JP2008304740A - Method for producing retardation film provided with inclined liquid crystal cured layer - Google Patents

Abstract

An object of the present invention is to provide a production method capable of obtaining a retardation film having a large tilt angle, a small thickness variation of a liquid crystal cured layer and a small retardation change under a high temperature environment with excellent productivity.
A method for producing a retardation film comprising a tilted and aligned liquid crystal cured layer comprising the following steps A to C; Step A; a substrate subjected to an orientation treatment; A step of applying a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent and an acrylic leveling agent on the surface of the alignment treatment to form a coating layer, step B; drying the coating layer Then, a step of forming an inclined aligned liquid crystal solidified layer, step C; a step of irradiating the liquid crystal solidified layer with ultraviolet rays to form an inclined aligned liquid crystal cured layer.
[Selection figure] None

Description

  The present invention relates to a method for producing a retardation film. Specifically, this invention relates to the manufacturing method of retardation film provided with the liquid crystal cured layer by which the inclination alignment was carried out.

  Liquid crystal display devices including a retardation film are widely used in portable devices such as mobile phones, watches, digital cameras, personal digital assistants (PDAs), and portable game machines. As one of the retardation films, there is known a retardation film including a liquid crystal cured layer in which a liquid crystal compound is inclined and aligned. Properties required for such a retardation film include (1) increasing the tilt angle (also referred to as tilt angle) of the liquid crystal compound, (2) reducing the thickness variation of the liquid crystal cured layer, and (3 ) Reducing the phase difference change under high temperature environment.

Conventionally, as one means for aligning a liquid crystal compound with a large tilt angle, it is known to use an alignment film containing a polyamic acid or polyamic acid ester having a side chain group and an organosilane compound (Patent Document 1). However, when such a special alignment film is used, the base material and solvent for forming the alignment film are limited. For this reason, there is a demand for a new production method that satisfies the above characteristics (1) to (3) by a method with higher productivity.
JP 2002-202483 A

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to provide a phase difference having a large tilt angle, a small thickness variation of the liquid crystal cured layer, and a small phase difference change under a high temperature environment. It is providing the manufacturing method which can obtain a film with the outstanding productivity.

  That is, the manufacturing method of the present invention is a manufacturing method of a retardation film including a liquid crystal cured layer that is tilted and aligned, and includes the following steps A to C; Step A; A step of applying a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent on the alignment treatment surface to form a coating layer, step B; drying the coating layer Step of forming a tilted and aligned liquid crystal solidified layer, Step C; Step of irradiating the liquid crystal solidified layer with ultraviolet rays to form a tilted and aligned liquid crystal cured layer.

  In a preferred embodiment, the liquid crystal compound is a compound that exhibits homeotropic alignment on a substrate that has not been subjected to alignment treatment.

  In a preferred embodiment, the content of the acrylic leveling agent in the liquid crystal composition is 0.1 to 1 part by weight with respect to 100 parts by weight of the polymerizable liquid crystal compound.

  In a preferred embodiment, the alignment process is a rubbing process.

  According to another aspect of the present invention, a retardation film is provided. This retardation film is obtained by the above production method.

  According to still another aspect of the present invention, a liquid crystal display device is provided. The liquid crystal display device includes the retardation film.

  According to the production method of the present invention, it is possible to obtain a retardation film having a large tilt angle, a small variation in thickness of the liquid crystal cured layer, and a small change in retardation in a high temperature environment. Furthermore, according to the production method of the present invention, since no special alignment film is required, the retardation film can be obtained with excellent productivity.

  The manufacturing method of this invention is a manufacturing method of retardation film provided with the liquid crystal hardening layer by which the inclination alignment was carried out, Comprising: The following process A-process C; Process A; This alignment process of the base material to which the alignment process was given A step of applying a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent and an acrylic leveling agent on the surface to form a coating layer, step B; drying the coating layer, and inclining A step of forming an aligned liquid crystal solidified layer, step C; a step of forming an inclined aligned liquid crystal cured layer by irradiating the liquid crystal solidified layer with ultraviolet rays. According to this production method, a retardation film having a large tilt angle, a small thickness variation of the liquid crystal cured layer, and a small retardation change under a high temperature environment can be obtained. Hereinafter, the present invention will be described in detail.

