WO1995018453A1

WO1995018453A1 - Conducting plastic material and method of producing such material

Info

Publication number: WO1995018453A1
Application number: PCT/FI1994/000572
Authority: WO
Inventors: Hannele Järvinen; Toivo Kärnä; Jukka Laakso; Kalle Levon; Heikki Ruohonen
Original assignee: Neste Oy
Priority date: 1993-12-27
Filing date: 1994-12-19
Publication date: 1995-07-06
Also published as: FI935855A0; FI935855A; AU1244895A

Abstract

The present invention is related to a conducting polyaniline-based, neutralized, melt-processible plastic material with good mechanical strength properties. The plastic material according to the invention employs a sulfonated terpolymer, advantageously neutralized with zinc acetate, as the plasticizing agent between the conducting polymer and the matrix polymer. Such a plastic material is elastically rubbery, whereby its properties including impact strength are improved. A further advantage of the plastic material according to the invention is that no noxious emissions or migration are incurred during its production and processing. The invention also concerns a method of producing said material.

Description

Conducting plastic material and method of producing such material
The present invention concerns a novel type of neutralized, polyaniline-based, electrically conducting plastic material which exhibits melt-processibility and high mechanical sty goth properties. The plastic material according to the invention contains polyaniline doped with a protic acid and a sulfonated, neutralized terpolymer. Besides its good mechanical and conducting properties, such a plastic material has the benefit of not presenting during its production and processing such additive emissions or migration that might pose an environmental hazard.

Currently, electrically conducting polymers are subjected to in-depth research worldwide.

Such polymers offer the possibility of replacing metallic conductors and semiconducting materials in a plurality of applications including batteries, transducers, switches, photocells, circuit boards, heating elements, antistatic protection (against ESD) and electromagnetic protection (against EMI). Conducting polymers possess, i.a., the following advantages over metals: light weight, advantageous mechanical properties, good corrosion resistance and lower production and processing costs.

Conducting plastics can be roughly categorized into two different groups: filled conducting plastics in which a thermosetting or thermoplastic resin is made conductive by the addition of a conductive filler such as, e.g., carbon black or lampblack, carbon fiber, metal powder, etc., and intrinsically conducting plastics based on polymers made conductive by an oxidation or reduction (doping) process.

The electrical conductivity of filled conducting plastics is dependent on the mutual contacts formed between the conductive filler particles. Typically, approx. 10...50 wt-% of well-dispersed filler material is required to achieve composites of high conductance.

Such conducting composite materials have, however, several drawbacks: The mechanical and certain chemical properties of such composites are decisively degraded with the increase in the filler content and decrease in the polymer content; their conductivity becomes difficult to control particularly in the semiconductor range; and stable and homogeneous dispersing of their filler into the matrix polymer becomes difficult.

Intrinsically conducting plastics can be produced from organic polymers having long chains formed by conjugated double bonds and heteroatoms. The polymers are made conducting by perturbing the 7r- and 7r-p electron systems of the double bonds and heteroatoms in the polymers by adding into the polymer matrix certain doping agents which can be either of electron donor or acceptor type. Thus, the backbone chain of the polymer can be modified to contain holes and/or excess electrons that provide pathways to electric current along the conjugated chain.

The benefits of intrinsically conducting plastics include easy modification of their conductivity as a function of the dopant concentration also termed as the doping level which is particularly accentuated in conjunction with low conductivities. By contrast, attaining low conductivities with filled conducting plastics is difficult. Exemplifying kinds of polymers known in the art to be suited for use in the production of intrinsically conducting plastics are polyacetylene, poly-p-phenylene, polypyrrole, polythiophene with its derivatives and polyaniline with its derivatives.

Plastics are manufactured into desired articles, fibers, films, etc., along two major lines: melt processing and solution processing. Melt processing is suited for multiple applications, whilst solution processing can be used principally only in the manufacture of fibers and films, but not for making shaped articles. However, the processing and doping of most intrinsically conducting plastics have problems in the handling, stability, homogeneity and other aspects of these materials.

