Indian Patents. 219451:"PREFORMED EMI/RFI SHIELDING COMPOSITIONS IN SHAPED FORM"

Title of Invention	"PREFORMED EMI/RFI SHIELDING COMPOSITIONS IN SHAPED FORM"
Abstract	Electrically conductive preformed compositions comprising sulfur-containing polymers in shaped form and the use of preformed compositions in shaped form to seal apertures are disclosed. The preformed compositions can be used to seal an aperture having EMI/RFI shielding effectiveness.

Full Text	[001] The present disclosure relates to preformed compositions in shaped form and the use of preformed compositions for sealkig apertures. The present disclosure further relates to preformed compositions in shaped form exhibiting BrVfl/KFI shielding effectiveness, and the use of such preformed compositions for sealing apertures. Introduction [002] Electromagnetic interference can be defined as undesired conducted or radiated electrical disturbance fiom an electrical or electronic source, including transients, which can interfere -with the operation of other electrical or electronic apparatus. Such disturbance can occur at frequencies throughout the electromagnetic spectrum. Radio frequency interference ("RET") is often used interchangeably with electromagnetic interference ("EMI"), although RM more properly refers to the radio frequency portion of the electromagnetic spectrum usually defined as between 10 kilohertz (KHz) and 100 gigahertz (GHz). • [003] Electronic equipment is typically enclosed in a housing. The housing can serve not only as a physical barrier to protect the internal electronics from the external environment, but also can serve to shield EMMRP1 radiation. Enclosures having the ability to absorb and/or reflect EMJ/RH energy can be employed to confine the EMI/RFI energy within the source device, as well as to insulate the source device or other external devices from other BMQ/RFI sources. To maintain accessibility to the internal components, enclosures can be provided with openable or removable accesses such as doors, hatches, panels, or covers. Gaps typically exist between the accesses and the corresponding mating surfaces associated with the accesses that reduce the efficiency of the electromagnetic shielding by presenting openings through which radiant energy may be emitted. Such gaps also present discontinuities in the surface and ground conductivity of the housing and in some cases, may generate a secondary source of EMI/RFI radiation by functioning as a slot antenna. [004] For filing gaps between the mating surfaces of the housing and removable accesses, gaskets and other seals can be used to maintain electrical across the structures, and to exclude environmental degredants such as particulates, moisture, and corrosive species. Such seals can be bonded or mechanically attached to one or both of the mating surfaces and can function to establish a continuous conductive path by conforming to surface irregularities under an applied pressure. [005] Conventional processes for manufacturing BMI/RFI shielding gaskets include extrusion, molding, and die-cutting. Molding includes the compression or injection molding of an uncured sealant or thermoplastic material into a certain configuration which is then cured to a foal shape. Die-cutting includes the forroing of a gasket from a cured polymeric material which is cut or stamped using a die into a certain configuration. Form-in-place ("FIP") processes are also wed for forming EMI/RFI shielding gaskets wherein the FIP process includes the application of a bead of a viscous, curable, eloctrically-conductive composition in a fluent state to a surface that is subsequently cured-in-place by the application of heat, atmospheric moisture, or ultraviolet radiation to form an electrically-conductive, BMI/RFI shielding gasket. [006] Electrical conductivity anil EM1/RF1 shielding effectiveness can be imparted to polymeric gaskets by incorporating conductive materials within the polymer matrix. The conductive elements can include, for example, metal or metal-plated particles, fabrics, meshes, fibers, awl combinations thereof. The metal can be in the form of, for example, to;a,emts, particles, flakes, or spherea,. Examples cf metals include copper, nickel, silver, aluminum, tin, and steel. Other conductive materials that can be used to impart EMl/RFI shielding effectiveness to polymer compositions include conductive particles or fibers comprising carbon or graphite. Conductive polymers such as polythiophenes, polypyrroles, polyaniline, poly(p-pheaylene) vinylene, polyphenylene sulfide, polyphenylene, and polyacetylene can also be used. [007J In addition to providing continuous electrical conductivity and BMI/RFI sihielding effectiveness, in certain applications it is desirable that gaskets or seals to surfaces exposed to the environment, such as in aviation and aerospace vr-hicica, not lead to corrosion of the mctil surfaces. When dissimilar metals and/or conductive composite materials are joined in the presence of an electrolyte, a galvanic potential is established at the interface between me dissimilar conductors. When the interfacial seal is exposed to the environment, particularly under severe environmental conditions such as salt fog or salt fog containing a high concentration of SO2, corrosion of the least noble of the conductive surfaces can occur. Corrosion may lead to a degradation in the EMI/RFI shielding effectiveness of the seal. Mechanians other than galvanic potentials, for example, crevice corrosion, may also comprotnise the electrical and mechanical integrity of the enclosure. [008] Polysulfide polymen are known in the art. The production of polysulfidc polymers is characterized by Fettes and Jotzak, Industrial Engineering Chemietry, November 1950, oopagee 2.217 - 2,223. The commercial use of polysulfide polymers in the manufacture of f ealautt for aerospace applications lias long been known and commercially used. For example, polyvulfide sealants have been used to to sea! an aircraft body because of the high tensile strength, high tear strength, thenal resistance, and resistance to high ultrsviolet light Polysulfide sealants have been used to seal auoaft fiwl tanks because of the resistance to ftel and adhsion upon exposure to fuel. (009] Polysulfide sealants are generally aookued toasurface by extrusion using a caulking gun. Such a process can be efficient for permanent panels installed on an airframe. However, extruding a sealant to seal apertures in and/or on an airframe such as those associated with access doors or panels can require a significant amount of additional effort. To extrude fin uocured sealant, the interior perimeer of the access door opening is masked and the exterior poiineter of the access door is coated with a release agent prior to extruding the sealant to the masked area of the acoess door opening to avoid sealing an access door shut. The access door is put in place and clamped down to force tie excess uncured sealant around the accew door. The sealant is then cured and the excess sealant is trimmed away, This process: is time intensive and can add significant labor to servicing aircraft with many access doors. Some aircraft can have as many tis a hundred or more access doors that are used to cover sensitive electronic equipment or fittings that must be periodically accessed and resealed. [010} Accordingly, it is desirable to provide a method for sealing access doors, for example those in an airframe of an aviation or aerospace vehicle, that does not require masking, reduces trimming and/or is not as lebor and time intensive as the conventional extrusion method for sealing the access doors. [O11] Electricallyconductive sealants that exhibit EMI/RFI shielding effectivenese are commercially available, For example, PRC-DeSoto international, Inc. (Glendale, CA) manufactures several clss B electrically conductive sealants specifically developed for aviation and aerospace applications, For example, PR-2200 Class B electrically conductive sealant is an electrically conductive polythioether sealant that meets toe requirements of MMS 327 (Boeing St. Louis Military Material Specification) test methods. These two-part, nickel-filled seaknti comprise polythioother polymer, PHRMAPOLP-3.1, and are aot corrosive when used on aluminuim alloys or between dissirolilar metals,, However, commcrcially available selants such as exemplified by the PR-2200 product are not provided as a preformed composition. (012] Therefore, it is further desirable to provide a method for sealing access doors to provide effective EMI/RFI shielding and cause minimal corrosion to conductive sirface in environments encountered in aviation and aerospace applications that does not require masking, reduces timming and/or is not as labor and time interasive as is the coaveotional extrusion method for sealing the access doors. Summary [013] In accordance with embodiments of the present disclosure, preformed compositions in shaped form comprinng a base composition compruing at least one sulfur-containing polymer, and at least one electrically conductive filler, and a cniring agent composition; wherein the preformel composition is capable of shielding EMI/RFI radiation, are provided. [014] In accordance with embodiments of the present disclosure, methods of sealing an aperture to provide EM1/RFI sheldinglding effectiveness comprising app lying a preformed composition in shaped-fom comprising at least one sulfur-containing polymer, and at least one electrically conductive filler to a surface associated with an aperture', and curing the preformed composition to »aal the aperture aad provide EMI/RFI shielding effectiveness, are disclosed. [015} Additional embodiments of the disdoaure arc set forth in the description which follows, or may be learned by practice of the embodiments of 1he present disclosure. Description ot Various Embodiments [016] In ortainernbodiraenta of tlie present dtetosure^ compositions in shaped form suitable for sealing apertures, foi example, elongated apertures in or on (be body of an aircraft, comprises at least one sulfur-conuuiami; polymer, and at least one electrically conductive filler. The tcnn "prefiwrned" refers to a compositioa that can be prepared into a particular dupe for ease of packaging, storage, and/or application. A composition that is preformed can be reshaped in [017] Tb6t«nn'>or [018] Preformed Kalant compositions of the present disclosure can be prepared by blending an electrically conductive base composition, aad a curing agent compositioa. A base composition and a (Airing agent composition can be prepared separately, blooded to form a sealant composition, and preformed to a particular shape. A conductive base composition ctfi comprise, for example, at least one sulfur* containing polymer, at least one plasb'cizer. at least one adhesion promoter, at least one corrosioa inhibitor, at least one electrically non-conductive filler, at l«ut one electrically conductive filler, and at least one adhesion promoter. A curing ageat composition can comprise, for example, at least one curing agent, at least one ptotitizer, it least one electrically con-conductive filler, and at least one cure accelerator. In eettiin embodiments, 5 to 20 pots by weight of • curing agent composition ere blended with 100 parts by weight of a base composition, and in certain embodiments, 8 to 16 parts by weight of airing agent composition we blended with 100 parts by weight of abase composition to form an electrically conductive sealant conapoiition. [019] In certain embodiments, twit-component curable compositions «t; preferred to me one-component curable compositions because the taro-componeut compositions provide the best theology for application and exhibit desirable physical and chemical properties in the resultant cured compootion. As used herein, the two component* are referred to as me hue composition, aol the curing agent oompcriticn. In certain embodiments, the bace composition can comprise poryiulfide polymers, polytbioether polymers, oxidizing agents, additives, fiUen, plasticizers, organic solvents, adhesion promoters, cotrosicm iuhibitora, and combinations thereof. fa certain embodiments, the curing agent composition can comprue curing agente, cure accelerators, owe retardattts, pluru'cizara, additives, fillets, aod combinations thereof. [020] In certJUD embodiments, roliar-wnuantng polymers useful in the practice of the present disclosure include polysulfide polymers that contain multiple Bulfid* groups, « e , -S-, in the polymer backbone nod/or in the terminal or peod«it positions on the polymer chain. Such polymers are described in U.S . Patent No . 