A. Process A
In step A, a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent is applied on the alignment-treated surface of the substrate that has been subjected to the alignment treatment. It is a process of forming.

A-1. Base material Any appropriate base material may be employed as long as it can develop a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent. Specific examples include glass substrates such as glass plates and quartz substrates, polymer substrates such as films and plastics substrates, metal substrates such as aluminum and iron, inorganic substrates such as ceramic substrates, and semiconductors such as silicon wafers. Examples include base materials. Preferably, the substrate is a polymer substrate. This is because the surface smoothness of the substrate and the wettability of the liquid crystal composition are excellent, and continuous production with a roll is possible, and the productivity can be greatly improved. Examples of the material for forming the polymer substrate include thermosetting resins, ultraviolet curable resins, thermoplastic resins, thermoplastic elastomers, and biodegradable plastics. Especially, as a base material, Preferably a cellulose film, More preferably, a triacetyl cellulose film is used. The base material may be a single layer or a laminate composed of a plurality of layers (for example, a laminate of a base material and an alignment film).

  Any appropriate thickness can be adopted as the thickness of the substrate. The thickness is preferably 1 μm to 200 μm, more preferably 5 μm to 150 μm, and particularly preferably 10 μm to 100 μm.

  Any appropriate orientation treatment is performed on the surface of the base material. Specific examples of the alignment treatment include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of the mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of the physical alignment process include a magnetic field alignment process and an electric field alignment process. Specific examples of the chemical alignment treatment include oblique vapor deposition and photo-alignment treatment. A rubbing process is preferred. In addition, arbitrary appropriate conditions may be employ | adopted for the process conditions of various orientation processes according to the objective.

A-2. Liquid Crystal Composition The liquid crystal composition used in the present invention contains one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent. The liquid crystal composition may be a dispersion or a solution as long as it can be spread on a substrate to form a uniform coating layer. Preferably, the liquid crystal composition is a solution in which a liquid crystal compound is uniformly dissolved in a solvent.

A-2-1. Polymerizable liquid crystal compound In the present invention, one or more polymerizable liquid crystal compounds (liquid crystal monomers) are used. In the present specification, the “liquid crystal compound” has a mesogenic group (central core) in the molecular structure, and forms a liquid crystal phase by temperature change such as heating and cooling, or by the action of a certain amount of solvent. A molecule. The “mesogen group” means a structural portion necessary for forming a liquid crystal phase, and usually contains a cyclic unit.

  The shape of the polymerizable liquid crystal compound may be any shape. For example, it may be a rod shape or a disk shape. Preferably, the polymerizable liquid crystal compound is a rod-like liquid crystal compound. In the present specification, the “rod-like liquid crystal compound” is a compound having a rod-like mesogen group in the molecular structure, and a side chain bonded to one side or both sides of the mesogen group by an ether bond or an ester bond. Say. Examples of the mesogen group include a biphenyl group, a phenylbenzoate group, a phenylcyclohexane group, an azoxybenzene group, an azomethine group, an azobenzene group, a phenylpyrimidine group, a diphenylacetylene group, a diphenylbenzoate group, a bicyclohexane group, a cyclohexylbenzene group, A terphenyl group etc. are mentioned. In addition, the terminal of these cyclic units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen group, for example. Especially, as a mesogenic group which consists of a cyclic unit etc., what has a biphenyl group and a phenylbenzoate group is used preferably.

  Preferably, the polymerizable liquid crystal compound is a compound that exhibits homeotropic alignment on a substrate that has not been subjected to alignment treatment. The homeotropic orientation refers to the property of aligning in the normal direction with respect to the substrate plane. A liquid crystal compound exhibiting such properties can be formed into a tilted orientation with a large tilt angle by mixing it with a solvent and an acrylic leveling agent and applying the mixture on an orientation-treated substrate.