A technically and commercially promising intrinsically conducting polymer is particularly polyaniline and its derivatives. An aniline polymer is based on an aniline unit in which the nitrogen atom is bonded to the para-carbon in the benzene ring of the next unit. Polyaniline can occur in several different forms such as leucoemeraldine, protoemeraldine, emeraldine, nigraniline and toluprotoemeraldine. For conducting polymer applications, the emeraldine form is mostly used having the formula
EMI2.1
wherein x is approx. 0.5.

Doping of polyaniline is performed in accordance with methods known in the art by virtue of conventionally using protic acids including among others HCl, 112SO4, HNO3, HCl04,
HBF4, HPF6, HF, acids of phosphorus, sulfonic acids, picric acid, n-nitrobenzoic acid, dichloroacetic acid and polymeric acids. Doping is advantageously performed with a sulfonic acid and most advantageously with dodecylbenzene sulfonic acid (DBSA). Protonation attacks the nonprotonated nitrogen atoms of the aniline units shown in the formula above, the proportion of such nonprotonated nitrogen atoms being approx. 50 % of all
N-atoms of the emeraldine base form of polyaniline. Herein reference is made to, e.g.,
US patent publications 3,963,498, 4,025,463 and 4,983,322, which are representative example of the publications in the art.

Numerous references to the doping of polyaniline with protic acids may also be found in the literature of the art.

Polyaniline doped with a protic acid has been found extremely useful when blended with an excess amount of said protic acid such as, e.g., the above-mentioned sulfonic acid or its derivative, whereby said acid is contained in the polymer blend sufficiently for both the doping and plasticization of the blend. In fact, using excess amounts of the protic acid in this manner makes the doped polyaniline suited for melt-processing as the protic acid serves for two functions in the blended compound. Such use of excess protic acid gives doped polyaniline with an acidic pH value. However, acidity may decisively hamper the use of a conducting polymer is most applications.

FI patent publication 923,580 discloses a method of reducing the acidity of a conducting polymer containing polyaniline doped with a protic acid, advantageously a sulfonic acid and most advantageously dodecylbenzene sulfonic acid. In the method according to cited publication, the polymer blend containing doped polyaniline is treated with a metallic compound. According to the preferred embodiment of the method, the compound suited for neutralizing the doped polyaniline is prepared by reacting a metallic compound, most advantageously zinc oxide, with any acid capable of forming with said metallic compound such a compound that acts as a plasticizer for the doped polyaniline. Such an acid is advantageously the same acid as that used for doping, namely, dodecylbenzene sulfonic acid (DBSA).

The reaction mixture is heated and plasticizing metallic compound thus formed is dried, cooled and milled prior to being blended with the doped polyaniline. To transform the doped polyaniline into a processible form, the solidification method based on heat treatment disclosed in application publication 915,760 is used.

Accordingly, the above-described method provides, most advantageously using a
ZnO/DBSA compound, a conducting polyaniline plastic having a neutral pH value, said polyaniline being blended to the end of achieving required mechanical properties with a suitable matrix polymer such as polyethylene, for instance. Thus, the zinc compound acts in this kind of a blend as a plasticity and compatibility improving agent between the conducting polymer and the matrix polymer.

One of the disadvantages in the production of the above-described type of conducting polymer material plasticized with a ZnO/DBSA compound include, however, the noxious gases which are emitted during both its formation and processing, whereby its production and processing require extremely well protected process conditions. Further, articles made from such a material exhibit undesirable migration. Moreover, the mechanical properties of a product formed using said zinc compound are not in all aspects sufficiently high for the needs of such demanding applications as packaging and coating, for instance.

It is an object of the present invention to achieve a polyaniline-based plastic material of high electrical conductivity suited for further processing by means of different solutionand melt-processing methods.

It is a further object of the invention to achieve a conducting plastic material of sufficiently neutral pH value, which is compatible with, i.a., different kinds of processing machinery.

It is another further object of the invention to provide a safe solution in terms of environmental protection and occupational health to the problem of eliminating the emission of noxious gases and vapours in the formation and processing of polyaniline-based conducting material prepared using prior-art methods.

It is still a further object of the invention to achieve a conducting plastic material whic: is free from the migration of gases and vapours even during a prolonged use of articles manufactured thereof.

