Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUSH1523 H
Publication typeGrant
Application numberUS 08/028,481
Publication dateApr 2, 1996
Filing dateMar 8, 1993
Priority dateMar 8, 1993
Publication number028481, 08028481, US H1523 H, US H1523H, US-H-H1523, USH1523 H, USH1523H
InventorsRobert J. Mammone, Michael Binder
Original AssigneeThe United States Of America As Represented By The Secretary Of The Army
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mixing solutions of polymers, casting together as solid composite film, and exposing to treating agent to dope or protonate
US H1523 H
Abstract
A polymer film having a conductivity gradient across its thickness is maderom a mixed solution of an insulating polymer, A and a polymer, B that can be made conducting by doping or protonation by a method including the steps of:
(A) mixing the solution of the insulating polymer, A and the polymer, B that can be made conducting by doping or protonation,
(B) casting the mixed solution together as a solid composite film, and
(C) exposing the film to a treating agent that can dope or protonate polymer B and make polymer B conductive and create a conductivity gradient across the thickness of the polymer films.
Images(3)
Previous page
Next page
Claims(5)
What is claimed is:
1. Method of making a polymer film that has a conductivity gradient across its thickness from a mixed solution of an insulating polymer, A, and a polymer, B that can be made conducting by doping or protonation, said method including the steps of
(A) mixing the solution of the insulating polymer A, and the polymer, B that can be made conducting by doping or protonation,
(B) casting the mixed solution together as a solid composite film, and
(C) exposing the film to a treating agent that can dope or protonate polymer B and make polymer B conductive and create a conductivity gradient across the thickness of the polymer film.
2. Method according to claim 1 wherein the treating agent is a dopant.
3. Method according to claim 1 wherein the treating agent is a protonator.
4. Method according to claim 1 wherein the treating agent is allowed to diffuse into the solid composite film as a function of time causing the polymer B molecules near the surface region to be converted to the conducting form.
5. Method according to claim 3 wherein the treating agent protonator is HCl gas and polymer B is "POMA" (poly-o-methoxyaniline).
Description
GOVERNMENT INTEREST

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.

FIELD OF INVENTION

The invention relates in general to a method of making an improved polymer film and in particular to such a method wherein a conductivity gradient is created across the thickness of the polymer film.

BACKGROUND OF THE INVENTION

One of the difficulties in preparing film to be used in metallized film or film foil capacitor has been that electric field gradients applied across the film thickness are large. This is because the conducting metal film or foil is contacting the generally insulating polymer directly. The extremely high electric field gradient can cause premature electrical breakdown.

SUMMARY OF THE INVENTION

An object of this invention is to overcome the aforementioned difficulty and to prepare improved films that will be used in metallized or film foil capacitors. A further object of the invention is to provide such a film foil capacitor wherein the polymer conductivity is graded across its thickness and wherein electric field gradient applied across the film thickness will not be as sharp as if a conducting metal were contacting an insulating polymer directly. A still further object of the invention is to replace metallized films or metal foil in electrical contact in capacitors and create an all-polymer capacitor. Another object of the invention is to fabricate optically transparent polymer films having a gradient in refractive index.

It has now been found that the aforementioned objects can be achieved by providing a method for making polymer film that has a conductivity gradient across the polymer film thickness. The volume conductivity is high near the film surface and decreases as a function of distance into the polymer film. In the method, a mixed solution of an insulating polymer, A, and another polymer, B, that can be made conducting by doping or protonation, is cast together as a solid composite film. The cast, solid polymer film, containing uniformly dispersed polymer A and polymer B is nonconducting. This film is then exposed to a treating agent in the form of a specific solution or gas that is capable of doping or protonating polymer B and, in the process, making polymer B conducting. The treating agent has no effect on polymer A. Since the treating agent in the form of a solution or gas diffuses into the polymer composite and only converts polymer B to its conducting form, polymer A remains nonconducting. However, since the treating agent, that is, gas or solution, diffuses into the bulk of the composite polymer as a function of time, polymer B molecules near the surface region become converted to the conducting form. The bulk of the polymer composite film remains nonconductive. Thus, a sandwich is formed of a thin conductive region on each side of a nonconductive film.

