Conductive plastics

Abstract

A conductive plastic and a method of manufacture are provided. The plastic comprises between 50wt% and 85wt% of polymer matrix, between 5wt% and 40wt% of conductive fibrous additive, and at least 5wt% of carbonous additive, for example at least 10wt% of carbonous additive, in particular carbon black additive with a BET nitrogen surface between 50 and 1000 m2 / g and ratio OAN / BET between 0.3 and 2.5 (in 100 m2 / ml) or graphite particles with a BET nitrogen specific surface between 5 and 25 m2 / g and wherein 90% of the graphite particles are under 100 microns.

Description

[0001] Conductive plastics

[0002] Field of the invention

[0003]

[0001] The invention relates to the field of conductive materials. More specifically it relates to conductive plastics which can be used for electromagnetic shielding.

[0004] Background of the invention

[0005]

[0002] Conductive plastics are a light alternative for other materials, such as metal, used as protection against undesirable effects of electromagnetic fields. These include protection electrostatic discharge (ESD) and shielding against electromagnetic interference (EMI).

[0006]

[0003] Conductive plastics usually comprise a polymeric material as embedding matrix, and added conductive additives, such as metal fibers. However, the applications of these products are limited. Additionally, the production costs increase due to the more expensive materials used.

[0007]

[0004] It would be desirable to provide conductive light-weight material which shows good shielding for a broad range of applications.

[0008] Summary of the invention

[0009]

[0005] It is an object of embodiments of the present invention to provide a conductive plastic which shows good EMI shielding for electromagnetic (EM) fields with a frequency of at least 50MHZ, with a relatively low additive amount, and in any case with at least 50wt% of polymer matrix.

[0010]

[0006] It is a further object to provide a method of manufacture of such plastic and use of such conductive plastic for EMI shielding.

[0011]

[0007] In a first aspect, the present invention provides a conductive plastic comprising between 50wt% and 85wt% of polymer matrix, between 5wt% and 40wt% of conductive fibrous additive, and at least 5wt% of carbonous additive, for example at least 10wt% of carbonous additive, in particular carbon black additive with a BET nitrogen surface between 50 and 1000 m2 / g and ratio OAN / BET between 0.3 and 2.5 or graphite additive with a BET nitrogen specific surface between 5 and 25 m2 / g and wherein 90% of the particles are under 100 microns. Herein, BET nitrogen surface area generally reflects the total surface area of the carbon black, i.e., including the external surface area and surface area attributable to mesopores and micropores. As used herein, the term "BET nitrogen surface area" means the surface area as determined by ASTM D6556-04, the entirety of which is incorporated herein by reference.

[0012]

[0008] It is an advantage of embodiments of the present invention that the conductive plastic can be used for EM shielding with a reduced cost and effective shielding.

[0013]

[0009] Where in embodiments of the present invention reference is made to carbon additive, reference is made to components containing carbon.

[0014]

[0010] In some embodiments of the present invention, the conductive plastic contains between 15wt% and 50wt% of additive including the conductive fibrous and carbon additives together. In some embodiments, it may comprise up to 40wt% of conductive fibrous additives. In some embodiments, it may comprise up to 40wt% of carbonous additives with the surface properties as specified above.

[0015] [Oil] It is an advantage of embodiments of the present invention that total cost can be reduced while providing good conductivity.

[0016]

[0012] In some embodiments of the present invention, the conductive fibrous additive comprises any of stainless steel fiber (SSF), carbon fiber (CF), nickel coated carbon fibers (NiCF), metal coated glass fiber, metal coated basalt fibers, and / or metal coated polymer fibers.

[0017]

[0013] In some embodiments of the present invention, the conductive fibrous additive comprises carbon fibers and / or fibers coated by conductive material.

[0018]

[0014] It is an advantage that coated fibers are light and allow higher shielding performance.

[0015] Particularly, in some embodiments, the conductive fibrous additive comprises any of nickel coated carbon fibers, metal coated glass fiber, metal coated basalt fibers, and / or metal coated polymer fibers.

[0019]

[0016] In some embodiments, the conductive fibrous additive comprises metallic fiber such as stainless steel fiber, aluminum fiber, copper fiber, titanium fiber.

