Method for preparing curable thermally conductive composition

Abstract

A process for the preparation of a curable thermally conductive composition and the process comprises the steps of: (I) preparing an admixture comprising the following components (A), (B1), (C), (D) and (E): (A) 3 wt% to 10 wt% of a Q-branched alkenyl functional polyorganosiloxane having at least three terminal alkenyl groups per molecule, and having a viscosity of from 25 mPa * s to 2000 mPa * s as determined at 25 DEG C according to ASTM D445-21 using a viscometer of the glass capillary Cannon-Finsky type; and a method for preparing the same, wherein the viscosity is from 25 mPa * s to 2000 mPa * s as determined at 25 DEG C using a viscometer of the glass capillary Cannon-Finsky type; (B1) a silyl-hydride functional polysiloxane crosslinker 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 (B1) to alkenyl groups in the Q-branched alkenyl functional polyorganosiloxanes in the range of 0.2 to 0.35; (C) 90 wt% or more of a thermally conductive filler; (D) a filler treatment agent; and (E) a platinum-based hydrosilylation reaction catalyst; (II) curing the admixture obtained from step (I) by heat, thereby forming a pre-cured composite material; and (III) mixing the pre-cured composite material obtained from step (II) with (B2) a silyl-hydride functional polysiloxane cross-linking agent containing at least two silyl-hydride groups per molecule; thereby obtaining a curable thermally conductive composition; wherein the molar ratio of the total silicon bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinkers (B1) and (B2) to the alkenyl groups in the Q-branched alkenyl functional polyorganosiloxane (A) is greater than 0.45; and wherein the weight percentages are relative to the weight of the curable thermally conductive composition.

Description

Technical Field

[0001] The present invention relates to a method for preparing a curable thermal conductive composition and a thermal conductive composition prepared therefrom. Background Art

[0002] The industrial drive for smaller and more powerful electronic devices has increased the demand for thermal conductive compositions that can be used to dissipate the heat generated in such devices. For example, the telecommunications industry is transitioning to the 400 Gigabit Ethernet (GbE) standard for faster switching and routing, which requires better thermal control of optical components such as optical transceivers and other optical modules to remove heat. Thermal interface materials are commonly used in electronic devices to thermally couple heat-generating components and heat-dissipating components.

[0003] One challenge with thermal interface materials is to have both thermal conductivity properties and low or no oil bleeding, while also being easy to extrude to allow precise application of the thermal material onto small components. Oil bleeding (also known as "exudation" or "flow separation") from thermal interface materials, especially from thermal gels, is a key risk in electronic and optical module applications because it causes many problems such as contact failures, contamination, and short circuits, which lead to a decrease in the reliability of electronic components and / or affect optical signal transmission.

[0004] Conventionally manufactured thermal pads are solid materials that do not worry about oil bleeding problems due to their degree of crosslinking, but are not extrudable. These thermal pads must be applied manually and do not meet the requirements of high-volume automated processes. In addition, the stress applied to improve the interfacial adhesion between the thermal pad and the electronic component may potentially damage the dedicated electronic component. The dispensable thermal gels that are liquid at room temperature (25 degrees Celsius (°C)) and have grease-like properties have many advantages over thermal pads, including little or no stress required for assembly in the manufacturing plants of electronic devices, and higher extrusion rates with higher efficiency through automated equipment. However, these dispensable thermal gels typically suffer from severe oil bleeding over time due to the migration of polysiloxane fluids. For example, when the gel is applied at room temperature at a thick adhesive layer (>1 mm), especially during high-temperature aging when the electronic device is in operation, the oil bleeding degree exceeds 10%. Specifically, for single-part dispensable thermal gels, it is more challenging to achieve an oil bleeding degree of no more than 10% both after 5 days at 25 °C and after aging for 2 days at 125 °C, while having an extrusion rate (ER) of at least 15 grams per minute and providing a cured material with a thermal conductivity greater than 3.0 watts per meter * Kelvin measured using a hot disk in accordance with ISO22007-2. The oil bleeding degree and ER are measured using the oil bleeding test and extrusion rate test defined below, respectively.

[0005] There is still a need to identify a thermally conductive composition that can achieve the above-mentioned oil bleeding degree without compromising the extrusion rate and thermal conductivity properties. Summary of the Invention

[0006] The present invention provides a curable thermally conductive composition having an oil bleeding degree of no more than 10% (≤10%) after being applied at 25 °C for 5 days and after aging at 125 °C for 2 days, respectively, and an extrusion rate ("ER") of 15 grams per minute (g / min) or greater as measured using the extrusion rate test defined below, and curing into a material having a thermal conductivity ("TC") of greater than 3.0 watts per meter per Kelvin (W / m*K) according to ISO 22007-2 using a hot disk. Surprisingly, it has been determined that such a composition can be prepared by a method involving a pre-curing step using a specific molar ratio of a Q-branched alkenyl-functional polyorganosiloxane (A) and a silyl-hydride-functional polysiloxane crosslinker (B1), which method further includes adding a silyl-hydride-functional polysiloxane crosslinker (B2).

[0007] In a first aspect, the present invention is a method for preparing a curable thermally conductive composition, the method comprising the following steps:

[0008] (I) Preparing an admixture comprising the following components (A), (B1), (C), (D), and (E):

[0009] (A) 3% to 10% by weight of a Q-branched alkenyl-functional polyorganosiloxane having at least three terminal alkenyl groups per molecule and having a viscosity of 25 millipascal seconds (mPa*s) to 2000 millipascal seconds as measured at 25 °C using a glass capillary Cannon-Fenske type viscometer according to ASTM D445-21;

[0010] (B1) A silyl-hydride-functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule and present at a concentration providing a molar ratio of silicon-bonded hydrogen atoms in (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane in the range of 0.2 to 0.35;

[0011] (C) 90% by weight or more of a thermally conductive filler;

[0012] (D) A filler treatment agent; and

[0013] (E) A platinum-based hydrosilylation reaction catalyst;

[0014] (II) Thermally curing the admixture obtained from step (I) to form a pre-cured composite material; and

[0015] (III) Mix the pre-cured composite material obtained in step (II) with (B2) a silyl-hydride functional polysiloxane crosslinking agent containing at least two silyl-hydride groups per molecule; thereby obtaining a curable thermally conductive composition;

[0016] wherein the molar ratio of the total silicon-bonded hydrogen atoms in (B1) and (B2) to the alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45;

[0017] wherein the weight percentages are relative to the weight of the curable thermally conductive composition.

