CA1307429C

CA1307429C - Production of an electrically conductive surface layer on moldings consisting of plastics

Info

Publication number: CA1307429C
Application number: CA000538749A
Authority: CA
Inventors: Alexander Aumueller; Peter Neumann; Gerd Blinne; Gerhard Lindenschmidt
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1986-06-11
Filing date: 1987-06-03
Publication date: 1992-09-15
Anticipated expiration: 2009-09-15
Also published as: KR880000502A; AU596424B2; EP0249125A2; DE3619606A1; US4897289A; DE3773748D1; BR8702946A; EP0249125A3; SG11392G; JPS6361031A; AU7408687A; EP0249125B1; HK78892A

Abstract

O.Z. 0050/38490 Abstract of the Disclosure: An electrically conductive surface layer is produced on moldings consisting of plastics which are soluble or swellable in organic sol-vents, the conductivity of the said layer being based on a system, incorporated therein, of - organic electron acceptors (I) on the one hand and - organic electron donors (II), iodides (III) or a mixture of (II) and (III) as electron donors, on the other hand, by a process in which the moldings are treated with or-ganic solutions of these components.
The products have a surface resistance of from 10 to 102 ohm and have the advantage that the remaining properties of the moldings are virtually unaffected by the agents (I) to (III).

Description

7a~9 - 1 ~ O.Z. 0050/38490 Production of an electrically conductive surface layer on_moLdings consisting of plastics The present invention relates to a novel process for the production of an electrically conductive surface layer on moldings consisting of plastics which are soluble or s~ellable in organic solvents, the conductivity of the said layer being based on a system, incorporated therein, of - organi~ electron acceptors tI~ on the one hand and - organic electron donors (II), iodides (II~) or a mixture of (II) and (III) as electron donors, on the other hand.
Plastics generally have a surface resistance of 1013 ohm or more and are therefore good electrical insu-lators~ Moldings cansisting of plastics can therefore become highly electrostatically charged; for many appli-cations, it is absoluteLy essential to avoid this. This applies in particular where explosive gas or dust/gas mixtures may be ign;ted by spark discharge.
A large number of additives have been developed for providing plastics with an antistatic treatment. These substances are applied to the surface of shaped articles (G. ~albach, Kunststoffe 67 (1977), 3). As a rule, how-ever, they become ineffective after a short time. Anti-static agents have also been incorporated into the plastics.
In these cases, the properties of the plastic frequently deteriorate or the additives diffuse out. The antistatic agents impart a certain degree of hydrophilicity to the plastic surface, so that a water film, dependent on the atmospheric humidity, can form on the surface, this film preventing charging.
To render plastics antistatic, a surfase resistance of 101 ohm or less is required.
Ho~ever, these minimum conductivities required to prevent electrostatic charging are not sufficient for many purposes in the electrical and electronic~ industries;

