CA1254330A - Electroconductive element, precursor conductive composition and fabrication of same - Google Patents

Abstract

ABSTRACT
A flowable conductive composition and an electroconductive element fabricated from the flowable conductive composition, in which the composition comprises mica flakes coated with conductive metal and an organic binder. An electroconductive element comprises mica flakes coated with conductive metal embedded in a matrix of organic material. Also disclosed are a silver-coated mica flake, for incorporation in composition and an electroconductive element, and methods for fabricating an electroconductive element. The electroconductive element is useful, for example, as a termination element for capacitors, as an internal conductive element in capacitors of the type used in thick-film technology applications, as an element for dissipation of electrostatic charge, or as electromagnetic shielding.

Description

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SPECIFICATI_ The present invention relates to flowable conductive compositions, such as molding compositions, conductive paste~, conductive paints, and to electro-conductive ele~ents fabricated from such composi~ions, to the making of electroconductive elements from the flowable conductive compositions, and to mica flakes having a conductive metal coating and suitable for making the above-mentioned conductive compositions and electro-conductive elements.
Backqround of the lnvention Prior to this invention, conductive paste has beenfabricated from silver particles, an inorganic bonding component, and an organic binding component. Typically, such a paste contains, by weight, 60 to 70% silver, 5 to 10%
glass frit and 20 to 35% of a mixture of various solvents, plasticizers and resins. This paste has been applied to a substrate, for example, a ceramic capacitor, and the substrate and paste fired to form a component comprising the ubstrate and a fired-on electroconductive body which provided an electrically conductive connection. Frequently, these components have been coated with solder for ready integration into a circuit at a later date.
A disadvantage of these precursor paste compositions and electroconductive bodies is that fabrication of the electroconductive body must be performed by heating the paste at high temperatures which may damage the substrate to which a paste has been applied.

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lZS~330 Attempts have been made to find satisfactory substitutes for the above-mentioned pastes and electroconductive bodies. It has been ~uggested that a conductive paste may be fired to produce an electroconductive body containing micron-sized glass spheres coated with a ncsle metal, such as palladium cr platln~m, or ~n alloy, for example of palladium, gold and silver, embedded in a matrix of glassy dielectric material having a fusion temperature lower than the softening temperature of the glass spheres. An electroconductive body consisting of particles of alumina coated by palladium, particles of alumina coated by palladium oxide and particles of silver embedded in a glassy matrix has also been suggested. The use of metals such as palladium and gold entails substantial expense in the production of the electroconductive body, and its precursor conductive paste. Also, disadvantages attendant to fabrication at high firing temperatures are not avoided with these substitutes.
It has also been suggested that a conductive paste comprising an organic resin binder and a particulated electrically conductive metal-containing material, for example, either silver-coated glass spheres or silver flakes, may be treated to form a conductive body. Other electrically conductive metals are also suggested.
Another proposal involves forming a conductive body from a paste comprising inorganic non-metallic particles coated with silver, silver particles and an organic binder formable into a matrix, or comprising inorganic non-metallic particles coated with silver, silver ~, ~12s~30 particles, particles of a glassy material fusible into a m~trix and an oryanic vehicle. In the conductive body, the silver particles ana silver-coated inorganic non-metallic particles are in effective contacting relationship within the matrix. One illustration of such a system ;s described in ~.S. Patént 4,419,279 g~ranted December 6, 1983~

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Summary ~he present invention provides an electro-conductive element with advanta~eous electrical and otherproperties, and materials from which it is made, at low expense in comparison to typical prior art embodiments.
One general object of this invention is to provide a new and improved flowable conductive composition or electroconductive element.
Another general object of this invention is to provide a new and improved conductive filler for converting a normally non-electrically conductive thermoplastic or thermosetting plastic into an electroconductive element.
More specifically, it is an object of this invention to provide a conductive composition and an electroconductive element at a relatively low cost.
It is also an object of this invention to provide a conductive composition, for example molding composition~
which is well-suited to injection, compression and/or extrusion molding applications without degradation, such as breaking up, of the conductive filler in the composi;tion.

~t is another object of this invention to provide, as a flowable conductive composition, conductive paste or 1~5~330 paint which has a consistency appropriate for screening on, or other application to, a sub~trat~.
It is yet another object of this invention to provide, as a flowable conductive composition, conductive paste which is formable into an electroconductive body at conditions not destructive to an attached substra_e.
It i8 still another object of this invention to provide an electroconductive element which is durable and exhibits acceptable conductivity for long periods of time during storage and operation.
It is a further object of this invention to provide an electroconductive element which, when attached to a substrate, exhibits acceptable adhesion to such substrate for long periods of time in storage and operation.
It is a still further object of this invention to provide a method for producing the foregoing electroconductive element.
It is also an object of this invention to provide a mica flake coated with a conductive metal, for example, a noble metal, copper or nickel, which is suited to the production of the foregoing flowable conductive composition and electroconductive element.
In accordance with a feature of the present invention, a flowable conductive composition consists essentially of a mixture of mica flakes coated with a conductive metal and of an organic component formable into a matrix. The metal-coated mica flakes are in the organic component thereby forming the composition. The composition, if a molding composition, is suitable for injection, compression or extrusion molding into an electroconductive element appropriately shaped for - illustratively -electromagnetic shielding applications, and if a conductive paste or paint i5 suitable for application to a substrate to form an electroconductive element such as a coating, body, etc. on the substrate.
It will be understood that for purposes of this invention a "flowable conductive composition" is one containing conductive metal-coated mica flakes (as well as other conductive filler material in some embodiments of the invention) and an organic binder as set forth above, and which flows at room temperature and atmospheric pressure, such as conductive paint and conductive paste, or can be made to flow by application of conventionally increased temperature and/or pressure conditions, such as a molding composition which flows under conditions conventionally imposed during injection, compression or extrusion molding.
In accordance with another feature of the invention, in several particularly advantageous embodiments, an electroconductive element consists essentially of mica flakes coated with a conductive metal, embedded in a matrix of organic material. The metal-coated mica flakes are in effective contacting relationship within said matrix.
For purposes of this invention an "electro conductive element" is an article of manufacture having a non-flowable organic matrix in which are embedded conductive metal-coated mica flakes (and, in some embodiments, other conductive filler material) such that the element will conduct electricity. The element is shaped in any suitable 12S~33V

form, and in various embodiments is either a termination element for capacitors, an internal conductive element in capacitors of the type used in thick-film technology applications, an element for dissipation of electrostatic charge, or electromagnetic shielding.
In an~ther aspect, the present invention relates to a method of making an electroconductive element, which comprises combining, to form a flowable composition, mica flakes coated with a conductive metal, and an organic binder formable into a matrix, and subjecting the flowable composition to conditions effective to form the organic binder into a matrix in which the metal-coated mica flakes are embedded.
A further aspect of the present invention relates to an article of manufacture useful in practicing the invention. This article comprises a mica flake which is coated on substantially its entire surface with a conductive metal, the metal preferably constituting at least 4~ by weight of the article.
Electroconductive elements in accordance with the claimed invention are characterized in that they have volume resistivities of less than 106 ohm-cm (a volume resistivity of 106 ohm-cm. or greater is generally viewed in the art as characterizing an insulating material). By way of giving a reference point, the volume resistivity of pure silver is 10 8 ohm-cm. It will be appreciated, however, that within the above-mentioned ranqe, electroconductive elements of the present invention exhibit volume resistivities which vary according to the intended use.

