Method for preparing a curable thermally conductive composition

Abstract

A method for making a curable thermally conductive composition, the method comprising: (I) mixing the following components (A), (B1), (C), (D), and (E): (A) a curable thermally conductive composition having at least three terminal alkenyl groups per molecule and a viscosity of 25 to 2000 mPa when determined at 25°C using a glass capillary Cannon-Fenske viscometer in accordance with ASTM D445-21; * (II) preparing a mixture comprising 3 weight percent (wt %) to 10 wt % of a Q-branched alkenyl-functional polyorganosiloxane having a viscosity of 1000 psi; (B1) a silyl-hydride functional polysiloxane crosslinker (B1) containing at least two silyl-hydride groups per molecule and present in a concentration that provides a molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane in the range of 0.2 to 0.35; (C) 90 wt % or more of a thermally conductive filler; (D) a filler treating agent; and (E) a platinum-based hydrosilylation reaction catalyst; and (II) preparing a mixture comprising the compound obtained from step (I). (III) mixing the pre-cured composite from step (II) with (B2) a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule, thereby obtaining the curable thermally conductive composition, wherein the molar ratio of the sum of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinkers (B1) and (B2) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45, and the weight percentages are based on the weight of the curable thermally conductive composition.

Description

[Technical Field]

[0001] The present invention relates to a method of making a curable thermally conductive composition and the thermally conductive composition made therefrom.

[0002] Introduction The trend in industry toward smaller and more powerful electronic devices has increased the demand for thermally conductive compositions useful for dissipating heat generated in such devices. For example, the telecommunications industry is moving to the 400 Gigabit Ethernet (GbE) standard for faster switching and routing, requiring optical components such as optical transceivers and other optical modules with better thermal control to remove heat. Thermally conductive interface materials are often used in electronic devices to thermally couple heat-generating components with heat-dissipating components.

[0003] The challenge with thermally conductive interface materials is to provide a combination of thermal conductivity properties with little or no oil bleed, while making the thermally conductive material easily extrudable so that it can be precisely applied onto small components. Oil bleed (also known as "bleed-out" or "flow separation") from thermally conductive interface materials, especially thermally conductive gels, is a significant risk for electronic and optical module applications because it can cause many problems, such as poor contact, contamination, and short circuits, resulting in reduced reliability of electronic components and / or impacting optical signal transmission.

[0004] Conventionally manufactured thermally conductive pads, which are solid materials, eliminate oil-bleed concerns during crosslinking reactions, but are not extrudable. These thermally conductive pads must be applied manually and cannot meet the requirements of high-volume automated processes. Furthermore, the stress applied to improve interfacial adhesion between the thermally conductive pad and electronic components can potentially damage dedicated electronic components. Dispensable thermally conductive gels, which are liquid at room temperature (25 degrees Celsius (°C)) and have properties similar to grease, offer many advantages over thermally conductive pads, including low or no stress required for assembly in electronic device manufacturing plants and higher extrusion rates with more efficient automated equipment. However, these dispensable thermally conductive gels typically suffer from severe oil-bleed over time caused by migration of polysiloxane fluids, e.g., oil-bleed levels exceeding 10% when the gel is applied to thick joints (>1 mm) at room temperature, especially during high-temperature aging while the electronic device is in operation. Specifically, the one-component, dispensable, thermally conductive gel achieves an oil-bleed of 10% or less after aging at both 25°C for 5 days and 125°C for 2 days, while having an extrusion rate (ER) of at least 15 grams / minute and an extrusion rate of 3.0 watts / meter when measured in accordance with ISO 22007-2 using a hot disc. * It is more difficult to provide a cured material with a thermal conductivity above 100° Kelvin. Oil-bleed and ER are measured using the Oil-Bleed Test and Extrusion Rate Test, respectively, defined herein below.

[0005] There remains a need to identify thermally conductive compositions that can simultaneously achieve the above oil-bleed levels without compromising extrusion speed and heat transfer properties. Summary of the Invention

[0006] The present invention has an oil bleed of 10% or less (≦10%) after application for 5 days at 25° C. and after aging for 2 days at 125° C., respectively, and an extrusion rate ("ER") of 15 grams per minute (g / min) or greater as measured using the Extrusion Rate Test defined herein below, and an extrusion rate of 3.0 watts / meter according to ISO 22007-2 using a hot disc. * Kelvin (W / m * The present invention provides curable thermally conductive compositions that cure to materials having a thermal conductivity ("TC") greater than 1000 K. Surprisingly, it has been found that such compositions can be prepared from a process that includes a pre-cure step using a Q-branched alkenyl-functional polyorganosiloxane (A) and a silyl-hydride-functional polysiloxane crosslinker (B1) in specific molar ratios, and further includes the addition of a silyl-hydride-functional polysiloxane crosslinker (B2).

[0007] In a first aspect, the present invention is a method of making a curable thermally conductive composition, the method comprising: (I) The following components (A), (B1), (C), (D), and (E): (A) having at least three terminal alkenyl groups per molecule and a viscosity of 25 to 2000 millipascals as determined by using a glass capillary Cannon-Fenske viscometer at 25°C in accordance with ASTM D445-21; * seconds (mPa * s) 3 wt.% to 10 wt.% of a Q branched alkenyl-functional polyorganosiloxane having a viscosity of (B1) a silyl-hydride functional polysiloxane crosslinker (B1) containing at least two silyl-hydride groups per molecule and present in a concentration that provides a molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane in the range of 0.2 to 0.35; (C) 90% by weight or more of a thermally conductive filler; (D) filler treatment agents, and (E) preparing a mixture containing a platinum-based hydrosilylation catalyst; (II) thermally curing the mixture resulting from step (I), thereby forming a pre-cured composite; (III) mixing the pre-cured composite obtained from step (II) with (B2) a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule, thereby obtaining a curable thermally conductive composition; the molar ratio of the sum of silicon-bonded hydrogen atoms in (B1) and (B2) to alkenyl groups in the Q branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; The method wherein the weight percentages are based on the weight of the curable thermally conductive composition.

[0008] In a second aspect, the present invention provides a curable thermally conductive composition comprising a mixture of a pre-hard composite and (B2) a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule, wherein the pre-cured composite comprising component (C), component (D), and the hydrosilylation reaction product of components (A), (B1), and (E): (A) having at least three terminal alkenyl groups per molecule and a viscosity of 25 to 2000 mPa when determined at 25°C using a glass capillary Cannon-Fenske viscometer in accordance with ASTM D445-21 * 3% to 10% by weight of a Q branched alkenyl-functional polyorganosiloxane having a viscosity of (B1) a silyl-hydride functional polysiloxane crosslinker (B1) containing at least two silyl-hydride groups per molecule and present in a concentration providing a molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) of from 0.2 to 0.35; (C) 90% by weight or more of a thermally conductive filler; (D) filler treatment agents, and (E) a platinum-based hydrosilylation catalyst, the molar ratio of the sum of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinkers (B1) and (B2) to alkenyl groups in the Q branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; the weight percentages are based on the weight of the curable thermally conductive composition; The curable thermally conductive composition has an extrusion rate of 15 g / min or more, an oil bleed rate of 10% or less after aging at 25°C for 5 days and at 125°C for 2 days, and a heat resistance of 3.0 W / m according to ISO 22007-2 using a hot disc. * A curable thermally conductive composition that cures to a material with a thermal conductivity greater than 1000 K.

[0009] In a third aspect, the present invention is a process for forming a thermally conductive silicone material on an electronic component, the process comprising: (i) providing a curable thermally conductive composition according to the second aspect; (ii) applying a curable thermally conductive composition onto an electronic component; (iii) thermally curing the curable thermally conductive composition, thereby forming a thermally conductive silicone material. DETAILED DESCRIPTION OF THE INVENTION

[0010] Test methods, unless a date is given with the test method number, refer to the test method most recent as of the priority date of this document. References to test methods include both references to the testing society and to the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods, and ISO refers to International Organization for Standardization standards.

[0011] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0012] "And / or" means "and, or as an alternative." All ranges are inclusive of endpoints unless otherwise indicated. All weight percent (wt%) values ​​are by weight of the composition unless otherwise stated.

