WO2009107524A1 - Method for manufacturing optical compensation sheet and optical compensation sheet - Google Patents

Abstract

Provided is a method for manufacturing an optical compensation sheet characterized by comprising the steps of applying an application liquid containing a nematic liquid crystal compound onto an alignment film previously formed on the surface of a long film that is running, aligning the nematic liquid crystal compound by drying the applied layer and thereafter heating the applied layer at a liquid crystal forming temperature T1 (°C), and polymerizing and curing the aligned applied layer, wherein the liquid crystal forming temperature T1 (°C) is in the range of T2-10≤T1<T2 when the liquid-liquid crystal phase transition temperature of the nematic liquid crystal compound is T2 (°C), and the heating time is maintained for at least 25 seconds.

Description

Optical compensation sheet manufacturing method and optical compensation sheet

The present invention relates to an optical compensation sheet manufacturing method and an optical compensation sheet used for liquid crystal displays and the like, and more particularly to a technique for forming an optically anisotropic layer containing a nematic liquid crystalline compound.

The optical compensation sheet (retardation plate) is provided between the pair of polarizing plates and the liquid crystal cell in order to improve the viewing angle characteristics of the liquid crystal display. As a general method for producing an optical compensation sheet, for example, there is a method in which a coating liquid containing a nematic liquid crystalline compound is applied on a transparent film on which an alignment film is formed, and then heated and aligned, and then fixed by cooling or a crosslinking reaction. It is used.

As a method for thermally aligning this nematic liquid crystalline compound, for example, in Patent Document 1, in a method for producing an optical compensation sheet, after applying a discotic liquid crystal on an alignment film, the discotic nematic liquid crystal phase has a solid-state transition temperature or higher. It has been proposed to heat and heat until the liquid crystal is aligned.

Patent Document 2 proposes that in a method for manufacturing a liquid crystal element, heating to a temperature higher than the glass transition temperature of a liquid crystal polymer by 50 ° C. or more and exhibiting a liquid crystal phase. Thereby, it is said that the domain-like alignment defects (also referred to as Schlieren defects) can be eliminated in a shorter time than when heating is continued at a low temperature. On the other hand, it is limited to liquid crystal polymers, and there is an aspect that it cannot be applied to liquid crystal compounds whose glass transition temperature cannot be defined.

Patent Document 3 discloses that in a method for producing an optical compensation sheet, a liquid crystalline compound is generalized in a nematic liquid crystal and heated at 25 to 300 ° C. for at least 30 seconds.

In Patent Document 4, in the method of manufacturing an optical compensation sheet, a discotic liquid crystal is aligned by heating a coating layer containing a discotic liquid crystal at a temperature of 50 ° C. or higher and 200 ° C. or lower for 10 seconds or longer and 240 seconds or shorter. It has been proposed.

As described above, in Patent Documents 1 to 4, in order to stably align the nematic liquid crystalline compound, it is necessary to heat it for a certain time at a relatively high temperature.
JP-A-8-5837 Japanese Patent Laid-Open No. 11-271532 JP 2004-46194 A JP 2004-29789 A

However, in the actual manufacturing process, as described in Patent Documents 1 to 4, heating at a high temperature for a long time has a problem that not only productivity is lowered but also product cost is increased. In addition, the base film and the coating layer are likely to be thermally deteriorated due to these thermal histories, which causes a decrease in optical characteristics.

On the other hand, a quantitative study has not yet been made on the heating conditions for obtaining a certain high orientation in the optical compensation sheet.

For this reason, there is a need for a policy that can cope with an increase in area and mass production of an optical compensation sheet while maintaining high optical characteristics stably.

The present invention has been made in view of such circumstances, and can be applied to increase the product area and mass production, and can improve the alignment of the nematic liquid crystalline compound without impairing the productivity. It aims at providing the manufacturing method of a sheet | seat.

In order to achieve the above object, the first aspect of the present invention comprises a step of applying a coating liquid containing a nematic liquid crystalline compound on an alignment film previously formed on the surface of a traveling long film, and the coating After the layer is dried, an optical compensation sheet comprising a step of aligning the nematic liquid crystalline compound by heating at a liquid crystal forming temperature T1 (° C.), and a step of polymerizing and curing the aligned coating layer In the method, the liquid crystal formation temperature T1 (° C.) is in the range of T2-10 ≦ T1 <T2 when the liquid-liquid crystal phase transition temperature of the nematic liquid crystalline compound is T2 (° C.), and the heating time is There is provided a method for producing an optical compensation sheet, characterized by maintaining for at least 25 seconds.