lZS4330 Hence, conductive paste of this invention is useful as an intermediate in the manufacture of an electroconductive element, and more specifically as a vehicle by which the components of an electroconductive body or electroconductive coating are conveniently applied to substrates, such as capacitors, die~ectric compenents, and the like. Electroconductive bodies and coatings of this invention are, in turn, useful to provide an electrically conductive connection or film on a substrate. For instance, the electroconductive bodies find application as termination elements for ceramic capacitors, such as those of the multi-layer variety. Such electroconductive bodies may also be useful as internal conductive elements employed in combination with nonconductive elements in, for example, a multi-layer capacitor or a capacitor of the type employed in thick-film technology applications.
Additionally, various embodiments of the electroconductive element of the claimed invention are useful in the dissipation of an electrostatic charge, or as electromagnetic shielding. In the former, the electro-conductive element serves as a medium through which the electrostatic charge can be moved at a controlled rate (depending on the volume resistivity, typically at least 103 ohm-cm), while in the latter the element is to at least a substantial extent reflective of electromagnetic energy (volume resis~ivity typically being in the range of 1 ohm-cm).
The metal-coated mica flake of this invention is useful as a component of the flowable conductive composition _7_ 12S~330 and electroconductive element of this invention, contributing to the favorable properties thereof and, senerally, d~creasing production cost.
~ he present invention affords the advantages of providing a flowable conductive composition wh$ch is relatively inexpensive and comprises easily obtcina~le materials and which is well-suited for conversion to an electroconductive element in a variety of applications. In this connection, the flowability of the conductive composition is especially favorable. The electroconductive elements, themselves, are additionally advantageous because of their versatility and desirable performance characteristics, particularly in res~ect of their wide range of attainable conductivities and their ability to adhere to substrates. A further advantage of the present invention is that the metal-coated mica flake, preferably containing at least 4~ by weight conductive metal, provides a convenient, relatively low-cost starting material for making an electroconductive element and precursor flowable conductive composition. Through employment of this coated flake a normally non-electrically conductive thermoplastic or thermosetting plastic is converted into an electroconductive element.
The present invention, as well as further objects and features thereof, will be more fully understood from the following description of certain preferred embodiments, when read with reference to the accompanying drawings.

1~54330 Brief Descri~tion of Drawinqs Figure 1 i8 an enlarged fragmentary sectional view of flowable conductive composition in accordance with the invention.
Figure 2 is an enlarged fragmentary ~ectional view of an electroconductive element made from a flowzble conductive composition, all in accordance with the invention.
Figure 3 is an enlarged fragmentary sectional view of an alternative embodiment of flowable conductive composition in accordance with the invention.
Figure 4 is an enlarged fragmentary sectional view of an alternative embodiment of an electroconductive element made from a flowable conductive composition, all in accordance with the invention.
Figure 5 is a plot of volume resistivity of various electroconductive elements against the volume % of conductive filler therein.
Figure 6 is a plot of volume resistivity of various electroconductive elements against the weight % of conductive filler therein.
It will be understood that the views shown in the drawings are not to scale, but that certain aspects, such as amount of organic component, amount of matrix, distances between particles and the like, have been emphasized for purposes of clarity.
Description of Preferred Embodiments Referring to Figure 1 of the drawing, there is shown a flowable conductive composition comprising an ~ZS~33~) organic material 10, illustratively, an acrylic resin, such as Rohm 6 ~aas B-66 acryloid resin, in which are suspended mica flakes 12 having a 6ilver coating 14. A silver coating 14 on a mica flake 12 constitutes, illustratively, 20 to 70%
by weight of the flake and coating.
This ~ilver coating on a mica flake s~-ves aisG to illustrate a silver-coated mica flake containing at least 44, and preferably at least 124, by weight silver. As typical, the conductive composition is deposited on an appropriate substrate 16.
In Figure 2, there is shown an electroconductive element comprising a matrix of an organic material 42, in this embodiment comprising a hardened acrylic resin, in this instance Rohm 6 Haas B-66 acryloid resin, in which are embedded mica flakes 20, having a silver coating 22.
Again, as typical, the electroconductive element is deposited on and adheres to a substrate 44. A silver coating 22 on a mica flake 20 constitutes, illustratively, 20 to 704 by weight of the flake and coating. Adjacent silver-coated mica flakes are in intersurface contact with one another at locations 24, or are close enough together, at locations 26, 28, 30 and 32, so that electrons can pass between them. It will be noted that the flakes overlap, thus providing an advantageously large conductive area. At location 34 the coated flake forms part of the surface of the electroconductive element. Also, for instance at locations 36, 38 and 40, silver-coated mica flakes are sufficiently close to the surface of the electroconductive element or substrate 44 to allow passage of the electrons 125~330 between the surface and the silver-coated flakes. Thus, conductive paths through the electroconductive element are established.
Alternative embodiments of a flowable conductive composition of the present invention also contain particles of pure conductive metal and/or inorganic non-metallic particles coated with same. Referring to Figure 3, an embodiment of the conductive composition wherein both are present is illustrated. The composition comprises an organic binder S0, in this embodiment containing an acrylic resin, again Rohm & Haas B-66 acryloid resin, in which are suspended mica flakes 52 having a gold coating 54, alumina granules 56 havinq a gold coating 58 and pure gold particles in the form of flake~ 60. Gold coatings 54 and 58 on a mica flake 52 and alumina granule 56, respectively, constitute, illustratively, 20 to 70~ by weight of the total weight of the coated flake and coated granule. The composition also contains carbon black particles 62. As typical, the conductive paste is deposited on an appropriate substrate 63.
In Figure 4 is illustrated an electroconductive body comprising a matrix of an organic material 108, in this embodiment containing a hardened acrylic resin, illustratively Rohm 6 ~aas B-66 acryloid resin, in which are embedded mica flakes 64 having a gold coating 66, alumina granules 68 having a gold coating 70, and pure gold particles in the form of flakes 72. The incorporation of gold (or other conductive metal) particles of other shapes is also within the scope of this invention; however, flakes lZS~330 of pure material are especially advantageous. The electroconductive element also contains carbon black particles 73. Again, ~s typical, the electroconductive body is deposited on and adheres to a ~ubstrate 106. Gold coatings 66 and 70 on a mica flake 64 and alumina granules 68, respectively, constitute, illustratively, 20 to 70~ ~;
weight of the total weight of the coated flake and coated granule. Adjacent qold-coated mica flakes are in intersurface contact with one another, at location 69, or are close enough together, at location 71, so that electrons can pass between them. Likewise, for adjacent gold-coated alumina granules at locations 74 and 76, respectively, as well as for adjacent gold flakes at locations 78 and 80, respectively. Also, an adjacent gold-coated mica flake and gold-coated alumina granule are in direct intersurface contact at location 82, a gold-coated alumina granule and gold flake at location 84; and, a gold-coated mica flake and pure gold flake at location 86. (It will be understood that, in comparison to overlapping of metal-coated flakes which greatly enhances the conductive capacity of the electroconductive element, the coated granules provide only tangential or point-to-point contact, and are in that respect somewhat less advantageous.) At location 88 a gold-coated flake and gold-coated granule are sufficiently close to allow passage of electrons. Such condition exists between a gold-coated flake and pure gold flake at location 90 and between a gold-coated granule and pure gold flake at - location 92. At locations 91 and 93 gold-coated mica flakes form part of the element's surface. Additionally, for instance at locations 94, 96 and 98, a gold-coated mica flake and qold-coated alumina granule and gold flake, respectively, are sufficiently close to the surface of the electroconductive body to allow passage of the electrons between the surface and themselves. And, a gold particle, a gold-coated mica flake and a gold-coated granule are sufficiently close to the substrate, at locations 100, 102 and 104, respectively, to allow passage of electrons therebetween. Accordingly, conductive paths through the electronconductive element are established.
The illustrations of Figures 1 to 4 serve to depict other electroconductive elements and precursor conductive compositions, such as electromagnetic shielding articles and precursor molding compositions. It will be understood that in most instances such articles and molding compositions are not attached to a substrate, and also are on the order of about 1/8 inch thick (whereas the layers illustrated in Figures 1 to 4 are typically about 30 microns thick); otherwise Figures 1 to 4 accurately represent an aforementioned shielding article and precursor composition.
The conductive metal incorporated in a flowable conductive composition in accordance with this invention, as its designation indicates, provides a conductive component in an electroconductive element ultimately fabricated from the conductive composition. Therefore, the amount and form of the conductive metal in the composition are in large part dependent on the properties desired for such an electroconductive element.