[0020]

[0017] It is an advantage that metallic fibers, or metal coated fibers are typical present high conductivity which is very important for EMI shielding. In particular, stainless steel fibers have the advantage that the volume fraction can be very low, so influences on plastic color, tensile strength, elongation, shrinkage, flowability, ... are limited.

[0021]

[0018] In some embodiments, the metallic fiber comprises 5wt% and 20wt% of stainless steel fiber.

[0022]

[0019] It is an advantage that the plastic presents a good compromise between cost and shielding.

[0020] In particular embodiments, the metallic fiber comprises stainless steel fiber of average under 1.5mm. For example, the stainless-steel fiber may be a drawn fiber with a tensile strength of 1600 MPa.

[0023]

[0021] In some embodiments wherein the conductive fiber is SSF, the martensite content is equal to or higher than 50wt%, for example higher than 75wt%.

[0024]

[0022] In some embodiments of the present invention, the carbon additive is carbon black.

[0025]

[0023] It is an advantage that the conductive plastic with such additive shows very effective shielding for high frequencies, over 200 MHz, e.g. over 1GHz.

[0026]

[0024] In some embodiments, the carbon additive is graphite.

[0027]

[0025] It is an advantage of embodiments of the present invention that shielding for frequencies over 1GHz is very effective combined with effective thermal conductivity.

[0028]

[0026] In some embodiments, the amount of carbonous additive is at most 40wt%.

[0029]

[0027] It is an advantage that the properties of the plastic are well balanced with the cost.

[0030]

[0028] In a second aspect, the present invention provides a method of providing a conductive plastic comprising providing a polymeric material and adding between 5wt% and 40wt% of conductive fibrous additive. The method comprises further adding at least 5wt% of carbonous additive, e.g. at least 10wt%, being carbon black additive with a BET nitrogen surface between 50 and 1000 m2 / g and with OAN / BET ratio between 0.3 and 2.5 (in 100 m2 / ml); or graphite additive with a BET nitrogen specific surface between 5 and 25 m2 / g and wherein 90% of the particles are under 100 microns so that the conductive plastic comprises between 50wt% and 85wt% of polymer matrix.

[0031]

[0029] In some embodiments, adding the fiber comprises adding a metal fiber, for example a stainless steel fiber, for example wherein the stainless steel fiber is at least 1 mm, for example at least 3 mm, for example between 3 mm and 15 mm, for example between 5 mm and 8 mm of length.

[0032]

[0030] Use of a conductive plastic according to any one of claims 1 to 11 for shielding of electromagnetic interference, for example between 50 MHz and 100 GHz, for example between 1 GHz and 100 GHz

[0033]

[0031] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0032] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

[0034] Brief description of the drawings

[0035]

[0033] FIG 1 illustrates a method for providing a conductive plastic in accordance with embodiments of the present invention.

[0036]

[0034] FIG 2 illustrates a cross section of a plastic containing conductive fiber and carbonous additive dispersed in a polymer matrix.

[0037]

[0035] The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

[0038]

[0036] Any reference signs in the claims shall not be construed as limiting the scope.

[0039]

[0037] In the different drawings, the same reference signs refer to the same or analogous elements.

[0040] Detailed description of illustrative embodiments

[0041]

[0038] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0042]

[0039] Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0043]

[0040] Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

[0044]

[0041] It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term "comprising" therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. Thus, the scope of the expression "a device comprising means A and B" should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0045]

[0042] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0046]

[0043] Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0047]

[0044] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0048]

[0045] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0049]

[0046] Where in embodiments of the present invention reference is made to "conductive fiber", reference is made to a fiber including material such that the material has a fiber shape (much longer than it is wide), wherein the resistivity is around or below 10A-4 ohm cm, for example, around 5 x 10A-6 ohm cm, for example below 5 x 10A-6 ohm cm . This can be a suitable metal fiber, a fiber (conductive or not) coated by conductive material, such as metal, etc. Where in embodiments of the present invention reference is made to a 'polymer matrix', reference is made to a matrix comprising polymeric material and optionally including fillers, in particular non-conductive fillers such as reinforcement fillers, e.g. glass fibers.

