JPH09183945A - Conductive polyaniline doped with camphorsulfonic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition useful to form an electromagnetic- wave-shielding highly conductive film on an electronic device, instrument or apparatus by mixing a polyaniline with a plurality of specified compounds.

SOLUTION: A polyaniline (in the form of an emeraldine base) is mixed with camphorsulfonic acid and an aromatic hydroxy compound, desirably m- cresol. An epoxy resin in an amount of desirably 10-50wt.%, based on the total weight of the final composition, is optionally added to the obtained mixture. The conductivity of the emeraldine base form polyaniline doped with camphorsulfonic acid dopant which improves the adhesion of a conductive film varies with the solvent used. The conductivity of a film prepared by using specially m-cresol as the solvent is the most excellent.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyaniline conductive film doped with camphorsulfonic acid and a coating composition for producing the film for electromagnetic wave shielding.

[0002]

2. Description of the Related Art It is known that electromagnetic waves generated by various electronic / electrical devices interfere with the operation of other devices and cause a disease when a person is exposed to electromagnetic waves for a long time. This phenomenon is caused by electromagnetic interference (EMI: Electromagneti).
c Interference), a method of shielding the electromagnetic waves emitted from the source equipment (EMI shielding) has been intensively studied for several years. In addition to the conventional EMI shielding method, the source device is attached to a metal case, or a conductive material (for example,
Carbon black, graphite, ferrite, stainless steel,
Silver, copper, nickel, lead, etc.) powder, fabric, mesh,
There is a method of surrounding with a plastic case containing in the form of ribbon or flake. However, the metal case is not practical due to its weight and cost, and the plastic case containing the conductive filler deteriorates the physical properties of the case, increases the manufacturing cost due to the complicated manufacturing process, and increases the conductivity. Low E that appears when the filler distribution is not uniform
There are problems such as MI shielding effect.

Recently, conductive polymers such as polypyrrole, polyacetylene, polyaniline and polythiophene have been developed and studied as new substances useful in many industrial fields including EMI shielding. Among the conductive polymers, polyaniline has a particularly high doping ability.
The undoped low molecular weight polyaniline having the structure of formula (I) is referred to as the emeraldine base form of polyaniline or simply "emeraldine base (EB)" (JG Master et al., " Syn.Met " ). . , 41 , 715 (1991) ”).

[0004]

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EB is soluble in many polar organic solvents, and such a solution containing EB is a solution of undoped polyaniline (dedoped polyaniline) by methods such as spreading it on a glass plate and then evaporating the solvent. It can be used to make films. This dedoped polyaniline film has a low electric conductivity of about 10 ⁻⁹ S / cm, but when the film is doped with protons (protons) by immersing the film in an aqueous HCl solution, a polysemiquinone of the following formula (II) is obtained. (Polysemiquin
one) conductivity is 1 because radical cations are formed
It increases by about 0 digits and becomes about 5 S / cm.

[0006]

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Japanese Patent Publication No. 92-348161 uses an N-methylpyrrolidone (NMP) solution containing a high molecular weight polyaniline having a reduced structure of formula (III), p-toluenesulfonic acid and an oxidizing agent. Disclosed is a conductive polyaniline film in which the film produced by the above is activated at high temperature.

[0008]

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In particular, when the NMP solution is spread on a glass plate and heated at 100 ° C. or higher, a conductive film having high mechanical strength is obtained due to the progress of the oxidizing proton-doping process. However, the polyaniline film produced by the above method has a relatively low conductivity of about 1 S / cm or less, and its surface resistance is about 10 ⁵ Ω / □.

The present inventors have conducted extensive research to develop a new low molecular weight substance for EMI shielding, and as a result, when a specific dopant and solvent were used in the production of a polyaniline coating solution, a doped emeraldine base film was used. It has been found that the conductivity of γ is significantly increased over the previously reported values and is 1-2 orders of magnitude higher.

[0011]

Accordingly, it is an object of the present invention to provide a new coating solution that can be used to form a highly conductive polyaniline film for EMI shielding on the case of electronic equipment or devices. Is.

