Electroconductive articles and a method of producing the same

An electroconductive article is disclosed, which comprises a polar group-containing high polymeric substrate, and an electroconductive layer of cupric sulfide formed therein and is produced by immersing the polar group-containing high polymeric substrate in an aqueous solution containing a bivalent copper compound and a reducing agent or an aqueous solution containing a monovalent copper compound, and at the same time or subsequently treating it in a solution of a sulfur releasable substance.

BACKGROUND OF THE INVENTION 
1. Field of the Invention; 
This invention relates to electroconductive articles and a method of 
producing the same. 
2. Description of the Prior Art; 
As an electroconductive polymer material, there have hitherto been known 
fibers, films and so on obtained by adhering cuprous sulfide as an 
electroconductive layer to high molecular weight substances having a 
nitrile group such as acrylic fibers, acrylic films and the like. These 
materials are produced by utilizing coordinate bond of monovalent copper 
ion to nitrile group as a copper dyeing process in a dyeing chemistry. In 
this case, cuprous sulfide (Cu.sub.2 S) of the electroconductive layer 
actually has a composition of Cu.sub.x S (1.75.ltoreq.x&lt;2) slightly 
deviated from stoichiometric quantity and is reported to exhibit a 
behavior of P-type semiconductor. However, the electroconductive articles 
comprising cuprous sulfide as the electroconductive layer are not yet 
satisfactory in view of electroconductivity. 
On the other hand, it is known that cupric sulfide (CuS) exhibits an 
electroconductivity higher by at least a figure than that of cuprous 
sulfide (Cu.sub.x S, 1.75.ltoreq.x&lt;2). However, bivalent copper ion is 
poor in the coordination ability to the functional group of the polymer 
material as compared with monovalent copper ion, so that it is very 
difficult to produce electroconductive articles containing cupric sulfide 
as the electroconductive layer. 
SUMMARY OF THE INVENTION 
The inventors have made various studies with respect to electroconductive 
articles utilizing the electroconductivity of cupric sulfide and found 
that electroconductive articles having a high electroconductivity can be 
produced by treating a high polymeric substrate provided with cuprous 
sulfide as an electroconductive layer in a solution of a sulfur releasable 
substance to convert a greater part of the electroconductive layer into 
cupric sulfide without damaging the adhesion performance of the 
electroconductive layer to the high polymeric substrate, and as a result 
the invention has been accomplished. 
According to a first aspect of the invention, there is the provision of an 
electroconductive article comprising a polar group-containing high 
polymeric substrate, and an electroconductive layer of cupric sulfide 
formed therein. 
According to a second aspect of the invention, there is the provision of a 
method of producing an electroconductive article, comprising immersing a 
polar groupcontaining high polymeric substrate in an aqueous solution 
containing a bivalent copper compound and a reducing agent or an aqueous 
solution containing a monovalent copper compound, and at the same time or 
subsequently treating it in a solution of a sulfur releasable substance. 
DETAILED DESCRIPTION OF THE INVENTION 
As the polar group-containing high polymeric substrate according to the 
invention, mention may be made of high molecular weight substances 
containing the polar group selected from nitrile group, urethane group, 
urea group, amido group, hydroxyl group, ether group, ester group and the 
like, which include nitrile group-containing polymers, polyvinyl chloride 
containing polyurethanes, polyamides, polyesters, polyethers, polyvinyl 
alcohols and so on. 
As the nitrile group containing polymer, use may be made of acrylic fibers, 
nitrile group-containing polyurethane foams (polyurethane foam containing 
polyol grafted with acrylonitrile and so on) and acrylonitrile; 
methacrylonitrile; ethacrylonitrile; derivatives of .alpha.-substituted 
acrylonitrile such as .alpha.-propyl acrylonitrile and the like; 
vinylidene cyanide; homopolymers of a compound containing at least one 
nitrile group in its molecule such as .alpha.-methylene glutaronitrile or 
the like; copolymers of the nitrile group-containing compound with a 
copolymerizable unsaturated vinyl compound (for example, acrylic acid, 
methacrylic acid or an ester thereof; acrylamide; vinyl acetate; vinyl 
chloride; vinylidene chloride; vinylsulfonic acid; methallyl sulfonic 
acid, p-styrene sulfonic acid or a salt thereof; dimethyl or diethyl 
aminoethyl ester of acrylic or methacrylic acid; N-substituted aminopropyl 
esters; N-substituted aminobutyl esters; vinylpyridine and the like) and 
so on. 