lZS~330 The conductive metal i~ suitably copper or nickel, or silver, gold, palladium, platinum or any other of the noble metals. In some embodiments, silver, gold and/or copper are preferred due to their advantageous conductivity and/or relatively low cost. While the deposition of metal pigments, such as titanium dioxide and iron oxides, on mica and their employment in coloring has been mentioned in the prior art, no use of conductive metal-coated mica flakes in conductive applications has been found.
The coating of conductive metal on mica flakes of the flowable conductive composition is a layer which covers su~stantially the entire surface of each such flake. It is preferred that this layer be of uniform thickness, but thickness may vary from point to point on the flake surface without departing from the present invention. The layer of conductive metal need only be of sufficient thickness to ensure the conductivity (at the level desired) of an electroconductive element produced from the conductive composition of the invention; however, thickness of the layer may be increased above this minimum, for instance, to the extent that cost considerations permit. Typically, the thickness of this layer of conductive metal is a minimum of 100 angstroms.
In accordance with the invention, a conductive metal-coated mica flake contains at least 4~, and up to 70~, by weight conductive metal coating. It is preferable that the conductive metal-coated mica flake contain at least 12%, and especially at least 16~, by weight metal coating.
Incorporation in the flowable conductive composition of such metal-coated flakes maintains good conductivity of a product electroconductive element without appreciable impairment of its electrical and other properties. It will be under~tood that cost advantages afforded by the employment Of conductive metal-coated mica flakes, as opposed to employment of pure metal (such as silver) alone, are also attendant to this embodiment.
The amount of conductive metal incorporated in an electroconductive element in accordance with the present invention ranges from 2 to 90% by weight. Depending on the amount of organic binder and other materials which are included in the flowable composition and survive formation of the electroconductive element (a parameter easily ascertainable by one of ordinary skill in the art), the amount of conductive metal incorporated in the precursor flowable conductive composition is up to 90~, but more typically about 15% or less.
The conductive metal coating, when deposited on a mica flake generally conforms to the contours of the flake, and, therefore, the shape of the metal-coated flake corresponds qenerally to the shape of the uncoated flake.
Including the metal layer, these coated flakes are of a size which is compatible with the attainment of the desired properties of the flowable conductive composition and electroconductive element of this invention. That is, the metal-coated flakes should be sized, for example, so that incorporation of same in the flowable conductive composition does not appreciably interfere with the ease of its flow properties in connection with application to a substrate or with injection, compression or extrusion molding, as appropriate. Typically, the metal-coated flakes are of a size from 0.1 to 200, preferably 0.5 to 44, microns in maximum dimension.
In accordance with the foregoing, the metal-coated flakes are pre~erably silver-coated mica flakes. Again, typically, the silver-coated flakec, including the silver layer, are preferably of a size from 0.5 to 44 microns in maximum dimension. Further examples of appropriately sized silver-coated mica flakes are those of a size from 44 to 74 microns and 74 to 200 microns.
The mica flakes, themselves, may be composed of either natural or synthetic mica. Micas are a group of laminated silica materials. The structures of micas have been rather extensively treated in the art, as for instance in L. Pauling, Proc. Nat'l. Acad. Sci., 16, 123 (1930); W.W.
Jackson and J. West, Z. Xrist., 76, 211 (1930); and J.W.
McCauley, R.E. Newnham and G.V. Gibbs, Am. Mineral., 58, 249 (1973). While having somewhat varying chemical composition, all contain hydroxyl and/or fluoride radicals, a silicate or germate group and an alkali or alkaline earth component.
Examples are biotite, muscovite, phlogopite, lepidolite, fluorophlogopite, barium disilicate and lead disilicate.
Typically, mica has the following properties: specific gravity 2.6-3.2; Mohs hardness 2.B-3.2; refractive index 1.56-1.60; dielectric constant 6.5-8.7; noncombustible; heat resistant to about 600C.
Natural mica occurs in the Vnited States, Canada, Madagascar, India, South Africa and South America.

