Patent Application
20100085531
1. Field of the Invention
The present invention relates to a liquid crystal molecule and to a liquid crystal material, a liquid crystal display device and a liquid crystal optical spatial modulation device each using the liquid crystal molecule.
2. Description of the Related Art
In recent years, a liquid crystal display device (LCD) of an active matrix driving type such as a TFT (thin film transistor) has been widely used over the range of from small mobile uses to large television sets.
In the LCD, techniques such as impulse driving have been being adopted, thereby attempting to realize a high response speed. However, it is the actual situation that the LCD is inferior to a plasma display (PDP), a field emission display (FED) and the like in display quality regarding dynamic images due to, for example, dynamic image blur to be caused by a slow response speed of a liquid crystal material itself.
Meanwhile, attempts have also been being made to increase a speed of the current 60 Hz frame rate drive to 120 Hz or 240 Hz (high frame rate drive), thereby enhancing the dynamic image display quality. Though the dynamic image display quality in the LCD partly depends upon the driving system including a TFT, it depends mostly on the response characteristics of the liquid crystal material itself. Namely, the foregoing problem may not radically be solved, and the high frame rate drive may not be realized, unless the liquid crystal material is responsible to a high speed.
In the light of the above, it is the situation that a liquid crystal material which can cope with the high frame rate drive and which can exhibit high-speed response permitting realization of a high dynamic image display quality is keenly demanded.
As a liquid crystal capable of realizing high-speed response, a nematic liquid crystal attended by a flexoelectric effect, a ferroelectric liquid crystal, an antiferroelectric liquid crystal and the like are known. The present inventors have paid attention to an electroclinic effect in a smectic A phase.
The electroclinic effect is a phenomenon in which in a smectic A phase, optical axes of liquid crystal molecules uniaxially aligned (liquid crystal molecule longitudinal axes) are inclined according to an intensity of an impressed electric field (see Garoff, et al., Physical Review Letters, Vol. 38, 1977, page 848). When this type of cell is disposed between orthogonal polarizing plates, a transmitted light quantity according to an angle (tilt angle) formed by an optical axis of the polarizing plate and an optical axis of the liquid crystal is obtained (see the following expression (A)), and a maximum transmittance is obtained at a tilt angle of ±45°.
T/T
o=sin2(2θ)×sin2(nΔnd/λ) (A)
Here, T represents a transmitted light quantity; To represents an incident liquid quantity; θ represents an angle (tilt angle) formed an optical axis of the polarizing plate and an optical axis of the liquid crystal; Δn represents a birefringence of the liquid crystal; d represents a thickness of the liquid crystal layer; and λ represents a wavelength of the transmitted light.
Results obtained by calculating the dependency of the transmittance on the tilt angle in case of a retardation (=Δnd) giving a maximum transmittance according to the foregoing expression (A) are shown in
A response time in the electroclinic effect is very fast as from several μseconds to several tens μseconds. Also, there is a merit that in a low electric field intensity, an inclination angle (tilt angle) of the optical axis is proportional (i.e., voltage modulation of transmitted light is possible). That is, it may be said that this is a display mode which is very suited for the active matrix driving.
However, so far, the temperature range where a smectic A phase where an electroclinic effect is revealed is displayed is relatively high so that there is produced a problem in practical use. Thus, it is desirable to realize a low temperature.
For example, Naciri, et al., Chem. Mater., 1995, 7, pages 1397 to 1402 discloses a liquid crystal material showing a large tilt angle. However, since the temperature range of its smectic A phase is from 23° C. to 55° C., a degree of which is slightly lower than room temperature, it is desirable to realize a low temperature to such an extent that it is thoroughly lower than room temperature.
Also, in the case of taking into consideration driving by a TFT device, since the effective voltage is lowered due to a polarization reversal current, it is preferable that the amount of polarization of a liquid crystal material is small. For that reason, a liquid crystal molecule is required to have a structure of a substituent with relatively low polarity, such as fluorine. However, the temperature range of a smectic A phase of such a structure is very high by substitution with large polarization of, for example, a nitro group as disclosed in Naciri, et al., Chem. Mater., 1995, 7, pages 1397 to 1402, and therefore, it is desirable to realize a low temperature.
Furthermore, JP-A-2008-150334 discloses a liquid crystal molecule having a structure having an asymmetric carbon atom and having a core portion containing a terminal phenyl group and an organosiloxane at positions opposite to each other interposing the asymmetric carbon atom therebetween. However, in this liquid crystal molecule, since the terminal group is an alkoxy-substituted phenyl group, it is not sufficiently satisfactory yet in view of the fact that the temperature range where a smectic A phase is displayed is high. Thus, it is desirable to realize a lower temperature.