1 7~74'?C~

- 2 O.I. 0050/384~0 instead, surface resistance of less than 108 ohm are required here. For example, there is an increasing demand for moldings capable of shielding electromagnetic fields. Of course, their use in this respect depends on the conductivity achieved. It is important that the re-maining properties of the plastics, such as thermal and mechanical stability, are not adversely affected by addi-tives which impaft conductivity.
In order to render polymers eLectrically conduc-tive, attempts have been made to incorporate inorganic,electricaLly conductive substances, for example metals, metal oxides, met~l sulfides, carbon black or graphite~
However, the amount required for a desired conductivity, which as a rule is from 10 to 30~ by weight, based on the plastic, causes a decisive deterioration in the mechani-cal properties of the plastic.
Organic additives which have a high electrical conductivity and are more compatible with plastics have also been used. These include charge-transfer complexes tCT complexes) and radical ion salts. The CT complexes are two-component systems consisting of certain organic compounds uhich act as electron acceptors and electron donors and ~hich together generally form crystalline complexes having freely mobile electrons or defect elec-trons which give rise to conductivity. The radical ionsalts formed from iodides and electron acceptors show similar behavior. Here, the I anion donates a charge to the eLectron acceptor and is oxidized to elemental iodine. An electron acceptor anion is produced in which the accepted electron is once again freely mobile, so that a crys~allite of a salt of this type has high elec-trical conductivity.
DE-A-31 31 251 discloses polystyrene moldings which are prepared in a particular manner and into ~hich from 0.8 to 1.6~ by ~eight of a CT compLex have been in-corporated. The specific conductivity of this material is from 10 6 to 10 2 S/cm, but it has the funclamental disadvantage that -the c'r complex is distributed over the entire ma-terial, which as a rule, for example for shieldin~
purposes, is not necessary.
Furthermore, DE-B-15 44 976 discloses that nitrogen-con-taining polymers can be rendered conduc-tive by adding radical ion salts to the melt.
According to EP-A-134 026, plastics molding having high surface conductivity are obtainable by using for their preparation polymers which contain from 0.2 to 5% by weight of an electron acceptor in the melt. After the shaping procedure, the molding is immersed in a bath which contains an e:Lectron donor~ The latter diffuses into the molding and, together with -the electron acceptor already present, :forms, in the surface :Iayer, the CT complex which imparts surface conductivity. rrhis process too has seri.ous disadvantages:
i) -the major part of the expensl.ve electron acceptor remains unused and;
ii) the other properties of the polymer are adverse:Ly affected by the large amount o.E elect:ron acceptor.
It is an object of ~he present invention to produce mo:l.dings hav:i.ng an electrically conductive surface layer and ~.o avoid tlle dl.sadvantages previously associated Wit~l t~li.S.
More particular.ly, the invention provides a process for making an electrica:Lly conductive surface layer on a molding made of p:Lastic which is soluble or swellable in organic solvents comprising:
i) coating said molding with a first solution of an organic electron accep-tor (I) selected from the group consisting of:
- the tetracyanoquinonedimethanes of the forrmula:

~ `

- 3a ~ 7 ~ 2 9 R~ R'~
NC )=~ CN
~C~ ~=C\
N C ~, CN
Rl Rl - the N,N'-dicyanoquinonediimines of the formula:

Rl R~

0 NC--N¢ )=N--CN

- and the mixtures of these compounds, where Rl, R2, R3 and R4 independently of one another are l.S each methyl, hydroyen, ethyl, propyl, isopropyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy, methylthio, fluo.rine, chlorine, bromine or cyano, or one of the rad:icals r~l and r~2 or one of the radical.s R3 and R4 or one oE the radical.s R1 and R2 and one of L-he rad.icals R3 and R4 are pheny:L or 20 butyl, or Rl and r~2 or R3 and R4 or RJ and R2 and R and R
toge ther form a radical o.E the :Eormulae:

~ ~ ~(C~ o--2 5 ¦ (CHI)~. O or CHl ~/ \~CIIl)~ O--where the fused aromatic rings are unsubstituted or monosubstituted or disubs-tituted by chlorine, bromine, methoxy or methyl, to obtain difEusi.on of said first solution only into the surface of said molding;
ii ) drying -the moldiny obtained in step i );
iii) coating the moldiny obtained in step ii) with a second solution of:

17n7~
- 3b --- an or~anic e:lectron donors (:[I) consisting of a tetrachalcogenaulvalene oE the forrnula:

R6 W Z ~Rt R~ X Y R7 where R , R , R and R8 independently of one another are each hydrogen, methyl, ethyl, phenyl, methylphenyl or me-thoxyphenyl, or R and R6 or R and R8 or R and R and R
and R8 together form a radical of the formulae:

~ ,(c~, (C~/12)~ ~C/~, (C~

(C~
S~ S ~S~
(C~), (CH~2)~ or ( and X, Y, W and Z are each seJ.en:ium or sulEur, - an .iodicle (IIC) of the :Eormu:La:

Mm ~ I -where M is an m-valent alkali metal, alkaline earth metal or transition rnetal, -tin, .I.ead, thallium, ammonium, phos-phonium, arsoniurn or stibonium, copper, silver, pyridinium, N-methylpyridinium, quinolinium, N-methylqui~lolinium, phenazinium, N- methylphenazinium, tetramethylammonium, tetraethylammonium, tetrabenzylammonium, trime-thylbenzyl-ammonium or triethylbenzylammonium, and m is 1, 2 or 3, - or a mixture of the above organic electron donor (II) and iodide (III), .~
, 1 7` 0~4~9 - 3c -in order to obtai.n d:iffusion of said second solution only into the surface of said molding; and iv) drying the molding obtained in step iii) to ob-tain a molding having thereon an electrically conductive surface layer and in which the compositional. integrity of the core of said molding has been unaffected by said s-teps i) to iv).

