JP2010078782A - Method for producing phase-difference film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily obtaining a phase-difference film by using molecules of liquid crystallinity, the phase-difference film having a refractive index anisotropy represented by nx>ny>nz or nx=ny>nz, the nz being small in value. <P>SOLUTION: The method for producing the phase-difference film has: a process A in which a thin film layer, which contains a two-color dye, is irradiated with polarized ultraviolet rays while rotating a polarizing axis in an x-y plane; a process B in which a polymerizable liquid crystal composition layer, which contains a bar-like liquid crystal compound having a polymerizable group, is formed on the thin film layer; and a process C in which the liquid crystal compound having the polymerizable group is curved. The phase-difference film is nearly parallel in an x-y plane direction and whose refractive indexes nx and ny in the x-y plane direction are larger than its refractive index nz in the thickness direction z. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a retardation film having an optically anisotropic layer formed from liquid crystalline molecules.

  The liquid crystal display device includes a liquid crystal cell, a polarizing element, and a retardation film (also referred to as an optical compensation sheet or a retardation plate). In a transmissive liquid crystal display device, two polarizing elements are attached to both sides of a liquid crystal cell, and one or two retardation films are disposed between the liquid crystal cell and the polarizing element. In the reflection type liquid crystal display device, a reflection plate, a liquid crystal cell, one retardation film, and one polarizing element are arranged in this order. The liquid crystal cell is composed of a rod-like liquid crystal molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. The liquid crystal cell is different in the alignment state of rod-like liquid crystal molecules. As for the transmission type, TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN (STN) Various display modes such as TN, HAN (Hybrid Aligned Nematic), and GH (Guest-Host) have been proposed for Supper Twisted Nematic (VA), VA (Vertically Aligned), ECB (Electrically Controlled Birefringence), and reflective type. .

  The retardation film is used in various liquid crystal display devices in order to eliminate image coloring and to widen the viewing angle. In particular, regarding the problem of viewing angle, if a retardation film having a refractive index anisotropy satisfying nx = ny> nz is disposed between the liquid crystal layer and the polarizing plate, the birefringence of the liquid crystal layer that occurs when observing from an oblique direction is caused. At least one layer having an optical anisotropy layer having a refractive index anisotropy of nx> ny = nz and an optical anisotropic layer having a refractive index anisotropy of nx = ny> nz. It is known that a wide viewing angle can be obtained by using each of them, or using at least one optically anisotropic layer having biaxial refractive index anisotropy of nx> ny> nz. Yes. (For example, see Patent Document 1)

  As such a retardation film, a stretched birefringent polymer film has been conventionally used. For example, the birefringent polymer film of Patent Document 1 has a biaxial refractive index anisotropy of nx> ny> nz and has an aromatic ring or an aromatic heterocycle in the polymer main chain direction. Since the refractive index is higher than the direction perpendicular to the main chain, it has a large birefringence as a molecule, and the molecular chain tends to be oriented parallel to the substrate. A large difference is easily obtained. However, since stretching is necessary, in order to obtain a retardation film having a small area, there is an inconvenience that a stretched film is cut out and used. In addition, there is a limit to reducing the refractive index in the thickness direction, and since a film thickness of a certain level or more is required to obtain a desired retardation, there is a disadvantage that the film thickness of the obtained retardation film is not sufficiently reduced. Further, there is a limit as a member of a liquid crystal display device that is becoming thinner.

On the other hand, it has also been proposed to use a retardation film having an optically anisotropic layer formed from liquid crystalline molecules on a transparent support. (For example, refer to Patent Documents 2 and 3) Since these methods can be applied to an arbitrary place to form a retardation film, they are suitable for a retardation film having a small area.
For example, the retardation film described in Patent Document 2 is formed from a transparent support and a discotic liquid crystalline molecule, and the transparent support has optical uniaxiality or optical biaxiality. It is a retardation film in which discotic liquid crystal molecules are aligned in a state where an average inclination angle between the disk surface and the transparent support surface is less than 5 °. Further, the retardation film described in Patent Document 3 is an optical anisotropic body formed between two substrates, and a plurality of alignments having different alignment directions are substantially parallel to the substrate with respect to one substrate. The retardation film has a hybrid structure having a region and having an orientation substantially perpendicular to the substrate with respect to the other substrate.

  However, since the retardation film described in Document 2 has a pseudo optical biaxial property composed of a biaxial transparent substrate and a uniaxial discotic liquid crystal layer coated thereon, There was a limit to viewing angle. Further, the optical axis is determined by the stretching conditions of the transparent substrate, and there is a problem that it cannot be set in an arbitrary direction because the stretching direction is limited. Alternatively, in the retardation film described in Document 3, x is a maximum refractive index direction in the plane of the retardation film, y is a direction perpendicular to x, z is a thickness direction, and nx is a refractive index in the x direction. Where ny is the refractive index in the y direction and nz is the refractive index in the z direction, it is a uniaxial retardation film satisfying the relationship of nx> ny = nz, and there is a limit to widening the viewing angle. There was a problem.

