Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-12-07
2001-05-22
Cameron, Erma (Department: 1762)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06235827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Description of the invention
The present invention relates to a polymer composition for coatings with high refractivity, conductivity and transparency. More particularly, the present invention relates to the use of an inorganic sol, an amide solvent and a sulfonic acid group (SO
3
H)-containing monomer dopant, in combination, in improving the refractivity, conductivity and transparency of a polythiophene-based polymer composition.
2. Description of the Prior Art
Representative of conductive polymers, polyanilines, polypyrroles, and polythiophenes, collectively called synthetic metal, have been suggested to be applicable for where conductivity and plastic properties are needed, such as electromagnetic wave-shielding materials, electrodes for secondary cells, transparent electrodes, etc, by virtue of their good conductivity and being easily polymerized. However, because they are very difficult to process in addition to being poor in stability against heat, atmosphere and UV light, only a few examples have been proved commercially successful.
Polyethylenedioxythiophene (PEDT), a conductive polymer, was disclosed as an antistaticity-imparting material, such as an antistatic coating, in U.S. Pat. Nos. 5,035,926 and 5,391,472, and its development is now being watched with keen interest because it is evaluated as solving the problems found in the above conductive polymers. With far superiority to polyanilines, polypyrroles and other polythiophene-based compounds in solubility, thermal and atmospheric stability, and resistance to UV light, PEDT can be used as a base material for coatings applicable to externally exposed parts to which the preexisting conductive polymers cannot be applied owing to their poor durability. Doped with a polymeric acid salt (e.g., polystyrene sulfonate), PEDT can be dispersed in water, and the dispersion is of good compatibility with lower alcohols, such as C1-C4 alcohol solvents, which are low in boiling point and ecologically favorable. The dilution in alcohols allows PEDT to be coated in various forms. Particularly, thin films made of such aqueous dispersions find numerous applications in cathode ray tube (CRT) glasses, plastic film surfaces, etc. Such water-dispersible PEDT polymers are now commercially available, representatively exemplified by Baytron P (Grade A4071) from Bayer.
To perfectly perform its characteristic functions, a coating for CRT external surfaces is required to be high in refractive index as well as conductivity. As being eligible for such a coating, inorganic thin films, such as ATO (antimontinoxide) and ITO (indiumtinoxide), have been used. A coating structure on a CRT glass panel is shown in FIG.
1
. As shown in
FIG. 1
, the coating structure on a CRT glass panel
1
is typically composed of two layers: a high refractive, conductive layer
2
and a low refractive layer
3
. Overlaying the conductive layer
2
, the low refractive layer
3
is usually formed of SiO
2
. A display which employs an ATO thin film or an ITO thin film as the conductive layer
2
can reduce the reflected light intensity of incident light on the CRT glass surface through an interference operation. Because the ATO or ITO thin film has a refractive index of 1.6 or higher, the reflected light from the surface of the ATO or ITO thin film shows a phase difference from that from the surface of the low refractive layer. This reflection-attenuating function is indispensable to almost all CRTs for computer monitors, near to which are the eyes of the users.
Details about the materials and structures of the reflection-attenuating coatings can be referred to U.S. Pat. Nos. 5,681,885, 5,572,086, 5,652,477 and 5,523,469.
As for a conventional PEDT conductive coating solution, it has a refractive index of only 1.30-1.40 when being formed into a film, which is even lower than 1.54, the minimal RI value required for CRT glass panels. Thus, superior as they are to the inorganic coatings in conductivity and transparency, conventional PEDT coatings have not been applied to CRT external glasses because of being insufficient in refractive index.
SUMMARY OF THE INVENTION
The intensive and thorough research on PEDT conductive thin films, repeated by the present inventors aiming to develop them for application to CRT glass panels, resulted in the finding that a highly refractive, inorganic sol, a dispersion medium comprising an amide solvent, and a sulfonic acid group (SO
3
H)-containing monomer dopant, in combination, could improve the refractivity, conductivity and transparency of a polythiophene-based polymer composition.
Therefore, it is an object of the present invention to provide a polymer composition, which can be formed into a coating with high refractivity, conductivity and transparency.
Based on the present invention, the object could be accomplished by a provision of a composition comprises 2-20 weight % of an aqueous polythiophene-based conductive polymer solution having a solid content of 1.2-1.5 weight %; 0.5-20 weight % of a highly refractive, inorganic sol solution having a solid content of 14-16 weight %; 50-97.4 weight % of an alcohol containing 1-3 carbon atoms; 0.1-10 weight % of an amide solvent; 0.005-0.1 weight % of a water- or an alcohol-soluble resin binder; and 0.005-0.05 weight % of a sulfonic acid group-containing monomer dopant. A thin film formed by spin- or spray-coating the composition on a transparent substrate and baking the coating, has a refractive index of 1.6-2.0, a transmittance of 90-98% and a surface resistance of 1×10
3
-1×10
8
&OHgr;/□.
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the figures.
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Jonas et al, Macromol. Symp. (1995), pp 169-173, 1994.*
Ghosh et al, Synth. Met. (1999), vol. 101(1-3), pp 413-416.*
Lee et al, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A (1999), vol. 337, pp 213-216.*
Lee et al, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A (1999), vol. 327, pp 237-240.
Chang Tu Won
Cheong Min Kyo
Chung Hae Ryong
Kim Hyun Don
Cameron Erma
Cheil Industries Inc.
Fish & Richardson P.C.
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