2,466,963 wherein the disclosed polymers have multiple -S-S- linkages in the polymer backbone. Other useful polysullide polymer* are those ia which the polysulfide linlugc is replaced with a polythioetlwr linkage, i.e., where a can be an integer tanging from 8 to 200 as described in U.S. Patent No. 4,366,307. The polysulfide polymer* can be terminated with non-reactive groups such u ajkyi, although in ccttain embodiments, the polysulfide polymers contain reactive groups in the terminal or pendent positions. Typical reactive groups M-e tbiol byxlrcxyl, sraino, and vinyl. Such polysvjfide polymers are described in. the aforemeatioaed U5. Patent No. 2,466,SKi3, U.S. Patent No. 4,356,307, and U.S. Patent No. 6,372,849, each of which is Lnoorportfcd herein by reference. Such polysulfide polymers am be cured with curing •goats Out are reactive with the reactive groups of the polysulfide polymer. [021] SulroTMxmtaining polymer* of the present disclosure can have number average molecular weights ranging from 5(0 to 8,000 grams per mole, and in certain embodiments, from 1,000 to 5,000 grams per mob, ai determined by gal permeation chramatography using t polystyrene standtni. For sulfur-containing polymers that contain reactive functional groups, tie sulf ur^onUining polymers can have averige functionalities ranging from 2.05 to 3.0, aid in certain embodiments ranging from 2.1 to 2,6. A specific average fiactlonality can be achieved by suitable selection of reactive components. Example* of anifig-contaiping polymers include mo«e avt Jable from PRC-DeSoto International, me, under the trademark PERMAPOL, specifically, PERMAPOLP-3.1 or PBRMAPOLP-3, end flora Ataos Chemicals, such as THIOPLASTG4. [022] A sulfur-containg polymer can be present in the conductive base composition in an amount ranging from 10% to 40% by weight of the total weight of the conductive base composition, and in certain embodiments can range from 2()% to 30% by weight, In certain embodiments, wherein a sulfur-containing polyraer comprues a combination of polysulfide polymer and a polythiocther polymer, the amount of polysulfide polymer and polytiiiocther polymer can be similar, For example, the amount of polysulfide polymer and the amount of polytbioether polymer in t bate composition can each range from 10% by weight to 15% by weight of the total weight of the conductive base composition [023] Preformed compositions of the ptesent disclosure comprise at lc ast one curing agent for curing the at least one tvilfur-coataining polymer. The term "curing agent" refers to any material that cac be added to a sulfur-containing polymer to accelerate the curing or gelling of the wjlfur-coatammg polymer. Curing agents are also known as accelerators, catalysts or cure pastes. In certain embodiments, the curing agent is reactive at a temperature ranging from 10 C to 80 C. The term "reactive" means capable of chemical reaction and includes any level of resction from partial to complete reaction of a reactant. In certain embodiments, a curing agent is reactive when it provides for cross-linking or gelling of a sulfur-containing polymer. [024] In certain ambodiments preformed compositions comprised curing agent that contains oxidizing agents capable of oxidizing terminal mercaptan groups of the sulfur-containing polymer to form disulfide bonds. Useful oxidizing, agents include, for example, lead dioxide, manganese dioxide, calcium dioxide, sodium perborate monohydrate, calcium peroxide, zinc peroxide, and dichromate. The amount of curing agent in a curing agent composition can range from 25% by weight to 75% by weight of the total weight of the curing agent composition. Additives such as sodium stearate can also be included to improve the stability of (be accelerator. For example, a curing agent composition can comprise an amount of cure accelerator ranging from 0,1% to 1.5% by weight based on the total weight of the curing agent composition. [025] In certain embodiment, preformed compositions of the present disclosure can comprise at least one curing agent containing at least one reactive functional group that is reactive with functional groups attached to the sulfur-containing polymer. Useful curing agents containing at least one reactive functional group that is reactive with functional groups attached to the sulfur-containing polymer include polythiols, such as polythioethers, for curing vinyl-terminated polymers; polyisocyanstes RICA as isophorone diisocyanate, hexamethylene diisocyanate, and mixtures and isooyanurate derivatives thereoof for curing thiol-, hydroxyl- and anuro-tenminated polymens; and, polyeporidw for curing amine- and thiol-terminated polymers. Bxamples of polyepoxides include hydantoin diepoxide, Bisphenol-/. epoxides, Bispheool-F epoxides, Novolac-type epoxides, aliphatic polyepoxides, and epoxidized unaatorited reains, and phenolic resins. The term "polyepoxide" refers to a material having a 1,2-epoxy eqalvalent greater man one and includes monomers, oligomeri, and polymers. [026] A performed sealant composition can comprise at Icastonecomixj'and to modify the rate of cure. For example, cure accelerants such as dipentamethylene/thiuram/polysulfide mixture can be included in a sealant compotition to accelerate the rate of cure, and/or at least one cure rotardant such a as stearic acid can be added to retard the rat: of cure and thereby exteud the work life of a sealant composition during application. In certain embodiments, a curing agent composition can comprise an amount of accerant ranging from 1% to 7% by weight, uod/orgn amount of cure retardwjtnngjng from 0.1% to 1% by weight, based on the total weight of the curing agent composition. To control the cure properties of UK: sealant composition, it can also be metal to include at least one material capable of at least partially removing moisture from the igalaat composition such u molecular sieve powder. In certain wnbodiniems, i curing agent compofitioa can comprise an amount of material capable of at least partially removing moisture ranging from 0.1% to 1.5% by weight, based on toe total weight of the curing agent composition. [027] In certain embodiments, prefonned compositions of the present disclosure can comprise fillers. As used herein, "filler" refers to a non-reactive component in the preformed oompositioa that provides a desired property, such vs, for example, electrical conductivity, density, viscosity, mechanical strength. EMI/W1 shielding effectiveness, and me like. [028] Examples of electrically noa-conductive fillers include materials rach as, but not limited to, calcium carbonate, roica, poryamide, fiuaed silica, molecular sieve powder, nucroapherw, titaniom dioxide, chalks, alkaline blacks, cellulose, zinc culfide, heavy spar, alkaline earth oxides, ilkaiine earth hydroxides, and the like, Filters also include high band gap materials such as zinc sulfide and inorganic twium compounds. In certain embodiments, «n electrically conductive base composition can comprise an amount of electrically non-conductive filler ranging from 2% to 10% by weight, based on the total weight of the buse composition, and in certain embodimeuts, car. range from 3% to 7% by weight In certain embodiments, a (wring agent composition can comprise an amount of dactricaUy non-conductive filler ranging from less than 6 percent by weight, and in certain embodiments ranging from 05% to 4% by weight, based on the total weight of the coring agent composition. [029] HE«nus«dtounpartelcctac»lc plated mica; and othar such noble-metal conductive fillers. Non-noble metal-based materials can also be used and include, for example, non-noble metal-pitted non-noble metals such ai copper-coated iron particles or nickel plated copper, non-noble metals, e.g., copper, aluminum, nickel, cobalt; non-noble-metal-plated-noa metals, e.g., nickel-plated graphite and non-metal materials such as carbon black and graphite. Combinations of electrically conductive fillers can also be used to meet the desired conductivity, EMI/RFI shielding efectiveness, hardness, and other properties suitable for a particular application. [030] The dupe and size of the electrically conductive fillers used in the preformed composition! of the present disclosure can be any appropriate shape and size to impart EMI/RFI shielding effectiveness to the cured preformed composition. For example, fillers can be of any shape that is generally used in the manufacture of electrically conductive fillers, including spherical, flake, platelet, particle, powder, irregular, fiber, and toe tike. In certain preformed aealant compositions of the disclosure, a base composition oan compruie Mi-coated graphite as a particle, powder or flake, hi certain embodiments, the amount of Ni-coated graphite in a base composition can range from 40% to 80% toy weight, and in certain embodiments can range from 50% to 70% by weight, based on the total weight of the base composition. In certain embodiments, an electrically conductive filler can comprise Ni fiber. Ni fiber can have a diameter ranging from 10 \|im to 50 utt and have a length ranging from 250 Mm to 7SO fua A base composition can comprise, for example, an amount ofNi fiber ranging from 2% to 10%bywdght, and in certain embodiments, from 4% to 8% by weight, baaed on the total weight of the base compositioa. [031] Carbon fibers, particularly graphitized carbon fibers, can also be used to impart electrical conductivity to prefbnned compositions of the present disclosure. Carbon fibers formed by vapor phase pyrolysis methods and graphilized by bead treatment and which are hollow or solid with a fiber diameter ranging from 0.1 micron to several microns, have high electrical conductivity. As disclosed in U.S. Patent No. 6,184,280, carbon microfibers, nanotubes or carbon fibrils having an outer diameter of less than 0.1 micron to terms of nanorneters can be used as electrically conductive fillers. An example of graphitized carbon fiber suitable for conductive preformed compositions of the present disclosure include PANBX 30MF (Zoltek Companies, In, St Louis, Mo.), a 0.921 micron dimeter round fiber having an electrical resistivity of 0.00055 Ω-cm. (032] The avenge particle size of an electrically conductive filler can be within a range useful for imparting electrical conductivity to a polymer-based composition. For example, in certain embodiments, the particle size of the one or more fillers can range from 0.25 microns to 250 microns, in certain embodiments can range fiotu 0.25 microns to 75 microns, and in certain embodiments can range from 0.25 miaous to 60 micron. Da certain embodiments, preformed composition of'the present disclosure can comprise Ketien Black EC-600 JD (Akzo Nobel. Inc., Chicago, IL). an electrically conductive carbon black characterized by an iodine absorption of 1000-11500 mg/g (JO/84-5 test method), and a pore volume of 480-510 cm3/100 gm (DBP absorption, KTM 81-3504). In certain embodiments, an electrically conductive carbon black filler is Black Pearla 2000 (Cabot Corporation, Boston, MA). [033] to. certain embodiments, electrically conductive polymen can be used to impart or modify the electrical conductivity of preformed compositions of the present disclosure. Polymers having sulfur atoms incorporated into aromatic groups or adjacent to double bonds, such as in polyphcnylene sulfida, and polythioph.en:, are known to be dwdricalJy conductive. Otter electrically conductive polymers inc Iudc, for example, polypyrroles, polyaniline, poly(p-pbenylene) vinvieae, and polyacerylene. In certain embodiments, the] culfur-containing polynen forming a base composition can be polyaulfidefl and/or porytfaioethers. As such, the sulfur-containing polymers can comprise aromatic sulfur groups and sulfur atoms adjacent to conjugated double bonds such as virryloyolohexene-dimercaptcdioxaoctane groups, to enhance tie electrical conductivity of the preformed compositions of the present disclosure. [034] Preformed sealant compoiitions of the present disclosure can comprise more than one electrically conductive fillet, and (ho more than one electrically conductive filler can be of the same or different materials and/or shapes. For example, a prcfoOoed sealant composition can comprise electrically conductive Ni fibers, and electrically conductive Ni-coiled graphite in the form of powder, particles or flakes. The amount and type of electrically conductive filler can be selected to produce a preformed sealant composition which, when cured, exhibits a sheet resistance (four-point resistance) of less than 0.50 Ω/ , and in certain embodiment!, a sheet resistance less (ban 0.15 Ω/ , The amount and type of filler can also be selected to provide effective EMI/KFI shielding over a frequency range of from 1 MHz to 18 GHz for an aperture sealed uting a preformed sealant composition of the present disclosure. [035] Galvanic corrosion of dissimilar metal surfaces and the conductive compositions of the present disclosure can be minimized or prevented by adding corrosion inhibitors to the composition, and/or by selecting appropriate conductive fillers, In certain embodiments, cetiosion inhibitors include strontium chroioate, calcium ohroroate, magnesium chromate, arid copibinnrions thereof. U.S. Patent No. 5,284,388 and U.S. Patent No. 5,270,364 disclose the use of aromatic triazoles to inhibit corrosion of aluminum and steel surfaces. la certain embodiments, a sacrificial oxygen scavenger such as Zncati be used as a corrosion inhibitor. In certain embodiments, the corrosion iahibitdr can compose less than 10% by weight of the total weight of the electrically conductive preformed composition. In certain embodiments, the corrosion inhibitor can comprise an amount ranging from 2% by weight to 8% by weight of the total weight of the electrically conductive preformed compocition. Corrosion between dissimilar metal surfaces can also be minimized or prevented by die selection of the type, amount, and properties of the conductive Jillers composing the preformed composition. [036] In certain embodiments, preformed compositions of the present disclosure comprise plistidzers such as phthalate esters, chlorinated paraffins, hydrogenated terphorys, partially hydrogooated tophenyls, and the like. A preformed composition can comprise more than one plasticizer. The amount of placticizer in the base composition can range from 0.1% to 5% by weight based on the total weight of the base