Electrical conductive compositions

Compositions comprising a polymer and dendrite crystals of a salt consisting of the cation of 2-(4,5-dihydronaphtho[1,2-d]-1,3-dithiole-2-ylidene)-4,5-dihydronaphtho [1,2-d]-1,3-dithiole and an anion are useful in forming conductive coatings.

FIELD OF THE INVENTION 
The present invention relates to novel conductive compositions and 
elements. A novel process for making such compositions is also disclosed. 
BACKGROUND OF THE INVENTION 
The unwanted buildup of static electricity on an insulated support is a 
continuing problem. It is well known that a thin conductive layer will 
prevent static buildup and it is possible to formulate a conductive 
composition that can be coated on a support. However, it has been quite 
difficult to combine these conductive properties with other desirable 
physical properties such as physical stability. 
A number of charge transfer complexes are electrically conducting. For 
example, complex salts of 
2-(4,5-dihydronaphtho[1,2-d]-1,3-dithiol-2-ylidene)-4,5-dihydronaphtho[1,2 
-d]-1,3-dithiole (DTTF) with 7,7,8,8-tetracyanoquinodimethane(TCNQ) are 
electrically conducting. However, when such complexes are combined with an 
electrically insulating polymer composition to incorporate other physical 
properties, the resulting composition exhibits no useful electrical 
conductivity. As a result, charge transfer complexes have been limited in 
their utility in forming useful antistatic and conductive layers for 
elements such as electrographic, electrophotographic and photographic 
elements. 
It is desirable to obtain coating compositions of such charge transfer 
complexes with electrically insulating polymers as those polymers would 
provide physical stability for the coating, as well as other desirable 
properties required for many applications. 
SUMMARY OF THE INVENTION 
The present invention provides a composition comprising a polymer which is 
preferably organic solvent-soluble and a charge transfer complex 
characterized in that the charge transfer complex is (a) in the form of 
dendrite crystals throughout the polymer and is (b) a salt consisting of a 
cation of 
2-(4,5-dihydronaptho[1,2-d]-1,3-dithiol-2-ylidene)-4,5-dihydronaphtho-[1,2 
-d]-1,3-dithiole and an anion selected from the group consisting of 
7,7,8,8-tetracyanoquinodimethane (TCNQ.sup.-), ClO.sub.4.sup.-, 
BF.sub.4.sup.-, PF.sub.6.sup.-, F.sup.-, Cl.sup.-, I.sup.-, and 
I.sub.3.sup.-. The compound 
2-(4,5-dihydronaphtho[1,2-d]-1,3-dithiol-2-ylidene)-4,5-dihydronaphtho[1,2 
-d]-1,3-dithiole, hereinafter referred to as DTTF, has the structure 
##STR1## 
The compositions have resistivities in the range from 10.sup.4 to 
2.times.10.sup.8 ohm/sq. depending on the particular 
organic-solvent-soluble polymeric binder used. The compositions are useful 
in the form of self-supporting layers or as a coating on a support in any 
element in which it is desirable to both provide stability and to avoid 
the buildup of static electricity or to provide an electrically conductive 
layer. The dendrite crystals, in combination with an electrically 
insulating polymer results in an electrically conducting composition. 
The present invention also provides a method for making the novel 
electrically conductive composition of the invention. The method comprises 
the steps of: 
(a) forming a charge transfer complex from a cation of DTTF and an anion 
selected from the group consisting of TCNQ.sup.-, ClO.sub.4.sup.-, 
BF.sub.4, PF.sub.6, F.sup.-, Cl.sup.-, I.sup.- and I.sub.3.sup.- ; 
(b) mixing from about 1 to 20 parts of the charge transfer complex with 
about 5 to 200 parts of an electrically insulating polymer; and 
(c) aggregating the charged transfer complex in the polymer thereby forming 
dendrite crystals throughout the polymer. 
The preferred charge transfer complexes for the present invention comprise 
DTTF as the cation and an anion selected from the group consisting of 
TCNQ.sup.- and ClO.sub.4.sup.-. 
DETAILED EMBODIMENTS OF THE INVENTION 
The electrically conductive composition of this invention is formed by 
combining the charge transfer complex with an electrically insulating 
polymeric binder in an organic solvent for the polymer and then coating 
the resulting composition on a suitable support and drying. The insulating 
coating has a resistance greater than 2.times.10.sup.8 ohms/sq. 