It is desirable to provide a liquid crystal molecule having a low temperature range where a smectic A phase is displayed and capable of obtaining sufficient optical modulation.
Also, it is desirable to provide a liquid crystal material, a liquid crystal display device and a liquid crystal optical spatial modulation device each using a liquid crystal molecule having a low temperature range where a smectic A phase is displayed and capable of obtaining sufficient optical modulation.
The present inventors have found that the temperature range where a smectic A phase is displayed is significantly reduced to a low temperature by a compound having a structure in which an organosilane or organosiloxane structure is added to one of chiral ends having an asymmetric carbon atom, and a terminal phenyl group substituted with a hydrocarbon group is disposed in the other chiral end, namely a structure in which a functional group is bonded to a core portion via a C—C bond and made extensive and intensive investigations on the basis of this finding, leading to accomplishment of the present invention.
According to an embodiment of to the present invention, there is provided a liquid crystal molecule having a structure represented by the following general formula (1).
In the general formula (1), X1 is a group selected among groups represented by the following formula (2).
In the general formula (1), X2 is a group selected among groups represented by the following formula (3).
In the general formula (1), X3 is represented by the following formula (4).
In the formulae (1) to (4), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; R2 represents an optionally branched organosiloxane or organosilane having from 1 to 6 silicon atoms; and R3 and R4 are different from each other and each represents H, F, Cl, Br, CN, CH3, CF3 or OCH3.
Y1 and Y2 each represents —, —COO—, —CH2—, —CH2O—, —C2H2—, —C2— or —CF2O—.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; * represents a chiral center; and — means a connecting group.
According to another embodiment of the present invention, there is provided a liquid crystal molecule having a structure represented by the following general formula (5).
In the formula (5), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; and R13 represents F, Cl, Br, CN, CH3, CF3 or OCH3.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; m represents an integer of from 1 to 5; and * represents a chiral center.
According to a further embodiment of the present invention, there is provided a liquid crystal material including a liquid crystal molecule having a structure represented by the following general formula (5) and a liquid crystal molecule having a structure represented by the following general formula (6).
In the formulae (5) and (6), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; and R13 represents F, Cl, Br, CN, CH3, CF3 or OCH3.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; m represents an integer of from 1 to 5; and * represents a chiral center.
According to a yet another embodiment of the present invention, there is provided a liquid crystal display device including a pair of transparent substrates; a liquid crystal layer provided between the pair of substrates and having filled therein the liquid crystal molecules according to the embodiment of the present invention which display a smectic A phase where they are uniaxially aligned; and electrodes provided on the substrates, wherein a transmittance of the liquid crystal layer is regulated by inclining a longitudinal axis of the liquid crystal molecules through impression of an electric field on the liquid crystal layer from the electrodes.
According to an even another embodiment of the present invention, there is provided a liquid crystal optical spatial modulation device including a pair of transparent substrates; a liquid crystal layer provided between the pair of substrates and having filled therein the liquid crystal molecules according to the embodiment of the present invention which display a smectic A phase where they are uniaxially aligned; and electrodes provided on the substrates, wherein spatial modulation regarding light transmitting through the liquid crystal layer is carried out by impressing an electric field on the liquid crystal layer from the electrodes.
In accordance with the embodiments of the present invention, there is provided a liquid crystal molecule displaying a smectic A phase as a liquid crystal molecule in a temperature range for use and having a large tilt angle in an electroclinic effect, from which sufficient optical modulation for use in a liquid crystal display device and a liquid crystal optical spatial modulation device is obtainable.
In accordance with the embodiments of the present invention, there is provided a liquid crystal display device which is excellent in dynamic image display quality, bright and high in gradation properties and contrast. For example, the liquid crystal display device is applicable to a direct view type LCD or a projection display micro liquid crystal device (for example, LCoS (liquid crystal on silicon) and high-temperature polysilicon TFT-LCD). Also, in particular, it is possible to realize a color display device by field sequential driving using color sequential backlight illumination.
In accordance with the embodiments of the present invention, there is provided a high-speed optical spatial modulation device capable of achieving three-dimensional display and the like.
A liquid crystal molecule according to an embodiment of the present invention is hereunder described.
First of all, the liquid crystal molecule according to the embodiment of the present invention has a structure represented by the following general formula (1).
In the general formula (1), X1 is a group selected among groups represented by the following formula (2).
In the general formula (1), X2 is a group selected among groups represented by the following formula (3).
