AU663265B2 - Composites and methods for making same - Google Patents

Description

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1 Composites and Methods for Making Same Background of the Invention This invention relates to composites and methods for preparing them.

Various processes exist for dispersing solid fillers fibrous or particulate fillers) in solid or liquid matrices to form composite structurei'. These processes include compounding the filler-matrix mixture using blade mixers, high shear Waring-type blenders, roll mills, dough mixers, or internal Brabender-type mixers.

Reaction injection moulding is a moulding process in which one or more liquid or blending reactants are metered separately to a mixing head which combines them eg., by high-impingement mixing. The mixture then is injected into a mould where it polymerises to form a moulded part. In structural reaction injection moulding which is often referred to as reinforced reaction injection moulding reinforcements such as chopped glass fibre or particulate mineral fillers are added to the mixture prior to moulding. In another type of SRIM process, a low viscosity, partially polymerised RIM composition is injected into a mould filled with woven fibre mat, and the resulting composition moulded. In both the RIM and SRIM processes, the moulded parts are coated prior to use to provide ultraviolet protection and to match other parts.

A second type of moulding ,ocess involves premix. Premix is a moulding composition prepared prior to and apart from the moulding operation which contains all the components necessary for moulding, eg., resin, reinforcing agents, fillers, catalysts, release agents, etc. One type of premix is called sheet moulding 'compound SMC is a thin, semi-tacky sheet of thermosetting resin typically reinforced with chopped or continuous strand glass fibres. The sheet can be moulded to form a variety of parts using, eg., matched die moulding techniques.

A second type of premix is called bulk moulding compound BMC is prepared in the form of a putty that can be directly moulded. It can also be Sextruded in the form of a bar or log to facilitate handling. Like the RIM and SRIM moulded products, the moulded premix products also are often coated prior to use.

30 Various types of composites are also known. For example, polymer-based Selectrically conductive composites in the form of coatings or inks) are known.

These composites are rendered electrically conductive by incorporating an electrically conductive additive.

Hybrid composites are structures in which a matrix is reinforced with more than one type of reinforcement. The reinforcing agent present in the largest volume fraction (compared to the other reinforcing agents) is referred to as the primary reinforcing agent, while the remaining reinforcing agents are referred to as secondary reinforcing agents.

IN tIR f3 t of 3A 2 Elastomers have also been filled with a variety of materials. Such materials are used to improve the mechanical or electrical properties of the elastomer matrix, or to reduce cost.

Friction materials are materials which convert an applied force to heat in order to dissipate the force. Examples of applications of such materials include brakes, automatic transmission disks, and clutches. Reinforced organic polymers have been used as friction materials.

Carbon fibrils are carbon filaments having diameters less than 500 nanometres. Examples of particular carbon fibrils and methods for preparing them lo are described in WO89/07163; US. 4 663 230; US. 5 165 909; USSN 5 171 560; W090/07023; and W090/14221, all of which are hereby incorporated by reference in their entirity.

Summary of the Invention According to a broad fo-m of the present invention there is provided an electrically conductive composite comprising a matrix into whict, one or more fillers have been incorporated and said fillers are in the form of agglomerates substantially uniformly dispersed throughout said matrix, wherein said agglomerates have an average size no greater than 1000 times the size of the fillers and said fillers comprise carbon fibrils and/or a dimensional equivalent thereof.

Compounding Process This invention features a compounding process for preparing a composite that includes the steps of introducing one or more fillers and a matrix material into a stirred ball mill, and subjecting the fillers and matrix material to a combination of shear and impact 00g a 25 forces under reaction conditions including reaction time sufficient to reduce the size of agglomerates formed by the fillers to a value below a predetermined value to disperse the fillers throughout the matrix material.

In preferred embodiments, the predetermined value of the agglomerate size is 0 no greater than 1000 times the size of the filler, more preferably ne greater than 100 times, even more preferably no greater than 10 times. One or more of the characteristic dimensions of the filler (which is a measure of its size) preferably is less than 1tm, more preferably less than 0. 1[tm.

A viscosity modifier (ie. a material that modifies the intrinsic viscosity of the matrix-filler mix to facilitate dispersion) is preferably added to the stirred ball mill, Preferred viscosity modifiers include both materials that are removed following the S dispersion step, eg., solvents, and materials that are retained following the dispersion step; an example of the latter type of viscosity modifier is a reactive diluent that chemically reacts with the matrix material. In additional preferred embodiments, one or more milling media (ie. a particulate material that facilitates dispersion by supplying additional impact force) is added to the stirred ball mill.

[G:\WPUSER\LIBCIOO4231JOC Preferred fillers include whiskers (ie. single crystal fibres), discontinuous fibres, particulate fillers, and carbon fibrils. The fibrils preferably are tubes having graphitic layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the projection of the graphite layers on the fibril axis extends for a relatively long distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameters), as described in WO89/01763. These fibrils preferably are also free of a continuous thermal carbon overcoat (ie. pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the fibrils). The fibrils preferably have diameters between 3.5 and 75nm, inclusive, and a length to diameter ratio of at least five. Also preferred are fibrils having this morphology in which the outer surface of the graphitic layers is bonded to a plurality of oxygen-containing groups a carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester, hydroxy, alkoxy, isocyanate, or amide group), or derivatives thereof a sulfhydryl, amino, or imino group).

Preferred matrix materials include metal powder, ceramic powder glass powder), thermoplastic resins, thermoset resins, and elastomers, and matrix materials which are in the form of liquids. Preferred thermoplastic resins include thermoplastic polyester polyethylene terephthalate), polyurethane, polyether ether ketone, polyether sulfone, polyether imide, polyamide nylon), and polyurea resins. Preferred thermoset resins include phenolic, epoxy, thermosetting polyurethane, thermosetting polyester alkyd), polyimide, bismaleimide, polycyclopentadiene, and vinylacrylimide (such as the Arimix resins commercially available from Ashland Chemical Co., Columbus, Ohio). Preferred elastomers include styrene-butadiene rubber, natural rubber, ethylene-propylene-diene monomer (EPDM) rubber, silicone rubber, polybutadiene (both cis and trans 1,4 and 1,2-polybutadiene), polyisoprene, neoprene, chloroprene, fluoroelastomers fluorinated polyethylene), and urethane elastomers.

When the matrix material is a thermoplastic resin, the compounding process preferably includes cooling the contents of the stirred ball mill to a temperature at which the matrix material becomes brittle prior to the dispersion step, and maintaining that temperature throughout the dispersion step.

The invention also features a composite prepared according to the abovedescribed process.

The invention creates composites in which the filler is substantially uniformly dispersed throughout the matrix material, even when the mean filler diameter is on the order of l-im or less, leading to improved composite properties, eg., electrical, optical, mechanical, and magnetic properties. The degree of uniformity (as measured by the size of the filler agglomerates) can be tailored to the particular application for which the composite is intended by adjusting the milling time.

IN 83i10iL3 101 O if 34 The invention also makes it possible to co-disperse a variety of fillers having different diameters and/or shapes in a matrix. Moreover, the invention obviates the need for pre-treating the filler surface or adding chemical dispersants to achieve good filler dispersion throughout the matrix.

Composites for Electrostatic Overcoating This invention features a composite that includes a matrix into which carbon fibrils are incorporated, the amount of the fibrils being sufficient to permit the composite to be directly electrostatically overcoated (ie. without applying a primer coat first).

In one aspect, the composite includes a reaction injection moulded mtrix into which carbon fibrils have been incorporated. In a second aspect, the composite includes the moulded product of a premix that includes a resin matrix into which carbon fibrils have been incorporated. In preferred embodiments, the premix is a sheet moulding compound or a bulk moulding compound. The electrical conductivity of the composite preferably is greater than the electrical conductivity of a composite in which the same matrix is filled with an equivalent amount of carbon black. The amount of fibrils in the composite preferably is sufficient to impart to the composite an electrical conductivity sufficiently high to permit direct electrostatic overcoating. Also preferred are composites in which the amount of fibrils is sufficient to dissipate static electricity. Preferably, the amount is less than or equal to 20% by weight (based on resin), more preferably less than or equal to by weight.

The fibrils preferably are tubes having graphitic layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the 25 projection of the graphite layers on the fibril axis extends for a relatively long distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameters), as described in W089/01763. These S fibrils preferably are also free of a continuous thermal carbon overcoat (ie.

pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the fibrils). The fibrils preferably have diameters between 3.5 and inclusive, and a length to diameter ratio of at least five. Also preferred are fibrils having this morphology in which the outer surface of the graphitic layers is bonded to a plurality of oxygen-containing groups a carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester, hydroxy, alkoxy, isocyanate, or a3 amide group), or derivatives thereof a sulfhydryl, amino, or imino group).

Preferred matrix materials include thermoplastic resins polyamide, polyurethane, polyurea, or an elastomer) and thermoset resins (eg., polydicyclopentadiene, polyester, thermosetting polyurethane, or epoxy resins, or vinylacrylimide resins (such as the Arimix resins commercially available from INA IBC 2)0423 4 ol .34 11111 1

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Ashland Chemical Co., Columbus, Ohio). Resin mixtures may also be used.

Either composite preferably is moulded in the form of an automotive part for a car, truck, or bus.

