Claims
- 1. An electrically conductive textile material which comprises a textile material made predominantly of fibers selected from polyester, polyamide, acrylic, polybenzimidazole, glass and ceramic fibers; wherein said textile material is covered to a uniform thickness of from about 0.05 to about 2 microns through chemical oxidation in an aqueous solution with a coherent, ordered film of an electrically conductive, organic polymer selected from a pyrrole polymer and an aniline polymer.
- 2. The textile material of claim 1 wherein said textile material comprises a knitted, woven, or non-woven fibrous textile fabric
- 3. The textile material of claim 2 wherein said textile fabric is selected from woven or knitted fabrics.
- 4. The textile material of claim 3 wherein said textile fabric is constructed of continuous filament yarns.
- 5. The textile material of claim 1 wherein said textile fibers are high modulus fibers selected from aromatic polyester, aromatic polyamide and polybenzimidazole fibers.
- 6. The textile material of claim 1 wherein said textile fibers are high modulus inorganic fibers selected from glass and ceramic fibers.
- 7. The textile material of claim 1 wherein said textile fabric has a resistivity of from about 10 to about 500,000 ohms per square.
- 8. The textile material of claim 1 wherein said textile fibers are basic dyeable polyester fibers.
- 9. The textile material of claim 1 wherein said textile material is a wound yarn, filament or fiber.
- 10. The textile material of claim 1 wherein said polypyrrole polymer is made by polymerizing a pyrrole monomer selected from the group consisting of pyrrole, a 3- and 3,4-alkyl or aryl substituted pyrrole, N-alkyl pyrrole and N-aryl pyrrole.
- 11. The textile material of claim 1 wherein said pyrrole polymer is made by polymerizing a pyrrole monomer selected from pyrrole, N-methylpyrrole, or a mixture of pyrrole and N-methylpyrrole.
- 12. The textile material of claim 1 wherein said polyaniline polymer is made by polymerizing an aniline compound selected from chloro-, bromo-, alkyl or aryl-substituted aniline.
- 13. The textile material of claim 1 wherein said ordered film of said electrically conductive, organic polymer is formed by contacting in said aqueous solution the textile material with an oxidatively polymerizable compound selected from a pyrrole compound or an aniline compound and an oxidizing agent capable of oxidizing said compound to a polymer, said contacting being carried out in the presence of a counter ion which imparts electrical conductivity to said polymer, said contacting being under conditions at which the compound and the oxidizing agent react with each other to form a prepolymer in said aqueous solution before either the compound or the oxidizing agent are adsorbed by or deposited on or in the textile material but without forming a conductive polymer per se in said aqueous solution; adsorbing onto the surface of said textile material the forming polymer and allowing the adsorbed forming polymer to polymerize in an ordered configuration while adsorbed on said textile material so as to uniformly and coherently cover the textile material with a conductive, ordered film of said polymer.
Parent Case Info
This is a continuation-in-part of copending U.S. Ser. No. 07/175,783, filed Mar. 31, 1988, and now abandoned, which in turn is a division of Ser. No. 07/081,069, filed Aug. 3, 1987, now U.S. Pat. No. 4,803,096.
The present invention relates to a method for imparting electrical conductivity to textile materials and to products made by such a method. More particularly, the present invention relates to a method for producing conductive textile materials, such as fabrics, filaments, fibers, yarns, by depositing in status nascendi forming, electrically conducting polymers, such as polypyrrole or polyaniline, epitaxially onto the surface of the textile material.
Electrically conductive fabrics have, in general, been known for some time. Such fabrics have been manufactured by mixing or blending a conductive powder with a polymer melt prior to extrusion of the fibers from which the fabric is made. Such powders may include, for instance, carbon black, silver particles or even silver- or gold-coated particles. When conductive fabrics are made in this fashion, however, the amount of powder or filler required may be relatively high in order to achieve any reasonable conductivity and this high level of filler may adversely affect the properties of the resultant fibers. It is theorized that the high level of filler is necessitated because the filler particles must actually touch one another in order to obtain the desired conductivity characteristics for the resultant fabrics.
Such products have, as mentioned briefly above, some significant disadvantages. For instance, the mixing of a relatively high concentration of particles into the polymer melt prior to extrusion of the fibers may result in undesired alteration of the physical properties of the fibers and the resultant textile materials.
