Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-11-03
2001-06-19
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S379000, C524S210000, C524S158000
Reexamination Certificate
active
06248818
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Description of the invention
The present invention relates to a polythiophene-based polymer liquid composition, which can be formed into a coating with high conductivity and high transparency. More particularly, the present invention is concerned with the use of an amide solvent and a sulfonic acid group (SO
3
H)-containing monomer dopant in improving the conductivity and transparency of a polythiophene-based polymer liquid composition.
2. Description of the Prior Art
Polyethylenedioxythiophene (PEDT), a conductive polymer, was disclosed as an antistatic property-imparting material, such as an antistatic coating, in U.S. Pat. Nos. 5,035,926 and 5,391,472. Since then, intensive attention has been paid to polymer-based conductive coatings applicable to glass surfaces of Braun tubes.
In terms of electrical conductivity, this conductive polymer has advantages over well-known preexisting polymers, such as polyanilines, polypyrroles and polythiophenes. PEDT also shows excellent processability by virtue of its ability to be easily formed into a coating solution which is dispersible in water, along with salts of polymer acids (e.g., polystyrene sulfonate) as dopants. With this good water dispersibility, PEDT can be well dissolved in alcohol solvents, and the aqueous dispersions find numerous applications in Braun tube (CRT) glasses, plastic film surfaces, etc. The use of water and alcohols as solvents is ecologically very favorable.
Such water-dispersible PEDT polymers are now commercially available, representatively exemplified by Baytron P (Grade A4071) from Bayer.
Highly transparent as they are, conductive PEDT polymers must be coated at low PEDT contents (24% or less based on 1.3 wt % solution) in order to exhibit a transmittance of 92%. Accordingly, it is difficult to achieve a surface resistance of 100 k&OHgr; or less through ordinary techniques. In order to reinforce the strength of PEDT coatings, there is used silica sols prepared from alkoxy silane (e.g., alkyltriethoxysilane), represented by RSi(OR
1
)
3
wherein R is methyl, ethyl, propyl or isobutyl and R
1
is methyl or ethyl. In this case, the conductivity of the resulting coatings is aggravated owing to silica sol. Thus, it is more impossible for existing techniques to produce conductive coatings with a surface resistance of 100 k&OHgr;/□ or less. In fact, current techniques can use PEDT as an antistatic coating material only where low conductivity is required (see technical reference for Baytron P, Bayer).
Therefore, it is virtually impossible for currently prevailing techniques to achieve a transmittance of 92% in addition to a surface resistance of 1 k&OHgr;/□ or less, which satisfies TCO (Tianstemanners Central Organization) Standards for commercially competitive electromagnetic wave-shielding materials.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the problems encountered in prior arts and to provide a highly conductive and transparent polythiophene-based composition with which a coating having a surface resistance of 1 k&OHgr;/□ or less and a transmittance of 92% can be formed on a transparent substrate.
It is another object of the present invention to provide polythiophene-based compositions useful as electromagnetic wave-shielding materials which are applicable for Braun tube surfaces.
Leading to the present invention, the intensive and thorough research on the development of polythiophene-based compositions of high conductivity and transparency, repeated by the present inventor aiming to satisfy the TCO Standards in surface resistance, resulted in the finding that PEDT conductive polymer solutions can be greatly improved in electrical conductivity by the presence of amide-based organic solvents or sulfonic acid-containing monomer dopants, and even more improved by adding the solvents and the dopants in combination than alone.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
In accordance with a first embodiment of the present invention, there is provided a polythiophene-based polymer liquid composition of high conductivity and transparency comprising 16-32 weight % of an aqueous polythiophene-based conductive polymer solution, 56-82 weight % of an alcohol containing 1-4 carbon atoms, 1-12 weight % of an amide solvent, and 0.01-0.2 weight % of a monomer dopant containing a sulfonic acid group, characterized in that it provides a coating which is 1 k&OHgr;/□ or less in surface resistance, 92% or greater in transmittance, and B or smaller in pencil hardness. The composition of the present invention may be coated on transparent substrates which are used where large hardness is not required. If large hardness is necessary, a silica sol solution may be further applied on the coating of the present invention.
When being coated on transparent substrates, such as lass and synthetic plastic films, the composition of the resent invention promises to show a surface resistance of 1 k&OHgr;/□, a transmittance of 90-98%, and a hardness of 2-9 H.
The conductive polymer useful in the present invention is PEDT, such as that commercially available from Bayer, identified as “Baytron P”. Because of being doped with polystyrene sulfonate (PSS), the PEDT polymer is well dissolved in water in addition to exhibiting excellent thermal stability and atmospheric stability. Further, the aqueous polythiophene-based conductive polymer solution was found to maintain optimal water dispersibility when comprising PEDT and PSS at a total solid content of 1.0-1.5 weight %. High solubility in water, alcohol, and solvents of large dielectric constants makes it easy to prepare a coating solution of high coatability. Furthermore, the coatings have a great advantage over those of other conductive polymers, such as polyaniline and polypyrrole, in terms of transparency.
In the polythiophene-based composition, the conductive PEDT polymer is preferably used at an amount of 16-32 weight %. For example, if too little PEDT polymer is used, desired high conductivity, such as a surface resistance of as low as 1 k&OHgr;/□, cannot be achieved no matter how much the amide solvent and the sulfonic acid monomer dopant may be used. On the other hand, an amount greater than 32 weight % causes the resulting coatings to be lower in transmittance than 92% because light is shielded by the characteristic color that the PEDT itself retains.
Serving as a solvent for the conductive PEDT polymer, an alcohol is contained in the composition of the present invention. Useful are alcohols containing 1-4 carbon atoms, exemplified by methanol, ethanol, propanol, isopropanol and butanol. These alcohol solvents may be used alone or in combination. Most preferable is a mixture of two or three alcohols which are different from each other in boiling point. While being vaporized in sequence, the mixed alcohols assure the coating of a highly dispersed state of the PEDT conductive polymer.
Such an alcohol solvent is preferably used at an amount of 56-82 weight %. For example, when the alcohol solvent is used at an amount of less than 56 weight %, the coating is poor in dispersibility. On the other hand, an alcohol amount exceeding 82 weight % brings about a good result in dispersibility, but causes a significant problem in conductivity.
As for the amide solvent useful in the present invention, it is represented by the following formula:
R
1
(CO)NR
2
R
3
wherein, R
1
, R
2
and R
3
, which may be the same or different, each denotes H, CH
3
or —CH
2
CH
2
CH
2
—. Examples of the amide solvents include formamide (FA), N-methylformamide (NMFA), N,N-dimethylformamide (DMF), acetamide (AA), N-methylacetamide (NMAA), N,N-dimethylacetic amide (DMA), N-methylpropion amide (NMPA) and N-methylpyrrolidone.
As well as serve as a solvent in the polythiophene-based polymer solution, the amide compounds, alone or in combination, play a role in increasing conductivity. The increasing effects on conductivity are grouped according to the kinds of amide solvents in Table 1, below.
TABLE 1
Effect o
Chang Tu Won
Cheong Min Kyo
Chung Hae Ryong
Kim Hyun Don
Fish & Richardson P.C.
Rageuru U. K.
Samsung General Chemicals Co. Ltd.
Seidleck James J.
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