Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2002-11-05
2003-09-23
Huff, Mark F. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C349S117000
Reexamination Certificate
active
06623811
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to such a film employed in a liquid crystal display as a protective film, view angle enlarging film, an optically anisotropic film such as a phase difference film, a polarizing plate employing film, and a liquid crystal display.
A liquid crystal display operates at low voltage as well as low power consumption, and further, can be directly connected to an IC circuit. Specifically, it is possible to decrease its thickness. As a result, it is widely employed in word processors, personal computers, and the like, as the display. The basic structure of said liquid crystal display is such that polarizing plates are provided on the both sides of the liquid crystal cell.
In such liquid crystal displays, from the viewpoint of contrast and the like, those employing a twisted nematic liquid crystal (TN), having a twist angle of 90 degrees, have been replaced with those employing super twisted nematic liquid crystal (STN) having a twist angle of at least 160 degrees.
However, liquid crystal displays, employing STN, utilize double refraction or birefringence of the liquid crystal. As a result, the following problems which are tinted blue or yellow have occurred. Viewing angle decreases, and it is difficult to produce acceptable color images in TN.
In order to overcome these problems, that is, to compensate for adverse effects due to double refraction, a technique has been proposed in which a phase difference plate is provided under the aforementioned polarizing plate. By employing this technique, the aforementioned tint problem is overcome. However, the viewing angle problem is largely unsolved. Further, a technique has been proposed in which a double refraction film is prepared in which the refractive index in the thickness direction of said film is greater than that in the vertical direction against the optical axis of double refraction, and the resultant film is employed as the phase difference plate. Still further, a technique has been proposed in which one plate having a positive double refraction value and the other plate having a negative refraction value are employed as the phase difference plate, or a multilayer exhibiting such properties is employed as the phase difference plate. Still further, as shown in Japanese Patent Publication Open to Public Inspection No. 7-218724, a polarizing plate is proposed in which at least one of its protective films is a plastic film comprised of acetyl cellulose, having the retardation value of 30 to 70 nm in the in-plane direction when measured employing light having a wavelength of 590 nm.
As methods to overcome these problems, various types of proposals have been made. For example, Japanese Patent Publication Open to Public Inspection No. 63-149624 proposes an F-STN system employing a stretched resin film, and Japanese Patent Publication Open to Public Inspection Nos. 3-87720 as well as 4-333019 proposes a method to carry out color compensation employing a film in which molecules of a liquid crystallizing polymer are subjected to twisted orientation for the purpose of decreasing its weight as well as its wall thickness while maintaining the compensation performance of a D-STN system. The phase deference compensation board of said liquid crystal display is comprised of a transparent base board, an oriented layer formed on said base board, and a liquid crystal polymer layer which is fixed in a twisted orientation state on said oriented layer.
Further, currently, as disclosed in Japanese Patent Publication Open to Public Inspection No. 7-191217, trials to improve the viewing angle of a liquid crystal cell have been carried out as compensation of the viewing angle of a TFT and TN liquid crystal display in such a manner that a discotic liquid crystal film is provided on the upper and lower surfaces of a liquid crystal cell. Said compensation board for the TN type liquid crystal display is comprised of a transparent base board, an alignment layer formed on said base board, and a liquid crystal alignment layer formed on said alignment layer in the same manner as the phase difference compensation board of the liquid crystal display described in the aforementioned Japanese Patent Publication Open to Public Inspection Nos. 3-87720 and 4-333019.
As described above, in recent years, in STN liquid crystal displays, and also in TFT and TN liquid crystal displays, demanded is an optical film having more advanced compensation performance than before. As the means to meet said demand, an optical film, on which a liquid crystal compound is coated, has been investigated.
On the other hand, techniques have been developed in which improvement of a crystal mode makes it possible to improve the viewing angle. For example, Japanese Patent Publication Open to Public Inspection No. 2-176625 discloses a liquid crystal display employing the liquid crystal cell of a vertical alignment (VA) liquid crystal mode which orients a liquid crystal compound vertically during non-application of voltage and substantially orients the same horizontally during application of voltage. The vertical alignment (VA) liquid crystal mode is characterized in having a wider viewing angle and higher speed response compared to the conventional liquid crystal mode. The trial sample of the liquid crystal display of the vertical alignment (VA) liquid crystal mode was already exhibited earlier (based on Nikkei Microdevice No.136, page 147, 1996). The liquid crystal display of the vertical alignment (VA) liquid crystal mode exhibits a wider viewing angle than conventional liquid crystal displays. However, when compared to CRTs, further improvement is required. In order to improve the viewing angle, it is considered to employ an optical compensation sheet in the same manner as the conventional liquid crystal mode.
Said VA type liquid crystal display comprises the liquid crystal cell with a vertical alignment orientation mode in which when no voltage is applied, liquid crystal molecules are oriented vertical to the orientation plate, while when voltage is applied, they are oriented parallel to the orientation plate. As a result, in said liquid crystal display, black is displayed as genuine black, contrast increases, and the viewing angle is relatively wider, compared to the TN and STN types. However, in accordance with an increase in size of a liquid crystal screen, an increase in the viewing angle has been increasingly demanded.
In order to increase the viewing angle of said VA system liquid crystal, the present inventors investigated the protective film for a polarizing plate. During the course of the investigation, it was found that in the VA type liquid crystal display, even though a film, which allows to control the retardation value in the in-plane direction as shown in Japanese Patent Publication Open to Public Inspection No. 7-218724, is employed, the resulting effects were low.
Further, Japanese Patent Publication Open to Public Inspection No. 9-90101 proposes that casting can be carried out without using chlorine based hydrocarbons as the solvent, by increasing the solvent selection range through substituting an acetyl group and a propionyl group of the specified range, and also proposes fatty acid cellulose esters having a low retardation value in both in-plane and thickness directions with the purpose such that the high contrast of liquid crystal displays such as the TFT type and FSTN type in which high contrast has been realized, is not degraded.
Consequently, the investigation regarding a protective film for a polarizing plate was further conducted. As a result, it was discovered that when a film was employed in which the retardation value (Rt value in the aforementioned Formula 1) in the thickness direction which was a value showing anisotropy in the in-plane direction as well as in the thickness direction without employing the conventional retardation value in the in-plane direction in the viewing angle of the VA type liquid crystal display increased. Further, investigation was carried out regarding a method to increase the retardation value i
Honda Makoto
Kawakami Sota
Kubo Nobuo
Kuzuhara Noriyasu
Shibue Toshiaki
Huff Mark F.
Sadula Jennifer R.
LandOfFree
Optical film and liquid crystal display using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical film and liquid crystal display using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical film and liquid crystal display using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074613