[0018] In a second aspect, the present invention is a curable thermally conductive composition comprising an admixture of a pre-cured composite material and (B2) a silyl-hydride functional polysiloxane crosslinking agent containing at least two silyl-hydride groups per molecule;

[0019] wherein the pre-cured composite material comprises component (C); component (D); and the hydrosilylation reaction product of components (A), (B1), and (E):

[0020] (A) 3 wt% to 10 wt% of a Q-branched alkenyl-functional polyorganosiloxane having at least three terminal alkenyl groups per molecule and having a viscosity of 25 mPa*s to 2000 mPa*s as measured at 25 °C using a glass capillary Cannon-Fenske type viscometer in accordance with ASTM D445-21;

[0021]

[0022] (B1) A silyl-hydride functional polysiloxane crosslinking agent containing at least two silyl-hydride groups per molecule and present in a concentration to provide a molar ratio of the silicon-bonded hydrogen atoms in (B1) to the alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) of 0.2 to 0.35; and (E) a platinum-based hydrosilylation reaction catalyst; (C) 90 wt% or more of a thermally conductive filler;

[0023] (D) A filler treatment agent; and

[0024] (E) A platinum-based hydrosilylation reaction catalyst;

[0025] (E) A platinum-based hydrosilylation reaction catalyst;

[0026] wherein the molar ratio of the total silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxane crosslinking agents (B1) and (B2) to the alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45;

[0027] wherein the weight percentages are relative to the weight of the curable thermally conductive composition;

[0028] The curable thermal conductive compositions respectively have an extrusion rate of 15 g / min or greater and an oil bleeding degree of no more than 10% after 5 days at 25°C and after aging for 2 days at 125°C, and are cured into a material having a thermal conductivity greater than 3.0 W / m*K according to ISO 22007-2 using a hot plate.

[0029] In a third aspect, the present invention is a method for forming a thermal conductive silicone material on an electronic component. The method includes:

[0030] (i) providing the curable thermal conductive composition of the second aspect,

[0031] (ii) applying the curable thermal conductive composition on the electronic component, and

[0032] (iii) curing the curable thermal conductive composition by heat; thereby forming a thermal conductive silicone material. Detailed Description

[0033] When no test method number is used to indicate a date, the test method refers to the latest test method as of the priority date of this document. References to test methods include references to both the test society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods, and ISO refers to the International Organization for Standardization.

[0034] A product identified by its trade name refers to the composition that can be obtained under those trade names as of the priority date of this document.

[0035] "And / or" means "and, or as an alternative form". Unless otherwise specified, all ranges include endpoints. Unless otherwise stated, all weight percentage (wt%) values are relative to the weight of the composition.

[0036] Particles having a "spherical" shape refer to particles having an aspect ratio of 1.0 + / - 0.2. The aspect ratio of the particles is measured by imaging using a scanning electron microscope (SEM) and obtaining the average ratio of the longest dimension (major axis) and the shortest dimension (minor axis) of at least ten particles.

[0037] Particles having an "irregular" shape (which can be interchanged with "crushed" particles) have an aspect ratio other than 1.0 + / - 0.2 and have at least three faces that are obvious by SEM imaging (distinguishing these particles from "flakes" having 2 faces).

[0038] The particle size of the thermal conductive filler (which can be used interchangeably with "average particle size" and "D50") refers to the use of a Mastersizer from Malvern Instruments Limited TM(Trademark of Malvern Panalytical Limited) Volume weighted median (D50) of particle size distribution of the 3000 Laser Diffraction Particle Size Analyzer.

[0039] Unless otherwise indicated, the "viscosity" of the polysiloxane is determined at 25 degrees Celsius (°C) using a glass capillary Cannon-Fenske type viscometer in accordance with ASTM D445-21.

[0040] The present invention relates to a method for preparing a curable heat-conductive composition (which may be used interchangeably with the "curable composition"). Such a composition can be used as a heat-conductive gel, particularly a dispensable heat-conductive gel, and can be dispensed onto heat-generating components by an automated device, wherein the stress applied to the components of complex and precision electronic components is minimized. The curable heat-conductive composition is a liquid thermal interface material that cures into a gel-like structure by heat (such as the heat generated by the device applying the composition).

[0041] The method of the present invention comprises the steps of: (I) preparing an admixture comprising components (A), (B1), (C), (D) and (E); (II) curing the admixture obtained in step (I) by heat to form a pre-cured composite; and (III) mixing component (B2) with the pre-cured composite obtained in step (II); thereby forming a curable heat-conductive composition.

[0042] In step (I) of the method, the preparation of the admixture can be carried out by mixing components (A), (B1), (C), (D) and (E) in any order. Desirably, components (A), (B1) and (D) are first mixed, then further mixed with component (C), and then component (E) is added.

[0043] Component (A) is a Q-branched alkenyl-functional polyorganosiloxane (hereinafter also referred to as "Q-branched polyorganosiloxane"). "Alkenyl" means 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.

[0044] The Q-branched alkenyl-functional polyorganosiloxane (A) useful in the present invention has at least three terminal alkenyl groups (desirably, vinyl groups) per molecule. The Q-branched alkenyl-functional polyorganosiloxane may have four or more alkenyl groups per molecule. The alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane may all be at the terminals or a combination of terminals and side chains, and desirably, four of the alkenyl groups are at the terminal positions. Desirably, the Q-branched alkenyl-functional polyorganosiloxane is a Q-branched vinyl-functional polyorganosiloxane. The Q-branched alkenyl-functional polyorganosiloxane may contain at least one unit of the formula (SiO b 2SiO 2 / 2 ) z bonded to three or more polydiorganosiloxane chains of the formula (R 4 / 2 ) b , where R 4 / 2 is defined as in the following formula (I), and each subscript z is independently from 15 to 150. The Q-branched polyorganosiloxane may contain from 1 to 10, from 1 to 8, or from 1 to 2 units of the formula (SiO ). "End group" is located on the terminal siloxane group of the molecule. The "terminal" siloxane group is only connected to one other siloxane group. "Side group" is located on the internal siloxane group of the molecule, which is bonded to at least two other siloxane groups. "Siloxane group" is a group containing SiO bonded to another Si through the oxygen of SiO.

[0045] The Q-branched alkenyl-functional polyorganosiloxane has a viscosity in the range of 25 mPa·s to 2000 mPa·s. The Q-branched alkenyl-functional polyorganosiloxane can be a combination of two or more polyorganosiloxanes that can differ in one or more properties selected from molecular weight, structure, siloxane units, and sequence. When the Q-branched polyorganosiloxane is a combination of more than one Q-branched polyorganosiloxane, the viscosity is the combined viscosity of the Q-branched polyorganosiloxanes. As determined at 25 °C by using a glass capillary Cannon-Fenske type viscometer according to ASTM D445-21, the viscosity of the Q-branched alkenyl-functional polyorganosiloxane is 25 mPa·s or greater, and can be 30 mPa·s or greater, 40 mPa·s or greater, 50 mPa·s or greater, 60 mPa·s or greater, 70 mPa·s or greater, 75 mPa·s or greater, 78 mPa·s or greater, 80 mPa·s or greater, 100 mPa·s or greater, 125 mPa·s or greater, 150 mPa·s or greater, 175 mPa·s or greater, even 200 mPa·s or greater, and at the same time is 2000 mPa·s or less, and can be 1500 mPa·s or less, 1000 mPa·s or less, 500 mPa·s or less, 400 mPa·s or less, 300 mPa·s or less, 200 mPa·s or less, 150 mPa·s or less, 100 mPa·s or less, 90 mPa·s or less, even 80 mPa·s or less, and desirably is 100 mPa·s to 600 mPa·s, 150 mPa·s to 500 mPa·s, or 200 mPa·s to 400 mPa·s, or 300 mPa·s to 400 mPa·s.

