Thermal conductive paste containing silicon

Abstract

The present invention relates to a non-crosslinked thermally conductive silicone composition (Y) comprising: at least one non-crosslinked silicone composition (S) in an amount of -5 to 50% by volume; and at least one thermally conductive filler (Z) in an amount of 50 to 95% by volume having a thermal conductivity of at least 5 W / mK, provided that the non-crosslinked thermally conductive silicone composition (Y) has a thermal conductivity of at least 0.6 W / mK and contains at least 20% by volume of metal silicon particles as the thermally conductive filler (Z) satisfying the following characteristics: a) the median particle size x50 of the metal silicon particles is in the range of 30 to 200 μm; b) the metal silicon particles are mainly rounded and have an aspect ratio (aspect ratio b / l) of at least 0.76; and c) the distribution range SPAN ((x90 - x10) / x50) of the metal silicon particles is at least 0.28.

Description

Technical Field

[0001] The present invention relates to a thermally conductive silicone composition, and its production and use.

Background Art

[0002] Prior Art Thermally conductive silicone compositions are widely used in thermal management in the automotive and electronics industries. Examples of important forms of presentation include thermally conductive adhesives, thermally conductive pads, gap fillers and encapsulating compounds and pastes. A thermal paste is a paste that improves heat transfer between two objects, for example between an integrated circuit and the cooling surface / case of a heat sink. The assembly areas of heat sinks and components always contain more or less non-uniform variations in depth and flatness. The thermal paste fills this non-uniformity and thus enables good heat transfer to the cooling case or heat sink.

[0003] The prior art comprises different thermally conductive fillers added to improve the thermal conductivity of silicone compositions. However, these have significant drawbacks. For example, ceramic fillers such as aluminum oxide have a very high density and thus significantly increase the weight of the components. Furthermore, ceramic fillers are relatively expensive. Metallic fillers such as aluminum powder or silver powder are conductive and unacceptable for many applications. Many metals and alloys are furthermore relatively expensive.

[0004] Many further fillers with high thermal conductivity, such as carbon nanotubes, boron nitride and aluminum nitride, can also be used only to a very limited extent or in small amounts for specific applications due to their relatively high cost.

[0005] The prior art comprises various thermally conductive silicone compositions containing silicon particles as thermally conductive fillers. These are relatively light and inexpensive. Furthermore, silicon, being a semiconductor, has very low conductivity. However, the silicon particles according to the prior art are not suitable for use in electric vehicles and electronic components.

[0006] The Si particles used in the prior art are usually obtained by a grinding method. The drawback is that such particles have a large surface area and bind to a very large amount of polymer. This causes a very significant increase in the viscosity of the silicone composition. It is only possible to produce mixtures with relatively low filling levels and low thermal conductivities. When the filling level is high, the composition becomes very hard and can no longer be processed by conventional methods such as dispensers. It can also be seen that silicone compositions containing ground silicon particles are relatively highly flammable.

[0007] Using silicon particles smaller than 30 μm is also disadvantageous because such small particles have a relatively low minimum ignition energy, presenting a risk of dust explosion and thus requiring complex and costly safety measures in industrial processing.

[0008] Japanese Patent Application Laid-Open No. 2019-131669 teaches the use of metallic Si particles sized 0.1 to 200 μm and having an insulating coating as a thermally conductive filler for silicone-free organic resins. These particles can be produced by thermal destruction or melting or a grinding method, or obtained by polishing or a grinding method. The particles are provided with an insulating coating in a separate processing step. In the example, Japanese Patent Application Laid-Open No. 2019-131669 discloses an organic resin containing ground Si particles having an average particle size of 32 μm and a thermal conductivity up to 7 W / mK and up to 65 vol%. The drawback is the use of ground particles with relatively high flammability. The disclosed vulcanizates are non-elastic and thus not suitable for use as gap fillers in lithium-ion batteries.

[0009] U.S. Patent Application Publication No. 2016 / 122611 teaches an electrically and thermally conductive silicone elastomer composition containing a thermal conductivity filler of less than 30 μm, more preferably 2 - 8 μm, in combination with carbon black. The thermal conductivity filler may be silicon powder. Disclosed in the examples are compositions containing up to 60 wt% of ground Si particles having an average particle size of 5 μm, or up to 46 wt% of ground Si particles having an average particle size of 40 μm. The thermal conductivity of the composition is up to 1.0 W / mK. The drawback is the use of ground particles that permit only compositions with relatively high flammability, relatively low filling levels, and low thermal conductivity.

[0010] U.S. Patent Application Publication No. 2007 / 135555 teaches a thermally crosslinkable thermally conductive silicone composition containing spherical metallic Si particles produced by a melting method or ground metallic Si particles, with an average particle size of up to 100 μm, more preferably 2 - 25 μm respectively. Disclosed in the examples are compositions containing up to 71 wt% of ground Si particles having an average particle size of 12 μm, or up to 71 wt% of ground spherical Si particles having an average particle size of 5 μm, each in combination with an oxidation filler, such as Fe2O3 or Al2O3. The thermal conductivity of the composition is up to 1.2 W / mK. The drawback is the use of very small Si particles that permit only compositions with relatively high flammability, relatively low filling levels, and low thermal conductivity.

[0011] U.S. Patent Application Publication No. 2007 / 117920 teaches a thermally crosslinkable thermally conductive silicone composition containing spherical or crushed metallic Si particles having an average particle size of 2 to 100 μm, more preferably 2 to 25 μm. Disclosed in the examples are compositions containing up to 67 wt% of crushed Si particles having an average particle size of 5 to 12 μm as a sole filler or in combination with Al2O3. The viscosity of the mixture ranges from 30,000 to 260,000 mPa·s with a thermal conductivity of up to 1.0 W / mK. The drawback is the use of very small Si particles which only permit compositions having relatively high flammability, relatively high viscosity, low filling levels and low thermal conductivity.

[0012] U.S. Patent Application Publication No. 2001 / 051673 teaches a thermally crosslinkable thermally conductive silicone elastomer composition composed of a magnetic silicon-containing Fe-Si alloy and containing platelet-shaped particles having an average particle size of 0.1 to 350 μm or circular particles having an average particle size of 0.1 to 50 μm, preferably 0.5 to 20 μm, with platelets being preferred. Disclosed in the examples is a composition containing 30 vol% of spherical Fe-Si particles having an average particle size of 8 μm and consisting of 97 wt% Fe and 3 wt% Si in combination with 40 vol% of Al2O3 particles. The thermal conductivity is 4.0 W / mK. The drawback is the use of very small Fe-Si particles with a very high iron content. As a result, the particles are conductive, have a relatively high density and relatively high flammability. A further drawback is the use of a large amount of Al2O3, which means that the density of the composition is very high.