1 7(174~

This process is appLicable to moldings of all plastics which are soluble or swellable and hence perm;t diffusion of the ~re~tment solut;ons into the surface of the moldings. Suitable plast;cs are therefore primarily thermoplastics and mixtures of these, as well as mater;als which are onty stightly crosstinked and therefore still sw~llable. Homopolymers and copotymers which contain vinyl acetater vinyl carbazole, vinyl chtoride, vinylpyri-dine, vinylpyrrolidone, vinylidene chloride, vinylidene fluoride, p-methylstyrene, olefins, acrylic acid, acry-lates, acrylamide, methacrylic acid, methacrylates, meth-acrylamide, maleic ac;d or maleates and/or whose ma;n chain contains repeating linking units such as urethane, carbonate, ester, am;de, ether, thioether, acetal, ketone or sulfonyl groups, in particular homopolymers and copoly-mers of styrene, ~-methylstyrene, butadiene, acrylonit-rile, methacrylonitrile or C1 C1g-alkyl acrylates or methacrylates, are suitable. Examples are graft copoly-mers of styrene, acrylonitrile, butadiene and C1-C1g-alkyl 2~ acrylate and those of styrene, acrylonitrile and C1-C18-alkyl acrylates, or blends of these polymers with poly-mers which contain carbonate groups in the main chain.
These plastics are familiar to the skilled worker and are described in, for example, H~ Saechtin~, Kunststoff-Tas-chenbuch, 22nd edition, Carl Hanser Verlag 1983.
The solvents should have an adequate dissolving or swelling power for both the plastics and the compon-ents I to III. Solvents of this type are familiar to the skilled worker and can be readily determined by a few pre-liminary experiments. Since the components (I) and (II) are highly conjugated compounds, suitable solvents are primarily aromatic compounds such as benzene, toluene, xylene, chlorobenzene or dichloroben~ene, as well as non-aromatic solvents, such as d;chloromethane, chloroform or : ~ `

1 7,~7a~g - 5 - O.Z. 0050/38490 1,1,1-trichloroethane, especially since these generally also have a good dissolving power for plastics of all types. The so~vents for (III) should preferably be polar ones, for example acetonitrile, nitromethane, dimethyl-formamide, dichloromethane, chloroform, 1,1,1-trichloro-ethane or tetrahydrofuran. It is frequently advantageous to use solvent mixtures, such as toluene/acetonitrile, chlorobenzene/dimethylformamide or xylene/tetrahydrofuran.
The concentrations of (I), (Il) and (III) are preferably from 0.01 to 20~ by weight butr depending on the application conditions, may also be higher, for exam-ple up to 30% by weight.
The treatment with the components (I) to (III) can be carried out either with a solution which contains 15 (1)~ (II) and/or (III), or with separate solutions in succession in any desired order. The molding is prefer-ably brought into contact with the solutions by immer-sion, spraying or painting, and is then dried. The treat-ment may also be carried out several times with the same solution, preferably with intermediate drying.
The residence time of the molding in the solutions should be chosen so that the plast;c swells at the sur-face, so that on the one hand some of (I), (II) and/or (III) can diffuse into the surface of the molding and form the electrically conductive crystals there and, on the other hand, the molding is not irreversibly damaged. The residence time at room temperature is therefore usually from û.5 to 120, preferably from 1 to 30, minutes. In-creasing the temperature is known to accelerate physical processes, such as diffusion and swelling, so that the residence time at above room temperature can be corres-pondingly decreased. Drying can be effected by a con-ventional method, for example by means of heat or reduced pressure.
In the novel process, (I) to (III) are generally applied to the surface of the molding in a concentrat;on of from 10 3 to 20, in particular from 10 2 to 10, g/m2, 1 7~ ~7~2'~