[0046] The Q-branched alkenyl-functional polyorganosiloxane can have an alkenyl content of 0.1 wt% to 5.0 wt%, and can be 0.1 wt% or greater, 0.5 wt% or greater, 0.7 wt% or greater, 0.9 wt% or greater, even 1.2 wt% or greater, and at the same time is generally 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 percentage of the alkenyl group relative to the molecular weight of the Q-branched polyorganosiloxane. When the alkenyl group in the Q-branched polyorganosiloxane is a vinyl group, the above alkenyl content is the vinyl content. The vinyl content herein refers to the weight percentage of the vinyl group relative to the molecular weight of the Q-branched polyorganosiloxane.

[0047] Desirably, the Q-branched alkenyl-functional polyorganosiloxane has the chemical formula (I):

[0048]

[0049] wherein each R a is independently an alkenyl group, and each R b is independently a monovalent hydrocarbon group free of aliphatic unsaturated groups, and n is an integer from 15 to 150, representing the average chain length of the different branches of the polyorganosiloxane. In formula (I), n can be 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 usually 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, and desirably, n is from 35 to 85.

[0050] The alkenyl group of R a is as described above. Examples of particularly suitable alkenyl groups of R a are vinyl, allyl, butenyl, and hexenyl. Each R a can be the same or different. Desirably, each R a is selected from vinyl or hexenyl. More desirably, each R a is a vinyl group.

[0051] Examples of the monovalent hydrocarbon group of R b are alkyl groups having 1 to 6 carbon atoms or aryl groups having 6 to 10 carbon atoms. The alkyl groups suitable for R b can include, for example, methyl, ethyl, propyl (e.g., isopropyl 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-chain saturated hydrocarbon groups having 6 carbon atoms. Examples of the aryl groups suitable for R b are phenyl, tolyl, xylyl, naphthyl, benzyl, and dimethylphenyl. Each R b can be the same or different. Each R b can be an alkyl group. Desirably, each R b is independently methyl, ethyl, or propyl, and more desirably, each R b is methyl.

[0052] The Q-branched alkenyl-functional polyorganosiloxane can be a Q-branched polyorganosiloxane or a combination of two or more Q-branched polyorganosiloxanes of formula (I) that 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 dimethylvinylsilanyloxy-terminated polydimethylsiloxanes and desirably has a viscosity of from 200 mPa·s to 400 mPa·s. For example, the Q-branched polyorganosiloxane can be a Q-branched polyorganosiloxane or a combination of more than one Q-branched polyorganosiloxane selected from the group consisting of: (A-i) a Q-branched dimethylvinylsilanyloxy-terminated polydimethylsiloxane having a viscosity of 240 mPa·s and a vinyl content of 0.9 wt%, (A-ii) a Q-branched dimethylvinylsilanyloxy-terminated polydimethylsiloxane having a viscosity of 300 mPa·s and a vinyl content of 0.72 wt%, and (A-iii) a Q-branched dimethylvinylsilanyloxy-terminated polymethylvinylsiloxane having a viscosity of 400 mPa·s and a vinyl content of 0.6 wt%. The vinyl content of the Q-branched polyorganosiloxane is as defined above.

[0053] Based on the weight of the curable thermally conductive composition, the Q-branched alkenyl-functional polyorganosiloxane is present at a concentration of 3.0 wt% or 10 wt% and can be 3.0 wt% or greater, 3.5 wt% or greater, 4.0 wt% or greater, 4.5 wt% or greater, 5.0 wt% or greater, greater than 5 wt%, 6 wt% or greater, 7 wt% or greater, even 7.2 wt% or greater, and at the same time is generally 10.0 wt% or less and can be 9.0 wt% or less, 8.5 wt% or less, 8.0 wt% or less, 7.5 wt% or less, 6.5 wt% or less, or even 5.5 wt% or less, and desirably is from 4 wt% to 4.5 wt% or from 7.0 wt% to 7.5 wt%.

[0054] The method of preparing the curable thermally conductive composition may or may not include adding a component (A') additional alkenyl-functional polyorganosiloxane other than the above Q-branched alkenyl-functional polyorganosiloxane. When present, the additional alkenyl-functional polyorganosiloxane (A') can be added together with the above component (A) Q-branched polyorganosiloxane or added to the admixture obtained from step (I) of the method. Such additional alkenyl-functional polyorganosiloxanes (A') can be linear alkenyl-functional polyorganosiloxanes having an average chemical structure (II):

[0055] R b (3-c) Ra c SiO-(R a R b SiO) a -(R b 2SiO) b -SiR a d R b (3-d) (II)

[0056] wherein R a and R b are each independently as defined for R and R in formula (I) above, subscript a ≥ 0, subscript b > 0, subscript c is zero or 1, subscript d is zero or 1, (a + b) is from 20 to 350, and (a + c + d) ≥ 2. Subscript a can range from 0 to 5. Subscript b can range from 30 to 150. Desirably, each R a is methyl. Each R b can be vinyl. Desirably, subscript a is zero, subscript c is 1, and subscript d is 1. b a Based on the weight of the curable thermally conductive composition, the concentration of the additional alkenyl-functional polyorganosiloxane (A') can be from zero to less than 1 wt%, and can be zero or greater, 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, 0.3 wt% or less, 0.2 wt% or less, 0.1 wt% or less, 0.5 wt% or less, or even 0.01 wt% or less, and desirably from zero to less than 0.1 wt%. Desirably, the curable thermally conductive composition is free of the additional alkenyl-functional polyorganosiloxane (A').

[0057] Component (B1) is a silyl-hydride (SiH)-functional polyorganosiloxane crosslinking agent (also referred to as "SiH crosslinking agent (B1)"). The SiH-functional polyorganosiloxane crosslinking agent contains at least two silyl-hydride groups (i.e., at least two silicon-bonded hydrogen atoms per molecule), or even 3 or more silyl-hydride groups. The SiH groups can be side groups, end groups, or a combination of side groups and end groups. The SiH-functional polyorganosiloxane crosslinking agent can have an average chemical structure (III):

[0058] R

[0059] R bb (3-h) H h SiO-(HR bb SiO) e -(R bb 2SiO) f-SiH h' R bb (3-h') (III)

[0060] wherein R bb is independently selected, each time it appears, from alkyl groups having 1 to 6 carbon atoms and phenyl; the subscripts h and h′ are each independently selected, each time they appear, from values in the range of zero to 3, provided that the combination of e, h, and h′ is at least 2; the subscript e is from zero to 30; and the subscript f is from 5 to 200.

[0061] R bb groups may have one or more, 2 or more, 3 or more, 4 or more, even 5 or more carbons, while 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, even 2 or fewer carbons. Desirably, R bb groups are independently selected, each time they appear, from methyl and phenyl;

[0062] H is a hydrogen atom;

[0063] the subscripts h and h′ refer to the average number of terminal hydrogen atoms on either end, and are each independently selected, each time they appear, from values in the range of zero to 3, provided that the combination of e, h, and h′ is at least 2. Desirably, h and h′ are each independently zero or greater, one or greater, even 2 or greater, and at the same time 3 or less, 2 or less, even one or less. More desirably, h and h′ have the same value. Most desirably, both h and h′ are zero;

[0064] the subscript e is the average number of (HR bb SiO) groups per molecule. If both h and h′ are zero, then e is in the range of 2 to 30. If both h and h′ are not zero, then the subscript e can be from 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 two or greater, and can be 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, even 9 or greater, and at the same time is generally 30 or less, and can be 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, even 2 or less;

[0065] the subscript f is the number of (R bbThe average number of (2SiO) groups. Generally, the subscript f is 5 or greater, 10 or greater, 20 or greater, 25 or greater, 30 or greater, 40 or greater, 50 or greater, and can be 75 or greater, 100 or greater, 125 or greater, 150 or greater, 175 or greater, even 190 or greater, and at the same time is generally 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.