In the general formula (1), X3 is represented by the following formula (4).
In the formulae (1) to (4), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; R2 represents an optionally branched organosiloxane or organosilane having from 1 to 6 silicon atoms; and R3 and R4 are different from each other and each represents H, F, Cl, Br, CN, CH3, CF3 or OCH3.
Y1 and Y2 each represents —, —COO—, —CH2—, —CH2O—, —C2H2, —C2— or —CF2O—.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; * represents a chiral center; and — means a connecting group.
Also, it is more preferable that the liquid crystal molecule according to the embodiment of the present invention has a structure represented by the following general formula (5).
In the formula (5), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; and R13 represents F, Cl, Br, CN, CH3, CF3 or OCH3.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; m represents an integer of from 1 to 5; and * represents a chiral center.
Here, the liquid crystal molecule according to the embodiment of the present invention forms a smectic liquid crystal layer and preferably displays a smectic A phase in a temperature region where a liquid crystal displayer device or a liquid crystal optical spatial device is used, for example, from 20 to 50° C. The smectic liquid crystal layer is a liquid crystal layer in which the longitudinal axis directions of the liquid crystal molecules are aligned in a layer form (smectic layer). The term “smectic A phase” as referred to herein means that in such a liquid crystal layer, the normal line direction of the liquid crystal layer coincides with the longitudinal axis direction of the liquid crystal molecules.
Also, the liquid crystal material according to the embodiment of the present invention is a liquid crystal material including a liquid crystal molecule having a structure represented by the following general formula (5) and a liquid crystal molecule having a structure represented by the following general formula (6).
Here, in the liquid crystal material according to the embodiment of the present invention, it is preferable that the liquid crystal molecule having a structure represented by the following general formula (5) and the liquid crystal molecule having a structure represented by the following general formula (6) are incorporated in a weight ratio of from 1/1 to 1/5.
In the formulae (5) and (6), R1 represents a linear or branched hydrocarbon group having from 4 to 16 carbon atoms; and R13 represents F, Cl, Br, CN, CH3, CF3 or OCH3.
Z1 and Z2 each represents H, F, Cl, Br, OH, NO2, CN or CF3; Z3 and Z4 each represents H, F, Cl, Br, OH, NO2, CN or CF3; and Z5 and Z6 each represents H, F, Cl, Br, OH, NO2, CN or CF3, provided that Z5 and Z6 do not represent H at the same time.
n represents an integer of from 1 to 6; m represents an integer of from 1 to 5; and * represents a chiral center.
Next, the configuration of a liquid crystal display device according to an embodiment of the present invention is described. The liquid crystal display device as referred to herein means a so-called direct view type display device such that the display device using a liquid crystal material is viewed directly by a viewer.
As shown in
The TFT array substrate 1 and the counter substrate 2 are stuck to each other with a sealing material, and a liquid crystal layer 3 composed of a liquid crystal mixture (liquid crystal material) including the liquid crystal molecule according to the embodiment of the present invention is sealed in a gap between the TFT array substrate 1 and the counter substrate 2 via a non-illustrated alignment film and interposed therebetween. At that time, the liquid crystal molecules according to the embodiment of the present invention display a smectic A phase where the liquid crystal molecules are uniaxially aligned.
In the foregoing liquid crystal display device, a backlight unit such as an LED is provided on the back side. In the liquid crystal display device according to the embodiment of the invention, the transmission of light from the backlight unit can be regulated by varying the inclination (tilt angle) of the liquid crystal molecule by a voltage to be impressed between the pixel electrode 11 and the counter electrode 21 (by an electroclinic effect) to control a transmittance. Thus, in the liquid crystal display device according to the embodiment of the present invention, an image with gradation can be displayed.
As for a driving system in relation to an image signal, for example, a 1H reversal driving system (H means a horizontal scanning period) or a 1F reversal driving system (F means a field) or the like can be adopted. In such alternating current driving, the color level (gradation) of the liquid crystal can be varied by a height (magnitude of amplitude) of a driving voltage. In particular, at that time, the contrast of an image to be displayed can be further increased by increasing the driving voltage.
In the liquid crystal display device according to the embodiment of the present invention, since the liquid crystal molecule according to the embodiment of the invention is used, it is possible to display an image which is excellent in dynamic image display quality, bright and high in gradation properties and contrast.
Next, the configuration of a liquid crystal optical spatial modulation device according to an embodiment of the present invention is described.