The polyvinyl chloride containing polyurethane foams are generally known as 
a foam of a grade having flame retardant properties and may easily be 
produced or be available in the market. As such a foam, mention may be 
made of polyurethane foams containing 2 to 100 parts by weight, preferably 
5 to 40 parts by weight of finely divided polyvinyl chloride based on 100 
parts by weight of polyol, an example of which is a flexible polyurethane 
foam containing polyvinyl chloride, zinc oxide and antimony trioxide. When 
the content of polyvinyl chloride is less than 2 parts by weight, the 
adhesion of copper sulfide is insufficient and it is difficult to obtain 
practical electroconductivity, while when it exceeds 100 parts by weight, 
the effect of improving the electroconductivity is saturated and the 
viscosity of the mixed liquid consisting mainly of polyol increases to 
make good foaming difficult and also the properties of the resulting foam 
are degraded. This polyurethane foam according to the invention can easily 
be produced by compounding polyvinyl chloride dispersed polyol with 
polyisocyanate, foaming agent, catalyst, foam stabilizer and other 
additives and then foaming it. 
The shape of the polar group-containing high polymeric substrate 
(hereinafter referred to as a polymer substrate) is not critical and may 
take fiber, film, foam, powder, sheet or the like. 
According to the invention, an electroconductive layer of a cuprous 
compound is first formed in the polymer substrate by immersing the polymer 
substrate in an aqueous solution containing a bivalent copper compound and 
a reducing agent or an aqueous solution containing a monovalent copper 
compound. In this case, it is preferable that the immersion treatment is 
carried out by gradually heating from room temperature to a temperature of 
50.degree.-120.degree. C. Moreover, the immersion time is dependent upon 
the concentration of the copper compound used and the treating 
temperature, but it is required to be about 90 minutes for obtaining good 
adhesion of copper compound when the polymer substrate is immersed, for 
example, in an aqueous solution having a concentration of cuprous chloride 
of 0.4 mol/l at 60.degree. C. 
As the monovalent copper compound, mention may be made of cuprous chloride, 
cuprous iodide, cuprous cyanide, cuprous thiocyanate and the like. As the 
bivalent copper compound, mention may be made of cupric sulfate, cupric 
chloride, cupric nitrate, cupric acetate, cupric oxalate and the like. As 
the reducing agent, mention may be made of metallic copper, ferrous 
sulfate, sodium hypophosphite, hydroxylamine or a salt thereof, ammonium 
vanadate, furfural, glucose and the like. 
In case of using the monovalent copper compound, a dissolving aid such as 
hydrochloric acid, ammonium chloride or the like may be added, if 
necessary. Moreover, in the aqueous solution containing the cupric copper 
compound and the reducing agent, cupric ion is reduced to cuprous ion at 
90.degree.-120.degree. C. under a condition of pH=1.5-4.0, whereby the 
resulting cuprous ion is bonded by corrdination to the polar group of the 
polymer substrate. In order to efficiently enhance the adhesion of the 
cuprous compound to the polymer substrate, it is favorable that the 
surface of the polymer substrate is previously roughened by treating with 
an aqueous alkali solution or by removing cell membranes from the foam as 
the substrate according to explosive process and then treating with the 
aqeuous alkali solution. 
The amount of the cuprous compound adhered to the polymer substrate is not 
less than 1% by weight, preferably not less than 3% by weight. 
According to the invention, the thus treated polymer substrate is treated 
in a solution of a sulfur releasable substance during or after the above 
immersion treatment, whereby sulfurization reaction is caused to convert 
the cuprous compound into cupric sulfide. In this case, the concentration 
(by molar ratio) of sulfur in the solution is not more than 3 times, 
preferably not more than 2 times the concentration of the cuprous 
compound. Most preferably, the molar ratio of the sulfur concentration to 
the cuprous ion concentration is 1:1. 
