thermally conductive plastic

Abstract

The present invention relates to a thermally conductive plastic composition (Y) comprising 5-50% by volume of a plastic composition (S) and 50-95% by volume of at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK, with the proviso that said thermally conductive plastic composition (Y) has a thermal conductivity of at least 0.6 W / mK and at least 20% by volume of metallic silicon particles are contained as the thermally conductive filler (Z), said particles having the following characteristics: a) their average diameter x50 ranges from 30 to 200 μm; b) said particles are predominantly rounded and have a width / length ratio (aspect ratio b / l) of at least 0.76; and c) the distribution width SPAN ((x90-x10) / x50) of at least 0.28.

Description

[Technical Field]

[0001] The present invention relates to thermally conductive plastics, their production and their use. [Background technology]

[0002] Thermally conductive plastics are widely used for thermal management in the automotive and electronics industries. Important applications include thermally conductive adhesives, thermally conductive pads, gap fillers, potting compounds and pastes.

[0003] Plastics generally exhibit low thermal conductivity, typically in the range of approximately 0.2 to 0.3 W / mK.

[0004] The prior art discloses various thermally conductive fillers that are added to plastics to increase their thermal conductivity. However, these have significant drawbacks. Ceramic fillers, such as aluminum oxide, are very dense and therefore significantly increase the weight of the part. They are also relatively expensive. Metal fillers, such as aluminum powder and silver powder, are electrically conductive and therefore unacceptable for many applications. Many metals and alloys are also relatively expensive.

[0005] Furthermore, many high thermal conductivity fillers, such as carbon nanotubes, boron nitride, and aluminum nitride, are relatively expensive and may only be employed to a limited extent, in small quantities, or in specific applications.

[0006] The prior art discloses various thermally conductive plastic compositions containing silicon particles as a thermally conductive filler. These are relatively lightweight and cost-effective. Silicon is also a semiconductor, and therefore has very low electrical conductivity. However, the silicon particles of the prior art are not suitable for use in electric vehicles or electronic components.

[0007] Silicon particles are usually obtained by a crushing process. The drawback is that these particles have a large surface area and bind a large amount of polymer. This significantly increases the viscosity of the plastic composition. Only mixtures with a relatively low filler content and low thermal conductivity can be produced. At higher filler contents, the composition becomes very hard and can no longer be dispensed using classic processes, such as dispensers. Plastic compositions containing crushed silicon particles have also proven to be relatively flammable.

[0008] The use of silicon particles smaller than 30 μm is disadvantageous because such small particles have a relatively low minimum ignition energy, which poses a risk of dust explosion and requires complex and expensive safety measures during industrial processing.

[0009] JP 2019-131669A2 teaches the use of 0.1-200 μm metallic Si particles with an electrically insulating coating as a thermally conductive filler in silicone-free organic resins. The particles can be produced by pyrolysis, melting, and grinding processes, or by grinding and grinding processes. The particles are coated with an electrically insulating coating in a separate process step. An example in JP 2019-131669A2 discloses an organic resin containing up to 65% by volume of ground Si particles with an average particle size of 32 μm and a thermal conductivity of up to 7 W / mK. The use of relatively flammable ground particles is a disadvantage. The disclosed vulcanizate lacks elasticity, making it unsuitable for use as a gap filler in lithium-ion batteries.

[0010] CN106753140A claims an epoxy resin containing two types of spherical silicon particles with particle sizes of 20 μm and 27 μm.

[0011] JP 2013-221124 A2 claims a polyarylene sulfide resin containing silicon particles larger than 1 μm, of any shape and manufacturing method, in this example using irregularly shaped silicon particles of 6 μm and 17 μm.

[0012] US2015307764A (=EP2935432A1) claims a plastic composition that may contain metal silicon particles. The preferred size range is 1-50 μm. The shape is not further specified. In this example, 2.5 μm silicon particles are used. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2019-131669A2 [Patent Document 2] Publication No. CN106753140A [Patent Document 3] Japanese Patent Application Publication No. 2013-221124A2 [Patent Document 4] US2015307764A publication [Patent Document 5] EP2935432A1 publication Summary of the Invention [Problem to be solved by the invention]

[0014] Silicones are not preferred in many applications because they release volatile polydimethylsiloxanes that can impair the adhesion of parts and coatings.

[0015] It is therefore an object of the present invention to provide a non-silicone-based, and therefore polydimethylsiloxane-free, plastic composition that does not exhibit the above-mentioned drawbacks of the prior art and combines the properties of low density, low cost and high thermal conductivity. [Means for solving the problem]

[0016] This object is achieved by a thermally conductive plastic composition (Y) according to the invention, which contains relatively large Si particles with an average particle size of 30 to 200 μm, which are mainly rounded in shape and at the same time show a particularly large / broad particle size distribution. It has now been found, very surprisingly, by experiments, that these thermally conductive plastic compositions (Y) according to the invention show significantly reduced flammability.