It is further another object of the invention to achieve a conducting plastic material with improved mechanical properties such as extremely high impact strength, for instance.

Unexpectedly, it has recently been found that a neutralized, melt-processible conducting plastic material according to the present invention with extremely strong mechanical properties can be attained by first blending a neutralized, sulfonated terpolymer into a polyaniline polymer doped with a protic acid. The conducting complex polymer thus obtained is further blended with a desired matrix polymer in order to form a neutralized, melt-processible polymer material characterized by mechanical strength and good electrical conductivity. The neutralized, sulfonated terpolymer used in the invention replaces the conventional Jse of the ZnO/DBSA compound in the formation of polyaniline-based conducting plastic material. This novel approach gives the end product excellent mechanical properties and good conductivity.

The end product is also free from any undesirable migration. Moreover, the conducting plastic material according to the invention releases no noxious emissions during its formation or processing. The reduction of emissions and migration effects results from the strong tendency of the polymeric plasticizing agent to bond to the backbone of the polyaniline polymer. Hence, the conducting plastic material according to the invention is characterized by what is stated in the characterizing part of claim 1.

Whereas the use of sulfonated polymers in the formation of conducting aniline polymers is known in the art, their function has been to dope the polyaniline into a conducting polymer. E.g., EP patent publication 104,726 discloses the doping of polyaniline with a sulfonated polyethylene or sulfonated styrenebutadiene copolymer. By contrast, the present invention accomplishes the doping of polyaniline by means of a protic acid and the function of the sulfonated polymer is to act as a plasticizing agent in the composition and a compatibility improving agent between the conducting polymer and the matrix polymer.

Hence, the composition according to the invention has polyaniline doped with a protic acid blended with a neutralized, sulfonated terpolymer. Most advantageously, said sulfonated terpolymer is a sulfonated ethylene-propylene-diene terpolymer neutralized with a zinc compound such as zinc acetate or zinc stearate. Accordingly, the polymer thus obtained is most advantageously a Zn-sulfonated ethylene-propylene-diene terpolymer.

Zinc-neutralized sulfonated ethylene-propylene-diene terpolymers as such are compounds known in art. They have been found capable of improving some mechanical properties of
HD polyethylene such as compressive strength. For details, reference can be made to, e.g., publication X. Xu, X. Zeng and H. Li, J. Appl. Polym. Sci., 44, 2225 (1992). Yet, cited publication does not teach the use of said terpolymer to the end discovered in the present invention nor its use in conducting polymer compositions. Cited publication, however, discloses a sulfonation and zinc neutralization method of ethylene-propylenediene terpolymer, which method is also employed in the conversion of commercially available ethylene-propylene-diene terpolymer into the zinc-sulfonated ethylene-propylenediene terpolymer used in the invention.

Consequently, the polyaniline-based conducting plastic material according to the invention containing a zinc-sulfonated ethylene-propylene-diene terpolymer is a novel composition, and the use of said terpolymer as a plasticizing agent according to the invention is also a novel use for said terpolymer.

The zinc-neutralized, sulfonated ethylene-propylene-diene terpolymer is formed using the method of the above-cited publication by first preparing a solution of ethylene-propylenediene terpolymer in cyclohexane. To this solution is added acetylsulfate or acetylsulfonate.

The acetylsulfate is obtained by reacting acetic acid anhydride with 97 % sulfuric acid, and the acetylsulfonate is correspondingly obtained from acetic acid anhydride and a sulfonic acid such as dodecylbenzene sulfonic acid. The amount of added acetylsulfate/sulfonate is dependent on the amount of diene monomer in the ethylenepropylene-diene monomer. The mixture is allowed to react approximately half an hour, and the reaction is terminated with ethanol. The mixture is neutralized with zinc acetate, and the solvents are evaporated in a rotavapor-type rotary evaporator. Hence, this procedure affords a zinc-sulfonated ethylene-propylene-diene terpolymer.

Additionally, zinc stearate may be mixed into the zinc-sulfonated ethylene-propylene-diene terpolymer prepared according to the above-described method by approx. 0 - 15 wt-% of the amount of the terpolymer at a temperature not greater than 200 "C. This mixture is further blended with a complex formed by polyaniline and a protic acid, advantageously dodecylbenzene sulfonic acid and a matrix polymer such as HD polyethylene.

