Electrically conductive article

Microporous material comprising (1) a matrix consisting essentially of thermoplastic organic polymer, (2) a large proportion of finely divided water-insoluble siliceous filler, and (3) interconnecting pores is coated with electrically conductive coating and/or printed with electrically conductive printing ink. The resulting products have many uses as electrically conductive articles, including electromagnetic interference shields and printed circuit boards. Three-dimensional printed circuit boards are disclosed.

The present invention is directed to microporous material coated or printed 
wholly or partially with electrically conductive coating or electrically 
conductive printing ink wherein the microporous material comprises a large 
proportion of siliceous particles. 
Accordingly, one embodiment of the invention is an electrically conductive 
article comprising: (a) at least one sheet of microporous material having 
generally opposing sides, the microporous material on a coating-free, 
printing ink-free, and impregnant-free basis comprising: (1) a matrix 
consisting essentially of substantially water insoluble thermoplastic 
organic polymer, (2) finely divided substantially water-insoluble filler 
particles, of which at least about 50 percent by weight are siliceous 
particles, the filler particles being distributed throughout the matrix 
and constituting from about 50 to about 90 percent by weight of the 
microporous material (3) a network of interconnecting pores communicating 
substantially throughout the microporous material, the pores constituting 
at least about 35 percent by volume of the microporous material; and (b) 
electrically conductive coating or electrically conductive printing ink on 
at least a portion of at least one of the sides. 
Another embodiment of the invention is a printed circuit comprising: (a) at 
least one sheet of microporous material having generally opposing sides, 
the microporous material on a coating-free, printing ink-free, and 
impregnant-free basis comprising: (1) a matrix consisting essentially of 
substantially water insoluble thermoplastic organic polymer, (2) finely 
divided substantially water-insoluble filler particles, of which at least 
about 50 percent by weight are siliceous particles, the filler particles 
being distributed throughout the matrix and constituting from about 50 to 
about 90 percent by weight of the microporous material, (3) a network of 
interconnecting pores communicating substantially throughout the 
microporous material, the pores constituting at least about 35 percent by 
volume of the microporous material; and (b) electrically conductive 
printing ink on at least a portion of at least one of the sides. 
Yet another embodiment of the invention is a method for producing a 
three-dimensional printed circuit board comprising: (a) printing 
electrically conductive printing ink upon at least one side of a sheet of 
microporous material having generally opposing sides, the microporous 
material on a coating-free, printing ink-free, and impregnant-free basis 
comprising: (1) a matrix consisting essentially of substantially water 
insoluble thermoplastic organic polymer, (2) finely divided substantially 
water-insoluble filler particles, of which at least about 50 percent by 
weight are siliceous particles, the filler particles being distributed 
throughout the matrix and constituting from about 50 to about 90 percent 
by weight of the microporous material, (3) a network of interconnecting 
pores communicating substantially throughout the microporous material, the 
pores constituting at least about 35 percent by volume of the microporous 
material; (b) molding the printed microporous material with organic 
polymer to bond the printed microporous material to the organic polymer 
and to form the three-dimensional printed circuit board. 
There are many advantages in using the microporous material described 
herein as a coating and/or printing substrate. 
One such advantage is that the substrate need not be pretreated with any of 
the pretreatments customarily used to improve adhesion between the coating 
and/or printing ink and the thermoplastic organic polymer substrate such 
as flame treatment, chlorination, or especially corona discharge treatment 
which is most commonly employed. This is especially surprising in the case 
of polyolefins inasmuch as untreated polyolefins such as polyethylene and 
polypropylene cannot ordinarily be successfully printed because of a lack 
of adhesion between the polyolefin printing ink and the polyolefin 
substrate. The microporous material substrates used in the present 
invention may be pretreated to further improve coating-substrate adhesion 
and/or ink-substrate adhesion, but commercially satisfactory results can 
ordinarily be attained without employing such methods. 
Another advantage is that the microporous material substrates accept a wide 
variety of coatings and printing inks, including most organic 
solvent-based coatings and inks which are incompatible with water, organic 
solvent-based coatings and inks which are compatible with water, and 
water-based coatings and inks. 
Yet another advantage is very rapid drying of most printing inks to the 
tack-free stage upon printing the microporous material substrates. This 
advantage is quite important in high speed press runs, in multicolor 
printing, and in reducing or even eliminating blocking of stacks or coils 
of the printed substrate. 
A further advantage is the sharpness of the printed image that can be 
attained. This is especially important in electronic circuit applications 
where fine lines and detailed drawings are to be printed. 
Many known microporous materials may be employed in the present invention. 
Examples of such microporous materials are described in U.S. Pat. Nos. 
2,772,322; 3,351,495; 3,696,061; 3,725,520; 3,862,030; 3,903,234; 
3,967,978; 4,024,323; 4,102,746; 4,169,014; 4,210,709; 4,226,926; 
4,237,083; 4,335,193; 4,350,655; 4,472,328; 4,585,604; 4,613,643; 
4,681,750; 4,791,144; 4,833,172; and 4,861,644, the disclosures of which 
are, in their entireties, incorporated herein by reference. 
The matrix of the microporous material consists essentially of 
substantially water-insoluble thermoplastic organic polymer. The numbers 
and kinds of such polymers suitable for use of the matrix are enormous. In 
general, substantially any substantially water-insoluble thermoplastic 
organic polymer which can be extruded, calendered, pressed, or rolled into 
film, sheet, strip, or web may be used. The polymer may be a single 
polymer or it may be a mixture of polymers. The polymers may be 
homopolymers, copolymers, random copolymers, block copolymers, graft 
copolymers, atactic polymers, isotactic polymers, syndiotactic polymers, 
linear polymers, or branched polymers. When mixture of polymers are used, 
the mixture may be homogeneous or it may comprise two or more polymeric 
phases. Examples of classes of suitable substantially water-insoluble 
thermoplastic organic polymers include the thermoplastic polyolefins, 
poly(halo-substituted olefins), polyesters, polyamides, polyurethanes, 
polyureas, poly(vinyl halides), poly(vinylidene halides), polyestyrenes, 
poly(vinyl esters), polycarbonates, polyethers, polysulfides, polyimides, 
polysilanes, polysiloxanes, polycaprolactones, polyacrylates, and 
polymethacrylates. Hybrid classes exemplified by the thermoplastic 
poly(urethane-ureas), poly(ester-amides), poly(silane-siloxanes), and 
poly(ether-esters) are within contemplation. Examples of suitable 
substantially water-insoluble thermoplastic organic polymers include 
thermoplastic high density polyethylene, low density polyethylene, 
ultrahigh molecular weight polyethylene, polypropylene (atactic, 
isotactic, or syndiotatic as the case may be), poly(vinyl chloride), 
polytetrafluoroethylene, copolymers of ethylene and acrylic acid, 
copolymers of ethylene and methacrylic acid, poly(vinylidene chloride), 
copolymers of vinylidene chloride and vinyl acetate, copolymers of 
vinylidene chloride and vinyl chloride, copolymers of ethylene and 
propylene, copolymers of ethylene and butene, poly(vinyl acetate), 
polystyrene, poly(omega-aminoundecanoic acid) poly(hexamethylene 
adipamide), poly(epsilon-caprolactam), and poly(methyl methacrylate). 