[0017] In the context of the present invention, "predominantly rounded" Si particles are understood to have a spherical to ellipsoidal shape with a smooth surface. They can also be described as potato-shaped. Figure 1 shows, by way of example, the predominantly rounded shape of these Si particles according to the present invention. The Si particles of the present invention have a width / length ratio (aspect ratio w / l) of at least 0.76. Non-inventive Si particle shapes with a width / length ratio (aspect ratio w / l) of less than 0.76 are shown as "sputtered particles" in Figure 2, "nodular" particles in Figure 3, and "acute" and "pointed" particles in Figure 4. Those skilled in the art will recognize that there is a wide overlap between different particle shapes. The metallic Si particles of the present invention have a width / length ratio (aspect ratio w / l) of at least 0.76 and are preferably neither substantially angular nor pointed, and are preferably neither sputtered nor nodular nor pointed. However, it should be understood that this means that the particles of the present invention described above may contain such particles in the context of impurities without interfering with the effect of the invention.

[0018] The properties of the Si particles according to Figures 1 to 4 are further shown in the table below. [Table 1]

[0019] The present invention provides a thermally conductive plastic composition (Y), - 5 to 50% by volume of a plastic composition (S), and - 50 to 95% by volume of at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK Contains, however, The thermally conductive plastic composition (Y) has a thermal conductivity of at least 0.6 W / mK, and Thermally conductive filler (Z) has the following characteristics: a) The average diameter x50 is within the range of 30-200 μm; b) be predominantly rounded, with a width / length ratio (aspect ratio w / l) of at least 0.76; c) The distribution width SPAN ((x90-x10) / x50) is at least 0.28 A thermally conductive plastic composition (Y) is provided in which the metallic silicon particles are present in an amount of at least 20% by volume.

[0020] The plastic composition according to the invention preferably has the following characteristics: d) Contains 1.5% by mass or less of silicon particles smaller than 2 μm Also satisfies.

[0021] In the context of the present invention, the terms "heat-conducting," "thermoconductive," or "thermally conductive" are synonymous.

[0022] In the context of the present invention, the term "thermally conductive filler (Z)" is understood to mean a filler having a thermal conductivity of at least 5 W / mK.

[0023] In the context of the present invention, the term "thermally conductive plastic composition (Y)" is understood to mean a plastic composition having a thermal conductivity significantly higher than that of plastics without fillers and additives, generally about 0.2 to 0.3 W / mK, and is characterized by having a thermal conductivity of at least 0.6 W / mK.

[0024] In the context of the present invention, all parameters describing particle size (parameter: mean diameter x 50), particle size distribution (parameters: standard deviation Sigma and distribution width SPAN) or particle shape (parameters: aspect ratio w / l and sphericity SPHT) relate to the volumetric distribution. The mentioned indicators can be measured, for example, by dynamic image analysis according to ISO 13322-2 and ISO 9276-6, for example using a Camsizer X2 device from Retsch Technology.

[0025] Those skilled in the art will recognize that standard deviation is not normalized and is a useful characteristic for assessing particle size distributions of different samples only when the average particle sizes of the comparative samples are approximately equal. Thus, in the context of the present invention, the relative width of a particle size distribution is described using the average particle size x 50 weighted width of the particle size distribution, the dimensionless distribution width, SPAN, defined as: SPAN = (x90 - x10) / x50. The aspect ratio is used as an index to describe particle shape. In older prior art, the aspect ratio is often expressed as the ratio of length to width (l / w), which gives a value greater than or equal to 1. In newer literature, e.g., ISO 9276-6, the aspect ratio is calculated as the inverse ratio of width to length (w / l), which gives a value less than or equal to 1. The two indices can be interconverted by forming their reciprocals. In the context of the present invention, the aspect ratio is defined as the ratio of width to length (w / l) of a particle. The particle width is the minimum value of all the largest measured chords of the particle projections, x c min The particle length is defined as x, which is the longest Feret diameter of all measured Feret diameters of the particle. Fe max More detailed information can be found, for example, in "Operating Instructions / Manual Particle Size Analysis System CAMSIZER®", Retsch Technology GmbH, 42781 Haan; Doc. No. CAMSIZER V0115. The aspect ratio can then be calculated using the following formula: b / l=x c min / xFe max . The sphericity SPHT is calculated from the projected area A of the analyzed particle relative to the area of ​​a circle having the same circumference P as the projected particle according to the following formula (more detailed information can be found, for example, in "Operating Instructions / Manual Particle Size Analysis System CAMSIZER®", Retsch Technology GmbH, 42781 Haan; Doc. CAMSIZER V0115): SPHT=4πA / P 2 . The parameter SPHT corresponds to the square of the circularity C according to ISO 9276-6.

[0026] In order to avoid excessive page count in the description of the invention, only preferred embodiments of individual features are specified below. However, the professional reader should expressly understand such disclosure to mean that all combinations of different preferred levels are also expressly disclosed and expressly desired. DETAILED DESCRIPTION OF THE INVENTION

[0027] (Plastic composition (S)) Suitable plastics include all known classical non-silicone based elastomers, thermoplastic or thermosetting polymers and copolymers, as described in the prior art, for example, in Ullmann, Vol. 15, p. 457 ff., Verlag VCH.

[0028] Suitable thermoplastic polymers are, for example, polyolefins, such as polyethylene, polypropylene and polystyrene, polyamides, polyimides, polyesters, polyetheresters, polyphenylene ethers, polyacetals, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polymethyl methacrylate, polyvinyl acetal, polycarbonates, polyacrylates, acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylic acid ester (ASA), styrene-acrylonitrile (SAN), polycarbonates, polyureas, silane-modified polymers (SMPs), polyurethanes, polyethersulfones and polyetherketones, and also copolymers, mixtures and / or polymer blends thereof, such as PC / ABS, MABS. Suitable thermosetting polymers are, for example, phenolic resins, thermosetting polyurethanes, melamine resins, polyesters and epoxy resins, acrylic resins.