In a third aspect, the invention features a composite in a form suitable for reaction injection moulding that includes one or more liquid reactants capable of polymerising to form a reaction injection moulded matrix and carbon fibrils.

In a fourth aspect, the invention features a premix that includes a resin into which carbon fibrils are incorporated.

In preferred embodiments, the liquid reactants include one or more polyols, o1 polyisocyanates, or polyamines. The premix preferably is a bulk moulding compound or a sheet moulding compound. The amount of fibrils is preferably less than or equal to 20% by weight, more preferably less than or equal to 4% by weight. Preferred fibrils and resins are those described above.

The invention also features methods for preparing the above-described composites.

The reaction injection moulded composite is prepared by a method that includes mixing the fibrils with liquid reactants capable of polymerising to form the matrix; introducing the mixture into a mould; and moulding the mixture under reaction conditions including pressure and temperature to prepare the composite in the form of a moulded part.

The sheet moulding compound composite is prepared by a method that includes mixing the fibrils with a resin and forming the mixture into a sheet. The bulk moulding compound composite is prepared by a method that includes mixing the fibrils with a resin to form a putty suitable for moulding. Both methods preferably include a moulding step in which the composite is prepared in the form of a moulded part under reaction conditions that include temperatue and pressure.

The moulded parts prepared according to the above-described methods are preferably directly electrostatically coated once moulding is complete.

The invention provides reaction injection moulded composites and moulded 0. 3o composites prepared from premix sheet moulding compound or bulk moulding compound) that are electrically conductive at relatively low fibril loadings. This enables moulded parts prepared from the composites to be electrostatically coated just as metal parts currently are, thereby eliminating the need for applying a conductive primer coat in a separate application. Further advantages that the fibrils provide include good mechanical properties (eg., hardness and impact strength) and the ability to use reduced amounts of additives such as flame retardants. The fibrils also provide inherent EMI shielding.

The use of fibrils offers several processing advantages as well, including good batch to batch consistency with respect to electrical and mechanical properties. In the case of RIM processing, the fibrils, due to their small size, do not plug small IN ALSN 00121 UW I o 34 lines and orifices in the processing equipment at the low fibril loadings used.

Moreover, the fibrils need not become preferentially oriented during processing; thus, they do not contribute to part warpage. In the case of SMC, the increase in viscosity due to the fibrils makes it possible s to eliminate thickeners needed to form the tacky sheet.

Electrically Conductive Coatings and Inks This invention features an electrically conductive composite in a form suitable for applying to the surface of a substrate, the composite comprises a polymeric binder into which carbon fibrils are incorporated.

In preferred embodiments, the composite is in the form of a powder or liquid coating. The amount of fibrils in the coating preferably is sufficiently high to permit a substrate to which the coating is applied to be electrostatically overcoated directly. Preferably, the amount is less than or equal to 15% by weight (based on resin), more preferably between 0.5 and 10% by weight. Even more preferred are coatings in which the amount of fibrils is between I and 4% by weight. The coatings may include one or more pigments.

In another preferred embodiment, the coating is in the form of a resistive ink suitable for screen printing on the surface of a substrate to form an electronic component. Preferably, the amount of fibrils in the resistive ink is sufficient to decrease bulk resistivity of the binder to a value between 10' 2 and 106 cm (more preferably between 10-' and 10 4 cm) when applied to a substrate. The preferred amount of fibrils is between 1 and 30% by weight.

In another preferred embodiment, the coating further comprises electrically conductive graphite or metal particles silver flakes, metal-coated chopped fibres, or metal powder) and is in the form of conductive ink suitable for printing on the surface of a substrate; the amount of fibrils in the ink is sufficient to decrease the bulk resistivity of the particle-filled binder (measured in the absence of carbon fibrils) by a predetermined amount when applied to a substrate.

Preferably, the bulk resistivity of the particle-filled binder is greater than Iccm 30 and the amount of fibrils is sufficient to reduce the bulk resistivity to less than l)cm. Even more preferred are conductive inks in which the bulk resistivity of the particle-filled binder is greater than 10 *ncm and the amount of fibrils is sufficient to reduce the bulk resistivity to less than 10"lcm. The preferred amount of fibrils is between 20 and 50% by weight.

The fibrils preferably are tubes having graphitic layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the projection of the graphite layers on the fibril axis extends for a relatively long distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameters), as described in WO89/01763. These IN IiEt I- p_4. 1 0Itt 6 of 14 7 fibrils preferably are also free of a continuous thermal carbon overcoat (ie.

pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the fibrils). The fibrils preferably have diameters between 3.5 and sive, and a length to diameter ratio of at least five.

Preicfred polymeric binders include thermoplastic resins polyethylene, polypropylene, polyamide, polyurethane, polyvinyl chloride, or thermoplastic polyester resin such as polyethylene terephthalate) and thermoset resins a thermosetting polyester resin or an epoxy resin).

The invention also features a substrate coated with a fibril-filled electrically o1 conductive composite. Preferably, the conductivity of the composite is sufficiently high to permit the coated substrate to be electrostatically overcoated directly. Also preferred are substrates for printed circuit boards in which the composite is a resistive ink printed on the substrate in the form of an electronic component a resistor) or a conductive ink printed on the substrate in the form of a conductive trace for electrically connecting electronic components. Also featured are methods for preparing coated substrates (which are amenable to direct electrostatic coating) and for screen printing fibril-filled inks on a substrate.

The fibril-filled composites are electrically conductive at low fibril loadings.

As a result, coatings and inks having predetermined resistivity values can be prepared without excessive increases in viscosity due to the added fibrils; such increases are undesirable because they make application difficult. The properties of the composites also do not vary significantly from batch to batch because the fibrils exhibit good resistance to shear degradation caused by the shear mixing used to prepare the composites. In addition, the resistivity of the composites is 23 relatively insensitive to temperature fluctuations.

When used as a primer on a moulded part an automotive part) for subsequent electrostatic overcoating, the coatings permit direct electrostatic overcoating at lower energy, thereby reducing corona effects and providing Suniform coverage. Moreover, the fibril-filled composites can be overpigmented so 30 that the finished composite does not appear black. The coatings are also sufficiently electrically conductive to be used in combination with sacrificial anode materials on the exposed surface of a metal or moulded plastic part to help prevent corrosion, When applied to plastic substrates, the coatings exhibit good mechanical adhesion and permit metal to be plated directly onto the plastic.

Fibril-filled composites in the form of resistive or conductive inks offer additional advantages. When printed on a substrate, the resistivity of the ink and its ability to adhere to the substrate do not deteriorate due to creasing or bending of the substrate. The inks are also scuff- and scratch-resistant. In the case of conductive inks, the fibril-filled inks are lighter than inks in which the conductive filler is 100% metal particles (thereby facilitating application) and exhibit improved IN LIACI:-423 l 7 I of 14 corrosion resistance. Moreover, the fibrils allow the resistivity of the metal particle-containing conductive inks to be fine tuned for application-specific uses, thereby achieving resistivity values not readily attainable using metal particles alone.

Elastomers This invention features a composite in which carbon fibrils are incorporated in an elastomer matrix. In one aspect, the fibrils are characterised as having a morphology consisting of tubes that are free of a continuous thermal carbon overcoat (ie. pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the fibrils) and have graphitic layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the projection of the graphite layers on the fibril axis extends for a relatively long distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameiers), as described in W089/07163. These fibrils preferably have diameters less than 100nm, more preferably between and 75nm, inclusive, and a length to diameter ratio of between 5 and 100.

In a second aspect, the fibrils are characterised as having a crystalline graphitic structure and a morphology defined by a fishbone-like arrangement of the graphite layers along the fibril axis. Examples of such fibrils are described in the aforementioned WO/89/07163 and in EP 0 198 558. These fibrils preferably have diameters less than 100nm.

The amount of fibrils in the composite is preferably sufficiently high to permit S curing of the composite by resistive or inductive heating or to permit at least one of S the physical properties of the composite to be monitored electrically; preferably, 25 this amount is less than 25 parts per 100 parts of elastomer, more preferably less than 10 parts per 100 parts of elastomer. In the case of masterbatches (ie. fibrilfilled elastomer precursors which are subsequently blended with additional elastomer in order to prepare the final composite structures), however, the amount of fibrils is preferably greater than 25 parts per 100 parts of elastomer.

30 Preferred elastomer matrices include natural rubber, styrene-butadiene rubber (both random and block copolymers), polyisoprene, neoprene, chloroprene, polybutadiene (both cis and trans 1,4 and 1,2-polybutadienes), fluorolastomers fluorinated polyethylene), silicone rubbers, and urethane elastomers. In addition to the fibrils, the elastomer preferably contains one or more fillers, eg., carbon black, silica, or a combination thereof; the ratio of the amount of fibrils in the composite to the total amount of the fillers is at least 1:4 or better 1:6, etc.). The composites are preferably provided in the form of a tyre or component thereof tyre tread or casing), seal, solution, or adhesive.

IN L :IOI:43 -orC 80 34

I

In a third aspect, the invention features a method for curing an elastomer that includes the steps of preparing a composite by incorporating carbon fibrils in an elastomer matrix, the amount of the fibrils being sufficient to impart to the composite an electrical conductivity sufficiently high to permit resistive or inductive heating, and heating the composite resistively or inductively to effect cure.