  The polymerizable liquid crystal compound preferably has two or more polymerizable (crosslinkable) functional groups in a part of the molecular structure. This is because the cross-linked structure produced by the polymerization reaction increases the mechanical strength and provides a retardation film having excellent durability. Examples of the polymerizable (crosslinkable) functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. Examples of the commercially available liquid crystal compound having two or more polymerizable (crosslinkable) functional groups include a product name “Paliocolor LC242” manufactured by BASF, a product name “CB483” manufactured by HUNTSMAN, and the like.

  The content of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 40 parts by weight or more and less than 99.9 parts by weight, more preferably 50 parts by weight with respect to 100 parts by weight of the total solid content of the liquid crystal composition. The amount is less than 99.88 parts by weight, and particularly preferably 70 parts by weight to 99.85 parts by weight.

A-2-2. Solvent Any appropriate solvent capable of dissolving or dispersing the polymerizable liquid crystal compound and the following acrylic leveling agent may be employed as the solvent. Preferably, a solvent that uniformly dissolves the polymerizable liquid crystal compound and the acrylic leveling agent and that does not excessively erode the base material or inhibit the regulating ability of the alignment treatment may be used. The type of the solvent used can be appropriately selected according to the type of the liquid crystal compound. Specific examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, methylene chloride, trichloroethylene, tetrachloroethylene, chlorobenzene, and orthodichlorobenzene, phenol, p-chlorophenol, and o-chlorophenol. , M-cresol, o-cresol, p-cresol and other phenols, benzene, toluene, xylene, mesitylene, methoxybenzene, 1,2-dimethoxybenzene and other aromatic hydrocarbons, acetone, methyl ethyl ketone (MEK), methyl Ketone solvents such as isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone and N-methyl-2-pyrrolidone, ester solvents such as ethyl acetate, butyl acetate and propyl acetate, t Alcohol solvents such as butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol, dimethylformamide, dimethylacetamide Examples thereof include amide solvents such as nitrile solvents such as acetonitrile and butyronitrile, ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran and dioxane, carbon disulfide, ethyl cellosolve, butyl cellosolve, and ethyl cellosolve acetate. These solvents may be used alone or in combination of two or more. Of these, ketone solvents are preferable, and cyclopentanone is more preferable.

A-2-3. Acrylic Leveling Agent Any appropriate one can be adopted as the acrylic leveling agent. In the production method of the present invention, by using an acrylic leveling agent, a retardation film having a large tilt angle, a small variation in the thickness of the liquid crystal cured layer, and a small retardation change under a high temperature environment can be obtained. . The mechanism by which such an effect is achieved is unknown in detail, but is presumed as follows. That is, the acrylic leveling agent is excellent in compatibility with the polymerizable liquid crystal compound as compared with other leveling agents such as a silicone leveling agent. According to such a leveling agent, when the coating layer is formed, it is unevenly distributed on the surface of the coating layer and does not excessively reduce the surface tension. It becomes easy to stand. As a result, a large tilt angle can be obtained. Furthermore, even when the ultraviolet ray is intensely irradiated to sufficiently progress the polymerization of the polymerizable liquid crystal compound (as a result, the surface temperature of the liquid crystal solidified layer becomes high), a large tilt angle can be maintained. In addition, since the acrylic leveling agent is excellent in compatibility with the polymerizable liquid crystal compound and has a high surface adjusting ability, it is possible to form a liquid crystal cured layer having a small thickness variation.

（式中、Ｒ_１は、水素原子またはメチル基であり、Ｒ_２は、炭素数1〜１０の直鎖状または分岐状アルキル基、炭素数１〜１０のハロゲン化アルキル基、ポリエステル基、またはポリエーテル基である。） The acrylic leveling agent preferably has a unit represented by the following general formula (I) in the molecular structure.

(In the formula, R ₁ is a hydrogen atom or a methyl group, and R ₂ is a linear or branched alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, a polyester group, or (It is a polyether group.)

R ₂ is preferably a C 1-10 perfluoroalkyl group.