[0050]

[0047] The present invention relates to EMI shielding using conductive plastics. A conductive plastic has a tailored conductivity such that it can be used as electromagnetic shield. For example, a conductive plastic may show a volume resistivity between 10A10 ohm.m and 1 ohm.m. For example, a conductive plastic may show a volume resistivity of 100 ohm.m or below, e.g. 2 ohm.m or below. The present invention also relates to manufacture by addition of conductive fibers to a polymer matrix over a predetermined range, which results in a plastic material which can be considered conductive enough for shielding purposes. The range is related to the percolation threshold of the additive, which is the minimum amount of additive in the polymer at which there is a sudden resistance drop of the plastic material.

[0051]

[0048] The higher the amount of conductive fibers, the better the shielding properties, but on the other hand costs add up, since fibers are usually expensive. Thus, aside of conductive fibrous additive, other additives are included, which may increase the conductivity. Additives such as carbon-based, non-polymeric additives present improvement in conductivity and / or shielding with low costs. Such additive will be referred to as 'carbonous additive' throughout the present description. Low cost carbonous additives include carbon black and graphite.

[0052]

[0049] The inventors found that carbonous additive with specific particle surface properties provide a much better conductivity and thermal behavior than other additives. In particular, shielding for high frequencies within the GHz range can be obtained, and be combined with improved thermal conductivity. This is especially advantageous for shielding for data transmission applications.

[0053]

[0050] In a first aspect, a conductive plastic is provided with a content of polymer matrix of at least 50wt%. The polymer matrix may comprise any suitable polymeric material. In some embodiments, thermoplastics are used. For example, these may include Acrylonitril- butadieen-styreen (ABS), Liquid-crystal polymer(LCP), poly amide (PA), Polybutyleentereftalaat (PBT), Polyethyleentereftalaat (PET), poly carbonate (PC), poly ethylnene (PE), Polyetheretherketon (PEEK), poly ether imide (PEI), poly ether sulphone (PES), Polyoxymethyleen (POM), poly propylene (PP), Polyphthalamide (PPA), Poly(p-phenylene oxide) (PPO), Polyfenyleensulfide (PPS), polystyrene (PS), poly sulphone (PSU), poly vinyl chloride (PVC), Styrene-acrylonitrile resin (SAN), and more specifically PC, ABS & mixtures thereof, PA, PPS, PPA, PBT, PET and mixtures thereof.

[0054]

[0051] In some embodiments, thermo-elastomers can be used as polymeric material, including for example styrene-ethylene-butylene-styrene (SEBS), Syndiotactic Polystyrene (SPS), Thermoplastic Polyimide (TPI), Thermoplastic Polyurethane (TPU).

[0055]

[0052] In some embodiments, thermosets can be used as polymeric material, including for example acrylics, esters, epoxies, PU, rubber (Ethyleen-Propyleen-Dieen-Monomeer (EPDM), natural or synthetic rubber, ...), silicones.

[0056]

[0053] The polymer matrix may comprise polymeric material and non-conductive additives such as reinforcement additives, fire retardants, etc.

[0057]

[0054] The conductive plastic of the present invention includes conductive fiber and carbonous additives. In some embodiments, the conductive plastic includes 15wt% or more of conductive fiber and carbonous additives together, for example up to 50wt%, so the sum of the polymer matrix and the additives is 100wt%.

[0058]

[0055] FIG 2 shows a cross section of a conductive plastic 100 according to embodiments of the present invention, wherein conductive fibrous additives 102, such as SSF, and carbonous additive 103 in form of particles, are dispersed in a polymer matrix 101.

[0059]

[0056] Focusing on the conductive fiber additive, the fiber additive may be any suitable fiber with high conductivity. For example, it may be a metal fiber. The metal may be any suitable metal, including Cu, Al, Si, Ti, SSF, etc.

[0060]

[0057] In some embodiments the conductive fiber additive may comprise for example a conductive or non-conductive fiber coated in conductive material, e.g. coated in metal. For example the conductive fibers may comprise in general coated fibers, nickel-coated carbon fibers (NiCF), coated glass fiber (CGF), coated basalt fibers, coated polymer fibers, for example silver coated polyamide or polyester fibers.

[0061]

[0058] In some embodiments of the present invention, the conductive plastic may comprise conductive fiber additive where the fibers (e.g. SSF) have an average length under 1.5 mm.

[0059] All these fibers should present high conductivity, and can provide high conductivity to the plastic, which is advantageous for EMI. Fibers that confer high conductivity at low volume fraction are usually preferred to keep the costs low. In some embodiments the amount of conductive fibrous additive is between 5wt% and 40wt%.