Synthetic mica is produced by any known or common technique, for example, by qrowing a single crystal electrothermally.
An interesting example of a synthetic mica is fluorophlogopite (i.e., a fluorine derivative of phlogopite) which, illustratively, is made by a technique involving melting raw materials co~.prising potassium silica fluoride, alumina, silica, potassium feldspar and magnesia in an internal resistance furnace and cooling the melt slowly down through the crystallization temperature during which crystals of the synthetic mica form. This product has a higher temperature stability than natural mica, and its dielectric properties and machinability are about the same.
As a group, micas are characterized by excellent cleavage properties. ~ence, they can be split into very thin flexible elastic sheets. This property affords control over the thickness of the mica which is to be employed.
Cleavage is suitably effected by grinding a mica, but other common or known methods are also acceptable. In such manner, mica flakes of desired thickness can be obtained for practice of the present invention. The aspect ratio of these flakes is generally greater than 20.
Conductive metal-coating of the mica flakes is suitably carried out by numerous means known in the art.
For example, the sil~er-coating is applied by fluidization by dry or wet methods, by electroless plating, and the like.
See, for instance, U.S. Patent No. 3,635,824, granted January 18, 1972 to Raymond G. Brandes et al.
A flowable conductive composition, such as a paste or molding composition, containing conductive metal-coated lZ54330 mica flakes is advantageous in that it has favorable flow and distribution properties. That i6 to ~ay, the paste or molding composition of the invention flows sufficiently well so that it is conveniently applicable to substrates, i6 suitable for injection molding without undue resi6tance, etc. Likewise, assuming conventional techniques are followed, this conductive composition is such that the distribution of metal-coated flakes after application is quite uniform, thereby minimizing local variations in properties of an electroconductive element made from the flowable conductive composition. Furthermore, the mica flakes are quite resistant to breakdown, that is, breaking apart into smaller particles during operations such as injection, compression and extrusion molding.
And, due to the aforementioned overlapping, or areal instead of point-to-point contact, of conductive metal-coated mica flakes and their high surface area, the total metal-coated-flake loading of an electroconductive element made from the flowable conductive composition of the invention is typically only about 20% by volume. Indeed, this loading of the electroconductive element is, in some embodiments, as low as 5~ by volume, on a cured basis.
However, in other embodiments it is cuitably as high as 90~, preferably as high as 50%, especially as high as 40%, by volume. Depending on the amount of organic binder and other materials which are included in the flowable conductive composition and survive formation of the electroconductive element, the amount of these metal-coated flakes which is - l~S4330 incorporated in the precursor conductive composition is up to 90~ by volume, typically about 30~ by volume or leEs.
While a metal-coated-mica-flake-containing conductive composition is highly advantageou8, ~n some embodiments of the invention inorganic non-metallic particles coated with a conductive metal, conductive metal particles, fi~er~ coated with a conductive metal, or a combinàtion of two or more of the foregoing, are also incorporated in the conductive paste.
The coating of conductive metal on inorganic non-metallic particles or on fiber material is also a layer which covers substantially the entire surface of each such particle or fiber. Again, it is preferred that this layer be of uniform thickness, but thickness may vary from point-to-point on the particle or fiber surface without departing from the present invention. The layer of conductive metal need only be of sufficient thickness to maintain conductivity ~at the desired level) in an electroconductive element; however, thickness of the layer may be increased above this minimum, for instance, to the extent that cost consiâerations permit. Typically, the thickness of this layer of conductive metal ranges up to 10 of the minimum dimension of an inorganic non-metallic particle, and/or up to 10~ of the diameter of the fiber material. It will be appreciated that even when conductive fill material other than conductive metal-coated mica flakes is incorporated in the electroconductive element and precursor flowable conductive composition the total volume loading of the element generally remains in the range of lZ5433U

from 5 to 90%, preferably 5 to 50%. Thus, if the element and its precursor conductive composition incorporate conductive metal-coated ~norganic non-metallic particles and/or fibers in addition to conductive metal-coated mica flakes, the volume ~ loading of the element ~nd precursor composition with the coated mica flakes decreases correspondingly. Likewise, since the total weight ~ loading of the element with conductive metal generally is in the range of from 2 to 90~ even when conductive filler material other than conductive metal-coated mica flakes is incorporated, the weight % loading of the element and precursor composition with metal from the coated mica flakes correspondingly decreases. It will be appreciated that with the above-mentioned metal-coated inorganic non-metallic particles and metal-coated fibers, the metal coating makes up from 4 to 70% of the total weight.
Turning now particularly to the above-mentioned conductive metal-coated inorganic non-metallic particles, these preferably contain at least 8%, especially at least 12%, by weight metal coating. It is also especially preferable that the metal be gold or copper. In some embodiments, incorporation of these metal-coated particles aids in attaining and maintaining good rheological properties of the flowable conductive composition and good conductivity of an ultimately formed electroconductive element without appreciable impairment of its electrical or physical properties, such as adhesion. It will be understood that cost advantages afforded by the employment of conductive metal-coated inorganic non-metallic particles as opposed to employment of pure conductive metal alone, are also attend~nt to these embodiments. It is al~o within the scope of the present invention to ~ncorporate in flowable conductive composition conductive metal-coated inorganic non-m~tallic parti~les cont~ining up to 60~ by weight metal coating, for example, of from 25% to 60~ by weight thereof. And metal-coated particles containing somewhat less than 25% by weight metal are suitable in ~everal advantageous embodiments. In some other especially preferable embodiments, the metal-coated particles contain from 4 to 16% by weight metal coating. Examples of these are particles containing approximately 4%, 8%, 12~ and 16%
by weight metal coating.
The inorganic non-metallic particles, themselves, are suitably irregular in shape, or, alternatively, substantially regular in shape. Thus, these particles are, for example, granules, spheres or spheroids. Since the conductive metal coating generally conforms to the contours of the particle, the shape of the coated particle corresponds to the shape of the uncoated particle. The coated particles are sized to be compatible with the attainment of the desired properties of the conductive paste and electroconductive body of this invention, as previously and hereinafter described. Typically, the metal-coated particles are of a size from 1 to 200 microns in maximum dimension, on average.
The inorganic non-metallic particles are suitably composed of any of a wide range of materials which exhibit lZS'~3;~0 properties and physical characteristics consistent with attainment of the objectives of thi8 invention. In this connection, it will be understood that ~non-metallic~ refers to the properties And physical characteristic6 of these materials, and does not preclude the presence of metal atoms or ions as long as "non-metallic" properties and physical characteristics are exhibited. Suitable materials typically display non-electroconductive properties. Accordingly, these materials are, typically, glasses, ceramic substances and naturally occurring mineral substances. The following are other examples of suitable materials: oxides, such as bauxite, corundum, ilmenite, brookite, anatase, rutile and magnetite, and hydroxides such as brucite; sulfides, such as galena, pyrite, chalcopyrite and sphalerite: halides, such as sodium chloride, sylvite and fluorite; carbonates such as calcite, magnesite and siderite, nitrates, such as sodium nitrate, and borates, such as borax and kernite; sulfates, chromates and molybdates, examples being celestite, anhydrite and gypsum; and phosphates, such as bivianite, apatite and pyromorphite, arsenates such as erythrite, and vanadates, such as bavanadinite. Additional examples of suitable materials are conveniently classified into categories as follows: the tectosilicates, including the silica group, the feldspar group, the feldspathoid group, the zeolite group; various philosilicates, including kaolinite, talc and vermiculite; the inosilicates, including the amphibole group, for instance the cummingtonite series, the pyroxene group, including the hypersthene series, for instance ~podumene, and the pyroxenoid group; the 12S~30 cyclosilicates including beryl and tourmaline; the sorosilicate group, ~or instance, idocrase; the neosilicates, including the olivine series, such AS
magnesium iron silicate, and also including willemite; the aluminum silicate group; the garnet group; and silicates of indeterminate struct~re such as prehnite, chrys~colla ar.~
dumortierite. It will be understood that synthetic, as well as naturally occurring, inorganic non-metallic materials are suitable for practicing this invention.
In general, the composition of the inorganic non-metallic particles selected must be such that the particles do not soften or appreciably distort in shape under processing conditions to which the flowable conductive composition of this invention is subjected in making an electroconductive element therefrom.
The particles of inorganic non-metallic material are produced in any known, or common, manner.
As with the aforementioned coated mica flakes, conductive metal-coating of the inorganic non-metallic particles is suitably effected by any of a range of means known in the art. Silver-coating is, illustratively, applied by fluidization by dry or wet methods, by electroless plating, and the like. See previously cited U.S. Patent No. 3,635,824.
Incorporation of conductive metal-coated inorganic non-metallic particles, such as spherical or spheroidal particles, can be advantageous in embodiments whPre enhanced flow and distribution characteristics are especially desired, since the coated particles can be adapted to be i2si~330 particularly well-suited to impart such characteristics to a flowable conductive composition. It i6 also possible that the conductivity of an electroconductive element per unit ~ilver content can be increased by incorporating such conductive metal-coated spherical particles. However, as will be appreciated, the amount of such coated sphe i.al particles incorporated should be carefully controlled. That is to say, despite indications that certain conductive bodies containing only ~ilver-coated spheres as conductive filler material are more conductive per unit silver content than a conductive element containing only silver-coated mica flakes, the former conductive body constitutes a system which is much too rigid for feasible application in the fabrication of membrane switches; the material constituting the button for the switch, if made from the coated-sphere containing material is too rigid to be deformed so as to make contact with a counterpart component of the switch. In contrast, a conductive element in accordance with the invention can provide a system which is amply flexible while still being much more conductive than a system containing only pure silver conductive filler.
As indicated previously, in some embodiments of the invention a flowable conductive composition also contains conductive metal-coated fibers, either in combination with the conductive metal-coated mica flakes solely or along with conductive metal-coated inorganic non-metallic particles. Incorporation of such coated fibers in some respects offers significant advantages. For example, it provides a filler in the conductive element -lZS433(3 which has a high aspect ratio ~nd high ~urface area.
~owever, such incorporation also involves certain drawbacks:
as previously indicated these fibers can break thereby altering the properties ~f an electrocondu~tive element, and further they at best afford line-to-line contact with other filler materials thereby decreasing potential conductive efficiency. With the claimed invention, these drawbacks can be effectively minimized. Incorporation of conductive metal-coated mica flakes along with these coated fibers increases conductivity because the coated flakes have an areal overlap instead of just line-to-line contact; thus, improved conductivity is obtained. Also, coated flakes are more resistant to breakdowr. than appropriately coated fibers. Thus, coated fiber-containing flowable conductive compositions and electroconductive elements are rendered highly advantageous in certain applications with the present invention.
Conductive metal coated fibers suitable for practicing the claimed invention are commercially available and well-known to those skilled in the art.
As with mica flakes, the conductive metal coating, when deposited on a fiber, generally conforms to the fiber contours, and hence the shape of the coated fiber corresponds to the shape of the uncoated fiber. It will be ~ppreciated that these coated fibers are of a ~ize and shape which is compatible with the attainment of the desired properties of the flowable conductive composition and 12S~330 electroconductive element of this invention, for instance, so as not to interfere appreciably with the ease of application of the composition to a substrate, or with its flow properties during injection, compression or extrusion molding.
The fibers are suitably composed of any of a wide range of materials which exhibit properties and physical characteristics consistent with attainment of the objectives of this invention. Such materials are, typically, glasses, such as fiberglass, ceramic substances and naturally occurring mineral substances. The following are examples of suitable materials:
glass, asbestos, amphibole and wollastonite. It will be understood that synthetic, as well as naturally occurring, inorganic materials are suitable for practicing this invention.
Also suitable are various metals such as aluminum, copper, nickel.
Conductive metal coating of the fibers -is suitably effected by means known in the art, as previously discussed.
As mentioned above, in various embodiments of the invention a portion of conductive metal, such as gold, platinum, palladium or copper is incorporated in the flowable conductive composition as particles of substantially pure metal.
Preferably, the coating metal is the same as that which constitutes the particles, and the particles are in the form of flakes. However, it is within the scope of this invention for the particles to be of other shapes. Particularly in cases in which the conductive metal coating is of relatively low amount, the particles typically make up 0.5% to 40% by weight of the flowable conductive composition. In some embodiments, the particles constitute at least 10% by weight of the paste.

