JP2002202406A - 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 unpolarized ultraviolet rays irradiation. SOLUTION: A mixture of a photosensitive polymer and a low molecular weight compound is applied (by spin coating or casting) to 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 unpolarized ultraviolet rays 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]

The present invention relates to a retardation film in which a film (film) of a mixture of a photosensitive polymer and a low-molecular compound is irradiated with non-polarizing ultraviolet light to incline the optical axis to orient molecules. And a method of manufacturing 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. It is substantially impossible to incline the optical axis for orientation in the stretching direction. 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-7-2871
No. 19 and JP-A-7-287120 disclose 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. As a method of expressing a phase difference by light irradiation, Japanese Patent Application Laid-Open No. 7-138308 discloses that a photosensitive polymer such as polyvinyl cinnamate has a linear polarization property (U
V) A method of irradiating light is described, but in this method, the optical axis cannot be tilted because anisotropy develops in a direction perpendicular to the electric field vibration of the irradiated polarized UV light, so that the viewing angle is increased. hard. 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. A general dichroic polarizer used for such polarization conversion is PVA.
(Polyvinyl alcohol) uniaxially stretched sheet impregnated with iodine is TAC (triacetyl cellulose)
Some are sandwiched between. 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 natural crystals of calcite as prisms, so LCDs
There is no large prism capable of irradiating the entire surface of the substrate as used in the above.

[0003]

In a retardation film produced by stretching a polymer film, it is extremely difficult to tilt the optical axis because the molecules are oriented in the stretching direction. 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 an inclined optical axis 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 film (film) of a mixture of a photosensitive polymer and a low-molecular compound is irradiated with non-polarizing ultraviolet light to thereby tilt the optical axis to express a phase difference. The present invention relates to a retardation film subjected to the method. In the method for producing a retardation film of the present invention (a retardation film), a mixture of a photosensitive polymer and a low-molecular compound is formed into a film, and a non-polarized ultraviolet ray having a specific inclination angle with respect to the film surface. By irradiating, it is possible to provide a retardation film in which molecules in the film are oriented in a tilt direction of the irradiated non-polarized ultraviolet light, 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. . Examples of the low-molecular compound to be mixed also include compounds having substituents such as biphenyl, terphenyl, phenylbenzoate, and azobenzene, which are frequently used as a mesogen component, and compounds having crystallinity or liquid crystallinity. The low molecular compound to be mixed is not limited to a single compound, and a plurality of compounds can be mixed. Furthermore, it is possible to add an alignment aid for improving alignment to the extent that liquid crystallinity is not impaired or a crosslinking agent for improving heat resistance, or a monomer that does not exhibit liquid crystallinity without impairing liquid crystallinity. May be copolymerized with a photosensitive polymer. However, the photosensitive polymer and the low molecular compound are not limited to the above.

The present invention will be described in detail with reference to examples. A mixture of a photosensitive polymer and a low molecular compound is applied (spin-coated or cast) to form a film. The film is isotropic at the time of film formation, and the side chain portion of the photosensitive polymer and the low molecular compound are not oriented in a specific direction. This state will be described with reference to FIG. FIG. 2 schematically shows the film after film formation. In the film (20), a side chain (2a, 2b) having a photosensitive group represented by a long ellipse and a low molecular compound (2c) represented by a cylinder are randomly present (coexist). When the film is irradiated with a non-polarizing ultraviolet ray pseudo-parallel light beam (L), a side chain (2
In the case of a), the photoreaction is selectively promoted since the side chain (2b) oriented in the parallel direction is more sensitive to light. This is because the conjugate system of the photosensitive portion containing a benzene ring or the like extends in the long axis direction of the side chain. When such a side chain is placed in a radiation field such as light, the electric field of the light This is because the interaction becomes maximum when the vibration direction coincides with the long axis direction of the side chain, and the interaction becomes minimum when the traveling direction of light coincides with the long axis direction of the side chain. From this, it is possible to obtain a film in which a photoreaction in a specific direction is suppressed by irradiation with non-polarized ultraviolet light. In order to promote this photoreaction, irradiation with light having a wavelength at which the photosensitive group can react is required. This wavelength varies depending on the type of the photosensitive group, but is generally 200-500 nm,
In particular, the effectiveness of 250-400 nm is often high.