composition, and in certain embodiments, can range from 0.5% to 3% by weight The amount of pLuticizer in the curing agent composition can range from 20% to 60% by weight of the total weight of the curing agent composition, and in ceiuuu embodiments, cen range from 30% to 40% by weight. [037J In certain embodiments, preformed compositions further comprise an organic solvent, such as a ketone or an alcohol, for example methyl ethyl keton s, and isopropyl alcohol, or a combination thereof. [038] In [039] m certain embodiments, a base composition can be prepared by batch mixing at least one rattur-cootainm\| polymer, additives, and/or filler in a double plaoetary mixer under vacuum, Other suftita mixing equipment includes a loeader extruder, sigma mixer, or double "A" aim mixer. For example, a owe composition can be prepared by miring at least one suUor-coclaining polymer, plasticizer. and phenolic adhesion promoter After the mixture ie thoroughly blended, additional constituents can be aopatately added and mixed using a high shear grinding blade, such as a Cowtan blade, until cut it Examples of additional constituents that can be added to a base composition include corrosion inhibitors, non-conductive fillets, electrically conductive fiber, electrically conductive Sake, and silane adhesion promoters. The mixture can feen be mixed for 111 additional 15 to 20 minutes under a vacuum of 27 inches of mercury or greater to reduce or remove entrapped air and/or gases. The base compontioa can then extruded from the nuxer using a high-pressure piston nm. [040] A ciniogagert composition can be prepared by batch mixing a curing agent, additives, and fillers. In certain embodiments, 75V* of the total plasticizor such as partially hydrogenated terpheayl and an accelerant such as a dipentameuylene/diiunnVpolysulfide mixture ue mixed in a single-shaft anchor mixer. Molecular sieve powder is theo added and mixed for 2 to 3 minutes. Fifty percent of the total manganese dioxide ic then mixed until cut in. Stead c acid, sodium stearate, and the remaining plasticizer are men inked uotil cut in fojQowed by the remaining 50% of the manganese dioxide which ii mixed until cot in. Fumed silica is then raked until cut in. If (he nature u too thick iiuik^t any be added to increase wetting. The curing agecrt composition ig then mixed for2 to 3 minutes, passed over a three-roll paint mill to achieve » grind, tod returned to the single-shaft anchor mixer and mixed for anadditional 5 to 10 minotea. The curing agent composition c«o then be removed from the mixer with a piston ram and placed into storage containers and aged foi at toast 5 days prior to combining with a hue competition. [041] to form a preformed sealant composition. A base composition aod a curing agent compositioa caa be combined is (be desired ratio wring meter mix equipment fitted with a dynamic mix head. Pressure from ths meter mix equipment forces me baa> and owing agent compositioni through Hie dynamic mix head tod an extrusion die. In certain embodimentc, a preformed competition is extruded into a toninar form such ts a tape or sheet Aprejjrmedeooipoan^oainsheetibnnciabeeuttoanydeviivd shapemwhasdefinedbytheoaneasiousofaDiperturctobejealed, In certain embodiments, the shaped form e«& be coiled, with release paper separating each i-ing for packaging proposes, Tne shaped form [042] For sealing an aperture, the temperature of the preformed composition is raised TO a use taaperatare ranging from 4"C to 32°C (40T to 90F) prior to application to one or more surfaces associated with the aperture. This it done such that the preibnned composition reaches use temperature for no more than 10 minutes prior to application. [043] In certwflKiibo adjacent to the perimeter of an opening ban aircraft fuselage. Adhesion promoter is fitst brushed on the perimeter of the access punel opening after the surfcce has been cleaned with « cleaning solvent such as DBSOCLBAN (PRC-DeSoto fcttenuaooaJ, Inc.). The surface of the aooef s panel is then cleaned and coated with a release agent prior to applying the preformed composition. Ibe preformed competition in shaped form it manually applied to the surface adjacent to the perimeter of the access panel opening, to the surface adjacent to flu perimeter of the access panel, or to both. Hie access panel is then positioned against the svir&cc adjacent to the opening and damped down to force the excess preformed composition around the edges of the acce» panel. Bxceas preformed composition is easily removed by using, for example, a flat surface. Excess prefonned compositicm can be removed either prior to curing or after the preformed composition has cured, and preferably after the preformed composition cures. [044] Tlw integrity, moisture resiiaint^ aad r^ resulting from application of preformed compositions of the present disclosure cao be evaluated by performing the teats identified in specification MMS 327. An acceptable seal will be tight add resistant to moiiture and aircraft fuel. [045] R is noted that, as used in this apecificatioo and the appended claims, the singular forms "a," "an." sod, "the" include plural referents unless expressly aod unequivocally limited to one referent Thus, for example, reference to "a filler" includes one or mote fillers. Also it is noted that, as used herein, the term "polymer" refers to polymers, oligomera, homopolymers, and copolymers. [046] For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities of ingredients or percentages or proportions of other materials, reaction cooditiona, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about," Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims ere approximations that may vary depending upon the desired properties sought to be obtained by the prasent disclosure [047] Eoibodinjents of the present disclosure can be further defined by reference to the following examples, whi'/h describe in detail the preparation of compositions of the present disclosure ted msthods for using compositions of the present disclosure. It will be apparaat to those skilled in the art that modifications, both to materials aod methods, may be practiced without departing from the scope of the present disclosure. Example 1 [048] Example 1 provides an electrically conductive preformed composition it shaped form exhibiting EMI/KPT shielding effectiveness. The following truUeriiils were mixed in the proportions according to Table I to provide an electrically conductive base composition: PERMAPOL P 3.1 polyonocthcr polymer from PRO DeSoto International, Inc., THIOPLAST G4 polysulfide polymer from Akcros Chetnieals (New Brunswick, HI), pbeaolic rem adhesion promoter from PRC-DeSoto International, Inc. and HB-40 modified polypbenyl plasticizer from Solun'a, Inc. (St. Louis, Missouri). Using a high shear grinding blade (Cowlesi blade), th« following material were individually added and blended until outia: calcium chtomate corKwkn inhibitor (Wayne Pigment Corp., Milwaukee, WO, hydrophobia fumed sifica (R202, from Aeroril/Degotsa, Diamond Bar CA), Nl fiber (30 juo diameter, SOO uat length; from latnmicroa, Binuinghtm, AL), Ni-co«ted graphite (I) (60% Ni-coatcd \|jmphite; from Nowaet, Wyckoff; NJ), Ni-coated graphite (II) (60% Ni-ooated graphite: from Sulzer Metoo/Anibeoa, Switzeriand), mercq>to aiane adhesion promoter (Silaoe A189; OB Specialty Materials, Wilton, CK), and epony silane adhesion promoter (Silanc A187; QB Specialty Materials, Wilton, CN). [049] Tsbk I. Electrically (Table Remove) [050] Separately, the following material* were mixed in the amount* according to Table H to form a curing agent compoaition: manganese dioxide from BaglePioher (Phoenix, AZ), partially hydrogeastod terphenyl, stearic acid, fumed silica, sodium steatite from Witco ChemicaLi, molecular sieve powder to remove excess moisture from the curing agent, and dtpootamefliyleoWthiurtm/polysalfide mixture from Akrochem Corporation (Akron, QH) to accelerate the cure. Thecuriag agent compoiition was allowed to set or age for at least 5 days before combining vrith the bate composition. (Table Remove) [052] One hundred parts by weight of the electrically conductive base oompoatioo according to Table I, and 10 parta by weight of the curing agent composition of Table H were combined to prepare the electrically conductive preformed composition. After thorough mixing and degassing, the electrically conductive preformed compotition thus formed was extruded into a tape form aad refrigerated at -40°C. [OS3] The surface adjacent to tbe perimeter of an aircraft access panel was first coaled isith tow VOC epoxy primer sscordisg to qwification MMS-423 tiad cured. The surface was cleaned aad then coated with adhesion promoters PR-148 or PR-184 from PRC-DcSoto International, IDC. Tbe access panel was made from titanium alloy conforming to AMS-T-9046. After the refrigerated electrically conductive preformed composition equilfbrated to use temperature, 4 °C to 32 °C (40 °F to 90 °F), the electrically conductive preformed composition in tape form was manually applied to me surface adjacet to the perimeter of the access panel. The access panel was put in place to cover (he access opening and clamped down, forcing the excess electrically conductive preformed composition around the edges of the access panel to fill the aperture. Excess electrically conductive preformed composition was easily removed. After 3 to 4 hours at a temperature of 4°C to 32°C (40°F to 90°F), a tight seal, resistant to moisture and aircraft fuel, resulted. [054] The curred sealant exhibited a sheet resistance (four-point probe) of less than 0.50 Ω/ . Seals to apertures between an aluminum test fixture and a carbon/epoxy lid exhibited hielding effectivencess from 1 MHz to 200 MHz wher tested in anechoic chamber. Similarly sealed aperture also exhibited shielding effeetivaaecss from 0.1 GHz to 18 GHz when tested in a stirred mode chamber, [055] Other embodiments of the present disclosure will be apparent to those skilled in the art 6am consideration of the ipecification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with me true scope and spirit of the present disclosure being indicated by the following claims. We claim: 1. A preformed composition in shaped-form comprising: (a) a base composition comprising a polysulfide polymer and a polythioether polymer, and at least one electrically conductive filler such as herein described; and (b) a curing agent composition such as herein described; (c) the balance, if any, comprising one or more conventional additives; the curing agent being present in an amount in the range of 5 parts to 20 parts by weight for 100 parts of the base composition. 2. A preformed composition as claimed in claim 1, wherein the combination of the polysulfide polymer and the polythioether polymer is present in an amount ranging from 10% by weight to 50% by weight of the total weight of the base composition. 3. A preformed composition as claimed in claim 1, wherein the at least one electrically conductive filler is present in an amount ranging from 40% to 80% by weight of the total weight of the base composition. 4. A preformed composition as claimed in claim 1 wherein the at least one electrically conductive filler is selected from the group comprising Ni fiber, Ni-coated graphite and any mixture thereof. 5. A preformed composition as claimed in claim 4, wherein the Ni fiber is present in an amount ranging from 4% to 8% by weight of the total weight of the base composition, and the Ni-coated graphite is present in an amount ranging from 50% to 70% of the total weight of the base composition. 6. A preformed composition as claimed in claim 1, wherein said conventional additive comprises at least one corrosion inhibitor such as herein described. 7. A preformed composition as claimed in claim 6 wherein the at least one corrosion inhibitor comprises calcium chromate. 8. A preformed composition as claimed in claim 6, wherein the at least one corrosion inhibitor is present in an amount ranging from 3% by weight to 7% by weight of the total weight of the base composition. 9. A preformed composition as claimed in claim 1 wherein said conventional additive comprises at least one adhesion promoter such as herein described. 10. A preformed composition as claimed in claim 9, wherein the at least one adhesion promoter comprises a phenolic adhesion promoter, a mercapto-silane adhesion promoter, and an epoxy-silane adhesion promoter. 11. A preformed composition as claimed in claim 9, wherein the at least one adhesion promoter is present in an amount ranging from 1 % by weight to 6% by weight of the total weight of the base composition. 12. A preformed composition as claimed in claim 1, wherein the preformed composition is curable at a temperature ranging from 10°C to 30°C. 13. A preformed composition as claimed in claim 1, wherein the cured preformed composition exhibits a surface resistivity of less than 0.50Q/. 14. A preformed composition as claimed in claim 1, wherein the curing agent composition comprises a manganese dioxide curing agent. 15. A preformed composition as claimed in claim 14, wherein the manganese dioxide is present in the curing agent composition in an amount ranging from 25% to 75% by weight of the total weight of the curing agent composition. 16. A preformed composition as claimed in any preceding claim for use in sealing an aperture to provide EMI/RFI shielding effectiveness by applying said pre-formed composition in a manner such as herein before described to a surface associated with an aperture.

