DE19653196A1 - High conductivity poly:aniline film-forming composition e.g. for electronic shields - Google Patents

Abstract

Coating composition used to give a conductive film serving as an EMI shield for electronic equipment contains polyaniline, camphor sulphonic acid (dopant) and an aromatic hydroxy compound (solvent).

Description

The present invention relates to a conductive film Polyaniline doped with combat sulfonic acid, and a Coating composition for producing the film for electromagnetic shielding.

It is known that electromagnetic waves caused by ver different electronic / electrical devices are produced that interfere with other devices and also healthy cause problems in people who receive such rays exposed for a long period of time. This phenomenon is referred to as electromagnetic interference (EMI) and Method of preventing electromagnetic leakage waves from the device producing them (EMI shielding mung) have been the subject of intense unions over the past decade investigations.

Conventional methods of EMI shielding include on close such devices with a metal shell or a plastic sleeve that contains a conductive material such as B. carbon black, Graphite, ferrite, stainless steel, silver, copper, nickel, lead etc. in the form of a powder, fabric, sieve, ribbon or contains flakes. However, a metal shell is because of it Weight and cost impractical while conductive filling plastic-containing plastic sleeves which have problems in that the physical properties of the casing deteriorate, their manufacturing costs because of the complicated manufacturing procedures increase and the effectiveness of EMI shielding often fig is unsatisfactory if the distribution of the conductive Filler occurs unevenly.  

Efforts have been made recently to conductive polymers such as polypyrrole, polyacetylene, polyaniline and polythiophene, which is a new class of mate rialien, which for many industrial applications including EMI shielding are useful. Among the Its conductive polymers have a particularly high polyaniline Doping capacity. The undoped form of polyaniline with low molecular weight and structure (I) is practiced licher than the emeraldine base form of polyaniline or simply referred to as the "Emeraldine Base" (EB) [J. G. Masters et al., Syn. Met., 41, 715 (1991)].

EB is soluble in many polar organic solvents and such solutions can be used in the production of an undoped polyaniline film, e.g. B. by pouring an EB containing the solution on a glass plate and evaporating the solvent, can be used. Such an undoped film has a low conductivity in the range of 10 ^-9 S / cm, but if it is coated with a proton, e.g. B. is doped by soaking the film in an aqueous HCl solution, the conductivity increases because of the formation of a polysemichinone radical cation of structure (II)

by ten orders of magnitude to approximately 5 S / cm.  

Japanese Patent Publication No. 92-348161 discloses a conductive polyaniline film using an N-methylpyrrolidone (NMP) solution, which a polyaniline with a high molecular weight and the reduced graced structure (III), p-toluenesulfonic acid and an oxidation contains medium, the film at an elevated temperature is activated:

In a special way, the NMP solution is placed on a glass plate pour and heated to about 100 ° C, an oxidative Ver drive with proton doping taking place to conduct capable film with a high mechanical strength put. The polyaniline films produced by this process however, have a relatively low conductivity of about 1 S / cm or less while their surface resistance in the Order of magnitude of 10⁵ Ω /.

During intensive efforts to create new lightweight materials The inventors of the present invention have developed EMI shielding Invention surprisingly found that the Conductivity of an Emeraldine-based film in Ver Relationship to previous films dramatically increased by one or two sizes orders increases when a special combination of doping agents and solvents in the manufacture of a coating solution is used to produce the film.

It is accordingly an object of the present invention to provide a to provide new coating solution, which to form a Coating film made of a highly conductive polyani lin on a case of an electronic device or off armor can be used for EMI shielding.

It is another object of the present invention, one Case for an electronic device or equipment to sit down, the effective for EMI shielding Be has layered film.

According to another aspect of the present invention a coating composition is provided, the Po lyaniline, camphor sulfonic acid and an aromatic hydroxyver bond includes.

According to another aspect of this invention, a Cover provided for an electronic device that comprises a conductive film which do with combat sulfonic acid contains polyaniline.