The liquid crystal optical spatial modulation device as referred to herein means a device for planarly splitting light from a light source and varying the intensity, phase or the like of each of the individual light beams thus obtained. This liquid crystal optical spatial modulation device includes a micro-display (LCoS) or light valve used in a projector display, or a phase modulation device such as a light deflection switch. As a specific example of the light valve, the liquid crystal display device shown in
As shown in
Liquid crystal molecules 34 according to the embodiment of the present invention are sealed between the transparent substrates 31a and 31b. The liquid crystal molecules 34 display a smectic A phase in the use environment for the liquid crystal optical spatial modulation device and are aligned vertically to the principal surfaces of the transparent substrates 31a and 31b in a state where an electric field is not impressed by the action of the vertical aligning agent.
In the liquid crystal optical spatial modulation device, an incident light L is made incident in parallel to the normal line of the substrate (vertically to the substrate) from the side of the substrate 31a. The incident light L is deflected by an electric field to be impressed between the electrodes 32a and 32b into a direction orthogonal to the electric field direction and then emitted. For example, when an electric field E is 0, shifting of the incident light is not generated, whereas when the electric field E is more than 0, the incident light is deflected and shifted into a prescribed direction (+direction) orthogonal to the electric field direction and then emitted. Also, when the electric field E is less than 0, the incident light is deflected and shifted into a reverse direction (−direction) to the direction in the case where the electric field E is more than 0 and then emitted. Also, a shifting amount thereof can be regulated by the intensity of the electric field.
Embodiments according to the present invention are more specifically described below with reference to the following Examples.
A liquid crystal molecule of an embodiment according to the present invention was obtained by the following procedures.
After adding dropwise benzoyl chloride to a pyridine solution of 4,4′-biphenol, the mixture was stirred at room temperature overnight, and the thus obtained deposit was filtered and subjected to column chromatography with a silica gel to obtain 4′-hydroxy-4-biphenyl benzoate.
The thus obtained 4′-hydroxy-4-biphenyl benzoate was dispersed in acetic acid, nitric acid was added dropwise to the dispersion while keeping it at 15° C., and water was further added thereto, followed by stirring. The thus obtained deposit was recrystallized from ethanol/acetic acid to obtain 4′-hydroxy-3′-nitro-4-biphenyl benzoate.
An argon-purged flask was charged with the thus obtained 4′-hydroxy-3′-nitro-4-biphenyl benzoate, triphenylphosphine and a tetrahydrofuran (THF) solution of (S)-5-hexen-2-ol, a THF solution of diethyl azodicarboxylate was added dropwise thereto, and the mixture was stirred at room temperature overnight. After evaporating off the solvent, the residue was subjected to column chromatography to obtain 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-yl benzoate.
A lithium hydroxide aqueous solution was added to a methanol solution of the thus obtained 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-yl benzoate, and the mixture was stirred at room temperature overnight. After evaporating off the solvent, the residue was neutralized with hydrochloric acid, and a desired material was extracted with diethyl ether. Subsequently, after dehydrating the extract with magnesium sulfate, the solvent was evaporated off, and the residue was subjected to column chromatography to obtain 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-ol.
The thus obtained 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-ol, p-dodecylbenzoic acid and a dichloromethane solution of 4-dimethylaminopyridine were added to 1-(3-(dimethylamino)-propyl)-3-ethylcarbodiimide methiodine, and the mixture was stirred at room temperature overnight. Subsequently, the thus obtained solution was washed with water, subjected to liquid separation and then dried over sodium sulfate. After evaporating off the solvent, the residue was subjected to column chromatography to obtain 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-yl 4-(dodecyloxy)benzoate.
Dichloro(dicyclopentadienyl)platinum(II) as a catalyst was added to the thus obtained 4′-{[(R)-1-methyl-4-pentenyl]oxy}-3′-nitro(1,1′-biphenyl)-4-yl 4-(dodecyloxy)benzoate and a THF solution of 1,1,3,3,3-pentamethyldisiloxane, and the mixture was stirred in an argon atmosphere at 60° C. for 24 hours. After evaporating off the solvent, the residue was subjected to column chromatography to obtain 4′-{[(S)-1-methyl-5-(1,1,3,3,3-pentamethyldisiloxanyl)pent yl]-oxy}-3′-nitro[1,1′-biphenyl]-4-yl 4-(dodecyl)benzoate which is a final product (final product 1). A structural formula of each of this final product 1 and final products 2 to 4 as described later is shown below.
The final product 1 displayed a smectic A phase at from 14° C. to 25° C.
Determination of the phase transition temperature and identification of the smectic A phase were carried out by means of differential scanning calorimetry and polarizing microscope observation with a hot stage.