[0029] Suitable elastomers are, for example, styrene butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), fluororubber (FKM), butadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), silane-modified polymers (SMPs), polyacrylate elastomers, polyurethane.

[0030] Mixtures and copolymers of different polymers are also suitable. The term copolymer includes variants in which prepolymers or monomers of different chemical structure are polymerized together. Suitable examples include ethylene-vinyl acetate copolymers (EVA, VAE). Mixtures of two or more substances, also known as terpolymers, are also suitable.

[0031] Preferred plastics are selected from polyurethanes, polyacrylates, epoxy resins, acrylic resins, polyureas, ethylene-vinyl acetate copolymers (EVA, VAE), silane-modified polymers (SMPs), polyethylene, polypropylene and polystyrene. Particularly preferred plastics are polyurethanes, polyacrylates, epoxy resins, acrylic resins and silane-modified polymers (SMPs).

[0032] The plastic composition (S) of the present invention may also contain further additives and additives, which are known to those skilled in the art and described in the prior art. Examples of further additives are processing aids, stabilizers, flame retardants, fungicides, fragrances, active or inactive fillers, plasticizers, flame retardants, agents for influencing electrical properties, dispersants, solvents, pigments, impact modifiers, heat stabilizers, dyes, nesosilicates, adhesion promoters.

[0033] The addition-crosslinkable plastic composition (S) of the present invention can contain an alkyltrialkoxysiloxane (F) as a further additive to reduce its viscosity. If present, it is present in an amount of preferably 0.1 to 8% by weight, more preferably 0.2 to 6% by weight, based on the total weight of the plastic composition (S). The alkyl group is a saturated or unsaturated, linear or branched alkyl group having 2 to 20 carbon atoms, preferably 8 to 18 carbon atoms, and the alkoxy group may contain 1 to 5 carbon atoms. Examples of alkoxy groups include methoxy, ethoxy, propoxy, and butoxy groups, with methoxy and ethoxy groups being particularly preferred. Particularly preferred alkyltrialkoxysiloxanes (F) are n-octyltrimethoxysilane, n-dodecyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane.

[0034] (Thermal conductive filler (Z)) The thermally conductive plastic composition (Y) of the present invention contains at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK, provided that the thermally conductive plastic composition (Y) of the present invention contains at least 20% by volume of metal silicon particles as the thermally conductive filler (Z), which also satisfies at least the further specific characteristics a) to c), and the total amount of the thermally conductive filler (Z) is at least 50% by volume.

[0035] a) The average diameter x50 of these metal silicon particles (Z) of the present invention is in the range of 30 to 200 μm, preferably in the range of 35 to 180 μm, and more preferably in the range of 40 to 160 μm.

[0036] b) The silicon metal particles (Z) of the present invention are mainly rounded and are preferably produced by a melting process. The mainly rounded shape of the particles according to the present invention is characterized by a width / length ratio (aspect ratio w / l) of at least 0.76, preferably at least 0.77, more preferably at least 0.78, and in particular at least 0.79.

[0037] The silicon particles (Z) of the present invention have a sphericity SPHT of at least 0.77, preferably at least 0.78, particularly preferably at least 0.79. In a particularly preferred embodiment, the silicon particles (Z) of the invention have an aspect ratio of at least 0.76 and simultaneously a sphericity SPHT of at least 0.77, preferably at least 0.78, particularly preferably at least 0.79.

[0038] c) The particle size distribution width (SPAN) is defined as SPAN = (x90 - x10) / x50. The SPAN of the metal silicon particles (Z) of the present invention is at least 0.28, preferably at least 0.30, particularly preferably at least 0.35, and particularly preferably at least 0.38. In a preferred embodiment, the SPAN is between 0.40 and 2.5, preferably between 0.41 and 2.2, and particularly preferably between 0.5 and 2.0. It is not important whether a single fraction of silicon particles (Z) whose SPAN falls within the range of the present invention is used, or whether two or more fractions of silicon particles are mixed to achieve the particle size distribution width of the present invention according to characteristic c) of the silicon particles (Z) of the present invention. When two or more fractions of silicon particles are mixed, they may be mixed before being mixed with one or more components of the composition of the present invention, or the fractions of silicon particles may be mixed separately with one or more components of the composition of the present invention. The order of addition is not important. Preferably, four or fewer fractions of silicon particles are mixed to achieve the distribution width of the present invention, preferably three or fewer fractions of silicon particles are mixed to achieve the distribution width of the present invention, particularly preferably two or fewer fractions of silicon particles of the present invention are used to achieve the distribution width of the present invention, and particularly preferably only a single silicon powder of the present invention is used.

[0039] In a preferred embodiment, the silicon particles (Z) also satisfy the following characteristic d): d) The silicon particles (Z) of the present invention preferably contain 1.5% by mass or less, preferably 1% by mass or less, particularly preferably 0.5% by mass or less of silicon particles smaller than 2 μm, in each case based on the total amount of the silicon particles (Z). Particularly preferred silicon particles (Z) are substantially free of particle fractions smaller than 2 μm. The term "substantially free" should be understood to mean that the presence of such particles is acceptable in the context of "impurities" of the particles (Z) of the present invention and does not interfere with the effects of the invention.