Fig. 1 explains schematically the measurement of the shielding effectiveness; and

Figure 2 illustrates the shielding effectiveness of the film of the invention in the 10-1000 MHz range.

The term "polyaniline" is used in the present description used to form the Polyani Emeraldine Base (EB) form lin (structure I) and this is also referred to as EB net. EB generally has a low molecular weight in Range from 8,000 to 20,000 and is in polar organic Solvents, e.g. B. N-methylpyrrolidone (NMP), chloroform,  Formic acid, phenolic compounds, etc. soluble. Such Solution containing EB can not do in the preparation of a tated polyaniline film can be used.

An organic solution that is both EB and an organic Contains sulfonic acid, even under special conditions can be prepared and this solution can be used directly for production of a doped EB film can be used. It was infrequent teter way found that by this method to manufacture doping EB film that is considerably easier than the method for doping an undoped EB film in a separate step, the film a wide range of elek trical properties can be conferred. For example, especially ri the conductivity of a doped EB film, the under Use of camphor-10-sulfonic acid (CSA) as the dopant tel has been produced from 0.5 S / cm to 5 S / cm to 190 S / cm when the solvent changes from chloroform to formic acid m-cresol was changed. On the other hand, if m-cresol as Lö was used, the conductivity of the Films from 0.6 S / cm to 15 S / cm to 190 S / cm if the doping medium from naphthalenesulfonic acid (NSA) to dodecylbenzenesulfone acid (DBSA) was changed to CSA. The size of the change the conductivity observed above is compared to State of the art completely unexpected. This can be due to this rest that depending on the solvent used and the dopant used different crystal structures of the endowed EB are formed.

The coating solution of the present invention used for Manufacture of a highly conductive film from doped Polyaniline can be used contains at least three com components; (i) polyaniline in the form of the emeraldine base, (ii) one bulky bulky alkanesulfonic acid, e.g. B. Kamp  fer-10-sulfonic acid and (iii) a solvent that has an aroma Tables hydroxy compound, which is selected from the group is chosen from phenol, cresols, xylenols and derivatives of it exists. The most preferred coating together The present invention includes polyaniline, Kamp fer-10-sulfonic acid and m-cresol.

The coating composition of the present invention can be used to cover the surface of a case electronic device for effective shielding from EMI to coat with a film. In this application, the Surface of the cover for better adhesion of the conductive film then z. B. pretreated by pre-coating with a primer will. Alternatively, the adhesion of the conductive capable film of the present invention that a coating composition is used which an epoxy resin in an amount of 10 to 50 wt .-%, bezo to the total weight of the final composition, or by using other suitable means based on are known in the field.

The following examples are intended to specifically illustrate the present invention explain more without restricting the scope of the invention.

In the examples and comparative examples, the effectiveness of the electromagnetic shielding was measured as follows. In Fig. 1, with reference, a film sample ( 3 ) is placed between a generator of electromagnetic waves ( 1 ) and a detector ( 2 ) and the effectiveness of the shielding is determined as follows:
Shielding effectiveness (dB) = 10 log (P₁ / P₂)
wherein P₁ is the incident electromagnetic power and P₂ is the transmitted electromagnetic power received by the detector.

If the distance between the source and the sample is more than λ / 2π, the effectiveness of the shielding was verified under Ver application of a flanged test device for coaxial trans Leadership according to ASTM procedure: D4935-89 be Right.

Manufacturing example Manufacture of polyaniline (Emerald base)

20 ml (about 0.22 mol) of aniline were dissolved in 300 ml of 1N hydrochloric acid Solution, cooled to 0 ° C and this was during a Period of 2 minutes while stirring and maintaining the temperature at 0 ° C a solution that by dissolving 11.5 g (about 0.05 mol) ammonium peroxydisulfate [(NH₄) ₂S₂O₈] in 200 ml of 1N salt acid had been produced. The mixture that after 5 minutes deep green, was stirred at 0 ° C for 90 minutes. Of the solid precipitate was filtered off, washed with 1N hydrochloric acid Wash until the filtrate became colorless and run for 10 minutes dried, giving 50% protonated polyaniline powder has been. The protonated polyaniline powder was dissolved in 500 ml of 0.1N Dispersed NH₄OH solution, stirred for 15 hours, during the pH was adjusted to 9 with a 1N NH₄OH solution neutralized polyaniline powder filtered, with 0.1 N NH₄OH solution solution and thoroughly washed at 10 torr for 48 hours dries, which gives the emeraldine base form of the polyaniline a molecular weight of about 70,000 was obtained. This  Polyaniline product was ge with a mortar and pestle grind and store.