[0062]

[0060] Focusing now on the carbonous additive, these may comprise any suitable carbon allotrope or compound that provides high shielding combined with the metal fibers. The carbonous additives are additives based on carbon, usually in the form of powder. In some embodiments, they are non-fibrous carbonous additives. They can be distinguished from conductive fiber in that the conductive fiber is more conductive than the carbonous additives. For example, a conductive fiber may have a resistivity lower than 5 x 10A-6 Ohm cm, while carbonous additive, e.g. carbon fiber, has a resistivity higher than 5 x 10A-6 Ohm cm. For example, carbon black has a resistivity close to 10A-4 Ohm cm.

[0063]

[0061] While the present invention may include nanocarbon tubes and graphene layers, carbon black and graphite are preferred. They enable effective shielding and they are inexpensive compared to carbon nanostructures and monolayers.

[0064]

[0062] In particular, it has been found that carbonous additives with specific surface area and surface porosity within a range, combined with the conductive fibers, provide a highly effective EMI shielding, better than the sum of the contributions of each type of additive on its own. In some embodiments, the amount of carbonous additive is at least 5wt%, for example 10wt% or more, for example llwt% or more, of carbonous additive. In some embodiments it may be up to 40wt%.

[0065]

[0063] In some embodiments, the sum of carbonous and conductive additives is between 15wt% and 50wt%.

[0066]

[0064] In some embodiments, the carbon black additive has specific surface parameters which indicate the surface available for adsorption of a gas. This gives a better approximation of the actual surface of a particle, since microstructural features of the surface (for example microporosities and other micro-irregularities) become covered by the adsorbed gas molecules during the measurement, so these features are taken into account in the BET surface value. The gas used for the test is generally nitrogen, unless the specific surface requires other gas for meaningful results. In the case of carbonous material, nitrogen is usually enough. The parameter is the so-called Brunauer-Emmett-Teller (BET) nitrogen surface, or simply 'BET surface'. The units of the BET surface are given in m*m / g, or m2 / g. In embodiments of the present invention, the carbon black additive has BET surface between 50 m2 / g 1000 m2 / g. In some embodiments, the BET surface falls between 50 m2 / g and 100 m2 / g.

[0067]

[0065] In some embodiments the oil absorption number (OAN) of the carbon black, which reflects the ability to absorb liquid property of the structure, has a predetermined value between 50 m2 / g and 250 m2 / g, for example between 150 m2 / g and 250 m2 / g, in oil absorption index units (ml / lOOg). Oil absorption number (OAN) is a measure of the ability of a carbon black to absorb liquids. This property is a function of the structure of the carbon black. ISO 4656:2012 specifies a method using an absorptometer for the determination of the oil absorption number of carbon black. In particular embodiments, the carbon black shows a BET / OAN ratio between 0.3 and 2.5 (in 100 m2 / ml). In some embodiments, that particular BET / OAN ratio is found combined with the specific BET surface range of 50 m2 / g to 1000 m2 / g.

[0068]

[0066] In yet another embodiment, the carbon black has a preferred BET surface between 50 m2 / g and 100 m2 / g, and an OAN between 150 and 250 (ml / lOOg).

[0069]

[0067] In some embodiments, the carbonous additive comprises graphite particles with a BET surface between 5 m2 / g and 25 m2 / g, also measured by nitrogen adsorption.

[0070]

[0068] In some embodiments, 90% of the graphite particles are under 100 microns (pm, or micro meter) before the integration in the matrix (which is known as D90 of 100 microns). In some examples, the graphite has a BET between 5 m2 / g and 25 m2 / g and D90 of 100 microns (or less).

[0071]

[0069] In particular examples, the average particle size is under 50 microns. For instance, the average size may be under 50 microns combined with a D90 of 100 microns.

[0072]

[0070] In some embodiments, the graphite shows an OAN of 120 or higher, e.g. 150 or higher.

[0071] Such conductive plastics can be used for shielding of EMI at frequencies of 50 MHz or more, e.g. 200MHz or more. Preferably the thermal conductivity is improved.