[0066] The SiH-functional polysiloxane crosslinker can have a silicon-bonded hydrogen atom (H) (“SiH”) content (i.e., SiH content) of 0.1 wt% to 1.0 wt%, and can be 0.1 wt% or greater, 0.11 wt% or greater, 0.15 wt% or greater, 0.2 wt% or greater, 0.25 wt% or greater, 0.30 wt% or greater, even 0.35 wt% or greater, and at the same time is generally 1.0 wt% or less, and can 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, even 0.36 wt% or less, and desirably is 0.1 wt% to 0.8 wt%. The SiH content refers to the weight percentage 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.

[0067] Suitable SiH-functional polysiloxane crosslinkers can include, for example, trimethylsiloxy-terminated poly(dimethylsiloxane / methylhydrogensiloxane), trimethylsiloxy-terminated polymethylhydrogensiloxane, hydrogen-terminated polydimethylsiloxane, hydrogen-terminated poly(dimethylsiloxane / methylhydrogensiloxane), or mixtures thereof. The crosslinker can be a combination of two or more crosslinkers that can be different in one or more properties selected from molecular weight, structure, siloxane units, and sequence. Specific examples of SiH crosslinkers include those having the following average chemical structures: Me3SiO(Me2SiO)7(MeHSiO)3SiMe3, Me3SiO(Me2SiO) 108 (MeHSiO) 10 SiMe3, Me3SiO(Me2SiO) 22 (MeHSiO)2SiMe3 or HMe2SiO(Me2SiO) 25(MeHSiO)1SiMe2H; or mixtures thereof. Suitable commercially available SiH crosslinkers include SiH-functionalized crosslinkers available under the names HMS-071, HMS-501, and DMS-H11 from Gelest, Inc. Desirably, the crosslinker can be a polymer or a combination of two polymers selected from the group consisting of: (B-i) trimethyl-capped dimethyl-co-hydrogenmethyl polysiloxane having a viscosity of 10 mPa*s to 15 mPa*s and an SiH content of 0.36 wt%; and (B-ii) hydride-capped polydimethylsiloxane having a viscosity in the range of 7 mPa*s to 10 mPa*s and an SiH content of 0.16 wt%.

[0068] To ensure the desired dispensability and reduced bleeding properties of the curable thermally conductive composition, the amount of SiH crosslinker (B1) used in step (I) should provide a molar ratio (also referred to as the "SiH B1 / Vi ratio") of silicon-bonded hydrogen atoms from the SiH crosslinker (B1) to the alkenyl groups (desirably, vinyl groups) in the Q-branched alkenyl-functional polyorganosiloxane (A) in the range of 0.2 to 0.35 (and can be 0.2 or greater, 0.21 or higher, 0.22 or higher, 0.23 or higher, 0.24 or higher, even 0.25 or higher, and at the same time 0.35 or less, and can be 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, and desirably 0.22 to 0.28). If the SiH B1 / Vi ratio is too low, the resulting curable composition tends to provide unsatisfactory bleeding properties. If the SiH B1 / Vi ratio is too high, the resulting curable composition tends to provide an extrusion rate that is too low to be dispensed.

[0069] Component (C) comprises one or more thermally conductive fillers. The thermally conductive filler (C) can comprise both electrically conductive fillers and electrically insulating fillers. Component (C) comprises metal fillers, inorganic fillers, fusible fillers, or combinations thereof. Metal fillers include metal particles, examples being aluminum, copper, gold, nickel, silver, and combinations thereof. Examples of inorganic fillers are aluminum trihydrate; magnesium hydroxide; diamond, metal oxides such as alumina, 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. Fusible fillers can include Bi, Ga, In, Sn, and their alloys, and can also optionally include Ag, Au, Cd, Cu, Pb, Sb, Zn, and combinations thereof.

[0070] The shape of the thermally conductive filler particles can be spherical or irregular. 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 of the following properties, such as particle shape, average particle size, particle size distribution, and filler type. The average particle size of the thermally conductive filler will depend on various factors, including the type of thermally conductive filler selected for component (B) and the exact amount added to the curable composition, as well as the bond layer thickness of the device in which the cured product of the composition will be used (i.e., the maximum particle size should be less than the bond layer thickness). The D50 particle size of the thermally conductive filler can range 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.

[0071] 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 is capable of incorporating a high amount of component (C), i.e., ≥ 90 wt% based on the weight of the curable thermally conductive composition, which is usually added in step (I) of the method. Thus, compared with the conventional methods in the art, it achieves a reduction in oil leakage without compromising ER and TC. Based on the weight of the curable thermally conductive composition, the total concentration of component (C) can be 90 wt% or greater, and can be 90.5% or greater, 90.8 wt% or greater, 91 wt% or greater, 91.2 wt% or greater, 95 wt% or greater, 95.4% or greater, or even 95.5 wt% or greater, and at the same time is usually 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 ideally is 91 wt% to 94 wt%.

[0072] Ideally, component (C) comprises at least three different thermally conductive fillers, i.e., a combination of (c1), (c2), and (c3) described below, or can consist of them.

[0073] The first thermal conductive filler (c1) has a D50 particle size of 10 μm to 120 μm, and can have a D50 of 10 μm or greater, 20 μm or greater, 25 μm or greater, 30 μm or greater, 40 μm or greater, 50 μm or greater, even 70 μm or greater, and at the same time has a D50 particle size of 120 μm or less, and can have a D50 of 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 45 μm or less, even 35 μm or less. The first thermal conductive filler (c1) can be selected from alumina, aluminum nitride, magnesium oxide, or a mixture thereof. Ideally, the first thermal conductive filler particles (c1) are spherical in shape. Based on the weight of the curable composition, the concentration of (c1) can be 30 wt% to 65 wt%, and can be 30 wt% or greater, 35 wt% or greater, 40 wt% or greater, 45 wt% or greater, 50 wt% or greater, 52 wt% or greater, or even 52.4 wt% or greater, and at the same time is generally 65 wt% or less, and can be 60 wt% or less, 58 wt% or less, 54 wt% or less, 53.5 wt% or less, 53 wt% or less, even 52.5 wt% or less. Ideally, based on the weight of the curable composition, the first thermal conductive filler is 40 wt% to 60 wt% of alumina particles with a D50 of 20 μm to 50 μm.

[0074] The second thermal conductive filler (c2) has a D50 particle size of 1 μm to less than 10 μm, and can have a D50 of 1 μm or greater, 1.5 μm or greater, even 2 μm or greater, and at the same time has a D50 particle size of less than 10 μm, and can have a D50 of 9 μm or less, 8 μm or less, 6 μm or less, 5 μm or less, 3 μm or less, even less than 3 μm. Based on the weight of the curable composition, the concentration of (c2) is 20 wt% to 40 wt%, and can be 20 wt% or greater, 22 wt% or greater, 25 wt% or greater, 26 wt% or greater, even 27 wt% or greater, and at the same time is 40 wt% or less, and can be 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, even 27 wt% or less. The second thermal conductive filler can be selected from alumina, aluminum nitride, or a mixture thereof, and ideally is crushed or irregular alumina. More ideally, the second thermal conductive filler is 20 wt% to 30 wt% of irregular alumina particles with a D50 of 1 μm to 5 μm.