- 6 - O.Z. 0050/38490 so that the surf3ce resistance of the ~olding generally decreases to 108 ~o 102 ohm.
Electron acceptors I which have proven useful are the tetracyanoquinodimethanes of the formula (IV) R R
Nc\ ~ ~ CN
NC ~ ~' ~ C N
,R1 R2 and the N,N'-dicyanoquinonediimines of the formuLa (V) R3 R~
NC-N =~= N-CN

nhich are disclosed in DE-A-34 37 814. Suitable electron donors (II) are the tetrachalcogenafulvalenes of the for-mula ~VI) 5 ~ X ~ <Y ~ 7 In formulae (IV) and (V), R1, R2, R3 and R4 indepen-dentLy of one another are each methyl, ethyl, propyl, iso-propyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy, methylthio, fluorine, chlorine, bromine, cyano or, in particular, hydrogen, or one of the radicals R1 and R2 and/or one of the radicaLs R3 and R4 are each phenyl or butyl, or R1 ancl RZ and/or R3 and R4 together form a radical of the formula 1 3n7429 - 7 - O.Z. 005~/38490 ( C H ) ( C ~ ` ~ O-~ ( C ~ 2 ) ~

wnere the fused aromatic rings are unsubstituted or mono-substituted or disubstituted by chlorine, bromine or methoxy and/or methyl. In formuLa (VI), R5, R, R7 and R8 independentLy of one another are each methyl, ethyl, phenyL, methyLphenyL, methoxyphenyl or, in particular, hydrogen, or R5 and R6 and/or R7 and R8 together form a radical of the formula (CH3~2 (C\2)3 ~ (~\2)4 ~ (C~2)5 ' ~C~)3 S / S S
(CH~) , (CH~ 2 or (C ~ 3 and X, Y, W and Z are each selenium or, preferably, sul-fur. Iodides (III) which are usually employed are the salts of the formula Mm~ I -where M is an m-valent alkali metal, alkaline earth metal or transition metal, tin, lead, thallium, ammonium, phos-phonium, arsonium or stibonium, in particular copper, sil-ver, pyridinium, N-methylpyr;dinium, quinolinium, N-methyl-quinolinium, phenazinium, N-methylphenazinium, tetramethyl-ammonium, tetraethylammonium, tetrabenzylammonium, tri-methylbenzylammonium or triethylbenzylammoniumr and m is1, 2 or 3.
Other suitable electron acceptors (I) are metal ~ ~07~29 - 8 - O.Z. 0050/38490 complexes of the formula ~ Me R9 `5~ ~5 R3 where Me is Pt or Pd and R9 is -CN, -CH3 or -CF3, or their ammonium salts, 2,4,5-trinitro-9-(dicyanomethylene)-fluorene or tetracyanoethylener and other suitable elec-tron donors (II) are N-methylcarbazole, tetracene, penta-cene, tetrathiatetracene S~ ~
~',`,~3 or the diazo compound _ l~-`S~
l CH3 J 2 These and other suitable compounds are descr;bed in R.C. Wheland et a(., J. Amer. Chem. Soc. 98 t1976), 3916.
Usually, moldings such as fibers, films or sheets, or parts produced by calendering, extrusion, injection molding or centrifugal casting, are subjected to the novel process so that they can be used as electromagnetic shielding and/or for conducting away electrostatic charges or as electric circuit paths.
The novel process can be used to produce plastics moldings which have a conductive surface and whose other properties are not adversely affected by foreign sub-stances in the interior of the molding, such moldings being produced without loss of active substance. The 1 ~`07~9 - 9 - o.Z. 0050/3~490 process can be applied to virtually any moldings of any swellable plasti~s, the electrically conductive layer applied according to the invention adhering firmly to the surface of the molding.

A mo~ding of a commercial AEIS p~astic consisting of an emulsion graft copolymer of 54% by weight of styrene, 18% by weight Ot butadiene and 28% by ueight of acrylonit-ri~e and having a Vicat softening temperature of 99C, 10 measured accordins to ~IN 53,460 (VST/~/S0) and a melt flow index of 1~ 9/10 min, measured according to DIN
53,735 (220/10), was immersed for 5 minutes in a solution of 1.7 9 of N,N'-dicyano-p-benzoquinonediimine in 250 ml of toluene. After drying in the air, the same molding was immersed in a solution of 30 9 of copper(I) iodide in 200 ml of acetonitrile, the said molding becoming coated with a bluish black layer. It was then dried in the air.
The surface resiseance of the molding decreased from 1013 ohm before the treatment to 1.106 ohm after the treatment.