These listings are by no means exhaustive, but are intended for purposes 
of illustration. The preferred substantially water-insoluble thermoplastic 
organic polymers comprise poly(vinyl chloride), copolymers of vinyl 
chloride, or mixtures thereof; or they comprise essentially linear 
ultrahigh molecular weight polyolefin which is essentially linear 
ultrahigh molecular weight polyethylene having an intrinsic viscosity of 
at least about 18 deciliters/gram, essentially linear ultrahigh molecular 
weight polypropylene having an intrinsic viscosity of at least about 6 
deciliters/gram, or a mixture thereof. Essentially linear ultrahigh 
molecular weight polyethylene having an intrinsic viscosity of at least 
about 18 deciliters/gram is especially preferred. 
Inasmuch as ultrahigh molecular weight (UHMW) polyolefin is not a thermoset 
polymer having an infinite molecular weight, it is technically classified 
as a thermoplastic. However, because the molecules are essentially very 
long chains, UHMW polyolefin, and especially UHMW polyethylene, softens 
when heated but does not flow as a molten liquid in a normal thermoplastic 
manner. The very long chains and the peculiar properties they provide to 
UHMW polyolefin are believed to contribute in large measure to the 
desirable properties of microporous materials made using this polymer. 
As indicated earlier, the intrinsic viscosity of the UHMW Polyethylene is 
at least about 18 deciliters/gram. In many cases the intrinsic viscosity 
is at least about 19 deciliters/gram. Although there is no particular 
restriction on the upper limit of the intrinsic viscosity, the intrinsic 
viscosity is frequently in the range of from about 18 to about 39 
deciliters/gram. An intrinsic viscosity in the range of from about 18 to 
about 32 deciliters/gram is preferred. 
Also as indicated earlier the intrinsic viscosity of the UHMW polypropylene 
is at least about 6 deciliters/gram. In many cases the intrinsic viscosity 
is at least about 7 deciliters/gram. Although there is no particular 
restriction on the upper limit of the intrinsic viscosity, the intrinsic 
viscosity is often in the range of from about 6 to about 18 
deciliters/gram. An intrinsic viscosity in the range of from about 7 to 
about 16 deciliters/gram is preferred. 
As used herein and in the claims, intrinsic viscosity is determined by 
extrapolating to zero concentration the reduced viscosities or the 
inherent viscosities of several dilute solutions of the UHMW polyolefin 
where the solvent is freshly distilled decahydronaphthalene to which 0.2 
percent by weight, 3,5-di-tertbutyl-4-hydroxyhydrocinnasic acid, 
neopentanetetrayl ester [CAS Registry No. 6683-19-8] has been added. The 
reduced viscosities or the inherent viscosities of the UHMW polyolefin are 
ascertained from relative viscosities obtained at 135.degree. C. using an 
Ubbelohde No. 1 viscometer in accordance with the general procedures of 
ASTM D 4020-81, except that several dilute solutions of differing 
concentration are employed. ASTM D 4020-81 is, in its entirety, 
incorporated herein by reference. 
The nominal molecular weight of UHMW polyethylene is empirically related to 
the intrinsic viscosity of the polymer according to the equation: 
EQU M=5.37.times.10.sup.4 [.eta.].sup.1.37 
where M is the nominal molecular weight and [.eta.] is the intrinsic 
viscosity of the UHMW polyethylene expressed in deciliters/gram. 
Similarly, the nominal molecular weight of UHMW polypropylene is 
empirically related to the intrinsic viscosity of the polymer according to 
the equation: 
EQU M=8.88.times.10.sup.4 [.eta.].sup.1.25 
where M is the nominal molecular weight and [.eta.] is the intrinsic 
viscosity of the UHMW polypropylene expressed in deciliters/gram. 
The essentially linear ultrahigh molecular weight polypropylene is most 
frequently essentially linear ultrahigh molecular weight isotactic 
polypropylene. Often the degree of isotacicity of such polymer is at least 
about 95 percent, while preferably it is at least about 98 percent. 
When used, sufficient UHMW polyolefin should be present in the matrix to 
provide its properties to the microporous material. Other thermoplastic 
organic polymer may also be present in the matrix so long as its presence 
does not materially affect the properties of the microporous material in 
an adverse manner. The amount of the other thermoplastic polymer which may 
be present depends upon the nature of such polymer. In general, a greater 
amount of other thermoplastic organic polymer may be used if the molecular 
structure contains little branching, few long sidechains, and few bulky 
side groups, than when there is a large amount of branching, many long 
sidechains, or many bulky side groups. For this reason, the preferred 
thermoplastic organic polymers which may optionally be present are low 
density polyethylene, high density polyethylene, 
poly(tetrafluoroethylene), polypropylene, copolymers of ethylene and 
propylene, copolymers of ethylene and acrylic acid, and copolymers of 
ethylene and methacrylic acid. If desired, all or a portion of the 
carboxyl groups of carboxyl-containing copolymers may be neutralized with 
sodium, zinc, or the like. It is our experience that usually at least 
about 50 percent UHMW polyolefin, based on the weight of the matrix, will 
provide the desired properties to the microporous material. Often at least 
about 70 percent by weight of the matrix is UHMW polyolefin. In many cases 
the other thermoplastic organic polymer is substantially absent.

As present in the microporous material, the finely divided substantially 
water-insoluble siliceous particles may be in the form of ultimate 
particles, aggregates of ultimate particles, or a combination of both. In 
most cases, at least about 90 percent by weight of the siliceous particles 
used in preparing the microporous material have gross particle sizes in 
the range of from about 5 to about 40 micrometers as determined by use of 
a Model TAII Coulter counter (Coulter Electronics, Inc.) according to ASTM 
C 690-80 but modified by stirring the filler for 10 minutes in Isoton II 
electrolyte (Curtin Matheson Scientific, Inc.) using a four-blade, 4.445 
centimeter diameter propeller stirrer. Preferably at least about 90 
percent by weight of the siliceous particles have gross particle sizes in 
the range of from about 10 to about 30 micrometers. It is expected that 
the sizes of filler agglomerates may be reduced during processing of the 
ingredients to prepare the microporous material. Accordingly, the 
distribution of gross particle sizes in the microporous material may be 
smaller than in the raw siliceous filler itself. ASTM C 690-80 is, in its 
entirety, incorporated herein by reference. 
Examples of suitable siliceous particles include particles of silica, mica, 
montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, 
vermiculite, natural and synthetic zeolites, cement, calcium silicate, 
aluminum silicate, sodium aluminum silicate, aluminum polysilicate, 
alumina silica gels, and glass particles. Silica and the clays are the 
preferred siliceous particles. Of the silicas, precipitated silica, silica 
gel, or fumed silica is most often used. 
In addition to the siliceous particles, finely divided substantially 
water-insoluble non-siliceous filler particles may also be employed. 
Examples of such optional non-siliceous filler particles include particles 
of titanium oxide, iron oxide, copper oxide, zinc oxide, antimony oxide, 
zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium 
sulfate, strontium sulfate, calcium carbonate, magnesium carbonate, 
magnesium hydroxide, and finely divided substantially water-insoluble 
flame retardant filler particles such as particles of 
ethylenebis(tetra-bromophthalimide), octabromodiphenyl oxide, 
decabromodiphenyl oxide, and ethylenebisdibromonorbornane dicarboximide. 
