GB2297755A - Electrically-conductive fibre filled elastomer foam - Google Patents

Abstract

An elastomer foam comprises, dispersed therein, electrically-conductive fibres, such that the foam is electrically-conductive.

Description

1 2297755

ELECTRICALLY-CONDUCTIVE FIBRE FILLED ELASTOMER FOAM AND METHOD OF MANUFACTURE THEREOF Field of the Invention

This invention relates to an electrically-conductive fibre filled elastomer foam.

Background of the Invention:

2 This invention relates to an electrically conductive elastomeric fbain and a method of making the same. More particularly, this invention relates to a new electrically conductive elastomeric foam, incorporating electrically conductive fibers, which exhibits improved conductivity over other electrically conductive foam materials, and which retains good mechanical and physical properties such as resiliency, compression set resistance, low duroineter hardness, small unil'on-n cell structure, strength and wear resistance.

The field of soling materials in elgctrostatic dissipative (ESD) footwear and tile field of rollers, belts and other members used in contact with photoreceptor members in elecLrophotography are particularly pertinent, so these fields will be discussed for purposes of illustration of the features, utility and advantages of this invention. Howcvcr.

it is to be understood that this invention is not limited to either field; rather this invention is generally well suited for any application utilizing electrically conductive elastomeric foam (particularly polyurethane foam) and this invention is especially well suited for any application in which ESID and EMI/RFI shielding is desired.

Accumulation of static electrical charge in certain working environments has long been recognized as undesirable. Many widely used synthetic materials, for example polyurethane and polyvinyl chloride are electrical insulators and articles of these materials Illay thus accumulate a substantial static electric charge.

C-lastonicric lbatils. including polyurethanc loanis, arc widely used in the footwear industry to prepare electrostatic inner soles, outer soles and insole inserts.

Electrically conductive materials are used to prevent electrical charges from building up on the worker's body. These electrostatic charges can pose a serious threat of injury if the air contains combustible gases or flammable liquid vapors. When a worker touches a grounded metal object, the buildup of electrostatic charge may cause a spark, which in turn may cause airborne combustibles to explode. In addition, electrically conductive 3 footwear is useful for workers who handle electronic equipment, which is easily damaged by static discharges.

Electrically conductive fbotwcar keeps electrostatic charges from accumulating by providing a conductive path of relatively low electrical resistance firom the foot to tile floor. Use of electrically conductive outersoles arid insoles maintain a conductive path, allowing electrical charges to be transferred from the user's foot to the conductive shoe.

Patents which describe various types ofelectrically conductive sole arid sole inserts include: U.S. Patent Nos. 4,861,805 issued to Saavedra et al (directed to a shoe sole) and 5,3 19,867 issued to Weber (directed to a. shoe insole).

In the conventional electrophotographic process, toiler is metered from a toner cartridge onto a photoreccptor oil which a latent electrostatic image has been Ibri-ned.

The toiler is then transfierred to and I ixed oil paper or other substratc or print nictlia. 1.1ach step ofthe electrophotographic process requires precise control of tile amount of electrostatic charge present. The steps perfonned around the central photoreceptor (PC) drum are drum charging, exposing and developing, transfer of toner froin the drum to the print medium (usually paper), and drum cleaning. Each of these steps, except exposing, can use electrically conductive elastomeric rollers, belts or other members. The electrical conductivity requirements depend on the function performed and the machine design.

Tile conductivity range can require clastonicric materials with volume resistivities ranging fironi 10 to the power o173 to 10 to the power of' 10 olim-cm. Several of these functions including charging, transferring and cleaning can be improved through the use of conductive elastomeric foam members. Elastomenc foam provides higher compliance (lower durometer hardness, or lower compression force deflection) which provides a greater footprint against the PC drum with lower pressure and therefore lower abrasive wear compared to noti-fbanicd (solid) elastomers. Low modulus (high compliance) foam rolls also have utility as toiler supply rolls, which are part of the PC drum developing system. An application for a patent describing an electrically conductive polyurethane 4 foam for use in rollers in conventional electrophotographic process is Japanese Application No. 1 IL. 12-262715 [262,715/1990].