In a fourth aspect, the invention features a method for monitoring the physical condition of an elastomer that includes the steps of preparing a composite by incorporating an electrically conductive additive in an elastomer matrix, the amount of the additive being sufficient to impart to the composite an electrical conductivity sufficiently high to permit the physical condition of the elastomer to be monitored electrically, and monitoring the electrical properties resistivity) of the composite as an indication of the physical condition of the elastomer. In a preferred embodiment of this aspect, the electrically conductive additive includes 1i carbon fibrils. In another preferred embodiment, the composite is in the form of a tyre and ihe pressure inside the tyre is monitored. The method is also preferably used to monitor an elastomer in the form of a conveyor belt or hose) ,or the presence of rips, tears, or perforations.

In preferred embodiments of the third and fourth aspects, the amount of fibrils in the composite is less than 25 parts per 100 parts elastomer, more preferably less than 10 parts per 100 parts elastomer. Preferred fibrils are those described above.

In a fifth aspect, the invention features a method for preparing an elastomer composite that includes the steps of preparing a masterbatch by dispersing in an S 25 elastomer at least 25 parts of fibrils per 100 parts of elastomer, and compounding a predetermined portion of the masterbatch with an additional amount of an elastomer which may be the same as or different from the elastomer used to prepare the masterbatch) to prepare the composite. Preferably, the amount of fibrils in the final composite is less than 25 parts per 100 parts elastomer, more so preferably less than 10 parts. Preferred fibrils are as described above. Carbon black may also be added to the composite, either during preparation of the masterbatch or during the compounding step.

In a sixth aspect, the invention features a method for reinforcing an elastomer that includes incorporating into an elastomer matrix an amount of carbon fibrils sufficient to improve the mechanical properties of the elastomer. The fibrils are as described above for the first and second aspects of the invention.

The invention provides fibril-reinforced elastomer composites exhibiting good stiffness, tensile strength, tear strength, creep and die swell resistance, and green strength (ie. strength prior to cure). The composites also exhibit good hardness, stress-strain properties, and abrasion resistance (even with relatively soft elastomer IN >tIBCICC42J JOt 3 of I" matrices), and have low specific gravity. The improved abrasion resistance makes it possible to achieve an advantageous balance of traction, rolling resistance, and tread wear in articles fabricated from the composites. Moreover, these advantages are achieved at low fibril loadings.

Further advantages result from the electrical properties of the fibrils. Because the fibrils are electrically conductive, they can be used to perform the dual functions of reinforcing an elastomer matrix and at the same time rendering the matrix electrically conductive. The electrically conductive composites can be cured by resistive or inductive heating, thus avoiding the problems of thermal transfer and high cost often associated with conventional heat curing. The ability to be cured electrically makes the fibril-filled composites particularly useful as adhesives in a variety of bonding operations such as forming rubber-rubber bonds in bonding tyre treads to tyre casings), rubber-metal bonds, and rubberceramic bonds, and in rubber repair systems for products such as tyres and conveyor belts.

The electrical conductivity of the composites is also useful in applications such as the extrusion of rubber tubes, treads, and related products. In addition, the composites can be partially electrically cured to impart additional dimensional stability to the composite. The invention also makes possible the design products in which physical changes in the composite such as internal pressure can be monitored electrically. For example, the state of a tyre, air spring, hose, or conveyor belt can be monitored simply and effectively.

Friction Materials This invention features, in a first aspect, a brake or component thereof 25 prepared from a friction material that includes a matrix into which carbon fibrils have been incorporated.

In a second aspect, the invention features a clutch or component thereof prepared from a friction material that includes a matrix into which carbon fibrils have been incorporated.

30 In a third aspect, the invention features an automatic transmission disk or component thereof prepared from a friction material that includes a matrix into which carbon fibrils have been incorporated.

In a fourth aspect, the invention features a composite in the form of a friction material that includes a matrix into which carbon fibrils have been incorporated.

In preferred embodiments, the amount of fibrils is less than or equal to by weight (based on resin), more preferably between 5 and 10% by weight.

The fibrils preferably are tubes having graphitic layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the projection of the graphite layers on the fibril axis extends for a relatively long INALIC100423 JOC 10o( 34 distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameters), as described in W089/07163. These fibrils preferably are also free of a continuous thermal carbon overcoat (ie.

pyrolytically deposited carbon resulting from thermal cracking of the gas feed used s to prepare the fibrils). The fibrils preferably have diameters between 3.5 and inclusive, and a length to diameter ratio of at least five. Also preferred are fibrils having this morphology in which the outer surface of the graphitic layers is bonded to a plurality of oxygen-containing groups a carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester, hydroxy, alkoxy, isocyanate, or amide group), or derivatives thereof a sulfhydryl, amino, or imino group).

Preferred matrix materials are carbon and thermosetting resins, eg., phenolic, polyester, and epoxy resins. One or more additional fillers preferably are added as well. Examples of preferred fillers include metal, glass, ceramic, carbon, or polyaramide fibres, or particulates such as graphite, clay, barium sulfate, diatomaceous earth, silica, magnesia, beryllia, alumina, silicon carbide, boron carbide, titanium dioxide, or carbon black. Examples of preferred applications for the friction materials include clutches, automatic transmission disks, and brakes linings for brake pads and shoes).

Articles fabricated from the friction materials prepared from fibril-containing composites exhibit good friction properties and fade resistance. These properties are retained at elevated temperatures, a quality particularly useful for heavy duty applications including off-road vehicles, racing cars, heavy machinery, and automotive disc brakes which are often subjected to such temperatures. Moreover, the friction materials resist spalling and cracking at elevated temperatures.

25 Hybrid Composites This invention features, in a first aspect, a hybrid composite that includes a matrix into which is incorporated a primary fibrous reinforcing agent and a secondary reinforcing agent uniformly dispersed throughout the matrix and randomly oriented relative to the primary reinforcing agent.

30 In preferred embodiments, the mean diameter of the primary reinforcing agent is at least 10 times greater than the mean diameter of the secondary reinforcing agent, more preferably at least 100 times greater. The majority of agglomerates formed by the secondary reinforcing agent in the matrix preferably are no greater than 10in, preferably no greater than The secondary reinforcing agent preferably includes carbon microfibres (ie.

carbon fibres having diameters less than or equal to Ilm), whiskers (ie. single crystal fibres), chopped fibres (ie. discontinuous fibres whose lengths are on the order of 1.5mm to 50mm), and particulate materials, eg., silica or carbon black.

Also preferred are carbon fibrils, preferably those which are tubes having graphitic I J8GIBCCI 423 JC I of 34 layers that are substantially parallel to the fibril axis. One aspect of substantial parallelism is that the projection of the graphite layers on the fibril axis extends for a relatively long distance in terms of the external diameter of the fibril at least two fibril diameters, preferably at least five diameters), as described in W089/07163. These fibrils preferably are also free of a continuous thermal carbon overcoat (ie. pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare the fibrils). The fibrils preferably have diameters between 3.5 and 75nm, inclusive, and a length to diameter ratio of at least five.

The amount of the secondary reinforcing agent incorporated in the matrix preferably is less than or equal to 20% by volume, more preferably between 1 and by volume.

Preferred primary reinforcing agents include continuous fibres. Examples of preferred continuous fibres include carbon, glass, ceramic boron, alumina, or silicon carbide), and polyaramide Kevlar) fibres. These fibres may be woven, knit, crimped, or straight. Also preferred are primary reinforcing agents which include discontinuous fibres made of the same types of materials as the continuous fibres.

Preferred matrix materials include organic thermoset and thermoplastic resins. Examples of preferred thermoset resins include epoxy, bismaleimide, polyimide, and polyester resins. Examples of preferred thermoplastic resins include polyethylene, polypropylene, polyamide nylon), polyurethane, polyvinyl chloride, thermoplastic polyester resin, polyether ether ketone, polyether sulfone, polyether imide, oriented polyethylene, liquid crystalline polymers, and reaction injection moulded resins. Other preferred matrix materials include inorganic polymers a polymeric inorganic oxide such as glass), metals (eg., aluminium or titanium alloys), ceramics Portland cement or concrete), and carbon.

In a second aspect, the invention features a hybrid composite that includes a matrix into which is incorporated a primary fibrous reinforcing agent and a secondary fibrous reinforcing agent, the primary reinforcing agent having a mean diameter that is at least 1000 times greater than the mean diameter of the secondary reinforcing agent.

In preferred embodiments of the second aspect, the secondary reinforcing agent is dispersed uniformly throughout the matrix and randomly oriented relative as to the primary reinforcing agent. Preferred secondary reinforcing agents are carbon fibrils, as described above. Preferred matrix materials, primary reinforcing agents, agglomerate sizes, and amounts of secondary reinforcing agents are as described above.

The invention also features methods for preparing the hybrid composites.