As a result of quantitatively studying heating conditions (liquid crystal formation temperature, heating time) for obtaining a certain orientation in the step of thermally aligning the nematic liquid crystalline compound, the present inventors have conducted a quantitative study on the orientation. On the other hand, we have found that there is a temperature range that dramatically improves.

The present invention has been made based on such findings. According to the first aspect, the liquid crystal forming temperature is maintained at T1 (° C.) and the temperature range of T2-10 ≦ T1 <T2 is maintained for at least 25 seconds. A constant high orientation can be stably obtained with a short heating time. The reason for setting the heating time to at least 25 seconds is that if the heating time is 25 seconds or more, a substantially constant high orientation can be obtained regardless of the heating time. The heating time can be 25 to 90 seconds, preferably 25 to 35 seconds in view of the safety factor.

Here, the liquid-liquid crystal phase transition temperature of the nematic liquid crystal compound refers to a temperature at which the nematic liquid crystal compound undergoes a phase transition from the liquid crystal phase to the liquid phase.

According to a second aspect of the present invention, in the first aspect, the liquid crystal formation temperature T1 (° C.) is in a range of T2-5 ≦ T1 <T2, and the heating time is maintained for at least 30 seconds. .

According to the second aspect, a constant high orientation can be obtained in a shorter heating time.

The third aspect of the present invention is characterized in that, in the first or second aspect, the wet thickness of the coating layer is 50 μm or less.

According to the third aspect, since the wet thickness of the coating layer is 50 μm or less, the alignment regulating force of the alignment film can be effectively functioned.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the nematic liquid crystalline compound is a discotic liquid crystalline compound.

According to the fourth aspect, an optical compensation sheet using a discotic liquid crystalline compound as a nematic liquid crystalline compound is suitable for a liquid crystal display.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, in the step of orienting, hot air is blown onto the surface of the applied layer of the long film, and the same surface is sprayed. By discharging hot air on at least one of the upstream side and the downstream side, an air flow along the running direction of the long film is generated.

According to the fifth aspect, since the hot air is heated along the running direction of the long film, the heating temperature can be maintained in the above temperature range without causing uneven distribution.

According to a sixth aspect of the present invention, in the fifth aspect, the step of measuring the ambient temperature in the vicinity of the coating layer and the coating layer based on the measurement result such that the ambient temperature becomes the liquid crystal formation temperature. And a step of controlling the temperature of the hot air to be blown.

According to the sixth aspect, while sensing the ambient temperature in the vicinity of the coating layer, the hot air temperature can be controlled so that the ambient temperature is in the above temperature range. Thereby, it can set accurately so that an application layer may become the said temperature range.

The seventh aspect of the present invention is characterized in that, in the fifth or sixth aspect, the air flow along the running direction of the long film has a wind speed of 20 m / sec or less.

According to the seventh aspect, the coating layer can be heated without producing a non-uniform temperature distribution.

According to an eighth aspect of the present invention, there is provided an optical compensation sheet manufactured by the method for manufacturing an optical compensation sheet according to any one of the first to seventh aspects, in order to achieve the above object.

According to the present invention, it is possible to cope with an increase in product area and mass production, and the orientation of the nematic liquid crystalline compound can be improved without impairing productivity.

FIG. 1 is a schematic view showing an example of a manufacturing process of an optical compensation sheet in the present embodiment; FIG. 2 is a schematic diagram showing an example of the configuration of the heating device in the present embodiment; FIG. 3 is a schematic view showing the air outlet of the heating device in the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical compensation sheet manufacturing apparatus 16 ... Transparent film 16A ... Coating layer 18 ... Rubbing apparatus 26 ... Coating machine 28 ... Drying apparatus 30 ... Heating apparatus 64 ... Temperature sensor 66 ... Three-dimensional wind speed sensor 46 ... Controller 44 ... Blowing fan 46 ... Exhaust fan

Hereinafter, preferred embodiments of a method for producing an optical compensation sheet according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic view showing an example of the optical compensation sheet manufacturing process 10 in the present embodiment.

An alignment film forming resin layer is formed in advance on the surface of the long transparent film 16 delivered from the film roll 12 by the delivery device 14. The traveling speed of the transparent film 16 can be set to 0.1 to 1.5 m / second, for example.

The transparent film 16 is conveyed to a rubbing device 18 and subjected to a rubbing process. The rubbing device 18 includes a rubbing roller 20, a guide roller 22 fixed to a roller stage with a spring, and a dust remover 23 provided on the rubbing roller. The surface of the alignment film thus formed is dedusted by a surface dust remover 24 provided on the downstream side of the rubbing device 18.

