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[0013]

(Example 1) 3.75% by weight of polymer 1 and 1.25% by weight of liquid crystal material E7 (Merck Japan) were dissolved in dichloroethane and applied on a quartz substrate to a thickness of about 3 μm. . The substrate is arranged at an angle of 45 degrees with respect to the horizontal plane so that the application surface is the irradiation surface, and 10 mW is passed through a quartz plate in which four substrates are arranged so as to be inclined at 57 degrees with respect to the horizontal plane
/ Cm ² of non-polarized ultraviolet light was irradiated from the vertical direction at room temperature for 10 seconds, and then the substrate was turned upside down and irradiated similarly for 10 seconds.
The degree of polarization at this time: P−S / P + S × 100 (%) is
Calculated as 54 (%). Next, after heating to 100 ° C., it was cooled to room temperature. In the substrate thus obtained, the optical axis was inclined in a direction of 67 ° from the normal direction of the substrate, and the in-plane phase difference was 55 nm.

Example 2 3.75% by weight of polymer 1 and 1.25% by weight of low molecular weight compound 1 were dissolved in dichloroethane and applied on a quartz substrate to a thickness of about 3 μm. The substrate is arranged at an angle of 45 degrees with respect to the horizontal plane so that the application surface is the irradiation surface, and is placed at a non-unbiased position of 10 mW / cm ² through a quartz plate in which four substrates are arranged so as to be inclined at an angle of 57 degrees with respect to the horizontal plane. UV light is irradiated from the vertical direction at room temperature for 10 seconds,
The substrate was irradiated upside down for 10 seconds in the same manner. Next, at 100 ° C
And then cooled to room temperature. In the substrate thus obtained, the optical axis was inclined at 67 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 46 nm.

[0015]

According to the present invention, a transparent substrate such as a quartz plate or a substrate coated with a dielectric material or a metal thin film is inclinedly arranged in an optical path of a commonly used light irradiation device or between the light irradiation device and an object to be irradiated. By a simple operation of irradiating the obtained ultraviolet ray in which the completely polarized component and the non-polarized component are mixed, a retardation film could be obtained without using a stretching step as in the prior art. Furthermore, by changing the irradiation direction of the ultraviolet light, it is possible to produce regions having different optical axes in the same substrate, and it is expected to be used for various optical elements. Further, the retardation 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, such a retardation film having an inclined optical axis could not be produced at low cost. However, according to the present invention, a simple and easy method of irradiating an ultraviolet ray in which a completely polarized component and a non-polarized component are mixed from an oblique direction. The operation has made it possible to increase the area.

[0016]

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram showing a side chain exposed by irradiation of ultraviolet light in which a completely polarized component and a non-polarized component are mixed.

FIG. 3 is a schematic diagram showing a film oriented by molecular motion after irradiation with ultraviolet light in which a completely polarized component and a non-polarized component are mixed.

FIG. 4 shows the angle of incidence of non-polarized light incident on a quartz plate (refractive index: 1.4585), the transmittance of P and S components, and the degree of polarization of transmitted light: PS / (P + S) × 100 (%). )

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Mixed film (film) 13 ... Ultraviolet lamp 14 ... Transparent plate 15 ... Collective mirror 16 ... Plane mirror 17 ... Integrator lens 18 ... Collimator lens

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 1/04 G02B 1/04 // G02F 1/13363 G02F 1/13363 F-term (Reference) 2H049 BA06 BA42 BA42 BB42 BC01 BC05 BC22 2H091 FA11X FA11Z FB02 FB04 FB12 FC23 LA12 4F071 AA04 AA33 AC10 AF35 AH16 BA02 BB02 BC02 4J002 AA031 BG071 EH076 FD146 GP03

Claims (11)

[Claims] 1. A phase difference produced by a process including an operation of irradiating a mixed film of a photosensitive polymer and a low-molecular compound with light in which a completely polarized component and a non-polarized component are mixed. Film and method for producing the film. 2. The retardation film and the method for producing the retardation film according to claim 1, wherein the non-polarized ultraviolet light emitted from the light irradiation device is obliquely passed through at least one light-transmitting substrate to completely polarize the component. And a method for producing the retardation film, wherein the retardation film is converted into light having a mixture of light and non-polarized light. 3. The retardation film according to claim 1 or 2, wherein a light in which a completely polarized component and a non-polarized component are mixed is irradiated from an oblique direction. 4. The method according to claim 1, wherein the film is prepared by a process including an operation of irradiating a mixed film of a photosensitive polymer and a low molecular compound with light from both the front and back surfaces. And a method for producing the same. 5. The retardation film according to claim 1, wherein the photosensitive polymer has liquid crystallinity, and a method for producing the same. 6. The retardation film according to claim 1, wherein the low molecular compound has crystalline or liquid crystal properties, and a method for producing the same. 7. The retardation film according to claim 1, 2, 3, 4, 5, or 6, wherein the low-molecular compound has reactivity, and a method for producing the same. 8. The retardation film and the method for manufacturing the retardation film according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the steps of heating and cooling are performed. A retardation film and a method for producing the retardation film, wherein the retardation film is produced by including the same. 9. The retardation film according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8, and cross-linking. A retardation film and a method for producing the same, comprising the steps of: 10. The photosensitive polymer according to claim 1, wherein at least one of the photosensitive polymers has a structure represented by Chemical Formula 1 to Chemical Formula 8, and a main chain represented by Chemical Formula 9 is hydrocarbon or acrylate. A retardation film having a structure represented by a photosensitive homopolymer or copolymer such as methacrylate, maleimide, maleimide, N-phenylmaleimide, or siloxane, and a method for producing the same. Embedded image 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 A group or a group obtained by fluorinating them;
x: y = 100-0: 0-100, n = 1-12, m =
1 to 12, h = 1 to 12, X, Y = none, -COO,-
OCO -, - N = N - , - C = C-or-C 6 H 4 -, W 1,
W ₂ = a structure represented by Chemical Formula 1, Chemical Formula 2, Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, Chemical Formula 6, Chemical Formula 7, or Chemical Formula 8. 11. The retardation film according to claim 2, wherein a light-transmitting substrate is coated with a dielectric or metal thin film, and a method for manufacturing the same.