Process for the preparation of a porous material layer covered w

Details Process for the preparation of a porous material layer covered w Process for the preparation of a porous material layer covered w

1995-10-23

1997-11-04

Engel, James

Coating processes

Electrical product produced

Cellulosic or fibrous base

427177, 427342, B05D 512, B05D 300

Patent

active

056837445

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a process for the preparation of layers of porous materials such as paper or textiles, covered with an electronically conductive polymer and in particular cloth layers.
It is used more particularly in the production of electricity conducting textiles having a low surface resistance of e.g. 5 to 20 Ohm.sup.2, which can in particular be used as Joule effect heating elements or as electromagnetic shields.
More specifically, it relates to a process for depositing an electronically conductive polymer on a layer of porous material, e.g. paper or textile, by the in situ polymerization of a precursor monomer of the electronically conductive polymer by means of an oxidizing agent.
2. Discussion of the Background
Various processes for the deposition of electronically conductive polymers using in situ polymerization are known.
Thus, US-A-4 803 096 (Milliken Research Corp) describes a process for the production of electrically conductive textile materials by contacting the textile with an aqueous solution containing a monomer and an oxidizing agent in the presence of a counterion or a doping agent able to give an electrical conductivity to the polymer, under conditions such that in the solution is formed a prepolymer, which is adsorbed or deposited in the textile material, where it is polymerized so as to cover the cloth.
In this process it is possible to use doping agents constituted by sulphonic acid derivatives and in particular non-metallic oxidizing agents such as nitric acid, peroxides and persulphates.
With this process, a prepolymer is formed in the solution whose exact nature is not known and which is deposited by epitaxy on the fibres of the cloth. However, it is difficult to obtain a uniform thickness, particularly when it is wished to produce a conductive polymer covering on a large cloth or fabric. Thus, on using in this case method D described in column 13 of said document, which consists of immersing the wound cloth in a prepolymer solution, the latter does not completely penetrate the cloth and does not uniformly wet it, which cannot bring about a homogeneous thickness. Moreover, this process requires very long impregnation times for obtaining final, low, electric surface resistances of e.g. 3000 to 4000 Ohm.sup.2 Thus, this process is not appropriate for the production of highly conductive textiles, e.g. having a surface resistance of 10 to 20 Ohm.sup.2.
EP-A-206 133 (BASF) describes a process for depositing layers of conductive polymer (polypyrrole) on various materials by simultaneously or successively contacting the material with the precursor monomer (pyrrole), in liquid or gaseous form, and the dissolved oxidizing agent. This process also does not make it possible to obtain high electrical conductivities. Moreover, it requires the use of organic solvents, which leads to a rise in production costs and can be prejudicial to the environment. In addition, during the reaction, the polymer may polymerize in powder form, which reduces the polymer deposition efficiency on the material. It is also not very easy with this process to cover textile layers of great length, large amounts of solution being needed.
Bjorklund and Lundstrom in Journal of Electronic Materials, vol. 13, No. 1, 1984, pp 211-230 describe a paper impregnation process using polypyrrole, according to which the paper substrate is impregnated in an oxidizing agent solution and then the thus treated substrate is contacted with liquid or gaseous pyrrole.
As in the case of the preceding processes, the conductivities obtained are relatively low. In addition, the polypyrrole largely polymerizes in powder form, which reduces the efficiency of the polypyrrole deposited on the paper and large solution volumes are required for covering small paper surfaces, so that it is difficult to use the process industrially.


SUMMARY OF THE INVENTION

The present invention relates to a process for the production of layers of porous material covered with an electronically c

REFERENCES:
patent: 4617228 (1986-10-01), Newman et al.
patent: 4847115 (1989-07-01), Warren et al.
patent: 5108829 (1992-04-01), Kuhn
patent: 5407699 (1995-04-01), Myers
Database WPI, Derwent Publications, AN-87-059938, JP-A-62-013435, Jan. 22, 1987.

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