[0013] U.S. Patent No. 4,292,223 teaches a crosslinkable thermally conductive silicone elastomer composition having an average particle size of 40 to 300 μm and comprising, for example, silicon, preferably an alloy. The particles may be spherical or irregular in shape and have an aspect ratio of up to 8 (corresponding to an aspect ratio (w / l) of 0.125 or more according to ISO 9276-6). Thus, the particles may be either spherical with an aspect ratio of 1 or rod-shaped where the length may be up to 8 times the width, so the definition of possible particle shapes is very broad. Disclosed is a composition containing 28 wt% of ground Si particles having an average particle size of 44 μm and no disclosure of the w / l ratio. The drawback is the use of ground particles which are relatively highly flammable. Further, since the ground particles have a relatively high surface area, compositions containing the ground particles have a relatively high viscosity and are difficult to process. The crosslinked material has low flexibility and is brittle.

[0014] U.S. Patent Application Publication No. 2006 / 228542 describes a thermally conductive elastomer containing two thermally conductive fillers of different sizes. The elastomer may be, inter alia, silicone. The first thermally conductive filler is formed from an electrically insulating and thermally conductive ceramic. As one of several examples of suitable ceramic materials, “silicone” is incorrectly described instead of “silica”. However, while silicon metal is not a ceramic, since fused silica ceramic (i.e., SiO2 ceramic) is very well known, it will be completely clear to those skilled in the art from reading this disclosure that what is actually meant is silica ceramic. Further, the first thermally conductive filler has a unimodal distribution and has an average particle size of at least 20 μm. The first filler particles are disclosed to be elliptical or spherical and may be hollow. The preferred average particle size is 30 to 95 μm and the standard deviation is 15 to 40 μm. This is a very non-specific definition of the possible distribution range, so the particles may have a very narrow or very broad distribution.

[0015] This is shown by the following observation examples: A standard deviation of 40 μm with an average particle size of 30 μm corresponds to a very wide particle size distribution, while a standard deviation of 15 μm with an average particle size of 95 μm corresponds to a very narrow particle size distribution. U.S. Patent Application Publication No. 2006 / 228542 does not teach about the influence of the standard deviation of the filler particle size distribution on the properties of the elastomer. SUMMARY OF THE INVENTION

[0016] Accordingly, an object of the present invention was to provide a non-crosslinkable thermally conductive silicone 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.

[0017] This object is achieved by the non-crosslinkable thermally conductive silicone composition (Y) of the present invention, which contains relatively large Si particles having an average particle size of 30 to 200 μm and mainly rounded shapes, and at the same time has a particularly large or wide particle distribution range. Quite surprisingly, it has been experimentally found that these non-crosslinkable thermally conductive silicone compositions (Y) of the present invention clearly have a reduced flammability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

[0019] In the context of the present invention, "substantially rounded" shaped Si particles are understood to mean particles having a spherical to elliptical shape with a smooth surface. These particles may also be referred to as potato-shaped. FIG. 1 shows, by way of example, these Si particles of the present invention having a substantially rounded shape. The shapes of Si particles not of the present invention are shown in FIG. 2 for "sputtered" particles, in FIG. 3 for "nodular" particles, and in FIG. 4 for "angular" and "sharp" particles. The metallic Si particles of the present invention are thus not sputtered, not nodular, or not angular or sharp. However, the metallic Si particles of the present invention may contain such particles to an extent that does not interfere with the effects of the present invention.

[0020] The characteristics of the Si particles according to FIGS. 1 to 4 are further shown in the following table.

[0021] [Table 1]

[0022] The present invention relates to - 5 to 50% by volume of a non-crosslinkable silicone 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 comprising a crosslinkable thermally conductive silicone composition (Y), provided that the non-crosslinkable thermally conductive silicone composition (Y) has a thermal conductivity of at least 0.6 W / mK, at least 20% by volume of the metallic silicon particles present as the thermally conductive filler (Z) have the following characteristics: a) The median particle size x50 of the metallic silicon particles is in the range of 30 to 200 μm, b) The metallic silicon particles are substantially rounded and have an aspect ratio (w / l) of at least 0.76, c) The distribution range SPAN ((x90 - x10) / x50) of the metal silicon particles is at least 0.28, to provide a non-crosslinkable thermally conductive silicone composition (Y) that satisfies the above.

[0023] In the context of the present invention, the terms "heat-conducting" and "thermally conductive" are equivalent.

[0024] The thermally conductive filler (Z) in the context of the present invention is understood to mean any filler having a thermal conductivity of at least 5 W / mK.

[0025] The thermally conductive silicone composition (Y) in the context of the present invention clearly exceeds the thermal conductivity of polydimethylsiloxane without fillers and additives, typically about 0.2 W / mK, and the silicone composition is understood to mean a silicone composition having a thermal conductivity of at least 0.6 W / mK.

[0026] In the context of the present invention, all parameters describing the particle size (parameter: median particle size x50), particle size distribution (parameters: standard deviation σ and distribution range SPAN), or particle shape (parameters: aspect ratio w / l and sphericity SPHT) are based on a volume-based distribution. The mentioned indices may be measured, for example, by dynamic image analysis in accordance with ISO 13322-2 and ISO 9276-6 using a Camsizer X2 manufactured by Retsch Technology.

[0027] Those skilled in the art will recognize that the standard deviation is not standardized and is a feature that enables the evaluation of the particle size distribution of different samples only when the average particle size of the comparison samples is approximately the same. To describe the relative spread of the particle size distribution in the context of the present invention, therefore, the particle size distribution range weighted by the median particle size x50, the dimensionless distribution range SPAN defined as follows: SPAN = (x90 - x10) / x50, is used.