[0013] A particle having a "spherical" shape refers to a particle having an aspect ratio of 1.0 + / - 0.2. The aspect ratio of a particle is determined using scanning electron microscope (SEM) imaging by taking the average ratio of the longest dimension (major axis) to the shortest dimension (minor axis) of at least 10 particles.

[0014] "Irregular" shaped particles (used interchangeably with "comminuted" particles) have an aspect ratio other than 1.0 + / - 0.2 and have at least three faces evident by SEM imaging (distinguishing them from two-sided "plates").

[0015] The particle size (used interchangeably with "average particle size" and "D50") of the thermally conductive filler refers to the volume-weighted median (D50) of the particle size distribution using a Mastersizer™ (trademark of Malvern Instruments Limited) 3000 laser diffraction particle size analyzer from Malvern Instruments.

[0016] The viscosity of the polysiloxanes is determined using a glass capillary Cannon-Fenske viscometer at 25 degrees Celsius (°C) according to ASTM D445-21 unless otherwise specified.

[0017] The present invention relates to methods of making curable thermally conductive compositions (used interchangeably with "curable compositions"). Such compositions can be used as thermally conductive gels, particularly dispensable thermally conductive gels, that can be dispensed by automated equipment onto heat-generating components with minimal stress on the assembly of complex and delicate electronic components. Curable thermally conductive compositions are liquid thermal interface materials that cure into a gel-like structure upon exposure to heat, such as heat generated by the device to which the composition is applied.

[0018] The method of the present invention includes the steps of: (I) preparing a mixture containing components (A), (B1), (C), (D), and (E); (II) curing the mixture obtained from step (I) with heat, thereby forming a pre-cured composite; and (III) combining the pre-cured composite obtained from step (II) with component (B2), thereby forming a curable thermally conductive composition.

[0019] In step (I) of the present method, the mixture can be prepared by mixing components (A), (B1), (C), (D), and (E) in any order. Preferably, components (A), (B1), and (D) are first mixed, followed by mixing component (C), and then adding component (E).

[0020] Component (A) is a Q-branched alkenyl-functional polyorganosiloxane (hereinafter also referred to as "Q-branched polyorganosiloxane"). "Alkenyl" refers to a branched or unbranched monovalent hydrocarbon group having one or more carbon-carbon double bonds. The alkenyl groups in the Q-branched polyorganosiloxane are capable of undergoing a hydrosilylation reaction. The alkenyl groups typically have 2 to 8 carbon atoms, 2 to 6 carbon atoms, or 2 to 4 carbon atoms. Suitable alkenyl groups may include vinyl, allyl, butenyl, and hexenyl.

[0021] The Q-branched alkenyl-functional polyorganosiloxane (A) useful in the present invention has at least three terminal alkenyl groups (preferably vinyl groups) per molecule. The Q-branched alkenyl-functional polyorganosiloxane can have four or more alkenyl groups per molecule. The alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane can all be terminal or a combination of terminal and pendant, and desirably, four of the alkenyl groups are in terminal positions. Desirably, the Q-branched alkenyl-functional polyorganosiloxane is a Q-branched vinyl-functional polyorganosiloxane. The Q-branched alkenyl-functional polyorganosiloxane has the formula (R b 2SiO 2 / 2 ) z ) bonded to three or more polydiorganosiloxane chains of the formula (SiO 4 / 2 ) wherein R b is as defined in formula (I) below, where each subscript z is independently 15 to 150. Q branched polyorganosiloxane is a polyorganosiloxane having 1 to 10, 1 to 8, or 1 to 2 units of the formula (SiO 4 / 2 ). A "terminal" group is on the terminal siloxane group of a molecule. A "terminal" siloxane group is bonded to only one other siloxane group. A "pendant" group is on an internal siloxane group of a molecule (a siloxane group bonded to at least two other siloxane groups). A "siloxane group" is a group containing SiO that is bonded to another Si through an oxygen in the SiO.

[0022] Q Branched alkenyl-functional polyorganosiloxanes have a viscosity of 25-2000 mPa *The Q-branched alkenyl-functional polyorganosiloxane may be a combination of two or more polyorganosiloxanes that may differ in one or more properties selected from molecular weight, structure, siloxane units, and sequence. When the Q-branched polyorganosiloxane is a combination of two or more Q-branched polyorganosiloxanes, the viscosity is the combined viscosity of the Q-branched polyorganosiloxanes. The viscosity of the Q-branched alkenyl-functional polyorganosiloxane is in the range of 25 mPa (25 mPa), as determined by using a glass capillary Cannon-Fenske viscometer at 25°C according to ASTM D445-21. * s or more, 30 mPa * s or more, 40mPa * s or more, 50mPa * s or more, 60mPa * s or more, 70mPa * s or more, 75mPa * s or more, 78mPa * s or more, 80mPa * s or more, 100mPa * s or more, 125mPa * s or more, 150mPa * s or more, 175mPa * s or more, even 200mPa * s or more and at the same time, 2000 mPa * s or less, 1500mPa * s or less, 1000mPa * s or less, 500mPa * s or less, 400mPa * s or less, 300mPa * s or less, 200mPa * s or less, 150mPa * s or less, 100mPa * s or less, 90mPa * s or less, and even 80mPa * s or less, preferably 100 to 600 mPa * s, 150-500mPa * s, 200-400mPa * s, or 300-400mPa * It can be s.

[0023] The Q-branched alkenyl-functional polyorganosiloxane may have an alkenyl content of 0.1 wt% to 5.0 wt%, and may be 0.1 wt% or more, 0.5 wt% or more, 0.7 wt% or more, 0.9 wt% or more, or even 1.2 wt% or more, while generally being 5.0 wt% or less, 2.0 wt% or less, 1.5 wt% or less, 1.2 wt% or less, 1.0 wt% or less, 0.8 wt% or less, or even 0.6 wt% or less. The alkenyl content refers to the weight percent of alkenyl groups relative to the molecular weight of the Q-branched polyorganosiloxane. When the alkenyl groups in the Q-branched polyorganosiloxane are vinyl groups, the alkenyl content is the vinyl content. The vinyl content herein refers to the weight percent of vinyl groups relative to the molecular weight of the Q-branched polyorganosiloxane.

[0024] Desirably, the Q branched alkenyl-functional polyorganosiloxane has the formula (I):

[0025] [ka] In the formula, each R a are independently an alkenyl group, and each R b are independently monovalent hydrocarbon groups free of aliphatic unsaturation, and n is an integer from 15 to 150, representing the average number of different branch chain lengths in the polyorganosiloxane. In formula (I), n is a value of 15 or greater, and can be 30 or greater, 40 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, or even 90 or greater, and at the same time is generally 150 or less, and can be 120 or less, 100 or less, 85 or less, 75 or less, 65 or less, 55 or less, 45 or less, 35 or less, or even 25 or less; desirably, n is 35 to 85.

[0026] R a The alkenyl group of R is as described above. a Particularly suitable alkenyl groups for each R are exemplified by vinyl, allyl, butenyl, and hexenyl. amay be the same or different. Desirably, each R a is selected from vinyl or hexenyl. More preferably, each R a is a vinyl group.

[0027] R b Examples of the monovalent hydrocarbon group R include an alkyl group having 1 to 6 carbon atoms and an aryl group having 6 to 10 carbon atoms. b Suitable alkyl groups for R may include, for example, methyl, ethyl, propyl (e.g., iso-propyl and / or n-propyl), butyl (e.g., isobutyl, n-butyl, tert-butyl, and / or sec-butyl), pentyl (e.g., isopentyl, neopentyl, and / or tert-pentyl), hexyl, and branched saturated hydrocarbon groups of 6 carbon atoms. b Examples of suitable aryl groups for each R are exemplified by phenyl, tolyl, xylyl, naphthyl, benzyl, and dimethylphenyl. b may be the same or different. b can be an alkyl group. Desirably, each R b are independently methyl, ethyl, or propyl, and more preferably each R b is methyl.