Full Text

[001] The present disclosure relates to preformed compositions in shaped
form and the use of preformed compositions for sealkig apertures. The present
disclosure further relates to preformed compositions in shaped form exhibiting
BrVfl/KFI shielding effectiveness, and the use of such preformed compositions for
sealing apertures.
Introduction
[002] Electromagnetic interference can be defined as undesired conducted or
radiated electrical disturbance fiom an electrical or electronic source, including
transients, which can interfere -with the operation of other electrical or electronic
apparatus. Such disturbance can occur at frequencies throughout the electromagnetic
spectrum. Radio frequency interference ("RET") is often used interchangeably with
electromagnetic interference ("EMI"), although RM more properly refers to the radio
frequency portion of the electromagnetic spectrum usually defined as between 10
kilohertz (KHz) and 100 gigahertz (GHz).
• [003] Electronic equipment is typically enclosed in a housing. The housing
can serve not only as a physical barrier to protect the internal electronics from the
external environment, but also can serve to shield EMMRP1 radiation. Enclosures
having the ability to absorb and/or reflect EMJ/RH energy can be employed to
confine the EMI/RFI energy within the source device, as well as to insulate the source
device or other external devices from other BMQ/RFI sources. To maintain
accessibility to the internal components, enclosures can be provided with openable or
removable accesses such as doors, hatches, panels, or covers. Gaps typically exist
between the accesses and the corresponding mating surfaces associated with the
accesses that reduce the efficiency of the electromagnetic shielding by presenting
openings through which radiant energy may be emitted. Such gaps also present
discontinuities in the surface and ground conductivity of the housing and in some
cases, may generate a secondary source of EMI/RFI radiation by functioning as a slot
antenna.
[004] For filing gaps between the mating surfaces of the housing and
removable accesses, gaskets and other seals can be used to maintain electrical
across the structures, and to exclude environmental degredants such as particulates, moisture, and corrosive species. Such seals can be bonded or mechanically attached to one or both of the mating surfaces and can function to establish a continuous conductive path by conforming to surface irregularities under an applied pressure.
[005] Conventional processes for manufacturing BMI/RFI shielding gaskets include extrusion, molding, and die-cutting. Molding includes the compression or injection molding of an uncured sealant or thermoplastic material into a certain configuration which is then cured to a foal shape. Die-cutting includes the forroing of a gasket from a cured polymeric material which is cut or stamped using a die into a certain configuration. Form-in-place ("FIP") processes are also wed for forming EMI/RFI shielding gaskets wherein the FIP process includes the application of a bead of a viscous, curable, eloctrically-conductive composition in a fluent state to a surface that is subsequently cured-in-place by the application of heat, atmospheric moisture, or ultraviolet radiation to form an electrically-conductive, BMI/RFI shielding gasket.
[006] Electrical conductivity anil EM1/RF1 shielding effectiveness can be imparted to polymeric gaskets by incorporating conductive materials within the polymer matrix. The conductive elements can include, for example, metal or metal-plated particles, fabrics, meshes, fibers, awl combinations thereof. The metal can be in the form of, for example, to;a,emts, particles, flakes, or spherea,. Examples cf metals include copper, nickel, silver, aluminum, tin, and steel. Other conductive materials that can be used to impart EMl/RFI shielding effectiveness to polymer compositions include conductive particles or fibers comprising carbon or graphite. Conductive polymers such as polythiophenes, polypyrroles, polyaniline, poly(p-pheaylene) vinylene, polyphenylene sulfide, polyphenylene, and polyacetylene can also be used.
[007J In addition to providing continuous electrical conductivity and BMI/RFI sihielding effectiveness, in certain applications it is desirable that gaskets or seals to surfaces exposed to the environment, such as in aviation and aerospace vr-hicica, not lead to corrosion of the mctil surfaces. When dissimilar metals and/or conductive composite materials are joined in the presence of an electrolyte, a galvanic potential is established at the interface between me dissimilar conductors. When the
interfacial seal is exposed to the environment, particularly under severe environmental conditions such as salt fog or salt fog containing a high concentration of SO2, corrosion of the least noble of the conductive surfaces can occur. Corrosion may lead to a degradation in the EMI/RFI shielding effectiveness of the seal. Mechanians other than galvanic potentials, for example, crevice corrosion, may also comprotnise the electrical and mechanical integrity of the enclosure.
[008] Polysulfide polymen are known in the art. The production of polysulfidc polymers is characterized by Fettes and Jotzak, Industrial Engineering Chemietry, November 1950, oopagee 2.217 - 2,223. The commercial use of polysulfide polymers in the manufacture of f ealautt for aerospace applications lias long been known and commercially used. For example, polyvulfide sealants have been used to to sea! an aircraft body because of the high tensile strength, high tear strength, thenal resistance, and resistance to high ultrsviolet light Polysulfide
sealants have been used to seal auoaft fiwl tanks because of the resistance to ftel and adhsion upon exposure to fuel.
(009] Polysulfide sealants are generally aookued toasurface by extrusion using a caulking gun. Such a process can be efficient for permanent panels installed on an airframe. However, extruding a sealant to seal apertures in and/or on an airframe such as those associated with access doors or panels can require a significant amount of additional effort. To extrude fin uocured sealant, the interior perimeer of the access door opening is masked and the exterior poiineter of the access door is coated with a release agent prior to extruding the sealant to the masked area of the acoess door opening to avoid sealing an access door shut. The access door is put in place and clamped down to force tie excess uncured sealant around the accew door. The sealant is then cured and the excess sealant is trimmed away, This process: is time intensive and can add significant labor to servicing aircraft with many access doors. Some aircraft can have as many tis a hundred or more access doors that are used to cover sensitive electronic equipment or fittings that must be periodically accessed and resealed.
[010} Accordingly, it is desirable to provide a method for sealing access doors, for example those in an airframe of an aviation or aerospace vehicle, that does
not require masking, reduces trimming and/or is not as lebor and time intensive as the conventional extrusion method for sealing the access doors.
[O11] Electricallyconductive sealants that exhibit EMI/RFI shielding effectivenese are commercially available, For example, PRC-DeSoto international, Inc. (Glendale, CA) manufactures several clss B electrically conductive sealants specifically developed for aviation and aerospace applications, For example, PR-2200 Class B electrically conductive sealant is an electrically conductive polythioether sealant that meets toe requirements of MMS 327 (Boeing St. Louis Military Material Specification) test methods. These two-part, nickel-filled seaknti comprise polythioother polymer, PHRMAPOLP-3.1, and are aot corrosive when used on aluminuim alloys or between dissirolilar metals,, However, commcrcially available selants such as exemplified by the PR-2200 product are not provided as a preformed composition.
(012] Therefore, it is further desirable to provide a method for sealing access doors to provide effective EMI/RFI shielding and cause minimal corrosion to conductive sirface in environments encountered in aviation and aerospace applications that does not require masking, reduces timming and/or is not as labor and time interasive as is the coaveotional extrusion method for sealing the access doors. Summary
[013] In accordance with embodiments of the present disclosure, preformed compositions in shaped form comprinng a base composition compruing at least one sulfur-containing polymer, and at least one electrically conductive filler, and a cniring agent composition; wherein the preformel composition is capable of shielding EMI/RFI radiation, are provided.
[014] In accordance with embodiments of the present disclosure, methods of sealing an aperture to provide EM1/RFI sheldinglding effectiveness comprising app lying a preformed composition in shaped-fom comprising at least one sulfur-containing polymer, and at least one electrically conductive filler to a surface associated with an aperture', and curing the preformed composition to »aal the aperture aad provide EMI/RFI shielding effectiveness, are disclosed.
[015} Additional embodiments of the disdoaure arc set forth in the description which follows, or may be learned by practice of the embodiments of 1he present disclosure. Description ot Various Embodiments
[016] In ortainernbodiraenta of tlie present dtetosure^ compositions in shaped form suitable for sealing apertures, foi example, elongated apertures in or on (be body of an aircraft, comprises at least one sulfur-conuuiami; polymer, and at least one electrically conductive filler. The tcnn "prefiwrned" refers to a compositioa that can be prepared into a particular dupe for ease of packaging, storage, and/or application. A composition that is preformed can be reshaped in [017] Tb6t«nn'>or [018] Preformed Kalant compositions of the present disclosure can be prepared by blending an electrically conductive base composition, aad a curing agent compositioa. A base composition and a (Airing agent composition can be prepared separately, blooded to form a sealant composition, and preformed to a particular shape. A conductive base composition ctfi comprise, for example, at least one sulfur* containing polymer, at least one plasb'cizer. at least one adhesion promoter, at least one corrosioa inhibitor, at least one electrically non-conductive filler, at l«ut one electrically conductive filler, and at least one adhesion promoter. A curing ageat composition can comprise, for example, at least one curing agent, at least one
ptotitizer, it least one electrically con-conductive filler, and at least one cure accelerator. In eettiin embodiments, 5 to 20 pots by weight of • curing agent composition ere blended with 100 parts by weight of a base composition, and in certain embodiments, 8 to 16 parts by weight of airing agent composition we blended with 100 parts by weight of abase composition to form an electrically conductive sealant conapoiition.
[019] In certain embodiments, twit-component curable compositions «t; preferred to me one-component curable compositions because the taro-componeut compositions provide the best theology for application and exhibit desirable physical and chemical properties in the resultant cured compootion. As used herein, the two component* are referred to as me hue composition, aol the curing agent oompcriticn. In certain embodiments, the bace composition can comprise poryiulfide polymers, polytbioether polymers, oxidizing agents, additives, fiUen, plasticizers, organic solvents, adhesion promoters, cotrosicm iuhibitora, and combinations thereof. fa certain embodiments, the curing agent composition can comprue curing agente, cure accelerators, owe retardattts, pluru'cizara, additives, fillets, aod combinations thereof.
[020] In certJUD embodiments, roliar-wnuantng polymers useful in the practice of the present disclosure include polysulfide polymers that contain multiple Bulfid* groups, « e , -S-, in the polymer backbone nod/or in the terminal or peod«it positions on the polymer chain. Such polymers are described in U.S . Patent No . 2,466,963 wherein the disclosed polymers have multiple -S-S- linkages in the polymer backbone. Other useful polysullide polymer* are those ia which the polysulfide linlugc is replaced with a polythioetlwr linkage, i.e.,