The term "sulfur releasable substance" used herein means substances capable 
of releasing sulfur atom and/or sulfur ion, an example of which includes 
elemental sulfur, sodium thiosulfate, sodium sulfide, sodium 
hydrogensulfite, sulfurous acid, sodium dithionite, dithionous acid, 
Rongalit (trade name), ammonium sulfide, potassium sulfide, ammonium 
polysulfide, sodium polysulfide, potassium polysulfide, sulfur dioxide, 
hydrogen sulfide and the like. 
As the solution of sulfur releasable substance, there is used a solution of 
elemental sulfur in benzene, toluene, xylene, ether, alcohol or the like. 
In this case, an amine for generating free sulfur from the sulfur 
solution, such as n-butylamine, ethanolamine, morpholine, ethylenediamine, 
piperidine or the like may be added to promote sulfurization reaction. In 
the sulfur solution, the concentration of sulfur is within a range of 
0.5-3% by weight, and the concentration of amine is within a range of 
0.1-3% by weight. 
In addition to the sulfur solution, an aqueous solution of the sulfur 
releasable substance such as ammonium sulfide, sodium sulfide, potassium 
sulfide, ammonium polysulfide, sodium polysulfide, potassium polysulfide 
or the like may also be used. In this case, the concentration of such a 
sulfur releasable substance is preferable within a range of 2-20% by 
weight. 
Furthermore, an aqueous solution obtained by blowing a sulfur-containing 
gas such as sulfur dioxide, hydrogen sulfide or the like into water may be 
used as the solution of the sulfur releasable substance. 
According to the invention, the sulfurization treatment with the solution 
of sulfur releasable substance is carried out at a temperature above room 
temperature, preferably at a temperature of 50.degree.-120.degree. C. For 
example, when the treating temperature is 60.degree. C., the treating time 
is suitable to be about 90 minutes. As the treating temperature rises, the 
treating time is shortened, but when the treating temperature exceeds 
120.degree. C., the strength of the resulting electroconductive article 
unfavorably lowers. Moreover, the treating time can be shortened by 
irradiating ultraviolet ray, electron radiation, .gamma.-ray or the like 
to the solution of sulfur releasable substance. Particularly, when the 
polyvinyl chloride containing polyurethane foam is used as the polymer 
substrate, the adhesion of cupric sulfide is higher than the case of using 
the polymer substrate other than the above polyurethane foam even if the 
sulfurization treatment is carried out at the same temperature for the 
same time, and the electroconductivity is largely improved. 
In the electroconductive article according to the invention, the amount of 
cupric sulfide adhered to the polymer substrate is not less than 1% by 
weight, preferably 3 to 30% by weight. When the amount of cupric sulfide 
is less than 1% by weight, the desired electroconductivity can not be 
obtained, while when it exceeds 30% by weight, the electroconductivity is 
substantially saturated and the properties of the article such as 
strength, flexibility and the like are unfavorably deteriorated. 
According to the invention, it is preferable that the cuprous compound as 
the electroconductive layer is completely changed into cupric sulfide by 
the sulfurization treatment because the electroconductivity of the 
resulting article is highest. However, when at least 20% of the cuprous 
compound is converted into the cupric compound, the electroconductivity is 
at least 2 times that of the electroconductive layer composed of only the 
cuprous compound, which can sufficiently be put into practical use. 
The electroconductive articles according to the invention are widely used 
for various applications, for example, wall covering, ceiling, floor 
covering and the like in dark room as a radio wave absorbing material; 
gasket and the like in office supplies and OA supplies as an 
electromagnetic wave shielding material; molded laminate with unsaturated 
polyester resin in a parabolic antena as a radio wave reflecting material; 
sheet heating resistance element, tape-like heating resistance element and 
the like as a heating resistor; foam for the prevention of static fault as 
a material in the field of static electricity; static shielding material 
in the field of electron material; conductive mat for collector; 
electroflooring mat, sleeping mat, mattress, small size mat for hot 
compress and the like as a material for low frequency or static treatment, 
and so on. Particularly, when the polyvinyl chloride containing 
polyurethane foam is used as the polymer substrate, the copper sulfide is 
absorbed by the foam in a uniformly dispersed state, so that the resulting 
electroconductive article is very excellent in the electroconductivity and 
still holds the good foam texture, and also the burning speed is 
considerably slow as compared with the conventional article because of its 
flame retardant properties, which is suitable for use in interior parts of 
automobiles. 
