Abstract:
The present invention relates to a conductive material and a process for producing said conductive material. More particularly, the present invention relates to a conductive material comprising (a) a substrate obtained from a polycarbodiimide resin and (b) a dopant, which is superior in oxidation resistance, mechanical strengths and flexibility, and useful as a material for electronic field, as well as to a process for producing said conductive material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a conductive material and a process for producing said conductive material. More particularly, the present invention relates to a conductive material comprising (a) a substrate obtained from a polycarbodiimide resin and (b) a dopant, which is superior in oxidation resistance, mechanical strengths and flexibility, and useful as a material for electronic field, as well as to a process for producing said conductive material. 
     2. Prior Art 
     In recent years, there have been movements of utilizing properties of polymer materials in a variety of application fields. These movements include the development of conductive polymer materials having a high conductivity. 
     Conductive polymer materials have heretofore been produced by doping a conjugated polymer such as polyacetylene, polyparaphenylene or the like to increase the conductivity, or by heating a polymer material to 1,000-3,000° C. to carbonize it. 
     These conventional conductive materials, however, have drawbacks. 
     That is, the conductive polymer materials produced by the former process, when allowed to stand in air after doping, are oxidized by the oxygen in the air and thus unstable; the conductive polymer materials produced by the latter process lack in flexibility. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to eliminate the drawbacks of the prior art and to provide a conductive material superior in oxidation resistance, mechanical strength and flexibility, and useful as a material for electronics field, as well as a process for producing the conductive material. 
     According to the present invention, there are provided a conductive material comprising (a) an insoluble and infusible substrate obtained by heat-treating a polycarbodiimide resin and (b) an electron-donating dopant or an electron-accepting dopant, and a process for producing a conductive material, which comprises heat-treating a polycarbodiimide resin to obtain an insoluble and infusible substrate and doping the substrate with an electron-donating dopant or an electron-accepting dopant. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is described in detail below. 
     The polycarbodiimide resin used in the present invention can be a known polycarbodiimide resin or a polycarbodiimide resin which can be produced in the same manner as that for a known polycarbodiimide resin [reference is made to U.S. Pat. No. 2,941,966; Japanese Patent Publication No. 33297/1972; J. Org. Chem., 28, 2069-2075 (1963); Chemical Review, 1981, Vol. 81, No. 4,619-621; etc.]. It can be easily produced by subjecting an organic diisocyanate to a condensation reaction wherein the elimination of carbon dioxide takes place. 
     The organic diisocyanate used in the production of a polycarbodiimide resin can be any of aliphatic type, alicyclic type, aromatic type, aromatic-aliphatic type, etc. They can be used alone or in combination of two or more (the latter case gives a copolymer). 
     The polycarbodiimide resin used in the process of the present invention includes a homopolymer or a copolymer each having at least one repeating unit represented by the formula 
     
         --R--R═C═N--                                       (I) 
    