[0028] The Q-branched alkenyl-functional polyorganosiloxane can be a single Q-branched polyorganosiloxane or a combination of two or more Q-branched polyorganosiloxanes of formula (I), which can differ in one or more properties selected from molecular weight, structure, siloxane units, and sequence. Suitable Q-branched polyorganosiloxanes can include those disclosed in U.S. Patent No. 6,806,339. In particular, the Q-branched alkenyl-functional polyorganosiloxane can include one or more Q-branched dimethylvinylsiloxy-terminated polydimethylsiloxanes, desirably having a viscosity of 200 to 400 mPa. * For example, Q branched polyorganosiloxane has a viscosity of (Ai) 240 mPa *Q branched dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 300 mPa.s and a vinyl content of 0.9 wt.%; (A-ii) 300 mPa.s * Q branched dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 400 mPa.s and a vinyl content of 0.72 wt.%, and (A-iii) 400 mPa.s * and a Q-branched dimethylvinylsiloxy-terminated polymethylvinylsiloxane having a viscosity of 0.5 s and a vinyl content of 0.6 wt %, where the vinyl content of the Q-branched polyorganosiloxane is as defined above.

[0029] The Q branched alkyl-functional polyorganosiloxane is present in a concentration of 3.0 wt% to 10 wt%, and can be 3.0 wt% or more, 3.5 wt% or more, 4.0 wt% or more, 4.5 wt% or more, 5.0 wt% or more, greater than 5 wt%, 6 wt% or more, 7 wt% or more, or even 7.2 wt% or more, based on the weight of the curable thermally conductive composition, and at the same time generally not more than 10.0 wt%, not more than 9.0 wt%, not more than 8.5 wt%, not more than 8.0 wt%, not more than 7.5 wt%, not more than 6.5 wt%, or even not more than 5.5 wt%, desirably 4 wt% to 4.5 wt%, or 7.0 wt% to 7.5 wt%,

[0030] The method for producing a curable thermally conductive composition may or may not further include adding an additional alkenyl-functional polyorganosiloxane (Component (A') other than the above-mentioned Q-branched alkenyl-functional polyorganosiloxane). When present, the additional alkenyl-functional polyorganosiloxane (A') may be added together with the above-mentioned Q-branched polyorganosiloxane of Component (A), or may be added to the mixture obtained by Step (I) of the method. Such additional alkenyl-functional polyorganosiloxane (A') has the average chemical structure (II): R b (3-c) R a c SiO-(R a R bSiO) a -(R b 2SiO) b -SiR a d R b (3-d) (II) wherein R a and R b represents, independently at each occurrence, R in formula (I) above. a and R b where subscript a≧0, subscript b>0, subscript c is 0 or 1, subscript d is zero or 1, (a+b) is 20 to 350, and (a+c+d)≧2. Subscript a can have a value ranging from 0 to 5. Subscript b can have a value ranging from 30 to 150. Desirably, each R b is methyl. Each R a may be vinyl. Desirably, subscript a is zero, subscript c is one, and subscript d is one.

[0031] The concentration of the additional alkenyl-functional polyorganosiloxane (A') can be zero to less than 1 wt%, or can be zero to 0.9 wt%, 0.8 wt%, 0.7 wt%, 0.6 wt%, 0.5 wt%, 0.4 wt%, 0.3 wt%, 0.2 wt%, 0.1 wt%, 0.5 wt%, or even 0.01 wt% or less, desirably zero to less than 0.1 wt%, based on the weight of the curable thermally conductive composition. Desirably, the curable thermally conductive composition does not contain any additional alkenyl-functional polyorganosiloxane (A').

[0032] Component (B1) is a silyl-hydride (SiH)-functional polysiloxane crosslinker (also referred to as "SiH crosslinker (B1)"). The SiH-functional polysiloxane crosslinker contains at least two silyl-hydride groups (i.e., containing at least two silicon-bonded hydrogen atoms) per molecule, or even three or more silyl-hydride groups. The SiH groups can be pendant, terminal, or a combination of both pendant and terminal. The SiH-functional polysiloxane crosslinker has the following average chemical structure (III): R bb (3-h) H h SiO-(HR bb SiO) e -(R bb 2SiO) f -SiH h’ R bb (3-h’) (III) wherein R bb is independently selected at each occurrence from alkyl groups having 1 to 6 carbon atoms, and phenyl; subscripts h and h' are each independently selected at each occurrence from a value ranging from zero to 3, provided that the combination of e, h, and h' is at least 2; subscript e is zero to 30; and subscript f is 5 to 200.

[0033] R bb The group can have 1 or more carbons, 2 or more carbons, 3 or more carbons, 4 or more carbons, or even 5 or more carbons, and at the same time, 6 or fewer carbons, 5 or fewer carbons, 4 or fewer carbons, 3 or fewer carbons, or even 2 or fewer carbons. bb The group is independently selected at each occurrence from methyl and phenyl. H is a hydrogen atom, The subscripts h and h' refer to the average number of terminal hydrogen atoms at both ends, and are each independently selected from a range of zero to three at each occurrence, provided that the combination of e, h, and h' is at least two. Preferably, h and h' are independently selected at each occurrence from zero or more, one or more, or even two or more, and simultaneously are not more than three, not more than two, or even not more than one. More preferably, h and h' have the same value. Most preferably, h and h' are both zero. The subscript e indicates the (HR bb is the average number of SiO) groups. When h and h' are both zero, e is in the range of 2 to 30. When h and h' are not both zero, the subscript e can be zero to 30, provided that the combination of e, h, and h' is 2 or greater. Desirably, the subscript e is 1 or greater, and can be 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, or even 9 or greater, and simultaneously is typically 30 or less, and is 25 or less, 20 or less, 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or even 2 or less. The subscript f represents the number of (R bb 2SiO) groups. Generally, the subscript f is 5 or more, 10 or more, 20 or more, 25 or more, 30 or more, 40 or more, 50 or more, and can be 75 or more, 100 or more, 125 or more, 150 or more, 175 or more, or even 190 or more, and at the same time is typically 200 or less, 175 or less, 150 or less, 125 or less, 100 or less, 75 or less, 50 or less, 40 or less, 30 or less, 25 or less, or even 20 or less.

[0034] The SiH-functional polysiloxane crosslinker may have a silicon-bonded hydrogen atom (H) ("SiH") content (SiH content) of 0.1 wt% to 1.0 wt%, and may be 0.1 wt% or more, 0.11 wt% or more, 0.15 wt% or more, 0.2 wt% or more, 0.25 wt% or more, 0.30 wt% or more, or even 0.35 wt% or more, and generally 1.0 wt% or less, and may be 0.9 wt% or less, 0.8 wt% or less, 0.7 wt% or less, 0.6 wt% or less, 0.5 wt% or less, 0.4 wt% or less, or even 0.36 wt% or less, desirably 0.1 wt% to 0.8 wt%. The SiH content refers to the weight percent of silicon-bonded hydrogen atoms relative to the molecular weight of the SiH-functional polysiloxane crosslinker and can be determined using Fourier transform infrared (FTIR) spectroscopy.

[0035] Suitable SiH functional polysiloxane crosslinkers include, for example, trimethylsiloxy-terminated poly(dimethylsiloxane / methylhydrogensiloxane), trimethylsiloxy-terminated polymethylhydrogensiloxane, hydrogen-terminated polydimethylsiloxane, hydrogen-terminated poly(dimethylsiloxane / methylhydrogensiloxane), or mixtures thereof. The crosslinker may be a combination of two or more crosslinkers that may differ in one or more properties selected from molecular weight, structure, siloxane units, and sequence. Specific examples of SiH crosslinkers include those with the average chemical structure Me3SiO(Me2SiO)7(MeHSiO)3SiMe3,Me3SiO(Me2SiO) 108 (MeHSiO) 10 SiMe3,Me3SiO(Me2SiO) 22 (MeHSiO)2SiMe3, or HMe2SiO(Me2SiO) 25 Examples of suitable crosslinkers include those having (MeHSiO)1SiMe2H, or mixtures thereof. Suitable commercially available SiH crosslinkers include those available under the designations HMS-071, HMS-501, and DMS-H11, all available from Gelest. Desirably, the crosslinker has a (Bi)10-15 mPa * (B-ii) a trimethyl-terminated dimethyl-co-hydrogenmethylpolysiloxane having a viscosity of 7-10 mPa.s and a SiH content of 0.36 wt.%;* hydride terminated polydimethylsiloxane having a viscosity in the range of 0.50 to 1.005 s and a SiH content of 0.16 wt % or a combination of both polymers.