where a can be an integer tanging from 8 to 200 as described in U.S. Patent No. 4,366,307. The polysulfide polymer* can be terminated with non-reactive groups such u ajkyi, although in ccttain embodiments, the polysulfide polymers contain reactive groups in the terminal or pendent positions. Typical reactive groups M-e tbiol byxlrcxyl, sraino, and vinyl. Such polysvjfide polymers are described in. the aforemeatioaed U5. Patent No. 2,466,SKi3, U.S. Patent No. 4,356,307, and U.S. Patent No. 6,372,849, each of which is Lnoorportfcd herein by reference. Such
polysulfide polymers am be cured with curing •goats Out are reactive with the reactive groups of the polysulfide polymer.
[021] SulroTMxmtaining polymer* of the present disclosure can have number average molecular weights ranging from 5(0 to 8,000 grams per mole, and in certain embodiments, from 1,000 to 5,000 grams per mob, ai determined by gal permeation chramatography using t polystyrene standtni. For sulfur-containing polymers that contain reactive functional groups, tie sulf ur^onUining polymers can have averige functionalities ranging from 2.05 to 3.0, aid in certain embodiments ranging from 2.1 to 2,6. A specific average fiactlonality can be achieved by suitable selection of reactive components. Example* of anifig-contaiping polymers include mo«e avt Jable from PRC-DeSoto International, me, under the trademark PERMAPOL, specifically, PERMAPOLP-3.1 or PBRMAPOLP-3, end flora Ataos Chemicals, such as THIOPLASTG4.
[022] A sulfur-containg polymer can be present in the conductive base composition in an amount ranging from 10% to 40% by weight of the total weight of the conductive base composition, and in certain embodiments can range from 2()% to 30% by weight, In certain embodiments, wherein a sulfur-containing polyraer comprues a combination of polysulfide polymer and a polythiocther polymer, the amount of polysulfide polymer and polytiiiocther polymer can be similar, For example, the amount of polysulfide polymer and the amount of polytbioether polymer in t bate composition can each range from 10% by weight to 15% by weight of the total weight of the conductive base composition
[023] Preformed compositions of the ptesent disclosure comprise at lc ast one curing agent for curing the at least one tvilfur-coataining polymer. The term "curing agent" refers to any material that cac be added to a sulfur-containing polymer to accelerate the curing or gelling of the wjlfur-coatammg polymer. Curing agents are also known as accelerators, catalysts or cure pastes. In certain embodiments, the curing agent is reactive at a temperature ranging from 10 *C to 80 *C. The term "reactive" means capable of chemical reaction and includes any level of resction from partial to complete reaction of a reactant. In certain embodiments, a curing agent is reactive when it provides for cross-linking or gelling of a sulfur-containing polymer.
[024] In certain ambodiments preformed compositions comprised curing agent that contains oxidizing agents capable of oxidizing terminal mercaptan groups of the sulfur-containing polymer to form disulfide bonds. Useful oxidizing, agents include, for example, lead dioxide, manganese dioxide, calcium dioxide, sodium perborate monohydrate, calcium peroxide, zinc peroxide, and dichromate. The amount of curing agent in a curing agent composition can range from 25% by weight to 75% by weight of the total weight of the curing agent composition. Additives such as sodium stearate can also be included to improve the stability of (be accelerator. For example, a curing agent composition can comprise an amount of cure accelerator ranging from 0,1% to 1.5% by weight based on the total weight of the curing agent composition.
[025] In certain embodiment, preformed compositions of the present disclosure can comprise at least one curing agent containing at least one reactive functional group that is reactive with functional groups attached to the sulfur-containing polymer. Useful curing agents containing at least one reactive functional group that is reactive with functional groups attached to the sulfur-containing polymer include polythiols, such as polythioethers, for curing vinyl-terminated polymers; polyisocyanstes RICA as isophorone diisocyanate, hexamethylene diisocyanate, and mixtures and isooyanurate derivatives thereoof for curing thiol-, hydroxyl- and anuro-tenminated polymens; and, polyeporidw for curing amine- and thiol-terminated polymers. Bxamples of polyepoxides include hydantoin diepoxide, Bisphenol-/. epoxides, Bispheool-F epoxides, Novolac-type epoxides, aliphatic polyepoxides, and epoxidized unaatorited reains, and phenolic resins. The term "polyepoxide" refers to a material having a 1,2-epoxy eqalvalent greater man one and includes monomers, oligomeri, and polymers.
[026] A performed sealant composition can comprise at Icastonecomixj'and to modify the rate of cure. For example, cure accelerants such as dipentamethylene/thiuram/polysulfide mixture can be included in a sealant compotition to accelerate the rate of cure, and/or at least one cure rotardant such a as stearic acid can be added to retard the rat: of cure and thereby exteud the work life of a sealant composition during application. In certain embodiments, a curing agent composition can comprise an amount of accerant ranging from 1% to 7% by weight,
uod/orgn amount of cure retardwjtnngjng from 0.1% to 1% by weight, based on the total weight of the curing agent composition. To control the cure properties of UK: sealant composition, it can also be metal to include at least one material capable of at least partially removing moisture from the igalaat composition such u molecular sieve powder. In certain wnbodiniems, i curing agent compofitioa can comprise an amount of material capable of at least partially removing moisture ranging from 0.1% to 1.5% by weight, based on toe total weight of the curing agent composition.
[027] In certain embodiments, prefonned compositions of the present disclosure can comprise fillers. As used herein, "filler" refers to a non-reactive component in the preformed oompositioa that provides a desired property, such vs, for example, electrical conductivity, density, viscosity, mechanical strength. EMI/W1 shielding effectiveness, and me like.
[028] Examples of electrically noa-conductive fillers include materials rach as, but not limited to, calcium carbonate, roica, poryamide, fiuaed silica, molecular sieve powder, nucroapherw, titaniom dioxide, chalks, alkaline blacks, cellulose, zinc culfide, heavy spar, alkaline earth oxides, ilkaiine earth hydroxides, and the like, Filters also include high band gap materials such as zinc sulfide and inorganic twium compounds. In certain embodiments, «n electrically conductive base composition can comprise an amount of electrically non-conductive filler ranging from 2% to 10% by weight, based on the total weight of the buse composition, and in certain embodimeuts, car. range from 3% to 7% by weight In certain embodiments, a (wring agent composition can comprise an amount of dactricaUy non-conductive filler ranging from less than 6 percent by weight, and in certain embodiments ranging from 05% to 4% by weight, based on the total weight of the coring agent composition.
[029] HE«nus«dtounpartelcctac»lc plated mica; and othar such noble-metal conductive fillers. Non-noble metal-based materials can also be used and include, for example, non-noble metal-pitted non-noble metals such ai copper-coated iron particles or nickel plated copper, non-noble metals, e.g., copper, aluminum, nickel, cobalt; non-noble-metal-plated-noa metals, e.g., nickel-plated graphite and non-metal materials such as carbon black and graphite. Combinations of electrically conductive fillers can also be used to meet the desired conductivity, EMI/RFI shielding efectiveness, hardness, and other properties suitable for a particular application.
[030] The dupe and size of the electrically conductive fillers used in the preformed composition! of the present disclosure can be any appropriate shape and size to impart EMI/RFI shielding effectiveness to the cured preformed composition. For example, fillers can be of any shape that is generally used in the manufacture of electrically conductive fillers, including spherical, flake, platelet, particle, powder, irregular, fiber, and toe tike. In certain preformed aealant compositions of the disclosure, a base composition oan compruie Mi-coated graphite as a particle, powder or flake, hi certain embodiments, the amount of Ni-coated graphite in a base composition can range from 40% to 80% toy weight, and in certain embodiments can range from 50% to 70% by weight, based on the total weight of the base composition. In certain embodiments, an electrically conductive filler can comprise Ni fiber. Ni fiber can have a diameter ranging from 10 |im to 50 utt and have a length ranging from 250 Mm to 7SO fua A base composition can comprise, for example, an amount ofNi fiber ranging from 2% to 10%bywdght, and in certain embodiments, from 4% to 8% by weight, baaed on the total weight of the base compositioa.
[031] Carbon fibers, particularly graphitized carbon fibers, can also be used to impart electrical conductivity to prefbnned compositions of the present disclosure. Carbon fibers formed by vapor phase pyrolysis methods and graphilized by bead treatment and which are hollow or solid with a fiber diameter ranging from 0.1 micron to several microns, have high electrical conductivity. As disclosed in U.S. Patent No. 6,184,280, carbon microfibers, nanotubes or carbon fibrils having an outer diameter of less than 0.1 micron to terms of nanorneters can be used as electrically conductive fillers. An example of graphitized carbon fiber suitable for conductive preformed compositions of the present disclosure include PANBX 30MF (Zoltek
Companies, In, St Louis, Mo.), a 0.921 micron dimeter round fiber having an electrical resistivity of 0.00055 Ω-cm.
(032] The avenge particle size of an electrically conductive filler can be within a range useful for imparting electrical conductivity to a polymer-based composition. For example, in certain embodiments, the particle size of the one or more fillers can range from 0.25 microns to 250 microns, in certain embodiments can range fiotu 0.25 microns to 75 microns, and in certain embodiments can range from 0.25 miaous to 60 micron*. Da certain embodiments, preformed composition of'the present disclosure can comprise Ketien Black EC-600 JD (Akzo Nobel. Inc., Chicago, IL). an electrically conductive carbon black characterized by an iodine absorption of 1000-11500 mg/g (JO/84-5 test method), and a pore volume of 480-510 cm3/100 gm (DBP absorption, KTM 81-3504). In certain embodiments, an electrically conductive carbon black filler is Black Pearla 2000 (Cabot Corporation, Boston, MA).
[033] to. certain embodiments, electrically conductive polymen can be used to impart or modify the electrical conductivity of preformed compositions of the present disclosure. Polymers having sulfur atoms incorporated into aromatic groups or adjacent to double bonds, such as in polyphcnylene sulfida, and polythioph.en:, are known to be dwdricalJy conductive. Otter electrically conductive polymers inc Iudc, for example, polypyrroles, polyaniline, poly(p-pbenylene) vinvieae, and polyacerylene. In certain embodiments, the] culfur-containing polynen forming a base composition can be polyaulfidefl and/or porytfaioethers. As such, the sulfur-containing polymers can comprise aromatic sulfur groups and sulfur atoms adjacent to conjugated double bonds such as virryloyolohexene-dimercaptcdioxaoctane groups, to enhance tie electrical conductivity of the preformed compositions of the present disclosure.
[034] Preformed sealant compoiitions of the present disclosure can comprise more than one electrically conductive fillet, and (ho more than one electrically conductive filler can be of the same or different materials and/or shapes. For example, a prcfoOoed sealant composition can comprise electrically conductive Ni fibers, and electrically conductive Ni-coiled graphite in the form of powder, particles or flakes. The amount and type of electrically conductive filler can be selected to produce a preformed sealant composition which, when cured, exhibits a sheet
