Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2000-11-29
2002-10-22
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S588000, C252S589000, C106S171100, C524S100000, C524S325000, C524S351000
Reexamination Certificate
active
06468609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a UV-absorbing cellulose triacetate film (CTA) containing a particular type of UV-absorbing substance.
BACKGROUND OF THE INVENTION
UV-absorbing sheets can be used in a number of applications. For instance, they can be used as UV-cut off films for sunglasses or polarizing glasses, as colour correction filters for recording and printing in colour photography, and for other special uses such as separation filter, masking filter for photomechanical process, and visual sensivity filter. Recently such films have found use as a protective foil for a polarizing plate in a Liquid Crystal Device.
In the field of electronic display systems flat panel displays (FDPs) devices have become of increasing importance and are replacing older technologies such as CRTs especially due to the advent of hand-held, laptop and portable computers. FDPs can be categorized into different types, a recent survey of which can be found in chapter 3 of “Electronic displays”, second edition (1996) by Sol Sherr, edited by J. Wiley and Sons. Among the so-called electroluminescent devices the most successful representative is the light-emitting diode or LED. It is a solid device emitting light upon the application of an electric field. Gas-discharge displays, also called plasma display panels use the ionisation of the gas by the application of a field across the gas and radiative recombinations of the ions and the electrons. They are used to a considerable extent as displays for portable computers and are among the leading contenders for FDP products. Still other types of flat panel display devices include vacuum fluorescent displays (VFDs), electromagnetic displays (EMDs), incandescent displays (INDs), electrochemical displays (ECDs) and electrophoretic image displays (EPIDs).
However, the most popular and widely accepted type of flat panel display device in recent times is without any doubt the liquid crystal display device or LCD which has become the market leader. Liquid crystal display devices are used nowadays in numerous applications such as clocks, household appliances, electronic calculators, audio equipment, etc. There is a growing tendency to replace cathode ray tubes by liquid crystal display devices being favoured for their smaller volume and lower power consumption. In some applications like e.g. laptop computers and pocket TV's liquid crystal display devices are even without competition.
High definition television in its ultimate version will require screen diagonals exceeding 50 inch (see P. Plezhko in the periodical Information Display September 1991, Vol. 7 no. 9, p. 19 a.f.). Although not yet in existence CRT-based 50 inch screens can be expected to be very impractical because of their weight and size. Liquid crystal technology is basically able to produce high definition television (HDTV) screens with moderate weight and size.
Liquid crystal display devices generally include two parallel spaced glass panels connected to each other, which define a sealed cavity, which is filled with a liquid crystal material. The liquid crystals exhibit a specific geometrical molecular orientation depending on their type that can be changed under influence of an electric field. The glass plates are each covered with a transparent electrode layer facing the cavity which may be patterned in such a way that a mosaic of picture elements (pixels) is created or that a defined electronic pattern is created e.g. having a defined alpha-numerical shape. Finally the front and rear glass plates are at the outside covered with light polarizing elements. As a result of change in the geometrical orientation of the liquid crystal molecules due to an applied electric voltage difference between the electrodes the light transmittance properties of a background illumination source are simultaneously changed.
In general, there are from a chemical point of view two important types of polarizers, iodine type (I-type) and chromophore or dye type polarizers. The dye types (D-type) are in general stretched poly(vinyl alcohol) films comprising a diazo compound. They are more stable against humidity and heat than the I-type sheets which on the other hand show a higher transmittance. However, both types are extremely sensitive to deterioration by UV radiation so that they have to be shielded off completely from UV by means of a UV-cut off protecting sheet. Such a protective polymeric sheet can furtheron assure protection against mechanical damage, evenness of surface, and little change of dimension depending on variation of temperature and humidity.
According to recent patent publications cellulose triacetate film in which a UV-absorbing compound is incorporated is a preferred polymeric material for use as protective element for polarizers in a LCD. Cellulose triacetate is apparently preferred because it has a high transparency, is optically isotropic, has good adhesion to the polarizing plate and a little change of dimension depending on variation of temperature and humidity. For instance, unexamined Japanese patent publications JP-A 10-237186, 10-152568 and 7-11056 disclose benzotriazole derivatives as UV absorbers in cellulose triacetate sheets for the latter purpose. JP-A 08-134241 describes a benzophenone derivative as UV-absorber in cellulose triacetate. JP-A 08-239509, equivalent to U.S. Pat. No. 5,806,834, discloses UV-cut off polymeric films comprising R1R2NCR3:CR4CR5:CXY compounds as UV absorbers and their use in polarizers of LCD's. Furtheron, benzophenone compounds, salicylate compounds and benzotriazole compounds have been described in UV absorbing sheets in JP-A 05-265078.
However, the UV absorbing films as described in prior art exhibit several drawbacks. For instance, the gradient in their transmittance curve (the rise of the curve) is not steep enough around 400 nm. Such a film shows a yellow hue and/or an incomplete cut off of UV.
The present invention extends the teachings on polymeric films comprising an UV absorber, and their use as protective sheet for a polarizer in a LCD.
OBJECTS OF THE INVENTION
It is the object of the invention to provide an ultraviolet-absorbing polymer film capable of transmitting almost thoroughly light in a wavelength region of longer than 400 nm and cut off almost thoroughly light in a wavelength region shorter than 400 nm.
It is a further object of the present invention to provide a polarizer element efficiently protected by such a UV-absorbing polymer film.
It is still a further object of the present invention to provide an LCD comprising polarizers protected against deterioration by UV-radiation.
SUMMARY OF THE INVENTION
The above mentioned objects are realised by providing a cellulose triacetate film comprising a UV absorber according to general formula (I)
wherein Z represents 4-alkoxy-2-hydroxyphenyl which can be further substituted,
Ar represents substituted or unsubstituted aryl, and
R represents alkyl, aryl, alkoxy, aryloxy, alkylthio or arylthio, each of which can be further substituted.
The invention further encompasses polarizing elements protected by such CTA films, and LCD devices comprising such polarizers.
Further advantages and embodiments of the present invention will become apparent from the following description.
DETAILED DESCRIPTION OF THE INVENTION
The synthesis of 2-hydroxyphenyl-s-triazines is disclosed in U.S. Pat. No. 3,896,125.
The most preferred 4-alkoxy-2-hydroxyphenyl-s-trazine UV-absorbers used in accordance with the present invention are following compounds:
Other useful UV-absorbers include
The cellulose triacetate film of the invention is capable of transmitting almost all light in a wavelength region of longer than approx. 400 nm and cutting off almost all light in a wavelength region of not longer than approx. 400 nm, and further its transmittance curve steeply rises around 400 nm. Hence, the polymer film can be suitably employed as a protective film for a polarizing plate showing excellent light resistance.
Furtheron, the film of the invention can be utilized, optionally in combination wi
Mariën August
Moeyersons Bart
Agfa-Gevaert
Dawson Robert
Guy Joseph T.
Nexsen Pruet Jacobs & Pollard LLC
Zimmer Marc S
LandOfFree
UV-absorbing film and its use as protective sheet does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with UV-absorbing film and its use as protective sheet, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and UV-absorbing film and its use as protective sheet will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2999735