As present in the microporous material, the finely divided substantially 
water-insoluble non-siliceous filler particles may be in the form of 
ultimate particles, aggregates of ultimate particles, or a combination of 
both. In most cases, at least about 75 percent by weight of the 
non-siliceous filler particles used in preparing the microporous material 
have gross particle sizes in the range of from about 0.1 to about 40 
micrometers as determined by use of a Micromeretics Sedigraph 5000-D 
(Micromeretics Instrument Corp.) in accordance with the accompanying 
operating manual. The preferred ranges vary from filler to filler. For 
example, it is preferred that at least about 75 percent by weight of 
antimony oxide particles be in the range of from about 0.1 to about 3 
micrometers, whereas it is preferred that at least about 75 percent by 
weight of barium sulfate particles be in the range of from about 1 to 
about 25 micrometers. It is expected that the sizes of filler agglomerates 
may be reduced during processing of the ingredients to prepare the 
microporous material. Therefore, the distribution of gross particle sizes 
in the microporous material may be smaller than in the raw non-siliceous 
filler itself. 
The particularly preferred finely divided substantially water-insoluble 
siliceous filler particles are precipitated silica. Although both are 
silicas, it is important to distinguish precipitated silica from silica 
gel inasmuch as these different materials have different properties. 
Reference in this regard is made to R. K. Iler, The Chemistry of Silica, 
John Wiley & Sons, New York (1979), Library of Congress Catalog No. QD 
181.S6144, the entire disclosure of which is incorporate herein by 
reference. Note especially pages 15-29, 172-176, 218-233, 364-365, 
462-465, 554-564, and 578-579. Silica gel is usually produced commercially 
at low pH by acidifying an aqueous solution of a soluble metal silicate, 
typically sodium silicate, with acid. The acid employed is generally a 
strong mineral acid such as sulfuric acid or hydrochloric acid although 
carbon dioxide is sometimes used. Inasmuch as there is essentially no 
difference in density between the gel phase and the surrounding liquid 
phase while the viscosity is low, the gel phase does not settle out, that 
is to say, it does not precipitate. Silica gel, then, may be described as 
a nonprecipitated, coherent, rigid, three-dimensional network of 
contiguous particles of colloidal amorphous silica. The state of 
subdivision ranges from large, solid masses to submicroscopic particles, 
and the degree of hydration from almost anhydrous silica to soft 
gelatinous masses containing on the order of 100 parts of water per part 
of silica by weight, although the highly hydrated forms are only rarely 
used in the present invention. 
Precipitated silica is usually produced commercially by combining an 
aqueous solution of a soluble metal silicate, ordinarily alkali metal 
silicate such as sodium silicate, and an acid so that colloidal particles 
will grow in weakly alkaline solution and be coagulated by the alkali 
metal ions of the resulting soluble alkali metal salt. Various acid may be 
used, including the mineral acids and carbon dioxide. In the absence of a 
coagulant, silica is not precipitated from solution at any pH. The 
coagulant used to effect precipitation may be the soluble alkali metal 
salt produced during formation of the colloidal silica particles, it may 
be added electrolyte such as a soluble inorganic or organic salt, or it 
may be a combination of both 
Precipitated silica, then, may be described as precipitated aggregates of 
ultimate particles of colloidal amorphous silica that have not at any 
point existed as macroscopic gel during the preparation. The sizes of the 
aggregates and the degree of hydration may vary widely. 
Precipitated silica powders differ from silica gels that have been 
pulverized in ordinarily having a more open structure, that is, a higher 
specific pore volume. However, the specific surface area of precipitated 
silica as measured by the Brunauer, Emmet, Teller (BET) method using 
nitrogen as the adsorbate, is often lower than that of silica gel. 
Many different precipitated silicas may be employed in the present 
invention, but the preferred precipitated silicas are those obtained by 
precipitation from an aqueous solution of sodium silicate using a suitable 
acid such as sulfuric acid, hydrochloric acid, or carbon dioxide. Such 
precipitated silicas are themselves known and processes for producing them 
are described in detail in U.S. Pat. No. 2,940,830, in U.S. Pat. No. 
4,681,750, the entire disclosures of which are incorporated herein by 
reference, including especially the processes for making precipitated 
silicas and the properties of the products. 
In the case of the preferred filler, precipitated silica, the average 
ultimate particle size (irrespective of whether or not the ultimate 
particles are agglomerated) is less than about 0.1 micrometer as 
determined by transmission electron microscopy. Often the average ultimate 
particle size is less than about 0.05 micrometer. Preferably the average 
ultimate particle size of the precipitated silica is less than about 0.03 
micrometer. 
The finely divided substantially water-insoluble filler particles 
constitute from about 50 to 90 percent by weight of the microporous 
material. Frequently such filler particles constitute from about 50 to 
about 85 percent by weight of the microporous material. From about 60 
percent to about 80 percent by weight is preferred. 
At least about 50 percent by weight of the finely divided substantially 
water-insoluble filler particles are finely divided substantially 
water-insoluble siliceous filler particles. In many cases at least about 
65 percent by weight of the finely divided substantially water-insoluble 
filler particles are siliceous. Often at least about 75 percent by weight 
of the finely divided substantially water-insoluble filler particles are 
siliceous. Frequently at least about 85 percent by weight of the finely 
divided substantially water-insoluble filler particles are siliceous. In 
many instances all of the finely divided substantially water-insoluble 
filler particles are siliceous. 
Minor amounts, usually less than about 5 percent by weight, of other 
materials used in processing such as lubricant, processing plasticizer, 
organic extraction liquid, surfactant, water, and the like, may optionally 
also be present. Yet other materials introduced for particular purposes 
may optionally be present in the microporous material in small amounts, 
usually less than about 15 percent by weight. Examples of such materials 
include antioxidants, ultraviolet light absorbers, reinforcing fibers such 
as chopped glass fiber strand, dyes, pigments, and the like. The balance 
of the microporous material, exclusive of filler and any coating, printing 
ink, or impregnant applied for one or more special purposes is essentially 
the thermoplastic organic polymer. 
On a coating-free, printing ink free, impregnant-free, and pre-bonding 
basis, pores constitute at least about 35 percent by volume of the 
microporous material. In many instances the pores constitute at least 
about 60 percent by volume of the microporous material. Often the Pores 
constitute from at least about 35 percent to about 95 percent by volume of 
the microporous material. From about 60 percent to about 75 percent by 
volume is preferred. As used herein and in the claims, the Porosity (also 
known as void volume) of the microporous material, expressed as percent by 
volume, is determined according to the equation: 
EQU Porosity=100[1-d.sub.1 /d.sub.2 ] 
where d.sub.1 is the density of the sample which is determined from the 
sample weight and the sample volume as ascertained from measurements of 
the sample dimensions and d.sub.2 is the density of the solid portion of 
the sample which is determined from the sample weight and the volume of 
the solid portion of the sample. The volume of the solid portion of the 
same is determined using a Quantachrome stereopycnometer (Quantachrome 
Corp.) in accordance with the accompanying operating manual. 
The volume average diameter of the pores of the microporous material is 
determined by mercury porosimetry using an Autoscan mercury porosimeter 
(Quantachrome Corp.) in accordance with the accompanying operating manual. 
