Mixtures comprising thiophene/anion dispersions and certain additives for producing coatings exhibiting improved conductivity, and methods related thereto

#The present invention relates generally to electrically conductive organic polymers, more specifically to aqueous mixtures comprising thiophene/anion dispersions and additives, and coatings and articles produced therefrom. These mixtures provide significant improvements in electrical conductivity without detracting from optical transmission and without requiring high temperature thermal treatment.

#Conducting polymers (CP's) have received considerable attention in recent years due to their potential applications in a variety of electronic devices. CP's are presently used in commercial products, such as anti-static coatings on plastics, photographic film and electronic packaging materials. Other CP applications include solid electrode capacitors, through-hole plating of printed circuit boards, coatings for cathode ray tubes (to prevent dust attraction), hole injecting layers on indium tin oxide (ITO) substrates for electroluminescent devices, and sensors. Future applications, such as an ITO replacement leading to completely flexible, organic electronic devices, will require improvement in conductivity without sacrificing other properties such as optical transparency.

#A variety of conducting polymers are described in the art, and several are commercially available, such as Baytron®P (product of Bayer AG) and Panipol® (product of Panipol Ltd.). Of the different CP families, (i.e., polyacetylenes, polyphenylenes, poly(p-phenylenevinylene)s, polypyrroles, polyanilines, and polythiophenes) polythiophenes are arguably the most stable thermally and electronically [see, “Handbook of Oligio- and Polythiophenes”, D. Fichou, Editor, Wiley-VCH, New York (1999), J. Roncali, Chem. Rev., 97, 173 (1997), A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem., 110, 416 (1998), J. Roncali, J Mater. Chem., 9, 1875 (1999), J. Roncali, Annu. Rep. Prog. Chem. Sec. C., 95, 47 (1999), A. J. Heeger, Synth. Met., 55-57, 3471 (1993) and G. Kobmehl and G. Schopf, Adv. Polym. Sci., 129, 1 (1996)]. The Baytron®P product is a polythiophene/polystyrene sulfonate composition available as an aqueous dispersion containing about 1.3% solids. This aqueous dispersion is typically used to prepare coatings on various substrates. Baytron®P is prepared from 3,4-ethylenedioxythiophene (EDT) in aqueous or predominately aqueous media in the presence of polystyrene sulfonic acid (PSS, a dopant) using an oxidant such as iron trichloride [see, L. B. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and J. R. Reynolds, Adv. Mater., 12(7), 481 (2000)]. Coatings derived from Baytron®P have been reported to exhibit a wide range of surface resistance depending upon coating thickness. The surface conductivity of Baytron®P, and that of other CP based coatings, will increase with increasing coating thickness while the optical transmission will decrease. In most coating applications, the coatings must exhibit a useable combination of electrical conductivity, optical transparency and environmental stability (i.e., stability to moisture and oxygen). The appropriate balance of these properties is of critical importance; thus a means for improving this balance of properties would represent a significant advancement and enable new applications for these materials.

#The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

#FIGS. 1A, 1B and 1C illustrate the chemical structures of the preferred additives according to an embodiment of the present invention;

#FIG. 2 graphically illustrates the surface resistance of multiple Baytron®P coatings on polycarbonate, coated with a primer, after drying for 5 minutes at 80° C.;

#While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

#The present invention pertains to aqueous mixtures containing a thiophene/anion dispersion and an at least one additive. The term “thiophene/anion dispersion”, as used herein, refers to a dispersion consisting essentially of an oliogmer, dendrimer or polymer containing thiophene groups in a cationic form with an anionic compound, anionic oligomer, anionic dendrimer or anionic polymer, and water. The term “additive”, as used herein, describes the species that are combined with a thiophene/anion dispersion, particularly a polythiophene/polystyrene sulfonate aqueous dispersion, more particularly the commercially available dispersion Baytron®P, to arrive at mixtures for producing coatings that exhibit a significant improvement in the combination of electrical conductivity and processing characteristics with no decrease in optical transparency as compared to coatings produced from state-of-the-art mixtures. The term “state-of-the-art”, as used herein, refers to mixtures comprising polythiophene/polystyrene sulfonate aqueous dispersion and an additive (and coatings produced therefrom) as disclosed in U.S. Pat. No. 5,766,515 as this art reference discloses the most advanced technology comprising thiophene/anion aqueous dispersions, especially as pertaining to the polythiophene/polystyrene sulfonate aqueous dispersions, and additives known at this time.

#The improvements in electrical conductivity and processing characteristics of the coatings of the present invention are achieved while using relatively low drying temperatures (from about 80° C. to about130° C.). The present invention overcomes limitations of the state-of-the-art mixtures and coatings produced therefrom by providing a significant improvement in this combination of properties without requiring a high temperature heat treatment.