  The weight average molecular weight Mw of the acrylic leveling agent is preferably 2000 to 100,000, more preferably 2500 to 70000, and still more preferably 3000 to 40000, as measured by gel permeation chromatography.

  A commercial item can be used as said acrylic leveling agent. Commercially available acrylic leveling agents include, for example, trade name “BYK-340” manufactured by Big Chemie and trade name “LF-1980” manufactured by Enomoto Kasei.

  The content of the acrylic leveling agent in the liquid crystal composition is preferably 0.1 part by weight to 1 part by weight, more preferably 0.12 part by weight to 0.00 part by weight with respect to 100 parts by weight of the polymerizable liquid crystal compound. It is 95 weight part, More preferably, it is 0.15 weight part-0.9 weight part.

（式中、ｈは１４〜２０の整数であり、ｍとｎとの和を１００とした場合に、ｍは５０〜７０であり、ｎは３０〜５０である。） A-2-4. Other Components The liquid crystal composition may further contain a polymer liquid crystal compound (liquid crystal polymer). The polymer liquid crystal compound is used for the purpose of improving the orientation of the liquid crystal compound. The content of the polymer liquid crystal compound is preferably 10 to 40 parts by weight, and more preferably 15 to 30 parts by weight with respect to 100 parts by weight of the total solid content in the liquid crystal composition. Examples of the polymer liquid crystal compound include compounds represented by the following general formula (II).

(In the formula, h is an integer of 14 to 20, and when the sum of m and n is 100, m is 50 to 70 and n is 30 to 50.)

  The liquid crystal composition may further contain any additive as long as the object of the present invention is not impaired. Examples of the additive include a polymerization initiator, a surfactant, a lubricant, and a crosslinking agent. The content of these additives is preferably more than 0 and 30 parts by weight or less, more preferably more than 0 and 20 parts by weight or less, with respect to 100 parts by weight of the total solid content in the liquid crystal composition. Preferably it is more than 0 and 15 parts by weight or less. By setting it as the above range, a highly uniform retardation film can be obtained.

A-2-5. Preparation Method of Liquid Crystal Composition As a method for preparing the liquid crystal composition, a commercially available product may be used, and a solvent may be further added to the commercially available product. Further, the solid content of the liquid crystal compound and the acrylic leveling agent may be dissolved in various solvents and used, or the liquid crystal compound, the acrylic leveling agent, various additives, and the solvent may be mixed and dissolved.

  The solid content concentration of the liquid crystal composition varies depending on solubility, coating viscosity, wettability on the substrate, thickness after coating, etc., but in the liquid crystal composition, preferably 3 to 50 parts by weight, more preferably Is 5 to 40 parts by weight, particularly preferably 10 to 30 parts by weight. If it is said range, a phase difference film with high surface uniformity can be obtained.

A-3. Application means As the application means, any appropriate coating method using a coater can be selected and used. Specific examples of the above coater include reverse roll coater, forward rotation roll coater, gravure coater, knife coater, rod coater, slot orifice coater, curtain coater, fountain coater, air doctor coater, kiss coater, dip coater, bead coater, blade coater, cast Examples include a coater, a spray coater, a spin coater, an extrusion coater, and a hot melt coater. Among these, as a coater, a reverse roll coater, a normal rotation roll coater, a gravure coater, a rod coater, a slot orifice coater, a curtain coater, a fountain coater, and a spin coater are preferable. With the coating method using the above coater, the coating layer can be formed very thin and uniformly.

A-4. Coating layer In the present specification, the “coating layer” refers to a layer developed on a substrate, which contains one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent. The solvent may be evaporated to some extent. The solid content concentration of the coating layer is preferably 10% by weight to 40% by weight. The thickness of the coating layer is preferably 1 μm to 50 μm, more preferably 1 μm to 30 μm.

B. Process B
Step B is a step of drying the coating layer obtained in Step A to form a tilted and aligned liquid crystal solidified layer.

B-1. Any suitable drying means can be adopted as the drying means. For example, an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature adjustment, a heating method using a heat pipe roll or a metal belt, or a temperature control method Is mentioned.