The volume average pore radius for a single scan is automatically 
determined by the porosimeter. In operating the porosimeter, a scan is 
made in the high pressure range (from about 138 kilopascals absolute to 
about 227 megapascals absolute). If about 2 percent or less of the total 
intruded volume occurs at the low end (from about 138 to about 250 
kilopascals absolute) of the high pressure range, the volume average pore 
diameter is taken as twice the volume average Pore radius determined by 
the porosimeter. Otherwise, an additional scan is made in the low pressure 
range (from about 7 to about 165 kilopascals absolute) and the volume 
average pore diameter is calculated according to the equation: 
##EQU1## 
where d is the volume average pore diameter, v.sub.1 is the total volume 
of mercury intruded in the high pressure range, v.sub.2 is the total 
volume of mercury intruded in the low pressure range, r.sub.1 is the 
volume average pore radius determined from the high pressure scan, r.sub.2 
is the volume average pore radius determined from the low pressure scan, 
w.sub.1 is the weight of the sample subjected to the high pressure scan, 
and w.sub.2 is the weight of the sample subjected to the low pressure 
scan. Generally on a coating-free, printing ink-free, impregnant-free, and 
pre-bonding basis the volume average diameter of the pores is in the range 
of from about 0.02 to about 50 micrometers. Very often the volume average 
diameter of the pores is in the range of from about 0.04 to about 40 
micrometers. From about 0.05 to about 30 micrometers is preferred. 
In the course of determining the volume average pore diameter by the above 
procedure, the maximum pore radius detected is sometimes noted. This is 
taken from the low pressure range scan if run; otherwise it is taken from 
the high pressure range scan. The maximum pore diameter is twice the 
maximum pore radius. 
Inasmuch as some coating processes, printing processes, impregnation 
processes and bonding processes result in filling at least some of the 
pores of the microporous material and since some of these processes 
irreversibly compress the microporous material, the parameters in respect 
of porosity, volume average diameter of the pores, and maximum pore 
diameter are determined for the microporous material prior to application 
of one or more of these processes. 
Microporous material may be produced according to the general principles 
and procedures of U.S. Pat. Nos. 3,351,495; 4,833,172; and 4,861,644, the 
entire disclosures of which are incorporated herein by reference, 
including especially the processes for making microporous materials and 
the properties of the products. 
Preferably filler particles, thermoplastic organic polymer powder, 
processing plasticizer and minor amounts of lubricant and antioxidant are 
mixed until a substantially uniform mixture is obtained. The weight ratio 
of filler to polymer powder employed in forming the mixture is essentially 
the same as that of the microporous material to be produced. The mixture, 
together with additional processing plasticizer, is introduced to the 
heated barrel of a screw extruder. Attached to the extruder is a sheeting 
die. A continuous sheet formed by the die is forwarded without drawing to 
a pair of heated calender rolls acting cooperatively to form continuous 
sheet of lesser thickness than the continuous sheet exiting from the die. 
The continuous sheet from the calender then passes to a first extraction 
zone where the processing plasticizer is substantially removed by 
extraction with an organic liquid which is a good solvent for the 
processing plasticizer, a poor solvent for the organic polymer, and more 
volatile than the processing plasticizer. Usually, but not necessarily, 
both the processing plasticizer and the organic extraction liquid are 
substantially immiscible with water. The continuous sheet then passes to a 
second extraction zone where the residual organic extraction liquid is 
substantially removed by steam and/or water. The continuous sheet is then 
passed through a forced air dryer for substantial removal of residual 
water and remaining residual organic extraction liquid. From the dryer the 
continuous sheet, which is microporous material, is passed to a take-up 
roll. 
The processing plasticizer has little solvating effect on the thermoplastic 
organic polymer at 60.degree. C., only a moderate solvating effect at 
elevated temperatures on the order of about 100.degree. C., and a 
significant solvating effect at elevated temperatures on the order of 
about 200.degree. C. It is a liquid at room temperature and usually it is 
processing oil such as paraffinic oil, naphthenic oil, or aromatic oil. 
Suitable processing oils include those meeting the requirements of ASTM D 
2226-82, Types 103 and 104. Preferred are oils which have a pour point of 
less than 22.degree. C. according to ASTM D 97-66 (reapproved 1978). 
Particularly preferred are include Shellflex.RTM. 412 and Shellflex.RTM. 
371 oil (Shell Oil Co.) which are solvent refined and hydrotreated oils 
derived from naphthenic crude. Further examples of suitable oils include 
Arco Prime 400 oil (Atlantic Richfield Co.) and Kaydol.RTM. oil (Witco 
Corp.) which are white mineral oils. ASTM D 2226-82 and ASTM D 97-66 
(reapproved 1978) are, in their entireties, incorporated herein by 
reference. It is expected that other materials, including the phthalate 
ester plasticizers such as dibutyl phthalate, bis(2-ethylhexyl) phthalate, 
diisodecyl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, and 
ditridecyl phthalate will function satisfactorily as processing 
plasticizers. 
There are many organic extraction liquids that can be used. Examples of 
suitable organic extraction liquids include 1,1,2-trichloroethylene, 
perchloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane, 
1,1,2-trichloroethane, methylene chloride, chloroform, 
1,1,2-trichloro-1,2,2-trifluoroethane, isopropyl alcohol, diethyl ether, 
and acetone. 
In the above described process for producing microporous material, 
extrusion and calendering are facilitated when the substantially 
water-insoluble filler particles carry much of the processing plasticizer. 
The capacity of the filler particles to absorb and hold the processing 
plasticizer is a function of the surface area of the filler. It is 
therefore preferred that the filler have a high surface area. High surface 
area fillers are materials of very small particle size, materials having a 
high degree of porosity or materials exhibiting both characteristics. 
Usually the surface area of at least the siliceous filler particles is in 
the range of from about 20 to about 400 square meters per gram as 
determined by the Brunauer, Emmett, Teller (BET) method according to ASTM 
C 819-77 using nitrogen as the adsorbate but modified by outgassing the 
system and the sample for one hour at 130.degree. C. Preferably the 
surface area is in the range of from about 25 to 350 square meters per 
gram. ASTM C 819-77 is, in its entirety, incorporated herein by reference. 
Preferably, but not necessarily, the surface area of any non-siliceous 
filler particles used is also in at least one of these ranges. 
Inasmuch as it is desirable to essentially retain the filler in the 
microporous material, it is preferred that the substantially 
water-insoluble filler particles be substantially insoluble in the 
processing plasticizer and substantially insoluble in the organic 
extraction liquid when microporous material is produced by the above 
process. 
The residual processing plasticizer content is usually less than 10 percent 
by weight of the microporous sheet and this may be reduced even further by 
additional extractions using the same or a different organic extraction 
liquid. Often the residual processing plasticizer content is less than 5 
percent by weight of the microporous sheet and this may be reduced even 
further by additional extractions. 
On a coating-free, printing ink free, impregnant-free, and pre-bonding 
basis, pores constitute from about 35 to about 80 percent by volume of the 
microporous material when made by the above-described process. In many 
cases the pores constitute from about 60 to about 75 percent by volume of 
the microporous material. 
The volume average diameter of the pores of the microporous material when 
made by the above-described process, is usually in the range of from about 
0.02 to about 0.5 micrometers on a coating-free, printing ink-free, 
impregnant-free, and pre-bonding basis. Frequently the average diameter of 
the pores is in the range of from about 0.04 to about 0.3 micrometers. 
From about 0.05 to about 0.25 micrometers is preferred. 
Microporous material may also be produced according to the general 
principles and procedures of U.S. Pat. Nos. 2,772,322; 3,696,061; and/or 
3,862,030, the entire disclosures of which are incorporated herein by 
reference, including especially the processes for making microporous 
materials and the properties of the products. These principles and 
procedures are particularly applicable where the polymer of the matrix is 
or is predominately poly(vinyl chloride) or a copolymer containing a large 
proportion of polymerized vinyl chloride. 