Accumulation of electrical charge in certain equipment environments has also long been recognized as undesirable. Accumulation of electrical charge on equipment components may attract dust, which may adversely afTect the quality of manufactured products; electrical discharge may disturb the performance of electromagnetic machines, such as computers, in the vicinity of the discharge; fire or explosion may result Erom such discharge in environments used to store combustible materials, or in grain elevators. It has long been known that grounded artic.les of electrically conductive material will dissipate electrical charge.

As is apparent from the foregoing discussion, there presently exists a need lbr electrically conductive chestonicric Riani.s. particularly clectrically conductive polyurethane foams. Currently, one method of rendering elastonleric foanis electrically conductive is by the incorporation of ionic compounds therein. For example, U.S. Patent No. 4,861,805 discloses that a polyurethane shoe insole or outersole may be rendered electrically conductive by incorporating a non-volatile ionizable metal salt therein.

However, the use of ionic compounds in elastomeric foams suffers from certain limitations and drawbacks. For example, the lowest electrical resistance (highest conductivity) achievable using ionic compounds in elastomeric foams is about 1 x 10' ohni-cm. In addition, conductivity lbr such lbanis with ionic conduction is very sensitive to temperature and humidity. In addition, because conductivity is afTected by ion mobility, conductivity changes over time due to ion depletion.

These disadvantages can be at least partly overcome by the incorporation of conductive fillers. U.S. Patent No. 4,505,973 discloses a rigid polyurethane foam rendered electrically conductive by incorporating therein various carbon blacks.

Japanese Application No. HEI 2-262715 [262,71511990] describes an electrically conductive polyurethane foam incorporating a carbon micropowder of particle size smaller than 100 pin. However, the use ofconductive fillers in elastomeric roams suffers l1rorn tile need to use high filler loadings. High filler loadings adversely affect processing and the mechanical properties ofthe finished lbani, especially polyurethaile lbanis. and often makes the finished fbain relatively expensive.

Conductive fibers have been added into insulating polymers, such as polyurethane, to render them electrically conductive with lower additive concentration than would be required with particulate conductive filler, according to U. S. Patent No.

4,228,194. This patent discloses conductive fibers coated with silicone oil to effect high conductivity at low fiber loadings. I-lowpver, silicone oil has a destabilizing effect oil lbarn structure in the processing ofelastomeric foams. This approach is not expected to be applicable to lbained clastoincrs with good mechanical properties and fille (snlall) uniforni cell structure.

Fibers, including electrically conductive fibers, can be incorporated into elastoniedc silicone foam according to U.S. Patent 4,572,917. However, these foams do not possess the high level of mechanical properties, such as strength, toughness and abrasion resistance, necessary for many applications including the ESD footwear inner and outer sole materials and the efectrophotographic rollers and other members mentioned previously.

Summa[y of the Invention:

Tile above-discussed and other problems and deficiencies of the prior art are overcome or alleviated by the electrically conductive elastomeric foam of the present invention. Preferably, the elastomeric foam comprises polyurethalle foam. In accordance with an important feature of this invention, the elastomeric foam is rendered electrically conductive by incorporating therein electrically conductive fibers. As used herein, a "fiber" has a diameter greater than or equal to one micron, and an aspect ratio (length/diameter) greater than or equal to fifteen. In accordance with the method of the 6 present invention, the elastonleric foam is prepared from a polyurcthane stock comprised of a polyhydroxyl compound, an organic polyisocyanate cornpou nd. a catalyst, a Foam stabilizer and an amount ofelcurically conductive liber which is effective to render the elastomeric foam electrically conductive. This effective amount is preferably in the range of about five to thirty weight percent.

In a preferred embodiment, a coupling agent or a dispersing agent is used to more unil'briuly disperse the electrically conductive fiber throughout the elastomeric foam thus leading to enhanced electrical and physical uniformity of the foam of this illvcntioll.