lZS~3;~0 For purposes of some embodiments of this invention the conductive metal particle suitably is a composite of more than one metal, in which a conductive metal coats a core of another metal or metals. Thus, suitable conductive metal particles comprise, for example, iron coated with copper or with a noble metal, such as silver or gold. The entire particle, its outer layer or its core is sometimes an alloy; brass and stainless steel are examples, although other common alloys such as those of gold, platinum, palladium and or copper, can be employed. In some embodiments of the invention, employment of this type of conductive metal particle affords opportunity for cost economies in that a large amount of conductive metal is replaced by a more readily available and/or less expensive core.
The total amount of conductive metal incorporated in the flowable conductive composition is at least 2% by weight of the composition. This amount of conductive metal is incorporated in the form of coating(s) on the mica flakes (and inorganic non-metallic particles and fibers, if any) and conductive metal particles - again, if any. In some embodiments, more than one elemental metal and or alloy is suitably incorporated to constitute the total amount. It is preferable to incorporate enough conductive metal in the composition to constitute at least 5%, especially at least 10%, by weight of the composition.
In some embodiments of the invention the conductive fill material in the flowable conductive composition co~prises, in addition to conductive metal-coated mica flakes and optionally one or more of the other conductive fill materials described in preceding paragraphs, particles of carbon black. The carbon black need not be specially treated, and may illustratively be ~ 125~33() used directly as it is produced "in the furnacen. Virtually any type of carb~n black is ~uitable, as long as the size of the particles thereof do not interfere with the desired flow characteristics of the conductive composition. Suitably sized particles are typically of from 20 to 30 microns in ma>;imum dimen5ior.. Examp~-s Gf suitable carbon biacks are those sold under the trade marks Ketjen BlacX EC, ~ulcan XC-72 and Acetylene Black.
The flowa~le conductive composition also contains an organic binder from which the matrix of organic material of an electroconductive element made from the composition is formed. The organic binder suitably comprises an inert organic material or materials formable into the matrix; the binder imparts to the composition the proper rheology, for instance, an appropriate consistency for application on a substrate by screening, painting (e.g., electrostatically or with a brushl, dipping (followin~ rack loading), continuous machine dipping, and the like, or for injection, c~mpression or extrusion molding operations.
In many embodiments the organic binder contains one or more resins and one or more solvents to give the conductive composition the desired consistency, but in some embodiments, for instance in molding compositions, the organic binder is typically solventless. Examples of suitable substances are low molecular wei~ht aliphatically unsaturated organic polymers, or a mixture of an aliphatically unsaturated organic polymer and a copolymerizable aliphatically unsaturated organic monomer, such as styrene. These substances, illustratively, have a .~;. . .~.