[0036] To ensure the desired pourability and reduced oil-bleed characteristics of the curable thermally conductive composition, the SiH crosslinker (B1) used in step (I) is in an amount that provides a molar ratio of silicon-bonded hydrogen atoms from the SiH crosslinker (B1) to alkenyl groups (desirably vinyl groups) in the Q-branched alkenyl-functional polyorganosiloxane (A), further defined as "SiH B1 The SiH / Vi ratio is in the range of 0.2 to 0.35, and can be 0.2 or more, 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, or even 0.25 or more, and at the same time can be 0.35 or less, 0.34 or less, 0.33 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, or even 0.28 or less, desirably 0.22 to 0.28. B1 If the SiH / Vi ratio is too low, the resulting curable composition tends to exhibit undesirable oil-bleed characteristics. B1 If the / Vi ratio is too high, the resulting curable composition tends to provide an extrusion rate that is too low to dispense.

[0037] Component (C) includes one or more thermally conductive fillers. The thermally conductive filler (C) may include both conductive and insulating fillers. Component (C) includes a metal filler, an inorganic filler, a meltable filler, or a combination thereof. Metal fillers include particles of metals such as aluminum, copper, gold, nickel, silver, and combinations thereof. Inorganic fillers include metal oxides such as aluminum nitride, magnesium hydroxide, diamond, aluminum oxide, beryllium oxide, magnesium oxide, and zinc oxide, nitrides such as aluminum nitride and boron nitride, carbides such as silicon carbide and tungsten carbide, and combinations thereof. The meltable filler may include Bi, Ga, In, Sn, and alloys thereof, and may optionally further include Ag, Au, Cd, Cu, Pb, Sb, Zn, and combinations thereof.

[0038] The thermally conductive filler particles can be spherical or irregular in shape. Component (C) can be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one characteristic, such as particle shape, average particle size, particle size distribution, and type of filler. The average particle size of the thermally conductive filler will depend on various factors, such as the type of thermally conductive filler selected for component (C), the exact amount added to the curable composition, and the thickness of the bond in the device in which the curable product of the composition will be used (i.e., the maximum particle size must be smaller than the thickness of the bond). The thermally conductive filler can have a D50 particle size ranging from 0.1 micrometers (μm) to 120 μm, 0.1 μm to 100 μm, 0.1 μm to 50 μm, 0.1 μm to 35 μm, 0.1 μm to 10 μm, or 0.1 μm to 5 μm.

[0039] The amount of component (C) depends on various factors, including the TC properties of the filler selected for component (C). The method of the present invention allows for the incorporation of high amounts of component (C), i.e., ≥ 90 wt% of component (C) based on the weight of the curable thermally conductive composition, typically added in step (I) of the method, thus achieving reduced oil-bleed without compromising ER and TC compared to conventional methods in the art. The total concentration of component (C) is, based on the weight of the curable thermally conductive composition, 90 wt% or more, and can be 90.5 wt% or more, 90.8 wt% or more, 91 wt% or more, 91.2 wt% or more, 95 wt% or more, 95.4 wt% or more, or even 95.5 wt% or more, and at the same time is typically 96.5 wt% or less, and can be 96 wt% or less, 95.5 wt% or less, 95.2 wt% or less, 95 wt% or less, 94.5 wt% or less, or even 94 wt% or less, and desirably 91 wt% to 94 wt%.

[0040] Desirably, component (C) can comprise or consist of a combination of at least three different thermally conductive fillers, namely (c1), (c2), and (c3) described below.

[0041] The first thermally conductive filler (c1) has a D50 particle size of 10 μm to 120 μm, and may have a D50 of 10 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or even 70 μm or more, and simultaneously have a D50 particle size of 120 μm or less, and may have a D50 of 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 45 μm or less, or even 35 μm or less. The first thermally conductive filler (c1) may be selected from aluminum oxide, aluminum nitride, magnesium oxide, or a mixture thereof. Desirably, the first thermally conductive filler particles (c1) are spherical. The concentration of (c1) may be 30% to 65% by weight, and may be 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 52% or more, or even 52.4% or more by weight, based on the weight of the curable composition, and at the same time generally not more than 65% by weight, and may be 60% or less, 58% or less, 54% or less, 53.5% or less, 53% or less, or even 52.5% or less by weight. Desirably, the first thermally conductive filler is 40% to 60% by weight, based on the weight of the curable composition, of aluminum oxide particles having a D50 of 20 to 50 μm.

[0042] The second thermally conductive filler (c2) has a D50 particle size of 1 μm to less than 10 μm, and may have a D50 of 1 μm or more, 1.5 μm or more, or even 2 μm or more, and simultaneously have a D50 particle size of less than 10 μm, and may have a D50 of 9 μm or less, 8 μm or less, 6 μm or less, 5 μm or less, 3 μm or less, or even less than 3 μm. The concentration of (c2) is 20 wt% or more to 40 wt% or more, based on the weight of the curable composition, and may be 20 wt% or more, 22 wt% or more, 25 wt% or more, 26 wt% or more, or even 27 wt% or more, and simultaneously may be less than 40 wt%, 38 wt% or less, 36 wt% or less, 35 wt% or less, 34 wt% or less, 33 wt% or less, 32 wt% or less, 31 wt% or less, 30 wt% or less, or even 27 wt% or less. The second thermally conductive filler may be selected from aluminum oxide, aluminum nitride, or mixtures thereof, and is preferably crushed or irregular aluminum oxide. More preferably, the second thermally conductive filler is 20-30 wt. % irregular aluminum particles having a D50 of 1-5 μm.

[0043] The third thermally conductive filler (c3) has a D50 particle size of 0.1 μm to less than 1 μm, and may have a D50 of 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.5 μm or more, 0.7 μm or more, 0.8 μm or more, or even 0.9 μm or more, and simultaneously have a D50 particle size of less than 1 μm, and may have a D50 of 0.8 μm or less, 0.5 μm or less, less than 0.5 μm, or even 0.2 μm or less. The concentration of the third thermally conductive filler (c3) may be 8 wt% or more, 10 wt% or more, 12 wt% or more, or even 12.6 wt% or more, based on the weight of the curable composition, and simultaneously may be 20 wt% or less, 19 wt% or less, 18 wt% or less, 17 wt% or less, 15 wt% or less, 13 wt% or less, or even 12.6 wt% or less. The third thermally conductive filler may be selected from zinc oxide, aluminum oxide, or a mixture thereof, and preferably the third thermally conductive filler is irregular zinc oxide. More preferably, the third thermally conductive filler is 10-15 wt. % irregular zinc oxide particles having a D50 of 0.1-0.5 μm.

[0044] The thermally conductive filler (C) may contain fillers in addition to the three thermally conductive fillers described above, or may contain no thermally conductive fillers other than these three (i.e., the thermally conductive filler consists of (c1), (c2), and (c3)). The particles described above may each independently have any shape, such as spherical, irregular, crushed, or plate-like.

[0045] Desirably, the thermally conductive filler (C) comprises or consists of: (c1) 40 to 60% by weight of aluminum oxide particles, preferably spherical aluminum oxide particles, having a D50 of 20 to 50 μm; (c2) 25 to 40 wt. % aluminum oxide particles, preferably milled aluminum oxide particles, having a D50 of 1 to 5 μm; and (c3) 10 to 20% by weight of zinc oxide particles, preferably milled zinc oxide, having a D50 of 0.1 to 0.5 μm.