The following examples are given in illustration of the invention and are 
not intended as limitations thereof. In these examples, all percentages 
are by weight unless otherwise stated.

EXAMPLE 1 
A woven cloth (thickness : 1.1 mm) obtained by knitting acryl fibers 
(Sandarlon SS-N.RTM., made by Nippon Sanmo Senshoku K.K.) into a 
tortoise-shell form was treated with an aqueous solution containing 1 
mol/l of cupric sulfate and 1 mol/l of sodium thiosulfate to form cuprous 
sulfide as an electroconductive layer. Then, five samples were cut out 
from this treated cloth at a size of 54 mm in fiber continuing direction 
and 50 mm in a direction perpendicular thereto. Among them, four samples 
were subjected to sulfurization treatment under the following conditions, 
respectively. 
Treatment 1: The sample was immersed in a toluene solution of 1% sulfur for 
1 day. 
Treatment 2: The sample was immersed in a toluene solution of 1% sulfur and 
1% of morpholine for 1 day. 
Treatment 3: The sample was immersed in a toluene solution of 1% of sulfur 
and 1% of n-butylamine for 1 day. 
Treatment 4: Immediately after the sample was immersed in a toluene 
solution of 1% of sulfur, it was exposed to ultraviolet ray generated from 
a high pressure mercury lamp (power: 4 kW, made by Toshiba Corporation) 
for 30 seconds. 
These four samples after the above treatment were thoroughly washed with 
toluene, dried, coated at both ends in fiber continuing direction with an 
electroconductive silver paint (Dotite D-550, trade name, made by Fujikura 
Kasai K.K.) over a width of 2 mm, and left to stand for more than 2 hours, 
to which was connected a copper electrode, and thereafter the surface 
resistance of the sample cloth with a side of 50 mm was measured by means 
of a resistance measuring device. And also, the value of resistance in the 
non-treated sample was measured. The measured results are shown in the 
following Table 1. The treated samples turned green or deep green, while 
the non-treated sample was olive. 
TABLE 1 
______________________________________ 
Surface Volume 
resistance 
resistivity 
Sample .OMEGA. .OMEGA. .multidot. cm 
______________________________________ 
non-treated 28.3 3.11 
treatment 1 10.5 1.16 
treatment 2 9.5 1.05 
treatment 3 6.6 0.73 
treatment 4 8.6 0.95 
______________________________________ 
As a result of X-ray diffraction on these samples, the non-treated samples 
showed diffraction peaks corresponding to Cu.sub.1.8 S at diffraction 
angles 2.theta. of 46.3.degree., 32.1.degree. and 27.7.degree., while the 
treated samples reduced the diffraction peaks of Cu.sub.1.8 S in the order 
of the reduction of the resistance and newly showed diffraction peaks 
corresponding to CuS at 2.theta. of 47.8.degree., 31.7.degree. and 
29.2.degree.. 
EXAMPLE 2 
The same four samples as in Example 1 were immersed in an aqueous solution 
of 5% of ammonium polysulfide under conditions as shown in the following 
Table 2 and then the surface resistance in fiber continuing direction was 
measured by the same method as described in Example 1 to obtain results as 
shown in Table 2. 
TABLE 2 
______________________________________ 
Immersing Immersing Surface 
Volume 
temperature 
time resistance 
resistivity 
No. .degree.C. hr .OMEGA. 