Antistatic fabrics may also be made by incorporating conductive carbon fibers, or carbon-filled nylon or polyester fibers in woven or knit fabrics. Alternatively, conductive fabrics may be made by blending stainless steel fibers into spun yarns used to make such fabrics. While effective for some applications, these "black stripe" fabrics and stainless steel containing fabrics are expensive and of only limited use. Also known are metal-coated fabrics such as nickel-coated, copper-coated and noble metal-coated fabrics, however the process to make such fabrics is quite complicated and involves expensive catalysts such as palladium or platinum, making such fabrics impractical for many applications.
It is known that polypyrrole may be a convenient material for achieving electrical conductivity for a variety of uses. An excellent summary in this regard is provided in an article by G. Bryan Street of IBM Research Laboratories Volume 1, "Handbook of Conductive Polymers", pages 266-291. As mentioned in that article, polypyrrole can be produced by either an electrochemical process where pyrrole is oxidized on an anode to a desired polymer film configuration or, alternatively, pyrrole may be oxidized chemically to polypyrrole by ferric chloride or other oxidizing agents. While conductive films may be obtained by means of these methods, the films themselves are insoluble in either organic or inorganic solvents and, therefore, they cannot be reformed or processed into desirable shapes after they have been prepared.
Accordingly, it has been suggested that the polypyrrole may be made more soluble in organic solvents by providing one or two aliphatic side chains on a pyrrole molecule. More recently, it has been suggested that the pyrrole may be polymerized by a chemical oxidation within a film or fiber (see U.S. Pat. No. 4,604,427 to A. Roberts, et al.). A somewhat similar method has been suggested wherein ferric chloride is incorporated into, for instance, a polyvinyl alcohol film and the composite is then exposed to pyrrole vapors resulting in a conductive polymeric composite.
Another method for making polypyrrole products is described in U.S. Pat. No. 4,521,450 to Bjorklund, et al. wherein it is suggested that the oxidizing catalyst be applied to a fiber composite and thereafter exposed to the pyrrole monomer in solution or vapor form. A closely related process for producing electrically conductive composites by precipitating conductive pyrrole polymer in the interstitial pores of a porous substance is disclosed in U.S. Pat. No. 4,617,228 to Newman, et al.
However, while the examples of the aforementioned patents to Roberts, et al., Bjorklund, et al. and Newman, et al. show increased conductivity for various non-porous synthetic organic polymer films, impregnable cellulosic fabrics, and porous substances, respectively, these processes each have various drawbacks. For example, they require relatively high concentrations of the pyrrole compound applied to the host substrate. Another problem inherent to these processes is the requirement for separate applications of pyrrole monomer and oxidant, with one or the other first being taken up by the fabric, film, fiber, etc. and then the other reactant being applied to the previously impregnated host material. This dual step approach may involve additional handling, require drying between steps, involve additional time for first impregnation and then reaction. The process of Bjorklund, et al. as pointed out by Roberts, et al. has the additional deficiency of not being applicable to non-porous polymeric materials. On the other hand, the Roberts, et al. process requires use of organic solvents in which the pyrrole or substituted pyrrole analog is soluble, thus requiring handling and recovery of the organic solvent with the corresponding environmental hazards associated with organic solvents. Still further, it is, in practice, difficult to control the amount of conductive polymer deposited in or on the substrate material and may result in non-uniform coatings, loosely adherent polypyrrole ("pyrrole black") and inefficient use or waste of the pyrrole monomer. Furthermore, as will be shown hereinafter, under the conditions used to effect epitaxial deposition of the in status nascendi forming polymer of pyrrole or aniline, the presence of organic solvents interferes with the deposition and prevents formation of an electrically conductive film on the textile material.
On the other hand the electrochemical deposition of polypyrrole on the surface of textiles could only be achieved if these fabrics would be per se electrically conductive. H. Naarmann, et al. describes such a process in DE 3,531,019A using electrically conductive carbon fibers or fabrics as the anode for the electrochemical formation of polypyrrole. It is obvious that such a process would be inoperative on regular textiles which are predominantly insulators or not sufficiently conductive to provide the necessary electrical potential to initiate polymerization.