In the mixture the mole ratio of the polyaniline to the protic acid acting as the dopant is in the range 1:0.1 - 1:3, more advantageously in the range 1:0.25 - 1:1, and most advantageously in the range 1:0.5 - 1:0.7. The function of the zinc stearate in the blend is to neutralize the possibly remaining excess acid, whereby the end product is a conducting polymer material with a neutral pH value. Neutral pH in this context must be understood to refer to a material having a pH in the range pH 3 - 8, more advantageously in the range pH 5 - 7. Whilst the permissible acidity of the material is chiefly dictated by the acid-proofness of equipment employed in the formation and processing of the material, also the end products may be required to have neutral or almost neutral pH values.

Neutralized, sulfonated terpolymer is added to polyaniline doped with a protic acid in a weight ratio of 1:4 - 1:1, more advantageously in a weight ratio of 1:2.5 - 1:1.5 when the weight ratio is determined as the weight ratio of the zinc-sulfonated ethylenepropylene-diene terpolymer to the polyaniline doped with dodecylbenzene sulfonic acid.

By virtue of varying the weight ratio, different properties can be obtained in terms of the extent of migration as well as the homogeneity, surface quality and electrical conductivity of the material. For instance, a product with improved homogeneity and surface quality can be achieved by increasing the amount of the plasticizing agent. Alternatively, a larger proportion of the Zn-sulfonated polymer reduces migration, and increasing the proportion of the polyaniline-DBSA complex enhances conductivity. When required, the end result of neutralization can be improved by adding zinc oxide to the blend by 0 - 10 wt-% of the amount of the polyaniline-proti acid complex. The conducting polymer thus obtained is then blended with the matrix polymer.

The blending temperature is advantageously in the range 140 - 250 "C, more advantageously in the range 180 - 210 "C. The most generally used matrix polymers include, e.g., polyethylene, polypropene, ethylvinylacetate, polystyrene, styrenebutadiene, polyester, polycarbonate and polyamide (nylon) resins. The blending temperature is determined by the selected matrix polymer so that with ethylvinylacetate, for instance, the blending temperature may be as low as 140 "C, and also with polyethylene, temperatures as low as below 200 "C can be employed, whereas for polypropene the blending temperature is approx. 200 "C, and for instance, polyamide and polycarbonate require a blending temperature as high as approx. 250 "C.

The proportion of the conducting polymer material in the blended plastic is attempted to be minimized for both technical and economical reasons. Accordingly, the content of the conducting polymer in the conducting plastic material can be approx. 1 - 50 wt-%, advantageously 1 - 25 wt-% and most advantageously 5 - 15 wt-%.

The neutral plastic material achieved as the end result of the above-described method has an essentially elastically rubbery consistency, whereby such factors as its impact strength are significantly improved, and yet, its electrical conductivity properties are in the same order with those of the prior-art plastic material containing a ZnO/DBSA-polyaniline complex. Noxious emissions during formation and processing remain to an insignificant level with the novel conducting plastic material prepared in accordance with the method of the present invention, and moreover, an end product made thereof is free from any undesirable migration.

Next, the formation of the conducting plastic materials according to the invention and properties thereof are described in greater detail with the help of the following examples.

Example 1
Preparation of zinc-sulfonated ethylene-propylene-diene terpolymer:
A commercial ethylene-propylene-diene terpolymer grade (DSM product code Keltan 778P) having a 4 % content of diene monomers is dissolved in cyclohexane to obtain a 5 % solution. To the solution is added 1 - 15 % of acetylsulfate or acetylsulfonate. The mixture is reacted for about half an hour and the reaction is terminated with ethanol. The mixture is neutralized with zinc acetate and the solvents are evaporated in a rotavapor-type rotary evaporator thus obtaining the end product which is zinc-sulfonated ethylenepropylene terpolymer.