The transparent film 16 on which the alignment film is formed is conveyed to a coating machine 26 by a driving roller, and a coating liquid containing a discotic nematic compound is applied onto the alignment film. For example, the coating layer may have a wet thickness of 50 μm or less. Although there is no restriction | limiting in particular as the coating device 26, A well-known coating device, for example, various bar coaters, a gravure coater, a die coater etc. can be used.

The transparent film 16 on which the coating layer has been formed is dried at room temperature to 100 ° C. in a drying device 28, for example. Here, for example, it is preferable that the residual solvent evaporates by 50% or more, preferably evaporates to 75% or more and is dried. The coating layer in which the solvent has evaporated to some extent is heated in the heating device 30 at a discotic nematic phase formation temperature (liquid crystal formation temperature) for a predetermined time. This orients the discotic nematic phase.

The coating layer is crosslinked by being irradiated with ultraviolet rays from an ultraviolet (UV) lamp 32. In order to crosslink, it is necessary to use a liquid crystalline discotic compound having a crosslinkable functional group as the liquid crystalline discotic compound. When a liquid crystal discotic compound having no crosslinkable functional group is used, this ultraviolet irradiation step is omitted and the liquid crystal is immediately cooled. In this case, the cooling needs to be performed rapidly so that the discotic nematic phase is not destroyed during cooling.

The transparent film 16 on which the coating layer (optically anisotropic layer) is formed in this way is measured for optical characteristics on the surface of the transparent film by the inspection device 34 and inspected for any abnormality. Next, the protective film 36 is laminated on the surface of the optically anisotropic layer by a laminating machine 38 and wound up by a winding device 40.

In the present embodiment, the example in which the optically anisotropic layer is formed using the winding film having the alignment film forming resin layer once wound up has been described. From the step of forming the alignment film forming resin layer, You may perform the process from making an optical compensation sheet to winding up continuously by integrated production.

By the way, in the step of heat alignment, heating is performed at a predetermined liquid crystal forming temperature in order to align the coating layer of the coating liquid for the optically anisotropic layer. In the process of studying the heating conditions, the inventors have remarkably improved the orientation at a certain temperature above the liquid-liquid crystal phase transition temperature, and the desired orientation in a short heating time in this temperature range. It was found that can be obtained.

On the other hand, since the discotic nematic compound becomes isotropic phase above the liquid-liquid crystal phase transition temperature, it does not show orientation. Therefore, it is preferable to maintain the coating solution at a temperature lower than the liquid-liquid crystal phase transition temperature and very close to the liquid-liquid crystal phase transition temperature. However, since variations in temperature are likely to occur in an actual manufacturing process, it is extremely difficult to maintain the temperature at a high temperature that is not lower than the liquid-liquid crystal phase transition temperature and is close to the liquid-liquid crystal phase transition temperature.

Therefore, in the present invention, a temperature range in which a certain high orientation is stably obtained is defined in consideration of temperature variations in an actual manufacturing process. Specifically, when the liquid-liquid crystal phase transition temperature is T2 (° C.), the liquid crystal formation temperature T1 (° C.) is in the range of T2-10 ≦ T1 <T2, and preferably in the range of T2-5 ≦ T1 <T2. And When the liquid crystal forming temperature is lower than (T2-10) ° C., it is not preferable because it takes about twice or more of the heating time to obtain a certain high orientation, and the productivity is lowered.

The liquid-liquid crystal phase transition temperature is mainly determined by the type of nematic liquid crystalline compound contained in the coating liquid for the optically anisotropic layer, but also depends on the composition of the coating liquid for the optically anisotropic layer. For this reason, it is necessary to obtain the liquid-liquid crystal phase transition temperature by conducting a test in advance with the coating solution for the optically anisotropic layer to be used.

As a method for measuring the liquid-liquid crystal phase transition temperature, for example, a coating solution for an optically anisotropic layer containing a discotic liquid crystalline compound is spun on a transparent glass substrate so as to have a desired film thickness (for example, 5 μm). There is a method of observing the coated sample plate with a polarizing microscope while raising the temperature. That is, in observation with a polarizing microscope, light leakage from the sample plate occurs at a temperature exhibiting liquid crystallinity, whereas light leakage from the sample plate disappears above the liquid-liquid crystal phase transition temperature, resulting in a completely dark image. The temperature that becomes the boundary of whether or not this light leakage occurs can be set as a liquid-liquid crystal phase transition temperature. The method for measuring the liquid-liquid crystal phase transition temperature is not limited to the above embodiment.

The orientation of the nematic liquid crystal is related to the fluidity of the liquid crystal molecules. The closer the liquid-liquid crystal phase transition temperature is, the higher the fluidity of the liquid crystal molecules is. Since the aligned state of the liquid crystal molecules is in an equilibrium state, it can eventually be brought into a highly oriented state by maintaining it at a temperature higher than the solid-liquid crystal phase transition temperature and lower than the liquid-liquid crystal phase transition temperature. .