125~330 viscosity of from about 50 to 10,000 centipoises at 25C.
Particularly ~s to ~molding composition~ - embodiments of the invention, examples of suitable organic binders are polypropylene, polystyrene, high density polyetbylene, polyvinyl chloride and nylon. Additional examples ~re: low molecular weight polyim~des containing acrylamide unsaturation, for instance as described in U.S. Patent No.
3,535,148, granted October 20, 1970 to Abraham Ravve; low molecular weight polyesters containin~ acrylic unsaturation, such as shown in U.S. Patent No. 3,567,494, granted March 2, 1971, to Chester W. Fitko; acrylate esters, and methacrylic esters of polyhydric alcohols, for instance as set forth in U.S. Patent Nos. 3,551,246 and 3,551,235, granted December 29, 1970 to Robert W. ~assemir et al. (see also U.S. Patent No. 3,551,311, granted December 29, 1970 to Gerald I. Nass et al.); acrylate and methacrylate esters of silicone resins; malamine; epoxy resins; allyl ethers of polyhydric alcohols; allyl esters of polyfunctional aliphatic and aromatic acids; low molecular weight maleimido substituted aromatic compounds; cinnamic esters of polyfunctional alcohols; mixtures of two or more of the foregoing: and the like. Further examples are unsaturated polymers, such as polyesters from glycols and ~-, g-saturated dicarboxylic acids, for instance maleic and fumaric acids, either with or without other dicarboxylic acids free of~~,B-unsaturation, for instance phthalic, isophthalic and succinic acids, dissolved in a copolymerizable aliphatically unsaturated organic solvent, such as styrene, vinyl toluene, divinyl benzene, methyl methacrylate, or mixtures of such solvents;

`` 1~5~330 ~uch systems are set ~orth in U.S. Patent No. 2,673,151, granted March 23, 1954 to Howard L. Gerhart and U.S. Patent No. 3,326,710, granted June 20, 1967 to Mary G. Brodie.
Some other examples ~re unsaturated organosiloxanes of from 5 to 18 ~ilicon atoms, and such siloxanes in combination with a vinylic organic monomer. Illustratively, the org2nic binder is an acrylic resin or an epoxy resin. Examples of suitable acrylic resins are methacrylate polymers. Examples of suitable epoxy resins are any monomeric, dimeric, oligomeric or polymeric epoxy material containing one or a plurality of epoxy functional groups, for instance bisphenol-A and diglycidyl ether. In a particularly preferred embodiment, the organic binder is an acryloid resin, i.e., a synthetic polymer of acrylic acid ester.
Suitable solvents are coal tar hydrocarbons, chlorinated hydrocarbons, ketones, esters, ether alcohols and ether esters. Examples are xylene, toluene, methylethyl ketone and alcohols, such as aliphatic alcohols of up to 20 carbon atoms, for instance ethanol and propanol. The organic binder may also contain various common additives such as catalysts and substances which sensitize the binder to radiation, for example, ultraviolet radiation. The sensitizers, for example, are suitably incorporated in small amounts, such as 0.5 to 5~ by weight of the binder.
Examples are ketones, such as benzophenone, acetophenone, and the like, benzoins and substituted benzoins, thiourea and aromatic disulfides: also examples are azides, thioketones and mixtures thereof. The binder is incorporated in the paste in an amount suitable to impart t:

125~330 the above-discussed desired flowability or rheology, for instance in an amount up to 35 to ~0~ by weight of the paste, but sometimes as low as 15~, and occasionally even down to from 5 to 10~, by weight of the paste.
The flowable conductive composition i6 made, for example, by co~bining condu_tive m~tal-coated mica flakes, as well as conductive metal-coated inorganic non-metallic particles, conductive metal-coated fibers, conductive metal particles and/or carbon black in some embodiments, and an organic binder formable into a matrix. For example, if conductive metal particles are incorporated in a conductive paste, they - in admixture with the organic binder - can be wetted in a three-roll mill; the coated mica flakes, along with the coated inorganic non-metallic particles, fibers and/or carbon black (if employed), can be incorporated and appropriately mixed into the organic binder (or such binder containing conductive metal particles) in a suitable apparatus, for example, a SPEX mixer or a common paint shaker. Alternatively, in forming a molding composition containing such conductive metal particles, these particles along with an organic binder and mica flakes coated with conductive metal are introduced into a ~compounder~
apparatus to effect mixing. The resulting flowable conductive composition, as such, is then molded into a desired shape, or applied to a substrate, for example, a capacitor or a resistor or other dielectric component, etc., in connection with the fabrication of a further circuit component, or is packaged, and stored or shipped for subsequent use.