.OMEGA. .multidot. cm 
______________________________________ 
1 25 0.5 11.4 1.25 
2 25 2 6.1 0.67 
3 60 0.5 4.7 0.52 
4 60 2 4.7 0.52 
non-treated sample 28.3 3.11 
______________________________________ 
As a result of the measurement of X-ray diffraction of the sample treated 
under the condition No. 4, the peaks of Cu.sub.1.8 S near 2.theta. of 
46.3.degree., 32.1.degree. and 27.7.degree. substantially disappeared, and 
the peaks of CuS at 2.theta. of 47.8.degree., 31.7.degree. and 
29.2.degree. clearly appeared. 
EXAMPLE 3 
To 100 parts by weight of polymer polyol containaing 20% of acrylonitrile 
were added 4.4 parts by weight of water, 48.5 parts by weight of TDI-80 
(trade name) and given amounts of foam stabilizer and catalyst to produce 
a nitrile groupcontainig polyurethane foam with a density of 0.025 
g/cm.sup.3, from which cell membranes were removed by an explosive 
process. The thus obtained foam was immersed in an aqueous solution of 15% 
of sodium hydroxide for 30 minutes, washed with water, dried, subjected to 
a heat treatment in an aqueous solution containing 0.1 mol/l of cupric 
sulfate and 0.1 mol/l of sodium thiosulfate of 60.degree. C. for 60 
minutes, washed with water and dried to obtain a greyish black foam. This 
foam had a volume resistivity of 17.8 .OMEGA..multidot.cm. Then, the foam 
was immersed in an aqueous solution of 5% of ammonium polysulfide at 
60.degree. C. for 20 minutes, washed with water and dried to obtain a 
black foam. The latter foam had a volume resistivity of 2.72 
.OMEGA..multidot.cm. 
EXAMPLE 4 
A solution of 3.3% of powdery polyacrylonitrile in dimethylformamide was 
applied to a glass plate, from which a film of 5 .mu.m in thickness was 
formed by a solvent evaporation process. This film was treated in an 
aqueous solution containing 0.05 mol/l of each of cupric sulfate and 
sodium thiosulfate at 60.degree. C. for 90 minutes to obtain an 
electroconductive film having a volume resistivity of 0.58 
.OMEGA..multidot.cm. This film was further immersed in a toluene solution 
of 1% of sulfur and 1% of n-butylamine at 60.degree. C. for 60 minutes, 
washed and dried to obtain an electroconductive film having a volume 
resistivity of 0.09 .OMEGA..multidot.cm. 
EXAMPLES 5 AND 6 
To 100 parts by weight of polymer polyol containing 20% of acrylonitrile 
were added 4.4 parts by weight of water, 48.5 parts by weight of TDI-80 
and given amounts of foam stabilizer and catalyst to form a foam with a 
density of 0.0250 g/cm.sup.3, from which cell membranes were removed by an 
explosive process. 
The resulting foam was immersed in an aqeuous solution containing 15% by 
weight of sodium hydroxide for 60 minutes, washed with water, dried and 
again immersed in a solution of 39.6 g of cuprous chloride and 8 g of 
hydrochloric acid in 1 l of water at 60.degree. C. for 90 minutes (Example 
5) or 120 minutes (Example 6). Thereafter, the foam was lightly washed 
with water, immersed in an aqueous solution of 5% by weight of ammonium 
polysulfide at 60.degree. C. for 30 minutes, washed with water and dried. 
The thus obtained foam turned deep blackish green and had surface 
resistance (.rho.s) and volume resistivity (.rho.v) as shown in the 
following Table 3. As a result of the measurement of X-ray diffraction, 
diffraction peaks corresponding to CuS appeared at 2.theta. of 
29.2.degree., 31.7.degree. and 47.8.degree. in all samples. Moreover, the 
adhesion rate (% by weight) of CuS is shown in Table 3. 
TABLE 3 
______________________________________ 
Immersing time 
Adhesion 
in CuCl.sub.2 
rate .rho.s .rho.v 
Example (min.) (wt. %) (.OMEGA.) 
(.OMEGA. .multidot. cm) 
______________________________________ 
5 90 6.9 1.1 .times. 10.sup.2 
1.5 .times. 10.sup.2 
6 120 7.7 8.5 1.1 .times. 10.sup. 