[0075] The third thermal 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 greater, 0.2 μm or greater, 0.3 μm or greater, 0.5 μm or greater, 0.7 μm or greater, 0.8 μm or greater, or even 0.9 μm or greater, and at the same time has 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 less, or even 0.2 μm or less. Based on the weight of the curable composition, the concentration of the third thermal conductive filler (c3) is 8 wt% or greater, and may be 10 wt% or greater, 12 wt% or greater, or even 12.6 wt% or greater, and at the same time is 20 wt% or less, and may be 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 thermal conductive filler may be selected from zinc oxide, alumina, or a mixture thereof, and preferably, the third thermal conductive filler is irregular zinc oxide. More preferably, the third thermal conductive filler is selected from irregular zinc oxide particles having a D50 of 0.1 μm to 0.5 μm and a content of 10 wt% to 15 wt%.

[0076] The thermal conductive filler (C) may contain fillers other than the above three thermal conductive fillers or may not contain fillers other than these three (i.e., the thermal conductive filler consists of (c1), (c2), and (c3)). Each of the above particles may independently have any shape, such as spherical, irregular, crushed, or flaky.

[0077] Preferably, the thermal conductive filler (C) comprises or consists of the following:

[0078] (c1) 40 wt% to 60 wt% of alumina particles, preferably spherical alumina particles having a D50 of 20 μm to 50 μm;

[0079] (c2) 25 wt% to 40 wt% of alumina particles, preferably crushed alumina particles having a D50 of 1 μm to 5 μm; and

[0080] (c3) 10 wt% to 20 wt% of zinc oxide particles, preferably crushed zinc oxide having a D50 of 0.1 μm to 0.5 μm.

[0081] Component (D) is a filler treatment agent or a combination of more than one filler treatment agent. The filler treatment agent (D) may comprise or consist of any combination of one trialkoxysilyl diorganopolysiloxane or more than one trialkoxysilyl diorganopolysiloxane, which is a diorganopolysiloxane containing a -Si(OR e )3 group, where R eindependently at each occurrence as described hereinafter for (IV) R e as described. Desirably, the trialkoxysilyl diorganopolysiloxane is a mono-trialkoxysilyloxy-terminated diorganopolysiloxane. Suitable mono-trialkoxysilyl-terminated diorganopolysiloxanes include those having the average chemical structure (IV):

[0082] R c 3SiO[R d 2SiO] g Si(OR e )3 (IV)

[0083] wherein R c , R d and R e are each independently selected, at each occurrence, from hydrocarbyl groups having from 1 to 10 carbon atoms, such as alkyl and aryl groups, for example having 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, even 8 or more carbon atoms, and typically having 10 or less, 8 or less, 6 or less, 4 or less, even 2 or less carbon atoms at the same time; and the subscript g has a value of 20 or greater, 25 or greater, 30 or greater, 40 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, 90 or greater, 100 or greater or even 110 or greater, and 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. Each R c , R d and R e can be the same or different. Examples of suitable alkyl groups for R c , R d and R e are methyl, ethyl, propyl (e.g., isopropyl 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-chain saturated hydrocarbon groups having 6 carbon atoms. R c , R d and R e can each independently be an alkyl group, such as methyl, ethyl and propyl. Desirably, each R c , R d and R e is methyl. R c , R d and R eSuitable aryl groups may include phenyl and dimethylphenyl. Particularly desirable monotrialkoxysiloxy-terminated diorganopolysiloxanes are monotrimethoxysiloxy- and trimethylsiloxy-terminated polydimethylsiloxanes, such as those having an average chemical formula of (CH3)3SiO[(CH3)2SiO] 30 Suitable monotrialkoxysilyloxy-terminated dimethylpolysiloxanes can be synthesized according to the teachings in US 2006 / 0100336.

[0084] The filler treating agent (D) may or may not contain one or a combination of more than one alkyltrialkoxysilane. Suitable alkyltrialkoxysilanes include those of formula (V):

[0085] R f Si(OR g )3(V)

[0086] Where 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 is typically at each occurrence an alkyl group having 20 or fewer, 18 or fewer, 16 or fewer, 14 or fewer, 12 or fewer, or even 10 or fewer carbon atoms; and R g is independently at each occurrence an alkyl group having 1 or more, 2 or more, 3 or more, 4 or more, or even 5 or more carbon atoms, and typically at the same time having 6 or less, 5 or less, 4 or less, 3 or less, or even 2 or less carbon atoms. Ideally, R f is independently at each occurrence an alkyl group having 6 to 20 carbon atoms. g Ideally, it is a methyl group so as to form a methoxy group attached to the silicon atom. Particularly desirable alkyltrialkoxysilanes are n-decyltrimethoxysilane, n-octyltrimethoxysilane, or mixtures thereof. Suitable alkyltrialkoxysilanes include n-decyltrimethoxysilane, which can be DOWSIL TM Z-6210 silane is available from The Dow Chemical Company or from Gelest under the designation SID2670.0.

[0087] Based on the weight of the curable thermally conductive composition, the filler treatment agent (D) useful in the present invention may be present in a total concentration of 0.1 wt% to 2.0 wt%, and may be 0.1 wt% or greater, 0.2 wt% or greater, 0.3 wt% or greater, 0.4 wt% or greater, 0.5 wt% or greater, 0.6 wt% or greater, 0.7 wt% or greater, 0.8 wt% or greater, 0.9 wt% or greater, 1.0 wt% or greater, 1.2 wt% or greater, 1.3 wt% or greater, or even 1.4 wt% or greater, and while typically being 2.0 wt% or less, and may be 1.8 wt% or less, 1.6 wt% or less, 1.5 wt% or less, or less, 1.4 wt% or less, 1.3 wt% or less or even 1.2 wt% or less. Desirably, based on the weight of the curable thermally conductive composition, the trialkoxysilyl diorganopolysiloxane is present in a concentration of zero to 2.0 wt%, and may be 0.3 wt% or greater, 0.4 wt% or greater, 0.5 wt% or greater, 0.6 wt% or greater, 0.7 wt% or greater, 0.8 wt% or greater, 0.9 wt% or greater, 1.0 wt% or greater, 1.1 wt% or greater, 1.2 wt% or greater, 1.3 wt% or greater, or even 1.4 wt% or greater, and while typically being present in a concentration of 2.0 wt% or less, and may 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. Simultaneously or alternatively, based on the weight of the curable thermally conductive composition, the alkyltrialkoxysilane may be present in a concentration of zero or greater, and may be 0.01 wt% or greater, 0.05 wt% or greater, 0.1 wt% or greater, 0.2 wt% or greater, 0.3 wt% or greater or even 0.4 wt% or greater, and while typically being present in a concentration of 0.5 wt% or less, and may be 0.4 wt% or less, 0.3 wt% or less or even 0.2 wt% or less. The filler treatment agent (D) may be a mixture of a trialkoxysilyl diorganopolysiloxane (such as a polydimethylsiloxane capped with monotrimethoxysilyloxy and trimethylsilyloxy) and an alkyltrialkoxysilane. For example, the curable thermally conductive composition may comprise a polydimethylsiloxane capped with monotrimethoxysilyloxy and trimethylsilyloxy, such as (CH3)3SiO[(CH3)2SiO] 30 Si(OCH3)3 or a combination thereof with n-decyltrimethoxysilane. Desirably, based on the weight of the curable thermally conductive composition, the curable thermally conductive composition comprises 0.1 wt% to 0.3 wt% of n-decyltrimethoxysilane and 0.5 wt% to 1.5 wt% of a polydimethylsiloxane capped with monotrimethoxysilyloxy and trimethylsilyloxy.

