Method for manufacturing a conductive polymer film

Details Method for manufacturing a conductive polymer film Method for manufacturing a conductive polymer film

2000-02-04

2001-10-30

Cameron, Erma (Department: 1762)

Coating processes

Electrical product produced

C427S385500

Reexamination Certificate

active

06309694

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of manufacturing a conductive polymer film, and in particular, to a method for forming, a conductive polymer film directly from a solution.
BACKGROUND OF THE INVENTION
Recently, a great deal of research has been made for conducting polymers. These polymers have both metallic and polymeric properties and thus have electric conductivity. Due to this advantageous characteristic of conducting polymers, their utilities are very wide and have an indefinite potential for application in various industrial fields.
In electronic/electric component fields, conducting polymers have been applied to an electrolytic capacitor, an electric dual layer condenser, a switching device, a non-linear device, a field effect transistor, a photo-recording material, a display device, an anisotropic conducting sensor and other components, and research is continuously performed for further application of those conducting polymers.
In order for a polymer to show electric conductivity, it should undergo a doping process. Various doping processes can be used for doping on a polymer. In particular, protonic acid doping phenomena were first observed from polyacetylene, and thereafter it has been found that if an organic compound containing different species of elements, such as polyaniline, polypyrrole and etc., was treated with a protonic acid, their electric and magnetic properties would be significantly changed.
Among various conducting polymers, protonic acid doping for polyaniline, which is stable in the air and can be easily produced, has been widely researched. The conductivity of polyaniline synthesized chemically or electrochemically may be also changed by its pH. It may show a very wide range of conductivity values with respect to the pH, such as about 5 S/cm for pH=−1~+1, while about 10
−10
S/cm for pH=5~6.
Since such a conducting polymer is hardly dissolved in a solvent after protonic acid doping, many problems are raised in treating or applying it.
Recently, it has been found that conducting polymer films can be formed from an organic acid doped polyaniline solution, and they show the conductivity of about 100 to 400 S/cm.
However, because those films may be formed from various organic acids, they are very brittle and the effect of aging on their electric conductivity is very severe. Indeed, since organic acids and solvents used in forming those films do not have an environmental affinity, many problems occur in treating or in using them.
According to a conventional method of a conducting polymer, a polymer is prepared in non-conducting powder or film form and then chemically treated in a certain manner to show conductivity.
Conducting polymers produced in this way will exhibit different conductivities in terms of chemical agents used in producing them, in concentrations thereof, and in treating processes employed. However, once they have an electrically conducting property, their workability rapidly deteriorates, thereby making it impossible to use them in a desired purpose or shape.
SUMMARY OF THE INVENTION
In order to solve the above problems, the disclosed embodiments of the present invention provide a method for manufacturing a conducting polymer film, by dissolving a dopant in a solution containing a dopant already dissolved therein, and then forming a conducting polymer film from the solution, whereby the resultant conducting polymer has excellent workability, so that the electronic/electric components using the conducting polymer film can be suitably fitted for the purpose of using them in various fields.
In order to achieve the foregoing, the embodiments of the present invention provide a method for manufacturing a conducting polymer comprising the steps of: solving a lithium salt in an organic solvent; after the lithium salt is completely dissolved in the organic solvent, solving a conducting polymer in the organic solvent while adding the conducting polymer little by little in many separate doses into the organic solvent until obtaining a deep blue colored solution; leaving the deep blue colored solution as it stands over seven days and coating it on a flat surface; and evaporating the solvent from the coated solution.
According to another aspect of the present invention, the organic solvent preferably consists of a polarized matter that can dissolve both a lithium salt and a conducting polymer.
In particular, it is preferable that the organic solvent consists of N-methyl-2-pyrrolidinone (NMP).
In order to achieve the foregoing more effectively, the concentration of lithium salt dissolved in the step of dissolving salt is 0.3 to 0.01 moles.
Furthermore, the lithium salt may be selected from the group consisting of LiClO
4
, LiPF
6
, LiBF
6
, LiAsF
6
, LiCF
3
SO
3
, LiN(CF
3
SO
2
)
2
, LiC(CF
3
SO
2
)
3
and a combination thereof.
According to a further aspect of the present invention, it is preferred that the lithium salt be completely dissolved in the step of dissolving lithium salt by stirring the lithium salt using a magnetic stirrer within a drying box for about one hour.
Also, the conducting polymer used in the above method may be selected from the group consisting of polyaniline, polypyrrole, polythiophene, derivatives of these polymers, and a combination thereof.
In the above method, the step of dissolving a conducting polymer may consist of adding and dissolving the polymer in many separated doses, each of which is 1 to 10 wt %, preferably about 3 wt %, over 1.5 hours and then stirring it for 3 hours using a magnetic stirrer.
The above method may further comprise a step of filtering a deep blue colored solution obtained in the step of dissolving a conducting polymer using a filter paper to remove residually undissolved polymer particles before the step of leaving the deep blue colored solution as it stands.
In the evaporating step, the solvent of the solution coated on the flat surface at a certain thickness is evaporated at the temperature of about 80° C. raised by solution evaporation-drying method or spin coating method for 3 to 4 hours.
The method according to the present invention may further comprise a step of dual doping a protonic acid on the conducting polymer to improve conductivity. It is preferred that the protonic acid is HCl.
According to another aspect of the present invention, there is provided a method for manufacturing a conducting polymer film showing different conductivities at its opposite surfaces, comprising the steps of: solving a lithium salt in a organic solvent, adding and dissolving conducting polymer little by little in many separate doses in the organic solvent containing the dissolved lithium until obtaining deep blue colored solution; coating the obtained deep blue colored solution on a flat surface to obtain the film with a desired thickness; and raising the temperature of the flat surface to 70° C. and continuously heating it for 10 to 15 hours, thereby obtaining a conducting polymer film having different conductivities at its opposite surface.
In the polymer film obtained from this method, the surface in contact with the flat surface is more conductive than the other surface exposed in the air.


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