A molding of a commercia~ ASA plastic consisting of 55% by weight of styrene, 17% by weight of n-butyl acry-late and 28% by weight of acrylon;trile and having a Vicat softening temperature of 98C, measured according 25 to DIN 53,460 (VST/EI/50) and a melt flow index of 8 9/10 min, measured according to DIN 53,735 t220/10), was immersed for 5 minutes in a solution of 1.7 9 of N,N'-di-cyano-p-benzoquinonediimine in 250 ml of toluene. After drying in the air, the molding was immersed for 1 minute 30 in a solution of 2 9 of copper(I) iodide in 200 ml of aceto-nitrile, the said molding becoming coated with a bluish black layer. The surface resistance of the molding de-creased from 7.1013 ohm before the treatment to 4.2.105 ohm after the treatment.

A molding of a commercial blend consisting of oO%
by weight of a polycarbonate based on bisphenol A and 40%

1 ~742~
- 10 - O.Z. 0050/38490 by weight of an ASA polymer of 30% by weight of butyl acrylate, 53~ by ~ight of styrene and 17% by weight of acrylonitrile, having a Vicat softening temPerature of 121C, measured according to DIN 53,460 (VST/~/50~ and a melt flow index of 4 g/1û min, measured according to DIN 53,735 (220/10), was treated as described in Example 2. The surface resistance decreased from 7.1013 ohm to 7 1.105 ohm as a result of the treatment.

10 The samples treated as described in Examples 1 to 3 ~ere stored in the air at 80C, and the increase in the resistance was measured as a function of time~ The results are summarized in the Table.
TABLE 5 Surface resistance [n] after storage in air at 80C, as a fun~tion of time.
Time ~days] Example 1 Example 2 Example 3 0 1 106 4.2 105 7.1 105 2.5 107 4.1 106 3.5 106 2020 7.4 107 2.3 107 3.7 107 3Q 1.8 108 1.7 108 6.3 108 A molding of the plastic used in Example 3 was immersed for S minutes in a solution of 1.7 9 of N,N'-di-cyano-p-benzoqu;noned;imine and 0.6 9 of 2,5-dimethyl-N,N'-dicyano-p-benzoquinonediimine ;n 250 ml of toluene.
After drying in the a;r, the molding was immersed for one minute in a solution of 2 9 of copper(I) iodide in 200 ml of acetonitrile, the said molding becoming coated with a bluish black layer. The surface resistance decreased from 7.1013 ohm to 4.2.105 ohm as a result of the treat-ment.

A molding of the plastic used in Example 2 was treated as described in Ex~mple 4. Its surface resistance decreased from 7.1013 ohm to 2.4.105 ohm.

)74~q - 11 - O.Z. 0050/38490 A moLding of the plastic stated in Example 2 was sPrayed with a solution of 1 g of copper(I) iodide in 10C ml of acetonitrile and dried in the air for 5 minute,.
Thereafter, the same molding was sprayed with a solution of 0.~5 9 of N , N ' - dicyanobenzoquinonediimine in 125 ml of toluene and again dried in the air. The surface resis-tance decreased to 1.105 ohm as a result of the treatment.

A molding of the plastic stated in Examp~e 3 was treated as in Example 6. Thereafter, spraying with the acceptor solution was repeated twice~ The surface resis-tance decreased to 2.105 ohm.
EXAMPLE c The procedure described in Example 7 was followed, except that the order of the treatment with copper(I) iodide solution and the acceptor solution was reversed.
The surface resistance decreased to 5.104 ohm~