resistance (four-point resistance) of less than 0.50 Ω/ , and in certain embodiment!, a sheet resistance less (ban 0.15 Ω/ , The amount and type of filler can also be selected to provide effective EMI/KFI shielding over a frequency range of from 1 MHz to 18 GHz for an aperture sealed uting a preformed sealant composition of the present disclosure.
[035] Galvanic corrosion of dissimilar metal surfaces and the conductive compositions of the present disclosure can be minimized or prevented by adding corrosion inhibitors to the composition, and/or by selecting appropriate conductive fillers, In certain embodiments, cetiosion inhibitors include strontium chroioate, calcium ohroroate, magnesium chromate, arid copibinnrions thereof. U.S. Patent No. 5,284,388 and U.S. Patent No. 5,270,364 disclose the use of aromatic triazoles to inhibit corrosion of aluminum and steel surfaces. la certain embodiments, a sacrificial oxygen scavenger such as Zncati be used as a corrosion inhibitor. In certain embodiments, the corrosion iahibitdr can compose less than 10% by weight of the total weight of the electrically conductive preformed composition. In certain embodiments, the corrosion inhibitor can comprise an amount ranging from 2% by weight to 8% by weight of the total weight of the electrically conductive preformed compocition. Corrosion between dissimilar metal surfaces can also be minimized or prevented by die selection of the type, amount, and properties of the conductive Jillers composing the preformed composition.
[036] In certain embodiments, preformed compositions of the present disclosure comprise plistidzers such as phthalate esters, chlorinated paraffins, hydrogenated terphorys, partially hydrogooated tophenyls, and the like. A preformed composition can comprise more than one plasticizer. The amount of placticizer in the base composition can range from 0.1% to 5% by weight based on the total weight of the base composition, and in certain embodiments, can range from 0.5% to 3% by weight The amount of pLuticizer in the curing agent composition can range from 20% to 60% by weight of the total weight of the curing agent composition, and in ceiuuu embodiments, cen range from 30% to 40% by weight.
[037J In certain embodiments, preformed compositions further comprise an organic solvent, such as a ketone or an alcohol, for example methyl ethyl keton s, and isopropyl alcohol, or a combination thereof.
[038] In [039] m certain embodiments, a base composition can be prepared by batch mixing at least one rattur-cootainm| polymer, additives, and/or filler* in a double plaoetary mixer under vacuum, Other suftita mixing equipment includes a loeader extruder, sigma mixer, or double "A" aim mixer. For example, a owe composition can be prepared by miring at least one suUor-coclaining polymer, plasticizer. and phenolic adhesion promoter After the mixture ie thoroughly blended, additional constituents can be aopatately added and mixed using a high shear grinding blade, such as a Cowtan blade, until cut it Examples of additional constituents that can be added to a base composition include corrosion inhibitors, non-conductive fillets, electrically conductive fiber, electrically conductive Sake, and silane adhesion promoters. The mixture can feen be mixed for 111 additional 15 to 20 minutes under a vacuum of 27 inches of mercury or greater to reduce or remove entrapped air and/or gases. The base compontioa can then extruded from the nuxer using a high-pressure piston nm.
[040] A ciniogagert composition can be prepared by batch mixing a curing agent, additives, and fillers. In certain embodiments, 75V* of the total plasticizor such as partially hydrogenated terpheayl and an accelerant such as a dipentameuylene/diiunnVpolysulfide mixture ue mixed in a single-shaft anchor mixer. Molecular sieve powder is theo added and mixed for 2 to 3 minutes. Fifty percent of the total manganese dioxide ic then mixed until cut in. Stead c acid, sodium stearate, and the remaining plasticizer are men inked uotil cut in fojQowed by the
remaining 50% of the manganese dioxide which ii mixed until cot in. Fumed silica is then raked until cut in. If (he nature u too thick iiuik^t any be added to increase wetting. The curing agecrt composition ig then mixed for2 to 3 minutes, passed over a three-roll paint mill to achieve » grind, tod returned to the single-shaft anchor mixer and mixed for anadditional 5 to 10 minotea. The curing agent composition c«o then be removed from the mixer with a piston ram and placed into storage containers and aged foi at toast 5 days prior to combining with a hue competition. [041]
to form a preformed sealant composition. A base composition aod a curing agent compositioa caa be combined is (be desired ratio wring meter mix equipment fitted with a dynamic mix head. Pressure from ths meter mix equipment forces me baa> and owing agent compositioni through Hie dynamic mix head tod an extrusion die. In certain embodimentc, a preformed competition is extruded into a toninar form such ts a tape or sheet Aprejjrmedeooipoan^oainsheetibnnciabeeuttoanydeviivd shapemwhasdefinedbytheoaneasiousofaDiperturctobejealed, In certain embodiments, the shaped form e«& be coiled, with release paper separating each i-ing for packaging proposes, Tne shaped form [042] For sealing an aperture, the temperature of the preformed composition is raised TO a use taaperatare ranging from 4"C to 32°C (40T to 90*F) prior to application to one or more surfaces associated with the aperture. This it done such that the preibnned composition reaches use temperature for no more than 10 minutes prior to application.
[043] In certwflKiibo
adjacent to the perimeter of an opening ban aircraft fuselage. Adhesion promoter is fitst brushed on the perimeter of the access punel opening after the surfcce has been cleaned with « cleaning solvent such as DBSOCLBAN (PRC-DeSoto fcttenuaooaJ, Inc.). The surface of the aooef s panel is then cleaned and coated with a release agent prior to applying the preformed composition. Ibe preformed competition in shaped form it manually applied to the surface adjacent to the perimeter of the access panel opening, to the surface adjacent to flu perimeter of the access panel, or to both. Hie access panel is then positioned against the svir&cc adjacent to the opening and damped down to force the excess preformed composition around the edges of the acce» panel. Bxceas preformed composition is easily removed by using, for example, a flat surface. Excess prefonned compositicm can be removed either prior to curing or after the preformed composition has cured, and preferably after the preformed composition cures.
[044] Tlw integrity, moisture resiiaint^ aad r^
resulting from application of preformed compositions of the present disclosure cao be evaluated by performing the teats identified in specification MMS 327. An acceptable seal will be tight add resistant to moiiture and aircraft fuel.
[045] R is noted that, as used in this apecificatioo and the appended claims, the singular forms "a," "an." sod, "the" include plural referents unless expressly aod unequivocally limited to one referent Thus, for example, reference to "a filler" includes one or mote fillers. Also it is noted that, as used herein, the term "polymer" refers to polymers, oligomera, homopolymers, and copolymers.
[046] For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities of ingredients or percentages or proportions of other materials, reaction cooditiona, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about," Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims ere approximations that may vary depending upon the desired properties sought to be obtained by the prasent disclosure
[047] Eoibodinjents of the present disclosure can be further defined by reference to the following examples, whi'/h describe in detail the preparation of
compositions of the present disclosure ted msthods for using compositions of the present disclosure. It will be apparaat to those skilled in the art that modifications, both to materials aod methods, may be practiced without departing from the scope of the present disclosure. Example 1
[048] Example 1 provides an electrically conductive preformed composition it shaped form exhibiting EMI/KPT shielding effectiveness. The following truUeriiils were mixed in the proportions according to Table I to provide an electrically conductive base composition: PERMAPOL P 3.1 polyonocthcr polymer from PRO DeSoto International, Inc., THIOPLAST G4 polysulfide polymer from Akcros Chetnieals (New Brunswick, HI), pbeaolic rem adhesion promoter from PRC-DeSoto International, Inc. and HB-40 modified polypbenyl plasticizer from Solun'a, Inc. (St. Louis, Missouri). Using a high shear grinding blade (Cowlesi blade), th« following material* were individually added and blended until outia: calcium chtomate corKwkn inhibitor (Wayne Pigment Corp., Milwaukee, WO, hydrophobia fumed sifica (R202, from Aeroril/Degotsa, Diamond Bar CA), Nl fiber (30 juo diameter, SOO uat length; from latnmicroa, Binuinghtm, AL), Ni-co«ted graphite (I) (60% Ni-coatcd |jmphite; from Nowaet, Wyckoff; NJ), Ni-coated graphite (II) (60% Ni-ooated graphite: from Sulzer Metoo/Anibeoa, Switzeriand), mercq>to aiane adhesion promoter (Silaoe A189; OB Specialty Materials, Wilton, CK), and epony silane adhesion promoter (Silanc A187; QB Specialty Materials, Wilton, CN). [049] Tsbk I. Electrically
(Table Remove)
[050] Separately, the following material* were mixed in the amount* according to Table H to form a curing agent compoaition: manganese dioxide from BaglePioher (Phoenix, AZ), partially hydrogeastod terphenyl, stearic acid, fumed silica, sodium steatite from Witco ChemicaLi, molecular sieve powder to remove excess moisture from the curing agent, and dtpootamefliyleoWthiurtm/polysalfide
mixture from Akrochem Corporation (Akron, QH) to accelerate the cure. Thecuriag agent compoiition was allowed to set or age for at least 5 days before combining vrith the bate composition.
(Table Remove)
[052] One hundred parts by weight of the electrically conductive base oompoatioo according to Table I, and 10 parta by weight of the curing agent composition of Table H were combined to prepare the electrically conductive preformed composition. After thorough mixing and degassing, the electrically conductive preformed compotition thus formed was extruded into a tape form aad refrigerated at -40°C.
[OS3] The surface adjacent to tbe perimeter of an aircraft access panel was first coaled isith tow VOC epoxy primer sscordisg to qwification MMS-423 tiad cured. The surface was cleaned aad then coated with adhesion promoters PR-148 or PR-184 from PRC-DcSoto International, IDC. Tbe access panel was made from
titanium alloy conforming to AMS-T-9046. After the refrigerated electrically conductive preformed composition equilfbrated to use temperature, 4 °C to 32 °C (40 °F to 90 °F), the electrically conductive preformed composition in tape form was manually applied to me surface adjacet to the perimeter of the access panel. The access panel was put in place to cover (he access opening and clamped down, forcing the excess electrically conductive preformed composition around the edges of the access panel to fill the aperture. Excess electrically conductive preformed composition was easily removed. After 3 to 4 hours at a temperature of 4°C to 32°C (40°F to 90°F), a tight seal, resistant to moisture and aircraft fuel, resulted.
[054] The curred sealant exhibited a sheet resistance (four-point probe) of less than 0.50 Ω/ . Seals to apertures between an aluminum test fixture and a carbon/epoxy lid exhibited hielding effectivencess from 1 MHz to 200 MHz wher tested in anechoic chamber. Similarly sealed aperture also exhibited shielding effeetivaaecss from 0.1 GHz to 18 GHz when tested in a stirred mode chamber,
[055] Other embodiments of the present disclosure will be apparent to those skilled in the art 6am consideration of the ipecification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with me true scope and spirit of the present disclosure being indicated by the following claims.