[0040] The silicon particles (Z) of the present invention preferably comprise a particle fraction having a diameter of 20 μm or less, in each case based on the total amount of silicon particles, of less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 10% by weight.

[0041] The silicon particles (Z) of the present invention preferably comprise a particle fraction having a diameter of 10 μm or less, in each case based on the total amount of silicon particles, of less than 15% by weight, preferably less than 10% by weight, particularly preferably less than 5% by weight.

[0042] In a particularly preferred embodiment, no silicon particles having an average diameter of 10 μm or less are intentionally added, and it is also preferred that no silicon particles having a particle size of 15 μm or less are added. It is particularly preferred that no silicon particles having an average diameter of 20 μm or less are intentionally added.

[0043] The very fine or pulverized silicon particles employed in the prior art also have the disadvantage that such particles have a relatively large surface area and bind a large amount of polymer. This significantly increases the viscosity of the plastic composition, resulting in a mixture with a relatively low filler content and therefore low thermal conductivity. At higher filler contents, the composition becomes very hard and can no longer be dispensed using traditional processes, such as dispensers. Plastic compositions containing pulverized silicon particles have also proven to be relatively flammable. The relatively large, substantially rounded silicon particles of the present invention, which simultaneously satisfy characteristics a) to c), have the advantage of making it possible to obtain a plastic composition of the present invention with a high filler content and high thermal conductivity, which exhibits good processability and relatively low flammability.

[0044] Metallic silicon has several highly advantageous properties for use as a thermally conductive filler (Z). For example, the very high thermal conductivity of the silicon particles (Z) improves the thermal conductivity of the thermally conductive plastic composition (Y) produced therefrom. The low density of the silicon particles (Z) reduces the weight of the composition and the parts produced therefrom, helping to reduce costs. The low electrical conductivity enables the production of electrically insulating parts and improves dielectric strength. The low Mohs hardness of the silicon particles (Z) reduces wear during processing. Those skilled in the art will recognize that a decrease in the purity of the silicon will result in the loss of all or part of the aforementioned advantages. The purity of the silicon particles (Z) of the present invention, i.e., the silicon content, is at least 80%, preferably at least 90%, and particularly preferably at least 95%.

[0045] Those skilled in the art further recognize that under certain conditions, metal silicon particles are flammable, and their dust poses an explosion hazard. Those skilled in the art also recognize that the risk of dust formation, flammability of metal powders, and explosion hazard increases significantly as the particle size decreases. This is why very small silicon particles of 30 μm or less are unsuitable for many applications. Due to their low minimum ignition energy, such particles are dangerous to handle, requiring complex and expensive safety measures during industrial processing. Furthermore, compositions containing very small silicon particles of 30 μm or less have been found to be relatively flammable.

[0046] Larger silicon particles, with an average particle size greater than 30 μm, exhibit a relatively high minimum ignition energy and are therefore simpler and safer to process in industrial processes. Nevertheless, compositions containing non-inventive crushed, sharp-edged silicon particles greater than 30 μm have proven to be relatively flammable.

[0047] Silicon particles with an average particle size greater than 200 μm are unsuitable for many applications of thermally conductive plastic compositions because they often cannot fit into the small gaps that gap fillers are intended to fill. Furthermore, even silicon particles with such large particle sizes have been found to be relatively flammable.

[0048] The use of spherical fillers to improve the flowability and processability of filled polymers is well known in the prior art. However, there are only a few documents in the prior art that describe the use of spherical silicon particles in thermally conductive plastics. The disclosed compositions only contain very small spherical silicon particles with an average particle size of less than 30 μm, and their drawbacks are as described above.

[0049] It has now been found, quite surprisingly, that the thermally conductive plastic composition (Y) of the present invention has thermal conductivity and exhibits low flammability at the same time when it contains the metal silicon particles of the present invention in a minimum necessary amount so as to simultaneously satisfy characteristics a) to c).

[0050] The plastic composition (Y) of the present invention contains at least 20% by volume, preferably at least 25% by volume, more preferably at least 30% by volume, and particularly preferably at least 35% by volume of such metal silicon particles (Z). If the plastic composition (Y) contains a smaller amount of metal silicon particles (Z), the desired beneficial effects of metal silicon, such as low density and high thermal conductivity, are no longer fully apparent.

[0051] The prior art discloses various methods for producing finely divided metal particles having a rounded shape. The silicon particles (Z) of the present invention are preferably produced from a molten state, and as a result, exhibit a relatively smooth surface and are substantially free of fractures, sharp edges, and sharp corners. This differs from conventional crushed particles, which are formed into their final shape by, for example, crushing, grinding, or milling. It is immaterial whether the particles are crushed in a cold state in an initial step, for example, by crushing, and then heated to above the melting point by, for example, heat treatment in a hot zone using plasma, to form a molten form, or whether a silicon melt is first produced and then crushed, for example, by atomization. It is preferred that the silicon particles of the present invention be formed into the solid particle shape of the present invention by spraying or atomizing a silicon melt and then cooling it.