Another conductive polymer which can be obtained by an oxidative polymerization from an aqueous solution and which has similar properties to polypyrrole is polyaniline. Such products are described in a paper by Wu-Song Huang, et al. In the Am Chem. Soc. Faraday Trans. 1, 1986 82, 2385-2400. As will be shown later herein, polyaniline can be epitaxially deposited in the in status nascendi form to the surface of textile materials resulting in conductive textile materials much like the corresponding materials made from pyrrole and its derivatives.
It is thus an object of the present invention to overcome the difficulties associated with known methods for preparing conductive materials and to produce a highly conductive, ordered, coherent film on the surface of textile materials. Such resultant textile materials may, in general, include fibers, filaments, yarns and fabrics. The treated textile materials exhibit excellent hand characteristics which make them suitable and appropriate for a variety of end use applications where conductivity may be desired including, for example, antistatic garments, antistatic floor coverings, components in computers, and generally, as replacements for metallic conductors, or semiconductors, including such specific applications as, for example, batteries, photovoltaics, electrostatic dissipation and electromagnetic shielding, for example, as antistatic wrappings of electronic equipment or electromagnetic interference shields for computers and other sensitive instruments.
According to one embodiment of the present invention, a method is provided for imparting electrical conductivity to textile materials by contacting the textile material with an aqueous solution of an oxidatively polymerizable compound selected from pyrrole and aniline and their derivatives and an oxidizing agent capable of oxidizing said compound to a polymer, said contacting being carried out in the presence of a counter ion or doping agent to impart electrical conductivity to said polymer, and under conditions at which the polymerizable compound and the oxidizing agent react with each other to form an in status nascendi forming polymer in said aqueous solution, but without forming a conductive polymer, per se, in said aqueous solution and without either the compound or the oxidizing agent being adsorbed by, or deposited on or in, the textile material; epitaxially depositing onto the surface of the textile material the in status nascendi forming polymer of the polymerizable compound; and allowing the in status nascendi forming compound to polymerize while deposited on the textile material so as to uniformly and coherently cover the textile material with an ordered, conductive film of polymerized compound.
According to another embodiment of the present invention an electrically conductive textile material is provided which comprises a textile material onto which is epitaxially deposited a film of an electrically conductive polymer.
The process of the present invention differs significantly from the prior art methods for making conductive composites in that the substrate being treated is contacted with the polymerizable compound and oxidizing agent at relatively dilute concentrations and under conditions which do not result in either the monomer or the oxidizing agent being taken up, whether by adsorption, impregnation, absorption, or otherwise, by the preformed fabric (or the fibers, filaments or yarns forming the fabric). Rather, the polymerizable monomer and oxidizing reagent will first react with each other to form a "pre-polymer" species, the exact nature of which has not yet been fully ascertained, but which may be a water-soluble or dispersible free radical-ion of the compound, or a water-soluble or dispersible dimer or oligomer of the polymerizable compound, or some other unidentified "pre-polymer" species. In any case, it is the "pre-polymer" species, i.e. the in status nascendi forming polymer, which is epitaxially deposited onto the surface of the individual fibers or filaments, as such, or as a component of yarn or preformed fabric or other textile material. Thus, applicant controls process conditions, such as reaction temperature, concentration of reactants and textile material, and other process conditions so as to result in epitaxial deposition of the pre-polymer particles being formed in the in status nascendi phase, that is, as they are being formed. This results in a very uniform film being formed at the surface of individual fibers or filaments without any significant formation of polymer in solution and also results in optimum usage of the polymerizable compound so that even with a relatively low amount of pyrrole or aniline applied to the surface of the textile, nonetheless a relatively high amount of conductivity is capable of being achieved.
The invention will now be explained in greater detail with the aid of specific embodiments and the accompanying drawings forming a part of this application.
As mentioned briefly above it is the in status nascendi forming compound that is epitaxially deposited onto the surface of the textile material. As used herein the phrase "epitaxially deposited" means deposition of a uniform, smooth, coherent and "ordered" film. This epitaxial deposition phenomenon may be said to be related to, or a species of, the more conventionally understood adsorption phenomenon. While the adsorption phenomenon is not necessarily a well known phenomenon in terms of textile finishing operations it certainly has been known that monomeric materials may be adsorbed to many substrates including textile fabrics. The adsorption of polymeric materials from the liquid phase onto a solid surface is a phenomenon which is known, to some extent, especially in the field of biological chemistry. For example, reference is made to U.S. Pat. No. 3,909,195 to Machell, et al. and U.S. Pat. No. 3,950,589 to Togo, et al. which show methods for treating textile fibers with polymerizable compositions, although not in the context of electrically conductive fibers.