The coating composition is rendered conductive by aggregating the charge 
transfer complex in the polymer. One technique for aggregating the charge 
transfer complex in the polymer is by contacting the composition of the 
charge transfer complex and polymer with vapors of a solvent which is 
capable of being absorbed into (penetrating) the layers. Such vapor 
exposure is generally effective to induce aggregation at about 70.degree. 
F. after about two minutes. Likewise, inhibition of solvent removal in an 
otherwise conventional coating of a dope solution comprising the dye and 
polymer results in aggregation. Immersing the coating in a solvent, or 
coating from an original solvent mixture which contains a high boiling 
solvent which persists in the coating during drying, are among other 
methods of inducing aggregation of the charge transfer complex. The 
aggregated coating is characterized by dendrite crystals throughout the 
polymeric binder. Useful organic solvents include chloroform, toluene, 
dichloromethane, acetone, acetonitrile, tetrahydrofuran, p-dioxane and 
trichloropropane. 
Examples of useful polymers are selected from polycarbonates, polyesters, 
polysulfones, polyacrylates, polymethacrylates, poly(vinylbutyrals), 
poly(vinylalcohol) and polyacetals. Specific examples of useful polymers 
include poly(4,4'-isopropylidenediphenylene carbonate), 
poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropyliden 
e-1,4-phenylene), 
poly[ethylene-co-isopropylidene-bis-(1,4-phenyleneoxy-ethylene)-terephthal 
ate], poly(vinylbutyral), and poly(n-butylmethacrylate-co-styrenesulfonic 
acid, potassium salt. 
In general, the amount of the charge transfer complex combined with the 
electrically insulating polymer to produce the electrically conducting 
compositions in layers of the present invention varies widely. All that is 
required is that enough of the charge transfer complex is used to form the 
network of dendrite crystals throughout the polymer. In general, the 
charge transfer complex is present in the electrically insulating polymer 
in an amount of about 0.1% to 20 weight percent based on the total weight 
of the composition. 
The compositions of the invention are usefully coated on a wide variety of 
supports to form useful antistatic or conducting elements. For example, 
the coating compositions described herein can be coated on polymeric 
materials such as poly(ethylene terephthalate), cellulose acetate, 
polystyrene, poly(methyl methacrylate) and the like as well as other 
supports such as glass, paper including resin-coated paper and metals. 
Fibers, including synthetic fibers, useful for weaving into cloth, are 
also examples of useful supports. Planar supports such as polymeric films 
are particularly useful for photographic elements. The compositions of the 
present invention are useful in virtually any article where it is desired 
to have a conductive coating. For example, the compositions are coated on 
small plastic parts to prevent the unwanted buildup of static electricity 
or coated on small polymeric spheres or other shapes such as those used 
for toners in electrography and the like. 
The compositions of the present invention are coated onto the support using 
any suitable method. For example, the compositions are coated by spray 
coating, fluidized bed coating, dip coating, doctor blade coating or 
extrusion hopper coating, to mention a few well-known coating techniques. 
In some embodiments, it is desirable to overcoat the layer of the 
compositions of the present invention with a protective layer. The 
protective layer is present for a variety of reasons. For example, the 
protective layer is an abrasion-resistant layer or a layer which provides 
other desirable physical properties. In many embodiments, for example, it 
is desirable to protect the conductive layers of the present invention 
from conditions which could adversely affect the aggregated composition. 
The protective layer is generally a film-forming polymer which is applied 
using coating techniques such as those described above for forming the 
conductive layer itself. 
The compositions of the present invention are particularly useful in 
forming antistatic layers for photographic elements or conductive layers 
in electrographic and electrophotographic elements. These elements 
comprise a support having coated thereon at least one radiation-sensitive 
layer. 
While the conductive layers described herein can be located anywhere in a 
photographic or electrophotographic element, it is preferred that the 
conductive layer be coated on the side of the support opposite the side 
having the coating of the radiation-sensitive material. The coating 
compositions of the present invention are advantageously coated directly 
on the support which has a thin subbing layer and are then overcoated with 
the described protective layer. Alternatively, the conductive layers of 
the present invention are on the same side of the support as the 
radiation-sensitive materials and the protective layers are included as 
interlayers or overcoats, if desired. 
The radiation-sensitive layers of the photographic or electrophotographic 
elements of the present invention can comprise photographic silver salt 
emulsions, such as silver halide emulsions; diazo-type compositions; 
vesicular image-forming compositions; photopolymerizable compositions; 
electrophotographic compositions comprising radiation-sensitive 
photoconductors and the like. Photographic silver halide emulsions are 
particularly preferred and are described, for example, in Product 
Licensing Index, Publication 9232, Vol. 92, December, 1971, pages 107-110. 