  The drying time is preferably 20 seconds to 20 minutes, more preferably 1 minute to 10 minutes, and particularly preferably 1 minute to 5 minutes. The drying temperature is preferably 30 ° C. or higher and a liquid crystal phase-isotropic phase transition temperature (Ti) or lower, and more preferably 30 ° C. to 120 ° C. The isotropic phase transition temperature (Ti) can be known by observing a sample of a liquid crystal composition containing a liquid crystal compound with a polarizing microscope while heating.

B-2. Liquid crystal solidified layer In the present specification, the “liquid crystal solidified layer” is a liquid crystal composition containing a polymerizable liquid crystal compound, a solvent, and an acrylic leveling agent. Say. The liquid crystal solidified layer may contain a solvent as long as it is in a substantially solid state. The solid content concentration of the liquid crystal solidified layer is preferably 80% by weight to 100% by weight. The thickness of the liquid crystal solidified layer is preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 3 μm.

  The liquid crystal solidified layer is one in which a liquid crystal compound is tilted and aligned. Inclination alignment of the liquid crystal compound occurs due to the difference between the regulation force due to the alignment treatment on the substrate side and the regulation force on the side opposite to the substrate (for example, the air side) and their balance during the drying process of the coating layer. It is estimated to be. The tilted orientation may have a uniform tilt angle in the thickness direction, or may have a different tilt angle in the thickness direction (for example, a “hybrid arrangement” in which the tilt angle gradually changes in the thickness direction). May be. Preferably, the liquid crystal solidified layer is aligned in a hybrid arrangement.

C. Process C
Step C is a step of irradiating the liquid crystal solidified layer obtained in Step B with ultraviolet rays to form a tilted and aligned liquid crystal cured layer. As described above, in the present invention, an acrylic leveling agent that has excellent compatibility with the liquid crystal compound and makes the liquid crystal compound easily stand in the normal direction of the substrate is used. ) Can also maintain a large tilt angle. Therefore, a stable network structure can be formed by sufficiently polymerizing the polymerizable liquid crystal compound while maintaining a large tilt angle. As a result, a retardation film having a large tilt angle, a liquid crystal compound that does not move even under a high temperature environment, and a small change in retardation can be obtained.

C-1. Dose at a wavelength 365nm irradiation conditions ultraviolet UV is preferably ^{400mJ / cm 2 ~1500mJ / cm 2} , more preferably from ^{600mJ / cm 2 ~1500mJ / cm 2} . If it is said conditions, even if the produced retardation film is exposed to a high temperature environment, orientation will not be disturbed substantially and a tilt angle will not fall. The surface temperature of the liquid crystal solidified layer at the time of ultraviolet irradiation is preferably 50 ° C. or lower, more preferably 30 ° C. to 50 ° C.

C-2. Irradiation means As the ultraviolet irradiation means employed in the present invention, any appropriate ultraviolet irradiation apparatus can be used as long as it can achieve the prescribed irradiation temperature and irradiation amount. The ultraviolet irradiation device preferably includes temperature control means (for example, a heating / cooling stage) for controlling the temperature of the liquid crystal solidified layer surface. Examples of the irradiation light source include an ultrahigh pressure mercury lamp, a flash UV lamp, a high pressure mercury lamp, a low pressure mercury lamp, a deep UV lamp, a xenon lamp, a metal halide lamp, and an electrodeless lamp.

  The wavelength of the light source can be determined according to the wavelength region in which the polymerizable (crosslinkable) functional group of the liquid crystal compound used in the present invention has optical absorption. The wavelength is preferably 210 nm to 380 nm, more preferably 250 nm to 380 nm. The wavelength of the light source is preferably used by cutting a region of 100 nm to 200 nm with a filter or the like in order to suppress a photodecomposition reaction such as a liquid crystal compound. If it is said range, a liquid crystal compound will fully harden | cure by superposition | polymerization or a crosslinking reaction, and the retardation film excellent in mechanical strength can be obtained.