[0028] The aspect ratio serves as an indicator for describing the shape of particles. In the prior art, the aspect ratio was often described in relation to the ratio of length to width (l / w). As a result, the value was 1 or greater. In more recent literature, for example, in accordance with ISO9276-6, the aspect ratio is calculated from the inverse ratio of width to length (w / l). As a result, the value is 1 or less. These two indicators can be mutually converted by forming reciprocals. In the context of the present invention, the aspect ratio is defined as the ratio of the width to the length (w / l) of the particle. In this specification, the particle width is the smallest of all the maximum chords measured in the particle projection image, x c min given by x, and the particle length is the longest Feret diameter among all the Feret diameters measured on the particle, x Fe max given by x. More detailed information can be found, for example, in "Operating Instructions / Manual Particle Size Analysis System CAMSIZER(Registered Trademark)", Retsch Technology GmbH, 42781 Haan; Doc.No. CAMSIZER V0115. This gives rise to the following equation for the aspect ratio: w / l = x c min / x Fe max

[0029] The sphericity SPHT is calculated from the projected area A of the analyzed particle with respect to the area of a circle having the same outer perimeter P as the projected particle by the following equation (more detailed information can be found, for example, in "Operating Instructions / Manual Particle Size Analysis System CAMSIZER(Registered Trademark)", Retsch Technology GmbH, 42781 Haan; Doc.No. CAMSIZER V0115): SPHT = 4πA / P 2

[0030] The index SPHT corresponds to the square of the roundness C compliant with ISO9276-6.

[0031] In the description of the present invention, only the preferred embodiments of individual features are detailed in the description so as not to generate an excessive number of pages.

[0032] However, an expert reader will explicitly understand this disclosure method as any combination of different levels of selection is explicitly disclosed and desired as such.

[0033] Non-crosslinkable silicone composition (S) The following features: - The organopolysiloxane is linear, branched or cyclic, preferably linear, - End-capped at both ends, or terminated with one Si-OH or one alkoxysilyl, preferably end-capped at both ends, - Si-bonded side chains and terminal groups R 1 are independently substituted or unsubstituted C1-C18 hydrocarbon groups, preferably monovalent C1-C10 hydrocarbon groups, A non-crosslinkable silicone composition (S) containing one or a mixture of at least two organopolysiloxanes (T) having. R 1Examples include linear, branched, and cyclic alkyl, alkenyl, aryl, aralkyl, and haloalkyl groups. Suitable pure alkyl groups include methyl, ethyl, propyl, hexyl, and octyl groups. Suitable branched alkyl groups include isopropyl, isobutyl, tert-butyl, and 2-ethylhexyl groups. Suitable cyclic alkyl groups include cyclopentyl and cyclohexyl groups. Suitable alkenyl groups include vinyl and allyl groups. Suitable aryl groups include phenyl and tolyl groups. Suitable aralkyl groups include 2-phenylethyl and 2-methyl-2-phenylethyl groups. Suitable haloalkyl groups include 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and 2-(heptadecafluorooctyl)ethyl groups. Preferred R 1 is methyl or phenyl.

[0034] The process for preparing end-capped organopolysiloxanes has long been known to those skilled in the art and starts, for example, from dichloromethylsilane in the presence of water to give linear, end-capped polymethylpolysiloxanes.

[0035] The dynamic viscosities of these organopolysiloxanes (T) are from 35 to 1000000 mPas, preferably from 50 to 100000 mPas, at 25 °C. These organopolysiloxanes (T) have long been known to those skilled in the art and are often referred to as silicone oils.

[0036] In order to adjust the stability or rheology of the non-crosslinkable silicone composition (S) under load, so-called rheology additives (E) (= structure formers) can be added. These are known to those skilled in the art from the prior art.

[0037] Suitable rheology additives (E) are solid, fine inorganic fillers. Suitable examples are reinforcing and non-reinforcing fillers such as metal oxides or furnace black and acetylene black.

[0038] Suitable reinforcing fillers (E), i.e. fillers having a BET surface area of at least 50 m 2 / g, examples are fumed silica, precipitated silica or a mixture of silicon-aluminum oxides having a BET surface area of more than 50 m 2 / g. The fillers mentioned may be hydrophobized, for example, using organosilanes, organosilazanes or organosiloxanes, or by etherification of hydroxyl groups to alkoxyl groups. As a result of the surface treatment, such silica has a carbon content of at least 0.01 wt% to a maximum of 20 wt%, preferably 0.1 wt% to 10 wt%, more preferably 0.5 wt% to 6 wt%.

[0039] Examples of suitable non-reinforcing fillers (E), i.e. fillers having a BET surface area of less than 50 m 2 / g, include quartz, cristobalite, diatomaceous earth, calcium silicate, zirconium silicate, montmorillonite, for example bentonite, zeolites comprising molecular sieves such as sodium aluminum silicate, metal oxides such as aluminum oxide or zinc oxide or mixtures thereof, metal hydroxides such as aluminum hydroxide, barium sulfate, calcium carbonate, gypsum, powders of silicon nitride, silicon carbide, boron nitride, glass powder, carbon powder and polymer powder, and hollow glass and plastic beads. The BET surface area of the non-reinforcing filler is preferably less than 20 m 2 / g.

[0040] Even more preferred as rheology additives (E) are - at least one alkenyl-terminated polydiorganosiloxane having a degree of polymerization of at least 300 and - at least one organohydrosiloxane crosslinking agent having an average of 2 or more SiH groups per molecule A crosslinked hydrosilylation reaction product obtained from the reaction, wherein the ratio of the alkenyl-terminated polydiorganosiloxane and the organohydrosiloxane is adjusted such that the ratio of the SiH group to the alkenyl group is in the range of 0.5 to 2.0.

[0041] Crosslinking with this type of rheology additive (E) is known to those skilled in the art from the prior art and may precede the addition to the above non-crosslinkable silicone composition (S), or the structuring agent is crosslinked in situ in the above non-crosslinkable silicone composition (S).

[0042] Also more preferred as the rheology additive (E) are non-particulate organic rheology additives or those based on organic polymers. These are commercially available. BASF sells such rheology additives, for example, under the following trade names: RHEOVIS®, ATTAGEL®, ATTAFLOW® and EFKA®. More preferred rheology additives are sold by CRODA under the trade names Atlox Rheostrux™ 100 (a polyester block copolymer) or Atlox Rheostrux™ 200 (a polyamide).

[0043] One type of rheology additive (E) or a mixture of at least two types of rheology additives can be used.

[0044] When the rheology additive (E) is present, the rheology additive is preferably present in an amount of about 1 to 9% by weight, preferably 2 to 8% by weight, based on the total mass of the silicone composition (S).

[0045] The non-crosslinkable silicone composition (S) according to the present invention may contain an alkyltrialkoxysilane (F) as a further additive in order to lower its viscosity. When the alkyltrialkoxysilane is present, the alkyltrialkoxysilane is preferably present in an amount of about 0.1 to 8% by weight, preferably about 0.2 to 6% by weight, based on the total mass of the silicone composition (S). The alkyl group may be a saturated or unsaturated, linear or branched alkyl group having 2 to 20, preferably 8 to 18 carbon atoms, and the alkoxy group may have 1 to 5 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group, and the methoxy group and the ethoxy group are particularly preferred. Preferred for (F) are n-octyltrimethoxysilane, n-dodecyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane.