[0073]

[0072] In a further aspect, the present invention provides a method of manufacture a conductive plastic. The method comprises providing SOI a polymeric material, providing S02 a carbonous additive being graphite, and / or carbon black, with the surface properties as explained earlier, and providing S03 a conductive fibrous additive. The method comprises mixing S04 the polymeric material with the additives, resulting S05 in a conductive plastic with an amount of polymer matrix between 50wt% and 85wt% and the rest being additives, from which at least 10wt% are carbonous additives, and the rest of additives are conductive fibrous additives (between 5wt% and 40wt%). In some embodiments, both carbon black and graphite may be both used. In some embodiments, the amount of carbonous additives and conductive fibrous additives are between 15wt% and 50wt% of the final plastic.

[0074]

[0073] In some embodiments, the providing S03 conductive fibrous additive may comprise for example providing S13 coated fibers (e.g. NiCF, and / or any of the examples presented earlier), and / or providing S23 metal fibers (e.g. SSF, and / or any of the examples presented earlier). It is noted that the polymer matrix may include, aside of polymeric material, additional non- conductive additives, e.g. reinforcement additives, which have at most a negligible influence of conductivity of the conductive plastic, e.g. glass fiber.

[0075]

[0074] In some embodiments, a masterbatch of fibers is mixed with the polymeric material and the rest of additives. While in the conductive plastic after processing the fibers may be below 1.5mm, such as around 0.8 mm, the masterbatch of fibers may comprise fibers for example 1 mm or longer, for example 3 mm, for example up to 15 mm, for example between 5 mm and 8 mm. In some embodiments, the fibers may be provided as pellets of 2 mm or more. The pellet, for example for injection molding, may contain between 30% and 90% of SSF, in some embodiments the pellet may contain between 30% and 75% of SSF thus improving homogeneity of the mixing, for example the pellet may contain 75% of SSF. The SSF in the pellet may be wetted, thus advantageously improving mixing with the polymeric material. Due to the processing, the length of the fibers is not conserved in the final product, where the fibers are much shorter.

[0076]

[0075] The materials may be mixed S04 together, for example before forming the plastic. In some embodiments, the materials may be first pre-mixed or compounded S14. Compounding allows to advantageously include additives so that the conductive plastic has predetermined desired properties, for example fire-retardant additives, additives for reinforcing the plastic, etc.

[0077]

[0076] The conductive plastic can be, for example, injection-molded, extruded, formed as compression- molded parts, preferably as injection-molded parts. In some embodiments, the method comprises performing S15 injection molding. For example, mixing the material may be done in an injection molding machine, subsequently providing S15 injection molding, thus obtaining S05 the conductive plastic.

[0078]

[0077] In some embodiments providing metal fiber comprises S33 providing SSF. In some embodiments, the method comprises providing drawn fiber being SSF having tensile strength of 1600MPa. In some embodiments, the martensite content in the steel is equal to or higher than 50wt%and in some cases even more than 75wt%. Ductility is generally better than fibers with ceramic character such as carbon fiber, basalt fiber of glass fiber (although the present invention may comprise providing these fibers). Since SSF are drawn, the fibers break less and are straighter, so the percolation threshold is reached at lower amount of fibers.

[0079]

[0078] The amount of SSF can be between 5wt% and 40wt%, for example between 5wt% and 20wt%, e.g. between 5wt% and 10wt%.

[0080]

[0079] The step of providing the conductive fibrous additive may comprise providing coated fibers, such as basalt, polymer, carbon, glass... fibers coated with conductive material, such as for example nickel coated fibers. These are usually lighter than metallic fibers and may provide high shielding, but they involve higher costs.

[0081]

[0080] The step of providing carbonous additive may comprise providing carbon black. For example, the method may comprise providing SSF and carbon black with the polymeric material.

[0082]

[0081] The step of providing carbonous additive may comprise providing graphite. This is preferred in applications where good shielding and high thermal conductivity properties are required.

[0083]

[0082] In a further aspect, the present invention provides use of the conductive plastic of embodiments of the first aspect of the present invention, for EMI shielding. This may include shielding for electronics, mobile or automotive applications where reducing costs is very important. For example, the use of these conductive plastics may provide protection in EM frequencies between 50MHz and 100GHz, in particular between 1GHz and 100 GHz, for example around 80GHz, the present invention not being limited thereto. In particular embodiments, the use of the conductive plastics allows good conductivity and shielding at such frequencies.