[0088] Component (E) is one or more platinum-based hydrosilylation catalysts. Such hydrosilylation catalysts can include compounds and complexes such as platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt's catalyst), H2PtCl6, di-μ-carbonyl-di-π-cyclopentadienyldinickel, platinum-carbonyl complexes, platinum-divinyltetramethyldisiloxane complexes, platinum cyclohexenylmethylsiloxane complexes, platinum acetylacetonate (acac), platinum black, platinum compounds (such as chloroplatinic acid, chloroplatinic acid hexahydrate, reaction products of chloroplatinic acid with monohydric alcohols, bis(ethyl acetoacetato)platinum, bis(acetylacetonato)platinum, platinum dichloride), and 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 comprising complexes of platinum with low molecular weight organopolysiloxanes, which complexes include complexes of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with platinum. These complexes can be microencapsulated or non-encapsulated in a resin matrix (usually, in a phenyl resin). The resin matrix for microencapsulating the complexes can be a phenyl resin, an acrylate polymer, a polycarbonate, or other 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 WO2014017671A1. The catalyst can be a complex of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with platinum. Platinum-based hydrosilylation catalysts are commercially available, for example, SYL-OFF TM 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 are activated at different temperatures can be added. The two different catalysts can be (E1) a complex of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with platinum, and (E2) an encapsulated platinum catalyst such as a complex of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with platinum encapsulated in dimethylsiloxane containing phenylsilsesquioxane.

[0089] Based on the weight of the curable heat-conductive composition, the amount of the platinum-based hydrosilylation catalyst (E) is sufficient to provide from 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, and at the same time is usually 300 ppm or less, and can be 200 ppm or less, 130 ppm or less, 100 ppm or less, or even 50 ppm or less of platinum. Alternatively, based on the weight of the curable heat-conductive composition, the amount of the platinum-based hydrosilylation catalyst can be from 0.01 wt% to 0.6 wt%. The platinum-based hydrosilylation catalyst (E) can be added in step (I) or can optionally be added after step (I).

[0090] In step (II) of the method of the present invention, the additive obtained in step (I) can be subjected to a crosslinking reaction ("curing") under heating to form a pre-cured composite material. The crosslinking reaction includes a hydrosilylation reaction between the Q-branched vinyl-functional polyorganosiloxane and the SiH crosslinking agent (B1). Step (II) of the method (i.e., the pre-curing 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, and at the same time is usually 150°C or lower, and can be 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 time of the pre-curing step can vary depending on the temperature, for example, from 30 minutes to 120 minutes. Alternatively, the pre-curing step can be carried out at 90°C to 120°C for 30 minutes to 60 minutes, or at 60°C to 90°C for 60 minutes to 120 minutes.

[0091] Step (III) of the method for preparing the curable heat-conductive composition includes mixing the obtained pre-cured composite material with the component (B2) silyl-hydride-functional polyorganosiloxane crosslinking agent, which contains at least two silyl-hydride groups per molecule (hereinafter referred to as "SiH crosslinking agent (B2)"). Mixing the pre-cured composite material with the SiH crosslinking agent (B2) in step (III) can be carried out at a temperature below 30°C, and ideally at room temperature (25°C). The SiH crosslinking agent (B2) is as described above for the SiH crosslinking agent (B1) of component (B1). The SiH crosslinking agent (B2) and the SiH crosslinking agent (B1) can be the same or different independently of each other. The amount of the SiH crosslinking agent (B2) should provide a molar ratio of the total silicon-bonded hydrogen atoms from the SiH crosslinking agents (B1) and (B2) to the vinyl groups (ideally, vinyl groups) in the Q-branched vinyl-functional polyorganosiloxane (A) greater than 0.45 (also referred to as "(SiHB1 +SiH B2 ) / Vi ratio”), and can be 0.46 or higher, 0.47 or higher, 0.48 or higher, 0.5 or higher, 0.6 or higher, 0.7 or higher, 0.8 or higher, or even 0.9 or higher. (SiH B1 +SiH B2 ) / Vi ratio can 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 desirably 0.5 to 0.6.

[0092] The method for preparing the curable thermally conductive composition of the present invention may include adding optional components, which optional components include component (F) inhibitor, component (E') additional platinum-based hydrosilylation catalyst, other optional components described below, or mixtures thereof. One or more than one of these optional components may be added after obtaining the pre-cured composite material in step (II), and before, during, and / or after adding the SiH crosslinking agent (B2). The method may include adding an additional platinum-based hydrosilylation catalyst (E') to catalyze the hydrosilylation reaction of the SiH crosslinking agent (B2). The additional platinum-based hydrosilylation catalyst (E') includes those described above for component (E), and may be the same as or different from the platinum-based hydrosilylation catalyst (E) added in step (I) above. Desirably, the method of the present application includes adding component (F). Component F and component (B2) (i.e., the SiH crosslinking agent (B2)) may be added together, or component (F) may be added before or after adding component (B2). Component (F) comprises a hydrosilylation inhibitor (also referred to as an "inhibitor") or a combination of more than one hydrosilylation inhibitor. The inhibitor can be used to stabilize the curable thermally conductive composition against premature curing and provide storage stability to the composition. Examples of suitable inhibitors include any combination of any one or more than one of the following: acetylene 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-(propargyloxy)trimethylsilane; and methyl(tris(1,1-dimethyl-2-propargyloxy))silane; ene-yne compounds, such as 3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne; triazoles, such as benzotriazole; hydrazine-based compounds; phosphine-based compounds; thiol-based compounds; cycloalkenyl siloxanes, including methyl vinyl cyclosiloxanes, such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane.

[0093] Based on the weight of the curable thermally conductive composition, the concentration of the inhibitor (F) is zero or greater, and may be 0.001 wt% or greater, 0.002 wt% or greater, even 0.003 wt% or greater, and at the same time is generally 0.5 wt% or less, and may be 0.3 wt% or less, 0.1 wt% or less, 0.05 wt% or less, 0.01 wt% or less, 0.005 wt% or less, 0.004 wt% or less, even 0.003 wt% or less.

[0094] Other optional components may include any one or any combination of more than one of the following components: heat stabilizers and / or pigments (such as copper phthalocyanine powder), thixotropic agents, pyrogenic silica (desirably, surface-treated), and parting additives (such as glass beads). Based on the weight of the curable thermally conductive composition, the total concentration of these additional components may range from zero to 1 wt%, and may be 0 or greater, 0.1 wt% or greater, 0.2 wt% or greater, 0.3 wt% or greater, 0.4 wt% or greater, or even 0.5 wt% or greater, and at the same time is typically 1 wt% or less, and may be 0.9 wt% or less, 0.8 wt% or less, or even 0.6 wt% or less.