[0046] The non-crosslinkable silicone composition (S) according to the present invention may optionally contain a further constituent (G). These optional additives are resinous polyorganosiloxanes, bactericides, fragrances, corrosion inhibitors, antioxidants, light stabilizers, flame retardants, and compositions for influencing electrical properties, dispersion aids, solvents, pigments, dyes, organic polymers, heat stabilizers, and the like.

[0047] Thermally conductive filler (Z) The non-crosslinkable thermally conductive silicone composition (Y) according to the present invention contains at least one thermally conductive filler (Z) having a thermal conductivity of at least 5 W / mK, provided that the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention still needs to satisfy at least further specific features a) to c), and in a preferred embodiment also d). As the thermally conductive filler (Z), it contains at least 20% by volume of metal silicon particles, and the total amount of the thermally conductive filler (Z) is at least 50% by volume.

[0048] a) The median particle size x50 of these metal silicon particles (Z) according to the present invention is in the range of 30 to 200 μm, preferably in the range of 40 to 180 μm, more preferably in the range of 50 to 160 μm.

[0049] b) The metal silicon particles (Z) according to the present invention are mainly rounded and are preferably produced by a melting method. The mainly rounded shape of the particles according to the present invention is characterized in that the aspect ratio (aspect ratio w / l) is at least 0.76, preferably at least 0.77, more preferably at least 0.78, particularly at least 0.79.

[0050] The silicon particles (Z) according to the present invention preferably have a sphericity SPHT of at least 0.75, preferably at least 0.76, more preferably at least 0.78, particularly preferably at least 0.79.

[0051] In a particularly preferred embodiment, the silicon particles (Z) according to the present invention have an aspect ratio of at least 0.76 and simultaneously a sphericity SPHT of at least 0.75, preferably at least 0.76, more preferably at least 0.78, particularly preferably at least 0.79.

[0052] c) The particle size distribution range (SPAN) is defined as SPAN = (x90 - x10) / x50. The SPAN of the metal silicon particles (Z) according to the present invention is at least 0.28, preferably at least 0.30, more preferably at least 0.35, particularly preferably at least 0.38. In a preferred embodiment, SPAN is 0.40 to 2.5, preferably 0.41 to 2.2, particularly 0.5 to 2.0.

[0053] Here, it is not important whether a single fraction of silicon particles (Z) having a SPAN within the scope of the present invention is used, or whether two or more fractions of silicon particles are mixed, whereby the particle size distribution range of the present invention according to feature c) of the silicon particles (Z) of the present invention is achieved. When mixing two or more fractions of silicon particles, this may precede the mixing with one or more components of the composition according to the present invention, or the fractions of silicon particles may also be mixed separately from one or more components of the composition according to the present invention. The order of addition here is not questioned.

[0054] Preferably, in order to achieve the distribution range of the present invention, silicon particles of four or fewer fractions are mixed, preferably silicon particles of three or fewer fractions are mixed, more preferably silicon particles of two or fewer fractions of the present invention are used, and particularly preferably only a single silicon powder of the present invention is used.

[0055] d) The silicon particles (Z) of the present invention, in each case based on the total amount of the silicon particles (Z), in a preferred embodiment, contain silicon particles of 1.5% by weight or less with a size of less than 2 μm, preferably 1% by weight or less, more preferably 0.5% by weight or less. Particularly preferred silicon particles (Z) essentially do not contain a particle fraction of less than 2 μm. What is meant by "essentially does not contain" is that the presence of such particles is within the range of "impurities" in the particles (Z) of the present invention and does not interfere with the effects of the present invention.

[0056] The silicon particles (Z) of the present invention, in each case based on the total amount of the silicon particles (Z), preferably contain a particle fraction having a diameter of 20 μm or less of less than 20% by weight, more preferably less than 15% by weight, and particularly preferably less than 10% by weight.

[0057] The silicon particles (Z) of the present invention, in each case based on the total amount of the silicon particles (Z), preferably contain a particle fraction having a diameter of 10 μm or less of less than 15% by weight, more preferably less than 10% by weight, and particularly preferably less than 5% by weight.

[0058] In a particularly preferred embodiment, silicon particles having an average diameter of 10 μm or less are not intentionally added. It is preferred not to add silicon particles of 15 μm or less. It is particularly preferred not to intentionally add silicon particles having an average diameter of 20 μm or less.

[0059] Very fine silicon particles or ground silicon particles have a relatively large surface area and bind with a very large amount of polymer, so such particles are also disadvantageous. As a result, since they have a relatively low filler level, the viscosity of the silicone composition increases very significantly so as to make it possible to produce only mixtures with a low thermal conductivity. When the filler level is high, the composition becomes very hard and can no longer be processed by conventional methods such as dispensers. It can also be seen that silicone compositions containing ground silicon particles are relatively highly flammable.

[0060] Metallic silicon has a plurality of very advantageous properties for use as a thermal conductivity filler (Z). For example, due to the extremely high thermal conductivity of the silicon particles (Z), the thermal conductivity of the thermally conductive silicone composition (Y) produced therefrom is improved. When the viscosity of the silicon particles (Z) is low, the weight of the composition and the weight of the components produced therefrom are reduced, and the cost is reduced. When the electrical conductivity is low, it becomes possible to produce an electrically insulating component, and the electrical breakdown resistance is improved. When the Mohs hardness of the silicon particles (Z) is low, the wear during the processing process is reduced. It is obvious to those skilled in the art that the mentioned advantages are completely or partially lost as the purity of the silicon decreases. The purity of the silicon particles (Z) according to the present invention, and thus the silicon content, is at least 80%, preferably at least 90%, more preferably at least 95%.

[0061] It is also obvious to those skilled in the art that metallic silicon particles are flammable under certain conditions and that the dust poses an explosion risk. Those skilled in the art also recognize that the dust formation, flammability and explosion risk associated with metal powders increase significantly with decreasing particle size. Therefore, very small silicon particles with a size of less than 30 μm are unsuitable for many applications. Such particles are dangerous to handle because they have a low minimum ignition energy and require complex and costly safety precautions in industrial processing. It has also been found that compositions containing very small silicon particles with a size of less than 30 μm are relatively highly flammable.