[0084]

[0083] In some embodiments, combination from SSF and CB may be provided, being advantageous for applications where good shielding is required for frequencies of 50 MHz or more, e.g. 200MHz or higher, e.g. up to 100GHz.

[0085]

[0084] In some embodiments combination of SSF and graphite may be provided, being advantageous for applications where good thermal properties are required in combination with shielding for frequencies of 1 GHz or more, e.g. up to 100 GHz, and additionally improving thermal conductivity of the conductive plastic. This is advantageous for applications where shielding at high frequencies can cause thermal issues in, e.g. electronics being shielded.

[0085] In the following, a particular embodiment of the present invention is discussed. The embodiment is a conductive plastic comprising SSF and carbonous additive, for example a carbon black.

[0086]

[0086] As explained earlier, metal fibers usually increase the production costs of conductive plastic. However, SSF has the advantage that its influence on the color, tensile strength, elongation, shrinkage, flowability, and other physical and mechanical properties is small. This is due to the fact that the volume fraction of SSF required to have good shielding is very low. With other fibers the required volume fraction is much higher, e.g. volume of carbon fiber for the same weight is 4 times that of SSF. However, the present invention is not limited to SSF, and other fibers may be used since costs are also reduced.

[0087]

[0087] The combination of SSF and carbonous additives allows reduction of SSF for the same shielding effectiveness, which also reduces costs. Although the shielding performance provided by only CB and graphite is poor, the combination with SSF increases dramatically the shielding performance.

[0088]

[0088] The following tables show the synergetic effect of commercial CB or graphite combined with SSF, at a lower expense for the same performance. Especially at higher frequencies a conductive plastic with carbon black reaches significant gain in, while a conductive plastic including graphite, the thermal conductivity improves, which is important for high frequency applications.

[0089]

[0089] Table I shows the electromagnetic shielding (SE) at frequencies between 1 GHz and 15 GHz, for different amounts of SSF and for different amounts of carbon black (CB) and graphite. While at higher frequency there is a strong synergetic effect between CB and SSF for shielding, even at low frequencies the amount of SSF can be reduced (with the advantageous reduction in costs) by adding CB to SSF. The effect is also noticeable when using graphite, especially at higher frequencies (>lGHz). The numbers on the table are the performance of the shielding for the indicated additives, while the numbers in parenthesis are the combination of the performance of the shielding of a plastic with only SSF and with only carbonous additive. As it can be seen, results are synergistically higher than the sum of its components. For high amounts of graphite and SSF high thermal conductivity and a good EMI shielding are provided. It is believed graphite, although it does not provide shielding on its own, improves thermal conductivity, while SSF improves shielding although does not impact thermal conductivity significantly.

[0090] Table II shows the thermal conductivity (W / mK) for different amounts of SSF and for different amounts of carbon black (CB) and graphite. Each time the thermal conductivity is given in Through plane and in plane. The calculated values are between round brackets, the other values are real values. For carbon black and metal fibers the real values are always lower than the calculated values (sum of the thermal conductivity of SSF and CB). For Graphite the real thermal conductivity is at least the same of slightly better than the sum of the thermal conductivities, which is a great result. Taking into account the synergy in shielding at higher frequencies and the results of the thermal conductivity this could be game changer in a lot of new applications, where high frequencies are important.

[0090]

[0091] Table I - Average shielding performance (in dB) of polymers with only SSF, only carbonous additives, and polymers combining both carbonous additives and SSF.

[0091]

[0092] Table II - Thermal conductivity, both in plane and through the plane of the plastic

[0092]

[0093] Table III - Total cost reduction (TCO reduction) for the plastic with SSF and CB or graphite, at different amounts of material required to obtain the different indicated shielding performances (in dB).

[0093]

[0094] Table IV -Total cost reduction, frequency up to 1GHz for the electric far field, to obtain the different indicated shielding performances (in dB).

[0094]

[0095] Table V -Total cost reduction, frequency between 10 MHz and 500 MHz forthe electric magnetic near field at 3 mm, to obtain the different indicated shielding performances (in dB).

[0095]

[0096] Regarding thermal conductivity, as shown in Table II, graphite mixed with SSF shows a synergistic increase. The thermal conductivity of a conductive plastic including both additives (at a predetermined amount of each) is higher than the sum of conductivities of a plastic including only the predetermined amount of fiber additive or including only the predetermined amount of carbonous additive.