12S~330 In accordance with this invention, ~n electroconductive element i6 fabricated from a flowable conductive composition by subjecting the compositions to conditions sufficient to form the binder into a matrix in which the metal-coated flakes, etc. are embedded. During formation of the matrix, any solvent component present in the organic constituent is for the most part, preferably completely, eliminated.
Typical techniques and conditions for forming the matrix from the organic binder are: air-drying of the flowable conductive composition at room or elevated temperature; heating of the composition up to a temperature of about 350C for a time sufficient for matrix formation:
ultraviolet irradiation of the composition; catalyzed curing of the composition at a temperature within a range suitable for operation with the selected catalyst. Other commonly practiced methods for forming the organic binder into a matrix, for instance curing, are also suitable. The resultant matrix is an organic material produced by the action of the selected forming technique and/or co~ditions.
Thus, the organic matrix is suitably a material formed from a resin or resins, as previously described, in the organic binder, such resin or resins being polymerized, cross-linked, or the like to make up the matrix. It will be understood that the technique and conditions selected for forming of the matrix are dependent on the type of organic binder employed and that such technique and conditions should cause formation of a suitable matrix without deforming the conductive metal-coated mica flakes and any l~S4330 other such filler material present, or otherwise sltering the components of the ~ystem, 80 as to impede performance, especially conductivity, o~ the electroconductive element.
Regarding those embodiments of the invention in which the flowable conductive composition is a conductive paste or paint or the like suita~le for application to a substrate, such as a ceramic multi-layer capacitor, it is within the scope of the invention to form an electroconductive body from the paste, etc. directly on a substrate to which the paste has been applied. For example, a paste is deposited on a substrate and suitably air-dried, heated, irradiated, catalytically cured or fired alGng with the substrate to which it has been applied. It will be understood that conditions for forming the electroconductive body directly on the substrate are the same as those set forth previously for such formation, with the additional consideration that forming techniques or conditions should not damage or deform the substrate, or, for that matter the conductive metal-coated mica flakes, inorganic non-metallic particles or fibers, and conductive metal particles. Thus, the conductive paste, etc. of the invention is typically deposited on a substrate made of insulatin~ material to form a conductive circuit thereon, or on a capacitor as "termination paste" or sandwiched around a dielectric material to provide terminal or internal conductive members of various capacitor components. Application is suitably effected by any known or common technique, for instance, screen-printing, doctor-blading or spraying. In this manner, conveniently sized and used capacitors, often termed lZS4330 "chips~, can be obtained for packaging for later use, for encapsulation in a hermetic package of glass Iwhich, generally, itself requires firing) or an organic system, for dipping in solder to provide components which are readily integrated into circuits as desired, or for leading lusually by solder-dipping~.
In some other embodiments, such as forming electromagnetic shielding, the flowable conductive composition is a molding composition and is formed into a separate integral body, shaped as desired, by injection, compression or extrusion molding or the like. The considerations for formation are the same as mentioned above, except of course that there is no substrate. As to these embodiments especially, an aforementioned significant advantage of incorporating coated flakes over fibers or coated fibers in the paste is brought out; the flakes are more resistant to breakdown, that is to say breaking up into smaller particles, than are fibers. Since breakdown changes the aspect ratio of the filler flakes and fibers, thereby modifying performance of the final electroconductive element, minimization of breakdown is desirable.
As previously indicated, another aspect of this invention is an electroconductive element which comprises a matrix of organic material with conductive metal-coated mica flakes embedded therein. In this embodiment, the conductive metal-coated mica flakes are in effective contacting relationship to define one or more electroconductive paths through the matrix. For the purpose of this invention, ~effective contacting relationship~ means that coated flakes iZS~330 adjacent one another are in direct intersurface, generally areal contact, or close enough ~o that electrons can pass from one to the next. This is illustrated in Figure 2. For those embodiments in which conductive metal-coated inorganic non-metallic particles, conductive metal particles, conductive metal-c~ated fibers and/~r carbon black are additionally i~corporated as fill material, then effective contacting relationship exists for a sufficient number of adjacent fill material bodies to establish one or more conductive paths through the matrix. It is not necessary that such relationship be between filler material of the same type, e.g., coated flake/coated flake, but is suitably also between filler materials of different types, e.g., coated flake/coated fiber, coated flake/conductive metal particle, coated flake/carbon black particle, etc. This is illustrated in Figure 4.
The size of the conductive metal-coated mica flakes, conductive metal-coated inorganic non-metallic particles, conductive metal-coated fibers and conductive metal particles and carbon black particles does not change appreciably during the fabrication of the electroconductive body from the flowable conductive composition.
Illustratively, in an electroconductive element the coated mica flakes are of from 0.1 to 200 microns in maximum dimension, inorganic non-metal~ic particles are typically of a si~e from 1 to 200 microns in maximum dimension.
Preferred sizes are as previously discussed.
Similarly, the distribution and thickness of the metal layer on the mica flakes, inorganic non-metallic lZS'~330 particles and/or fibers, as well as the amount of metal in the layer, is not appreciably altered in this fabrication.
~herefore, as previously indicated, the thickness of the metal layer is preferably substantially uniform; but it is consistent with practicing of this invention that the thickness of such layer vary over a surface, as long as conductivity of the electroconductive element is not appreciably impaired. Typical and preferred thicknesses are as set forth in the foregoing discussion.
In many embodiments, about 5 to 90%, preferably 5 to 50~, of the total volume of the electroconductive element is made up of conductive metal-coated mica flakes or such coated flakes in combination with coated inorganic non-metallic particles, fibers and/or carbon black particles. ~he total amount of conductive metal in the electroconductive element suitably ranqes from at least 2~, preferably at least 10%, by weight, up to 90~ by weight. In some embodiments it is desirable that the total amount of conductive metal be at least 25~, and even at least 40% by weight of the element. Suitable for many applications is an electroconductive element incorporating conductive metal-coated mica flakes, optionally with the aforementioned metal-coated inorganic non-metallic particles, fibers and/or carbon black particles, wherein the metal constitutes less than 25%, illustratively of from 4 to 16~, by weight.
Examples are electroconductive elements containing conductive metal-coated flakes, coated inorganic non-metallic particles, coated fibers and/or carbon black lZS4330 particles wherein conductive metal constitutes 4~, 8~, 12%
and 16~ by weight.
As to embodiments involving inclusion of conductive metal particles, it will be undertstood that the less the amount of conductive metal incorporated as flake-, particle- or fiber-coG~ins, the grea er the amou-t cf su^h metal which i8 incorporated as substantially pure particles, preferably flakes, to achieve the desired electrical and other properties. In this connection, particularly where the amount of conductive metal in the coatings is relatively low, the amount of conductive metal in the conductive metal particles in the electroconductive element advantageously constitutes at least 5% by weight of the element; in some embodiments it is preferable that conductive metal particles constitute at least 10%, and even at least 25%, by weight of the electroconductive element. However, it is generally preferred that as much conductive metal as feasible be incorporated in the form of coatings on mica flakes, inorganic non-metallic particles and/or fibers, so as to maximize the amount of such metal available for conducting electrons in the element.
The total amount of conductive metal present in the electroconductive element of this invention is selected based on the performance characteristics desired for the component in which the element is to be used. Thus, the conductivity, adhesion to a selected substrate, solderability, ~older-leaching resistance, dissipation factor and the like, which are required of the electroconductive element to perform compatibly with other 12S~330 materials, should be considered in selecting the total amount of conductive metal. In general, all of the foregoing characteristic6 will be enhanced by increasing the total amount of conductive metal in the electroconductive element. It will be understood that, even with increased conductive metal content to enhance one or more properties of an electroconductive element, the electroconductive element of the claimed invention generally exhibits comparable or superior properties at lower cost than with an element in which the conductive component is solely silver, or other conductive metal, particles.
Another factor to be taken into account in selecting materials for some embodiments of this invention is formation conditions which the flowable conductive compositions will be required to undergo in connection with the fabrication of the electroconductive element. It is sometimes the case that a relatively high firing temperature will be necessary, for instance, to effect adhesion of an electroconductive body to a substrate with which it is used.
Generally, the temperature at which the precursor conductive composition can be fired is increased by employing, in addition to mica, refractory materials capable of withstanding higher temperatures, for example silica, feldspar or bauxite.
It is a distinct advantage that flowable conductive compositions and electroconductive elements of this invention comprise, in significant part, conductive metal-coated units having cores of mica, inorganic non-metallic material or appropriate fiber material. This l~S~330 is in direct contrast to those prior conductive pastes wherein the conductive metal component was present entirely in the form of pure particles. In 6uch prior conductive pastes containing silver, that metal was typically incorporated in amounts of from 60 to 85~ by weight. Due to employment of the above-mentioned cores a significant amount of the volume previously occupied by conductive metal is now taken up by much less expensive material, thereby affording a significant cost saving. Nevertheless, despite the substitution of other material for a significant amount of the conductive metal employed in prior paste compositions, the conductivity of an electroconductive element made with the flowable conductive composition of the invention is at least as ~reat as that of an electroconductive element containing 90~ by weight silver, and made from a prior paste. Furthermore, this electroconductive element exhibits favorable electrical and other properties, such as conductivity, adhesion to a substrate and durability. Additionally, the invention affords convenience and cost advantages since materials employable in the flowable conductive composition and electroconductive element are easily obtainable and often relatively inexpensive. Thus, the objects of the invention are fulfilled in the provision of an electroconductive element exhibiting favorable performance characteristics, which is conveniently fabricated from available materials at comparatively low cost.
A greater understanding of the invention may be gained from the following examples.

l~S~330 An electroconductive element containing 23.59 weight % silver and 14.67 volume % silver-coated mica flakes was fabricated in accordance with the invention as follows.
27.21 g. of acrylic resin, specifically ~ohm ~ Haas type B-66 ACRYLOID Resin (50% solids by weight) and 10.11 g. of silver-coated mica flakes (the mica flakes were of size -325 U.S. mesh plus pan, and were water-ground natural mica) in which the silver constitutes 57.2% by weight of the coated ~lake were each weighed on a SARTORIUS digital top-loading balance (Model #1202MP) to the nearest 0.01 gram. ACRYLOID
and SARTORIUS are trade marks. The acrylic resin and silver-coated mica flakes were mixed together by hand.
Toluene was added as necessary to adjust the viscosity to approximately 6500 centipose. The mixture was poured onto a glass plate which had been coated with a silicone release agent, namely Silicone Spray Mold Release from Mark V
Laboratory, Inc. The mixture was doctor-bladed at a blade height of from 0.02 inches to 0.040 inches using a Gardener Knife of about 3-inch width from Paul N. Gardener Company.
The mixture was dried overnight at room temperature, and then cured in an air over for at least 48 hours at 75C to remove all solvent. The dried mixture was then removed from the glass plate and cut into 4-inch long by 1-inch wide test strips. The resistance of a sample strip was tested using either a Hewlett-Packard Model #4328A Milliohmmeter or a Keithley Instruments Model #610C Electrometer. The exact thickness, length and width of a sample was measured wi h micrometer, and the volume resistivity calculated accordingly.
The average volume resistivity was 0.015 ohm-cm.