[0062] Larger silicon particles having an average particle size exceeding 30 μm have a relatively high minimum ignition energy and are thus safer and more easily processable in industrial processes. Nevertheless, it has been found that compositions containing comminuted angular silicon particles not according to the present invention larger than 30 μm are relatively highly flammable.

[0063] Silicon particles having an average particle size exceeding 200 μm often do not fit into the fine gaps that need to be filled with, for example, a gap filler, and such large particle size silicon particles are therefore unsuitable for many applications of thermally conductive silicone compositions. Furthermore, it has been found that such large particle size silicon particles also exhibit relatively high flammability.

[0064] The use of spherical fillers to improve the fluidity and processability of filled polymers is well known in the art. However, there are only few prior art documents using spherical silicon particles in thermally conductive silicone compositions. The disclosed compositions exclusively contain very small spherical silicon particles having an average particle size of less than 25 μm, the disadvantages of which have been described.

[0065] Quite surprisingly, it has been found that the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention is thermally conductive and at the same time has low flammability when containing the metal silicon particles of the present invention that simultaneously meet features a) to c) in the required minimum amounts.

[0066] The non-crosslinkable silicone composition (Y) according to the present invention contains at least 20% by volume, preferably at least 25% by volume, more preferably at least 30% by volume, particularly preferably at least 35% by volume of such metal silicon particles (Z)%. If the silicone composition (Y) contains a smaller amount of metal silicon particles (Z), the desired advantageous effects of the metal silicon, such as low density and high thermal conductivity, are no longer provided sufficiently.

[0067] The prior art includes various methods for manufacturing fine metal particles having a rounded shape. The silicon particles (Z) according to the present invention are preferably manufactured from a molten state, and as a result, have a relatively smooth surface and essentially do not contain cracks, sharp edges, and pointed corners. Thus, the silicon particles (Z) according to the present invention are different from conventional ground particles that have been converted to their final form, for example, by crushing, grinding, or milling. Here, it is not important whether the particles are ground at a low temperature in a first processing step, for example, by grinding, and then converted to a molten form by heating above their melting point, for example, by heat treatment in a high-temperature range, for example, by plasma, or whether a silicon melt is first produced and then ground, for example, by atomization. The silicon particles according to the present invention are preferably converted to the solid form according to the present invention by spraying or atomizing the silicon melt and subsequent cooling.

[0068] Suitable methods for manufacturing the silicon particles (Z) according to the present invention are known to those skilled in the art and are described, for example, in "Pulvermetallurgie", Chapter 2.2, Technologien and Werkstoffe [Powder Metallurgy: Technologies and Materials], Schatt, Werner, Wieters, Klaus-Peter, Kieback, Bernd, p. 5-48, ISBN 978-3-540-681112-0, E-Book: https: / / doi.org / 10.1007 / 978-3-540-68112-0_2. Preferred processes for manufacturing the silicon particles (Z) according to the present invention are inert gas atomization, also called gas atomization, pressurized water atomization, also called liquid atomization or water atomization, or melt spinning, also called centrifugal atomization or rotary atomization.

[0069] The described process enables the production of metal silicon particles in very different particle size ranges, in particular in the average particle size range from a few micrometers to a few millimeters. It is also possible to produce the metal silicon particles in very different particle morphologies, for example in a "sputtered" form, i.e., with a very irregular, elliptical, and very variable particle size distribution. Quite surprisingly, it has been found that the advantageous properties according to the invention, in particular the relatively low flammability, are shown only by silicon particles that are mainly rounded and at the same time satisfy features a) to c) of the invention.

[0070] The process for producing the metal silicon particles (Z) according to the invention should preferably be carried out in such a way that the particles are obtained in a mainly rounded shape according to the invention, thus satisfying features a) to c), and essentially do not contain sputtered, nodular, angular or sharp particles. The solidified particles may be separated by size in subsequent process steps by standard methods, for example by screening classification or by screening. In these methods, it is possible to separate aggregates and bound particles, but the particles are essentially not destroyed. What is meant by "mainly rounded" and "essentially not containing" is that the presence of such particles is tolerated within the range of "impurities" in the particles (Z) according to the invention and does not interfere with the effects of the invention.

[0071] The non-crosslinkable silicone composition (Y) according to the present invention may contain, in addition to these metal silicon particles (Z), a further thermally conductive filler (Z) having a thermal conductivity exceeding 5 W / mK. Examples of such further thermally conductive fillers (Z) are magnesium oxide, metallic silicon powder, metallic silver powder, zinc oxide, boron nitride, silicon carbide, aluminum nitride, aluminum hydroxide, aluminum oxide, graphite, and the like. Preferred further fillers are aluminum powder, magnesium oxide, aluminum hydroxide, zinc oxide, and aluminum oxide. Particularly preferred fillers are aluminum hydroxide and aluminum oxide, with aluminum hydroxide being particularly preferred. The shape of the further filler is basically not limited. The particles may be, for example, spherical, elliptical, needle-shaped, tubular, platelet, fibrous, or irregular in shape. The particles are preferably spherical, elliptical, or irregular in shape. The average diameter of the 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, more preferably in the range of 0.2 to 120 μm, and particularly in the range of 0.4 to 80 μm.

[0072] Fillers having a very high density significantly increase the weight of the components, which is disadvantageous, for example, in aircraft and electric vehicle applications. 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, more preferably 3.0 g / cm 3 or less.

[0073] The crosslinkable silicone composition (Y) of the present invention preferably contains a further thermally conductive filler (Z) having a density exceeding 5.0 g / cm 3 by 24% by weight or less, preferably 20% by weight or less, more preferably 16% by weight or less, and particularly preferably 12% by weight or less. In a particularly preferred embodiment, the non-crosslinkable silicone composition (Y) of the present invention does not contain a further thermally conductive filler (Z) having a density exceeding 5.0 g / cm 3 .

[0074] Preferably, the non-crosslinkable silicone composition (Y) of the present invention contains a further thermally conductive filler (Z) having a density of more than 3.0 g / cm 3 in an amount of 60% by weight or less, preferably 45% by weight or less, more preferably 30% by weight or less, and particularly preferably 20% by weight or less.

[0075] In many applications, the electrical conductivity of the thermally conductive composition is undesirable as it can lead to, for example, a short circuit. The composition (Y) according to the present invention preferably contains only a thermally conductive filler having a specific resistance of at least 1 Ω·mm 2 / m.