C-3. Liquid crystal cured layer In the present specification, the “liquid crystal cured layer” means a liquid crystal compound or a part or all of a mixture containing the liquid crystal compound is crosslinked by ultraviolet rays to be insoluble or insoluble and hardly soluble. Say things. The liquid crystal cured layer shows a liquid crystal phase before film formation, but after the film formation, the liquid crystal cured layer may form a network structure by a crosslinking reaction and does not show a liquid crystal phase.

  The thickness of the liquid crystal cured layer is preferably 1 μm to 5 μm, more preferably 1 μm to 3 μm. The liquid crystal cured layer is one in which a liquid crystal compound is tilted and oriented, preferably in a hybrid alignment.

  The average tilt angle (an average value of the tilt angle on one side of the liquid crystal compound (for example, the air interface) and the tilt angle on the other side (for example, the substrate or the alignment film interface)) of the liquid crystal compound that has been tilted is preferably Is 25 ° to 45 °, more preferably 25 ° to 42 °. Here, the tilt angle represents an angle formed between the adjacent layer surface and the liquid crystal compound molecules, and 0 ° is defined when the molecules are arranged in parallel in the plane.

D. Retardation Film The retardation film obtained by the production method of the present invention may contain other members as long as it has a liquid crystal cured layer that is inclined and oriented. For example, when the substrate is transparent and optically isotropic or has birefringence suitable for expanding the viewing angle of the liquid crystal cell, the retardation film comprises a substrate and a liquid crystal cured layer that is inclined and aligned. Prepare. In addition, the retardation film may be used by peeling a tilted liquid crystal cured layer from a substrate and transferring it to another film via an adhesive layer. The retardation film may be laminated with other retardation layers, polarizing elements, adhesive layers, hard coat layers, anchor coat layers, and the like.

D-1. Optical Properties of Retardation Film When the retardation film is composed only of a liquid crystal cured layer having a tilted orientation, the in-plane retardation Re of the retardation film can be, for example, 50 nm to 200 nm, preferably 70 nm to 180 nm. In this specification, “in-plane retardation Re” refers to a retardation value in a film (layer) plane measured with light having a wavelength of 590 nm at 23 ° C. Re represents the refractive index in the slow axis direction of the film (layer) at a wavelength of 590 nm (the direction in which the in-plane refractive index is maximized) and the fast axis direction (the direction perpendicular to the slow axis in the plane), respectively. nx, ny, where d (nm) is the thickness of the film (layer), it is determined by the formula: Re = (nx−ny) × d.

  The transmittance of the retardation film measured with light having a wavelength of 590 nm at 23 ° C. is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The theoretical upper limit of the transmittance is 100%.

D-2. Use of retardation film The retardation film is preferably used in a liquid crystal display device. Applications of the liquid crystal display device include, for example, OA devices such as personal computer monitors, notebook computers, and copiers, mobile phones, watches, digital cameras, personal digital assistants (PDAs), portable devices such as portable game machines, video cameras, and televisions. Household appliances such as microwave ovens, back monitors, monitors for car navigation systems, in-vehicle devices such as car audio, display equipment such as information monitors for commercial stores, security equipment such as monitoring monitors, nursing monitors, Nursing care and medical equipment such as medical monitors.

  The present invention will be further described using the following examples and comparative examples. In addition, this invention is not limited only to these Examples. In addition, each analysis method used in the Example is as follows.

(1) Measurement of thickness It measured using the spectrophotometer for thin films [Otsuka Electronics Co., Ltd. product name "instant multiphotometry system MCPD-2000"].

(2) Measurement of tilt angle (θ) The tilt angle (θ) is an average value of θ _air and θ _AL . θ _air and θ _AL are the retardation value (R) at the angle φ of the retardation film measured using the product name “Axoscan” manufactured by Optoscience, and the refractive index of ordinary light and extraordinary light obtained with an Abbe refractometer. The (n _o , n _e ) and the thickness (d) of the liquid crystal cured layer obtained by the above-described thin film spectrophotometer were obtained by substituting them into Witté's equations (I) and (II). The phase difference value (R) was measured in increments of 5 ° within an angle φ ranging from −40 ° to + 40 °. However, the normal direction is φ = 0 °. Θ _air represents the tilt angle on one side (for example, the air interface) of the liquid crystal compound, and θ _AL represents the tilt angle on the other side (for example, the substrate or the alignment film interface).