Example 2
Preparation of conducting plastic material:
The zinc-sulfonated ethylene-propylene-diene terpolymer prepared according to the method of Example 1 was mixed with zinc stearate in a weight ratio of 90 wt-% to 10 wt-% at 170 "C. The mixture obtained was further mixed with a polyaniline-DBSA complex (having a 1:4 weight ratio of polyaniline to DBSA) containing 7 wt-% of ZnO added to it, whereby the blending ratio was 40 wt-% of the terpolymer to 60 wt- % of the polyaniline complex, and the mixture was finally blended at different temperatures with the matrix polymer which in the example was HD polyethylene NCPE 3415 by Neste Oy.

The blending time was 80 s. The end product obtained was elastic, strong, conducting, melt-processible plastic material from which an injection-moulded test piece was made having a smooth surface and good impact strength.

Table 1 gives the conductivities of prepared conducting plastic materials for different amounts of matrix polymer and blending temperatures.

Table 1
EMI9.1

<tb> Matrix <SEP> resin <SEP> Amount <SEP> of <SEP> matrix <SEP> Blending <SEP> temperature <SEP> Electrical
<tb> <SEP> resin <SEP> [wt-%] <SEP> [ C] <SEP> conductivity <SEP> [S/cm]
<tb> NCPE <SEP> 3415 <SEP> 80 <SEP> 180 <SEP> 3.4 <SEP> 104 <SEP>
<tb> NCPE <SEP> 3415 <SEP> 80 <SEP> 190 <SEP> 5.8 <SEP> 104 <SEP>
<tb> NCPE <SEP> 3415 <SEP> 85 <SEP> 190 <SEP> 1.2-10-7 <SEP>
<tb>
Simple sensory tests also indicate that the amount of volatile components formed during the blending was significantly lower than when using a ZnO/DBSA compound instead of the zinc-sulfonated terpolymer.

Example 3
Migration in conducting plastic material, comparative test:
Using the method described in Example 2, conducting plastic materials were prepared the first of which representing the comparative material contained as the plasticizing agent a
Zn/DBSA compound according to the prior art, rather than the zinc-sulfonated ethylenepropylene-diene terpolymer prepared according to Example 1, whilst the second material contained zinc-sulfonated ethylene-propylene-diene terpolymer according to the invention.

The amount of the matrix polymer (NCPE 3415) in both material samples was 85 wt-%.

The material samples were made into pieces having a thickness of 0.5 mm and an area of 1 dm2. The test pieces were stored for 3 weeks at 90 "C and 30 % relative humidity.

After the storage period, the migration measured for the comparative test piece was 0.7 wt-%, whilst for the test piece prepared according to the invention the migration was close to 0 wt-%, that is, a piece made from the material according to the invention exhibited no undesirable migration.

Simple sensory tests also indicate that the amount of volatile components formed during the processing of the conducting plastic material according to the invention did not release any noxious or gases normally present during processing.

Claims

1. A conducting, neutral, melt-processible plastic material formed by polyaniline doped with a protic acid and by matrix polymer, c h a r a c t e r i z e d in containing a neutralized, sulfonated terpolymer acting as a plasticizing agent between said polyaniline and said matrix polymer.

2. A conducting plastic material as defined in claim 1, c h a r a c t e r i z e d in that said neutralized, sulfonated terpolymer is a ethylene-propylene-diene terpolymer neutralized with zinc acetate, that is, a zinc-sulfonated ethylene-propylene-diene terpolymer.

3. A conducting plastic material as defined in claim 1, c h a r a c t e r i z e d in that said protic acid-doped polyaniline is polyaniline doped with a sulfonic acid or its derivative, advantageously dodecylbenzene sulfonic acid.

4. A conducting plastic material as defined in claim 1 or 3, c h a r a c t e r i z e d in that the mole ratio of the polyaniline to the protic acid acting as the dopant is in the range 1:0.1 - 1:3, more advantageously in the range 1:0.25 - 1:1 and most advantageously in the range 1:0.5 - 1:0.7.

5. A conducting plastic material as defined in claim 1, c h a r a c t e r i z e d in that the weight ratio of said neutralized, sulfonated terpolymer to the protic acid-doped polyaniline is in the range 1:4 - 1:1, more advantageously in the range 1:2.5 - 1:1.5 when determined as the weight ratio of the zinc-sulfonated ethylene-propylene-diene terpolymer to the polyaniline doped with dodecylbenzene sulfonic acid.