[0076] A preferred non-crosslinkable thermally conductive silicone composition (Y) according to the present invention contains the silicon metal particles according to the present invention as the only thermally conductive filler (Z) as the thermally conductive filler (Z), or in combination with up to three further thermally conductive fillers (Z). Up to 5% of impurities are not considered further fillers (Z) here.

[0077] When a preferred composition according to the present invention contains the silicon metal particles (Z) of the present invention as the only thermally conductive filler (Z) having a thermal conductivity of more than 5 W / mK, it is preferable to add a rheology modifier or a thickener to prevent sedimentation of the filler. Suitable rheology modifiers are known to those skilled in the art, and fumed silica is preferred.

[0078] The total amount of the thermally conductive filler (Z) in the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention is 50 to 95% by volume, preferably 60 to 90% by volume, more preferably 65 to 88% by volume. When the silicone composition (Y) contains a smaller amount of the thermally conductive filler (Z), the thermal conductivity is insufficient, and when the silicone composition (Y) contains a larger amount of the thermally conductive filler (Z), the composition (Y) has a high viscosity or is even brittle, making processing difficult.

[0079] The non-crosslinkable thermally conductive silicone composition (Y) according to the present invention has a thermal conductivity of at least 0.6 W / mK, preferably at least 0.8 W / mK, more preferably at least 1.2 W / mK, and particularly at least 1.5 W / mK.

[0080] The viscosity of the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention may vary within a very wide range and may be adapted to the requirements of the application. The viscosity of the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention is preferably adjusted by the content of the thermally conductive filler (Z) and / or the composition of the silicone composition (S) by standard methods from the art. These are known to those skilled in the art. It is preferred to adjust the viscosity through the selection and combination of the components (T) and (Z) and the optional addition of (E) and / or (F).

[0081] The dynamic viscosity of the thermally conductive non-crosslinkable silicone composition (Y) according to the present invention is in each case at a shear rate D = 10 s -1 and at 25 °C, preferably in the range of 100 to 1,000,000 mPa·s, preferably in the range of 1000 to 750,000 mPa·s, more preferably in the range of 2000 to 500,000 mPa·s, and particularly 250,000 mPa·s or less.

[0082] The density of the thermally conductive non-crosslinkable silicone composition (Y) according to the present invention is less than 4.5 g / cm 3 preferably less than 4.0 g / cm 3 more preferably less than 3.5 g / cm 3 even more preferably less than 3.3 g / cm 3 and particularly less than 3.3 g / cm.

[0083] The present invention further provides a process for producing the non-crosslinkable thermally conductive silicone composition (Y) according to the present invention by mixing the individual components.

[0084] The components may be mixed by conventional continuous and batch prior art methods. Suitable mixing devices are any of the known devices. These examples are single - or twin - shaft continuous mixers, twin rollers, Ross mixers, Hobart mixers, dental mixers, planetary mixers, kneaders and Henschel mixers or similar mixers. Mixing in a planetary mixer, kneader or continuous mixer is preferred. The non - crosslinked silicone composition (Y) may optionally be heated during the mixing process and is preferably mixed within a temperature range of 15 to 140 °C, more preferably within a temperature range of 15 to 60 °C. Procedures for producing the preferred non - crosslinked silicone composition (Y) are also known to those skilled in the art. In principle, the components may be added in any order. For example, components e) and optionally g) may be premixed and then mixed with components a) and / or b). Here, it is also possible to heat the mixture optionally. It is preferred to mix at least a part of a) and the alkoxysilane g) and then incorporate the thermally conductive filler (Z). The production is preferably carried out without active heating.

[0085] The non - crosslinked silicone composition (Y) according to the present invention has very good processing properties with respect to fluidity, gap filling and layer thickness control and can be applied precisely.

[0086] The present invention further provides the use of a non-crosslinkable thermally conductive silicone composition (Y) as a thermal paste for dissipating heat from a heat generating body in an electronic device. The non-crosslinkable thermally conductive silicone composition (Y) is applied to a heat generating body or a heat dissipating body, or the non-crosslinkable thermally conductive silicone composition (Y) is coated thereon. The heat generating body faces in power supply electronic devices and electronic devices such as supply transistors, power modules, transistors, thermocouples and temperature sensors, heat generating electronic components such as parts of integrated circuits such as CPUs, and batteries. Suitable heat dissipating bodies include heat distributors and heat dissipating components such as heat sinks and cooling lamellas. When the non-crosslinkable thermally conductive silicone composition (Y) is introduced between the heat generating body and the heat dissipating body, heat can be efficiently guided from the heat generating body to the heat dissipating body. Thereby, an efficient cooling effect on the heat generating body is achieved.

[0087] Test method Measurement of thermal conductivity λ The thermal conductivity is measured in accordance with ASTM D5470-12 using a TIM test device (Steinbeis Transferzentrum Warmemanagement in der Elektronik, Lindenstr.13 / 1, 72141 Walddorfhaslach, Germany). This measures the thermal resistance of the sample between two test cylinders by a constant heat flow. The layer thickness of the sample is used to calculate the effective thermal conductivity.

[0088] For the measurement, the sample is applied using a stencil, the measurement cylinder is manually narrowed to a thickness of 1.9 - 2.0 mm, and then the excess material is removed. The thermal conductivity is measured at a constant gap of 1.8 - 1.6 - 1.4 - 1.2 - 1.0 mm. The evaluation is performed by an integrated reporter position. After a validity test (linear determination coefficient > 0.998), the thermal conductivity λ is reported as the effective thermal conductivity in units of W / (m*K).

[0089] Measurement of dynamic viscosity The dynamic viscosity was measured using an Anton Paar MCR 302 rheometer in accordance with DIN EN ISO 3219:1994 and DIN 53019 with the following parameters: measurement type: T / D, temperature: 25.0 °C, measuring element: PP25, measuring gap: 0.50 mm, shear rate: 0.1 - 10 s-1, time: 120 seconds, measurement: 30 times using a flow curve. The viscosity reported in Pa·s is the interpolated value at a shear rate of D = 10 s -1 and is the interpolated value at a shear rate of D = 10 s

[0090] Measurement of density The density of the non-crosslinked thermally conductive silicone composition was confirmed in accordance with ISO 1183, and the density of the crosslinked thermally conductive silicone composition was confirmed in accordance with ISO 1184.

[0091] Particle size and particle shape analysis Using a Camsizer X2 from Retsch Technology (measurement principle: dynamic image analysis), in accordance with ISO 13322-2 and ISO 9276-6 (analysis method: dry measurement of powders and granules, measurement range: 0.8 μm - 30 mm, compressed air dispersion by X-Jet, dispersion pressure = 0.3 bar), the particle size (median particle size x50), particle size distribution (parameters: standard deviation σ and distribution range SPAN), and particle shape (parameters: aspect ratio w / l and sphericity SPHT) were analyzed. The evaluation was volume-based and was by the x c min model.