[0095] When used, the above-mentioned optional components may be added independently in step (I) and / or step (III), desirably in step (III), and these optional components are included in the composition together with the SiH crosslinking agent (B2), before or after its addition.

[0096] The method for preparing the curable thermally conductive composition may or may not include the step of adding a solvent. Based on the weight of the curable thermally conductive composition, the solvent (if present) may be less than 0.01 wt%, less than 0.005 wt% or even zero. Desirably, the curable thermally conductive composition is substantially free of solvent, that is, it contains no solvent or may contain trace amounts of residual solvent delivered from the starting materials in the composition. The concentration of the solvent can be measured by gas chromatography (GC). If the amount of the solvent is too high, voids tend to be generated during the curing of the curable thermally conductive composition, which results in a poor surface appearance or even leads to a reduced TC. The solvent may be an organic solvent, such as a saturated or unsaturated aliphatic or aromatic hydrocarbon, such as benzene, toluene, xylene, hexane, heptane, octane, isoparaffin, a hydrocarbon compound having 8 to 18 carbon atoms per molecule and at least one aliphatic unsaturated group, such as tetradecene; a ketone, such as acetone, methyl ethyl ketone or methyl isobutyl ketone; an acetate, such as ethyl acetate or isobutyl acetate; an ether, such as a glycol ether, such as propylene glycol methyl ether, dipropylene glycol methyl ether and propylene glycol n-butyl ether, diisopropyl ether or 1,4-dioxane; a cyclic or linear siloxane having an average degree of polymerization of 3 to 10, such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and / or decamethylcyclopentasiloxane; or a mixture thereof. The curable thermally conductive composition does not require the use of any solvent (such as those mentioned above) to achieve the above-mentioned desirable ER (i.e., good processability) and TC characteristics.

[0097] The present invention also relates to a curable thermally conductive composition prepared by the above method, or a curable thermally conductive composition comprising an admixture of a pre-cured composite material and a SiH crosslinking agent (B2). The pre-cured composite material 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., the SiH B1 / Vi ratio and the (SiH B1 +SiH B2 ) / Vi ratio) are as described in the above method. The curable thermally conductive composition can achieve all of the following properties: (i) the oil bleeding degree after 5 days of application at 25 °C does not exceed 10% (≤10%); (ii) the oil bleeding degree after 2 days of aging at 125 °C does not exceed 10% (≤10%); (iii) an ER of 15 g / min or greater; (iv) a TC greater than 3.0 W / m*K. The oil bleeding property is determined according to the test method described in the oil bleeding test. The ER herein is determined using a standard 30 cubic centimeter EFD syringe at a pressure of 0.62 megapascals (MPa) and 25 °C (further details are provided below under the extrusion rate test). The thermally conductive composition can have an ER of 15 g / min or greater, and can be 18 g / min or greater, or even 20 g / min or greater. The ER is a useful characteristic as a measure of extrudability, viscosity, and dispensability, which, for example, enables the curable thermally conductive composition to be easily dispensed for application to another material (such as an electronic component or a heat sink). The TC is measured using a hot disk with a cured sample according to ISO 22007-2 (further details are provided below under the thermal conductivity test), which can be greater than 3.0 W / m*K (>3.0 W / m*K), and can be 3.5 W / m*K or greater, or even 4.5 W / m*K or greater. Having such a high TC (providing effective heat dissipation), low oil bleeding, and being easily dispensable makes the curable thermally conductive composition particularly useful as a thermally conductive interface material for effectively transferring heat between two components. Thermally conductive interface materials are typically used to thermally couple heat-generating components and heat-dissipating components, especially in electronic devices. The thermally conductive composition can be provided in a single-part form.

[0098] The present invention also includes a method for forming a thermally conductive silicone material on an electronic component, the method comprising:

[0099] Step (i) providing a curable thermally conductive composition prepared by the above method;

[0100] Step (ii) applying the curable thermally conductive composition to the electronic component of the electronic device; and

[0101] Step (iii) curing the curable composition by heat; thereby forming a thermally conductive silicone material (i.e., a cured material).

[0102] Ideally, the application of the curable thermally conductive composition involves dispensing or extruding the curable thermally conductive composition. Due to the above properties of the curable thermally conductive composition, such as excellent dispensability and conformability, this method allows for automated dispensing and assembly (i.e., increased productivity) with minimal stress applied to fill complex geometries and different gaps, thus avoiding potential damage to electronic components.

[0103] In step (iii) of the method, the thermally conductive composition can be cured by heat, for example, at a temperature greater than 25 °C, and can be higher than 40 °C, such as 60 °C to 150 °C or 80 °C to 120 °C. The duration of curing can vary depending on the temperature and is typically from 0.5 hours to 24 hours. The curable thermally conductive composition can be cured by heating in an oven or by the heat generated by the electronic components. Ideally, when the electronic device is in operation, the heat generated by the electronic components typically cures the curable thermally conductive composition within a few hours, thus forming a cured material. The curing in step (iii) of the method is not carried out under humidity conditions, whereas conventional curing methods require these humidity conditions. Conventional curing methods use the moisture in the air to cure the composition and take a longer time (e.g., 7 days) to fully cure the composition, and thus are not suitable for electronic applications.

[0104] Due to the low concentration or absence of solvent in the curable thermally conductive composition, the method does not include (i.e., is free of) an additional procedure for removing the solvent, such as stripping or evaporating the solvent. Although still conferring the desirable ER and TC properties to the resulting composition as described above, the curable thermally conductive composition enables the method to use the composition without the aid of a solvent and also makes it suitable for directly dispensing (e.g., by extrusion) the composition onto the components of an article without the need to add a solvent to the composition prior to use.

[0105] Examples of electronic components that generate heat during the 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 located between and in contact with an electronic component and a heat sink component (such as a heat sink), or between and in contact with two electronic components of an electronic device, where at least one electronic component generates heat when the electronic device is in operation. Examples of heat sink components include heat sinks, cooling plates / pads, cooling tubes, and metal covers. The present invention also includes an electronic article that includes a thermally conductive composition and an electronic component on which the thermally conductive composition is applied. Examples of electronic devices include optical modules for communication, smart phones, digital cameras, computers, tablet devices, servers, and base stations.

[0106] Example

[0107] Some embodiments of the present invention will now be described in the following examples, where all percentages (%) are weight percentages relative to the weight of the composition unless otherwise specified, and all particle sizes of the filler are D50 particle sizes. Table 1 lists the materials of the thermally conductive composition for the samples described below. Note: "Vi" represents vinyl, and "Me" represents methyl. SYL-OFF is a trademark of Dow Corning Corporation.

[0108] Table 1

[0109]

[0110]

[0111] The "viscosity" of the vinyl polymer is measured at 25 °C by ASTM D445-21.

[0112] The "vinyl content" of the vinyl polymer refers to the wt% of vinyl groups relative to the molecular weight of the vinyl polymer. The "SiH content" refers to the wt% of H from SiH relative to the molecular weight of the SiH crosslinker.

[0113] The "Pt content" refers to the wt% of Pt relative to the molecular weight of the catalyst.

[0114] "TC filler" refers to a thermally conductive filler.