(3) Measurement of irradiation amount It measured using the illuminometer [The product name "EYE UV METER UVPF-A1" by Eye Graphics Co., Ltd.].

(4) Measurement of phase difference value (Re) Using a phase difference meter based on the parallel Nicol rotation method [product name “KOBRA21-ADH” manufactured by Oji Scientific Instruments Co., Ltd.], light at a wavelength of 590 nm at 23 ° C. It was measured.

(5) Retardation change rate The retardation value (Re) of a retardation film heated (dried) for 500 hours in an air circulation oven at 90 ° C. is measured, and dried with respect to the initial (before drying) retardation value (Re). The difference between the phase difference values (Re) before and after was obtained as a percentage. That is, the phase difference change rate is obtained by the following equation.
Phase difference change rate (%) = (phase difference value after drying (Re) −initial phase difference value (Re)) / initial phase difference value (Re) × 100

[Example 1]
1. Preparation of Liquid Crystal Composition 20 parts by weight of a polymer liquid crystal compound represented by the following formula (III) (weight average molecular weight: 5,000) and 80 parts by weight of a polymerizable liquid crystal compound [trade name “Palicolor LC242 manufactured by BASF Corporation] _{"(n e = 1.654, n o} = 1.523) and] was dissolved in cyclopentanone 200 parts by weight. 0.3 parts by weight of an acrylic leveling agent [trade name “LF-1980” manufactured by Enomoto Kasei Co., Ltd.] is added to the resulting solution, and further 7 parts by weight of a polymerization initiator [trade name “Irgacure 907” manufactured by Ciba Co., Ltd.] ] Was added. A liquid crystal composition was prepared by adding cyclopentanone to this solution so that the solid content concentration was 20% by weight.

2. Process A
A triacetyl cellulose film [trade name “TD80UL” manufactured by Fuji Film Co., Ltd.] was rubbed. On the rubbing surface, the above 1. The liquid crystal composition prepared in (1) was uniformly applied to form a coating layer. The thickness of the coating layer at this time was 8.5 μm.

3. Process B
2. The coating layer obtained in (1) was dried in an air-circulating constant temperature oven at 80 ° C. for 2 minutes to form a gradient-aligned liquid crystal solidified layer having a thickness of 1.7 μm.

4). Process C
3. above. The liquid crystal solidified layer obtained in (1) was irradiated with ultraviolet rays so that the irradiation amount at a wavelength of 365 nm on the solidified layer surface was 600 mJ / cm ² using an ultraviolet irradiation device equipped with a high-pressure mercury lamp. A 7 μm tilted liquid crystal cured layer was formed. It was 40-50 degreeC when the surface temperature of this solidified layer under ultraviolet irradiation was measured using the thermocouple.

  Through the steps A to C, a retardation film A including a base material and a liquid crystal cured layer was produced. Table 1 shows the physical properties measured by peeling the liquid crystal cured layer from the substrate. The transmittance of the liquid crystal cured layer at a wavelength of 590 nm was 90%, and the in-plane retardation value Re at a wavelength of 590 nm was 105 nm.

[Comparative Example 1]
In place of the acrylic leveling agent, a retardation film B was prepared in the same manner as in Example 1 except that a polyester leveling agent [trade name “BYK375” manufactured by Big Chemie Co., Ltd.] was used. Table 1 shows the physical properties measured by peeling the liquid crystal cured layer from the substrate.

[Comparative Example 2]
Instead of using an acrylic leveling agent, a polyester leveling agent [trade name “BYK375” manufactured by Big Chemie Co., Ltd.] was used, and irradiation with ultraviolet rays was performed so that the irradiation amount at a wavelength of 365 nm was 300 mJ / cm ^2. A retardation film C was prepared in the same manner as in Example 1. When the surface temperature of the solidified layer during the ultraviolet irradiation was measured using a thermocouple, it was 30 ° C to 40 ° C.