[0052] Suitable methods for producing the silicon particles (Z) of the present invention are known to those skilled in the art and are described, for example, in Chapter 2, Section 2 of "Pulvermetallurgie: Technologien und Werkstoffe, Schatt, Werner, Wieters, Klaus-Peter, Kieback, Bernd, S. 5-48, ISBN 978-3-540-681112-0, E-Book: https: / / doi.org / 10.1007 / 978-3-540-68112-0_2". Preferred methods for producing the silicon particles (Z) of the present invention are inert gas atomization, also known as gas atomization, pressurized water atomization, also known as liquid atomization or water atomization process, or centrifugal atomization, also known as rotary atomization, melt spinning process. The described method makes it possible to produce silicon metal particles with a very different particle size range, in particular with an average particle size range of a few micrometers to a few millimeters. Furthermore, the silicon metal particles can be produced with very different particle shapes, for example "sputtered", i.e. very irregular, ellipsoidal, spherical, and with very different particle size distribution widths. It has now been found, quite surprisingly, that exclusively silicon particles which are predominantly rounded and which at the same time meet characteristics a) to c) of the invention exhibit the advantageous properties of the invention, in particular their relatively low flammability.

[0053] The method for producing metallurgical silicon particles (Z) of the present invention is preferably carried out so that the particles are obtained with a predominantly rounded shape according to the present invention, thus satisfying characteristics a) to c), and are substantially free of sharp-edged or pointed particles. The method for producing metallurgical silicon particles (Z) of the present invention is preferably carried out so that the particles are obtained with a predominantly rounded shape according to the present invention, thus satisfying characteristics a) to c), and are substantially free of sputtered, nodular, sharp-edged, or pointed particles. The solidified particles can be separated by size by methods commonly used in subsequent processes, such as classification, sieving, or sifting. These methods make it possible to separate agglomerated or bonded particles without substantially destroying the particles. The terms "substantially rounded / substantially free" should be understood to mean that the presence of such particles is acceptable in the context of "impurities" in the particles (Z) of the present invention and does not interfere with the effects of the invention.

[0054] In addition to these metal silicon particles (Z), the plastic composition (Y) of the present invention may contain an additional thermally conductive filler (Z) having a thermal conductivity greater than 5 W / mK. Examples of such additional thermally conductive fillers (Z) include magnesium oxide, metallic aluminum powder, metallic silver powder, zinc oxide, boron nitride, silicon carbide, aluminum nitride, aluminum hydroxide, aluminum oxide, graphite, etc. Preferred additional fillers are aluminum powder, magnesium oxide, aluminum hydroxide, zinc oxide, and aluminum oxide. Particularly preferred additional thermally conductive fillers (Z) are zinc oxide, aluminum hydroxide, and aluminum oxide. The shape of the additional filler is not limited in principle. The particles may be, for example, spherical, ellipsoidal, acicular, tubular, flaky, fibrous, or irregularly shaped. They are preferably spherical, ellipsoidal, or irregularly shaped. The average diameter of said further thermally conductive filler (Z) is preferably in the range of 0.01 to 200 μm, preferably in the range of 0.1 to 150 μm, particularly preferably in the range of 0.2 to 120 μm, in particular in the range of 0.4 to 80 μm.

[0055] Fillers with very high densities are disadvantageous for use in, for example, aircraft or electric vehicles, since they increase the weight of the component very significantly. The further thermally conductive filler (Z) preferably has a density of 6.0 g / cm 3 or less, preferably 4.5 g / cm 3 or less, and particularly preferably 3.0 g / cm 3 It has the following density:

[0056] The plastic composition (Y) of the present invention has a viscosity of 5.0 g / cm 3 It is preferred that the further thermally conductive filler (Z) having a higher density is contained in an amount of 24% by weight or less, preferably 20% by weight or less, particularly preferably 16% by weight or less, and particularly preferably 12% by weight or less.

[0057] In many applications, electrical conductivity of the thermally conductive composition is undesirable, as it may lead to, for example, short circuits. The plastic composition (Y) of the present invention preferably has a resistivity of at least 1 Ω mm 2 / m.

[0058] A preferred thermally conductive plastic composition (Y) of the present invention contains the metal silicon particles of the present invention as the only thermally conductive filler (Z) or in combination with up to three additional thermally conductive fillers (Z). Impurities up to 5% are not considered to constitute additional fillers (Z).

[0059] The total amount of the thermally conductive filler (Z) in the thermally conductive plastic composition (Y) of the present invention is 50 to 95% by volume, preferably 60 to 90% by volume, and more preferably 65 to 88% by volume. If the amount of the thermally conductive filler (Z) contained in the plastic composition (Y) is small, the thermal conductivity will be insufficient, whereas if the amount of the thermally conductive filler (Z) contained in the plastic composition (Y) is large, the composition (Y) will become highly viscous and brittle, making it difficult to process.

[0060] The thermally conductive plastic composition (Y) of the present invention exhibits a thermal conductivity of at least 0.6 W / mK, preferably at least 0.8 W / mK, preferably at least 1.2 W / mK, in particular at least 1.5 W / mK.

[0061] The viscosity of the thermally conductive plastic composition (Y) of the present invention may vary over a very wide range and can be adapted to the requirements of its application. The viscosity of the thermally conductive plastic composition (Y) of the present invention is preferably adjusted via the content of the thermally conductive filler (Z) and / or the composition of the plastic composition (S) according to conventional methods from the prior art, which are known to those skilled in the art. The viscosity is preferably adjusted by selecting the combination of components (S) and (Z) and optionally adding additives.