[0092] The following examples illustrate the basic feasibility of the present invention, but are not intended to limit the content disclosed herein.

[0093] In the following examples, all numerical values regarding parts and percentages are based on weight, unless otherwise specified. Unless otherwise specified, the following examples are carried out at the pressure of the ambient atmosphere, i.e., about 1000 hPa, at room temperature, i.e., about 20 °C, or at the temperature established by the combination of reactants at room temperature without further heating or cooling.

Examples

[0094] Overview of the silicon powders and silicon powder mixtures of the present invention and not of the present invention used Table 1 summarizes the characteristics of the silicon powders of the present invention and those not of the present invention used in the examples.

[0095] Inventive Examples 1 to 3 use the silicon powder of the present invention obtained by inert gas atomization, thus mainly rounded and further having a relatively broad particle size distribution according to the present invention.

[0096] Comparative Examples V1 to V2 not of the present invention are obtained by inert gas atomization and thus are mainly rounded, but have a relatively narrow particle size distribution not of the present invention and do not satisfy feature c) of the present invention, and use silicon powders not of the present invention.

[0097] Comparative Examples V3 to V5 not of the present invention have a relatively broad particle size distribution, but are obtained by a grinding method and thus are essentially angular and have sharp edges and do not satisfy feature b) of the present invention, and use silicon powders not of the present invention. Comparative Example V5 has a content of silicon particles less than 2 μm of 3.8% by weight and thus further does not satisfy feature d).

[0098] Example 4: Production of silicon powder mixture 4 (of the present invention) 100 g of non-inventive silicon powder having an x50 of 68.6 μm, a SPAN of 0.20, a w / l of 0.85, and a SPHT of 0.84, 200 g of non-inventive silicon powder from Comparative Example V2, 400 g of non-inventive silicon powder having an x50 of 105.4 μm, a SPAN of 0.24, a w / l of 0.83, and a SPHT of 0.92, 200 g of non-inventive silicon powder having an x50 of 133.8 μm, a SPAN of 0.25, a w / l of 0.82, and a SPHT of 0.94, and 100 g of non-inventive silicon powder having an x50 of 162.1 μm, a SPAN of 0.22, a w / l of 0.82, and a SPHT of 0.94 are homogeneously mixed using a commercially available RW 28 laboratory stirring system (IKA® - Werke GmbH & CO.KG, 79219 Staufen, Germany). The resulting product is a silicon powder mixture having an x50 of 107.8 μm, a SPAN of 0.75, a w / l of 0.83, and a SPHT of 0.91, which even satisfies features a) to c) and d) of the present invention.

[0099] Abbreviations Ex. Example V Comparative Example Shape of PS particles r Mainly rounded e Angular n Nodular I The present invention NI Not of the present invention n.d. Undetermined

[0100]

Table 2

[0101] General method 1 (GM1) for the production of non-crosslinkable thermally conductive silicone powder-containing silicone compositions (inventive examples 5 to 8 and non-inventive examples V6 to V12) Step 1: Preparation of a silicone composition containing non-crosslinkable thermally conductive silicon powder 40.8 g of a trimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 1000 mPa·s and 5.18 g of a trimethylsiloxy-terminated polydimethylsiloxane having a viscosity of 200 mPa·s and an Si-bonded hydrogen content of 0.18 wt% were homogenized at a speed of 2350 rpm for 25 seconds using a SpeedMixer DAC 400 FVZ (Hauschild & Co KG, Waterkamp 1, 59075 Hamm, Germany). Thereafter, silicon powder was added in the ratios according to Table 2 or Table 3 in each case and mixed using the SpeedMixer at 2350 rpm for 25 seconds. The silicone composition containing silicon particles was stirred with a spatula to incorporate the silicon powder residue from the edge of the container. Thereafter, it was further homogenized at 2350 rpm by the SpeedMixer and cooled to room temperature.

[0102] A paste-like mass was obtained.

[0103] Example 9 Flammability test The flammability of the non-crosslinkable silicone composition of the present invention according to Example 5 and the silicone compositions not of the present invention according to Comparative Examples V6 to V8 is tested in a simplified test based on UL 94 HB.

[0104] The non-crosslinkable silicone composition of the present invention according to Example 5 and the silicone compositions not of the present invention according to Comparative Examples V6 to V8 are applied as a 2 mm thick layer to an aluminum plate having a length of 150 mm, a width of 10 mm and a thickness of 2 mm. The plate is fixed in a vertical position along the long right side such that the back of the aluminum is at the rear and the knife-coated sample is at the front. The burner is adjusted so that a blue flame with a length of 325 mm is formed. The flame is directed horizontally at a right angle to the test piece towards the front surface of the test piece such that the tip of the blue flame faces the front surface of the test piece 20 mm away from the left end of the test piece. After contacting for 30 seconds, the flame is removed.

[0105] Combustibility test and evaluation: During the application of the flame, observe the appearance of the flame and the possibility of dripping of the burning sample material. Record the afterglow time (total afterglow time and afterglow duration) of the test piece. The sample should show the appearance of a weak flame during the application of the flame and should not produce burning drops. Extinguish the sample immediately after removing the flame and it should show afterglow or afterglow duration of less than 1 second. The test is performed on three different test pieces and the average value of the afterglow time is determined. The results can be found in Table 2.

[0106] In Comparative Experiment V7, which is not of the present invention and contains silicon particles not of the present invention according to Comparative Example V5 of 62.5% by volume that did not particularly meet Feature b), a silicone composition with a very high viscosity was formed and could not be applied and tested as a uniform layer.

[0107]

Table 3

Table 4

[0108] In the combustibility test, it was found that Comparative Examples V6 and V8, which contain silicon powder not of the present invention according to Comparative Example V1 or V5 that do not meet one or more of Features a) to d), show relatively unfavorable combustion characteristics.

[0109] Quite unexpectedly, it was found that the silicon powder of the present invention from Example 1, which even simultaneously meets Features a) to c) and d), shows the advantage of the present invention of reduced combustibility.

[0110] Example 10 Flammability test Test the combustibility of the non-crosslinkable silicone composition of the present invention according to Examples 6 to 8 and the silicone composition not of the present invention according to Comparative Examples V9 to V12 in a simplified test based on UL 94 HB. For Example 9, the plate was fixed in a horizontal position such that the aluminum back was downward and the knife-coated sample was upward.