However, if the fluidity of the liquid crystal molecules is low, it takes time until the alignment is improved. Therefore, by increasing the fluidity of the liquid crystal molecules close to the liquid-liquid crystal phase transition temperature, the time required for improving the alignment can be shortened. Therefore, the heating temperature condition of the present application can be applied to any nematic liquid crystal.

Next, the heating device 30 that controls the temperature region in the present embodiment will be described. FIG. 2 is a schematic diagram illustrating an example of the configuration of the heating device 30.

The heating device 30 is formed of a rectangular casing 42 that is open at the top and bottom, and is mainly coated with a coating liquid 16A for the optically anisotropic layer on the transparent film 16 that runs while being guided by a plurality of pass rollers 44. The blow-out part 46 that blows hot air and the discharge part 48 that discharges the hot air are arranged on the side on which the coating layer is formed. The main body of the heating device 30 is partitioned in the casing 42 such that the blowout portion 46 and the discharge portion 48 are positioned on the upstream side and the downstream side in the traveling direction of the transparent film 16 by the partition plate 49.

A plurality of outlets 50 are provided below the outlet 46, and an outlet fan 54 whose rotation speed can be changed is provided at a hot air supply port 52 connected to a hot air generator (not shown). On the other hand, a discharge port 56 is provided below the discharge unit 48, and a discharge fan 58 whose rotation speed can be changed is provided above. The blower fan 54, the exhaust fan 58, and the hot air generator are controlled by a controller 60 that controls the heating device 30. The hot air supply port 52 is preferably provided with a filter 53 for removing impurities in the air.

Thereby, after the hot air taken into the blow-out part 46 from the hot air generator (not shown) is blown onto the coating layer 16A of the transparent film 16 traveling from the blow-out opening 50 and taken into the discharge part 48 from the discharge port 56. , Discharged outside the device. Thereby, the hot air blown to the coating layer 16A forms an air flow along the traveling direction of the transparent film 16 from the outlet 50 side to the outlet 56 side on the surface of the coating layer 16A.

In this air flow, from the viewpoint of suppressing uneven heating, the wind speed generated in the width direction of the transparent film 16 is preferably 1 m / second or less, more preferably 0.8 m / second or less. The wind speed in the traveling direction is preferably 20 m / second or less.

As the outlet 50, a slit nozzle, a slit plate, or a member having a porous opening such as punching metal can be used. FIG. 3 is a schematic view showing the air outlet 50, and is an example in which a plurality of slit nozzles 50 </ b> A that are long in the width direction of the transparent film 16 are arranged in the running direction of the transparent film 16. It is preferable that the width (L1) of the air outlet 50 be in the range of 1.05 to 2 times the width of the transparent film 16. Thereby, the wind speed of the airflow in the traveling direction of the transparent film 16 can be made substantially uniform over the width direction of the transparent film 16.

Further, a temperature sensor 64 is provided in the casing 42 of the blow-out portion 46, and a three-dimensional wind speed sensor 66 is disposed immediately above the coating layer 16A.

Thereby, the hot air temperature and the blown air speed blown to the coating layer 16A are monitored by the temperature sensor 64 and the three-dimensional wind speed sensor 66 and input to the controller 60. Based on the monitoring result, the controller 60 adjusts the rotation speed of the blower fan 54 and the discharge fan 58 and the hot air temperature of the hot air generator so that the wind speed and hot air temperature in the vicinity of the coating layer 16A satisfy the above-described conditions. Feedback control. For example, the hot air temperature is feedback-controlled so that the ambient temperature in the vicinity of the coating layer 16A is within the range of the liquid crystal formation temperature described above.

As the wind speed measuring device, for example, a three-dimensional ultrasonic anemometer (WA-390 type) manufactured by Kaijo Co., Ltd. can be used.

The heating time at the liquid crystal forming temperature may be adjusted by changing the traveling speed of the transparent film 16, or may be adjusted by changing the length of the heating zone in the film traveling direction. As described above, as a heating device that makes the film running direction length of the heating zone variable, for example, a plurality of heating devices 30 as shown in FIG. 2 may be arranged in parallel and operated as much as necessary. Alternatively, when it is desired to shorten the heating time, for example, in FIG. 2, a movable partition plate is installed on the upstream side in the casing 42, and the partition plate covers the outlet 50 of the outlet portion 46 only in a desired region. do it.

In the present embodiment, the heating device 30 is not limited to the above-described aspect, and may be a hot air heating device having another configuration, a heater heating device, or the like.