JP 2003-344856 A JP 2000-304931 A JP-A-2005-292241

  A problem to be solved by the present invention is that a retardation film having a refractive index anisotropy of nx> ny> nz or nx = ny> nz and having a small nz value is easily obtained using liquid crystalline molecules. It provides a method to obtain.

  The inventors of the present invention irradiate a thin film layer containing a dichroic dye with polarized ultraviolet rays while rotating the polarization axis in the xy plane, thereby forming a rod-like shape having a polymerizable group provided on the thin film layer. A polymerizable liquid crystal composition layer containing a liquid crystal compound is aligned with a refractive index anisotropy of nx> ny> nz or nx = ny> nz, and polymerizing the polymerizable liquid crystal composition layer, It has been found that a retardation film having a refractive index anisotropy of nx> ny> nz or nx = ny> nz can be obtained.

That is, the present invention is a method for producing a retardation film that is substantially parallel to the xy in-plane direction and has xy in-plane direction refractive indexes nx and ny larger than the refractive index nz in the thickness direction z. ,
A process for irradiating a thin film layer containing a dichroic dye with polarized ultraviolet rays while rotating the polarization axis in the xy plane, and a polymerizability containing a rod-like liquid crystal compound having a polymerizable group on the thin film layer There is provided a method for producing a retardation film, which comprises a step B for forming a liquid crystal composition layer and a step C for curing a liquid crystal compound having a polymerizable group.
(Where x represents the maximum refractive index direction in the plane of the retardation film, y represents the direction perpendicular to x, and z represents the thickness direction)

  Further, the present invention includes a liquid crystal alignment layer containing a dichroic dye on a substrate, and a layer made of a polymer of a liquid crystal composition that is polymerized in a state aligned by the liquid crystal alignment layer, nx A retardation film satisfying a relationship of> ny> nz is provided. (Where x represents the maximum refractive index direction in the plane of the retardation film, y represents the direction perpendicular to x, z represents the thickness direction, nx represents the refractive index in the x direction, and ny represents (Y represents the refractive index in the y direction, and nz represents the refractive index in the z direction)

According to the present invention, a retardation film having a biaxial refractive index anisotropy of nx>ny> nz can be easily obtained using liquid crystalline molecules.
The manufacturing method of the present invention has a wide control range of nz and can be set to a smaller value. Specifically, by the production method of the present invention, it is possible to obtain a retardation film in which ny is larger than nz and nx-nz is 0.06 or more, and nz is very small compared to nx and ny. is there. Therefore, the film thickness can be reduced, and the thickness of the resulting liquid crystal display device can be reduced.

(Thin film layer containing dichroic dye)
In the present invention, the thin film layer containing a dichroic dye is specifically a thin film layer provided with a coating film containing a dichroic dye on a substrate.
Dichroic dye means molecular orientation induction or isomerization reaction (eg azobenzene group), dimerization reaction (eg cinnamoyl group), photocrosslinking reaction (eg benzophenone group) due to Weigert effect due to photodichroism Alternatively, it represents a group (hereinafter abbreviated as a photoalignment group) that causes a photoreaction that is the origin of liquid crystal alignment ability, such as a photodecomposition reaction (eg, polyimide group).
Among them, those utilizing molecular orientation induction or isomerization reaction, dimerization reaction, or photocrosslinking reaction due to the Weigert effect resulting from photodichroism are excellent in orientation and can easily align polymerizable liquid crystal compounds. This is preferable.
The photo-alignment group is not particularly limited, but among them, at least one double bond selected from the group consisting of C = C, C = N, N = N, and C = O (however, it forms two aromatic rings). A group having (excluding a heavy bond) is particularly preferably used.
In the present invention, the Weigert effect means that the orientation direction of a molecule having a transition moment changes so that the transition moment of the molecule is perpendicular to the polarization direction of incident light.

Examples of groups having a C═C bond as these photo-alignable groups include groups having a structure such as a polyene group, a stilbene group, a stilbazole group, a stilbazolium group, a cinnamoyl group, a hemithioindigo group, and a chalcone group. It is done. Examples of the group having a C═N bond include groups having a structure such as an aromatic Schiff base and an aromatic hydrazone. Examples of the group having an N═N bond include groups having a structure such as an azobenzene group, an azonaphthalene group, an aromatic heterocyclic azo group, a bisazo group, a formazan group, and those having a basic structure of azoxybenzene. Examples of the group having a C═O bond include groups having a structure such as a benzophenone group, a coumarin group, and an anthraquinone group. These groups may have a substituent such as an alkyl group, an alkoxy group, an aryl group, an allyloxy group, a cyano group, an alkoxycarbonyl group, a hydroxyl group, a sulfonic acid group, and a halogenated alkyl group.
Among them, an azobenzene group or anthraquinone group that exhibits photoalignment by a photoisomerization reaction, or a benzophenone group, a cinnamoyl group, a chalcone group, or a coumarin group that exhibits photoalignment by a photodimerization reaction, are polarized light necessary for photoalignment. This is particularly preferable because the irradiation amount is small, and the obtained photo-alignment film has excellent thermal stability and stability over time. Of these, an azobenzene group is preferable.
Among these, a composition containing an azobenzene derivative is most preferable. A photo-alignment film made of an azobenzene derivative can be re-orientated even after it is once aligned with light, unlike other alignment films that involve generation or decomposition of chemical bonds accompanying light irradiation. Therefore, once the entire film is oriented in a specific direction, only a portion irradiated with light can be oriented in another direction using a photomask, so that a pattern orientation region can be obtained easily and accurately. Can do.