Another object of the present invention is to provide a film-coated electronic device or device case effective for EMI shielding.

[0013]

According to one aspect of the invention, there is provided a coating composition comprising polyaniline, camphorsulfonic acid and an aromatic hydroxy compound.

According to another aspect of the present invention, there is provided a case for an electronic device coated with a conductive film containing polyaniline doped with camphorsulfonic acid.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The term "polyaniline" as used herein refers to polyaniline (Formula (I)) in the emeraldine base (EB) form and may be used interchangeably with EB. EBs generally have a low molecular weight in the range of 8,000 to 20,000 and are soluble in polar organic solvents such as N-methylpyrrolidone (NMP), chloroform, formic acid, phenol derivatives and the like. The solution containing the EB can be used to prepare an undoped polyaniline film (dedoped polyaniline film).

A solution containing EB and an organic sulfonic acid can be prepared under specific conditions, and this solution can be directly used for preparing a doped EB film. This method of directly producing a doped EB film is much simpler than the method of doping a dedoped polyaniline film in a separate processing step, and it can also give the film a wide range of electrical properties. It was revealed. For example, E doped with camphor-10-sulfonic acid (CSA) as a dopant
The conductivity of the B film varies greatly depending on the solvent used. When the solvent is changed to chloroform, formic acid, or m-cresol, the conductivity is 0.5 S / cm, 5 S / cm, 190 S.
It changes with / cm. On the other hand, using m-cresol as a solvent, the dopant is naphthalene sulfonic acid (NSA),
When changed to dodecylbenzene sulfonic acid (DBSA) and CSA, the conductivity of the film is 0.6S / cm, 15S / cm.
cm and 190 S / cm. The large change in conductivity observed here was completely unexpected from the prior art, as the solvent used and the dopant formed doped EBs with different crystal structures. Guessed.

The coating solution of the present invention which can be used for the production of highly conductive films of doped polyaniline contains at least three components: (i) emeraldine base form of polyaniline, (ii) steric hindrance. Sterically crowded alkane sulfonic acids (eg camphor-10-sulfonic acid) and (ii
i) A solvent containing an aromatic hydroxy compound selected from the group consisting of phenol, cresol, xylenol and derivatives thereof. The most preferred coating composition of the present invention comprises polyaniline, camphor-10-sulfonic acid and m-cresol.

The coating composition of the present invention can be used to coat a conductive film on the surface of an electronic device case to effectively shield EMI. In such applications, the surface of the case can be precoated with a primer to form a conductive film with better adhesion. Another method of improving the adhesion of the conductive film of the present invention is to use a coating composition further containing an epoxy resin in an amount ranging from 10 to 50% by weight based on the total weight of the final composition. , And other suitable means known in the art may also be utilized.

The following examples serve to illustrate the present invention in more detail and do not limit the scope of the invention.

[0020]

[Examples] In Examples and Comparative Examples, the electromagnetic shielding effect was measured as follows. As shown in FIG. 1, the sample film (3) was placed between the electromagnetic wave generator (1) and the detector, and its shielding effect was determined by the following formula.

Shielding effect (dB) = 10 × log (P1 / P2)

(Where P1 is the power of the incident electromagnetic wave and P2 is the power of the electromagnetic wave received by the detector).

The distance between the electromagnetic wave source and the sample is λ / (2π)
If greater than ASTM (American Society for Testing and Materials): D4
The shielding effect was determined using a flange type coaxial transmission line measuring instrument according to 935-89.