!4 F 4 t I of 4 The invention provides hybrid composites having properties not attainable in composites containing only primary reinforcing agents. Because the secondary reinforcing agent is randomly oriented relative to the primary reinforcing agent and uniformly dispersed throughout the matrix (as measured by the small agglomerate size throughout the matrix), transverse and interlaminar properties, which ordinarily are dominated by the matrix rather than the primary reinforcing agent, are improved. Moreover, because the secondary reinforcing agent is substantially smaller than the primary reinforcing agent, its incorporation into the matrix does not impair the properties of the primary reinforcing agent. In addition, dispersing the secondary reinforcing agent throughout the matrix, rather than between layers of the primary reinforcing agent, avoids disrupting or distorting the primary reinforcement weave or lay-up.

Other features and advantages will be apparent from the following description of the preferred embodiments thereof, and from the claims.

Description of the Preferred Embodiments We first briefly describe the Figure.

The Figure is a schematic cross-sectional representation of a two-dimensional hybrid composite embodying the invention.

Compounding Process Composites are preferably prepared by introducing the matrix material and one or more fillers into a stirred ball mill of the type conventionally used for powder comminution. In the mill, these materials are subjected to both shearing forces due to the stirring action of a mechanical rotor and impact forces due to particulate milling media of the type conventionally used for powder comminution which are added to the mill during stirring; these particulates are removed once the milling operation is over. In the case of metal and ceramic matrices, however, it is not necessary to add separate milling media because the matrices themselves (which are added in the form of powders) are capable of supplying the impact force.

30 A viscosity modifier is added to viscous matrix-filler mixes to lower the intrinsic viscosity to a value sufficiently low to permit easy milling. Viscosity modifiers are particularly useful when the matrix material is a high molecular e. weight thermoplastic or a partially cured thermoset resin, Examples of suitable viscosity modifiers include solvents such as water, toluene, acetone, methyl ethyl ketone (MEK), isopropanol, or mineral oil. Following the milling operation the solvent is removed, eg., by vacuum drying, steam stripping, or freeze drying. The viscosity modifier may also be a material which becomes part of the matrix or filler once milling is complete. Examples of such modifiers include monomers called I N V :C1 4.3 I 34 14 reactive diluents styrene, triallylcyanurate, diallycyanurate, multi-functional acrylates, and divinylbenzene) which chemically react with the matrix material during milling. The viscosity modifier may also be built into the matrix. In such cases, the viscosity modifier may be present during manufacture of the matrix, eg., in solutions of solution-polymerised SBR and solutions of thermoplastics obtained from the polymerisation reaction.

Suitable fillers include discontinuous fibres chopped glass or carbon fibres), whiskers carbon or silicon carbide whiskers), particulate fillers (eg., silica or carbon black), carbon fibrils, or a combination of any or all of these fillers. Preferably, the mean filler diameter (ie. the diameter of the individual grains or fibres making up the filler) is on the order of a micron or less. Preferred fibrils have small diameters (preferably between 3.5 and 75nm, graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; US 5 165 909; USSN 871,676; W089/07163; and W090/07023. These fibrils are prepared as described in the aforementioned patent and patent applications. The fibrils may also be treated to introduce oxygen-containing functional groups onto the fibril •surface, as described in W090/14421. Preferred matrix materials include metal S and ceramic glass) powders, and organic matrices, eg., thermoplastic, 20 thermoset, and elastomer resins, as described in the Summary of the Invention, above. The preparation of carbon fibril-filled elastomers is described in Barber et al., USSN 368,828 entitled "Fibril-Filled Elastomers", and is hereby incorporated by reference in its entirety. In the case of thermoplastic resins, the composites are preferably prepared by introducing the resin and fillers into the stirred ball mill, 25 and then adding dry ice to the mill to cool the contents to a temperature at or near which the resin is transformed into a brittle solid. In this form, the resin is more easily broken up during milling, leading to more uniform dispersions. The dry ice evaporates during milling so that none is retained in the final dispersion.

The milling time determines the final size of the filler agglomerates and thus o30 the degree of dispersion, which in turn is a function of the end use for which the composite is targeted. For example, electrical applications, which rely on interparticle contact to establish a conductive network, can tolerate larger agglomerates than mechanical applications, where the agglomerates act as strengthlowering defects.

A composite in which carbon fibrils (prepared as described above) were dispersed in a styrene butadiene rubber (SBR) matrix was prepared using the above-described stirred ball milling procedure and its properties compared to a fibril-reinforced SBR matrix prepared using conventional internal mixing and roll milling compounding techniques. The results, which are shown in Table I, r" 1j demonstrate that the composite prepared using the stirred ball mill exhibits superior [G:\WPUSERLiCJC00423:JOC 1 3-11 properties.

Table I Property Roll Mill Ball Mill Ultimate Tensile Strength (MPa) 6.7 10.1 Elongation at Break 255 395 Modulus at Elongation (MPa) 100% 2.8 3.1 200% 5.2 5.4 300% Hardness (IRED) 64 64 Trouser Tear (KN/M) 5.4 Ring Fatigue (Kilocycles to failure) 12 DIN Abrasion: Loss 203 189 Index 95 102 Heat Build-up 70 Resistivity (Qcm) 2190 42 The compounding method can also be used to prepare prepregs for hybrid composites as described in Creehan et al., USSN 386,822 entitled "Hybrid 5 Composites", and is hereby incorporated by reference in its entirety.

i" Composites for Electrostatic Overcoating By way of the following examples, the preparation of sheet moulding compound (SMC) composites, bulk moulding compound (BMC) composites, and reaction injection moulded (RIM) composites into which carbon fibrils have been S 10 incorporated are described. Preferred fibrils have small diameters (preferably S: between 3.5 and 75nm), graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; US 5 171 560; US 5 165 909; W089/07163; and S' WO/90/07023. These fibrils are prepared as described in the aforementioned patent and patent applications. The fibrils may also be treated to introduce oxygencontaining functional groups onto the fibril surface, as described in W090/14421.

Example 1 RIM Fibril-containing RIM composites are prepared using conventional RIM processing equipment. Such equipment typically includes a material conditioning system, a high pressure metering system, a mix head, a mould, and a mould carrier.

The material conditioning system includes tanks that hold the reactants for preparing the composite (each reactant being stored in a separate tank), agitators to IG:\WPUSER\LIBC100423;JOC 16 maintain homogeneous temperature and composition conditions throughout the tanks, and a temperature control system for maintaining the proper level of dissolved gases in the reactants. The fibrils are preferably pre-mixed with one or more of the reactants in an amount sufficient to result in 1-4 weight fibrils in the s final moulded product. Additional tanks store additives such as pigments and catalysts, as well as any additional reinforcement, eg., chopped glass fibres.

Preferred reactants include polyols and polyisocyanates (for preparing polyurethane matrices) and polyamines and polyisocyanates (for preparing polyurea matrices).

The metering system, which typically consists of, eg., high pressure axial or radial piston pumps or lance-displacement cylinders, meters the proper amount of reactants, fibrils, and any additional fillers to the mixing head. The mixing head contains a chamber in which the reactants and fillers are mixed by direct impingement at pressures between, for example, 10 340 and 24 130kPa. When mixing is complete, the mixture is transported to a mould where the reactants polymerise to form the final part. Suitable mould constructions include machined steel or aluminium, cast aluminium or kirksite, spray metal or electroplated shells, and filled epoxy resin. Typical in-mould pressures during polymerisation are 170 to 690kPa. The moulding temperature varies according to the particular reactants being used, as one of ordinary skill in the art will readily appreciate. In the case of polyurethane forming reactants, the mould temperature is about 54 0 C 38 0

A

mould carrier orients the mould, provides a clamping force to overcome the inmould pressure, opens and closes the mould, and positions the mould for removal of the finished part, cleaning, and preparation for the next moulding operation.

The fibril-containing RIM composites are useful in a wide variety of moulded industrial and consumer products. They are particularly useful in automotive parts, eg., bumpers, trim parts, fascia, integral window seals, steering wheels, armrests, protective covers, and body panels for cars, trucks, or buses. The parts are coated prior to use. By incorporating carbon fibrils, the part can be electrostatically coated, making fabrication compatible with the processing of metal parts.

30 Example 2 SMC Fibril-containing SMC composites are prepared using conventional SMC processing equipment. This equipment, which may be continuous belt or beltless, typically includes a mixing system, a paste metering system, a compaction systen., and a take-up system.

The mixing system compounds the uncured resin (typically an unsaturated, thermosetting polyester or epoxy resin which cures upon application of heat) and additives such as catalysts, fillers, thickeners, mould release agents, pigments, thermoplastic polymers polyvinyl chloride polymers and copolymers and polyethylene powders for minimising shrinkage during moulding), flame IN l t10 4 3 ,16 of 34 -e ~~L retardants, and ultraviolet absorbers into a paste having the consistency of pancake batter suitable for forming into a sheet. The paste also contains carbon fibrils.

The mixing system may be of the batch, batch/continuous, or continuous type.

The paste is transported from the mixing system to a paste reservoir which, with the aid of adjustable doctor blad.- meters a predetermined thickness of paste onto upper and lower plastic polyethylene) carrier films. The height of the doctor blades determines the amount of resin paste in the final SMC composite.

Between the two paste-covered sheets, reinforcing agents, eg., chopped glass strand or continuous glass roving are applied to form a sandwich. Additional carbon fibrils may also be added at this stage. The total amount of carbon fibrils (ie. the sum of the fibrils added during compounding of the paste plus any fibrils applied directly to the paste-covered sheets) preferably is between 1 and 4% by weight based upon resin.