example 1 Polyaniline films doped with combat sulfonic acid

0.724 g of the polyaniline powder obtained in the preparation example verse and 0.927 g (0.004 mol) camphor-10-sulfonic acid were un Thoroughly mixed using mortar and pestle. The The resulting powder mixture was in 50 g of a solvent (m-cresol, chloroform, formic acid) for 10 minutes stirred and undissolved solid was by filtration removed, giving a clear solution, the poly aniline and camphor sulfonic acid contained. This solution was then Poured on a clear glass plate and in one for 15 hours Convection oven dried, which was kept at 60 ° C where through a self-supporting (free standing) film from with Kampersulfonic acid-doped polyaniline was obtained.

The conductivity of the film so produced depended as next depending on the solvent used:

The polyaniline film doped with camphor sulfonic acid using m-cresol as a solvent had an exceptionally high conductivity as shown above, and also had a low surface resistance of 2-5 Ω /. When measured using a flanged tester for coaxial transmission power, as shown in Fig. 2, it showed high EMI shielding effectiveness of 38-41 dB at a frequency range of 10 to 1000 MHz. These results are shown in Table 1.

Comparative Example 1 A doped with dodecylbenzenesulfonic acid ter polyaniline film

The procedure of Example 1 was followed using 0.004 Moles of dodecylbenzenesulfonic acid (DBSA) instead of combat sulfone repeated acid, whereby using m-cresol as Lö a self-supporting film made with dodecylbene bolsulfonic acid doped polyaniline was obtained. The lei Performance properties of this film are set out in Table 1 leads.

Comparative Example 2 Po doped with naphthalene sulfonic acid lyaniline film

The procedure of Example 1 was followed using 0.004 Moles of naphthalenesulfonic acid (NSA) instead of camphor sulfonic acid and repeated using m-cresol as solvent, making a self-supporting film from with naphthalene sul Fonic acid-doped polyaniline was obtained. The performance egg Properties of this film are listed in Table 1.

Comparative Example 3 HCl-doped polyaniline film

A procedure similar to that in Example 1 was used to using 0.004 mol HCl a Po doped with HCl  to produce lyanilin film. The performance characteristics of this Films are listed in Table 1.

Reference example Polyaniline film containing carbon black

2 g of the polyaniline powder contained in the production example verses were slowly added to 30 ml of NMP with stirring, and then 1.5 g of carbon black was dispersed therein. The resulting mixture was poured onto a clear glass plate and as in Example 2 dried, resulting in a self-supporting film made of soot retaining polyaniline was obtained. The performance characteristics of this film are shown in Table 1.  

Table 1

Performance properties of conductive films based on polyaniline

As can be seen from the results in Table 1, the in Example 1 using m-cresol as a solvent put inventive film compared to other Leitfä superior films as a conductor and as EMI shielding material.

While the present invention with reference to the specific embodiments have been described, it is clear that various changes and modifications can be carried out, which is also under the scope of present invention as defined by the following sayings is defined.

Claims (5)

1. Coating composition, the polyaniline, Kampfersul contains acid and an aromatic hydroxy compound. 2. A coating composition according to claim 1, wherein the aromatic hydroxy compound is m-cresol. 3. A coating composition according to claim 1 or 2, which further contains an epoxy resin. 4. Conductive film, the polyaniline and camphor sulfonic acid contains, the film using the coating composition according to claim 1, 2 or 3 has been prepared. 5. Case for an electronic device with a loading The conductive film layer of claim 4.