[0111] In the case of Comparative Experiment V10 which is not of the present invention, containing silicon particles not of the present invention according to Comparative Example V3 of 62.5% by volume that did not satisfy particularly Feature b), the result was a silicone composition with a very high viscosity that could not be applied and tested on a uniform layer.

[0112] Combustibility test and evaluation: During the application of the flame, observe the appearance of the flame and the possibility of drops of the burning sample material. Record the afterglow time (total afterglow time and afterglow duration) of the test piece. The sample should show the appearance of a weak flame during the application of the flame and should not produce burning drops. Extinguish the sample immediately after removing the flame and it should show an afterglow or afterglow duration of less than 1 second. The test is performed on three different test pieces and the average value of the afterglow time is determined. The results can be found in Table 3.

[0113]

Table 5

Table 6

[0114] It has been found that the non-crosslinkable silicone compositions of the present invention according to Examples 6 to 8 containing the silicon powder of the present invention from Examples 2 to 4 that satisfy Features a) to c) and even d) simultaneously exhibit the advantage of the present invention of reduced combustibility.

[0115] In Example 8 of the present invention, furthermore, quite surprisingly, when a plurality of silicon powders not of the present invention are mixed, it has been found that a silicon powder mixture of the present invention according to Example 4 can be produced which has the advantageous property according to the present invention of reduced combustibility under the condition that the resulting mixture satisfies Features a) to c) and even d).

[0116] Example 11 Production of non-crosslinkable thermally conductive silicone composition containing an in-situ mixture of silicon powder (of the present invention)

[0117] According to the general method GM1, the non-crosslinkable thermally conductive silicone composition of the present invention is prepared by separately adding 18.4 g of a non-inventive silicone powder having an x50 of 68.6 μm, a SPAN of 0.20, a w / l of 0.85, and a SPHT of 0.84 as silicone powder, 36.8 g of a non-inventive silicone powder from Comparative Example V2, 73.6 g of a non-inventive silicone powder having an x50 of 105.4 μm, a SPAN of 0.24, a w / l of 0.83, and a SPHT of 0.92, 36.8 g of a non-inventive silicone powder having an x50 of 133.8 μm, a SPAN of 0.25, a w / l of 0.82, and a SPHT of 0.94, and 18.4 g of a non-inventive silicone powder having an x50 of 162.1 μm, a SPAN of 0.22, a w / l of 0.82, and a SPHT of 0.94, and mixing them in situ to form a silicone powder mixture of the present invention.

[0118] What is obtained is a non-crosslinkable silicone composition of the present invention having silicone particles of the present invention with a content of 62.5% by volume. The thermal conductivity is 1.9 W / mK and the density is 1.82 g / cm 3 was. The paste-like mass according to the present invention has good processability, high thermal conductivity, and low density, and has very good compatibility for use in electronic components.

[0119] The flammability test according to Example 10 showed the appearance of a weak flame, a afterglow of less than 1 second, and no burning droplets.

Claims

1. - At least one non-crosslinkable silicone composition (S) in an amount of 5 to 50% by volume and - At least one thermally conductive filler (Z) in an amount of 50 to 95% by volume having a thermal conductivity of at least 5 W / mK comprising a non-crosslinkable thermally conductive silicone composition (Y), provided that the non-crosslinkable thermally conductive silicone composition (Y) has a thermal conductivity of at least 0.6 W / mK, at least 20% by volume of the metal silicon particles present as the thermally conductive filler (Z) have the following characteristics: a) The median particle size x50 of the metal silicon particles is in the range of 30 to 200 μm, b) The metal silicon particles are mainly rounded and have an aspect ratio (aspect ratio w / l) of at least 0.76, c) The distribution range SPAN ((x90 - x10) / x50) of the metal silicon particles is at least 0.28, satisfying a non-crosslinkable thermally conductive silicone composition (Y).

2. The non-crosslinkable silicone composition (S) has an organopolysiloxane (T) having the following characteristics: - The organopolysiloxane is linear, branched or cyclic, - It is end-capped at both ends or terminated with one Si-OH or one alkoxysilyl, -Si bonding side chain and terminal group R １ which are independently substituted or unsubstituted C1-C18 hydrocarbon groups The non-crosslinkable silicone composition (Y) according to claim 1, containing

3. The non-crosslinkable silicone composition (S) further contains a rheology additive (E) which functions to adjust the stability of the non-crosslinkable silicone composition under load. The non-crosslinkable silicone composition (Y) according to claim 2.

4. The non-crosslinkable silicone composition (Y) contains at least 25% by volume of metal silicon particles as the thermally conductive filler (Z). The non-crosslinkable silicone composition (Y) according to any one of claims 1 to 3.

5. In addition to the metal silicon particles (Z), the non-crosslinkable silicone composition (Y) contains only 1 to 3 additional types of thermally conductive fillers (Z). The non-crosslinkable silicone composition (Y) according to any one of claims 1 to 4.

6. In addition to the metal silicon particles (Z), the non-crosslinkable silicone composition (Y) contains a further thermally conductive filler (Z) having a density exceeding 5.0 g / cm ３ and having a content of 24% by weight or less, the non-crosslinkable silicone composition (Y) according to any one of claims 1 to 5.

7. In addition to the metal silicon particles (Z), the non-crosslinkable silicone composition (Y) contains a further thermally conductive filler (Z) having a density exceeding 3.0 g / cm ３ and having a density exceeding 3.0 g / cm ３ and being 60% by weight or less, the non-crosslinkable silicone composition (Y) according to any one of claims 1 to 6.

8. The metal silicon particles (Z) have a sphericity SPH T of at least 0.

75. The non-crosslinkable silicone composition (Y) according to any one of claims 1 to 7.

9. The non-crosslinkable silicone composition (Y) according to any one of claims 1 to 8, wherein the median particle diameter x50 of the metal silicon particles is in the range of 40 to 180 μm.

10. The metal silicon particles (Z) have the following characteristics: d) The metal silicon particles contain silicon particles less than 2 μm at 1.5% by weight or less. The non-crosslinkable silicone composition (Y) according to any one of claims 1 to 9, which satisfies the above.

11. A process for producing the non-crosslinkable silicone composition (Y) of the present invention according to any one of claims 1 to 9 by mixing the individual components.

12. Use of the non-crosslinkable silicone composition (Y) according to any one of claims 1 to 10 as a thermal paste for dissipating heat from a heating element in an electronic device.

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