A compactor compresses the sandwich to ensure that the resin paste wets the fibrils and any other reinforcement. Typically, the compactor consists of a series of serrated steel rollers or a dual wire mesh belt compaction module. The sheet exiting the compactor is then taken up, eg., by a wind-up turret to form a roll.

When a full roll of the composite is ready, the sheet (which typically is 600mm to wide) is cut and transferred to a second wind-up turret. The roll is then taped to prevent unwinding and a vapour barrier sleeve applied to prevent ultraviolet or moisture contamination. The roll is stored in a maturation room maintained at about 29 to 32 0 C for approximately 1 to 7 days to provide a uniform, reproducible viscosity for moulding. The sheet is then cut and moulded into the desired part using, eg., compression or matched die moulding.

The moulded components thus prepared are useful in a variety of applications. In the automotive industry, they are useful as components of heating and ventilating systems, hoods, trunks, side panels, fenders, roof panels, front end panels incorporating fender extensions, mounts for headlamps and grilles, and cab components hoods) for trucks. The moulded composites are also useful as :i so 30 electrical switchgear housings, housings for hand power tools such as electric drills, and housings for appliances such as air conditioners and dishwashers. As in the case of the fibril-containing RIM composites, the parts can be electrostatically coated.

Example 3 BMC Fibril-containing BMC composites are prepared using conventional BMC processing equipment. Typically, this equipment consists of two mixers. The first mixer, eg., a simple propeller type, or dissolver or disperser of the kind used in the paint industry, is used to mix the resin unsaturated thermosetting polyester or epoxy resin as in the case of SMC composites) and additives such as particulate NI&i C1,43 17 of 34 fillers, mould release agents, colorants, catalyst, thickeners, and low profile additives. The carbon fibrils also are preferably added to the resin mix. The components are well-mixed to disperse the additives and fibrils throughout the resin. The resulting mixture is then transferred to a second, heavy duty mixer, eg., a dough mixer or double arm mixer, and additional reinforcing agents such glass fibres (in the form of chopped strand or chopped spun roving), asbestos, sisal, and organic fibres are added. An additional amount of carbon fibrils may also be added at this time. The total amount of carbon fibrils ie. the sum of the fibrils added during both mixing stages) is between 1 and 4% by weight based upon resin.

The second mixer mixes the components until the resulting mixture has the consistency of putty. The putty is then aged for about 4 hours at 25 0

C).

When aging is complete, the putty can be moulded directly or stored in a sealed, refrigerated, plastic bag until needed. The putty can also be extruded in the form of bars or logs prior to aging to facilitate handling and storage.

The fibril-reinforced BMC premix is moulded using conventional thermoset moulding techniques, eg., compression, transfer, or thermoset injection moulding at pressures sufficient to cause the premix to flow into the extremities of the mould; typical moulding pressures range from about 689 to 10 342kPa. The 20 moulded parts are useful in many of the same applications as SMC moulded parts.

Additional uses include automobile heater housings and related ducting. Like the RIM and SMC moulded parts, the BMC moulded parts can be electrostatically coating without prior application of an electrically conductive primer coat.

in addition to the above-described examples, fibrils incorporated into a wide variety of matrices both thermoplastic and thermoset matrices) in order to render the resulting composite sufficiently electrically conductive to permit direct electrostatic overcoating.

Conductive Coatings and Inks A. Powder and Liquid Coatings Both powder and liquid coatings consist of a polymeric binder into which carbon fibrils are incorporated. Preferred binders for the powder coatings include the following thermoset resins: urethane polyesters, epoxy, epoxy polyesters, polyester triglycidyl isocyanurates, and urethane or epoxy-type polyesters.

Suitable thermoplastic resins include polyethylene, polypropylene, polyamide (eg., nylon), polyvinyl chloride, and thermoplastic polyesters polyethylene terephthalate). The molecular weight of the binder is sufficiently high such that it is a solid at room temperature. In the case of liquid coatings, preferred resins are thermoplastic polyesters and polyurethanes. The molecular weight of the binder is sufficiently low such that it is a liquid at room temperature.

,r vk ic'C4' q4,1 k Preferably, between 1 and 4% (by weight of resin) of carbon fibrils are incorporated into the 'binder to form an electrically conductive coating. Such loadings are sufficient to permit direct electrostatic overcoating of a dielectric part a plastic) to which the coating is applied. The resistivities of these coatings following application typically are on the order of 106 cm or less.

Preferred fibrils have small diameters (preferably between 3.5 and graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; USSN 871,675; US 5 165 909; W089/01763; and W090/07023. These fibrils are prepared as described in the aforementioned patent and patent applications. The fibrils may also be treated to introduce oxygen-containing functional groups onto the fibril surface, as described in W090/14421.

The coatings are prepared by combining the binder, fibrils, and additives such as pigments under shear mixing. Once the mixing is complete, the coatings are applied Idirectly to a metal or moulded plastic part or stored until needed.

The coatings are applied electrostatically in the mould to sheet moulding compound (SMC) and bulk moulding compound (BMC) compression moulded parts such as automotive body panels. The coated part can then be used as is or electrostatically overcoated with a second coating, eg., a finishing coat. In either 20 case, the addition of the fibrils to the binder to render the coating electrically conductive makes direct electrostatic overcoating possible.

B. Inks Preferred polymeric binders for the resistive and conductive inks are thermoset epoxy resins and thermoplastic polyester resins polyethylene 2s terephthalate). The inks may be provided in the form of solutions or solvent :i dispersions.

S. Preferred fibrils are those described above in the case of the powder and liquid coatings. The amount of fibrils incorporated in the binder is a function of the ,desired resistivity level, which in turn is governed by the application for which 30 the inks are intended. In general, for resistive inks having resistivities ranging from 10" 2 to 106cm, from 1 to 30% by weight of fibrils are incorporated. In the case of conductive inks, which already have relatively low resistivities due to the presence of eg., silver flakes, the fibrils are used to fine tune the resistivity of the ink, making it possible to achieve resistivity values that are impractical or impossible to obtain simply by adjusting the amount of silver flakes; thus, the amount of fibrils incorporated depends on the resistivity of the silver-filled binder and the targeted resistivity value. In general, between 20 and 50% by weight of fibrils are incorporated to lower the resistivity of silver-filled binders Inving resistivities 1lcm to a value I0cm.

INUA 4.4 VP10 A 14 t7 The inks are prepared using the same procedures described above for the conductive powder and liquid coatings. They are then screen printed on a substrate such as a printed circuit board substrate or a disposable donor sheet for such a substrate to form electronic components such as resistors (in the case of resistive inks) or conductive traces for interconnecting electronic components (in the case of conductive inks) by conventional screen printing techniques. The consistent conductivity of the inks eliminates the need for laser trimming, allowing the inks to be used in multilayer moulded circuit boards.

Elastomers The composites are prepared by dispersing fibrils in an elastomer matrix.

Preferred fibrils have small diameters (preferably between 3.5 and graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; US 5 171 560; US 5 165 909; W089/01763; and W090/07023. These fibrils are prepared as described in the aforementioned patent and patent applications. The fibrils may also be treated to introduce oxygen-containing functional groups onto the fibril surface, as described in W090/14421. Preferred elastomer matrices 0;6. include natural rubber, styrene-butadiene rubber (both random and block copolymers), polyisoprene, neoprene, chloroprene, polybutadiene (both cis and 20 trans 1,4 and 1,2-polybutadienes), fluoroelastomers fluorinated polyethylene), silicone rubbers, and urethane elastomers Spandex).

Low fibril loadings are preferred. In general, between 1 and 10 parts of fibrils are added per 100 parts elastomer. Fillers such as carbon black and silica may also be added; preferably, four parts filler are used for every one part fibrils.

25 The particular compounding method used to prepare the fibril-filled elastomer composites depends on the end property sought, the type of elastomer matrix, the degree of dispersion required, and the type of fillers added in addition to the fibrils. For example, in rubber matrices such as natural rubber which have a significant measure of strength even in the absence of any separately added S 30 reinforcing agents, conventional compounding equipment such as Banbury and two-roll mills can be used to prepare the composite. Where a high degree of uniform dispersion is desired, however, the fibrils are first broken up using techniques such as ball-milling. A particularly effective method for achieving welldispersed mixtures involves combining the fibrils, elastomer matrix, and any other fillers with a low viscosity additive an oil or liquid solvent) and a milling promoter abrasive particles) to form a slurry, and then agitating that slurry at high speeds in, eg., a stirred ball mill or attritor, as described in Creehan, EPO 04844447 entitled "Preparation of Uniform Dispersions", which is hereby incorporated by reference in its entirety, The viscosity modifier may also be built into the matrix, eg., in the case of solution polymerised SBR. Once agitation is complete, any solvents can be removed by, eg., vacuum drying, steam stripping, or freeze drying. The mixtures can then be moulded as is or subjected to further high shear compounding in, eg., the Banbury or two-roll mill and then moulded.

During compounding, the amount of fibrils may be chosen so as to match the desired amount of fibrils in the final composite and added directly to the elastomer matrix. However, the fibril-filled composites may also be prepred by first combining a high (25 parts) amount of fibrils with the elastomer to form a masterbatch. An appropriate amount of the masterbatch designed to achieve the targeted amount of fibrils in the final composite (eg. 5-10 parts) is then compounded with additional elastomer as described above to form the final composite.