The microporous material produced by the above-described processes may be 
used for producing electrically conductive articles of the present 
invention. However, many of them may optionally be stretched and the 
stretched microporous material used for producing such articles. When such 
stretching is employed, the products of the above-described processes may 
be regarded as intermediate products. 
It will be appreciated that the stretching both increases the void volume 
of the material and induces regions of molecular orientation. As is well 
known in the art, many of the physical properties of molecularly oriented 
thermoplastic organic polymer, including tensile strength, tensile 
modulus, Young's modulus, and others, differ considerably from those of 
the corresponding thermoplastic organic polymer having little or no 
molecular orientation. 
Stretched microporous material may be produced by stretching the 
intermediate product in at least one stretching direction above the 
elastic limit. Usually the stretch ratio is at least about 1.5. In many 
cases the stretch ratio is at least about 1.7. Preferably it is at least 
about 2. Frequently the stretch ratio is in the range of from about 1.5 to 
about 15. Often the stretch ratio is in the range of from about 1.7 to 
about 10. Preferably the stretch ratio is in the range of from about 2 to 
about 6. As used herein, the stretch ratio is determined by the formula: 
EQU S=L.sub.2 /L.sub.1 
where S is the stretch ratio, L.sub.1 is the distance between two reference 
points located on the intermediate product and on a line parallel to the 
stretching direction, and L.sub.2 is the distance between the same two 
reference points located on the stretched microporous material. 
The temperatures at which stretching is accomplished may vary widely. 
Stretching may be accomplished at about ambient room temperature, but 
usually elevated temperatures are employed. The intermediate product may 
be heated by any of a wide variety of techniques prior to, during, and/or 
after stretching. Examples of these techniques include radiative heating 
such as that provided by electrically heated or gas fired infrared 
heaters, convective heating such as that provided by recirculating hot 
air, and conductive heating such as that provided by contact with heated 
rolls. The temperatures which are measured for temperature control 
purposes may vary according to the apparatus used and Personal preference. 
For example, temperature-measuring devices may be placed to ascertain the 
temperatures of the surfaces of infrared heaters, the interiors of 
infrared heaters, the air temperatures of points between the infrared 
heaters and the intermediate product, the temperatures of circulating hot 
air at points within the apparatus, the temperature of hot air entering or 
leaving the apparatus, the temperatures of the surfaces of rolls used in 
the stretching process, the temperature of heat transfer fluid entering or 
leaving such rolls, or film surface temperatures. In general, the 
temperature or temperatures are controlled such that the intermediate 
product is stretched about evenly so that the variations, if any, in film 
thickness of the stretched microporous material are within acceptable 
limits and so that the amount of stretched microporous material outside of 
those limits is acceptably low. It will be apparent that the temperatures 
used for control purposes may or may not be close to those of the 
intermediate product itself since they depend upon the nature of the 
apparatus used, the locations of the temperature-measuring devices, and 
the identities of the substances or objects whose temperatures are being 
measured. 
In view of the locations of the heating devices and the line speeds usually 
employed during stretching, gradients of varying temperatures may or may 
not be present through the thickness of the intermediate product. Also 
because of such line speeds, it is impracticable to measure these 
temperature gradients. The presence of gradients of varying temperatures, 
when they occur, makes it unreasonable to refer to a singular film 
temperature. Accordingly, film surface temperatures, which can be 
measured, are best used for characterizing the thermal condition of the 
intermediate product. These are ordinarily about the same across the width 
of the intermediate product during stretching although they may be 
intentionally varied, as for example, to compensate for intermediate 
product having a wedge-shaped cross-section across the sheet. Film surface 
temperatures along the length of the sheet may be about the same or they 
may be different during stretching. 
The film surface temperatures at which stretching is accomplished may vary 
widely, but in general they are such that the intermediate product is 
stretched about evenly, as explained above. In most cases, the film 
surface temperatures during stretching are in the range of from about 
20.degree. C. to about 220.degree. C. Often such temperatures are in the 
range of from about 50.degree. C. to about 200.degree. C. From about 
75.degree. C. to about 180.degree. C. is preferred. 
Stretching may be accomplished in a single step or a plurality of steps as 
desired. For example, when the intermediate product is to be stretched in 
a single direction (uniaxial stretching), the stretching may be 
accomplished by a single stretching step or a sequence of stretching steps 
until the desired final stretch ratio is attained. Similarly, when the 
intermediate product is to be stretched in two directions (biaxial 
stretching), the stretching can be conducted by a single biaxial 
stretching step or a sequence of biaxial stretching steps until the 
desired final stretch ratios are attained. Biaxial stretching may also be 
accomplished by a sequence of one of more uniaxial stretching steps in one 
direction and one or more uniaxial stretching steps in another direction. 
Biaxial stretching steps where the intermediate product is stretched 
simultaneously in two directions and uniaxial stretching steps may be 
conducted in sequence in any order. Stretching in more than two directions 
is within contemplation. It may be seen that the various permutations of 
steps are quite numerous. Other steps, such as cooling, heating, 
sintering, annealing, reeling, unreeling, and the like, may optionally be 
included in the overall process as desired. 
Various types of stretching apparatus are well known and may be used to 
accomplish stretching of the intermediate product. Uniaxial stretching is 
usually accomplished by stretching between two rollers wherein the second 
or downstream roller rotates at a greater peripheral speed than the first 
or upstream roller. Uniaxial stretching can also be accomplished on a 
standard tentering machine. Biaxial stretching may be accomplished by 
simultaneously stretching in two different directions on a tentering 
machine. More commonly, however, biaxial stretching is accomplished by 
first uniaxially stretching between two differentially rotating rollers as 
described above, followed by either uniaxially stretching in a different 
direction using a tenter machine or by biaxially stretching using a tenter 
machine. The most common type of biaxial stretching is where the two 
stretching directions are approximately at right angles to each other. In 
most cases where continuous sheet is being stretched, one stretching 
direction is at least approximately parallel to the long axis of the sheet 
(machine direction) and the other stretching direction is at least 
approximately perpendicular to the machine direction and is in the plane 
of the sheet (transverse direction). 
After stretching has been accomplished, the microporous material may 
optionally be sintered, annealed, heat set and/or otherwise heat treated. 
During these optional steps, the stretched microporous material is usually 
held under tension so that it will not markedly shrink at the elevated 
temperatures employed, although some relaxation amounting to a small 
fraction of the maximum stretch ratio is frequently Permitted. 
Following stretching and any heat treatments employed, tension is released 
from the stretched microporous material after the microporous material has 
been brought to a temperature at which, except for a small amount of 
elastic recovery amounting to a small fraction of the stretch ratio, it is 
essentially dimensionally stable in the absence of tension. Elastic 
recovery under these conditions usually does not amount to more than about 
10 percent of the stretch ratio. 
The stretched microporous material may then be further processed as 
desired. Examples of such further processing steps include reeling, 
cutting, stacking, treatment to remove residual processing plasticizer or 
extraction solvent, coating or impregnation with various materials, and 
fabrication into shapes for various end uses. 