[0046] Component (D) is a filler treating agent or a combination of two or more filler treating agents. Filler treating agent (D) can comprise or consist of any combination of one or more trialkoxysilyldiorganopolysiloxanes, including —Si(OR e ) groups, wherein R e is independently set forth at each occurrence herein below as (IV). Desirably, the trialkoxysilyl diorganopolysiloxane is a mono-trialkoxysiloxy-terminated diorganopolysiloxane. Suitable monotrialkoxysiloxy-terminated diorganopolysiloxanes include those having the following average chemical structure (IV): R c 3SiO[R d 2SiO] g Si(OR e )3(IV) In the formula, R c , R d , and R eis independently selected from hydrocarbyls having 1 to 10 carbon atoms, such as alkyl and aryl groups, for example, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, or even 8 or more carbon atoms, and simultaneously typically having 10 or less, 8 or less, 6 or less, 4 or less, or even 2 or less carbon atoms; and the subscript g typically has a value of 20 or more, 25 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, or even 110 or more, and simultaneously typically has a value of 150 or less, and can be 125 or less, 120 or less, 110 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, or even 30 or less. Desirably, the subscript g has a value in the range of 25 to 110. c , R d , and R e may be the same or different. c , R d , and R e Suitable alkyl groups for R are exemplified by methyl, ethyl, propyl (e.g., iso-propyl and / or n-propyl), butyl (e.g., isobutyl, n-butyl, tert-butyl, and / or sec-butyl), pentyl (e.g., isopentyl, neopentyl, and / or tert-pentyl), hexyl, and branched saturated hydrocarbon groups of 6 carbon atoms. c , R d , and R e may each independently be an alkyl group such as methyl, ethyl, and propyl. Desirably, each R c , R d , and R e is methyl. c , R d , and R e Suitable aryl groups include phenyl and dimethylphenyl. Particularly desirable monotrialkoxysiloxy-terminated diorganopolysiloxanes are monotrialkoxysiloxy- and trimethylsiloxy-terminated polydimethylsiloxanes, such as those having the average formula (CH3)3SiO[(CH3)2SiO] 30Si(OCH3) 3. Suitable monotrialkoxysiloxy-terminated dimethylpolysiloxanes can be synthesized according to the teachings of U.S. Patent Application Publication No. 2006 / 0100336.

[0047] Filler treating agent (D) may or may not include a combination of one or more alkyltrialkoxysilanes. Suitable alkyltrialkoxysilanes include those having the following formula (V): R f Si(OR g )3(V) In the formula, R f is, independently at each occurrence, an alkyl group having 6 or more, 7 or more, 8 or more, 9 or more, or even 10 or more carbon atoms, and simultaneously is typically an alkyl group having 20 or fewer, 18 or fewer, 16 or fewer, 14 or fewer, 12 or fewer, or even 10 carbon atoms; R g is independently at each occurrence alkyl having 1 or more, 2 or more, 3 or more, 4 or more, or even 5 or more carbon atoms, and at the same time generally having 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, or even 2 carbon atoms. f R is, independently at each occurrence, an alkyl group having 6 to 20 carbon atoms. g is preferably methyl so as to form a methoxyl group bonded to the silicon atom. Particularly preferred alkyltrialkoxysilanes are n-decyltrimethoxysilane, n-octyltrimethoxysilane, or mixtures thereof. Suitable alkyltrialkoxysilanes include n-decyltrimethoxysilane, available from The Dow Chemical Company as DOWSIL™ Z-6210 silane or from Gelest under the designation SID2670.0.

[0048] The filler treating agent (D) useful in the present invention can be present in a total concentration that is 0.1 wt.% to 2.0 wt.% or more, based on the weight of the curable thermally conductive composition, and can be 0.1 wt.% or more, 0.2 wt.% or more, 0.3 wt.% or more, 0.4 wt.% or more, 0.5 wt.% or more, 0.6 wt.% or more, 0.7 wt.% or more, 0.8 wt.% or more, 0.9 wt.% or more, 1.0 wt.% or more, 1.2 wt.% or more, 1.3 wt.% or more, or even 1.4 wt.% or more, and at the same time typically 2.0 wt.% or less, 1.8 wt.% or less, 1.6 wt.% or less, 1.5 wt.% or less, 1.4 wt.% or less, 1.3 wt.% or less, or even 1.2 wt.% or less. Desirably, the trialkoxysilyldiorganopolysiloxane is present at a concentration of zero to 2.0 wt %, and can be greater than zero, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt % or more, 1.0 wt % or more, 1.1 wt % or more, 1.2 wt % or more, 1.3 wt % or more, or even 1.4 wt % or more, based on the weight of the curable thermally conductive composition, while typically being present at a concentration of 2.0 wt % or less, and can be 1.8 wt % or less, 1.7 wt % or less, 1.6 wt % or less, 1.5 wt % or less, or even 1.4 wt % or less. Alternatively, or simultaneously, the alkyltrialkoxysilane may be present in a concentration of zero or greater, such as 0.01% by weight or greater, 0.05% by weight or greater, 0.1% by weight or greater, 0.2% by weight or greater, 0.3% by weight or greater, or even 0.4% by weight or greater, based on the weight of the curable thermally conductive composition, and simultaneously, typically present in a concentration of 0.5% by weight or less, such as 0.4% by weight or less, 0.3% by weight or less, or even 0.2% by weight or less. The filler treating agent (D) may be a mixture of a trialkoxysilyldiorganopolysiloxane, such as a monotrialkoxysiloxy- and trimethylsiloxy-terminated polydimethylsiloxane, and an alkyltrialkoxysilane. For example, the curable thermally conductive composition may contain a monotrialkoxysiloxy- and trimethylsiloxy-terminated polydimethylsiloxane, such as (CH3)3SiO[(CH3)2SiO] 30Si(OCH3)3) or n-decyltrimethoxysilane. Desirably, the curable thermally conductive composition comprises 0.1 to 0.3 wt % n-decyltrimethoxysilane and 0.5 to 1.5 wt % monotrialkoxysiloxy- and trimethylsiloxy-terminated polydimethylsiloxane, based on the weight of the curable thermally conductive composition.

[0049] Component (E) is one or more platinum-based hydrosilylation catalysts, including platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt's catalyst), HPtCl, di-μ-carbonyldi-π-cyclopentadienyldinickel, platinum-carbonyl complexes, platinum-divinyltetramethyldisiloxane complexes, platinum-cyclovinylmethylsiloxane complexes, platinum acetylacetonate (acac), platinum black, platinum compounds such as chloroplatinic acid, chloroplatinic acid hexahydrate, reaction products of chloroplatinic acid with monohydric alcohols, platinum bis(ethylacetoacetate), platinum bis(acetylacetonate), platinum dichloride, complexes of platinum compounds with olefins or low molecular weight organopolysiloxanes, or platinum compounds microencapsulated in a matrix or core-shell structure. The hydrosilylation catalyst can be part of a solution containing a complex of platinum with a low molecular weight organopolysiloxane, including a platinum complex with 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane. These complexes can be microencapsulated in a resin matrix (typically a phenyl resin) or can be unencapsulated. The resin matrix for microencapsulating the complex can be a phenyl resin, an acrylate polymer, a polycarbonate, or another resin matrix with a melting point below 150°C to release Pt during thermal curing. Exemplary hydrosilylation catalysts are described in U.S. Pat. Nos. 3,159,601 and 3,220,972, and encapsulated platinum catalysts are described in WO 2014017671A1. The catalyst can be a platinum complex with 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane. Platinum-based hydrosilylation catalysts are commercially available, for example, SYL-OFF™ 4000 Catalyst, SYL-OFF 4500 Catalyst, and SYL-OFF 2700 Catalyst are available from Dow Silicones Corporation (SYL-OFF is a trademark of Dow Silicones Corporation).In some embodiments, two different catalysts (e.g., E1 and E2) that activate at different temperatures can be added. The two different catalysts can be encapsulated platinum catalysts such as (E1) a 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum, and (E2) a 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum encapsulated in dimethylsiloxane with phenylsilsesquioxane.

[0050] The amount of platinum-based hydrosilylation catalyst (E) is sufficient to provide 0.5 parts per million (ppm) to 300 ppm, and can be 0.5 ppm or more, 5 ppm or more, 10 ppm or more, 20 ppm or more, or even 30 ppm or more, based on the weight of the curable thermally conductive composition, and at the same time, generally is 300 ppm or less, 200 ppm or less, 130 ppm or less, 100 ppm or less, or even 50 ppm or less of platinum. Alternatively, the amount of platinum-based hydrosilylation catalyst can be 0.01 wt.% to 0.6 wt.% based on the weight of the curable thermally conductive composition. The platinum-based hydrosilylation catalyst (E) can be added in step (I), or optionally after step (I).