6. A conducting plastic material as defined in any of foregoing claims 1 - 5, c h a r a c t e r i z e d in that said material additionally contains zinc stearate and zinc oxide.

7. A conducting plastic material as defined in claim 6, c h a r a c t e r i z e d in that said zinc stearate is added by 0 - 15 wt-% of the amount of the neutralized, sulfonated terpolymer and the zinc oxide is added by 0 - 10 wt-% of the amount of the polyanilineprotic acid complex.

8. A conducting plastic material as defined in claim 1, c h a r a c t e r i z e d in that the matrix polymer employed is any polymer conventionally used as a matrix polymer, advantageously a thermoplastic resin.

9. A conducting plastic material as defined in claim 8, c h a r a c t e r i z e d in that in said conducting plastic material the proportion of the conducting polymer containing the protic acid-doped polyaniline complex is 1 - 50 wt-%, more advantageously 1 - 25 wt-% and most advantageously 5 - 15 wt-%, whilst the corresponding proportion of the matrix polymer is 99 - 50 wt-%, more advantageously 99 - 75 wt-% and most advantageously 95 - 85 wt-%.

10. A method of producing the conducting, neutral, melt-processible plastic material defined in claim 1 containing protic acid-doped polyaniline and a matrix polymer, c h a r a c t e r i z e d in that said neutralized, sulfonated terpolymer is blended with said protic acid-doped polyaniline and said matrix polymer at a temperature of 140 - 250"C, more advantageously at 180 - 2100C.

11. A method as defined in claim 10, c h a r a c t e r i z e d in that neutralized zincsulfonated ethylene-propylene-diene terpolymer is blended with said protic acid-doped polyaniline and said matrix polymer.

12. A method as defined in claim 10 or 11, c h a r a c t e r i z e d in that said protic acid-doped polyaniline is polyaniline doped with sulfonic acid or its derivative, most advantageously dodecylbenzene sulfonic acid.

13. A method as defined in any of foregoing claims 11 - 12, c h a r a c t e r i z e d in that in the mixture the mole ratio of the polyaniline to the protic acid acting as the dopant is in the range 1:0.1 - 1:3, more advantageously in the range 1:0.25 - 1:1, and most advantageously in the range 1:0.5 - 1:0.7.

14. A method as defined in claim 10, c h a r a c t e r i z e d in that the weight ratio of said neutralized, sulfonated terpolymer acting as the plasticizing agent to the protic aciddoped polyaniline is in the range 1:4 - 1:1, more advantageously in the range 1:2.5 - 1:1.5 when determined as the weight ratio of the zinc-sulfonated ethylenepropylene-diene terpolymer to the polyaniline doped with dodecylbenzene sulfonic acid.

15. A method as defined in any of foregoing claims 11 - 14, c h a r a c t e r i z e d in that zinc stearate and zinc oxide are additionally blended with the mixture formed by the polyaniline doped with a protic acid, advantageously dodecylbenzene sulfonic acid, by the neutralized, sulfonated terpolymer which advantageously is a zinc-sulfonated ethylenepropylene-diene terpolymer and by the matrix polymer.

16. A method as defined in claim 15, c h a r a c t e r i z e d in that the zinc stearate is added by 0 - 15 wt-% of the amount of the neutralized, sulfonated terpolymer and the zinc oxide is added by 0 - 10 wt-% of the amount of polyaniline-protic acid complex.

17. A method as defined in claim 10, c h a r a c t e r i z e d in that the matrix polymer employed is any polymer conventionally used as a matrix polymer.

18. A method as defined in claim 17, c h a r a c t e r i z e d in that in the conducting plastic material the proportion of the conducting polymer containing the protic acid-doped polyaniline complex is 1 - 50 wt-%, more advantageously 1 - 25 wt-% and most advantageously 5 - 15 wt-%, whilst the corresponding proportion of the matrix polymer is 99 - 50 wt-%, more advantageously 99 - 75 wt-% and most advantageously 95 - 85 wt-%.

19. Use of the neutralized, sulfonated terpolymer defined in claim 1 or 2 in a conducting plastic material as a plasticizing agent between a protic acid-doped polyaniline and a matrix polymer.