Electrically conductive microgel and method for preparing...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C523S137000, C523S201000, C528S378000, C528S422000, C528S423000, C252S500000, C428S407000

Reexamination Certificate

active

06399675

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrically conductive microgel. More particularly, the present invention relates to electrically conductive microgel in which electrically conductive polymers or oligomers can be polymerized on the surface of microgel particles dispersed in an organic solvent, in the presence of a dopant and an oxidative polymerization catalyst, granting excellent conductivity to the microgel Also, the present invention is concerned with a method for preparing such electrically conductive microgel.
2. Description of the Prior Art
A number of applications of electrically conductive polymers for surface tension control, electromagnetic wave shielding, fuel batteries, etc. have been under study. Particularly, polyaniline, polypyrrole, and polythiophene are stable in air with high electrical conductivity. Another advantage of these conductive polymers is that they can be easily synthesized through electrochemical or chemical polymerization. However, films made of the electrically conductive polymers synthesized through electrochemical polymerization, although being constant in electrical conductivity across their surface areas, are greatly limited in uses because they are not easily melted owing to the strong intermolecular attractive force thereof. Powders of the electrically conductive polymers synthesized through chemical polymerization require complicated post-treatment processing for their applications.
Recently, extensive research has been directed to improving the processability of electrically conductive polymers. Preparation of water-soluble multi-component composite particles through chemical polymerization is an example of such research. Korean Pat. Laid-Open Publication No. 99-018821 discloses a method of preparing polyaniline and polypyrrole within ABS emulsion latex while using an organic acid such as dodecylbenzene sulfonic acid or paratoluene sulfonic acid as a dopant and ammonium persulfate as an oxidant. This method, however, is disadvantageous in that, when the monomers are polymerized, the presence of ion groups within the dopant and the emulsifier of the emulsion latex causes the monomers to be in an unstable water dispersion, resulting in undesired precipitation of powder. In turn, this precipitated powder is difficult to form into transparent films as well as requires additional homogenizing processes, such as pulverization and fine dispersion, in order that the powder can be coated on cloth or used in extrusion molding.
U.S. Pat. No. 6,001,549 describes an antistatic composition comprising electrically conductive polymer particles and copolymer microgel particles. The antistatic composition shows good conductivity at relatively low volume fraction of the electrically conductive particles by including microgel particles, which are prepared using an aqueous medium. However, the electrically conductive particles, selected from metal oxides, metal antimonates and ceramic particles, are unsuitable to give transparent or low anti reflective coating films.
U.S. Pat. No. 6,025,462 discloses an electrically conductive dendrimer whose reactive functional groups on its surface are useful to synthesize an electrically conductive polymer for composite particles which have been shown to solve the above problem encountered in the previous patent to some degree. However, the preparation process is too complicated to avoid imposing limitations on its commercialization.
SUMMARY OF THE INVENTION
Leading to the present invention, the intensive and thorough research on electrically conductive microgel, conducted by the present inventors, resulted in the finding that electrically conductive polymers or oligomers can be polymerized in a dispersion of microgel particles in the presence of a dopant and an oxidative polymerization catalyst and adsorbed onto the particle, granting excellent conductivity to the microgel particles.
Therefore, it is an object of the present invention to provide a method for preparing an electrically conductive microgel, by which excellent electrical conductivity can be obtained. It is another object of the present invention to provide an electrically conductive microgel which has a three-dimensional array of electrically conductive polymers in association with a polymeric binder, thereby showing excellent electrical conductivity, electromagnetic wave shielding, electrostatic prevention and film performance even though a small quantity of electrically conductive polymers are present therein.
In accordance with the present invention, there is provided a method for preparing an electrically conductive microgel comprising adding 3 to 30 weight % of a monomer for synthesizing electrically conductive polymer and 1 to 20 weight % of a dopant to 15 to 80 weight % of an organic solution containing 5 to 60 weight % of microgel particles and polymerizing said monomer at a temperature of 0 to 80° C. under the addition of 2 to 40 weight % of an aqueous solution containing 1 to 40 weight % of an oxidative polymerization catalyst, in which the polymer adsorbed on the surface of the microgel particles.
In accordance with another object of the present invention, there is provided an electrically conductive microgel suitable for use in electrical conduction, electromagnetic-radio frequency interference shielding, electrostatic discharge protection and anti-fogging.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, electrically conductive microgel is prepared by synthesizing electrically conductive polymers on the surface of microgel particles dispersed in an organic solvent and adsorbing the synthesized polymers thereonto. The microgel particles useful in the present invention are intramolecularly crosslinked, ultra-fine polymer particles with an average diameter of 0.01 to 10 microns and can be typically prepared by two processes. For reference, the term “an organic solution containing microgel” or “a microgel-containing organic solution” as used herein refers to a dispersion of microgel particles in an organic solvent.
One process for preparing a dispersion of microgel particles in an organic solvent is described in U.S. Pat. No. 4,403,003, which teaches a non-aqueous dispersion (AND) process. Also, a dispersion of microgel particles in an organic solvent can be obtained by a combination of emulsion polymerization and aqueous-organic solvent conversion, as taught in European Pat. Pub. No. 029637.
In the AND process, vinyl monomers are polymerized to microgel through dispersion polymerization in the presence of a polymer stabilizer in an organic solvent. With a steric stabilization ability, the polymer stabilizer acts to inhibit the flocculation of the microgel produced. In detail, the polymer stabilizer provides an energy barrier against particle flocculation by forming a chain extended configuration of the polymer around individual microgel particles. In the '003 patent, the polymer stabilizer is prepared as follows. 12-Hydroxystearic acid is self-condensed to an acid value of about 31 to 34 mg KOH/g (corresponding to a number average molecular weight of 1650 to 1800) and then reacted with an equivalent amount of glycidyl methacrylate. The resulting unsaturated ester is copolymerized at a weight ratio of 2:1 with a mixture of methyl methacrylate and acrylic acid in the proportions of 95:5.
In another process, microgel can be prepared by the emulsion polymerization of vinyl monomers together with crosslinking monomers (e.g. divinyl monomers) in the presence of an emulsifier. Aqueous emulsions of microgel particles are being used industrially for an excellent metallic effect in paints for automobiles. In the present invention, however, a dispersion of microgel particles in an organic solvent is required, which can be obtained through the aqueous-organic solvent conversion process. This conversion process is known as a coagulation process as taught in WO 91/00895 and EP Publication No. 029638. When n-butanol is added to an aqueous microgel emulsion, coagulation of microgel particl

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