Claims

1. A process for making an electrically conductive surface layer on a molding made of plastic which is soluble or swellable in organic solvents comprising:
i) coating said molding with a first solution of an organic electron acceptor (I) selected from the group consisting of:
- the tetracyanoquinonedimethanes of the formula:
- the N,N'-dicyanoquinonediimines of the formula:
- and the mixtures of these compounds, where R1, R2, R3 and R4 independently of one another are each methyl, hydrogen, ethyl, propyl, isopropyl, methoxy, ethoxy, propoxy, butoxy, pentyloxy, methylthio, fluorine, chlorine, bromine or cyano, or one of the radicals R1 and R2 or one of the radicals R3 and R4 or one of the radicals R1 and R2 and one of the radicals R3 and R4 are phenyl or butyl, or R1 and R2 or R3 and R4 or R1 and R2 and R3 and R4 together form a radical of the formulae:

where the fused aromatic rings are unsubstituted or monosubstituted or disubstituted by chlorine, bromine, methoxy or methyl, to obtain diffusion of said first solution only into the surface of said molding;
ii) drying the molding obtained in step i);
iii) coating the molding obtained in step ii) with a second solution of:
- an organic electron donors (II) consisting of a tetrachalcogenafulvalene of the formula:
where R5, R6, R7 and R8 independently of one another are each hydrogen, methyl, ethyl, phenyl, methylphenyl or methoxyphenyl, or R5 and R6 or R7 and R8 or R5 and R6 and R7 and R8 together form a radical of the formulae:
and X, Y, W and Z are each selenium or sulfur, - an iodide (III) of the formula:
Mm + Im-where M is an m-valent alkali metal, alkaline earth metal or transition metal, tin, lead, thallium, ammonium, phos-phonium, arsonium or stibonium, copper, silver, pyridinium, N-methylpyridinium, quinolinium, N-methylquinolinium, phenazinium, N-methylphenazinium, tetramethylammonium, tetraethylammonium, tetrabenzylammonium, trimethylbenzyl-ammonium or triethylbenzylammonium, and m is 1, 2 or 3, - or a mixture of the above organic electron donor (II) and iodide (III), in order to obtain diffusion of said second solution only into the surface of said molding; and iv) drying the molding obtained in step iii) to obtain a molding having thereon an electrically conductive surface layer and in which the compositional integrity of the core of said molding has been unaffected by said steps i) to iv).

2. A process as claimed in claim 1, wherein the organic electron acceptor (I) that is used is a tetra-cyanoquinonedimethane (Ia), an N,N'-dicyanoquinonediimine (Ib) or a mixture thereof, (Ia) (Ib) or a derivative of these two compounds substituted in the nucleus.

3. A process as claimed in claim 1 or 2 wherein the organic electron donor (II) that is used is a tetrachalcogenafulvalene (IIa) of the formula:
(IIa) where X, Y, W and Z independently of one another are each sulfur or selenium, or a derivative thereof.

4. A process as claimed in claim 1 or 2, wherein the iodide (III) that is used is copper, silver, pyridinium, N-methylpyridinium, quinolinium, N-methylquinolinium, phena-zinium, N-methylphenazinium, tetramethylammonium, tetra-ethylammonium, tetrabenzylammonium, trimethylbenzylammonium or triethylbenzylammonium iodide.

5. A process as claimed in claim 1, wherein a molding of a homo- or copolymer of styrene, ?-methylstyrene, butadiene, acrylonitrile, methacrylonitrile or C1-C18-alkyl acrylates or methacrylates is treated.

6. A process as claimed in claim 1, wherein a molding of a graft copolymer of styrene, acrylonitrile, butadiene and/or C1-C18-alkyl acrylates, or blends of these with polymers which contain carbonate groups in the main chain, is treated.

7. Use of a molding obtained by a process as claimed in claim 1, as an electromagnetic shielding, as an antielectrostatic molding or as an electrical conductor path.

O.Z. 0050/38490 Abstract of the Disclosure: An electrically conductive surface layer is produced on moldings consisting of plastics which are soluble or swellable in organic sol-vents, the conductivity of the said layer being based on a system, incorporated therein, of - organic electron acceptors (I) on the one hand and - organic electron donors (II), iodides (III) or a mixture of (II) and (III) as electron donors, on the other hand, by a process in which the moldings are treated with or-ganic solutions of these components.
The products have a surface resistance of from 108 to 102 ohm and have the advantage that the remaining properties of the moldings are virtually unaffected by the agents (I) to (III).