     wherein R represents an organic diisocyanate residue. 
     As the R (organic diisocyanate residue) in the formula (I), there is particularly preferred an aromatic diisocyanate residue. In the present specification, the &#34;organic diisocyanate residue&#34; refers to a portion remaining after subtracting two isocyanate (NCO) groups from an organic diisocyanate molecule. 
     The polycarbodiimidization catalyst has no particular restriction and can be illustrated by conventionally used phosphorene oxides such as 1-phenyl-2-phosphorene-1-oxide, 3-methyl-2-phosphorene-1-oxide, 1-ethly-3-methyl-2-phosphorene-1-oxide, 1-ethyl-2-phosphorene-1-oxide and 3-phosphorene isomers thereof or the like. 
     Specific examples of the polycarbodiimide resin include the following. ##STR1## 
     In the above formulas, n is the degree of polymerization and is in the range of 10-10,000, preferably in the range of 50-5,000. 
     Incidentally, the terminal(s) of the polycarbodiimide resin may be blocked with a monoisocyanate or the like, and the polycarbodiimide resin described above can be obtained in a solution form, or as a powder precipitated from the solution. 
     Next, the thus obtained polycarbodiimide resin is molded into a desired shape such as a film, a sheet, a fiber or a composite thereof. The molding can be effected, for example, by casting a solution containing a polycarbodiimide resin, obtained by polymerization reaction, or a solution obtained by dissolving a polycarbodiimide resin powder in a solvent, on a flat and smooth glass plate or the like and then removing the solvent. As the solvent, there can be used tetrachloroetnylene, trichloroethylene, tetrahydrofuran, dioxane, monochlorobenzene, dichlorobenzene, dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylsulfoxide, etc. 
     The molding may also be effected by subjecting a polycarbodiimide resin powder to compression molding, roll molding, injection molding, transfer molding or the like. By the above solution or powder molding, there can be easily obtained a shaped article having a thickness of about 0.1-3 mm. 
     The thus obtained polycarbodiimide resin is then heat-treated to convert to an insoluble and infusible substrate. This heat treatment is effected at 350-900° C., preferably in vacuum or n an insert gas atmosphere. 
     Lastly, the insoluble and infusible substrate is doped with a dopant to obtain a conductive material of the present invention. The dopant can be an electron-donating dopant or an electron-accepting dopant. 
     The electron-donating dopant can be illustrated by metals of the group 1A of the periodic tale including lithium, sodium, potassium, rubidium and cesium. The electron-accepting dopant can be illustrated by halogens (fluorine, chlorine, bromine, iodine), halides (e.g. AsF5, PF5, BF5, BCl3, BBr3), oxides of nonmetallic elements (e.g. SO3, N2O3) and negative ions derived from inorganic acids such as H2SO4, HNO3, HClO4 or the like. 
     The present invention is described in more detail by way of Examples. 
     EXAMPLES 
     Preparation of Polycarbodiimide Film A 
     54 g of a mixture consisting of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (80/20) was subjected to a reaction in the presence of 1.12 g of a carbodiimidization catalyst (1-phenyl-3-methylphophorene oxide) in 500 ml of tetrachloroethylene at 120° C. for 4 hours, to obtain a polycarbodiimide solution. Using this solution, there was prepared a polycarbodiimide film of 20 μm in thickness by a dry method. 
     The film was heated from room temperature to desired temperatures at a temperature elevation rate of 5° C./min in a nitrogen current to obtain insoluble and infusible substrates. 
     The heating conditions of the film and the conductivities of the heated films (substrates) are shown below. 
     
         ______________________________________Symbol of substrate       Heating temperature                       Conductivity______________________________________A-1         150° C.  10.sup.-16A-2         350° C.  1.0 × 10.sup.-14A-3         500° C.  1.0 × 10.sup.-11A-4         700° C.  2.8 × 10.sup.0A-5         900° C.  9.0 × 10.sup.1A-6         1,200° C.                       2.0 × 10.sup.2______________________________________ 
    
     In the above, the unit of conductivity is Ω -1  cm -1 , and conductivity was measured by the four-probe method. 
     The substrates were then doped as follows. 
     EXAMPLES 1-4 
     Comparative Examples 1-2 
     Each of the substrates obtained in the above preparation A was placed in a vacuum line; the vacuum line was subjected to a vacuum of 10 -2  Torr or less; iodine gas was introduced into the vacuum line to effect doping for 3 minutes at room temperature. 
     EXAMPLES 5-7 
     The substrates A-2 to A-4 obtained in the preparation A above were placed in a vacuum line; the vacuum line was subjected to a vacuum of 10 -2  Torr or less; SO3 gas was introduced into the vacuum line to effect doping for 30 minutes at room temperature. 
     EXAMPLES 8-10 
     The substrates A-2 to A-4 obtained in the preparation A above were placed in a vacuum line; the vacuum line was subjected to a vacuum of 10 -2  Torr or less; AsF56 gas was introduced into the vacuum line to effect doping for 45 minutes at room temperature. 
     EXAMPLES 11-14 
     Using dehydrated tetrahydrofuran, naphthalene and metallic sodium, there was prepared a tetrahydrofuran solution containing sodium naphthalate. 
     The substrates A-2 to A-5 obtained in the preparation A above were immersed in the above solution to effect doping at room temperature for 24 hours. The doped substrates were washed with tetrahydrofuran and dried at room temperature under vacuum. 
     The results of the above doping are shown in Table 1. 
     As is clear from Table 1, the substrates A-2 to A-5, when doped, showed improved conductivities. They also showed sufficient flexibility, and good conductivity stability at room temperature. 
     In contrast, the substrates A-1 and A-6, when doped, showed no change in conductivity or a decease in conductivity. 
     