  As the azobenzene derivative, for example, a compound described in JP-A No. 2002-250924 or a compound described in SID01 Digest, 1170 (2001) can be used. These compounds can be used in combination of several kinds.

These azobenzene derivatives are dissolved in a suitable good solvent and are described later by methods such as spin coating, extrusion, gravure coating, die coating, bar coating, applicator and other application methods and flexographic printing methods. Apply onto the substrate. The solvent is not particularly limited, but the coating property of the photo alignment film compound solution on a substrate such as glass is good and a uniform film can be obtained. Therefore, N-methylpyrrolidone, butyl cellosolve, gamma-butyrolactone, dimethyl Formamide and the like are particularly preferable.
Since the solvent is volatilized and removed after being applied to the substrate, the solid content concentration of the compound (C) needs to be at least 0.2% by mass or more when used. Especially, the range of 0.3-10 mass% is especially preferable. In addition, a polymer material such as polyvinyl alcohol or polyimide can be mixed within a range not impairing the effects of the present invention.

  As for the film thickness of the coating film containing the dichroic dye, it is preferable that the film thickness is reduced because the ultraviolet energy used for the alignment treatment can be kept low and the production speed can be increased. It is easily affected by surface characteristics, and the uniformity of orientation is deteriorated. Therefore, 1-200 nm is preferable, 5-100 nm is still more preferable, and 10-40 nm is the most preferable.

(substrate)
The substrate is not particularly limited as long as it is substantially transparent, and glass, ceramics, plastics, and the like can be used. Examples of plastic substrates include cellulose derivatives such as cellulose, triacetyl cellulose, diacetyl cellulose, polycycloolefin derivatives, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polypropylene, and polyethylene. Polyolefin, polycarbonate, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, nylon, polystyrene, polyacrylate, polymethyl methacrylate, polyether sulfone, polyarylate and the like can be used.

(Process A)
Step A is a step of obtaining a photo-alignment film for forming a retardation film having a refractive index of nx = ny> nz or nx>ny> nz. Specifically, the photo-alignment film is obtained by irradiating the thin film layer containing the dichroic dye with polarized ultraviolet rays while rotating the polarization axis in the xy plane.
The polarized ultraviolet light preferably has a wavelength that can be absorbed by the dichroic dye to be used. For example, when an azobenzene derivative is used, ultraviolet light having a wavelength in the range of 350 to 500 nm corresponding to a strong absorption band due to the π → π ^* transition of azobenzene or Visible light is particularly preferred. Examples of the light source for irradiation light include a xenon lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a metal halide lamp, and an ultraviolet laser. In particular, since an ultra-high pressure mercury lamp is almost a point light source, it is particularly preferable because it is easy to obtain parallel light. Linearly polarized light can be obtained by passing light from the light source through a polarizing filter or a polarizing prism.

(Method for obtaining a photo-alignment film having a refractive index of nx = ny> nz)
The photo-alignment film irradiated with polarized ultraviolet rays from a direction perpendicular to the xy plane has a regulating force to align the liquid crystal molecules of the liquid crystal layer formed thereon in a specific azimuth direction parallel to the xy plane. . Therefore, when the oscillation direction (polarization axis) of the electric field of polarized ultraviolet light irradiating the photo-alignment film is rotated in the plane while being parallel to the xy plane, the direction of the orientation regulating force is not directed to a specific azimuth direction. The alignment film has a regulating force that is oriented in the direction, that is, in-plane orientation. When a liquid crystal layer is formed on this alignment film (step B described later), an in-plane aligned liquid crystal layer can be obtained.
The rotation speed of the polarization axis of polarized ultraviolet light irradiated to the thin film layer containing the dichroic dye varies depending on the amount of light irradiation required to develop the alignment regulating force of the photo-alignment film. That is, if the rotational speed is too low, an ultraviolet irradiation amount sufficient to cause the alignment regulating force is always irradiated, so that the alignment regulating force corresponding to the last polarization axis direction where the irradiation is stopped appears. That is, if a liquid crystal layer is laminated on this alignment film, the liquid crystal layer is aligned in the direction corresponding to the polarization axis of the last irradiation, and is not in-plane alignment but in a specific azimuth angle in the xy plane. It becomes a phase difference film. In order to prevent this, there are methods such as increasing the rotational speed, decreasing the ultraviolet irradiation intensity, or combining both of them to reduce the integrated light quantity.