FIG. 3 is a schematic view of a film whose orientation has been promoted after irradiating the film of FIG. 2 with unpolarized ultraviolet light. As shown in FIG. 3, the side chain (3d) or the low-molecular compound (3c) in the film (30), which did not cause a photoreaction, emits light in a specific direction due to molecular motion after irradiation with non-polarized ultraviolet light. The orientation is influenced by the anisotropy developed in the film due to the suppression of the reaction (the side chain (3a) is exposed by non-polarized light irradiation and reacts, and the side chain (3b) is the traveling direction of the irradiated ultraviolet light. And side chains which did not react because they were oriented in parallel.) As a result, the entire film can be oriented while being inclined in the traveling direction of the non-polarized ultraviolet light, and birefringence is induced. When the irradiation is performed 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 can be provided. For measuring the tilt of the optical axis, Japan J
own Applied Physics, Vo
l. 19, 2013 (1980), a crystal rotation method for measuring the transmission intensity of polarized light while rotating a measurement sample 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 non-polarized ultraviolet light is promoted by heating the film. The heating temperature of the membrane is
It is desirable that the softening point is lower than the softening point of the photoreacted portion and higher than the softening points of the side chains and low molecules that did not photoreact. In order to promote the orientation of the film, it is also effective to irradiate a non-polarized ultraviolet ray 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. Irradiating non-polarized ultraviolet light before and after Ti is effective. After irradiating the non-polarized ultraviolet light in this way, heating, or cooling the film irradiated with the non-polarized ultraviolet light to below the softening point of the polymer, the molecules are frozen, and the retardation film of the present invention is can get.

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 exposure amount 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 a retardation film can be manufactured even if wt% is added,
Preferably, the content is 5 wt% to 50 wt%. Here, when the compatibility between the polymer and the low molecular weight compound is not sufficient, the phase separation or the scattering of visible light can be induced by heating the film after forming the film or after irradiating non-polarized ultraviolet rays. Crystals and cause an increase in haze.

As a technique for obtaining a film having a larger phase difference by increasing the film thickness, a method of laminating films can be mentioned. In this case, in a step of applying a material solution on a film that has been formed and irradiated with non-polarizing ultraviolet light beforehand, and laminating, in order to prevent destruction of the previously formed film, a solvent having reduced solubility is used. It is effective to dissolve a polymer and a low molecular compound in the solution. When the photosensitive compound film is irradiated with non-polarizing ultraviolet light from the front and back surfaces, birefringence is more efficiently developed. The photosensitive compound is formed into a film by coating on a support or the like, and irradiation with non-polarized ultraviolet light may be performed directly on the compound or via the support. In the case where the support is interposed, the support may be made of any material as long as it has light transmittance of a wavelength that can react with the photosensitive compound, but the higher the light transmittance, the smaller the irradiation amount. This is advantageous in the manufacturing process. Alternatively, a photosensitive compound may be formed on a peelable support, and after peeling, a non-polarizing ultraviolet ray may be irradiated from the front and back surfaces of the film.

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

(Monomer 2) 4-Hydroxy-4'-hydroxyethoxybiphenyl was synthesized by heating 4,4'-biphenyldiol and 2-chloroethanol under alkaline conditions. This product was reacted with 1,6-dibromohexane under alkaline conditions to obtain 4- (6
-Bromohexyloxy) -4'-hydroxyethoxybiphenyl was synthesized. Then, lithium methacrylate was reacted to give 4-hydroxyethoxy-4 ′-(6-
(Methacryloylhexyloxy) biphenyl was synthesized. Finally, under basic conditions, 2-methoxycinnamoyl chloride was added to give the monomer 2 shown in Chemical Formula 11
Was synthesized.

Embedded image

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

(Polymer 2) This monomer 2 was dissolved in tetrahydrofuran, and a polymer 2 was obtained by adding AIBN as a reaction initiator and polymerizing. This polymer 2 also exhibited liquid crystallinity.

(Low molecular weight compound 1) 4,4'-biphenyldiol and 6-bromohexanol were reacted under alkaline conditions to synthesize 4,4'-bis (6-bromohexyloxy) biphenyl. Then, under basic conditions, cinnamoyl chloride was added and reacted, and the product was purified by column to synthesize a low-molecular compound 1 represented by Chemical Formula 12.

Embedded image

FIG. 1 shows an example of a method (apparatus) for producing a retardation film of the present invention. Mixing a non-polarized ultraviolet ray (16) generated by an ultraviolet lamp (11) excited by a power supply (12) with a photosensitive polymer and a low-molecular compound applied (coated) on a support (15). Irradiate the body membrane (14). Examples 1 to 3 are examples in which a retardation 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 on a quartz substrate (support) with a thickness of about 3 μm. The substrate is placed 45 degrees above the horizontal plane.
Tilted, placed so that the application surface is the irradiation surface, and apply non-polarized ultraviolet light at a room temperature of 120 m from a direction perpendicular to the horizontal plane.
J / cm ² was irradiated, followed by similarly unpolarized light of ultraviolet turned over the substrate was 120 mJ / cm ² irradiation. Next, 10
After heating to 0 ° C., it was cooled to 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 14 nm.