                       TABLE 1______________________________________  Substrate Conductivity                        Conductivity  (heated film)            (before doping)                        (after doping)______________________________________Comparative    A-1         10.sup.-16  10.sup.-16Example 1Example 1    A-2         1.0 × 10.sup.-14                            2.0 × 10.sup.-6Example 2    A-3         1.0 × 10.sup.-11                            1.0 × 10.sup.-5Example 3    A-4         2.8 × 10.sup.0                            2.0 × 10.sup.1Example 4    A-5         9.0 × 10.sup.1                            2.3 × 10.sup.2Comparative    A-6         2.0 × 10.sup.2                            5.0 × 10.sup.1Example 2Example 5    A-2         1.0 × 10.sup.-14                            5.0 × 10.sup.-6Example 6    A-3         1.0 × 10.sup.-11                            3.2 × 10.sup.-5Example 7    A-4         2.8 × 10.sup.0                            1.0 × 10.sup.1Example 8    A-2         1.0 × 10.sup.-14                            3.0 × 10.sup.-5Example 9    A-3         1.0 × 10.sup.-11                            2.4 × 10.sup.-4Example 10    A-4         2.8 × 10.sup.0                            9.0 × 10.sup.1Example 11    A-2         1.0 × 10.sup.-14                            5.0 ×  10.sup.-5Example 12    A-3         1.0 × 10.sup.-11                            3.5 × 10.sup.-5Example 13    A-4         2.8 × 10.sup.0                            2.0 × 10.sup.1Example 14    A-5         9.0 × 10.sup.1                            2.0 × 10.sup.2______________________________________ 
    
     In the above, the unit of conductivity is Ω -1 .cm -1 . 
     Preparation of Polycarbodiimide Film B 
     50 g of methylene diphenyldiisocyanate was subjected to a reaction in the presence of 0.13 g of a carbodiimmidization catalyst (1-phenyl-3-methylphosphorene oxide) in 820 ml of tetrachloroethylene at 120° C. for 6 hours. The resulting solution was cooled to room temperature, whereby a polycarbodiimide was precipitated. The precipitate was collected by filtration and dried at 100° C. for 2 hours to obtain a polycarbodiimide powder. 
     The powder was subjected to press molding at 180° C. at 80 kg/cm 2  to obtain a polycarbodiimide film of 20 μm in thickness. The film was heated in the same manner as in the preparation A above, to obtain insoluble and infusible substrates. 
     The heating conditions of the film and the conductivities of the heated films (substrates) are shown below. 
     
         ______________________________________Symbol of substrate       Heating temperature                       Conductivity______________________________________B-1         350° C.  2.1 × 10.sup.-19B-2         500° C.  1.8 × 10.sup.-11B-3         700° C.  3.5 × 10.sup.0B-4         900° C.  8.9 × 10.sup.1______________________________________ 
    
     In the above, the unit of conductivity is Ω -1 .cm -1 . 
     Preparation of Polycarbodiimide Film C 
     The powder obtained in the preparation B above was subjected to melt spinning to obtain a polycarbodiimide fiber of 10 μm in diameter and 10 mm in length. The fiber was layered and subjected to press molding at 150° C. at 100 kg/cm 2  to obtain a sheet-like material. And the sheet-like material was heated in the same manner as in the preparation A above, to obtain insoluble and infusible substrates. 
     The heating conditions of the fiber and the conductivities of the heated fibers (substrates) are shown below. 
     
         ______________________________________Symbol of substrate       Heating temperature                       Conductivity______________________________________C-1         500° C.  1.8 × 10.sup.-11C-2         700° C.  3.4 × 10.sup.0C-3         900° C.  8.8 × 10.sup.1______________________________________ 
    
     In the above, the unit of conductivity is Ω -1 . cm -1 . 
     EXAMPLES 15-18 and 19-21 
     The substrates B-1 to B-4 and the substrates C-1 to C-3 were doped with iodine in the same manner as in Examples 1-4 and Comparative Examples 1-2. 
     The results are shown in Table 2. 
     
                       TABLE 2______________________________________  Substrate (heated             Conductivity                         Conductivity  (film or fiber)             (before doping)                         (after doping)______________________________________Example 15    B-1          2.7 × 10.sup.-14                             3.2 × 10.sup.-6Example 16    B-2          1.8 × 10.sup.-11                             2.1 × 10.sup.-5Example 17    B-3          3.5 × 10.sup.0                             3.1 × 10.sup.1Example 18    B-4          8.9 × 10.sup.1                             2.0 × 10.sup.2Example 19    C-1          1.8 × 10.sup.-11                             2.0 × 10.sup.-5Example 20    C-2          3.4 × 10.sup.0                             3.0 × 10.sup.1Example 21    C-3          8.8 × 10.sup.1                             1.9 × 10.sup.2______________________________________ 
    
     In the above, the unit of conductivity is Ω -1 . cm -1 . 
     As appreciated from the above description, the conductive material of the present invention is free from the drawbacks of the conventional conductive polymer materials, for example, the high carbonization temperature of 1,000° C. or higher, the instability in air and the lack in flexibility. 
     Further, the conductive material of the present invention can be produced economically.