The electrically conductive elastgnieric foam of this invention offers many features and advantages. For example, the electrically conductive elastomeric foam of the present invention possesses favorable conductivity in the range of I x 102 to I x 101 ohni-cm. In addition, the W11-101.1s disadvantages ol'the prior ail arc overcome, in that the finished elastoincric floani provides stable and reproducible conductivity with respect to temperature and humidity. In addition, the foam has high compliance, resilience, durability, uniformity and chemical compatibility with organic photoreceptor drums used in electrophotography. In addition, the present invention allows the use of lower concentrations of fibers, resulting in less expense and an enhanced processability of the elastomeric foam when compared with the use ofcarbon blacks and other particulate fillers. The processability of the elastomeric foam is also enhanced by the lower surface area of fibers compared with carbon black.

The conductive l"barn ofthis invention finds particular utility wlicn used as a inaterial in footwear outersoics, insoles and inserts and other ESD applications, as well as a material in the manufacture of conductive rolls, belts and the like in electrophotographic equipment applications. The material of this invention also finds utility where EMI/R171 shielding is desired.

7 The above-discussed and other leatures and advantages of the present invention will be appreciated and understood by thosc skilled in the art 11rom the rollowing detailed description and drawings.

Brief Descrit)tion of the Drawings:

Referring now to the drawings wherein like elements are numbered alike in tile several FIGURES:

FIGURE I is a plan view of a shoe innersole; FIGURE 2 is a cross-sectional elevation view along the line 2-2 of FIGURE 1; FIGURE 3 is a perspective view of a roller suitable for use in conventional clectrophotography; FIGURE 4 is a cross-sectional elevation view along tile I ine 44 of FIGURE 3; FIGURE 5 is a micrograph l1rom a scanning electron microscope (SEM) cross- sectional view of the electrically conductive elastomeric foam of the present invention; FIGURE 6 is a graph of resistivity vs. concentration for the electrically conductive foam of this invention wherein the conductivity ranges between 1 x 10' to 1 x 10 " for fiber concentrations of 2.5 wt. % to 20 wt. %; FIGURE 7 is a graph of resistivity vs. concentration showing the effects of temperature and humidity oil the electrically conductive foam of this invention; and FIGURE 8 is a graph of resistivity vs. voltage for the electrically conductive foam of this invention.

Description of the Preferred Embodiment:

The electrically conductive elastomeric foam of the present invention comprises an elastomeric foam containing electrically conductive fibers. While elastomeric foarns from many other polymer systerns, such as po lyv inyl chloride (PVC), styrene butadiene 8 rubber (SBR), ethylene propylene dienc mononier (I:PDM), ethylene propylene rubber (F1PR), acrylic polynicr., all(( others, niny be utilized ii 1 this invention. prci'erably (lie loani comprises a foaniabic polyurethane fiorniing mixture. '['lie polyurethane fharning niixturc contains at least one polyhydroxyl compound, at least one organic polyisocyanate compound, a catalyst, and a foani stabilizing surfactant. Other optional additives such as fillers, pigments, dyes, process aids, flame retardants and other stabilizers may also be used; and as will be discussed ill niore detail below, prefierred embodiments of this invention incorporate coupling agents and dispersing agents. In accordance with all important feature of this invention, electrically conductive Fibers are used in the elastomeric foam to render (lie foarli conductive. The amount of conductive riber is equal to that effective to provide electrical conductivity to tile foam. Preferably, this effective aniount will be 1roill about 5 to about 30 weight percent electrically conductive [11bcr with respect to the total composition. Most preferably, the electrically conductive libers are in the amount of about 10 to 20 weight percent.

Examples of appropriate polyllydroxyl compounds include, but are not limited to, polyols well known in tile art, such as hydroxyl terminated polyether polyols, hydroxyl terminated polyester polyols, hydroxyl terminated polyols which are copolymers of polyethers and polyesters, polymer polyols produced by the polymerization of ethylenically unsaturated rnonomers (such as styrene or acrylonitrile or mixtures of these) in polyol, hydroxyl terininated polybutadiene, and low molecular weight alcohol materials such as butane diol, ethylene glycol, dipropylene glycol and many others.