[0062] The density of the thermally conductive plastic composition (Y) of the present invention is 4.5 g / cm 3 and preferably less than 4.0 g / cm 3 less than 3.5 g / cm 3 less than 3.3 g / cm 3 is less than.

[0063] [Method for producing thermally conductive plastic composition (Y)] The present invention further provides a method for producing the thermally conductive plastic composition (Y) of the present invention by mixing the individual components. The thermally conductive filler (Z) of the present invention can be compounded, for example, by compounding through a masterbatch, a paste, or by direct addition. The composition (S) of the present invention may optionally be mixed with further additives during the compounding of the thermally conductive filler (Z) of the present invention. In principle, the components may be added in any desired order. The components can be mixed by conventional continuous and batch methods known in the art. Suitable mixing equipment includes all known equipment, such as single- or twin-screw continuous mixers, double rollers, Ross mixers, Hobart mixers, dental mixers, extruders, planetary mixers, kneaders, and Henschel mixers or similar mixers. The preferred processing method generally depends on the polymer raw materials used.

[0064] The present invention further provides the use of a thermally conductive filler (Z) to improve the thermal conductivity of a plastic composition (S) selected from non-silicone-based elastomeric, thermoplastic, and thermosetting polymers and copolymers.

[0065] The present invention further provides a plastic product obtained by filling or coating and subsequent crosslinking or curing, said cured plastic product (e.g., a thermally conductive element) exhibiting excellent thermal conductivity and precise film thickness. The hardness of the thermally conductive plastic composition (Y) of the present invention may vary over a very wide range and can be adapted to the requirements of its application. Thus, for example, a relatively soft and flexible product is preferred for use in gap filler applications, while a relatively hard and rigid product is preferred for use in thermally conductive adhesive applications. The hardness of the thermally conductive plastic composition (Y) of the present invention is generally adjusted depending on the polymer raw materials used and is carried out according to conventional methods from the prior art, which are known to those skilled in the art. The plastic article according to the invention exhibits a thermal conductivity of at least 0.6 W / mK, preferably at least 0.8 W / mK, preferably at least 1.2 W / mK, in particular at least 1.5 W / mK.

[0066] The present invention further provides use of the thermally conductive plastic composition (Y) as a thermally conductive paste, gap filler (=thermally conductive element), thermally conductive pad, thermally conductive adhesive, and potting compound for dissipating heat from a heat generating body or a heat sink in an electronic device. The thermally conductive plastic composition (Y) is applied to a heat generating element or a heat dissipating element, or the heat generating element or the heat dissipating element is coated therewith, or the already crosslinked or cured thermally conductive plastic composition (Y) is introduced between the heat generating element or the heat dissipating element, for example in the form of a thermally conductive pad. Suitable heat-generating elements are found, for example, in electronic devices and electronic equipment for power supplies, such as supply transistors, power modules, transistors, thermocouples, and temperature sensors; and heat-generating electronic components, such as integrated circuit components like CPUs and batteries. In the automotive industry, heat-generating elements are particularly found near lithium-ion batteries, charging infrastructure, control devices, and sensors. Suitable heat dissipators consist of heat-dissipating components such as heat distributors, heat sinks, and cooling fins. When the thermally conductive plastic composition (Y) is introduced between a heat-generating element and a heat dissipating element, heat is efficiently conducted from the heat-generating element to the heat dissipating element, thereby enabling effective cooling of the heat-generating element. The thermally conductive plastic composition (Y) of the present invention is particularly suitable for use, for example, as a gap filler for lithium-ion batteries in electric vehicles and as a potting compound for electronic components in electric vehicles.

[0067] <Measurement method> <Measurement of thermal conductivity lambda> Thermal conductivity is measured according to ASTM D5470-12 using a TIM Tester (Steinbeis Transferzentrum Waermemanagement in der Elektronik, Lindenstr. 13 / 1, 72141 Wadorf-Heslach, Germany). The thermal resistance of a sample placed between two test cylinders is measured by constant heat flow. The sample's film thickness is used to calculate the sample's effective thermal conductivity. For measurements, a sample is applied using a stencil, and the measuring cylinder is manually adjusted to a thickness of 1.9-2.0 mm, with excess material removed. Thermal conductivity measurements are performed at a fixed gap of 1.8-1.6-1.4-1.2-1.0 mm. Evaluation is performed using an integrated reporting unit. After validity testing (linear coefficient of determination >0.998), the thermal conductivity lambda is reported as the effective thermal conductivity W / (m*K).

[0068] <Analysis of particle size and particle shape> Analysis of particle size (mean diameter x 50), particle size distribution (parameters: standard deviation sigma and distribution width SPAN) and particle shape (parameters: aspect ratio w / l and sphericity SPHT) was carried out in accordance with ISO 13322-2 and ISO 9276-6 using a Camsize X2 (measurement principle: dynamic image analysis) manufactured by Retsch Technology (analysis type: dry measurement of powders and granules; measurement range: 0.8 μm to 30 mm; compressed air dispersion using X-Jet, dispersion pressure = 0.3 bar). c min This was done on a volumetric basis in accordance with the model. [Example]

[0069] The following examples are provided to illustrate in principle how the invention can be put into practice, but they are not intended to limit the invention to that disclosed therein.