The orientation state of the thin film layer containing the dichroic dye after the light irradiation can be expressed by an order parameter, for example. The order parameter increases with the cumulative amount of polarized ultraviolet light, and eventually reaches a saturation value. Even if the alignment film in this state is further irradiated with ultraviolet rays having the polarization axis in the same direction, the value of the order parameter does not change. The integrated light quantity of ultraviolet rays that gives this saturated orientation state is defined as the saturated integrated light quantity. The amount of saturated integrated light varies depending on the alignment agent used. Since the polarized ultraviolet ray to be irradiated has a finite value of the extinction ratio of the polarized light, the azimuth angle of the polarization axis is not distributed exactly in one direction but in a certain width including the central direction. In the case of irradiating ultraviolet rays while rotating the polarization axis, the irradiation amount according to the distribution width and the rotation speed becomes the integrated light amount of the polarized ultraviolet rays used for the alignment processing in a certain direction. Accordingly, if the rotation speed of the ultraviolet ray having a rotating polarization axis is slow or the irradiation intensity is too strong, it is easy to give an irradiation amount close to or more than the saturation ultraviolet ray amount. When the irradiation is stopped under such irradiation conditions, an alignment state corresponding to the direction of the polarization axis irradiated to the photo-alignment layer at the end of the rotation is given. Therefore, in order to obtain a photo-alignment film that gives an in-plane alignment state, the ultraviolet irradiation intensity should be as small as possible and the rotation speed should be as large as possible so that the irradiation dose does not become too large. By increasing the rotation speed, it is possible to repeatedly irradiate polarized light having different polarization axes, and to improve the uniformity of in-plane orientation. A preferable range of the irradiation amount is less than 1/10 of the saturated integrated light amount while the polarization axis is rotated 180 ° in the azimuth direction, preferably 1/50 or less, more preferably 1/100 or less. Uniform in-plane orientation cannot be realized with the irradiation intensity and rotation speed of polarized ultraviolet light that should be an irradiation amount or more. Further, the rotation speed of the polarization axis of the irradiated polarized light should preferably be 1 rotation or more, more preferably 2 rotations or more, and even more preferably 5 rotations or more in one alignment treatment.
In particular, when the thin film layer containing the dichroic dye coated on the film is continuously irradiated with light, polarized ultraviolet rays having different polarization axes are irradiated a plurality of times within the irradiation time of the ultraviolet rays. In addition, it is necessary to adjust the rotation speed of the polarization axis and the film conveyance speed.

  In order to obtain polarized ultraviolet light whose polarization axis rotates, a polarizing plate is provided under the ultraviolet irradiation lamp, and the polarizing plate may be rotated so that the optical axis becomes the rotation axis. At that time, it is necessary that the polarization axis is substantially parallel to the xy plane of the photo-alignment layer, that is, the optical axis is perpendicular to the xy plane. As the polarizing plate, a polarizing filter made of a dielectric multilayer film, a polarizing filter made of a microgrid, or a polarizing prism such as Glan Thompson or Grant Taylor can be used. The ultraviolet irradiation lamp and the polarizing plate may be rotated at the same time, but in that case, there is a drawback that a cable and an exhaust device connected to the lamp must be adapted to the rotation, resulting in a large-scale device.

  There is also a method of irradiating circularly polarized light to irradiate polarized light having a rotating polarization axis. That is, when the circularly polarized light of ultraviolet rays is irradiated onto the photo-alignment film, the polarized light whose polarization axis rotates at the frequency of the light is irradiated, and in this case, different in order to improve the uniformity of in-plane alignment. Repeated irradiation with polarized light having a polarization axis is automatically performed. As described above, in order to realize a state with high in-plane uniformity, the plane of rotation of circularly polarized light needs to be parallel to the xy plane of the photo-alignment layer. As for the irradiation intensity of ultraviolet rays, since the rotation speed of the polarization axis is very large, there is practically no limitation as long as a normal ultraviolet lamp is used. However, the preferable range of irradiation amount is saturated integration while the polarization axis rotates 180 °. There is no change in the amount of irradiation with which the alignment state is less than 1/10 of the light amount, preferably 1/50 or less, and more preferably 1/100 or less. In order to irradiate circularly polarized light, a polarizing plate and a quarter wave plate are provided in this order under the ultraviolet irradiation lamp, and the slow axis of the quarter wave plate and the absorption axis of the polarizing plate are 45 °. What is necessary is just to install so that it may become an angle.