Examples of appropriate polyisocyanate compounds include, but are not limited to, isocyanates well known in the art, such as toluene diisocyanate (TDI), crude TDI, 4,4,'-dipenylinctilaiie diisocyanate (MDI), crude MIDI, aliphatic diisocyanates, mixtures of these isocyanates, and derivative prepolymers prepared by tile partial reaction of these isocyanates with polyols.

9 Examples of -appropriate catalysts include. but are not limited to, catalysts well known in the art, RICII is organonictallic compounds including dibutyltin dilauratc, stannous octoate, various tin and zinc waxes and metal acetyl acetonates, tertiary amincs inClUding triethylainine. tricthylenediaininc and iliany others.

Examples of appropriate lbani stabilizing surfactants include, but are not limited to, surfactants well known in the art, such as many members of tile family of organosilicone copolymer materials, Suitable materials for the electrically conductive fibers comprise electrically conductive materials such as metals and carbon fibers; glass, ceramic and polymeric fibers rendered conductive through coating with electrically conductive materials, such as metals. Electrically conductive metals include, for example, niobium, nickel, tungsten, iron, aluminum, carbon steel, chronic, nickel, stainless steel, copper or silver. Prellerably, the conductive fiber is comprised of a carbon fiber, including graphite fibers, meso face and isotropic pitch fibers and fibers made from polyacrylonitrile (PAN). The degree of carbonization of the carbon fiber will effect the electrical conductivity, as well as other electrical, thermal and mechanical properties. While PAN fibers are typically 93-94% carbonized, in the present invention, a preferred PAN fiber is carbonized approximately 99%. This leads to higher conductivity using lower amounts of fiber.

As mentioned, as used herein, a "fiber" is defined as having a diameter greater than or equal to I micron and an aspect ratio (i.e., lengtll/diameter) of greater than or equal to 15. The Foam ol"Ilic present invention may also contain an ionic additive in addition to the electrically conductive fibers, allowing improved stability of volume resistivity with respect to voltage, temperature and hurniclity over ionic additives used alone. Such ionic additives include, but are not limited to quaternary ammonium salts present in the range of 0.5 to 10 parts of die total llonnulation. Alternatively, the foani of the present invention may also contain conductive particulate fillers. The use of conductive particulate filters in addition to electrically conductive fibers will lower tile cost of manufacture since less fiber will bc nccdcd to achieve tile samc level of conductivity. Examples of conductive partiCLilatc fillers includc graphite, nickel, aluminum. stainless steel, metal coated glass.

The conductivity levels of the electrically conductive elastomeric foam depends on the composition of the Fibers, the density of the elastorneric foam, the uniformity and the orientation of the fibers within the foani, and the concentration of the fibers. This invention provides a distribution or the fibers within the foarri which allows hopping or propagation of the charge, thus enhancing conductivity.

This invention also allows use of low concentrations ofelectrically conductive fiber. Low concentrations of fiber allows easier incorporation into the foam, with a resulting acceptably sniall efflect on loam physical and nicchanical properties. 'HILIS L11C use ofelectrically conductivc fibersas described in this invcntion results in lbanis with good cell structures and mechanical properties. Low concentrations of fiber also provide interparticle contact that results in sufficiently low resistance for electron hopping thus enhancing conductivity. Typically, the relationship between resistivity and concentration of carbon fiber is shown in Table 1:

TABLE 1 wt.% fiber based on polyol 2.5 5.0 7.5 10 15 20 Volume resistivity. ohm.cm.

1.23EI I 9.331310 7.24E-8 2.8 8 E4 1.82E3 1.04E2 Referring to Table I above and FIGURE 6, the percolation behavior often observed in filled systems occurs between about 5 and 10 wt. % carbon fiber. Therefore, llor intcrniediatc concentrations of'carbon fibcr, the resistivity will be highly sensitive to the concentration. In Tabic I and FIGURE 6, (lie conductivity range is from I x 102 to I x 10" olim.cni corresponding to fibers being present in the range of from 2.5 wt. % to 20 wt. % fiber based on polyol. However, it should be undcrstood that the percolation 11 behavior is itself dependent on I iberorientation. For example, us ing an alternative fiber orien tat ion. percolation behaviorcan range between 10 and 20 wt.% I I bcr.