[0096]

[0097] Shielding in high frequency applications are increasingly important due to improvements in telecommunication, in particular for example mobile networks. With each new generation of networks, the data rate increases, allowing more data to be sent per second. This leads to a corresponding increase of frequency. 5G technology and car radars are in the range of GHz, up to even 80 GHz. In order to reduce heating on the electronics, the present invention provides an effective conductive plastic which not only provides effective protection against EMI, but also high thermal conductivity. The main contribution to the conductivity may be the SSF while the graphite contributes to the protection against thermal damage.

[0097]

[0098] The introduction of carbonous material allow reduction of SSF required to obtain comparable or better thermal conductivity and better shielding performance (at GHz range, and for 40 dB and 70 dB) than a plastic layer with the same amount of SSF but no carbonous material. In some cases, half of SSF may be used for equal or comparable results for shielding, when carbonous material is added. Based on the material costs, as shown in Table III to Table V, the reduction can be at least 25%, and it may reach up to 72%. The shielding properties also improve in case of conductive plastics with SSF and carbonous additive, for frequencies in the MHz range (10 MHz up to 1GHz), and allow reduction of costs (by reduction of SSF for the same shielding) of at least 33%, or more, up to 72%. These reductions of costs are provided by the reduction of expensive materials, in particular of relatively expensive conductive fiber, e.g. SSF. The shielding considering electric far field (plane wave) is also improved, allowing cost reduction of at least 11%.

Claims

Claims1. A conductive plastic (100) comprising between 50wt% and 85wt% of polymer matrix (101), between 5wt% and 40wt% of conductive fibrous additive (102), and at least 5wt% of carbonous additive (103) being carbon black with a BET nitrogen surface between 50 and 1000 m2 / g and ratio OAN / BET between 0.3 and 2.5 (in 100 m2 / ml) or graphite particles with a BET nitrogen specific surface between 5 and 25 m2 / g and wherein 90% of the graphite particles are under 100 microns.

2. The conductive plastic according to claim 1, wherein the conductive plastic contains between 15wt% and 50wt% of additive including the conductive fibrous and carbon additives (102, 103) together.

3. The conductive plastic according to any of the previous claims, wherein the conductive fibrous additive comprises carbon fibers and / or fibers coated by conductive material.

4. The conductive plastic according to the previous claim, wherein the conductive fibrous additive comprises any of nickel coated carbon fibers, metal coated glass fiber, metal coated basalt fibers, and / or metal coated polymer fibers.

5. The conductive plastic according to any of the previous claims, wherein the conductive fibrous additive comprises metallic fiber, optionally wherein the metallic fiber comprises stainless steel fiber, aluminum fiber, copper fiber or titanium fiber.

6. The conductive plastic according to claim 5, wherein the metallic fiber comprises 5wt% and 20wt% of stainless steel fiber.

7. The conductive plastic according to any one of claim 5 or 6, wherein the stainless steel fiber is drawn fiber with a tensile strength of 1600 MPa.

8. The conductive plastic according to any one of claims 5 to 7, wherein the martensite content of the stainless steel fiber is equal to or higher than 50wt%, for example higher than 75 wt%.

9. The conductive plastic according to any of the previous claims, wherein the carbon additive is carbon black with an amount of at least 10wt%.

10. The conductive plastic according to any of the previous claims, wherein the carbon additive is graphite with an amount of at least 10wt%.

11. The conductive plastic according to any of the previous claims, wherein the amount of carbon additive is at most 40wt%.

12. A method of providing a conductive plastic, comprising providing (SOI) a polymeric material and adding (S03) between 5wt% and 40wt% of conductive fibrous additive,and further adding (S02) at least 5wt% of carbonous additive being carbon black with a BET nitrogen surface between 50 and 1000 and OAN / BET ratio between 0.3 and 2.5 5 (in 100 m2 / ml) or graphite particles with a BET nitrogen specific surface between 5 and 25 and wherein 90% of the graphite particles are under 100 microns so that the conductive plastic comprises between 50wt% and 85wt% of polymer matrix.

13. Use of a conductive plastic according to any one of claims 1 to 11 for shielding of electromagnetic interference, for example between 50 MHz and 100 GHz, for example between 1 GHz and 100 GHz.

Images