Stretching is preferably accomplished after substantial removal of the 
processing plasticizer as described above. For purposes of this invention, 
however, the calendered sheet may be stretched in at least one stretching 
direction followed by substantial removal of the residual organic 
extraction liquid. It will be appreciated that as stretching may be 
accomplished in a single step or a plurality of steps, so likewise 
extraction of the processing plasticizer may be accomplished in a single 
step or a plurality of steps and removal of the residual organic 
extraction liquid may be accomplished in a single step or a plurality of 
steps. The various combinations of the steps stretching, partial 
stretching, processing plasticizer extraction, partial plasticizer 
extraction, removal of organic extraction liquid, and partial removal of 
organic extraction liquid are very numerous, and may be accomplished in 
any order, provided of course, that a step of processing plasticizer 
extraction (partial or substantially complete) precedes the first step of 
residual organic extraction liquid removal (partial or substantially 
complete). It is expected that varying the orders and numbers of these 
steps will produce variations in a least some of the physical properties 
of the stretched microporous product. 
In all cases, the porosity of the stretched microporous material is, unless 
coated, printed, or impregnated after stretching, greater than that of the 
intermediate product. On a coating-free, printing ink-free, and 
impregnant-free basis, pores usually constitute more than 80 percent by 
volume of the stretched microporous material. In many instances the pores 
constitute at least about 85 percent by volume of the stretched 
microporous material. Often the pores constitute from more than 80 percent 
to about 95 percent by volume of the stretched microporous material. From 
about 85 percent to about 95 percent by volume is preferred. 
Generally the volume average diameter of the pores of the stretched 
microporous material is in the range of from 0.6 to about 50 micrometers. 
Very often the volume average diameter of the pores is in the range of 
from about 1 to about 40 micrometers. From about 2 to about 30 micrometers 
is preferred. 
"Coating" and "printing" are by custom usually referred to separately, 
although they share many characteristics in common. In many applications, 
especially in the field of graphic arts, the differences become tenuous at 
best. Perhaps the distinction most often used is that "coating" is 
ordinarily thought of as involving application of the film-forming 
composition to relatively large areas of the substrate whereas "printing" 
is generally considered to involve application of the film-forming 
composition in finer detail to relatively small areas of the substrate. 
Nevertheless, application of film-forming composition to localized areas 
of the substrate is referred to sometimes as "coating" and at other times 
as "printing." Many processes used for coating may, with little or no 
modification, be used for printing, and vice versa. For purposes of the 
present specification and claims, the above-described distinction and 
general customs of the trade will be observed, although it should be 
recognized that in some situations the distinction will have more 
significance than in others. 
Microporous material substrate, whether or not stretched, may be coated 
and/or printed with a wide variety of electrically conductive coating 
compositions and/or electrically conductive printing inks using a wide 
variety of coating and/or printing processes. The electrically conductive 
coating compositions, coating processes, electrically conductive printing 
inks, and printing processes are themselves conventional. 
Examples of coating processes that can be used include brushing, spraying, 
roll coating, curtain coating, offset coating, powder coating, and the 
like. 
One class of printing processes that can be used is typographic printing 
where ink is placed on macroscopically raised areas of the printing plate. 
Examples of typographic processes include letterpress printing, 
flexography, and letterset printing which is also known as dry offset 
printing and as offset letterpress printing. 
Another class of printing suitable for use is intaglio printing, also known 
as gravure printing, where ink is placed on depressed areas of the 
printing plate. 
Yet another class of printing processes suitable for use is planographic 
printing where ink is placed on localized regions of a printing plate that 
is either smooth or contains only microscopically raised areas. A subclass 
of particular interest is lithography, which includes several variations. 
Conventional lithography uses oil-based inks while reverse lithography 
uses water-based inks. In direct lithography (whether conventional or 
reverse), printing ink is applied to the substrate directly from the 
lithographic printing plate. In offset lithography (whether conventional 
or reverse), the printing ink is transferred first from the lithographic 
printing plate to a printing blanket and then from the printing blanket to 
the substrate. Other types of planographic printing include collotype 
printing, autotype printing, laser printing, and xerography. 
Another class of printing processes that can be used is stencil printing, 
including screen printing. 
Various miscellaneous printing processes that can be used including ink ]et 
printing. 
Of the printing processes, screen printing, lithography, and letterpress 
printing are most often used. Of the lithographic processes, offset 
lithography is preferred, especially when the lithography is conventional 
lithography. 
The microporous substrate is suitable for line printing, halftone printing, 
and continuous tone printing. For electronic circuit boards, line printing 
is most often used. 
Printing is usually accomplished using a screen printer or a printing 
press. The three general types of printing presses commonly used for 
printing flat substrates are the platen press, the flat-bed cylinder 
press, and the rotary press. The rotary press, which may be sheet fed or 
web fed, is the type of printing press most often used. 
There are many differences in printing inks, some physical and some 
chemical. Consequently there is a wide variety of systems for classifying 
inks depending upon which similarities and differences it is desired to 
emphasize. Most inks used for printing are liquids or pastes, that is, the 
vehicle before drying contains a liquid. There are a few exceptions such 
as xerographic printing ink also known as toner, which is dry. Oil-based 
and most organic solvent based inks are not compatible with water, whereas 
water-based inks are not ordinarily compatible with oil. Inks usually dry 
by evaporation of liquid, by adsorption of liquid into the substrate, by 
crosslinking of the binder, by cooling or by a combination of two or more 
of these. Other systems of classification are based on the type of binder, 
such as rubber-based, drying oil based, non-drying oil based, natural 
resin-based, gilsonite-based, asphaltic-based, synthetic resin-based, and 
the like. Yet another classification system is based upon viscosity of the 
ink. Still another is based upon the types of colorant which may be 
present, such as pigment-based, toner-based, dye-based, pigment and dye 
based, clear, and the like. Other systems are based upon the printing 
processes employed for deposition of the ink on the substrate. 
In keeping with customary usage, the term "printing ink" is used herein 
with reference to the ink composition employed in printing and with 
reference to the printed composition on the substrate, whether before 
drying or after drying, partial drying, or hardening. The correct usage 
will be obvious from the context or expressly stated. 
Printing processes, printing equipment, and printing inks have been 
extensively discussed and documented. Examples of reference works that may 
be consulted include L. M. Larsen, Industrial Printing Ink, Reinhold 
Publishing Corp., (1962); Kirk-Othmer, Encyclopedia of Chemical 
Technology, 2d Ed., John Wiley & Sons, Inc., Vol. 11, pages 611-632 (1966) 
and Vol. 16, pages 494-546 (1968); and R. N. Blair, The Lithographers 
Manual, The Graphic Arts Technical Foundation, Inc., 7th Ed. (1983). 
For a more detailed description of printing on certain types of microporous 
material that may be employed in the present invention, see U.S. Pat. No. 
4,861,644, the entire disclosure of which is incorporated herein by 
reference. 
As is the case in respect of printing inks, there are many differences in 
coating compositions, some physical and some chemical, and likewise there 
is a wide variety of systems for classifying coating compositions 
depending upon which similarities and differences it is desired to 
emphasize. Most coating compositions are liquids or pastes, that is, the 
vehicle before drying contains a liquid. There are a few exceptions such 
as powder coating compositions which are dry. The classification systems 
for coating compositions are generally similar to those for printing inks 
described above. 
Electrically conductive coating compositions (i.e., coating compositions 
which upon application and drying produce an electrically conductive 
coating on the substrate) and electrically conductive printing ink 
compositions (in this context, printing ink compositions which upon 
application and drying produce electrically conductive ink on the 
substrate) are many and well known. The common characteristic of 
electrically conductive coatings and electrically conductive printing inks 
in their final forms on the substrate is that they are capable of 
conducting more than trivial amounts of electricity. The electrical 
resistance may be high or low, depending upon the many factors including 
the electrical properties of the coating or ink, and the dimensions of the 
applied material. For ordinary electrical conductors such as ordinarily 
used as flexible electrical conductors or on electronic circuit boards, 
low resistances are generally preferred. For resistors, higher resistances 
are usually desired. The resistance should not be so high, however, that 
for practical purposes it is not significantly conductive, as would be 
understood by those skilled in the art. 