The composites can be moulded by application of heat or by resistive or inductive heating into a variety of articles using conventional elastomer moulding techniques. Particularly useful articles include tyres and tyre components such as treads and casings, seals, and vibration damping agents. The uncured composites are useful as adhesives and bonding agents, eg., as repair compounds for tyres and conveyors. The adhesive can be cured in place by inductive or resistive heating.

The physical properties of articles prepared from the fibril-filled elastomers (eg., 20 the air pressure of a tyre) can be monitored electrically.

In addition to the above-described carbon fibrils, for example, fibrils having a crystalline graphitic structure and a morphology defined by a fishbone-like arrangement of the graphite layers along the fibril axis, as described in EP 0 198 558, are also suitable. These fibrils are prepared by vapour phase deposition of hydrocarbon gas onto a monocrystalline metal particle catalyst iron) having a diameter of at least 5nm at temperatures between 250 and 800 0

C.

Friction Materials Preferred friction materials contain an organic resin binder into which carbon fibrils and other fillers are incorporated. The relative amounts of the ingredients depend on the particular application for which the friction nmterial is intended, For example, for heavy duty applications such as brake s)ies for large trucks where fade resistance and stopping power are critical, lat amounts of fibrils may be used compared to disc brake pads for automobile:,. Typically, the amount of fibrils is up to 20% by weight of the composition bawd on resin.

The resin binder must be able to withstan: the elevated temperatures encountered in use. Phenolic resins, because of theitr superior resistance to thermal degradation and relatively low cost, are preferri;-., Preferred fillers in addition to the fibrils include metal brass) fibres, polyaramide fibres Kevlar fibres available commercially from E.I. Du Pont de Nemours and mineral fillers IN 1161 MfAit' 10f 1 9 14 such as diatomaceous earth and barium sulfate, graphite, and chopped carbon fibres. Incorporating the fibrils makes it possible to reduce the amounts of these additives relative to conventional friction material compositions.

Preferred fibrils have small diameters (preferably between 3.5 and s graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; USSN 871,675; US 5 165 909; WO89/01763; and W090/07023. These fibrils are prepared as described in the aforementioned patent and patent applications. The fibrils may also be treated to introduce oxygen-containing functional groups onto the fibril surface, as described in W090/14421.

The friction materials are prepared by dry mixing the resin, fibrils, and other additives under shear, and then moulding the resulting admixture at elevated temperatures using conventional thermoset moulding techniques, eg., compression or matched die moulding. A friction material containing 8% by weight carbon fibrils (as described above) in a phenolic resin that also included metal fibres, diatomaceous earth, barium sulfate, Kevlar polyaramide fibres, graphite, and carbon fibres was prepared in the form of disc brake backing plates. The brakes exhibited improved friction at high temperature with lower fade (as measured by Dynamometer testing) compared to compositions lacking the fibrils. The brakes 20 also exhibited improved resistance to cracking and spalling at high temperatures (400 0

C).

Hybrid Composites Preferred hybrid composites are those in which the primary reinforcing agent consists of continuous or discontinuous fibres having mean diameters on the order 25 of about 1 to 10ptm and the secondary reinforcing agent consists of carbon fibrils.

Preferred fibrils have small diameters (preferably between 3.5 and graphitic layers that are substantially parallel to the fibril axis, and are substantially free of a continuous thermal carbon overcoat, as described in US 4 663 230; USSN 871,675; US 5 165 909; W089/01763; and W090/07023. These fibrils are prepared as described in the aforementioned patent and patent applications, The fibrils may also be treated to introduce oxygen-containing functional groups onto the fibril surface, as described in W090/14421.

The composites may be unidirectional composites (ie. composites in which the primary reinforcing agents are individual continuous fibres, all of which are as arranged parallel to each other such that they reinforce the matrix primarily in one direction only), two-dimensional laminates or lay-ups of unidirectional tape or woven fabric (ie. composites in which the primary reinforcing agents are continuous fibres that reinforce the matrix in more than one direction within a single plane), multi-dimensional laminates or lay-ups (ie. composites in which IN. LIBC(10 423 !0r .of 23 reinforcement due to the continuous fibres is not confined to a single plane), and isotropic, discontinuous fibre-reinforced composites (ie. composites in which primary reinforcement discontinuous fibres, eg., chopped glass or carbon fibres, or carbon whiskers, are randomly oriented throughout the matrix to provide uniform reinforcement). Thermoset resins are preferred where the primary reinforcing agents are continuous fibres, while both thermoplastic and thermoset resins are suitable in the case of discontinuous fibres.

The Figure shows a two-dimensional woven laminate 10 in which an epoxy matrix 12 is reinforced with layers of primary reinforcing fibres 14 and carbon fibrils 16. Primary fibres 12 are polyacrylonitrile based carbon fibres. Each layer of primary fibres is woven to reinforce epoxy matrix 12 in two mutually perpendicular directions within a single plane. Carbon fibrils 16 are uniformly dispersed throughout matrix 12 and randomly oriented with respect to primary fibres 14.

The composites are prepared by dispersing the fibrils throughout the resin (which is in the form of a viscous liquid, paste, or melt to facilitate mixing) to form a prepreg. A particularly effective method for achieving well-dispersed prepregs in which the majority of fibril agglomerates have mean diameters less Sthan 0.5gm involves combining the fibrils, matrix, and any other fillers with a low t 20 viscosity additive an oil or liquid solvent) and a milling promoter (eg., abrasive particles such as grit particles) to form a slurry, and then agitating that slurry at high speeds in, eg., a stirred ball mill or attritor, as described in Creehan, EPO 04844447, entitled "Preparation of Uniform Dispersions", as the present application which is hereby incorporated by reference in its entirety. Once agitation is complete, any solvents can be removed by, eg., vacuum drying, steam stripping, or freeze drying. If the primary reinforcing agents are discontinuous fibres, they can be added to the resin along with the fibrils. If the primary reinforcing agents are continuous fibres, the resin-fibril mixture is applied to the primary reinforcing agents using conventional impregnation techniques, taking care sl* 30 to ensure that the resin-fibril mixture adequately wets the primary reinforcing agents. The composite is then moulded and cured using conventional moulding methods. The composite shown in the Figure was prepared as follows.

An uncured epoxy resin consisting of 9 parts N,N,N',N'-tetraglycidyl-4,4'methylenebisbenzeneamine (commercially available from Ciba-Geigy as MY720 epoxy), part Bisphenol-A with epichlorohydrin (commercially available from Ciba- Geigy as GY6010 epoxy), and 5 parts 4,4'-diaminodiphenyl sulfone hardener (commercially available from Ciba-Geigy as HT976 hardener) was combined with a volume of carbon fibrils (prepared as described in W089/01763) using a stirred ball mill until the fibrils were uniformly dispersed throughout the resin (as 0 described in the aforementioned Creehan application); the fibril volume fraction of [G:\WPUSER\LIBC100423:JOC the samples prepared varied from 0.01 to 0.05 based on total resin content. The mixture was then applied by hand to a six ply laminate of woven polyacrylonitrile based carbon fibre fabric [Techniweave 8 Harness Satin Weave 8hS style 3K-175- 8H of Celion 3K yarn having a yarn count of 24 x 23 and an areal density of 10.7 oz./yd 2 The composite fabric volume fraction was 0.60 ±0.02. The resulting composite was then moulded and cured to form the final composite structure. The properties of a composite in which the fibril volume fraction was 0.025 were measured and compared to a control sample containing no fibrils. The results demonstrated that the randomly oriented, uniformly dispersed fibrils improve matrix dominated properties such as compressive strength, short beam shear strength, in-plane shear strength, and trans-ply resistivity, and properties such as flexural strength and modulus which have a significant matrix compohent, without interfering with properties such as tensile strength and modulus which are dominated by the continuous fibres.

1i Other embodiments are within the following claims.

S*

S. *D a i J4 UB t423 Wer .f 34

Claims (32)

1. An electrically conductive composite comprising a solid or liquid matrix into which one or more fillers have been incorporated and said fillers are in the form of agglomerates substantially uniformly dispersed throughout said matrix, wherein said agglomerates have an average size no greater than 1000 times the size of the fillers and said fillers comprise carbon fibrils and/or a dimensional equivalent thereof.

2. A composite as claimed in claim 1, wherein said agglomerates have an average size no greater than 100 times the size of the filler.

3. A composite as claimed in claim 1, wherein said agglomerates have an average size no greater than 10 times the size of the filler.

4. A composite as claimed in any one of the preceding claims, wherein the fillers are uniformly dispersed by subjecting the fillers and matrix material to a combination of shear and impact forces under conditions and time sufficient to reduce the size of the agglomerates formed by the fillers to an average size no greater than 1000 times the size of the filler. A composite as claimed in any one of the preceding claims, wherein said matrix is curable by heat.