The method is particularly useful in preparing films that are to be used in metallized or film foil capacitors. Because the polymer conductivity is graded (or slowly decreases as a function of depth) across its thickness, electric field gradients applied across the film thickness are not as sharp as if a conducting metal were contacting an insulating polymer directly. Decreased electric field gradients are desirable in that they increase electric field breakdown strengths and capacitor reliability.

The method can be used to replace metallized films or metal foils as electrical contacts in capacitors and create all polymer capacitors.

The polymer films may also be used in making optically transparent polymer films having a gradient in refractive index.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A solution of polycarbonate, PC, is dissolved in a suitable solvent (such as mixtures of methylene chloride and chloroform) and approximately ,10% of poly-o-methoxyaniline, POMA, is added. A film is then cast from the above solution mixture and allowed to dry. The film is then exposed to HCl gas as the treating agent. Almost immediately, the film color changes from purple to green. Since HCl is known to protonate POMA and convert it to the conductive form, the observed color change is indicative of a conductivity change due to the conductive POMA. However, the measured bulk dielectric constant of the composite film does not change. This is an indication that POMA molecules in the bulk of the composite film have not yet become converted to the conductive form. Had these POMA molecules become converted to the conductive form, (perhaps after longer exposure times to the HCl) the dielectric constant of the bulk composite film would have risen sharply. This indicates that the observed color change in the film is due to changes in conductivity of primarily those POMA molecules near the film surface.

Applicants point out that similar effects can be obtained by coating an existing polymer film of any polymer, with a solution of POMA and PC in a suitable solvent, allowing it to dry, and then reacting it with HCl or another protonating agent. The POMA will become conducting and create a surface layer whose conductivity decreases as a function of depth into the bulk polymer.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described for obvious modification will occur to a person skilled in the art.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4803096 *Aug 3, 1987Feb 7, 1989Milliken Research CorporationOxidative polymerization of pyrroles or anilines directly onto fibers in presence of counter ions; antistatic agents
US4851487 *Feb 22, 1988Jul 25, 1989Lockheed CorporationConductive polymer materials and method of producing same
US4935164 *Jun 13, 1985Jun 19, 1990Zipperling Kessler & Co. (Gmbh & Co.)Process for producing mouldable polymer blends
US4935181 *Feb 3, 1989Jun 19, 1990Trustess Of The University Of PennsylvaniaProcess of making oriented films of conductive polymers
US4983690 *Mar 20, 1989Jan 8, 1991Lockheed CorporationSolution blending of conductive polyanilines or derivatives thereof with maleimide systems; curing
US5151221 *Feb 28, 1989Sep 29, 1992Berggren Oy AbConductive plastic composites
US5162135 *Sep 27, 1990Nov 10, 1992Milliken Research CorporationElectrically conductive polymer material having conductivity gradient
US5186860 *Oct 11, 1990Feb 16, 1993Amp IncorporatedInert electrode comprising a conductive coating polymer blend formed of polyanisidine and polyacrylonitrile
US5217649 *Jan 31, 1991Jun 8, 1993Americhem, Inc.Stable workable blends for electromagnetic wave shielding or electrostatic dissipation
JPS6215231A * Title not available
JPS6319705A * Title not available
JPS61279001A * Title not available
JPS63264641A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6200508 *Oct 27, 1997Mar 13, 2001Massachusetts Institute Of TechnologyDirected to the fabrication of small devices such as miniature switches, motors and the like.
US6346491May 28, 1999Feb 12, 2002Milliken & CompanyElectromagnetic textile fabric with conductive fibers; interference reduction; broadband microwave absorbers
US6716481Oct 26, 2001Apr 6, 2004Milliken & CompanyFelt having conductivity gradient
US7236139Dec 10, 2004Jun 26, 2007Bae Systems Information And Electronic Systems Integration Inc.Low backscatter polymer antenna with graded conductivity
Classifications
U.S. Classification264/104, 252/500, 264/204, 264/105
International ClassificationH01B1/12
Cooperative ClassificationH01B1/128
European ClassificationH01B1/12H6