A particularly useful element of the present invention is an electrographic 
element. The conductive layers of the present invention, because of the 
uniformity of their conductivity and the humidity independence of their 
conductivity, are excellent conductive layers for such an element. This 
embodiment comprises a support having coated thereon the conductive layer 
as described herein and, as the outermost layer, a dielectric layer. The 
dielectric layer is formed from any dielectric film-forming material. 
Examples of such materials include any of the electrically insulating 
polymers used in forming the compositions and layers of the invention and 
the polymers listed above as useful as the protective layer. 
Electrographic elements including electrophotographic elements, are well 
known in the art and are described, for example, by Dessauer and Clark, 
Xerography and Related Processes, Focal Press, 1965, Chapter XVI, pages 
439-450. 
The resistance of the surface of the coatings of the present invention is 
measured using well-known techniques. The resistivity is the electrical 
resistance of a square of a thin film of material measured in the plane of 
the material between opposite sides. This is described more fully in R. E. 
Atchison, Aust. J. Appl. Sci., 10 (1954). 
The salts of the invention were prepared according to the following 
procedures: 
Preparation I 
Preparation of DTFF:TCNQ Salts 
##STR2## 
A solution was made by dissolving 7.2 g (0.025 mole) of 
4,5-(3,4-dihydronaphtho[a])-1,3-dithioliumtetrafluoroborate in 55 ml of 
acetonitrile containing 7.59 g (0.075 mole) of triethylamine by adding the 
latter dropwise with magnetic stirring over 15 minutes. Another 15 ml of 
acetonitrile was added and the mixture stirred for one hour at ambient 
temperature. As the solution cooled in an ice bath, orange crystals 
precipitated. They were collected by filtration. After washing with cold 
acetonitrile, the product was air-dried. A yield of 4.32 g (85%) of DTFF 
as an orange solid was obtained. 
A solution of 0.126 mmoles of DTFF was dissolved in hot tetrahydrofuran 
(THF). 0.176 mmoles of TCNQ was dissolved in hot acetonitrile and added to 
the DTFF solution. The mixture was allowed to cool. The DTFF:TCNQ salt was 
obtained as a grey-black precipitate. 
Preparation II 
Preparation of DTFF:ClO.sub.4 Salts 
To a suspension of 1.00 mmole of DTFF in 60 ml of hot acetonitrile was 
added 1.007 mmoles of perchloric acid in acetonitrile and 0.504 mmole of 
H.sub.2 O.sub.2 in water. The solution was concentrated to 1/3 of its 
original volume and then cooled to room temperature. A DTFF:ClO.sub.4 of 
mixed composition was obtained as a green crystalline precipitate. The 
precipitate was filtered and washed with cold acetonitrile. 
The above procedure was used to prepare three separate compositions having 
the following stoichiometries: 
(a) C.sub.22 H.sub.16 S.sub.3.6 (ClO.sub.4).sub.0.32 +O.sub.0.76 
(b) C.sub.22 H.sub.18 S.sub.3.6 (ClO.sub.4).sub.0.35 +O.sub.0.71 
(c) C.sub.22 H.sub.16 S.sub.3.6 (ClO.sub.4).sub.0.32 +O.sub.1.22.

The following examples illustrate the conductivity achieved by the 
compositions of the present invention. 
EXAMPLE 1 
Preparation and Electrical Properties of 
poly(4,4'-isopropylidenediphenylene carbonate) Films Containing DTFF:TCNQ 
Salt 
To a solution of 5 mg of DTFF:TCNQ in 1:1 THF:acetonitrile (by volume) was 
added 2 ml of a solution containing 100 mg of 
poly(4,4'-isopropylidenediphenylene carbonate) in 1:1 
dichloromethane:p-dioxane. The solution was coated on unsubbed polyester 
support to a wet thickness 0.002 mil, and dried in air. Samples of the 
dried film were vapor-treated with various solvents for varying lengths of 
time and the resistance was measured on a 2 cm by 2 cm square sample using 
silver paste contacts. The results are disclosed in Table I. 