6. A composite as claimed in claim 5, wherein the amount of said fibrils or 990 oo o 0 0 *99 o*o 9 •o* .9* 9 9 9 09 9 9 9 99 9 *9 0

9.. *9 9 0 99* 20 equivalent thereof is sufficiently high to permit curing of resistive or inductive heating. 7. A composite as claimed in any one of claims 1 to 5, of said fibrils or equivalent thereof is 30% by weight or less. 8. A composite as claimed in any one of claims 1 to 5, 25 of said fibrils or equivalent thereof is 20% by weight or less. 9. A composite as claimed in any one of claims 1 to 5, of said fibrils or equivalent thereof is 15 by weight or less. A composite as claimed in any one of claims 1 to 5, of said fibrils or equivalent thereof is 0.5% to 10% by weight. 30 11. A composite as claimed in any one of claims 1 to 5, of said fibrils or equivalent thereof is 4% by weight or less. said composite by wherein the amount wherein the amount wherein the amount wherein the amount wherein the amount

12. A composite as claimed in any one of claims 1 to 5, wherein the amount of said fibrils or equivalent thereof is 1 to 4% by weight.

13. A composite as claimed in any one of the preceding claims, wherein said fibrils or equivalent thereof have a diameter of less than 100nm.

14. A composite as claimed in claim 13, wherein said diameter is between and A composite as claimed in any one of the preceding claims, wherein the N.ength to diameter ratio of said fibrils or equivalent thereof is at least

16. A composite as claimed in claim 15, wherein said ratio is between 5 to IG\WPUSER\LIBCIOO423.JOC I-- S. S* S 55 S S.. S SS S. S.. S** *S S

100. 17. A composite as claimed in any one of the preceding claims, wherein said fibrils have a crystalline graphite structure and a morphology defined by a fishbone-like arrangement of the graphite layers along the fibril axis. 18. A composite as claimed in any one of the preceding claims, wherein the amount of said fibrils or equivalent thereof is sufficient to impart to said composite an electrical conductivity sufficiently high to permit direct electrostatic overcoating. 19. A composite as claimed in any one of the preceding claims, wherein the electrical conductivity of said composi'. ,s greater than the electrical ceaductivity of a composite in which the same matrix is filled with an equivalent amount of carbon black. A composite as claimed in any one of the preceding claims, wherein said fibrils comprise tubes having graphitic layers that are substantially parallel to the fibril axis. 21. A composite as claimed in claim 20, wherein said fibrils are substantially free of a continuous thermal carbon overcoat. 22. A composite as claimed in claim 20 or claim 21, wherein the outer surface of said graphite layers has bonded thereto a plurality of oxygen-containing :o groups or derivatives thereof. 23. A composite as claimed in any one of the preceding claims, wherein said matrix comprises a thermoplastic material. 24. A composite as claimed in claim 23, wherein said thermoplastic material comprises a polyamide, polyurethane, polyurea, an elastomer or a mixture of any 25 two or more thereof. A composite as claimed in claim 23, wherein said thermoplastic material is a thermoplastic resin. 26. A composite as claimed in claim 25, wherein said thermoplastic resin comprises a polyester, polyurethane, polyether sulfone, polyether imide, 30 polyamide, polyurea, polyethylene, oriented polyethylene, polypropylene, polyvinyl chloride, polyether ktone, liquid crystalline polymer, a reaction- injection moulded resin or a mixture of any two or more thereof. 27. A composite as claimed in any one of claims 1 to 22, wherein said matrix comprises a thermoset material. 28. A composite as claimed in claim 27, wherein said thermoset comprises a polydicyclopentadiene, polyester, thermosetting polyurethane, vinylacrylamide, epoxy resin or a mixture of any two or more thereof. 29. A composite as claimed in claim 27, wherein said thermoset is a Sthermoset resin. A composite as claimed in claim 29, wherein said thermoset resin f ,,i IG \WPUSER\LIDBCI0423:JOC 27 comprises a phenolic, epoxy, thermosetting polyurethane, thermosetting polyester, polyimide, bismaleimide, polycyclopentadiene, vinylacrylamide resin or a mixture of any two or more thereof. 31. A composite as claimed in any one of claims 1 to 22, wherein said matrix comprises an elastomeric material. 32. A composite as claimed in claim 31, wherein said elastomeric material is a styrene-butadiene rubber, natural rubber, ethylene-propylene-diene monomer rubber, silicone rubber, polybutadiene, polyisoprene, neoprene, chloroprene, fluoro elastomer, urethane elastomer or a mixture of any two or more thereof. 33. A composite as claimed in claim 31 or claim 32, wherein the amount of said fibrils or equivalent thereof is less than 25 parts per 100 parts by weight of elastomeric material. 34. A composite as claimed in claim 33, wherein said amount is less than parts per 100 parts by weight of elastomeric material. 35. A composite as claimed in claim 31 or claim 32, wherein the amount of said fibrils or equivalent thereof is greater than 25 parts per 100 parts by weight of elastomeric material. 36. A composite as claimed in any one of claims 23 to 35, wherein the amount of fibrils in said composite is sufficiently high to permit at least one of the physical properties of said composite to be monitored electrically. 37. A composite as claimed in any one of claims 23 to 36, which is in the form of an elastomer solution. 38. A composite as claimed in any one of claims 23 to 36, wherein said composite is in the form of a tyre or component thereof. 39. The composite as claimed in any one of claims 23 to 36, wherein said composite is in the form of a seal. A composite as claimed in any one of claims 23 to 36, wherein said composite is in the form of an adhesive. 41. A composite as claimed in any one of claims 1 to 22, wherein said S 30 matrix is a reaction injection moulded matrix. 42. A composition in a form suitable for reaction injection moulding comprising one or more fillers, at least one of said fillers comprising carbon fibrils anudor a dimensional equivalent thereof and one or more liquid reactants capable of polymerising to form the composite as claimed in any one of claims 1 to S. 35 43. A composition as claimed in claim 42, wherein said liquid reactants comprise one or more polyols, polyisocyanates or polyamines. 44. A composite as claimed in any one of claims 1 to 30, which is in the form of a moulded product of a premix and said matrix is a resin matrix. 45. A composite as claimed in claim 44, wherein said premix is a sheet 40"pulding compound. IG:\WPUSER\LIBC00423:JOC 28 46. A composite as claimed in claim 44, wherein said premix is a bulk moulding compound. 47. A composite as claimed in any one of claims 1 to 30, which is electrically conductive and said matrix comprises a polymeric binder. 48. A hybrid composite comprising a composite as claimed in any one of the preceding claims which further comprises a primary fibrous reinforcing agent and a secondary fibrous reinforcing agent uniformly dispersed throughout said matrix and randomly oriented relative to said fibrils or dimensional equivalent thereof. 49. A hybrid composite as claimed in claim 48 wherein the mean diameter of said primary reinforcing agent is at least 10 times greater than the mean diameter of said fibrils or equivalent thereof. A hybrid composite as claimed in claim 48 wherein the mean diameter of said primary reinforcing agent is at least 100 times greater than the mean diameter of said fibrils or equivalent thereof, 51. A hybrid composite as claimed in claim 48 wherein the mean diameter of said primary reinforcing agent is at 16ast 1000 times greater than the mean diameter of said fibrils or equivalent thereof. 52. A hybrid composite as claimed in any one of claims 48 to 51 wherein said secondary reinforcing agent forms agglomerates which are no greater than 53. A hybrid composite as claimed in claim 52 wherein the majority of said agglomerates are no greater than :08 54. A hybrid composite as claimed in any one of claims 48 to 53 wherein said fibrils are carbon microfibres. 55. A hybrid composite as claimed in any one of claims 48 to 53 wherein said fibrils or equivalent thereof are whiskers. 56. A hybrid composite as claimed in any one of claims 48 to 53 wherein said fibrils or equivalent thereof comprise chopped fibres, 57 A hybrid composite as claimed in any one of claims 48 to 53 wherein 30 said fibrils or equivalent thereof are in the form of a particulate reinforcing agent. 58. A hybrid composite as claimed in any one of claims 48 to 57 wherein said reinforcing agent comprises continuous fibres. 59. A hybrid composite as claimed in claim 58 wherein said continuous fibres comprise carbon, glass, ceramic, polyaramide fibres or a mixture of any two 5 or more thereof. A hybrid composite as claimed in claim 58 or claim 59 wherein said continuous fibres are woven, knit, crimped or straight. 61. A hybrid composite as claimed in any one of claims 48 to 57 wherein said reinforcing agent comprises discontinuous fibres. 62, A hybrid composite as claimed in any one of claims 48 to 61 wherein (GO\WPUSEn\LOCIOO423:J.OC 29 said matrix comprises an inorganic polymer. 63. A hybrid composite as claimed in any one of claims 48 to 61 wherein said matrix comprises a metal. 64. A hybrid composite as claimed in any one of claims 48 to 61 wherein said matrix comprises a ceramic material. A hybrid composite as claimed in any one of claims 48 to 61 wherein said ceramic material comprises glass powder. 66. A hybrid composite as claimed in any one of claims 48 to 61 wherein said matrix comprises carbon. 67. A hybrid composite as claimed in any one of claims 48 to 66 wherein the amount of said fibrils or equivalent thereof is less than or equal to 20% by volume. 68. A hybrid composite as claimed in any one of claims 48 to 66 wherein the amount of said fibrils or equivalent thereof is between 1 and 10% by volume. 69. A composite as claimed in claim 47, which is in a form suitable for applying to a surface of a substrate. A composite as claimed in claim 69, which is in the form of a powder coating. 71. A composite as claimed in claim 69, which is in the form of a liquid coating. A composite as claimed in claim 70 or claim 71, wherein the amount of said fibrils or equivalent thereof is sufficiently high to permit a substrate to which said coating has been applied to be electrcstatically overcoated directly. 73. A composite as claimed in clai n 69, which is in the form of a resistive 2 5 ink suitable for screen printing on the surface of a substrate to form an electronic component. 74. A resistive ink as claimed in claim 73, wherein the amount of said fibrils or equivalent thereof is sufficient to decrease the bulk resistivity of said binder to a value between 10 2 and 106 ohm cm when applied to a substrate. S 30 75. A resistive ink as claimed in claim 66, wherein said resistivity is S between 10-1 and 10 4 ohm cm. 76. A composite as claimed in claim 69, wherein said composite further comprises electrically conductive graphite or metal particles and is in the form of a conductive ink suitable for printing on the surface of a substrate, S 35 the amount of said fibrils being sufficient to decrease the bulk resistivity of S. said binder by a predetermined amount when applied to a substrate, 77. A conductive ink as claimed in claim 76, wherein said bulk resistivity of said binder is greater than 1 ohm cm and the amount of said fibrils is sufficient to reduce said bulk resistivity to less than 1 ohm cm. 78. A conductive ink as claimed in claim 76, wherein said bulk resistivity of IGA:\WPUSER\%IDCIO423:JOC said binder is greater than 10-1 ohm cm and the amount of said fibrils is sufficient to reduce said bulk resistivity to less than 10-1ohm cm. 79. A conductive ink as claimed in any one of claims 76 to 78, wherein said metal particles comprise silver flakes. 80. A coating or ink as claimed in any one of claims 70 to 71, further comprising at least one pigment. 81. A substrate coated with the coating or ink as claimed in any one of claims 70 to 79. 82. A substrate- as claimed in claim 81, which is in the form of a printed circuit board and a resistive ink is printed on said substrate in the form of an electronic component. 83. A substrate as claimed in claim 82, wherein said electronic component is a resistor. 84. A substrate as claimed in claim 81, wherein said substrate comprises a substrate for a printed circuit board and a conductive ink is printed on said substrate in the form of a conductive trace for electrically connecting electronic components. A composite as claimed in any one of claims 1 to 30, which is in the form of a friction material. 86. A brake, or component thereof comprising the composite of claim 87. A clutch, or component thereof comprising the composite of claim 88. An automatic transmission disk, or component thereof, comprising a friction material as claimed in claim 89. A composite as claimed in any one of claims 85 to 88, wherein said matrix comprises carbon. A composite as claimed in any one of claims 85 to 89 which further comprises one or more additional fillers. 91. A composite as claimed in claim 90, wherein said fillers comprise metal, gass, ceramic, carbon, polyaramide fibres; graphite, clay, barium, sulfate, 30 diatomaceous earth, silica, magnesia, beryllia, alumina, silicon carbide, titanium dioxide, carbon black or a mixture of any two or more thereof. 92. A composite as claimed in claim 91, wherein said fillers aie particulate fillers. 93. A composite as claimed in claim 90 or claim 91 wherein the ratio of the 35 amount of said fibrils or equivalent thereof to the total amount of said fillers is at least 1:4. 94. A process for preparing a composite as claimed in any one of claims 31 to 40, comprising the steps of: preparing said composite by incorporating said fibrils or equivalent thereof in W' l o said elastomeric material, the amount of said fibrils or equivalent thereof being 1G:\WPUSER\LtBC100423:JOC sufficient to impart to said composite an electrical conductivity sufficiently high to permit resistive or inductive heating; and curing said composite by resistive or inductive heating. A process for preparing a composite as claimed in any one of claims 31 to 40, comprising the steps of: preparing a masterbatch by dispersing in an elastomeric material at least parts of said fibrils or equivalent thereof per 100 parts of elastomeric material; and compounding a predetermined portion of said masterbatch with an additional amount of an elastomeric material to prepare said composite. 96. A process as claimed in claim 94 or claim 95, further comprising incorporating carbon black in said elastomeric material. 97. A composite prepared by the process as claimed in any one of claims 94 to 96. 98. A process for preparing a composite as claimed in claim 41, comprising the steps of: mixing said fibrils or equivalent thereof with one or more liquid reactants to form a composition as claimed in claim 42 or claim 43; introducing the composition into a mould; and moulding the composition under reaction conditions including pressure and temperature to prepare said composite in the form of a moulded part. 99. A process for preparing a composite as claimed in claim 47, comprising the steps of: mixing said fibrils or equivalents thereof with said resin; and forming the mixture into a sheet. 25 100. A process for preparing a composite as claimed in claim 46, comprising the steps of mixing said fibrils or equivalent thereof with a resin to form a putty suitable for moulding.