Whether before or after coating and/or printing, the microporous material 
may be bonded to a wide variety of porous or nonporous materials. The 
resulting laminate may be flexible or it may be substantially rigid, 
depending upon the nature of the material to which the microporous 
material is bonded. 
Porous materials are those which are generally pervious to gases and which 
have a large number of pores, passageways, or channels through which 
matter can pass. These materials are those customarily recognized and 
employed for their porous properties. Examples of suitable materials 
include porous thermoplastic polymeric sheet or film, porous thermoset 
polymeric sheet or film, porous elastomeric sheet or film, and open celled 
foams. Other examples include fabrics, such as woven fabrics, knitted 
fabrics, nonwoven fabrics, and scrims. Still other examples include fiber 
mats, paper, synthetic paper, felt, and the like. Further examples of 
suitable porous materials include materials which are microporous such as 
the stretched microporous materials and precursor microporous materials 
described herein, as well as other materials which are microporous. In the 
porous materials which are based on fibers, the fibers may be natural, 
such as wood fibers, cotton fibers, wool fibers, silk fibers, and the 
like; or they may be any of the artificial fibers such as polyester 
fibers, polyamide fibers, acrylic fibers, modacrylic fibers, rayon fibers, 
and the like; or they may be combinations of differing kinds of fibers. 
The fibers may be staple and/or they may be continuous. Metal fibers, 
carbon fibers, and glass fibers are within contemplation. 
Substantially nonporous materials are those which are generally impervious 
to the passage of liquids, gases, and bacteria. On a macroscopic scale, 
substantially nonporous materials exhibit few if any pores, viz., minute 
openings through which matter passes. These materials include those 
customarily recognized and employed for their barrier properties. Examples 
of suitable materials include substantially nonporous thermoplastic 
polymeric sheet or film, substantially nonporous metalized thermoplastic 
polymeric sheet or film, substantially nonporous thermoset polymeric sheet 
or film, substantially nonporous elastomeric sheet or film, and 
substantially nonporous metal sheet or foil. Although the substantially 
nonporous material is most often in the form of sheet, film, or foil, 
other shapes may be used when desired, such as for example, plates, bars, 
rods, tubes, and forms of more complex shape. Examples of thermoplastic 
polymeric materials which are suitable for use include high density 
polyethylene, low density polyethylene, polypropylene, poly(vinyl 
chloride), saran, polystyrene, high impact polystyrene, the nylons, the 
polyesters such as poly(ethylene terephthalate), copolymers of ethylene 
and acrylic acid, and copolymers of ethylene and methacrylic acid. If 
desired, all or a portion of the carboxyl groups of carboxyl-containing 
copolymers may be neutralized with sodium, zinc, or the like. Examples of 
substantially nonporous thermoplastic sheets or films include extruded 
substantially nonporous thermoplastic sheet or film, coextruded 
substantially nonporous thermoplastic sheets or films of differing 
thermoplastic polymers, and substantially nonporous sheets or films coated 
with one or more differing thermoplastic polymers, and substantially 
nonporous thermoplastic sheets or films laminated to other thermoplastic 
sheets or films. An example of a metalized thermoplastic polymeric 
material is aluminized poly(ethylene terephthalate). Examples of thermoset 
polymeric materials include thermoset phenol-formaldehyde resin and 
thermoset melamine-formaldehyde resin. Examples of elastomeric materials 
include natural rubber, neoprene, styrene-butadiene rubber, 
acrylonitrile-butadiene-styrene rubber, elastomeric polyurethanes, and 
elastomeric copolymers of ethylene and propylene. Examples of metals 
include iron, steel, copper, brass, bronze, chromium, zinc, die metal, 
aluminum, nickel, and cadmium. Most often the metals employed are alloys. 
Bonding may be made by conventional techniques such as for example fusion 
bonding and adhesive bonding. Examples of fusion bonding include sealing 
through use of heated rollers, heated bars, heated plates, heated bands, 
heated wires, flame bonding, radio frequency (RF) sealing, and ultrasonic 
sealing. Heat sealing is preferred. Solvent bonding may be used where the 
substrate material is soluble in the applied solvent at least to the 
extent that the surface becomes tacky. After the microporous material has 
been brought into contact with the tacky surface, the solvent is removed 
to form a fusion bond. 
Many adhesives which are well known may be used to accomplish bonding. 
Examples of suitable classes of adhesives include thermosetting adhesives, 
thermoplastic adhesive, adhesives which form the bond by solvent 
evaporation, adhesives which form the bond by evaporation of liquid 
nonsolvent, and pressure sensitive adhesives. 
Foamable compositions may be foamed in contact with the microporous 
material to form a bond between the resulting foam and the microporous 
material. 
Powder bonding is a technique which is particularly useful for bonding the 
microporous material to nonwoven webs of staple and/or continuous fibers 
and to woven or knitted fibers. 
The bond may be permanent or peelable, depending upon the bonding technique 
employed, the adhesive employed, and/or the nature of the substrate 
material to which the microporous material is bonded. 
The microporous material may be essentially continuously bonded to the 
substrate material, or it may be discontinuously bonded to the substrate 
material. Examples of discontinuous bonds include bonding areas in the 
form of one or more spots, patches, strips, stripes, open-curved stripes, 
closed-curved stripes, irregular areas, and the like. When patterns of 
bonds are involved, they may be random, repetitive, or a combination of 
both. 
The microporous material may be brought into contact with thermosettable 
molding composition and the resulting composite may then be molded under 
heat and pressure such that the composite is shaped and the molding 
composition cured to the thermoset state. Electrically conductive coating 
or electrically conductive printing ink may be applied to the microporous 
material before or after the composite is formed. The final electrically 
conductive article may be in a wide variety of shapes, such as 
substantially planar or three-dimensional. 
The microporous material employed in the present invention is particularly 
useful for fusion bonding to thermoplastic organic polymeric substrates in 
the absence of extrinsic intervening adhesive. This technique is 
especially useful for producing many electrically conductive articles of 
the present invention, particularly printed circuit boards and 
electromagnetic interference shields. The method produces the best results 
when the thermoplastic organic polymer of the microporous material matrix 
is chemically similar to that of the substrate. This method is 
particularly useful when the thermoplastic organic polymer of the 
microporous material matrix and that of the substrate are polyolefinic in 
nature. The fusion bond obtained is ordinarily quite strong which is 
surprising inasmuch as the lamination of materials to polyolefins such as 
polyethylene and polypropylene is usually difficult unless special 
adhesives are used. 
Fusion bonding is especially useful for the in-mold formation of 
electromagnetic interference shields and similar devices manufactured by 
the blow molding process. In this procedure, one or more sheets of 
microporous material (usually having an electrically conductive coating on 
one of its sides) are placed against the sides of the opened mold, the 
mold is closed, a polyolefin parison is blown to form the 
three-dimensional part, the mold is opened, and the part is ejected. If 
the microporous material of the part was not pre-coated, electrically 
conductive coating may be applied. A major advantage is that extrinsic 
intervening adhesive need not be employed. 