TABLE I 
______________________________________ 
Resistance 
Vapor Treatment 
of Films 
Solvent Time (in seconds) 
(Ohm/Square) 
______________________________________ 
Untreated Film &gt;10.sup.9 
Chloroform 25 2.8 .times. 10.sup.5 
Dichloromethane 
25 5.1 .times. 10.sup.5 
Acetone 35 2.8 .times. 10.sup.5 
Acetonitrile 20 10 .times. 10.sup.5 
THF (tetrahydrofuran) 
15 80 .times. 10.sup.5 
THF 35 5.9 .times. 10.sup.5 
______________________________________ 
EXAMPLE 2 
Polysulfone Films Containing DTFF:TCNQ Salt 
A coating solution was made by dissolving 8.7 mg of DTFF:TCNQ in 1.74 ml of 
dioxane containing 174 mg of a polysulfone having the structure 
##STR3## 
The coatings were dried and vapor-treated as described in Example 2. 
Resistance values are disclosed in Table II. 
TABLE II 
______________________________________ 
Resistance 
Vapor Treatment 
of Films 
Solvent Time (in seconds) 
(Ohm/Square) 
______________________________________ 
Untreated Film &gt;10.sup.9 
Chloroform 20 9 .times. 10.sup.4 
Toluene 30 11 .times. 10.sup.4 
Trichloropropane 
30 1.6 .times. 10.sup.4 
Trichloropropane 
90 2.0 .times. 10.sup.4 
______________________________________ 
EXAMPLE 3 
Poly[ethylene-co-isopropylidenebis-(1,4-phenylene 
oxyethylene)-terephthalate] Films Containing DTFF:TCNQ Salt 
A mixture of 0.623 mmoles of DTFF was dissolved in hot THF, and 0.686 
mmoles of TCNQ dissolved in hot acetonitrile was concentrated from 75 ml 
to 20 ml by heating. On cooling, a 1:1 salt of DTFF:TCNQ was obtained as a 
grey-black product. This salt was coated in 
Poly[ethylene-co-isopropylidenebis-(1,4-phenyleneoxy-ethylene)-terephthala 
te] as in Example 2 and then vapor-treated with chloroform for 120 seconds. 
The resistivity was 2.2.times.10.sup.4 ohm/square. Microscopic examination 
of this film showed a multiplicity of connected dendrites or filament-like 
crystals of DTFF:TCNQ throughout the polyester. 
EXAMPLE 4 
Electrical Properties of the DTFF:ClO.sub.4 Salts in Polymeric Films 
A coating was made from a solution of 8.7 mg of DTFF:ClO.sub.4 prepared as 
in Example 5, dissolved in hot dichloromethane with 174 mg of different 
polymers in 1.7 ml of dichloromethane. The ratio of salt to polymer was 
1:20 by weight. The solution was coated with a wet thickness of 3 mils, 
dried, and vaportreated with several solvents. The resistance of 
DTTF:ClO.sub.4 salts in poly[ethylene-co-ethylene)-terephthalate] films 
are described in Table III. 
TABLE III 
______________________________________ 
Vapor Treatment 
Resistance 
Solvent Time (in seconds) 
(Ohm/Square) 
______________________________________ 
Acetonitrile 
35 1.8 .times. 10.sup.6 
Dioxane 120 1.2 .times. 10.sup.7 
Chloroform 60 1.15 .times. 10.sup.8 
______________________________________ 
The resistance of DTTF:ClO.sub.4 salt in poly(4,4-isopropylidenediphenylene 
carbonate) films are disclosed in Table IV. 
TABLE IV 
______________________________________ 
Vapor Treatment 
Resistance 
Solvent Time (in seconds) 
(Ohm/Square) 
______________________________________ 
Acetonitrile 60 2.6 .times. 10.sup.6 
Acetonitrile 180 1.2 .times. 10.sup.6 
Trichloropropane 
90 4 .times. 10.sup.6 
Trichloropropane 
360 8.4 .times. 10.sup. 4 
______________________________________ 
The resistance of DTTF:ClO.sub.4 salts in poly(vinyl butyral) films are 
disclosed in Table V. 
TABLE V 
______________________________________ 
Vapor Treatment 
Resistance 
Solvent Time (in seconds) 
(Ohm/Square) 
______________________________________ 
Acetonitrile 60 2.6 .times. 10.sup.6 
Trichloropropane 
60 1.1 .times. 10.sup.7 
Chloroform 60 6.6 .times. 10.sup.6 
Dioxane 60 7 .times. 10.sup.6 
Trichloropropane 
120 4.2 .times. 10.sup.6 
Poly(n-butylmethacrylate and p-styrene-sulfonic acid 
potassium salt) 
______________________________________ 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.