Epitaxial deposition of the in status nascendi forming pre-polymer of either pyrrole or aniline is caused to occur, according to the present invention, by, among other factors, controlling the type and concentration of polymerizable compound in the aqueous reaction medium. If the concentration of polymerizable compound (relative to the textile material and/or aqueous phase) is too high, polymerization may occur virtually instantaneously both in solution and on the surface of the textile material and a black powder, e.g. "black polypyrrole", will be formed and settle on the bottom of the reaction flask. If, however, the concentration of polymerizable compound, in the aqueous phase and relative to the textile material, is maintained at relatively low levels, for instance, depending on the particular oxidizing agent, from about 0.01 to about 5 grams of polymerizable compound per 50 grams of textile material in one liter of aqueous solution, preferably from about 1.5 to about 2.5 grams polymerizable compound per 50 grams textile per liter, polymerization occurs at a sufficiently slow rate, and the pre-polymer species will be epitaxially deposited onto the textile material before polymerization is completed. Reaction rates may be further controlled by variations in other reaction conditions such as reaction temperatures, etc. and other additives This rate is, in fact, sufficiently slow that it may take several minutes, for example 2 to 5 minutes or longer , until a significant change in the appearance of the reaction solution is observed. If a textile material is present in this in status nascendi forming solution of pre-polymer, the forming species, while still in solution, or in colloidal suspension will be epitaxially deposited onto the surface of the textile material and a uniformly coated textile material having a thin, coherent, and ordered conductive polymer film on its surface will be obtained.
In general, the amount of textile material per liter of aqueous liquor may be from about 1 to 5 to 1 to 50 preferably from about 1 to 10 to about 1 to 20.
Controlling the rate of the in status nascendi forming polymer deposition epitaxially on the surface of the fibers in the textile material is not only of importance for controlling the reaction conditions to optimize yield and proper formation of the polymer on the surface of the individual fiber but foremost influences the molecular weight and order of the epitaxially deposited polymer. Higher molecular weight and higher order in electrically conductive polymers imparts higher conductivity and most importantly higher stability to these products.
Pyrrole is the preferred pyrrole monomer, both in terms of the conductivity of the doped polypyrrole films and for its reactivity. However, other pyrrole monomers, including N-methylpyrrole, 3-methylpyrrole, 3,5-dimethylpyrrole, 2,2'-bipyrrole, and the like, especially N-methylpyrrole can also be used. More generally, the pyrrole compound may be selected from pyrrole, 3-, and 3,4-alkyl and aryl substituted pyrrole, and N-alkyl, and N-aryl pyrrole. In addition, two or more pyrrole monomers can be used to form conductive copolymer, especially those containing predominantly pyrrole, especially at least 50 mole percent, preferably at least 70 mole percent, and especially preferably at least 90 mole percent of pyrrole. In fact, the addition of a pyrrole derivative as comonomer having a lower polymerization reaction rate than pyrrole may be used to effectively lower the overall polymerization rate. Use of other pyrrole monomers, is, however, not preferred, particularly when especially low resistivity is desired, for example, below about 1,000 ohms per square.
In addition to pyrrole compounds, it has been found that aniline under proper conditions can form a conductive film on the surface of textiles much like the pyrrole compounds mentioned above. Aniline is a very desirable monomer to be used in this expitaxial deposition of an in status nascendi forming polymer, not only for its low cost, but also because of the excellent stability of the conductive polyaniline formed.
Any of the known oxidizing agents for promoting the polymerization of polymerizable monomers may be used in this invention, including, for example, the chemical oxidants and the chemical compounds containing a metal ion which is capable of changing its valence, which compounds are capable, during the polymerization of the polymerizable compound, of providing electrically conductive polymers, including those listed in the above mentioned patents 4,604,427 to Roberts, et al., 4,521,450 to Bjorklund, et al. and 4,617,228 to Newman, et al.