Prelbrably. COL1111ing and dispersing agents are used to improve tile electrically conductive fiber dispersion in the foani and thereby obtain niore uniform electrical and physical properties. Coupling agents arc molecular bridges at the interface between two dissimilar substrates, usually but not limited to, an inorganic filler and all organic polynier matrix. Coupling agents are defined primarily as materials that improve the adhesive bond of dissimilar surfaces. In the case of titanate coupling agents, they react with 1ree protons at the inorganic interface, resulting in the l"ornlation of orgallic mononiolecular layers oil the inorganic SUrface. Typically, ti tanate - treated inorganic fillers are hydrophobic, orgailophilic and organol'unctional, and therefore exhibit enhanced dispersability and bonding with the polymer or organic phase. Examples o I' coupling agents suitable for use in the present invention include but are not limited to silane, titanate and zirconate coupling agents. The coupling agents are added preferably at 0. 1 to 2 wt. % based oil (lie filler (e.g.. electrically conductive Fibers) weight.

Dispersing agents are surlace-active agent added to a suspending medium to promote uniform separation between fine solid particles. Most commonly used dispersing agents are anionic and non-ionic in character. Anionic dispersing agents prevent reagglonieration by imparting a negative charge to the surface of the aggregates thus making them unattractive to one another. Non-ionic agents provide an "insulating" layer which neutralizes attractive lbrccs thus accomplishing a sinlilar task. Examples ol' dispersing agents suitable lor use in the present invention include but are not limited to fatty acids, unsaturated polyamine amides and higher molecular weight acidic esters, and alkanolanimoniuni salts or a polyfunctional polymer with -anionic or non- ionic character.

The dispersing agents are added preferably at 0. 1 to 2 wt. % based oil the filler weight.

It is presently believed that dispersing agents provide improved results relative to coupling agents.

12 The use oCcoupling/dispersing agents provide inany advantages including the ability to obtain a 11101-C COMILICtiVe elastonicric foam thaii may be obtained WlthOL1t SLICII agents. In addition, the use ofcoupling/dispci-sing agents help to disperse the carbon fibers or electrically conductive fibers in the polynier matrix and reduce the resistivity variation compared to the absence of coupling/dispcrsing agent. The coupling/dispersing agents also may reduce the dispersion torque or shear that is generated during processing. The sniall amount of coup I i ng/d ispcrsi ng agents call be easily incorporated in the polyurethane mixture and still have an acceptably sniall (e.g., negligible) effect on the foam properties.

Referring now to FIGURES 1 and 2, the conductive elastorrieric foam of the present invention may be used as insoles, outersoles or sole inserts 10. As a shoc innersole a layer ofconductivc clastonieric 1oaili (prelerably polyurethane 1oatil) 12 ninde in accordance with the present invention may be supported on a conductive shoe board 14, for example Texon 411, supplied by Texon. When used as a shoe insole material, the volume resistivity ofthe elastonieric foam should be less than 1 x 10' olirn-cm depending on the particular application.

Referring now to FIGURES 3 and 4, a conductive roller for use in electrophoLographic equipment is shown generally at 16. Conductive roll 16 includes a cylindrical layer of the conductive elastomedc (preferably polyurethane) foam 18 which is molded, extruded or otherwise positioned onto a shaft 20. When used in clectropliotographic equipment. the volunie resistivity of the clastonicric foan] should be i ii (lie range o F 1 x 103 to 1 x 10... ohni-cm depending on the particular application. It will be appreciated that the elastomeric foam of this invention may be used in other applications for electrically conductive components in electrophotographic devices such as pads, belts or other members.

13 Example 1

The following non-limiting example demonstrates the preparation of all cicetrically conductive polyurcthanc 1oaiii oftlic present invention.

Resistivity was measured utilizing ASTM test nictliod D257 physical and mechanical properties werc measured according to ASI'M 3574. A conductive elastomeric foam sample was prepared according to Table 2.

TABLE2

Polyether polyol E35 1, Arco Chemical Co.