  Moreover, you may irradiate so that it may become an equivalent integrated light quantity using the two ultraviolet-rays by which a polarization axis orthogonally crosses. Here, the equivalent means an equivalent amount if two orthogonal ultraviolet rays are irradiated simultaneously. However, if sequential irradiation is performed, assuming that the integrated light amount of the polarized ultraviolet light irradiated first is 100, the second integrated light amount in the orthogonal direction to be irradiated next is suitably about 160 to 180. That is, since the second irradiation needs to generate an orientation component in the orthogonal direction while canceling the effect of the first irradiation, the second irradiation is not an equal amount but a large irradiation amount. However, in this method, it may be difficult to irradiate the equivalent amount of polarized ultraviolet rays that achieve in-plane orientation with good reproducibility.

(Method for forming an optical anisotropic body having a refractive index of nx>ny> nz)
As described above, an optical anisotropic body (nx = ny> nz) oriented in the xy plane by rotating the polarizing axis of polarized ultraviolet rays for irradiation as the first irradiation or by irradiating the polarized ultraviolet rays at right angles. Obtainable. After irradiating polarized ultraviolet light that induces such in-plane orientation, if irradiating polarized ultraviolet light having a polarization axis in a specific direction in the xy plane as the second irradiation, nx>ny> nz An optical anisotropic body can be obtained. In this case, the accumulated light quantity of the polarized ultraviolet light for the second time needs to be 1/10 or more of the saturated accumulated light quantity of the polarized ultraviolet light.
When irradiation is performed with the polarization axis of polarized ultraviolet light rotated, if ultraviolet light is irradiated instead of circularly polarized light, strong ultraviolet light is irradiated in the major axis direction of the ellipse. By controlling the axial ratio of elliptically polarized light, it is possible to give an intensity difference depending on the vibration direction of the ultraviolet rays and to give the orientation direction in a certain direction in the plane of the orientation film. The difference between the accumulated light quantity between the major axis and the minor axis is required to be 1/10 or more of the saturated accumulated light quantity of polarized ultraviolet light as described above.

When the dichroic dye to be used has a mechanism of molecular orientation induction or isomerization reaction due to the Weigert effect resulting from photodichroism, polarized UV light is applied to the thin film layer containing the dichroic dye. Even when no is irradiated, an optical anisotropic body oriented in the xy plane can be obtained. However, in this case, since an orientation component in the z direction also exists, an in-plane anisotropic body having a high in-plane orientation state cannot be formed.
Further, without rotating the polarization axis in the xy plane on the alignment film using the dichroic dye, for example, light having a random vibration direction of ultraviolet rays is directed in a direction perpendicular to the xy plane (z Direction), the molecules of the dichroic dye are oriented in the direction that minimizes the energy to be absorbed, and the orientation component in the xy plane increases because the orientation component in the z direction increases. The body cannot be formed. If the irradiation dose is further increased, the alignment component in the z direction increases, and the liquid crystal layer on the alignment film becomes a retardation film satisfying nz> nx = ny.

(Step B: Forming a polymerizable liquid crystal composition layer containing a rod-like liquid crystal compound having a polymerizable group on the thin film layer)
(Bar-shaped liquid crystal compound having a polymerizable group)
The rod-shaped liquid crystal compound having a polymerizable group used in the present invention is not particularly limited as long as it is a compound having a polymerizable functional group that exhibits liquid crystallinity alone or in a composition with another liquid crystal compound. For example, Handbook of Liquid Crystals (D. Demus, J. W. Goodbye, GW Gray, H. W. Spiss, V. Vill, edited by Wiley-VCH, 1998), Quarterly Chemical Review. 22, Liquid Crystal Chemistry (Edited by Chemical Society of Japan, 1994), or JP-A-7-294735, JP-A-8-3111, JP-A-8-29618, JP-A-11-80090, 1,4-phenylene group, 1,4-cyclohexene, as described in Kaihei 11-148079, JP-A 2000-178233, JP-A 2002-308831, and JP-A 2002-145830. Examples thereof include a rod-like polymerizable liquid crystal compound having a rigid site called a mesogen in which a plurality of structures such as a sylene group are connected and a polymerizable functional group such as a (meth) acryloyl group, a vinyloxy group, and an epoxy group.

(Photopolymerization initiator)
When polymerizing the polymerizable liquid crystal compound, it is preferable to blend a known and commonly used photopolymerization initiator or thermal polymerization initiator.
Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone (“Irgacure 184” manufactured by Ciba Specialty Chemicals), 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one ( “Darocur 1116” manufactured by Merck & Co.), 2-methyl-1-[(methylthio) phenyl] -2-morpholinopropane-1 (“Irgacure 907” manufactured by Ciba Specialty Chemicals), benzylmethylketal ( “Irgacure 651” manufactured by Ciba Specialty Chemicals). Mixture of 2,4-diethylthioxanthone (“Kayacure DETX” manufactured by Nippon Kayaku Co., Ltd.) and ethyl p-dimethylaminobenzoate (“Kayacure EPA” manufactured by Nippon Kayaku Co., Ltd.), acylphosphine oxide (“Lucillin” manufactured by BASF TPO "), and the like. On the other hand, examples of the thermal polymerization initiator include organic peroxides such as benzoyl peroxide, bis (4-t-butylcyclohexyl) peroxydicarbonate, t-butyl peroxybenzoate, and methyl ethyl ketone peroxide. Azonitrile compounds such as 2′-azobisisobutyronitrile, azoamidin compounds such as 2,2′-azobis (2-methyl-N-phenylpropion-amidin) dihydrochloride, 2,2′azobis {2-methyl- Use azoamide compounds such as N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, alkylazo compounds such as 2,2′azobis (2,4,4-trimethylpentane), and the like. Can do. The amount of these polymerization initiators used is preferably 10% by mass or less, particularly preferably 0.5 to 5% by mass, based on the composition. (Hereinafter, a composition containing the polymerizable liquid crystal compound and a polymerization initiator is abbreviated as a polymerizable liquid crystal composition.)