Specifically, suitable chemical oxidants include, for instance, compounds of polyvalent metal ions, such as, for example, FeCl.sub.3, Fe.sub.2 (SO.sub.4).sub.3, K.sub.3 (Fe(CN).sub.6), H.sub.3 PO.sub.4.12MoO.sub.3, H.sub.3 PO.sub.4.12WO.sub.3, CrO.sub.3, (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6, CuCl.sub.2, AgNO.sub.3, etc., especially FeCl.sub.3, and compounds not containing polyvalent metal compounds, such as nitrites, quinones, peroxides, peracids, persulfates, perborates, permanganates, perchlorates, chromates, and the like. Examples of such non-metallic type of oxidants include, for example, HNO.sub.3, 1,4-benzoquinone, tetrachloro-1, 4-benzoquinone, hydrogen peroxide, peroxyacetic acid, peroxybenzoic acid, 3-chloroperoxybenzoic acid, ammonium persulfate, ammonium perborate, etc. The alkali metal salts, such as sodium, potassium or lithium salts of these compounds, can also be used.
In the case of pyrrole, a great number of oxidants may be suitable for the production of conductive fabrics; this is not necessarily the case for aniline. Aniline is known to polymerize to form at least five different forms of polyaniline, most of which are not conductive. At the present time the emeraldine form of polyaniline as described by Wu-Song Huang, et al., is the preferred species of polyaniline. As the name implies, the color of this species of polyaniline is green in contrast to the black color of polypyrrole. With regard to aniline the concentration in the aqueous solution may be from about 0.02 to 10 grams per liter. Aniline compounds that may be employed include in addition to aniline per se, various substituted anilines such as halogen substituted, e.g. chloro-or bromo-substituted, as well as alkyl or aryl-substituted anilines.
The suitable chemical oxidants for the polymerization include persulfates, particular ammonium persulfate, but conductive textiles could also be obtained with ferric chloride. Other oxidants form polyaniline films on the surface of the fibers such as, for instance, potassium dichromate and others.
When employing one of these non-metallic chemical oxidants for promoting the polymerization of the polymerizable compound, it is also preferred to include a "doping" agent or counter ion since it is only the doped polymer film that is conductive. For these polymers, anionic counter ions, such as iodine, chloride and perchlorate, provided by, for example, I.sub.2, HCl, HClO.sub.4, and their salts and so on, can be used. Other suitable anionic counter ions include, for example, sulfate, bisulfate, sulfonate, sulfonic acid, fluoroborate, PF.sub.6 -, AsF.sub.6 -, and SbF.sub.6 - and can be derived from the free acids, or soluble salts of such acids, including inorganic and organic acids and salts thereof. Furthermore, as is well known, certain oxidants, such as ferric chloride, ferric perchlorate, cupric fluoroborate, and others, can provide the oxidant function and also supply the anionic counter ion. However, if the oxidizing agent is itself an anionic counter ion it may be desirable to use one or more other doping agents in conjunction with the oxidizing agent.
In accordance with one specific aspect of this invention it has been discovered that especially good conductivity can be achieved using sulfonic acid derivatives as the counter ion dopant for the polymers. For example, mention can be made of the aliphatic and aromatic sulfonic acids, substituted aromatic and aliphatic sulfonic acids as well as polymeric sulfonic acids such as poly (vinylsulfonic acid) or poly (styrenesulfonic acid). The aromatic sulfonic acids, such as, for example, benzenesulfonic acid, para-toluenesulfonic acid p-chlorobenzenesulfonic acid and naphthalenedisulfonic acid, are preferred. When these sulfonic acid compounds are used in conjunction with, for example, hydrogen peroxide, or one of the other non-metallic chemical oxidants, in addition to high conductivity of the resulting polymer films, there is a further advantage that the reaction can be carried out in conventional stainless steel vessels. In contrast, FeCl.sub.3 oxidant is highly corrosive to stainless steel and requires glass or other expensive specialty metal vessels or lined vessels. Moreover, the peroxides, persulfates, etc. have higher oxidizing potential than FeCl.sub.3 and can increase the rate of polymerization of the compound.
Generally, the amount of oxidant is a controlling factor in the polymerization rate and the total amount of oxidant should be at least equimolar to the amount of the monomer. However, it may be useful to use a higher or lower amount of the chemical oxidant to control the rate of polymerization or to assure effective utilization of the polymerizable monomer. On the other hand, where the chemical oxidant also provides the counter ion dopant, such as in the case with FeCl.sub.3, the amount of oxidant may be substantially greater, for example, a molar ratio of oxidant to polymerizable compound of from about 4:1 to about 1:1, preferably 3:1 to 2:1.