Polyester polyol Catalyst . 120 parts TONE 0305, Union Carbidc Corp 7 parts LC5615, OSI Specialty Inc 2 parts Silicone surfactant L5614, OSI Specialty Inc. 9 parts modified MDI Isonate 143L, Dow Chemical Co......

....................... 18 parts Carbon Fibers Textron Specialty Materials 20 parts A mixture containing the above-described polyol, catalyst, surfactant and carbon fibers were stirred in a nitrogen-blanketed tank. The MDI was added and the mixture was mechanically frothed. Tlic resulting mixture was poured into a mold to cure, yielding an electrically conductive elastomeric foarn with the following properties:

14 TABLE4

Density, pet' Volume Resistivity, ohni-cill Surface Resistivity, olim/sq Hardness, Shore 0 Compression Force Deflection psi at 25% Deflection Compression Set. % original thickness 2.4 (at 70 0 C) As shown in Table 4, this example provides an electrically conductive foam having good physical and mechanical properties as well as good cell structure.

1 X lO, 1 X 101 22 18 Example 2

This example demonstrates the preparation of another electrically conductive polyurethane foam in accordance with the present invention. This example corresponds to the samples described in Table 1 and FIGURE 6.

Resistivity was measured utilizing ASTM test method D257 physical and mechanical properties were measured according to ASTM 3574. A conductive elastomeric foam sample was prepared according to Table 5.

TABLE 5

Polyctlicr polyof 1:35 1, Arco Clicillical Co......

.............................. 36 parts NIAX LG56, Arco Chemical Co 35 parts Polyelliter polyol Glycol Dipropylene glycol, Olin Chemicals...

..................... 1.

. 4 parts Catalyst LC5615, OSI Specialty Ine..

.......................... 2 parts Silicone surfactant L5614, OSI SpecialtY llic.

.. 1 3 parts Modified MD1 Isonate 143L, Dow Chemical Co.

....... 1 17 parts Carbon fibers Textron Specialty Materials...

.... 20 pails A mixture containing [lie ibove-described polyol. catalyst, surfactant and carbon libers were stirred in a ilitrogen-blanketed tank. The MD1 was added and the mixture was mechanically firothed. The resulting mixture was poured into a mold to cure, yielding an electrically conductive elastonieric foam with tile following properties:

TABLE6

Density, pcf Volume Resistivity, ohm-cm Surface Resistivity, ohni/sq Hardness, Shore 0 Compression Force Deflection 18 psi at 25% Deflection 1 X to, 1 X to! 22 Compression Set, % original 2.4 thickness (at 70C) As shown in Table 6. this example provides an electrically conductive foam having mechanical properties as well as good cell structure.

1 16 Example 3

This example shows the cf"l'ccts ofenvironniental factors such is telliperaturc and humidity on the lbani ofthis invention cojiipai-cd to prior art conductive lbanis. It xvil I be recalled that prior art conductive tbanis incorporating ionic compounds are Sensitive to temperature and humidity. 1 lowever, as demonstrated in Table 7 and FIGURE 7, these drawbacks are not present using the fiber filled elastomeric foam of this invention.

TABLE7

Teni ci-ature and Humidity Dependence (IOV, 2mAl Condition R, Olim CM3 Temp C % RII Voltage 514, Catafor 5%, Textron 5% Catafor PU PU (Ionic (Carbon + 10% Textron Compound) Fiber) Carbon Fiber 22 55 0.1 1.0 1 E9 1.44E 1, 1 7.55118 to 20 0.1 3.38E10 1.21El 1 5.78119 Table 7 above and FIGURE 7 show that the resistivity of the fiber filled elastomeric Iloani is less sensitive to temperature and humidity compared to ionically filled elastomeric foam. The hybrid elastomeric foam which combines both fibers and ionic compound show some sensitivity to temperature and humidity but that observed for elastomeric foam filled with ionic compound only.

not as much as 17 Exam[ 4 This example shows the voltage dependence for elastomeric foam madc in accordance with the present invcntion filled with a combination ol'both ionic compounds and carbon fibers. Referring to Table 8 and FIGURE 8, it will be appreciated that the resistivity of the ionically filled elastomeric Foam is very uniforin for voltage ranging from 10 to 500 V. However, some variation in resistance (although for some applications, this variation may not be significant), is obscrved for the fiber filled foam.