[0051] In step (II) of the method of the present invention, the mixture resulting from step (I) can undergo a crosslinking reaction ("cure") under heating, thereby forming a pre-cured composite. The crosslinking reaction involves a hydrosilylation reaction between the Q-branched alkenyl-functional polyorganosiloxane and the SiH crosslinker (B1). Step (II) of the method (i.e., the pre-cure step) can be carried out by heating at a temperature greater than 50°C to 150°C, and can be 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, or even 100°C or higher, while generally being 150°C or lower, and 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, or even 90°C or lower. The duration of the pre-cure step can vary depending on the temperature, for example, 30 to 120 minutes. Alternatively, the pre-curing step can be carried out at 90°C to 120°C for 30 to 60 minutes, or at 60°C to 90°C for 60 to 120 minutes.

[0052] Step (III) of the method for preparing a curable thermally conductive composition involves mixing the resulting pre-cured composite with component (B2), a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule (hereinafter referred to as "SiH crosslinker (B2)"). The mixing of the pre-cured composite with the SiH crosslinker (B2) in step (III) can be carried out at a temperature below 30°C, preferably at room temperature (25°C). The SiH crosslinker (B2) is as described for the SiH crosslinker (B1) of component (B1) above. The SiH crosslinker (B2) and the SiH crosslinker (B1) can each independently be the same or different. The SiH crosslinker (B2) is selected from the group consisting of SiH crosslinkers (B1) and (B2) in a molar ratio of total silicon-bonded hydrogen atoms to alkenyl groups (preferably vinyl groups) in the branched alkenyl-functional polyorganosiloxane (A) (SiH B1 +SiH B2 It is used in an amount such that the (SiH) / Vi ratio (also referred to as the "SiH / Vi ratio") is greater than 0.45, and may be 0.46 or greater, 0.47 or greater, 0.48 or greater, 0.5 or greater, 0.6 or greater, 0.7 or greater, 0.8 or greater, or even 0.9 or greater. B1 +SiH B2 The ) / Vi ratio may generally be 1.5 or less, and can be 1.4 or less, 1.2 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.58 or less, or even 0.54 or less, and is preferably 0.5 to 0.6.

[0053] The method for making the curable thermally conductive composition of the present invention may include the addition of optional components, including component (F) an inhibitor, component (E'), an additional platinum-based hydrosilylation catalyst, other optional components described below, or mixtures thereof. One or more of these optional components may be added after obtaining the pre-cured composite from step (II) before, during, and / or after the addition of the SiH crosslinker (B2). The method may include adding an additional platinum-based hydrosilylation catalyst (E') to catalyze the hydrosilylation reaction of the SiH crosslinker (B2). The additional platinum-based hydrosilylation catalyst (E') includes those described for component (E) above and may be the same as or different from the platinum-based hydrosilylation catalyst (E) added in step (I) above. Desirably, applications of the present application include the addition of component (F). Component F and component (B2) (i.e., SiH crosslinker (B2)) can be added together, or component (F) can be added before or after the addition of component (B2). Component (F) comprises a hydrosilylation reaction inhibitor or a combination of one or more hydrosilylation reaction inhibitors (also referred to as "inhibitors"). Inhibitors can serve to stabilize the curable thermally conductive composition from premature curing and provide storage stability to the composition.Examples of suitable inhibitors include acetylenic compounds such as 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, 3-phenyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,1-dimethyl-2-propynyl)oxy)trimethylsilane, and methyl(tris(1,1-dimethyl-2-propynyloxy))silane, 3-methyl-3-penten-1-yne, and 3,5-dimethyl acetylene-type compounds, such as ene-yne ​​compounds such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane; triazoles such as benzotriazole; hydrazine-based compounds; phosphine-based compounds; mercaptan-based compounds; cycloalkenylsiloxanes including methylvinylcyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane;

[0054] The concentration of the inhibitor (F) can be greater than or equal to zero, greater than or equal to 0.001 wt.%, greater than or equal to 0.002 wt.%, or even greater than or equal to 0.003 wt.%, and at the same time typically less than or equal to 0.5 wt.%, less than or equal to 0.3 wt.%, less than or equal to 0.1 wt.%, less than or equal to 0.05 wt.%, less than or equal to 0.01 wt.%, less than or equal to 0.005 wt.%, less than or equal to 0.004 wt.%, or even less than or equal to 0.003 wt.%, based on the weight of the curable thermally conductive composition.

[0055] Other optional components may further include any one, or a combination of two or more of the following additional components: heat stabilizers and / or pigments (such as copper phthalocyanine powder), thixotropic agents, fumed silica (desirably surface-treated), and spacer additives (such as glass beads). The total concentration of these additional components may range from zero to 1 wt. % based on the weight of the curable thermally conductive composition, and may be zero or more, 0.1 wt. % or more, 0.2 wt. % or more, 0.3 wt. % or more, 0.4 wt. % or more, or even 0.5 wt. % or more, and at the same time typically be 1 wt. % or less, 0.9 wt. % or less, 0.8 wt. % or less, or even 0.6 wt. % or less.

[0056] When the optional components are used, they may be added independently in step (I) and / or step (III), and preferably in step (III) together with, before, or after the addition of the SiH crosslinker (B2).

[0057] The method for making a curable thermally conductive composition may or may not include the step of adding a solvent. If present, the solvent may be less than 0.01 wt %, less than 0.005 wt %, or even zero, based on the weight of the curable thermally conductive composition. Desirably, the curable thermally conductive composition is substantially free of solvent, i.e., it contains no solvent, or it may contain trace amounts of residual solvent from the delivery of the starting materials in the composition. The solvent content can be measured by gas chromatography (GC). If the amount of solvent is too high, voids tend to be generated during the curing of the curable thermally conductive composition, which can result in a poor surface appearance or even a reduced TC. Solvents may include saturated or unsaturated aliphatic or aromatic hydrocarbons, such as hydrocarbon compounds having 8 to 18 carbon atoms per molecule and at least one aliphatic unsaturation, such as benzene, toluene, xylene, hexane, heptane, octane, isoparaffin, and tetradecene; ketones, such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; acetates, such as ethyl acetate and isobutyl acetate; glycol ethers, such as propylene glycol methyl ether, dipropylene glycol methyl ether, and propylene glycol n-butyl ether; ethers, such as diisopropyl ether and 1,4-dioxane; cyclic or linear siloxanes having an average degree of polymerization of 3 to 10, such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and / or decamethylcyclopentasiloxane; or mixtures thereof. The curable thermally conductive composition does not require the use of any solvents, such as those listed above, to achieve the desired ER (i.e., good processability) and TC properties.

[0058] The present invention further relates to a curable thermally conductive composition prepared from the above method or comprising a mixture of a pre-cured composite and a SiH crosslinker (B2). The pre-cured composite comprises component (C), component (D), and the hydrosilylation reaction product of components (A), (B1), and (E). All components are as described above. The concentrations and molar ratios of these components in the composition (e.g., SiH B1 / Vi ratio and (SiH B1 +SiH B2 The curable thermally conductive composition may achieve all of the following properties: (i) an oil-bleed of 10% or less (≦10%) after application at 25° C. for 5 days, (ii) an oil-bleed of 10% or less (≦10%) after aging at 125° C. for 2 days, (iii) an ER of 15 g / min or greater, and (iv) an ESR of 3.0 W / m * The TC is greater than 3.0 W / m. Oil-bleed properties are determined according to the test method described in the Oil-Bleed Test. Herein, the ER is determined using a standard 30 cubic centimeter EFD syringe package at 0.62 MegaPascal (MPa) pressure and 25°C (further details are provided below under Extrusion Rate Test). The thermally conductive composition may have an ER of 15 g / min or greater, 18 g / min or greater, or even 20 g / min or greater. ER is a useful property as a measure of extrudability, viscosity, and dispenseability, making the curable thermally conductive composition easily dispenseable for application onto another material, such as an electronic component or heat sink. TC is measured using a hot disk according to ISO 22007-2 using a cured sample (further details are provided below under Thermal Conductivity Test) and is greater than 3.0 W / m. * Super K(>3.0W / m * K), 3.5W / m * K or even 4.5W / m * K or higher. Such high TC (providing efficient heat dissipation), low oil bleed, and easy dispensability make the curable thermally conductive composition particularly useful as a thermally conductive interface material for efficiently transferring heat between two components. Thermally conductive interface materials are typically used, particularly in electronic devices, to thermally couple heat-generating and heat-dissipating components. The thermally conductive composition can be supplied as a one-part product.