Within the amounts of polymerizable compound and oxidizing agent as described above, the conductive polymer is formed on the fabric in amounts corresponding to about 0.5% to about 4%, preferably about 1.0% to about 3%, especially preferably about 1.5% to about 2.5%, such as about 2%, by weight based on the weight of the fabric. Thus, for example, for a fabric weighing 100 grams a polymer film of about 2 gm may typically be formed on the fabric.
Furthermore, the rate of polymerization of the polymerizable compound can be controlled by variations of the pH of the aqueous reaction mixture. While solutions of ferric chloride are inherently acidic, increased acidity can be conveniently provided by acids such as HCl or H.sub.2 SO.sub.4 ; or acidity can be provided by the doping agent or counter ion, such as benzenesulfonic acid and its derivatives and the like. It has been found that pH conditions from about five to about one provide sufficient acidity to allow the in status nascendi epitaxial adsorption of the polymerizable compound to proceed. Preferred conditions, however, are encountered at a pH of from about three to about one.
Another important factor in controlling the rate of polymerization (and hence formation of the pre-polymer adsorbed species) is the reaction temperature. As is generally the case with chemical reactions, the polymerization rate will increase with increasing temperature and will decrease with decreasing temperature. For practical reasons it is convenient to operate at or near ambient temperature, such as from about 10.degree. C. to 30.degree. C., preferably from about 18.degree. C. to 25.degree. C. At temperatures higher than about 30.degree. C., for instance at about 40.degree. C. or higher, the polymerization rate becomes too high and exceeds the rate of epitaxial deposition of the in status nascendi forming polymer and also results in production of unwanted oxidation by-products. At temperatures below about 10.degree. C., the polymerization rate becomes slower but a higher degree of order and therefore better conductivities can be obtained The polymerization of the polymerizable compound can be performed at temperatures as low as about 0.degree. C. the freezing temperature of the aqueous reaction media) or even lower where freezing point depressants, such as various electrolytes, including the metallic compound oxidants and doping agents, are present in the reaction system. The polymerization reaction must, of course, take place at a temperature above the freezing point of the aqueous reaction medium so that the prepolymer species can be epitaxially deposited onto the textile material from the aqueous reaction medium.
Yet another controllable factor which has significance with regard to the process of the present invention is the rate of deposition of the in status nascendi forming polymer on the textile material. The rate of deposition of the polymer to the textile fabric should be such that the in status nascendi forming polymer is taken out of solution and deposited onto the textile fabric as quickly as it is formed. If, in this regard, the polymer or pre-polymer species is allowed to remain in solution too long, its molecular weight may become so high that it may not be efficiently deposited but, instead, will form a black powder which will precipitate to the bottom of the reaction medium.
The rate of epitaxial deposition onto the textile fabric depends, inter alia, upon the concentration of the species being deposited and also depends to some degree on the physical and other surface characteristics of the textile material being treated. The rate of deposition, furthermore, does not necessarily increase as concentrations of the polymeric or pre-polymer material in the solution increase On the contrary, the rate of epitaxial deposition of the in status nascendi forming polymer material to a solid substrate in a liquid may actually increase as concentration of the material increases to a maximum and then as the concentration of the material increases further the rate of epitaxial deposition may actually decrease as the interaction of the material with itself to make higher molecular weight materials becomes the controlling factor. Deposition rates and polymerization rates may be influenced by still other factors. For instance, the presence of surface active agents or other monomeric or polymeric materials in the reaction medium may interfere with and/or slow down the polymerization rate. It has been observed, for example, that the presence of even small quantities of nonionic and cationic surface active agents almost completely inhibit formation on the textile material of the electrically conductive polymer whereas anionic surfactants, in small quantities, do not interfere with film formation or may even promote formation of the electrically conductive polymer film. With regard to deposition rate, the addition of electrolytes, such as sodium chloride, calcium chloride, etc. may enhance the rate of deposition.
The deposition rate also depends on the driving force of the difference between the concentration of the adsorbed species on the surface of the textile material and the concentration of the species in the liquid phase exposed to the textile material. This difference in concentration and the deposition rate also depend on such factors as the available surface area of the textile material exposed to the liquid phase and the rate of replenishment of the in status nascendi forming polymer in the vicinity of the surfaces of the textile material available for deposition.