In order to form a polymerizable liquid crystal composition layer containing a rod-like liquid crystal compound having a polymerizable group on the thin film layer, a spin coating method, an extrusion method, a gravure coating method, a die coating method, a bar coating method, an application Known methods such as a coating method such as a coating method and a printing method such as a flexo method can be used.
The film thickness varies depending on the target retardation film, but is generally preferably 0.1 μm to 10 μm.

(Step C: curing the liquid crystal compound having a polymerizable group)
Examples of the method for polymerizing and fixing the aligned polymerizable liquid crystal composition layer through the steps 1 and 2 include a method of irradiating active energy rays and a thermal polymerization method, but heating is required. However, the method of irradiating active energy rays is preferable because the reaction proceeds at room temperature, and among them, the method of irradiating light such as ultraviolet rays is preferable because the operation is simple. The temperature at the time of irradiation is preferably set to 25 ° C. or less as much as possible in order to avoid the induction of thermal polymerization of the polymerizable liquid crystal composition so that the polymerizable liquid crystal composition can maintain the liquid crystal phase. The liquid crystal composition usually has a liquid crystal phase in the range from the C (solid phase) -N (nematic) transition temperature (hereinafter abbreviated as C-N transition temperature) to the NI transition temperature in the temperature rising process. Indicates. On the other hand, in the temperature lowering process, a non-equilibrium state is taken thermodynamically, so that the liquid crystal state may be maintained without being solidified even at a temperature lower than the CN transition temperature. This state is called a supercooled state. In the present invention, the liquid crystal composition in a supercooled state is also included in the state in which the liquid crystal phase is retained. The ultraviolet irradiation intensity is preferably in the range of 1 W / m ^{2 to} 10 kW / m ² . In particular, a range of 10 W / m ^{2 to 2} kW / m ² is preferable. When the ultraviolet intensity is less than 1 W / m ² , it takes a lot of time to complete the polymerization. On the other hand, when the strength exceeds ² kW / m ² , liquid crystal molecules in the polymerizable liquid crystal composition tend to be photodegraded, or a large amount of polymerization heat is generated to increase the temperature during polymerization. The parameter may change, and the retardation of the film after polymerization may be distorted. The optimum integrated light quantity of such ultraviolet rays varies depending on the absorption efficiency of the photoinitiator added to the polymerizable liquid crystal, the added amount, the atmosphere in which the polymerizable liquid crystal is placed, and the like, but is generally 100 J / m ^{2 to} 100 kJ / m. ² are preferred, especially ^1kJ / ^{m 2 ~40kJ} / m 2 is preferred.
Further, it is desirable that the ultraviolet rays to be irradiated be polarized light having the same polarization axis direction as that of the polarized ultraviolet rays irradiated to the photo-alignment film. This is to eliminate the possibility that the alignment direction of the photo-alignment layer is affected by the ultraviolet rays irradiated in this step.

  The thickness of the obtained retardation film varies depending on the target retardation, but is preferably as thin as possible. Considering the ease of controlling the film thickness and the birefringence of the polymerizable liquid crystal cured film, the preferred film thickness of the thin film layer containing the dichroic dye and the polymerizable liquid crystal layer is preferably 0.1 to 20 μm. 1 to 10 μm is more preferable, and 0.1 to 5 μm is most preferable.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

(Preparation of thin film layer composition (A) containing dichroic dye)
50 parts by mass of the compound represented by the formula (1) and 50 parts by mass of the compound represented by the formula (2) are mixed and dissolved in a mixed solvent composed of ethylene glycol monoethyl ether and ethylene glycol monobutyl ether (1 ) And (2) was a 0.5 mass% solution. This solution was filtered through a filter having a pore diameter of 0.45 μm to obtain a composition solution (A) containing a dichroic dye. The thin film composition (A) had a saturated integrated light amount of 1 kJ / m ² .