101. A process as claimed in claim 99 or claim 100, further comprising S moulding said composite under reaction conditions including pressure and 30 temperature to prepare said composite in the form of a moulded part.

102. A process as claimed in claim 100 or claim 101, further comprising directly electrostatically overcoating said moulded part.

103. A composite prepared according to the process as claimed in any one of claims 98 to 102. 35 104. A compounding process for preparing a composite as claimed in any one of claims 1 to 30 or 85 to 93, comprising the steps of: introducing one or more fillers, at least one of which comprises said fibrils or equivalent thereof and said matrix material into a stirred ball mill; and jj, subjecting said fibrils or equivalent thereof and said matrix material to a combination of shear and impact forces under reaction conditions including IG;AWPUSER\LIBCIO423:JOC I 32 reaction time sufficient to reduce the size of agglomeiates formed by said fibrils or equivalent thereof to a value below a predetermined value to disperse said fillers throughout said matrix material.

105. A compounding process as claimed in claim 104, wherein said predetermined value of said agglomerate size is no greater than 1000 times the size of said fibre or equivalent thereof.

106. A compounding process as claimed in claim 105, wherein said predetermined value is no greater than 100 times.

107. A compounding process as claimed in claim 105, wherein said predetermined value is no greater than 10 times.

108. A compounding process as claimed in any one of claims 104 to 107, wherein one or more of the characteristic dimensions of said filler is less than 1 .m.

109. A compounding process as claimed in claim 108, wherein one or more of the characteristic dimensions of said filler is less than 0.1 VLm.

110. A compounding process as claimed in any one of claims 104 to 109, further comprising adding a viscosity modifier to said stirred ball mill.

111. A compounding process as claimed in claim 110, wherein said viscosity modifier is removed folk!wing the dispersion step.

112. A compoun6dci. process as claimed in claim 110 or claim 111, wherein said viscosity modifier is a solvent.

113. A compounding process as claimed in claim 110 or claim 112, wherein said viscosity modifier is retained following the dispersion step.

114. A compounding process as claimed in any one of claims 110 to 113, wherein said viscosity modifier is a reactive diluent that chemically reacts with said matrix material.

115. A compounding process as claimed in any one of claims 110 to 114, further comprising adding one or more milling media to said stirred ball mill.

116. A process for preparing a hybrid composite as claimed in any one of 30 claims 48 to 68, which process comprises combining said matrix with said fibrous reinforcing agent and said fibrils or equivalent thereof such that said reinforcing agent is uniformly dispersed throughout said matrix and randomly oriented relative to said fibrils and/or equivalent thereof.

117. A method for coating the sub,:Ate as claimed in any one of claims 81 to 84, comprising the steps of: ;preparing said coating or ink by incorporating said fibrils or equivaleat thereof into said polymeric binder; and applying said coating or ink to said substrate.

118. The method of claim 117, further comprising electrostatically applying v i..o an overcoating directly to said coated substrate. 1G:\WPUSER\LIBC100423:JOC 33

119. A method for printing on a substrate comprising the steps of: preparing an ink as claimed in any one of claims 73 to 80 by incorporating fibrils or equivalent thereof in said polymeric binder; and screen printing said ink on said substrate.

120. A composite substantially as hereinbefore described with reference to any one of the Examples.

121. A process for preparing a composite substantially as hereinbefore described with reference to any one of the Examples.

122. A composite prepared by the process as claimed in any one of claims 97 to 116 or 121. Dated 24 July, 1995 Hyperion Catalysts International, Inc. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 0.. *-the *"w 9 O.. w f 6I .9 a a. a IG\WPUSER\LIBC100423:JOt Composites and Methods for Making Same Abstract This invention relates to composites and methods for preparing them. The invention provides a composite comprising a solid or liquid matrix into which one or more fillers have been incorporated, wherein at least one of said fillers comprises carbon fibrils and/or a dimensional equivalent thereof. The Figure shows a two-dimensional woven laminate 10 in which an epoxy matrix 12 is reinforced with layers of primary reinforcing fibres 14 and carbon fibrils 16. Primary fibres 12 are polyacrylonitrile based carbon fibres. Each layer of primary fibres is woven to reinforce epoxy matrix 12 in two mutually perpendicular directions within a single plane. Carbon fibrils 16 are uniformly dispersed throughout matrix 12 and randomly oriented with respect to primary fibres 14. *too t oo The Figure S. 9* Te Figure o INAW0ICO413 JOC 0ol24