Table 8

Vultige Dependence Condition R, Olirn Cnis Temp " C % Rif Voltage 5'14, Catafor PU 5% Textron Carbon Fiber 22 55 500 1.36E9 5.49E 10 22 55 100 1.4 1 E9 7.92E]O 22 55 50 1.4 0 E9 8.48 U 10 22 55 10 1.27E9 1.44E I I Example 5

This example shows use of a coupling agent in the conductive foam of this invention. In nddition to (lie materials described in Example 1. 0.2 wt. % ot'Litailate coupling agent (LICA 38 from Kenrich Petrochemicals, Inc.) is added to the polyurethane stock. The polyol, catalyst, surfactant and coupling agent is stirred in a

nitrogen blanketed tank. The carbon fibers are then added, followed by MDI. The mixture is then mechanically frothed; the resulting mixture is then poured into a mold or cast onto release paper. Voluine resistivity measured is E2 ollm.cin Por 0. 12Y' thick samples and 18 1.3 nliiii.ciii for 0.189" thick samples, nicasured tit i I izing the AS'I'M tcst ilictliod D25778. The polyurethane foani sample 11 as su r (Lice resistivity of V2 oiiiii.ciii. Samples using polyester polyol hased polytirelhane Formulation has volunte resistivity o(I.A to ko 011111.clil.

Carbon ribers Modified MPI Mixing techniques should be employed which avoid localization and wilich achieve the desired monoiliolecular formation throughout the entire matrix. For example. (lie addition of'coupling agent ill the polymer mix beffire addition olcarbon libel-.,; will provide superior results when compared to merely dumping the coupling agent together with the fibers.

Example 6

This example shows the use of a dispersing agent ill the conductive lbaili of this invention. 'I'lle example has the llorinulation shown in Tabic 9 bclow.

Tible 9 Polyether Polyol E3 5 1, Arco Chemical Co. 28 Polymer Polyol NIAX 34-45, Arco Chemical Co. 35 Polyexter Polyol Tone 020 1, Union Carbide Corp.12 Glycol Catalyst Dipropylene glycol, Olin Chemicals 7 LC5615, OS I Spcciality Clicinical 2 Silicone surfactant L5614, OS I Spccialty Inc. 3 Dispersing agctit BYK W980, BYK - Clicinic USA 0.2 Textron Speciality Materials 20 Isonate 143L, Dow Chemical Co. 27 19 BYK-W980 contains salts of'unsaturatcd POIYaniinc amidcs and higher molecular weight acidic esters. hi the reRdtillg 60am. the conductivityand fibcr uniformity was improved while maintaining compression sets typically observed for polyurethane foam (approximately 4 to 8%). In an example using 20 wt. % carbon fibers based on polyol for a formulation which consists of polymer, polyester and polyester polyol, both the volume and surface resistivity are 133-134 ohm.cin and compression set is 4 to 5%.

The conductive elastomeric foam of' this invention offers significant features and advantages over prior art conductive foams which utilize either ionic compounds or particulate conductive fillers. The use of conductive fibers in accordance with this invention permits much lowcr loading level to achieve comparable conductivities as coniparcd to particulaLc lillcrs such as discloscd in allorciiientioncd Japanese Kokai patcnt 2-262715. The present invention also leads to improved consistency in conductivity as opposed to the variability associated with particulate fillers. In addition, the many drawbacks associated with ionic compounds such as sensitivity to temperature and humidity, ion mobility, migration and the like are not present using the fiber filled elastomeric foams of this invention.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing froin the spirit and scope of the invention. Accordingly, it is to be understood that tile present invention has been described by way of illustrations and not limitation.

Claims (32)

1. An elastomeric foam comprising, dispersed therein, electricallyconductive fibres, such that the foam is electrically-conductive.