We claim:
1. A preformed composition in shaped-form comprising:
(a) a base composition comprising a polysulfide polymer and a polythioether polymer,
and at least one electrically conductive filler such as herein described; and
(b) a curing agent composition such as herein described;
(c) the balance, if any, comprising one or more conventional additives;
the curing agent being present in an amount in the range of 5 parts to 20 parts by weight for 100 parts of the base composition.
2. A preformed composition as claimed in claim 1, wherein the combination of the
polysulfide polymer and the polythioether polymer is present in an amount ranging from
10% by weight to 50% by weight of the total weight of the base composition.
3. A preformed composition as claimed in claim 1, wherein the at least one electrically
conductive filler is present in an amount ranging from 40% to 80% by weight of the total
weight of the base composition.
4. A preformed composition as claimed in claim 1 wherein the at least one electrically
conductive filler is selected from the group comprising Ni fiber, Ni-coated graphite and any
mixture thereof.
5. A preformed composition as claimed in claim 4, wherein the Ni fiber is present in an
amount ranging from 4% to 8% by weight of the total weight of the base composition, and
the Ni-coated graphite is present in an amount ranging from 50% to 70% of the total weight
of the base composition.
6. A preformed composition as claimed in claim 1, wherein said conventional additive
comprises at least one corrosion inhibitor such as herein described.
7. A preformed composition as claimed in claim 6 wherein the at least one corrosion
inhibitor comprises calcium chromate.
8. A preformed composition as claimed in claim 6, wherein the at least one corrosion
inhibitor is present in an amount ranging from 3% by weight to 7% by weight of the total
weight of the base composition.