~`
.~

lZS4330 The data relating to the foregoing experiment are set forth in the following t~ble, to the right of thP
notation Example 5A. Additional experiments were performed wherein one or more of the weight ~ ~ilver in the silver-coated mica flakes, weight ~ silver in the co~ductive element and volume ~ conductive filler in the conductive element were varied. Data relating to these experiments are also set forth in the table, following the designations 5B, 5C, 6A-6D and 7A-7D. The electroconductive elements evaluated in these experiments were produced in the same manner as set forth above, save for appropriate adjustment of the amount of silver in the silver-coated mica flakes, and the respective amounts of silver-coated mica flakes and B-66 Acryloid Resin. Resùlting volume resistivities (which are, in each case, an average of volume resistivities obtained with 4 or 5 different strips) are noted in the right-most column of the table.
Additionally, several test samples were obtained in the foregoing fashion, with the exceptions that pure silver flakes (these flakes were obtained from Metz Metallurgical Laboratories and are generally considered suitable for thick film paste uses) were substituted for silver-coated mica flakes and the amounts of silver flakes and acrylic resin were adjusted appropriately to obtain the data set forth in the table following the designations Examples 8A, 8B and 8C.

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l~S4330 Figures ~ and 6 illustrate graphically the results of the above-described experiments. Figure 5 is a plot of volume resistivity of the electroconductive elements against the corresponding volume ~ of conductive filler in those elements. Figure 6 is a plc~ of volume resistivity of each electroconductive element against the correspondlng weight 4 of silver in the element. As can be seen, with the present invention a wide range of volume resistivities can be obtained by varying the amount of silver in the silver-coated flakes, the weight of silver in the electroconductive element and/or the volume of the conductive filler in the electroconductive element; in contrast, when pure silver flake is used as the conductive filler the volume resistivity drops precipitously over a rather narrow range of weight % of silver and volume 4 of conductive filler in the electroconductive element. This illustrates the relative ease with which electroconductive elements in accordance with the present invention can be fabricated to exhibit a specific volume resistivity - that is, the volume resistivity of such an electroconductive element is not disadvantageously sensitive to minor variations in weight ~ of silver or volume ~ of conductive filler in the electroconductive element. Furthermore, it can be seen that comparably low volume resistivities to those obtained with electroconductive elements containing pure silver flake alone can be obtained with the present invention, in many instances using less than half the amount of silver in the electroconductive element. This is a major lZS4330 factor in reducing cost through practice of the present invention.
~ he terms and expressions which have been employed are used as terms of description and not of limit~tion, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, it being recognized that various modifications are possible within the scope of the invention.

-4g-

Claims (19)

WHAT IS CLAIMED IS:

1. An electroconductive element, which consists essentially of mica flakes coated with a conductive metal embedded in a matrix of organic material, the conductive metal constituting at least 4% by weight of the electroconductive element, said matrix comprising an acrylic resin, said conductive metal-coated mica flakes being in effective contacting relationship within said matrix.

2. An electroconductive element as defined in claim 1, which is in the form of electromagnetic shielding.

3. An electroconductive element as defined in claim 1, which is in the form of an article suitable for dissipation of an electrostatic charge.

4. An electroconductive element as defined in claim 1, which is attached to a substrate thereby providing an electrically conductive connection or film on the substrate.

5. An electroconductive element, which consists essentially of conductive metal-coated mica flakes of a size of from 0.1 to 200 microns in maximum dimension, carbon black particles and an organic binder which is formable into a matrix having embedded therein said conductive metal-coated mica flakes, the conductive metal constituting at least 4% by weight of the electroconductive element.

6. An electroconductive element as defined in claim 5, wherein said conductive metal is silver.

7. An electroconductive element, which consists essentially of mica flakes coated with conductive metal, and conductive metal particles, said conductive metal particles consisting of a coating of a conductive metal deposited on a core of another metal, said particles being formed of one or more metals selected from the group consisting of gold, platinum, palladium, copper and alloys thereof, both embedded in a matrix of organic material, said conductive metal particles and conductive metal-coated mica flakes being in effective contacting relationship within said matrix, the conductive metal constituting at least 4% by weight of the electroconductive element.

8. An electroconductive element as defined in claim 7, wherein the conductive metal is silver, gold or copper.

9. A flowable conductive composition suitable for forming an electroconductive element, which consists essentially of mica flakes coated with conductive metal in an organic binder which is formable into a matrix having embedded therein said conductive metal-coated mica flakes, said organic binder comprising an acrylic resin, the conductive metal constituting at least 4% by weight of the electroconductive element.

10. A flowable conductive composition as defined in claim 9, wherein the organic binder contains one or more solvents.

11. A flowable conductive composition as defined in claim 9, which is a molding composition.
LCR68.12 46

12. A flowable conductive composition as defined in claim 9, which is a conductive paste.

13. A flowable conductive composition as defined in claim 9, which is a conductive paint.

14. A flowable conductive composition suitable for forming an electroconductive element, which consists essentially of conductive metal-coated mica flakes of a size of from 0.1 to 200 microns in maximum dimension, carbon black particles and an organic binder which is formable into a matrix having embedded therein said conductive metal-coated mica flakes, said conductive meal being silver, the conductive metal constituting at least 4% by weight of the electroconductive element.

15. A flowable conductive composition suitable for forming an electroconductive element, which consists essentially of mica flakes coated with conductive metal, and conductive metal particles, said particles being formed of one or more metals selected from the group consisting of gold, platinum, palladium, copper and alloys thereof, in an organic binder formable into a matrix having embedded therein said coated mica flakes and conductive metal particles, said conductive metal particles consisting of a coating of a conductive metal deposited on a core of another metal, the conductive metal constituting at least 4% by weight of the electroconductive element.

16. A conductive particle for use in an LCR58.12 electroconductive organic matrix, said particle consisting essentially of mica flakes coated with a conductive metal, the conductive metal constituting at least 4% by weight of the particle.

17. A conductive particle as defined in claim 16, in which the conductive metal is silver.

18. A conductive particle as defined in claim 16, in which the conductive metal is gold.

19. A conductive particle for use in an electroconductive organic matrix, said particle consisting essentially of mica flakes coated with nickel, the nickel coating constituting at least 4% by weight of the particle.

LCR68.12