As described above, according to the method for producing an optical compensation sheet according to the present invention, a constant high orientation can be stably obtained in a short heating time. For this reason, the quality of a product can be maintained without impairing productivity. Moreover, even when the kind of liquid crystalline compound and the composition of the coating liquid for the optically anisotropic layer are different, high orientation can be stably obtained by applying the present invention.

Hereinafter, each material used in this embodiment will be described.

The transparent film used in the present embodiment (the transparent film serving as a base before forming the alignment film) is not particularly limited as long as it is a transparent material, but a transparent film having a light transmittance of 80% or more is used. Is preferred. The transparent film is preferably one that does not easily exhibit birefringence due to external force. The transparent film contains a hydrolyzable bond (bond to be saponified) such as an ester bond or an amide bond. An ester bond is preferred, and it is more preferred that the ester bond be present on the side chain of the polymer. A typical example of the polymer having an ester bond in the side chain is a cellulose ester. Lower fatty acid esters of cellulose are more preferable, cellulose acetate is more preferable, and cellulose acetate having an acetylation degree of 59.0 to 61.5% is most preferable. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

When a transparent film is used for the optical compensation sheet, the transparent film preferably has a high retardation value. The Re retardation value and Rth retardation value of the film are defined by the following formulas (I) and (II), respectively.

Re and Rth preferably satisfy the following formulas (R-1) and (R-2).

Formula (R-1): 0 nm ≦ Re ≦ 300 nm
Formula (R-2): 10 nm ≦ Rth ≦ 300 nm
More preferably, the following formulas (R-3) and (R-4) are satisfied.

Formula (R-3): 20 nm ≦ Re ≦ 200 nm
Formula (R-4): 20 nm ≦ Rth ≦ 200 nm
Here, Re and Rth are in-plane retardation and retardation in the thickness direction, respectively, and are represented by the following formulas (R-5) and (R-6).

Formula (R-6): Re = | nx−ny | × d
Formula (R-7): Rth = {(nx + ny) / 2−nz} × d
(Nx, ny, and nz are the slow axis, the fast axis direction, and the refractive index in the thickness direction, respectively, and d is the film thickness)
The optically anisotropic layer in the present embodiment is formed directly from a liquid crystalline compound on the transparent film 16 or from a liquid crystalline compound via an alignment film. The alignment film preferably has a thickness of 10 μm or less. A preferable example of the alignment film is described in JP-A-8-338913.

The optically anisotropic layer is prepared by preparing a coating liquid (optically anisotropic layer coating liquid) containing at least one liquid crystalline compound described below and additives such as a polymerization initiator and a fluorine-based polymer as required. It can be formed by applying and drying the coating solution on the surface of the alignment film.

Examples of the fluorine compound include conventionally known compounds. Specific examples include fluorine compounds described in paragraphs [0028] to [0056] of JP-A-2001-330725. It is done.

As the solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg N, N-dimethylformamide), sulfoxides (eg dimethyl sulfoxide), heterocyclic compounds (eg pyridine), hydrocarbons (eg benzene, hexane), alkyl halides (eg , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

When producing a highly uniform optical compensation sheet, the surface tension of the coating solution is preferably 25 mN / m or less, and more preferably 22 mN / m or less.

As the nematic liquid crystalline compound, for example, a discotic liquid crystalline compound can be used. The liquid crystal compound used in the present embodiment includes a discotic liquid crystal compound. The discotic liquid crystalline compound may be a polymer liquid crystal or a low molecular liquid crystal.

Discotic liquid crystalline compounds include C.I. Benzene derivatives described in a research report of Destrade et al. (Mol. Cryst. 71, 111 (1981)), C.I. Destrode et al. (Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990)), a truxene derivative described in B. The cyclohexane derivatives described in the research report of Kohne et al. (Angew. Chem. 96, 70 (1984)) and M.M. Lehn et al. (JCS, Chem. Commun., 1794 (1985)), J.C. Azacrown-type and phenylacetylene-type macrocycles described in the research report of Zhang et al. (J. Am. Chem. Soc. 116, 2655 (1994)) are included.

As the discotic liquid crystalline compound, for example, a discotic liquid crystalline compound can be used. The discotic liquid crystalline compound also includes a compound having a structure in which a linear alkyl group, an alkoxy group, and a substituted benzoyloxy group are radially substituted as a side chain of the mother nucleus with respect to the mother nucleus at the center of the molecule. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation. The optically anisotropic layer formed from the discotic liquid crystalline compound does not necessarily require that the compound finally contained in the optically anisotropic layer is a discotic liquid crystalline compound. Also included are compounds having a group that reacts with heat or light and, as a result, polymerized or cross-linked by reaction with heat or light, resulting in a high molecular weight and loss of liquid crystallinity. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206. The polymerization of discotic liquid crystalline compounds is described in JP-A-8-27284.