______________________________________ 
COMATIVE EXAMPLE 1 
The same foam as used in Example 5 was immersed in an aqueous solution of 
15% by weight of sodium hydroxide for 60 minutes, washed with water, dried 
and immersed in an aqueous solution containing 39.6 g/l of cuprous 
chloride, 8 g/l of hydrochloric acid and 5% by weight of ammonium 
polysulfide at 60.degree. C. for 60 minutes. Then, the thus treated foam 
was washed with water and dried to obtain a foam having a substantially 
unchanged color, surface resistance and volume resistivity of not less 
than 10.sup.7 and no diffraction peak of CuS as measured from X-ray 
diffraction. 
On the other hand, blackish green powder produced in the reaction liquid 
showed diffraction peaks corresponding to CuS as measured from X-ray 
diffraction. 
It is understood from the above that CuS is produced by one-step process 
but does not adhere to the surface of the foam. 
EXAMPLE 7 
A flexible ether-series polyurethane foam with a size of 10 cm.times.10 
cm.times.1 cm, whose cell membranes being removed by an explosive process, 
was immersed in an aqueous solution of 15% by weight of sodium hydroxide 
for 1 hour, washed with water, immersed in 500 cc of an aqueous solution 
of 0.10 mol/l of cupric sulfate at 60.degree. C. for 60 minutes and then 
held in the same solution further containing 500 cc of an aqueous solution 
of 0.10 mol/l of sodium thiosulfate at 60.degree. C. for 60 minutes. The 
thus treated foam was washed with water and dried to obtain a blackish 
brown foam having a volume resistivity of 7.6.times.10.sup.2 
.OMEGA..multidot.cm. 
Then, this foam was immersed in an aqueous solution of 5% by weight of 
ammonium polysulfide at 60.degree. C. for 30 minutes, washed with water 
and dried to obtain a blackish green foam having a volume resistivity of 
1.7.times.10.sup.2 .OMEGA..multidot.cm. This fact shows that the 
electroconductivity is improved by the sulfurization treatment. 
As a result of the measurement on X-ray diffraction, the foam before the 
treatment with ammonium polysulfide showed diffraction peaks corresponding 
to Cu.sub.1.8 S at 2.theta. of 46.3.degree., 32.1.degree. and 
27.7.degree., while the foam after the treatment with ammonium polysulfide 
showed diffraction peaks at 2.theta. of 47.8.degree., 31.7.degree. and 
29.2.degree., which corresponded to CuS. 
EXAMPLE 8 
An open-cell, flexible ester series polyurethane foam was treated by the 
same procedure as described in Example 7. 
As a result, the foam after the treatment with cupric sulfate and sodium 
thiosulfate was blackish brown and had a volume resistivity of not less 
than 10.sup.7 .OMEGA..multidot.cm, while the foam after the treatment with 
ammonium polysulfide turned blackish green and had a volume resistivity of 
2.4.times.10.sup.2 .OMEGA..multidot.cm. Further, the latter foam clearly 
showed diffraction peaks of CuS as measured from X-ray diffraction. 
EXAMPLE 9 
The same flexible ester series polyurethane foam as used in Example 8 was 
treated by the same procedure as described in Example 7, except that the 
foam was first immersed in an aqueous solution containing 0.10 mol/l of 
cupric sulfate and 0.10 mol/l of sodium thiosulfate while gradually 
warming from room temperature to 60.degree. C. and holding at 60.degree. 
C. for 60 minutes. The foam after the treatment with cupric sulfate and 
sodium thiosulfate was blackish brown and had a volume resistivity of not 
less than 10.sup.7 .OMEGA..multidot.cm, while the foam after the treatment 
with ammonium polysulfide turned blackish green and had a volume 
resistivity of 9.6.times.10 .OMEGA..multidot.cm. 