(Preparation of polymerizable liquid crystal composition)
A polymerizable liquid crystal composition is prepared by mixing the compounds represented by the formulas (3) and (4) so that the mass ratio is 50:50, and chlorinated polypropylene is added to the polymerizable liquid crystal composition 100. 0.6 parts by mass was mixed with respect to parts by mass. 96 parts by mass of this polymerizable liquid crystal composition was mixed with 4 parts by mass of a photopolymerization initiator “Irgacure 907” manufactured by Ciba Specialty Chemicals Co., Ltd. and 395 parts by mass of a mixed solvent composed of xylene and cyclohexyl acetate, and a pore size of 0.45 μm. To obtain a polymerizable liquid crystal composition solution (B). The liquid crystal composition after evaporating the mixed solvent from the polymerizable liquid crystal composition solution (B) exhibited a liquid crystal phase at 25 ° C. Therefore, in the following examples, the liquid crystal composition was used at 25 ° C.

  The birefringence of the retardation film obtained in the examples shown below was measured at a wavelength of 589.3 nm using an automatic birefringence meter (Cobra 21ADH (manufactured by Oji Scientific Instruments)). The results are shown in Table 1, where the in-plane birefringence is nx-ny and the birefringence in the thickness direction is nx-nz.

Example 1
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. In order to induce in-plane orientation as the first irradiation, the film was irradiated from the normal direction of the surface of the thin film layer by rotating the polarization axis of the linearly polarized ultraviolet light while transporting the TAC film with the thin film layer. Polarized light whose polarization axis has been rotated is obtained by placing a polarizing plate under an ultraviolet lamp and rotating the polarizing plate on a plane of rotation parallel to the film surface. At this time, the film conveyance speed was 0.5 m / min, and the time required to pass through the ultraviolet irradiation region was 25 seconds. The irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 5 W / m ² , and the rotation speed of the polarization axis was 10 rotations / minute.
Next, as the second irradiation, linearly polarized light in which the vibration direction of polarized light is inclined by 75 ° with respect to the longitudinal direction of the film while the TAC film with the thin film layer after the light irradiation is conveyed and the polarization axis is not rotated. The photo-alignment layer (A-1) was obtained by irradiating with ultraviolet rays. At this time, the irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 4 W / m ² , and the time required to pass through the ultraviolet irradiation region was 25 seconds.
The polymerizable liquid crystal composition solution (B) was applied on the photo-alignment layer (A-1) with a die coater and dried at 60 ° C. Polarized ultraviolet light whose polarization axis is not rotated was irradiated so that the vibration direction was 75 ° with respect to the longitudinal direction of the film. Irradiation was performed in an air atmosphere so that the integrated light amount was 6 kJ / m ^2, and a retardation film (1) having an azimuth angle of 165 ° with respect to the longitudinal direction of the slow axis film was obtained.

(Example 2)
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. In order to induce in-plane alignment, the photo-alignment layer (A-2) is obtained by rotating the polarization axis of the linearly polarized ultraviolet light and irradiating from the normal direction of the layer surface while transporting the TAC film with the thin film layer. It was. Polarized light whose polarization axis has been rotated is obtained by placing a polarizing plate under an ultraviolet lamp and rotating the polarizing plate on a plane of rotation parallel to the film surface. At this time, the film conveyance speed was 0.5 m / min, and the time required to pass through the ultraviolet irradiation region was 25 seconds. The irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 5 W / m ² , and the rotation speed of the polarization axis was 10 rotations / minute.
The polymerizable liquid crystal composition solution (B) was applied on the photo-alignment layer (A-2) with a die coater and dried at 60 ° C. The phase difference film (2) was obtained by irradiating ultraviolet rays that were not polarized light in an air atmosphere so that the integrated light amount was 6 kJ / m ² .

(Example 3)
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. While conveying the TAC film with a thin film layer, circularly polarized ultraviolet rays were irradiated from the normal direction of the film surface. Circularly polarized ultraviolet light is obtained by placing a quarter wave plate between the polarizing plate and the photo-alignment layer. At this time, the film conveyance speed was 0.5 m / min, and the time required to pass through the ultraviolet irradiation region was 25 seconds. The irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, and the irradiation intensity was 20 W / m ² .
Next, while conveying the TAC film with the light-irradiated thin film layer as the second irradiation, the polarized ultraviolet light whose oscillation direction of linearly polarized light is inclined by 75 ° with respect to the longitudinal direction of the film and whose polarization axis is not rotated. Was obtained to obtain a photo-alignment layer (A-3). At this time, the irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 4 W / m ² , and the time required to pass through the ultraviolet irradiation region was 25 seconds.
The polymerizable liquid crystal composition solution (B) was applied on the photo-alignment layer (A-3) with a die coater and dried at 60 ° C. Polarized ultraviolet light whose polarization axis is not rotated was irradiated so that the vibration direction was 75 ° with respect to the longitudinal direction of the film. Irradiation was performed in an air atmosphere, and irradiation was performed so that the integrated light amount was 6 kJ / m ^2. Thus, a retardation film (3) having an azimuth angle of 165 ° with respect to the longitudinal direction of the slow axis film was obtained.