[0059] The present invention further includes a process for forming a thermally conductive silicone material on an electronic component, the process comprising: (i) providing a curable thermally conductive composition prepared by the method described above; (ii) applying a curable thermally conductive composition onto an electronic component for an electronic device; and step (iii) thermally curing the curable composition, thereby forming a thermally conductive silicone material (i.e., a cured material).

[0060] Desirably, application of the curable thermally conductive composition can involve dispensing or extruding the curable thermally conductive composition. Due to the above-mentioned properties of the curable thermally conductive composition, such as excellent dispensability and conformability, this process allows for automated dispensing and assembly (i.e., increased productivity) with minimal stress applied to fill complex shapes and various gaps, thus avoiding potential damage to electronic components.

[0061] In step (iii) of the process, the thermally conductive composition can be cured by heat, for example, at temperatures above 25°C, and can be above 40°C, e.g., 60-150°C or 80-120°C. The duration of curing can vary depending on the temperature and is typically 0.5-24 hours. The curable thermally conductive composition can be cured by heating in an oven or with heat generated by electronic components. Desirably, when the electronic device is operating, the heat generated by the electronic components typically cures the curable thermally conductive composition within a few hours, thereby forming a cured material. The curing in step (iii) of the process is not performed under the moisture conditions required for conventional curing approaches. Conventional curing approaches use moisture in the air to cure the composition, which requires a longer time (e.g., 7 days) for the composition to fully cure, and are therefore not suitable for electronic applications.

[0062] Due to the low or absent concentration of solvent in the curable thermally conductive composition, the process does not involve (i.e., does not include) extra steps to remove the solvent, such as stripping or evaporating the solvent. The curable thermally conductive composition allows for a process to use the composition without the aid of a solvent, while still providing a resulting composition having the desired ER and TC properties described above, and also makes it applicable to directly dispense (e.g., by extrusion) the composition onto an article component without the need to add a solvent to the composition prior to use.

[0063] Examples of electronic components that generate heat during operation of an electronic device include a central processing unit (CPU), a graphics processing unit (GPU), a memory chip, a driver chip, and an optical module. The thermally conductive composition can be applied to one or two heat-generating electronic components. The thermally conductive composition can be between and in contact with one electronic component and a heat-dissipating component such as a heat sink, or between and in contact with two electronic components of an electronic device, at least one of which generates heat during operation of the electronic device. Heat-dissipating components include heat sinks, cooling plates / pads, cooling tubes, metal covers, etc. The present invention also includes electronic articles comprising the thermally conductive composition and an electronic component to which the thermally conductive composition is applied. Examples of electronic devices include optical modules, smartphones, digital cameras, computers, pad devices, servers, and communication base stations. [Example]

[0064] Some embodiments of the present invention will now be described in the following examples, where all percentages (%) are by weight of the composition and all particle sizes of fillers are D50 particle sizes unless otherwise specified. Table 1 shows materials for use in the sample thermally conductive compositions described herein below. Note: "Vi" stands for vinyl and "Me" stands for methyl. SYL-OFF is a trademark of Dow Corning Corporation.

[0065] [Table 1] * The "viscosity" of the vinyl polymer was measured at 25°C according to ASTM D445-21. The "vinyl content" of a vinyl polymer refers to the weight percent of vinyl groups relative to the molecular weight of the vinyl polymer. "SiH content" refers to the weight % of H from SiH relative to the molecular weight of the SiH crosslinker. "Pt content" refers to the weight percent of Pt relative to the molecular weight of the catalyst. "TC filler" refers to a thermally conductive filler.

[0066] IE1~5 samples The component compositions of the IE samples are shown in Table 2, and the amount of each component is reported in grams (g). The samples were prepared by mixing the components together at room temperature (RT) using a SpeedMixer™ DAC 400 FVZ from FlackTek Inc., unless otherwise noted. The silicone matrix components, including the vinyl polymer (A), SiH crosslinker (B1), and treating agent (D), were weighed into the cup of the SpeedMixer. The TC filler (C3) was then weighed and added to the cup. This mixture was mixed by the SpeedMixer at 1000 revolutions per minute (RPM) for 20 seconds, then at 1500 RPM for 20 seconds. The TC filler (C2) was then added and mixed in the same manner. The TC filler (C1) was then added under the same mixing conditions. The resulting composition in the cup was scraped and mixed again. A Pt catalyst (E), including catalyst E-1 and, optionally, catalyst E-2, was added and mixed. The materials were then placed in an oven and maintained at 70°C for 60 minutes (the "heating step"). This temperature is below the activation temperature of catalyst E-2. The contents of the cup were then cooled to room temperature. The SiH crosslinker (B2), inhibitor (F), and pigment (G) were then added to the cup and mixed at 1000 RPM for 30 seconds to obtain a curable thermally conductive silicone composition sample.

[0067] CE1~5 samples The component compositions of the CE samples are shown in Table 3, with the amount of each component reported in grams (g). The CE1 sample was prepared following the same procedure as for preparing the IE sample above, except that the SiH crosslinker (B2) was not used. The CE2, CE3, and CE5 samples were prepared following the same procedure for preparing the IE sample.

[0068] The CE4 sample was prepared following the same procedure as IE above, except that the heating step was omitted.

[0069] The thermally conductive composition samples obtained above were evaluated for ER, TC, oil bleeding, and hardness according to the following test methods.

[0070] Extrusion Speed ​​Test The extrusion rate ("ER") of the sample is measured using a Nordson EFD dispensing device. The sample material is packaged in a 30 cubic centimeter syringe (EFD Syringe from Nordson Company) with a 2.54 millimeter (mm) opening. The sample is dispensed through the opening at 25°C by applying a pressure of 0.62 MPa to the syringe. The mass of the sample in grams (g) extruded after 1 minute corresponds to the extrusion rate (grams / min). The objective of this invention is to achieve an extrusion rate of at least 15 g / min.

[0071] Of note, some samples are reported as having an ER of 0 because they were highly viscous pastes that could not be extruded (thermal conductivity was not measured and is therefore reported as "NA").

[0072] Thermal Conductivity Test Determine thermal conductivity (TC) according to ISO 22007-2 using a hot disc. The TC of the cured samples was measured with a hot disc TPS 2500 S instrument equipped with a 3.189 mm Kapton sensor (model 5465). * 25mm *Cured samples were prepared by curing curable thermally conductive composition samples having dimensions of 8 mm at 120°C for 60 minutes. * The goal is to achieve a TC greater than K.

[0073] Oil Bleed Test A curable thermally conductive composition sample (0.6 mL) was applied to an A4 sheet of paper and measured over a 5 cm * The sample was sandwiched between two 5 cm glass plates, and the thickness of the sample was adjusted to 1.5 mm using a spacer. The initial diameter of the sample (denoted as "D0") was then measured. The resulting test specimen was placed horizontally at 25°C ("RT") for 5 days and at 125°C for 2 days. The degree of oil bleeding on the paper was evaluated as the percentage increase between the diameter of the oil bleeding from the composition (denoted as "D1", i.e., the diameter of the circular sample after oil migration) and the initial diameter of the composition (D0). Oil bleeding rate = [(D1-D0) / D0] x 100%

[0074] The objective of the present invention is to achieve both an oil bleed requirement of 10% or less (≦10%) after aging at RT for 5 days and at 125° C. for 2 days, respectively.

[0075] Hardness Test The hardness of the cured samples was determined by durometer Shore A. The cured samples were prepared according to the same procedure as described in the thermal conductivity test. The highest value was recorded. The objective of this invention is to achieve a Shore A hardness >5.

[0076] Each sample was characterized for ER using the Extrusion Rate Test, for TC using the Thermal Conductivity Test, for oil-bleed using the Oil-Bleed Test, and for hardness using the Hardness Test described above.