After fabricating a polyimide alignment film on a glass substrate provided with ITO (indium tin oxide), the film was rubbed by a buffed roller, and a cell was prepared by use of an ultraviolet ray-curable resin having dispersed therein silica balls with a diameter of 2.4 μm. Subsequently, the liquid crystal molecule (final product 6) synthesized by the foregoing method was poured into the cell at a temperature for promising an isotropic phase, thereby forming an evaluation cell.
The thus obtained evaluation cell was evaluated as to a maximum tilt angle, a transmittance and a response time.
As to the maximum tilt angle, the evaluation cell was disposed between orthogonal polarizing plates, a transmitted light quantity was measured while impressing a rectangular wave electric field on the cell, and a half of the angle formed between an optical axis of the polarizing plate and an optical axis of the evaluation cell at which a minimum light quantity was given in positive- and negative-polarity electric fields, respectively was designated as a tilt angle.
Also, as to the transmittance, an optical axis of the evaluation cell at the time of impressing no electric field was set so as to coincide with an optical axis of a polarizing plate of a polarizing microscope, a transmitted light quantity upon impressing an electric field giving a maximum tilt angle was measured by a spectrophotometer, and the transmittance was calculated by taking a value with parallel polarizing plate arrangement as 100%.
Also, as to the response time, the same optical disposition as that for the measurement of a transmittance was used, and a rise time in the case where a voltage was impressed stepwise from a zero electric field so as to give a maximum tilt angle was taken as the response time.
Synthesis was carried out in the same manner as in Example 1, except for using a fluorinating agent MEC-31 (manufactured by Daikin Industries, Ltd.) in place of nitric acid, thereby obtaining 4′-{[(S)-1-methyl-5-(1,1,3,3,3-pentamethyldisiloxanyl)pent yl]-oxy}-3′-fluoro[1,1′-biphenyl]-4-yl 4-(dodecyl)benzoate (final product 2).
The final product 2 displayed a smectic A phase at from 52° C. to 65° C.
Synthesis was carried out in the same manner as in Example 1, except for using p-dodecaoxybenzoic acid in place of p-dodecylbenzoic acid, thereby obtaining 4′-{[(S)-1-methyl-5-(1,1,3,3,3-pentamethyldisiloxanyl)pent yl]-oxy}-3′-nitro[1,1′-biphenyl]-4-yl 4-(dodecyloxy)benzoate (final product 3).
The final product 3 displayed a smectic A phase at from 37° C. to 56° C.
Synthesis was carried out in the same manner as in Example 1, except for using a fluorinating agent MEC-31 (manufactured by Daikin Industries, Ltd.) in place of nitric acid, thereby obtaining 4′-{[(S)-1-methyl-5-(1,1,3,3,3-pentamethyldisiloxanyl)pent yl]-oxy}-3′-fluoro[1,1′-biphenyl]-4-yl 4-(dodecyloxy)benzoate (final product 4).
The final product 4 displayed a smectic A phase at from 85° C. to 94° C.
4′-{[(S)-1-Methyl-5-(1,1,3,3,3-pentamethyldisiloxany 1)pentyl]-oxy}-3′-nitro[1,1′-biphenyl]-4-yl 4-(dodecyl)benzoate (final product 1) and 4′-{[(S)-1-methyl-5-(1,1,3,3,3-pentamethyldisiloxanyl)pent yl]-oxy}-3′-nitro[1,1′-biphenyl]-4-yl
4-(dodecyloxy)benzoate (final product 3) were mixed in a weight ratio of 25/75.
The thus obtained mixture displayed a smectic A phase at from 18° C. to 48° C.
A temperature range, a temperature width and a maximum tilt angle of the smectic A phase of each of Examples 1 to 3 and Comparative Examples 1 to 2 are shown in the following Table 1.
Furthermore, by mixing the compound of Example 1 in the compound of Comparative Example 1 (Example 3), the temperature width where a smectic A phase is displayed is widened to 30K including room temperature while keeping a very large maximum tilt angle as 30°.
In the light of the above, according to the embodiment of the present invention, it is possible to realize a liquid crystal molecule having a wide temperature range where a smectic A phase is displayed and exhibiting an electroclinic effect having a large tilt angle, i.e., a large transmittance by a compound having a structure in which an organosilane or organosiloxane structure is added to one of chiral ends having an asymmetric carbon atom, and a terminal phenyl group substituted with a hydrocarbon group is disposed in the other chiral end.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-261263 filed in the Japan Patent Office on Oct. 8, 2008, the entire contents of which is hereby incorporated by reference.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-261263 | Oct 2008 | JP | national |