  As shown in Table 1, in Comparative Example 1, a retardation film having a small change in retardation even under a high temperature environment was obtained, but the tilt angle was decreased and the variation in tilt angle was further increased. This is thought to be because the polymerization of the polymerizable liquid crystal compound progressed sufficiently by the strong irradiation of ultraviolet rays, so that a stable network structure was formed, but the alignment of the liquid crystal compound molecules was disturbed by the strong ultraviolet irradiation. It is done. In Comparative Example 2, a retardation film having a large tilt angle and a small tilt angle variation could be obtained, but the phase difference change under a high temperature environment was large. This is considered to be because the alignment of the liquid crystal compound molecules was maintained by weakly irradiating ultraviolet rays, but the polymerization of the polymerizable liquid crystal compound was insufficient with weak ultraviolet irradiation.

  From the results of Comparative Examples 1 and 2, it is necessary to increase the ultraviolet irradiation when forming the liquid crystal cured layer in order to reduce the phase difference change under a high temperature environment. It turns out that becomes small. Moreover, in order to obtain a large tilt angle, it is necessary to weaken the ultraviolet irradiation, but it can be seen that under such conditions, the phase difference change under a high temperature environment becomes large. That is, it can be seen that increasing the tilt angle and reducing the phase difference change in a high temperature environment are in a trade-off relationship.

  On the other hand, it can be seen from the results of Example 1 that both a large tilt angle and a small phase difference change can be achieved by using an acrylic leveling agent having excellent compatibility with the liquid crystal compound. Moreover, since an acrylic leveling agent is excellent in surface adjustment ability, it turns out that a retardation film with small thickness variation can be obtained.

[Reference Example 1]
When the liquid crystal composition prepared in Example 1 and Comparative Example 1 was used, the relationship between the tilt angle and the surface temperature of the liquid crystal solidified layer during ultraviolet irradiation (the irradiation amount at a wavelength of 365 nm was 600 mJ / cm ² ). Examined. The results are shown in FIG. As shown in FIG. 1, it can be seen that when the acrylic leveling agent is not used, the tilt angle becomes remarkably small when the surface of the liquid crystal solidified layer becomes high temperature. Specifically, when the surface temperature of the liquid crystal solidified layer is 45 ° C. or higher, only a tilt angle of less than 40 ° can be obtained. On the other hand, when an acrylic leveling agent is used, a tilt angle of 40 ° or more can be obtained even when the surface of the liquid crystal solidified layer is 50 ° C.

  Since the production method of the present invention can obtain a retardation film having a large tilt angle, a small variation in thickness of the liquid crystal cured layer, and a small retardation change under a high temperature environment with sufficient productivity, the retardation film It can be suitably applied in the manufacturing field.

FIG. 1 is a graph showing the relationship between the surface temperature of the liquid crystal solidified layer and the tilt angle under ultraviolet irradiation (irradiation amount at a wavelength of 365 nm is 600 mJ / cm ² ).

Claims (6)

A method for producing a retardation film comprising a tilted liquid crystal cured layer, comprising the following steps A to C:
Step A: Applying a liquid crystal composition containing one or more polymerizable liquid crystal compounds, a solvent, and an acrylic leveling agent on the alignment-treated surface of the substrate subjected to the alignment treatment to form a coating layer The process of
Step B; drying the coating layer to form a tilted liquid crystal solidified layer;
Step C: a step of irradiating the liquid crystal solidified layer with ultraviolet rays to form a tilted and aligned liquid crystal cured layer.   The manufacturing method according to claim 1, wherein the liquid crystal compound is a compound that exhibits homeotropic alignment on a substrate that has not been subjected to alignment treatment.   The manufacturing method of Claim 1 or 2 whose content of the said acrylic leveling agent in the said liquid-crystal composition is 0.1-1 weight part with respect to 100 weight part of said polymeric liquid crystal compounds.   The manufacturing method according to claim 1, wherein the alignment treatment is a rubbing treatment.   A retardation film obtained by the production method according to claim 1. A liquid crystal display device comprising the retardation film according to claim 5.

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