Production Example : Production of polyaniline (emeraldine base) 20 ml (about 0.22 mol) of aniline was added to a 1N hydrochloric acid solution 3
It was dissolved in 00 ml and cooled to 0 ° C., and to this was added 200 ml of 1N hydrochloric acid solution ammonium peroxodiphosphate [(NH
₄ ) ₂ S ₂ O ₈ ] 11.5 g (about 0.05 mol) was dissolved and the resulting solution was added over 2 minutes while stirring at 0 ° C. The mixture (turned dark green after 5 minutes) was stirred at 0 ° C. for 90 minutes. The formed solid precipitate was filtered, washed with a 1N hydrochloric acid solution until the filtrate became colorless, and air-dried for 10 minutes to obtain a 50% protonated polyaniline powder. This protonated polyaniline powder was added to 0.1N NH ₄ OH 5
In addition to 00 ml, neutralized polyaniline powder was obtained by stirring for 15 hours while adjusting the pH to 9 with 1N NH ₄ OH solution, and the powder was filtered and washed with 0.1N NH ₄ OH solution, and then 10 It was dried under a Toll (1333.2 Pa) for 48 hours to obtain polyaniline in the form of emeraldine base having a molecular weight of about 70,000, which was stored as a powder with a mortar and pestle.

Example 1 : Polyaniline film doped with camphorsulfonic acid 0.724 g of the polyaniline powder obtained in the preparation example and 0.927 g (0.004 mol) of camphor-10-sulfonic acid were used in a mortar and pestle. Mixed well. The obtained powder mixture was put in 50 g of a solvent (m-cresol, chloroform, or formic acid) and stirred for 10 minutes, and a small amount of insoluble matter was removed by filtration to obtain a transparent solution containing polyaniline and camphorsulfonic acid. . The solution was poured onto a glass plate and then dried in a convection oven maintained at 60 ° C. for 15 hours to obtain a camphorsulfonic acid-doped polyaniline film.

The conductivity of the thus-produced film changed as follows depending on the solvent used.

[0027]

The camphorsulfonic acid-doped polyaniline film prepared using m-cresol as a solvent has a remarkably high conductivity as described above,
It also had a low surface resistance of 2 to 5 Ω / □. When the EMI shielding effect was measured using a flange type coaxial transmission line measuring machine, as shown in FIG.
It showed a high EMI shielding effect of 38 to 41 dB in the frequency range of. Table 1 shows the results of measuring the physical properties of a film produced using this m-cresol as a solvent.

Comparative Example 1 : Polyaniline Film Doped with Dodecylbenzene Sulfonic Acid 0.004 mol of dodecylbenzene sulfonic acid (DBSA) was used in place of camphor sulfonic acid and m-cresol was used as the solvent in the procedure of Example 1. By repeating the above, a polyaniline film doped with dodecylbenzenesulfonic acid was obtained. Table 1 shows the physical properties of this film.

Comparative Example 2 : Polyaniline film doped with naphthalene sulfonic acid The procedure of Example 1 is repeated using 0.004 mol of naphthalene sulfonic acid (NSA) instead of camphor sulfonic acid and using m-cresol as the solvent. Thus, a polyaniline film doped with naphthalenesulfonic acid was obtained. Table 1 shows the physical properties of this film.

Comparative Example 3 Polyaniline Film Doped with HCl A HCl-doped polyaniline film was prepared by the same procedure as in Example 1 using 0.004 mol of HCl. Table 1 shows the physical properties of this film.

Reference Example : Polyaniline Film Containing Carbon Black 2 g of the polyaniline powder obtained in the Production Example was added to 30 m of NMP.
After gradually adding to 1 liter with stirring, 1.5 g of carbon black was added thereto and mixed. The resulting mixture was poured onto a glass plate and dried as in Example 1 to obtain a polyaniline film containing carbon black. Table 1 shows the physical properties of this film.

[0033]

[Table 1]

As can be seen from the results shown in Table 1, the film of the present invention prepared by using m-cresol as a solvent in Example 1 is a conductor and EM as compared with other conductive films.
I has excellent performance as a shielding material.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a shielding effect measuring method.

FIG. 2 is a graph showing the shielding effect of the film of the present invention in the range of 10 to 1000 MHz.

Claims (5)

[Claims] 1. A coating composition comprising polyaniline, camphor sulfonic acid and an aromatic hydroxy compound. 2. The coating composition according to claim 1, wherein the aromatic hydroxy compound is m-cresol. 3. The coating composition according to claim 2, further comprising an epoxy resin. 4. A conductive film comprising polyaniline and camphor sulfonic acid produced using the coating composition of claim 1, 2 or 3. 5. An electronic device case coated with the conductive film according to claim 4.