(Comparative Example 1)
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. While conveying a TAC film with a thin film layer, the polarization direction of polarization is tilted by 75 ° with respect to the longitudinal direction of the film, and the polarized light with the polarization axis not rotating is irradiated to obtain a photo-alignment layer (AH-1). It was. At this time, the irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 4 W / m ² , and the time required to pass through the ultraviolet irradiation region was 25 seconds.
The polymerizable liquid crystal composition solution (B) was applied on the photo-alignment layer (AH-1) with a die coater and dried at 60 ° C. Polarized ultraviolet light whose polarization axis is not rotated was irradiated so that the vibration direction was 75 ° with respect to the longitudinal direction of the film. Irradiation was performed in an air atmosphere, and irradiation was performed so that the integrated light amount was 6 kJ / m ^2. Thus, a retardation film (H1) having an azimuth angle of 165 ° with respect to the longitudinal direction of the slow axis film was obtained.

(Comparative Example 2)
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. While transporting a TAC film with a thin film layer, the polarization vibration direction is inclined by 75 ° with respect to the longitudinal direction of the film, and the polarized UV light whose polarization axis does not rotate is irradiated to form a photo-alignment layer (AH-2). . At this time, the irradiated polarized ultraviolet rays were transmitted through a 365 nm band pass filter, the irradiation intensity was 40 W / m ² , and the time required to pass through the ultraviolet irradiation region was 25 seconds.
The polymerizable liquid crystal composition solution (B) was applied on the photo-alignment layer (AH-2) with a die coater and dried at 60 ° C. Ultraviolet light that is not polarized light was irradiated in an air atmosphere so that the integrated light amount was 6 kJ / m ² to obtain a retardation film (H2).

(Comparative Example 3)
After corona treatment of the TAC film, a composition solution (A) containing a dichroic dye is continuously formed by a die coater and dried at 80 ° C. to form a thin film layer containing a dichroic dye having a thickness of 17 nm. did. The polymerizable liquid crystal composition solution (B) was applied to this with a die coater and dried at 60 ° C. A retardation film (H3) was obtained by irradiating ultraviolet light that was not polarized light in an air atmosphere so that the integrated light amount was 6 kJ / m ² .
Table 1 summarizes the results of birefringence of the retardation films of Examples 1 to 3 and Comparative Examples 1 and 2.

As a result, in the retardation film obtained by rotating the polarization axis as the alignment treatment of the photo-alignment layer, the polymerizable liquid crystal molecules are aligned substantially parallel in the xy plane, ny is larger than nz, and nx-nz had a large value of 0.06 or more. That is, the retardation film obtained by the methods of Examples 1 and 3 has a property of nx>ny> nz, and the retardation film obtained by the method of Example 2 has a property of nx = ny> nz. It was a phase difference film. Since this has a large birefringence, it can be made thin and can be applied to a thin liquid crystal display device.
On the other hand, Comparative Example 1 and Comparative Example 2 are examples in which a retardation film is formed by irradiating polarized ultraviolet rays without rotating the polarization axis, but this method tends to be three-dimensionally isotropic. In other words, a retardation film satisfying nx>ny> nz or nx = ny> nz and having a large nx−nz, that is, a very small nz could not be obtained. Comparative Example 3 is an example in which ultraviolet rays are not irradiated, that is, a thin film layer containing a dichroic dye is not photo-aligned, but nx>ny> nz or nx = ny> nz and nx−nz is large, that is, A retardation film having a very small nz could not be obtained.

Claims (3)

A method for producing a retardation film that is substantially parallel to an xy in-plane direction and has xy in-plane direction refractive indexes nx and ny larger than a refractive index nz in a thickness direction z,
A process for irradiating a thin film layer containing a dichroic dye with polarized ultraviolet rays while rotating the polarization axis in the xy plane, and a polymerizability containing a rod-like liquid crystal compound having a polymerizable group on the thin film layer A method for producing a retardation film, comprising: a step B for forming a liquid crystal composition layer; and a step C for curing a liquid crystal compound having a polymerizable group.
(Where x represents the maximum refractive index direction in the plane of the retardation film, y represents the direction perpendicular to x, and z represents the thickness direction) 2. The method for producing a retardation film according to claim 1, wherein in the step A, the polarized ultraviolet rays are irradiated while rotating the polarization axis in the plane, and the polarized ultraviolet rays are irradiated until nx> ny is satisfied in the x direction. . On a substrate, it has a liquid crystal alignment layer containing a dichroic dye and a layer made of a polymer of a liquid crystal composition that is polymerized in a state aligned by the liquid crystal alignment layer, and nx>ny> nz. A retardation film characterized by satisfying the relationship.
(Where x represents the maximum refractive index direction in the plane of the retardation film, y represents the direction perpendicular to x, z represents the thickness direction, nx represents the refractive index in the x direction, and ny represents (Y represents the refractive index in the y direction, and nz represents the refractive index in the z direction)