Example 2 3.75% by weight of polymer 2 and 1.25% by weight of liquid crystal material E7 (Merck Japan)
Was dissolved in dichloroethane and applied on a quartz substrate (support) with a thickness of about 3 μm. The substrate is placed 45 degrees above the horizontal plane.
Tilted, placed so that the application surface is the irradiation surface, and apply non-polarized ultraviolet light at a room temperature of 120 m from a direction perpendicular to the horizontal plane.
J / cm ² was irradiated, followed by similarly unpolarized light of ultraviolet turned over the substrate was 120 mJ / cm ² irradiation. Next, 10
After heating to 0 ° C., it was cooled to room temperature. In the substrate thus obtained, the optical axis was inclined by 25 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 20 nm.

Example 3 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 (support) to a thickness of about 3 μm. . The substrate is tilted at 45 degrees with respect to the horizontal plane, the coating surface is arranged so as to be the irradiation surface, and non-polarized ultraviolet rays are irradiated at 120 mJ / cm ² from the direction perpendicular to the horizontal plane at room temperature. Turn the same non-polarized UV light
Irradiation was performed at 20 mJ / cm ² . Next, after heating to 100 ° C., it was cooled to room temperature. In the substrate thus obtained, the optical axis was inclined by 7 ° from the normal direction of the substrate, and the phase difference in the substrate plane was 1 nm.

Irradiation of ultraviolet rays to the retardation film with an inclined optical axis produced in these examples further promotes the photoreaction of unreacted photosensitive groups, thereby firmly fixing the orientation in the film. Can be. Such a retardation film was excellent in heat resistance and light stability and was sufficient for practical use. From these examples, it is possible to produce a film whose optical axis is controlled by irradiating a non-polarizing ultraviolet ray, which is effective for expanding the viewing angle of a liquid crystal display device without using a practical polarizing element as in the prior art. It has been proved that it is possible to produce a retardation film in which the optical axis direction is controlled.

[0020]

By the simple operation of irradiating a non-polarized ultraviolet ray, a retardation film can be obtained without using a stretching step as in the prior art. Further, by changing the irradiation direction of the non-polarized ultraviolet light, regions having different optical axes can be manufactured in the same substrate, and the application to various optical elements is expected. 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 large-area retardation film having an inclined optical axis could not be produced at low cost. However, according to the present invention, the large-area retardation film can be enlarged by a simple operation of irradiating non-polarized ultraviolet light from an oblique direction. It has become possible.

[0021]

[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 view showing a side chain exposed by irradiation with non-polarizing ultraviolet light.

FIG. 3 is a schematic view showing a film oriented by molecular motion after irradiation with non-polarizing ultraviolet light.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Ultraviolet lamp 12 ... Power supply 14 ... Film (film) 15 ... Substrate (support) 16 ... Ultraviolet light (non-polarized light)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 1/04 G02B 1/04 4J027 G02F 1/13363 G02F 1/13363 G03F 7/004 521 G03F 7/004 521 7/038 501 7/038 501 // C08L 101: 00 C08L 101: 00 F term (reference) 2H025 AB14 AC01 BC31 BC81 BD21 BD43 BD54 2H049 BA06 BA42 BB42 BB46 BB50 BC05 BC22 2H091 FA11X FA11Z FB02 FC23 LA19 LA30 4F07A AA A14A AA67 AC10 AF29 AF35 AG15 AH19 BA02 BB02 BC01 4J011 AA05 QA12 QB01 QB02 QB03 QB25 UA01 WA10 4J027 AA01 AA08 AF01 AF04 AF05 BA19 BA30 CC02 CC05

Claims (10)

[Claims] 1. A retardation film and a method for producing the retardation film, which are produced by a step including irradiating a non-polarized light to a mixed film of a photosensitive polymer and a low molecular compound. 2. A retardation film and a retardation film produced by a process including an operation of irradiating a non-polarized light to both sides of a mixed film of a photosensitive polymer and a low molecular compound to a film. Production method. 3. A process comprising an operation of irradiating a non-polarized light to a mixed film of a photosensitive polymer and a low molecular compound formed on a support from both directions of a front surface and a back surface via the support and the support. A retardation film and a method for producing the same, which are produced. 4. The film according to claim 1, 2 or 3, wherein the film of the mixture of the photosensitive polymer and the low-molecular compound is irradiated with non-polarized light in an oblique direction with respect to the film surface. A retardation film and a method for producing the retardation film, wherein the film is produced in a step including an operation. 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 method according to claim 1, wherein the low molecular weight compound has a reactive group which is crosslinked or polymerized by light and / or heat in claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6. Phase difference film and manufacturing method thereof. 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 in the method for producing the retardation film. A retardation film and a method for producing the same, comprising the steps of: 10. The photosensitive polymer according to claim 1, wherein the photosensitive polymer has at least a structure represented by Chemical Formula 1 to Chemical Formula 8, and a main chain represented by Chemical Formula 9 is hydrocarbon, acrylate, methacrylate, Maleimide, N-
A retardation film having a structure represented by a photosensitive homopolymer or copolymer such as 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.