Therefore, it follows that best results in forming uniform coherent conductive polymer films on the textile material are achieved by continuously agitating the reaction system in which the textile material is in contact during the entire polymerization reaction. Such agitation can be provided by simply shaking or vibrating or tumbling the reaction vessel in which the textile material is immersed in the liquid reactant system or alternatively, the liquid reactant system can be caused to flow through and/or across the textile material.
As an example of this later mode of operation, it is feasible to force the liquid reaction system over and through a spool or bobbin of wound textile filaments, fibers (e.g. spun fibers), yarn or fabrics, the degree of force applied to the liquid being dependent on the winding density, a more tightly wound and thicker product requiring a greater force to penetrate through the textile and uniformly contact the entire surface of all of the fibers or filaments or yarn. Conversely, for a loosely wound or thinner yarn or filament package, correspondingly less force need be applied to the liquid to cause uniform contact and deposition. In either case, the liquid can be recirculated to the textile material as is customary in many types of textile treating processes. Yarn packages up to 10 inches in diameter have been treated by the process of this invention to provide uniform, coherent, smooth polymer films. The observation that no particulate matter is present in the coated conductive yarn package provides further evidence that it is not the polymer particles, per se--which are water-insoluble and which, if present, would be filtered out of the liquid by the yarn package-- that are being deposited onto the textile material.
As an indication that the polymerization parameters, such as reactant concentrations, temperature, and so on, are being properly maintained, such that the rate of epitaxial deposition of the in status nascendi forming polymer is sufficiently high that polymer does not accumulate in the aqueous liquid phase, the liquid phase should remain clear or at least substantially free of particles visible to the naked eye throughout the polymerization reaction.
One particular advantage of the process of this invention is the effective utilization of the polymerizable monomer. Yields of pyrrole polymer, for instance, based on pyrrole monomer, of greater than 50%, especially greater than 75%, can be achieved.
When the process of this invention is applied to textile fibers, filaments or yarns directly, whether by the above-described method for treating a wound product, or by simply passing the textile material through a bath of the liquid reactant system until a coherent uniform conductive polymer film is formed, or by any other suitable technique, the resulting composite electrically conductive fibers, filaments, yarns, etc. remain highly flexible and can be subjected to any of the conventional knitting, weaving or similar techniques for forming fabric materials of any desired shape or configuration, without impairing the electrical conductivity.
Furthermore, another advantage of the present invention is that the rate of oxidative polymerization can be effectively controlled to a sufficiently low rate to obtain desirably ordered polymer films of high molecular weight to achieve increased stability, for instance against oxidative degradation in air. Thus, as described above, reaction rates can be lowered by lowering the reaction temperature, by lowering reactant concentrations (e.g. using less polymerizable compound, or more liquid, or more fabric), by using different oxidizing agents, by increasing the pH, or by incorporating additives in the reaction system.
While the precise identity of the adsorbing species has not been identified with any specificity, certain theories or mechanisms have been advanced although the invention is not to be considered to be limited to such theories or proposed mechanisms. It has thus been suggested that in the chemical or electrochemical polymerization, the monomer goes through a cationic, free radical ion stage and it is possible that this species is the species which is adsorbed to the surface of the textile fabric. Alternatively, it may be possible that oligomers or pre-polymers of the monomers are the species which are deposited onto the surface of the textile fabric. In the case of the oxidative polymerization of aniline a similar mechanism to the polymerization of pyrrole may occur. It is believed that in the case of polyaniline formation, a free radical ion is also formed as a prepolymer and may be the species which is actually adsorbed.
In any event, if the rate of deposition is controlled as described above, it can be seen by microscopic investigation that a uniform and coherent film of polymer is deposited onto the surface of the textile material Analyzing this film, by dissolving the fibers of the textile fabric from under the composite, washing the residual polymer with additional solvent and then examining the resulting array with a light microscope, shows that the film is actually in the form of burst tubes, thus evidencing the uniformity of the formed electrically conductive film. Surprisingly, each film or fragment of film is quite uniform in these photomicrographs, as best seen from FIGS. 1-A, 1-B, 4-A, 4-B, 5-A and 5-B. The films are either transparent or semi-transparent because the films are, in general, quite thin and one can directly conclude from the intensity of the color observed under the microscope the relative thickness of the film. In this regard, it has been calculated that film thickness may range from about 0.05 to about 2 microns, preferably from 0.1 to about 1 micron. Further, microscopic examination of the films show that the surface of the films is quite smooth, as best seen in FIGS. 2-A, 2-B, 3 and 6. This is quite surprising when one contrasts these films to polypyrrole formed electrochemically or by the prior art chemical methods, wherein, typically, discrete particles may be found within or among the polymeric films.