[0070] In the following examples, all amounts reported in parts and percentages are by weight unless otherwise specified. Unless otherwise specified, the following examples are carried out at atmospheric pressure, i.e., about 1000 hPa, and at room temperature, i.e., about 20°C, or at a temperature established by combining the reactants at room temperature without further heating or cooling.

[0071] <Summary of the silicon powders and silicon powder mixtures used in accordance with the present invention and other non-inventive methods> Table 1 summarizes the properties of the inventive and non-inventive silicon powders used in this example. Inventive Example 1 uses silicon powder according to the invention, which is obtained by inert gas atomization and therefore has a predominantly rounded and relatively broad particle size distribution according to the invention. The non-inventive comparative example C1 uses a non-inventive silicon powder obtained by inert gas atomization and therefore having a predominantly rounded, but relatively narrow, non-inventive particle size distribution, which does not satisfy feature c) of the present invention. Non-invention comparative example C2 uses a non-invention silicon powder that has a relatively broad, inventive particle size distribution, but is obtained by a milling process and therefore has substantially sharp and angular shapes, not satisfying feature b) of the invention.

[0072] <abbreviation> Example: C Comparative example PS particle shape r Mainly rounded a. Angular I. The present invention NI Non-invention nd Not measured

[0073] Table 1: Overview of silicon powders used [Table 2]

[0074] <General Manufacturing Procedure 1 (GP1) of One-Component Curable Thermally Conductive Silicon Powder-Containing Plastic Molded Products (Invention Example 2 and Non-Invention Examples C3 to C5)> [Step 1: Preparation of a one-component curable thermally conductive silicone powder-containing plastic composition] The one-component curable thermally conductive plastic composition and silicone powder were mixed for 25 seconds at 2350 rpm using a SpeedMixer DAC 400 FVZ (Hauschild & Co. KG, Waterkamp 1, 59075 Hamm, Germany). The silicone particle-containing plastic composition was stirred with a spatula to mix in the remaining silicone powder from the edge of the container. The mixture was then homogenized for another 25 seconds at 2350 rpm using the SpeedMixer and cooled to room temperature. The ingredients and their amounts are shown in Table 2. A pasty mass was obtained. [Step 2: Manufacturing of plastic molded products containing curable thermally conductive silicon powder] The silicon powder-containing plastic composition from step 1 was cured according to the manufacturer's specifications and in accordance with the specific curing conditions for the plastic composition used, as shown in Table 2.

[0075] <General Manufacturing Procedure 2 (GP2) of Two-Component Plastic Composition Containing Thermally Conductive Silicon Powder (Invention Example 3 and Non-Invention Examples C6 to C8)> [Step 1: Preparation of a two-component thermally conductive silicon powder-containing plastic composition] The A and B components of the two-component plastic composition were each mixed separately with the silicone powder using a SpeedMixer DAC 400 FVZ (Hauschild & Co. KG, Waterkamp 1, 59075 Hamm, Germany) at 2350 rpm for 25 seconds. The silicone particle-containing plastic compositions were each stirred with a spatula to mix in the remaining silicone powder from the edge of the container. The mixtures were then homogenized using the SpeedMixer at 2350 rpm for another 25 seconds and cooled to room temperature. The raw materials and amounts used are shown in Table 3. A paste-like mass of each was obtained. [Step 2: Production of cross-linked thermally conductive silicon powder-containing plastic molded products] The silicon powder-containing A and B components prepared in step 1 were mixed and homogenized using a Speed ​​Mixer at 2350 rpm for 25 seconds. The two-component silicon powder-containing plastic composition was cured according to the manufacturer's specifications and the specific curing conditions for the plastic composition used. The conditions used are shown in Table 3.

[0076] <Example 4: Flammability test> Flammability testing is carried out using a simple test based on UL 94 HB. The inventive plastic compositions according to Examples 2 and 3, and the non-inventive plastic compositions according to Comparative Examples C3 to C6, are applied in 2-mm thick layers to aluminum plates 150 mm long, 10 mm wide, and 2 mm thick, and cured according to the details in Tables 2 and 3. The plate is fixed with the right long side vertical, with the aluminum substrate facing downwards and the knife-coated sample facing upwards. The burner is adjusted to produce a blue flame 325 mm long. The flame is directed horizontally toward the specimen, with the tip of the blue flame pointing toward the front of the specimen, 20 mm from the left edge of the specimen. The flame is removed after 30 seconds of irradiation. Flammability Test and Evaluation: During the application of the flame, the flame pattern and the height of the glowing flame are measured. The afterflame time (total time consisting of afterburn and afterglow) of the test specimen is recorded.

[0077] Table 2: Composition and flammability of one-component plastic compositions containing silicon powder [Table 3]

[0078] The non-inventive comparative test C3 contained 64.6% by volume of non-inventive crushed silicon particles according to comparative test C2, which in particular did not fulfill characteristic b), resulting in a plastic composition with a very high viscosity, which could not be applied in a uniform layer and could not be tested.

[0079] Table 3: Composition and flammability of two-component plastic compositions containing silicon powder [Table 4]

[0080] The non-inventive comparative test C6 contained 73.4 vol. % of non-inventive crushed silicon particles according to comparative test C2, which in particular did not fulfill characteristic b), resulting in a plastic composition with a very high viscosity, which could not be applied in a uniform layer and could not be tested.

[0081] It surprisingly becomes clear that the inventive plastic compositions according to Examples 2 and 3, which simultaneously fulfill characteristics a) to c), exhibit relatively low flammability.