In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula (5).

General formula (5)
D (-LQ) _r
(In the general formula (5), D is a discotic core, L is a divalent linking group, Q is a polymerizable group, and r is an integer of 4 to 12.)
An example of the disk-shaped core (D) is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q).

In the general formula (5), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. It is preferable that it is a bivalent coupling group. The divalent linking group (L) is a divalent combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, —CO—, —NH—, —O—, and —S—. More preferably, it is a linking group. The divalent linking group (L) is most preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, —CO— and —O— are combined. . The number of carbon atoms of the alkylene group is preferably 1-12. The alkenylene group preferably has 2 to 12 carbon atoms. The number of carbon atoms in the arylene group is preferably 6-10.

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (Q). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group).

L1: -AL-CO-O-AL-,
L2: -AL-CO-O-AL-O-,
L3: -AL-CO-O-AL-O-AL-,
L4: -AL-CO-O-AL-O-CO-,
L5: -CO-AR-O-AL-,
L6: -CO-AR-O-AL-O-,
L7: -CO-AR-O-AL-O-CO-,
L8: -CO-NH-AL-,
L9: -NH-AL-O-,
L10: —NH—AL—O—CO—,
L11: -O-AL-,
L12: -O-AL-O-,
L13: -O-AL-O-CO-,
L14: -O-AL-O-CO-NH-AL-,
L15: -O-AL-S-AL-,
L16: -O-CO-AL-AR-O-AL-O-CO-
L17: -O-CO-AR-O-AL-CO-,
L18: —O—CO—AR—O—AL—O—CO—,
L19: -O-CO-AR-O-AL-O-AL-O-CO-,
L20: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-,
L21: -S-AL-,
L22: -S-AL-O-,
L23: -S-AL-O-CO-,
L24: -S-AL-S-AL-,
L25: -S-AR-AL-.

The polymerizable group (Q) of the general formula (5) is determined according to the type of polymerization reaction. Examples of the polymerizable group (Q) are shown below.

The polymerizable group (Q) is preferably an unsaturated polymerizable group (Q1, Q2, Q3, Q7, Q8, Q15, Q16, Q17) or an epoxy group (Q6, Q18). More preferably, it is most preferably an ethylenically unsaturated polymerizable group (Q1, Q7, Q8, Q15, Q16, Q17). A specific value of r is determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and Q may differ, it is preferable that it is the same.

In the hybrid alignment, the angle between the major axis (disk surface) of the discotic liquid crystalline compound and the surface of the support, that is, the inclination angle is in the direction of the depth of the optically anisotropic layer (that is, perpendicular to the transparent support). And it increases or decreases as the distance from the plane of the polarizing film increases. The angle preferably increases with increasing distance. Further, the change in the tilt angle can be continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, or intermittent change including increase and decrease. . The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if a region where the angle does not change is included, it may be increased or decreased as a whole. However, it is preferred that the tilt angle changes continuously.

The average direction of the major axis (disk surface) of the discotic liquid crystalline compound (average of the major axis direction of each molecule) is generally selected by selecting the discotic liquid crystalline compound or the material of the alignment film, or selecting the rubbing treatment method. By doing so, it can be adjusted. The major axis (disk surface) direction of the discotic liquid crystalline compound on the surface side (air side) is generally adjusted by selecting the type of additive used together with the discotic liquid crystalline compound or the discotic liquid crystalline compound. be able to.

Examples of the additive used together with the discotic liquid crystalline compound include a plasticizer, a surfactant, a polymerizable monomer, and a polymer. The degree of change in the orientation direction of the major axis can also be adjusted by selecting liquid crystalline molecules and additives as described above.

The plasticizer, surfactant and polymerizable monomer used together with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound, and can change the tilt angle of the discotic liquid crystalline compound or change the orientation. It is preferable not to inhibit. Among the additive components, addition of a polymerizable monomer (eg, a compound having a vinyl group, a vinyloxy group, an acryloyl group and a methacryloyl group) is preferable. The amount of the above compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline compound. In addition, when a monomer having 4 or more polymerizable reactive functional groups is mixed and used, adhesion between the alignment film and the optically anisotropic layer can be improved.

The optically anisotropic layer may contain a polymer together with the discotic liquid crystalline compound. The polymer preferably has a certain degree of compatibility with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound. A cellulose ester can be mentioned as an example of a polymer. Preferable examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose and cellulose acetate butyrate. In order not to inhibit the orientation of the discotic liquid crystalline compound, the amount of the polymer added is preferably in the range of 0.1 to 10% by mass, preferably 0.1 to 8% by mass with respect to the discotic liquid crystalline compound. More preferably, it is in the range of 0.1 to 5% by mass.