A wide variety of textile materials may be employed in the method of the present invention, for example, fibers, filaments, yarns and various fabrics made therefrom. Such fabrics may be woven or knitted fabrics and are preferably based on synthetic fibers, filaments or yarns. In addition, even non-woven structures, such as felts or similar materials, may be employed. Preferably, the polymer should be epitaxially deposited onto the entire surface of the textile. This result may be achieved, for instance, by the use of a relatively loosely woven or knitted fabric but, by contrast, may be relatively difficult to achieve if, for instance, a highly twisted thick yarn were to be used in the fabrication of the textile fabric. The penetration of the reaction medium through the entire textile material is, furthermore, enhanced if, for instance, the fibers used in the process are texturized textile fibers.
Fabrics prepared from spun fiber yarns as well as continuous filament yarns may be employed. In order to obtain optimum conductivity of a textile fabric, however, it may be desirable to use continuous filament yarns so that a film structure suitable for the conducting of electricity runs virtually continuously over the entire surface of the fabric. In this regard, it has been observed, as would be expected, that fabrics produced from spun fibers processed according to the present invention typically show somewhat less conductivity than fabrics produced from continuous filament yarns.
A wide variety of synthetic fibers may be used to make the textile fabrics of the present invention. Thus, for instance, fabric made from synthetic yarn, such as polyester, nylon and acrylic yarns, may be conveniently employed. Blends of synthetic and natural fibers may also be used, for example, blends with cotton, wool and other natural fibers may be employed. The preferred fibers are polyester, e.g. polyethylene terephthalate including cationic dyeable polyester and polyamides, e.g. nylon, such as Nylon 6, Nylon 6,6, and so on. Another category of preferred fibers are the high modulus fibers such as aromatic polyester, aromatic polyamide and polybenzimidazole. Still another category of fibers that may be advantageously employed include high modulus inorganic fibers such as glass and ceramic fibers. Although it has not been clearly established, it is believed that the sulfonate groups or amide groups present on these polymers may function as a "built-in" doping agent.
Conductivity measurements have been made on the fabrics which have been prepared according to the method of the present invention. Standard test methods are available in the textile industry and, in particular, AATCC test method 76-1982 is available and has been used for the purpose of measuring the resistivity of textile fabrics. According to this method, two parallel electrodes 2 inches long are contacted with the fabric and placed 1 inch apart. Resistivity may then be measured with a standard ohm meter capable of measuring values between 1 and 20 million ohms. Measurements must then be multiplied by 2 in order to obtain resistivity in ohms on a per square basis. While conditioning of the samples may ordinarily be required to specific relative humidity levels, it has been found that conditioning of the samples made according to the present invention is not necessary since conductivity measurements do not vary significantly at different humidity levels. The measurements reported in the following example are, however, conducted in a room which is set to a temperature of 70.degree. F. and 50% relative humidity. Resistivity measurements are reported herein and in the examples in ohms per square (.OMEGA./sq) and under these conditions the corresponding conductivity is one divided by resistivity.
In general, fabrics treated according to the method of the present invention show resistivities of below 10.sup.6 ohms per square, such as in the range of from about 50 to 500,000 ohms per square, preferably from about 500 to 5,000 ohms per square. These sheet resistivities can be converted to volume resistivities by taking into consideration the weight and thickness of the polymer films. Some samples tested after aging for several months do not significantly change with regard to resistivity during that period of time. In addition, samples heated in an oven to 380.degree. F. for about one minute also show no significant loss of conductivity under these conditions. These results indicate that the stability of the conductive film made according to the process of the present invention on the surface of textile materials is excellent, indicating a higher molecular weight and a higher degree of order than usually obtained by the chemical oxidation of these monomers.
US Referenced Citations (4)
Divisions (1)
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Date |
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81069 |
Aug 1987 |
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Continuation in Parts (1)
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175783 |
Mar 1988 |
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Patent Grant
4975317