Another type of fusion bonding process is useful for forming printed 
circuit boards. The printed circuit boards may be planar, but the process 
is particularly suitable for producing three-dimensional circuit boards. 
In this process microporous material having a pattern of electrically 
conductive printing ink on at least one side is molded with thermoplastic 
organic polymer to fusion bond the printed microporous material to the 
thermoplastic organic polymer and to form the three-dimensional printed 
circuit board. Extrinsic intervening adhesive need not be used. 
The electrically conductive articles of the present invention have many and 
varied uses including substantially planar printed circuit hoards, 
three-dimensional printed circuit boards, electromagnetic interference 
shields, rigid conductors, flexible conductors, resistors for electronic 
circuits, and capacitors for electronic circuits. 
The invention is further described in conjunction with the following 
examples which are to be considered illustrative rather than limiting. 
Examples 1 and 2 
The preparation of microporous material is illustrated by the following two 
descriptive examples. Processing oil was used as the processing 
plasticizer. Silica, polymer, lubricant, and antioxidant in the amounts 
specified in Table I were placed in a high intensity mixer and mixed at 
high speed for 6 minutes. The processing oil needed to formulate the batch 
was pumped into the mixer over a period of 12-18 minutes with high speed 
agitation. After completion of the processing oil addition a 6 minute high 
speed mix period was used to complete the distribution of the processing 
oil uniformly throughout the mixture. 
TABLE I 
______________________________________ 
Formulations 
Example 1 2 
______________________________________ 
Ingredient 
UHMWPE (1), kg 19.50 7.08 
HDPE (2), kg 7.71 0.00 
Precipitated 40.82 40.37 
Silica (3), kg 
Lubricant (4), g 2700.0 200.0 
Antioxidant (5) g 
0.0 200.0 
(6) g 85.0 0.0 
Processing Oil (7), kg 
in Batch 61.1 61.1 
at Extruder .about.59.3 
.about.19.7 
______________________________________ 
(1) UHMWPE = Ultrahigh Molecular Weight Polyethylene, Himont 1900, Himont 
U.S.A., Inc. 
(2) HDPE = High Density Polyethylene, Hostalen .TM. GM 6255, Hoechst 
Celanese Corp. 
(3) HiSil .RTM. SBG, PPG Industries, Inc. 
(4) Petrac .RTM. CZ81, Desoto, Inc., Chemical Speciality Division 
(5) Irganox .RTM. B215, CibaGeigy Corp. 
(6) Irganox .RTM. 1010, CibaGeigy Corp. 
(7) Shellflex .RTM. 371, Shell Chemical Co. 
The batch was then covered to a ribbon blender where usually it was mixed 
with up to two additional batches of the same composition. Material was 
fed from the ribbon blender to a twin screw extruder by a variable rate 
screw feeder. Additional processing oil was added via a metering pump into 
the feed throat of the extruder. The extruder mixed and melted the 
formulation and extruded it through a 76.2 centimeter x 0.3175 centimeter 
slot die. The extruded sheet was then calendered. A description of one 
type of calender that may be used may be found in the U.S. Pat. No. 
4,734,229, the entire disclosure of which is incorporated herein by 
reference, including the structures of the devices and their modes of 
operation. Other calenders of different design may alternatively be used; 
such calenders and their modes of operation are well known in the art. The 
hot, calendered sheet was then passed around a chill roll to cool the 
sheet. The rough edges of the cooled calendered sheet were trimmed by 
rotary knives to the desired width. 
The oil filled sheet was conveyed to the extractor unit where it was 
contacted by both liquid and vaporized 1,1,2-trichloroethylene (TCE). The 
sheet was transported over a series of rollers in a serpentine fashion to 
provide multiple, sequential vapor/liquid/vapor contacts. The extraction 
liquid in the sump was maintained at a temperature of 
65.degree.-88.degree. C. Overflow from the sump of the TCE extractor was 
returned to a still which recovered the TCE and the processing oil for 
reuse in the process. The bulk of the TCE was extracted from the sheet by 
steam as the sheet was passed through a second extractor unit. A 
description of these types of extractors may be found in U.S. Pat. No. 
4,648,417, the entire disclosure of which is incorporated herein by 
reference, including especially the structures of the devices and their 
modes of operation. The sheet was dried by radiant heat and convective air 
flow. The dried sheet was wound on cores to provide roll stock for further 
processing. 
The microporous sheets were tested for various physical properties the 
results of which are shown in Table II. Breaking Factor and Elongation 
were determined in accordance with ASTM D 882-83 which is incorporated 
herein by reference. 
Property values indicated by MD (machine direction) were obtained on 
samples whose major axis was oriented along the length of the sheet. TD 
(transverse direction; cross machine direction) properties were obtained 
from samples whose major axis was oriented across the sheet. 
TABLE II 
______________________________________ 
Physical Properties of Microporous Sheet 
Example No. 1 2 
______________________________________ 
Thickness, mm 0.203 0.224 
Weight, g/m.sup.2 117.8 88.8 
Breaking Factor, kN/m 
MD 4.98 0.782 
TD 1.34 0.364 
Elongation at 
break, % 
MD 632 215 
TD 635 342 
Processing Oil 3.6 2.9 
Content, wt % 
Estimated Porosity, vol % 
69.6 
______________________________________ 
EXAMPLE 3 
Toilet seat lids were produced according to the following procedure. The 
bottom half of a toilet seat lid mold was lined with a sheet of 
microporous material similar to that of Example 1. A mixture of wood flour 
and phenolic resin was placed atop the microporous material and spread to 
distribute the mixture approximately uniformly across the mold. A second 
sheet of the microporous material was placed on the wood flour and 
phenolic resin mixture. The top half of the mold was mated with the lower 
half and heat and pressure were applied to cure the phenolic resin. The 
mold was opened and the molded part was removed and allowed to cool. The 
edges were sanded to remove flash from the lid. The lid was next coated 
with FFG G10945 Black Conductive Primer (PPG Industries, Inc.) using 
conventional flow coating techniques, baked at about 191.degree. C. for 
about 11 minutes, and then allowed to cool. The lid was electrically 
grounded and electrostatically sprayed with PPG G12831 White Baking Enamel 
(PPG Industries, Inc.) using a Graco high speed bell electrostatic 
sprayer. After completion of the electrostatic spraying, the lid was baked 
at about 163.degree. C. for about 8 minutes and allowed to cool. The 
appearance of the lid was excellent. 
EXAMPLE 4 
Thick film screen printing was used to print an electronic conductor on a 
sheet of the microporous material of Example 2. The printing was 
accomplished using a Porcelain Forslund Screen Printer, Model 35-00 
(Crystal Mark, Inc.). The electrically conductive printing ink employed 
was Acheson Electrodag 423 ss carbon paste. The printed conductor was 23 
millimeters long and 0.5 millimeter wide and was terminated at each end 
with enlarged terminals which were printed at the same time as the 
conductor. The resistance of the conductor was measured to be 9.3 
kiloohms. 
EXAMPLE 5 
A sheet of the microporous material of Example 2 was laminated to a 97 
percent alumina ceramic substrate using double-sided adhesive tape located 
between the microporous material and the ceramic substrate. Using the 
equipment and electrically conductive printing ink of Example 4, a pattern 
of fifteen substantially identical resistors was printed on the 
microporous material. 
Although the present invention has been described with reference to 
specific details of certain embodiments thereof, it is not intended that 
such details should be regarded as limitations upon the scope of the 
invention except insofar as they are included in the accompanying claims.