[0082] Example 5: Preparation of a thermally conductive plastic composition containing an in-situ mixture of silicon powder (present invention) A thermally conductive plastic composition of the present invention was prepared according to general procedure GP1, in which 46.0 g of Soudal "Transpacryl" (transparent acrylic) was used as the plastic composition, and the following silicon powders were added separately and mixed to form the in-situ silicon powder mixture of the present invention: 18.4 g of non-invention silicon powder having x50 of 68.6 μm, SPAN of 0.20, w / l of 0.85, and SPHT of 0.84; 3 g of non-invention silicon powder from comparative example C2; 6.8g, 73.6g of non-invention silicon powder having a x50 of 105.4μm, SPAN of 0.24, w / l of 0.83, and SPHT of 0.92, 36.8g of non-invention silicon powder having a x50 of 133.8μm, SPAN of 0.25, w / l of 0.82, and SPHT of 0.94, and 18.4g of non-invention silicon powder having a x50 of 162.1μm, SPAN of 0.22, w / l of 0.82, and SPHT of 0.94. This resulted in a plastic composition of the present invention containing 64.6% by volume of silicon particles of the present invention. The paste-like mass of the present invention has good processability. As a result of the flammability test according to Example 4, a medium flame pattern was produced, with a flame height of 9 cm and an afterflame time of 10 seconds, which indicates significantly weaker flammability than Comparative Examples C3 to C5, which used the same plastic composition as a reference.

Claims

1. A thermally conductive plastic composition (Y), - 5 to 50% by volume of a non-silicone-based plastic composition (S), and - 50 to 95% by volume of at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK The total of the non-silicone-based plastic composition (S) and the thermally conductive filler (Z) is equal to 100% by volume, with the proviso that the thermally conductive plastic composition (Y) has a thermal conductivity of at least 0.6 W / mK, and The thermally conductive filler (Z) has the following characteristics: a) the average diameter x50 is in the range of 30 to 200 μm; b) are predominantly rounded, with a width / length ratio (aspect ratio w / l) of at least 0.76; c) The distribution width SPAN ((x90-x10) / x50) is at least 0.28 A thermally conductive plastic composition (Y) in which at least 20% by volume of metal silicon particles satisfying the above formula are present.

2. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the plastic composition (S) is selected from non-silicone based elastomers, thermoplastic and thermosetting polymers, and copolymers.

3. The plastic composition (S) the group consisting of thermoplastic polymers: polyethylene, polypropylene and polystyrene, polyamides, polyimides, polyesters, polyetheresters, polyphenylene ethers, polyacetals, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polymethyl methacrylate, polyvinyl acetal, polycarbonates, polyacrylates, acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), styrene-acrylonitrile (SAN), polycarbonates, polyureas, silane-modified polymers (SMPs), polyurethanes, polyethersulfones and polyetherketones, as well as copolymers, mixtures and / or polymer blends thereof; - the group consisting of thermosetting polymers: phenolic resins, thermosetting polyurethanes, melamine resins, polyesters, epoxy resins, acrylic resins, the group consisting of elastomers: styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), fluororubber (FKM), butadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), silane-modified polymers (SMPs), polyacrylate elastomers, polyurethanes, their mixtures, as well as prepolymers or copolymers of the above polymers in which the monomers are polymerized with one another; The thermally conductive plastic composition (Y) according to claim 1, selected from:

4. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the plastic composition (S) is selected from polyurethane, polyacrylate, epoxy resin, acrylic resin, polyurea, ethylene-vinyl acetate copolymer (EVA, VAE), silane-modified polymers (SMPs), polyethylene, polypropylene and polystyrene, and mixtures and copolymers thereof.

5. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the plastic composition (S) is selected from polyurethanes, polyacrylates, epoxy resins, acrylic resins and silane-modified polymers (SMPs), and mixtures and copolymers thereof.

6. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the plastic composition (Y) contains at least 25% by volume of metal silicon particles as the thermally conductive filler (Z).

7. The metal silicon particles present as the thermally conductive filler (Z) satisfy the following additional conditions: d) Contains no more than 1.5% by volume of silicon particles smaller than 2 μm The thermally conductive plastic composition (Y) according to claim 1, which also satisfies the above conditions.

8. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the metallic silicon particles present as thermally conductive filler (Z) are produced from the molten state.

9. 2. The thermally conductive plastic composition (Y) according to claim 1, wherein the metallic silicon particles present as the thermally conductive filler (Z) are brought into solid particle form from a silicon melt by spraying or atomizing.

10. A method for producing the thermally conductive plastic composition (Y) according to any one of claims 1 to 9 by mixing the individual components.

11. 2. Use of said thermally conductive filler (Z) for improving the thermal conductivity of the plastic composition (S) according to claim 1, selected from non-silicone based elastomers, thermoplastic polymers and thermosetting polymers and copolymers.

12. A plastic product obtained by filling or applying the thermally conductive plastic composition (Y) according to any one of claims 1 to 9, followed by crosslinking or curing.

13. Use of the thermally conductive plastic composition (Y) according to any one of claims 1 to 9 as a thermally conductive paste, gap filler (= thermally conductive element), thermally conductive pad, thermally conductive adhesive and potting compound for heat dissipation from heat generating or heat sinking bodies in electronic devices.

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