EXAMPLE 10 
A flexible polyurethane foam with a density of 0.028 g/cm.sup.3 was 
prepared by adding 15 parts by weight of polyvinyl chloride to 100 parts 
by weight of polyol and then foaming it in the usual manner, from which a 
sample foam having a size of 10 cm.times.10 cm.times.1 cm was cut out. The 
sample foam was immersed in a solution of 25 g of cupric sulfate in 1,500 
g of water at 60.degree. C. for 60 minutes, and then a solution of 223 g 
of sodium thiosulfate in 500 g of water was added at 60.degree. C., in 
which was further immersed the foam for 90 minutes. Thereafter, the foam 
was taken out from the solution, washed with water and dried to obtain a 
deep blackish green foam. In the latter foam, the increment of weight was 
11.2% and the volume resistivity was as low as 1.19 .OMEGA..multidot.cm. 
As a result of the measurement on X-ray diffraction, peaks corresponding 
to CuS appeared at 2.theta. of 29.2.degree., 31.7.degree. and 47.8.degree. 
(X-ray used: CuK.alpha.). 
EXAMPLE 11 
A flexible polyurethane foam having a density of 0.0200 g/cm.sup.3 
(hereinafter referred to as foam A) was prepared by adding 15 parts by 
weight of polyvinyl chloride to 100 parts by weight of polyol and then 
foaming in usual manner. This foam was immersed in a solution of 25 g of 
cupric sulfate and 199 g of sodium thiosulfate in 2,000 g of water, while 
gradually warming from room temperature to 60.degree. C., for 150 minutes. 
After the immersion treatment, the foam A was washed with water and dried 
to obtain a deep blackish green foam A. The foam A had an increment of 
weight of 6.74% and a volume resistivity of 2.05.times.10.sup.-2 
.OMEGA..multidot.cm and showed peaks corresponding to CuS as measured from 
X-ray diffraction. 
Moreover, the electroconductive foam A was subjected to a burning test 
according to a method of MVSS No. 302. As a result, the burning rate was 
87 mm/min, which showed that the polyvinyl chloride containing 
polyurethane foam after the sulfurization treatment is very excellent in 
the flame retardant property. 
EXAMPLE 12 
The same foam A as used in Example 11 was immersed in a solution of 125 g 
of cupric sulfate in 500 g of water at 60.degree. C. for 60 minutes. Then, 
a solution of 122 g of sodium thiosulfate in 500 g of water was added to 
the above solution at 60.degree. C., and the foam was further immersed 
therein for 90 minutes. Thereafter, the foam was washed with water and 
dried to obtain a blackish green foam having an adhesion rate (increment 
of weight) of 9.04% and a volume resistivity of 3.3 .OMEGA..multidot.cm. 
Furthermore, the foam showed peaks corresponding to CuS as measured from 
X-ray diffraction. 
EXAMPLE 13 
The same foam A as used in Example 11 (size: 10 cm.times.10 cm.times.1 cm) 
was immersed in a solution of 79.2 g of cuprous chloride and 32 g of 
hydrochloric acid in 2,000 g of water at 60.degree. C. for 120 minutes, 
lightly washed with water, dehydrated, immersed in an aqueous solution of 
5% by weight of ammonium polysulfide at 60.degree. C. for 30 minutes, 
washed with water, and dried to obtain a blackish green foam. This foam 
had an adhesion rate (increment of weight) of 10.1% and a volume 
resistivity of 7.3.times.10.sup.3 .OMEGA..multidot.cm and showed peaks 
corresponding to CuS as measured from X-ray diffraction. 
As previously mentioned in detail, according to the invention, the cuprous 
compound adhered to the polar group-containing high polymeric substrate 
can directly be changed into cupric sulfide by sulfurization reaction with 
the solution of sulfur releasable substance. That is, according to the 
invention, the polymer substrate is immersed in an aqueous solution 
containing a bivalent copper compound and a reducing agent or an aqueous 
solution containing a monovalent copper compound and at the same time or 
subsequently treated in a solution of sulfur releasable substance, so that 
the electroconductive articles comprising cupric sulfide as an 
electroconductive layer can efficiently be produced in a high adhesion 
rate. Further, according to the invention, the number of treating steps 
can largely be reduced as compared with the prior art, and also the amount 
of the treating waste liquid can be made small, so that the invention has 
large merits in industry. Moreover, the electroconductive articles 
according to the invention have very excellent performances, so that they 
are very useful for wide applications.