2. The foam of claim 1, which comprises, by weight of the total composition, 5 to 30% of the fibres.

3. The foam of claim 1 or claim 2, wherein the foam is selected from polyvinyl chloride polymers, styrenebutadiene rubber polymers, ethylenepropylene rubber, ethylene-propylene diene monomer polymers, and acrylic polymers.

4. The foam of claim 1 or claim 2, wherein the foam comprises polyurethane foam.

5. The foam of claim 4, obtainable from a foamable polyurethane mixture comprising a polyhydroxy compound, an organic polyisocyanate, a catalyst, and a foam-stabilising surfactant.

6. The foam of claim 5, wherein the polyhydroxy compound is selected from hydroxyl -terminated polyether polyols, hydroxyl -terminated polyester polyols, hydroxy 1 -terminated polyols which are copolymers of polyethers and polyesters, polymer polyols produced by polymerisation of ethylenically-unsaturated monomers or mixtures thereof in polyol, hydroxyl-terminated polybutadiene, and low molecular weight alcohols.

7. The foam of claim 5 or claim 6, wherein the organic polyisocyanate compound is selected from toluene diisocyanate, 4,41-diphenylmethane diisocyanate, aliphatic diisocyanates, mixtures of the preceding diisocyanates, and polymers prepared by the partial reaction of these diisocyanates with polyols.

8. The foam of any of claims 5 to 7, wherein the catalyst is selected from dibutyltin dilaurate, stannous octoate, tin and zinc waxes, metal acetyl acetonates, and tertiary amines.

21

9. The foam of any of claims 5 to 7, wherein the foamstabilising surfactant comprises an organosilicone copolymer.

10. The foam of any preceding claim, wherein the electrically-conductive fibres are selected from metal f ibres, carbon fibres, and glass, ceramic and polymeric f ibres rendered electrical ly-conductive by coating with an electrically-conductive material.

11. The foam of claim 10, wherein the metal or said material is selected from niobium, nickel, stainless steel, chrome, nickel, copper and silver.

12. The foam of claim 10, wherein the fibres comprise carbon fibre.

13. The foam of claim 12, wherein the carbon fibre is selected from graphite fibres, meso face fibres, isotropic pitch fibres and PAN fibres.

14. The foam of claim 13, wherein the fibres comprise PAN fibres carbonised at least 99%.

15. The foam of any preceding claim, wherein the fibres have a diameter of at least 1 gm, and an aspect ratio of at least 15.

16. The foam of any preceding claim, further comprising an ionic additive.

17. The foam of claim 16, which comprises 0.5 to 10.0 wt%, based on the weight of the total composition of the ionic additive.

18. The foam of claim 16 or claim 17, wherein the ionic additive is a quaternary ammonium salt.

19. The foam of any preceding claim, further comprising an electrically-conductive particulate filler.

20. The foam of any preceding claim, which has a conductivity of 1 x 10 2 to 1 X 10 11 ohm.cm.

21. The foam of any preceding claim, including a coupling agent for improving the dispersion of the fibres in the foam.

22. The foam of claim 21, wherein the coupling agent is selected from silanes, titanates and zirconates.

22

23. The foam of claim 21 or claim 22, which comprises 0.1 to 2 wt%, based on the weight of the fibres, of the coupling agent.

24. The foam of any preceding claim, further comprising a dispersing agent for improving the dispersion of the fibres in the foam.

25. The foam of claim 24, wherein the dispersing agent is selected from fatty acids, unsaturated polyamine amides and higher molecular weight acidic esters and alkanolammonium salts of polyfunctional polymers.

26. The foam of claim 24 or claim 25, which comprises 0.1 to 2 wt%, based on the weight of the fibres, of the dispersing agent.

27. The foam of claim 1, substantially as exemplified herein.

28. A shaped article comprising the foam of any preceding claim.

29. A footwear insole comprising the foam of any of claims 1 to 27.

30. The insole of claim 29, which comprises an electrical ly-conductive shoe board and, supported thereon, a layer of the foam.

31. An electrically-conductive roller for electro photographic applications, comprising a shaft and, covering at least a portion of the shaft, a layer of the elastomeric foam of any of claims 1 to 27.

32. A pad, roller or belt comprising the foam of any of claims 1 to 27.