9. A preformed composition as claimed in claim 1 wherein said conventional additive
comprises at least one adhesion promoter such as herein described.
10. A preformed composition as claimed in claim 9, wherein the at least one adhesion
promoter comprises a phenolic adhesion promoter, a mercapto-silane adhesion promoter,
and an epoxy-silane adhesion promoter.
11. A preformed composition as claimed in claim 9, wherein the at least one adhesion
promoter is present in an amount ranging from 1 % by weight to 6% by weight of the total
weight of the base composition.
12. A preformed composition as claimed in claim 1, wherein the preformed composition
is curable at a temperature ranging from 10°C to 30°C.
13. A preformed composition as claimed in claim 1, wherein the cured preformed
composition exhibits a surface resistivity of less than 0.50Q/.
14. A preformed composition as claimed in claim 1, wherein the curing agent
composition comprises a manganese dioxide curing agent.
15. A preformed composition as claimed in claim 14, wherein the manganese dioxide is
present in the curing agent composition in an amount ranging from 25% to 75% by weight
of the total weight of the curing agent composition.
16. A preformed composition as claimed in any preceding claim for use in sealing an
aperture to provide EMI/RFI shielding effectiveness by applying said pre-formed
composition in a manner such as herein before described to a surface associated with an
aperture.

Documents:

4832-DELNP-2005-Abstract(14-12-2007).pdf

4832-delnp-2005-abstract.pdf

4832-delnp-2005-assignment.pdf

4832-DELNP-2005-Claims(14-12-2007).pdf

4832-delnp-2005-claims-30-04-2008.pdf

4832-delnp-2005-claims.pdf

4832-DELNP-2005-Correspondence-Others(14-12-2007).pdf

4832-delnp-2005-correspondence-others-30-04-2008.pdf

4832-delnp-2005-correspondence-others.pdf

4832-delnp-2005-description (complete)-30-04-2008.pdf

4832-delnp-2005-description (complete).pdf

4832-DELNP-2005-Description(Complete)(14-12-2007).pdf

4832-DELNP-2005-Form-1(14-12-2007).pdf

4832-delnp-2005-form-1.pdf

4832-delnp-2005-form-13.pdf

4832-delnp-2005-form-18.pdf

4832-DELNP-2005-Form-2(14-12-2007).pdf

4832-delnp-2005-form-2.pdf

4832-DELNP-2005-Form-3(14-12-2007).pdf

4832-delnp-2005-form-3.pdf

4832-DELNP-2005-Form-5(14-12-2007).pdf

4832-delnp-2005-form-5.pdf

4832-delnp-2005-gpa.pdf

4832-delnp-2005-pct-105.pdf

4832-delnp-2005-pct-220.pdf

4832-delnp-2005-pct-237.pdf

4832-delnp-2005-pct-401.pdf

4832-delnp-2005-pct-409.pdf

4832-delnp-2005-pct-search report.pdf

4832-DELNP-2005-Petition-137(14-12-2007).pdf

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Patent Number

219451

Indian Patent Application Number

4832/DELNP/2005

PG Journal Number

26/2008

Publication Date

27-Jun-2008

Grant Date

06-May-2008

Date of Filing

21-Oct-2005

Name of Patentee

PRC-DESOTO INTERNATIONAL, INC.

Applicant Address

5430 SAN FERNANDO ROAD, GLENDALE, CA 91209, USA.

Inventors:

#	Inventor's Name	Inventor's Address
1	BALLADARES, ADRIAN	134 VIRGINA STREET #A, EL SEGUNDO, CA 90245, USA.
2	BALLADARES, ADRIAN	134 VIRGINA STREET #A, EL SEGUNDO, CA 90245, USA.

PCT International Classification Number

C08L 81/00

PCT International Application Number

PCT/US2004/011269

PCT International Filing date

2004-04-30

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/466,981	2003-04-30	U.S.A.