[0077] Table 2 contains the characterization results of the IE1 to IE5 samples. As shown in Table 2, all of the IE1 to IE5 samples were subjected to an ER of ≥ 15 g / min at 25°C for 5 days (hereinafter referred to as "RT"). * 5D") and 125°C for 2 days (hereinafter referred to as "125°C* 2D") and ≦10% oil bleed and 3.0W / m * The requirement of TC above K was achieved.

[0078] Table 3 contains the characterization results of samples CE1 to CE5. As shown in Table 3, sample CE1 was pre-prepared by mixing (A-1) Q branched vinyl-terminated polymer, (B1-1) SiH crosslinker, and (E-1) Pt catalyst with heating for pre-cure, but without (B2) SiH crosslinker for post-cure during application, and did not meet the requirements for ER and oil-bleed at RT and 125°C.

[0079] The CE2 sample contained (A-2) linear vinyl-terminated polymer instead of (A-1)Q branched vinyl-terminated polymer in the pre-cure step, providing a much higher degree of oil-bleed (e.g., 38%) at RT.

[0080] The CE3 sample was prepared by combining (A-1) Q branched vinyl-terminated polymer, (B1-3) SiH crosslinker, and (E-1) Pt catalyst with a high SiH content using a pre-cure heating process. B1 The CE3 sample contained a 0 g / min ER (the material was too viscous) and therefore no other properties could be measured.

[0081] The CE4 sample does not include a heating process for pre-cure, but instead uses (A-2) + (A-3) linear vinyl-terminated polymers to replace (A-1)Q branched vinyl-terminated polymer, and adds (B2-3) SiH crosslinker and (E-2) Pt catalyst after filler loading for post-cure at the time of application. The CE4 sample exhibited high oil-bleed (>10%) at RT.

[0082] The CE5 sample was prepared by combining components (A-1) Q branched vinyl-terminated polymer, (B1-3) SiH crosslinker, (C), (D), and (E-1) Pt catalyst in a low SiH B1 / Vi ratio (<0.2) and further included (B2-2) SiH crosslinker for post-cure in application, providing much higher oil-bleed (>10%) at RT.

[0083] [Table 2] Note: In Table 2 and Table 3 below: "TC filler wt %" refers to the total weight % of thermally conductive fillers relative to the total weight in the curable thermally conductive composition. "SiH B1 " / Vi ratio" refers to the molar ratio of SiH functional groups from the SiH crosslinker (B1) to vinyl functional groups from the vinyl polymer (A). "(SiH B1 +SiH B2 The "(B1) / Vi ratio" refers to the molar ratio of the total SiH functional groups from the SiH crosslinker (B1) and the SiH crosslinker (B2) to the vinyl functional groups from the vinyl polymer (A). The "oil-bleed rate," "ER," "TC," and "hardness" were evaluated according to the test methods described above after 5 days at RT and 2 days at 120°C, respectively.

[0084] [Table 3]

Claims

1. 1. A method of making a curable thermally conductive composition, the method comprising: (I) the following components (A), (B1), (C), (D), and (E): (A) having at least three terminal alkenyl groups per molecule and a viscosity of 25 to 2,000 millipascals as determined by using a glass capillary Cannon-Fenske viscometer at 25°C in accordance with ASTM D445-21; ＊ 3% to 10% by weight of a Q-branched alkenyl-functional polyorganosiloxane having a viscosity of 1000 .mu.m to 1000 .mu.m seconds; (B1) a silyl-hydride functional polysiloxane crosslinker (B1) containing at least two silyl-hydride groups per molecule and present in a concentration providing a molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinker (B1) to alkenyl groups in said Q-branched alkenyl-functional polyorganosiloxane (A) in the range of 0.2 to 0.35; (C) 90% by weight or more of a thermally conductive filler; (D) a filler treating agent, and (E) preparing a mixture containing a platinum-based hydrosilylation catalyst; (II) curing the mixture resulting from step (I) with heat, thereby forming a pre-cured composite; (III) mixing the pre-cured composite obtained from step (II) with (B2) a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule, thereby obtaining the curable thermally conductive composition; the molar ratio of the sum of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinkers (B1) and (B2) to alkenyl groups in the Q branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; The method wherein the weight percentages are based on the weight of the curable thermally conductive composition.

2. 10. The method of claim 1, further comprising the addition of (F) an inhibitor, (E') an additional platinum-based hydrosilylation reaction catalyst, or a mixture thereof, during or after step (III).

3. The Q branched alkenyl-functional polyorganosiloxane (A) has the formula (I): 【Chemistry 1】 wherein each R ａ are independently an alkenyl group, and each R ｂ are independently monovalent hydrocarbon groups free of aliphatic unsaturation, and n is an integer from 15 to 150, representing the average number of chain lengths of different branches of the polyorganosiloxane. The method of claim 1 or 2.

4. 4. The method of claim 1, wherein the molar ratio of the silicon-bonded hydrogen atoms in the silyl-hydride-functional polysiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is in the range of 0.22 to 0.

28.

5. 5. The method of any one of claims 1 to 4, wherein in step (III), mixing the pre-cured composite with the silyl-hydride functional polysiloxane crosslinker (B2) is carried out at a temperature below 30°C.

6. The crosslinking agents (B1) and (B2) each independently have an average chemical structure (IV): R ｂｂ （３－ｈ） H ｈ SiO-(HR ｂｂ SiO) ｅ -(R ｂｂ ２ SiO) ｆ -SiH ｈ’］Ｒ ｂｂ （３－ｈ’） (IV) In the formula, R ｂｂ is independently selected at each occurrence from an alkyl group having 1 to 6 carbon atoms, and phenyl; subscripts h and h' are each independently selected at each occurrence from a value ranging from zero to 3, provided that the combination of e, h, and h' is at least 2; subscript e is zero to 30; and subscript f is 5 to 200.

7. 7. The method of any one of claims 1 to 6, wherein the thermally conductive filler (C) comprises: (c1) 40 to 60 wt. % aluminum oxide particles having a D50 of 20 to 50 μm; (c2) 25 wt. % to 40 wt. % aluminum oxide particles having a D50 of 1 to 5 μm; and (c3) 10 to 20 wt. % zinc oxide particles having a D50 of 0.1 to 0.5 μm, wherein the weight percentages are based on the weight of the curable thermally conductive composition.

8. A curable thermally conductive composition comprising a mixture of the pre-cured composite and (B2) a silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule, 1. The pre-cured composite comprising: component (C), component (D), and the hydrosilylation reaction product of components (A), (B1), and (E): (A) having at least three terminal alkenyl groups per molecule and a viscosity of 25 to 2,000 millipascals as determined by using a glass capillary Cannon-Fenske viscometer at 25°C in accordance with ASTM D445-21; ＊ 3% to 10% by weight of a Q-branched alkenyl-functional polyorganosiloxane having a viscosity of 1000 .mu.m to 1000 .mu.m seconds; (B1) a silyl-hydride functional polysiloxane crosslinker (B1) containing at least two silyl-hydride groups per molecule and present in a concentration providing a molar ratio of silicon-bonded hydrogen atoms in said silyl-hydride functional polysiloxane crosslinker (B1) to alkenyl groups in said Q-branched alkenyl-functional polyorganosiloxane (A) of from 0.2 to 0.35; (C) 90% by weight or more of a thermally conductive filler; (D) a filler treating agent, and (E) a platinum-based hydrosilylation catalyst; the molar ratio of the sum of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinkers (B1) and (B2) to alkenyl groups in the Q branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; the weight percentages are based on the weight of the curable thermally conductive composition; The curable thermally conductive composition has an extrusion rate of 15 grams / minute or greater, an oil-bleed index of 10% or less after aging at 25°C for 5 days and at 125°C for 2 days, and an oil-bleed index of 3.0 watts / meter according to ISO 22007-2 using a hot disk. ＊ A curable thermally conductive composition that cures to a material with a thermal conductivity above Kelvin.

9. 1. A process for forming a thermally conductive silicone material on an electronic component, the process comprising: (i) providing a curable thermally conductive composition according to claim 8; (ii) applying the curable thermally conductive composition onto the electronic component; (iii) thermally curing the curable thermally conductive composition, thereby forming the thermally conductive silicone material.

10. 10. The process of claim 9, wherein the applying of the curable thermally conductive composition involves dispensing the curable thermally conductive composition.

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