Aligned liquid crystalline molecules can be fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.

Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin compounds ( US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), Phenazine compounds (described in JP-A-60-105667 and US Pat. No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970) are included.

The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.

It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules. The irradiation energy is preferably in the range of ^{20mJ / cm 2 ~ 50J / cm} 2, more preferably in the range of ^{20mJ / cm 2 ~ 5000mJ / cm} 2, a range of ^{100mJ / cm 2 ~ 800mJ / cm} 2 More preferably. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.

Hereinafter, the features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention should not be construed as being limited by the specific examples shown below.
[Example A]
As the transparent film 16, a 2 weight percent solution of a long chain alkyl-modified bhopal [MP-203, manufactured by Kuraray Co., Ltd.] on triacetyl cellulose (Fujitack, manufactured by Fuji Film Co., Ltd.) having a width of 1000 mm and a thickness of 80 μm. After applying a predetermined amount, a film formed by drying to form an alignment film resin layer was used.

While the transparent film 16 on which the alignment film resin was formed was run at 30 m / min, a rubbing treatment was performed on the surface of the alignment film resin layer to form an alignment film. On the obtained alignment film, the coating liquid for optical anisotropic layer below is rotated continuously with the alignment film surface of the roll film by rotating the wire bar # 3.2 in the same direction as the running direction of the transparent film 16. Was applied. And after heating from room temperature to 100 degreeC continuously and drying a solvent, in the heating apparatus 30, the film surface wind speed which hits a discotic liquid crystalline compound layer will be 1.5 m / sec in parallel with a film running direction. Thus, the liquid crystal forming temperature T1 (° C.) shown in Table 1 below was heated for a predetermined time t (seconds). Thereby, the discotic liquid crystalline compound was aligned.

Next, the coating layer on the transparent film 16 is irradiated with ultraviolet rays having an illuminance of 600 mW for 4 seconds by an ultraviolet irradiation device (ultraviolet lamp 32: output 160 W / cm, light emission length 1.6 m), and the crosslinking reaction is allowed to proceed. The liquid crystal compound was fixed to the orientation. Then, it stood to cool to room temperature, and obtained the optical compensation sheet in which the optically anisotropic layer was formed. The thickness of the optically anisotropic layer was 1.3 μm.

<Composition of coating liquid for optically anisotropic layer>
The following composition was dissolved in 107 parts by mass of methyl ethyl ketone to prepare a coating solution.

Discotic liquid crystalline compound TE-8: 41.01 parts by mass Ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.): 4.06 parts by mass Cellulose acetate butyrate (CAB551-0. 2, Eastman Chemical Co., Ltd.): 0.9 parts by mass Cellulose acetate butyrate (CAB531-1, Eastman Chemical Co., Ltd.): 0.21 parts by mass Fluoro aliphatic group-containing polymer (Megafac F780, Dainippon Ink ( Co., Ltd.): 0.14 parts by mass Photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.): 1.35 parts by mass Sensitizer (Kayacure-DETX, manufactured by Nippon Kayaku Co., Ltd.): 0 .45 parts by mass In this example, the liquid-liquid crystal phase transition temperature of the coating liquid for the optically anisotropic layer is determined in advance by the following method. Asked.
<Measurement method of liquid-liquid crystal phase transition temperature>
The optically anisotropic layer coating solution was spin-coated on a transparent glass substrate to a thickness of 5 μm to prepare a sample plate. This sample plate was observed with a polarizing microscope while raising the temperature, and the temperature at which the light leakage from the sample plate occurred was defined as the liquid-liquid crystal phase transition temperature. The liquid crystal-liquid phase transition temperature (T2) of the coating liquid for optically anisotropic layer in this example was measured and found to be 140 ° C.

The optical compensation sheet thus obtained was sampled to a predetermined size, and the orientation was evaluated using (... apparatus name). That is, the evaluation was made according to the following three stages according to the number of schlieren defects within 1 mm square of the optical compensation sheet.

○: The number of schlieren defects within 1 mm square is 15 or less. Δ: The number of schlieren defects within 1 mm square is 16 or more. × ... The number of schlieren defects within 1 mm square is 26 or more.

As shown in Tests 1 to 4 in Table 1, when the liquid crystal formation temperature is set to 140 ° C. (liquid crystal-liquid phase transition temperature), the alignment does not show in the above heating time range, whereas in Tests 5 to 19 As shown, it was found that when the liquid crystal formation temperature was set to less than 140 ° C., high orientation was exhibited by heating for a predetermined time or longer.

In particular, at 130 ° C and 135 ° C where the liquid crystal forming temperature is the temperature range of the present invention, high orientation is obtained when the heating time is 25 seconds or more, and there is almost no change even if the heating time is further increased. I understood. Furthermore, it has been found that when the liquid crystal forming temperature is 135 ° C., good orientation can be obtained in a shorter time. On the other hand, it was found that when the liquid crystal forming temperature is 125 ° C., a heating time of 45 seconds or more is required to show a certain orientation, and thus productivity is lowered.

From the above, in the heating alignment step, the liquid crystal formation temperature T1 (° C.) is set to a temperature range below and close to the liquid crystal-liquid phase transition temperature, that is, T2-10 ≦ T1 <T2, preferably T2-5 ≦ T1 <T2. As a result, it was confirmed that a constant high orientation was stably obtained in a short time of less than 30 seconds.
[Example B]
Optical composition was the same as in Example A except that the composition of the coating liquid for the optically anisotropic layer was 3.25 parts by mass of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.). A compensation sheet was prepared. In this case, the liquid crystal-liquid phase transition temperature (T2) of the coating solution for the optically anisotropic layer was 150 ° C.

Further, the orientation of the optical compensation sheet was similarly evaluated by changing the liquid crystal formation temperature (T1) and the heating time (t) as shown in Table 2 below. The results are shown in Table 2.

As shown in Tests 1 to 5 in Table 2, when the liquid crystal formation temperature is set to 150 ° C. (liquid crystal-liquid phase transition temperature), the alignment does not show in the above heating time range, whereas in Tests 6 to 15 As shown, it was found that when the liquid crystal formation temperature was set to less than 150 ° C., high orientation was exhibited by heating for a predetermined time or longer.

In particular, when the liquid crystal forming temperature is 140 ° C., which is the temperature range of the present invention, orientation is obtained when the heating time is 25 seconds or more, and almost constant high orientation is obtained after 35 seconds. It was. On the other hand, it was found that when the liquid crystal forming temperature is 130 ° C., a heating time of 65 seconds or more is required to show a certain orientation, and the productivity is lowered.

From the above, in the heating alignment step, the liquid crystal formation temperature T1 (° C.) is set to a temperature range below and close to the liquid crystal-liquid phase transition temperature, that is, T2-10 ≦ T1 <T2, preferably T2-5 ≦ T1 <T2. As a result, it was confirmed that a constant high orientation was stably obtained in a short time of less than 30 seconds.

Claims (8)

1. A step of applying a coating liquid containing a nematic liquid crystalline compound on an alignment film formed in advance on the surface of a traveling long film, and drying the coating layer, followed by heating at a liquid crystal forming temperature T1 (° C.) In the method for producing an optical compensation sheet comprising the steps of orienting the nematic liquid crystalline compound and polymerizing and curing the oriented coating layer,
   The liquid crystal forming temperature T1 (° C.) is in the range of T2-10 ≦ T1 <T2 when the liquid-liquid crystal phase transition temperature of the nematic liquid crystalline compound is T2 (° C.), and the heating time is at least 25 seconds. A method for producing an optical compensation sheet, comprising: maintaining an optical compensation sheet.
2. 2. The method of manufacturing an optical compensation sheet according to claim 1, wherein the liquid crystal forming temperature T1 (° C.) is in a range of T2-5 ≦ T1 <T2, and the heating time is maintained for at least 30 seconds.
3. The method for producing an optical compensation sheet according to claim 1 or 2, wherein the wet thickness of the coating layer is 50 µm or less.
4. The method for producing an optical compensation sheet according to any one of claims 1 to 3, wherein the nematic liquid crystalline compound is a discotic liquid crystalline compound.
5. The step of orienting comprises
   Hot air was blown onto the surface of the coating layer of the long film, and the hot air was discharged on at least one of the upstream side or the downstream side of the same surface on which the blown film was aligned. The method for producing an optical compensation sheet according to any one of claims 1 to 4, wherein an air flow is generated.
6. Measuring the ambient temperature in the vicinity of the coating layer;
   Based on the measured result, a step of controlling the temperature of hot air sprayed on the coating layer so that the ambient temperature becomes the liquid crystal formation temperature;
   The method for producing an optical compensation sheet according to claim 5, comprising:
7. The method for producing an optical compensation sheet according to claim 5 or 6, wherein the airflow along the running direction of the long film has a wind speed of 20 m / sec or less.
8. An optical compensation sheet produced by the method for producing an optical compensation sheet according to any one of claims 1 to 7.

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