[0115] IE 1-5 samples

[0116] The formulation of the IE sample is given in Table 2, where the amount of each component is reported in grams (g). Unless otherwise specified, by using a SpeedMixer from Flack Tek Inc. TMThe DAC 400FVZ prepares samples by mixing components at room temperature (RT). The silicone matrix components including vinyl polymer (A), SiH crosslinking agent (B1), and treatment agent (D) are weighed into the cup of a SpeedMixer. Then the TC filler (C3) is weighed and added to the cup. The mixture is mixed by the SpeedMixer at 1000 revolutions per minute (RPM) for 20 seconds, followed by mixing at 1500 RPM for 20 seconds. Then the TC filler (C2) is added and mixed in the same manner. The TC filler (C1) is further added under the same mixing conditions. The resulting composition in the cup is scraped and mixed again. The Pt catalyst (E) containing catalyst E-1 and optionally catalyst E-2 is added and then mixed. Then the material is placed in an oven and held at 70 °C for 60 min (“heating step”). This temperature is lower than the activation temperature of catalyst E-2. After that, the content in the cup is cooled to RT. Then the SiH crosslinking agent (B2), inhibitor (F), and pigment (G) are added to the cup and mixed at 1000 RPM for 30 seconds to obtain a sample of curable thermally conductive silicone composition.

[0117] CE 1-5 samples

[0118] The formulations of the CE samples are given in Table 3, where the amount of each component is reported in grams (g). The CE 1 sample is prepared according to the same procedure as for preparing the above IE sample, except that the SiH crosslinking agent (B2) is not used. The CE 2, CE 3, and CE 5 samples are prepared according to the same procedure as for preparing the IE sample.

[0119] The CE 4 sample is prepared according to the same procedure as the above IE, except that the heating step is omitted.

[0120] The following test methods are used to evaluate the ER, TC, oil bleeding, and hardness of the above-obtained thermally conductive composition samples:

[0121] Extrusion rate test

[0122] The extrusion rate (“ER”) of the sample is determined using a Nordson EFD dispensing device. The sample material is loaded into 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 extruded after one minute in grams (g) corresponds to the extrusion rate in g / min. The object of the present invention is to achieve an extrusion rate of at least 15 g / min.

[0123] It should be noted that some samples are highly viscous pastes that cannot be extruded, so they are reported to have an ER of 0 (and the thermal conductivity was not measured, so it is reported as "NA").

[0124] Thermal conductivity test

[0125] The thermal conductivity (TC) was determined using a Hot Disk according to ISO 22007-2. The TC of the cured samples was measured using a Hot Disk TPS2500S instrument with a 3.189 mm Kapton sensor (model 5465). The cured samples were prepared by curing the curable thermally conductive composition samples at 120 °C for 60 min to a size of 25 mm * 25 mm * 8 mm. The objective of the present invention is to achieve a TC greater than 3.0 W / m*K.

[0126] Oil leakage test

[0127] A sample (0.6 mL) of the curable thermally conductive composition was applied on A4 paper and sandwiched between two glass panels with dimensions of 5 cm * 5 cm, and the thickness of the sample was adjusted to 1.5 mm using spacers. Then the initial diameter of the sample (denoted as "D0") was measured. The obtained test specimens were placed horizontally at 25 °C ("RT") for 5 days and at 125 °C for 2 days, respectively. The oil bleeding degree on the paper was evaluated as the incremental percentage between the diameter of the oil exuded 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):

[0128] Oil bleeding degree = [(D1 - D0) / D0] × 100%

[0129] The objective of the present invention is to achieve an oil bleeding requirement of no more than 10% (≤10%) after aging at RT for 5 days and at 125 °C for 2 days, respectively.

[0130] Hardness test

[0131] The hardness of the cured samples was determined using a Shore A durometer. 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 the present invention is to achieve a Shore A hardness > 5.

[0132] The ER of each sample was characterized using an extrusion rate test, the TC of each sample was characterized using a thermal conductivity test, the oil bleeding degree of each sample was characterized using an oil bleeding test, and the hardness of each sample was characterized using the hardness test described above.

[0133] Table 2 contains the characterization results of IE 1 to IE 5 samples. As shown in Table 2, all IE 1-5 samples achieved an ER ≥ 15 g / min, an oil leakage rate of ≤ 10% at 25°C for 5 days (hereinafter referred to as "RT*5D") and at 125°C for 2 days (hereinafter referred to as "125°C*2D"), and a TC greater than 3.0 W / m*K.

[0134] Table 3 contains the characterization results of CE 1 to CE 5 samples. As shown in Table 3, the CE 1 sample was prepared by mixing (A-1) Q-branched vinyl-terminated polymer, (B1-1) SiH crosslinker, and (E-1) Pt catalyst under heating pre-curing conditions, but during application, no (B2) SiH crosslinker was used for post-curing, which did not meet the requirements of ER and the oil leakage rates at RT and 125°C.

[0135] The CE 2 sample contained (A-2) linear vinyl-terminated polymer instead of (A-1) Q-branched vinyl-terminated polymer in the pre-curing step, providing a much higher oil leakage rate at RT (e.g., 38%).

[0136] The CE 3 sample contained (A-1) Q-branched vinyl-terminated polymer, (B1-3) SiH crosslinker, (E-1) Pt catalyst, which required heating pre-curing but had a high SiH B1 / Vi ratio (>0.35), and also contained (B2-4) SiH crosslinker for post-curing during application. The CE 3 sample showed an ER of 0 g / min (the material was too viscous), so other properties could not be measured.

[0137] The CE 4 sample did not include the heating process for pre-curing, but used (A-2)+(A-3) linear vinyl-terminated polymer instead of (A-1) Q-branched vinyl-terminated polymer, and added (B2-3) SiH crosslinker and (E-2) Pt catalyst for post-curing after the filler loading during application. The CE 4 sample showed a high oil leakage rate at RT (>10%).

[0138] The CE 5 sample contained (A-1) Q-branched vinyl-terminated polymer with a low SiH B1 / Vi ratio (<0.2), (B1-3) SiH crosslinker, (C), (D), and (E-1) Pt catalyst during the pre-curing heating process, and also contained (B2-2) SiH crosslinker for post-curing during application, providing a much higher oil leakage rate at RT (>10%).

[0139] Table 2

[0140]

[0141] In Tables 2 and 3 below:

[0142] "TC filler Wt%" refers to the wt% of the total thermal conductive filler relative to the total weight of the curable thermal conductive composition.

[0143] "SiH B1 / Vi ratio" refers to the molar ratio of the SiH functional groups from the SiH crosslinking agent (B1) to the vinyl functional groups from the vinyl polymer (A).

[0144] "(SiH B1 +SiH B2 ) / Vi ratio" refers to the molar ratio of the total SiH functional groups from the SiH crosslinking agent (B1) and the SiH crosslinking agent (B2) to the vinyl functional groups from the vinyl polymer (A).

[0145] "ER", "TC", "oil bleeding degree" (respectively for 5 days at RT and for 2 days at 120 °C), and "hardness" are evaluated according to the above test methods.

[0146] Table 3

[0147]

Claims

1. A method for preparing a curable thermally conductive composition, the method comprising the following steps: (I) Preparing an additive comprising the following components (A), (B1), (C), (D) and (E): (A) 3 wt% to 10 wt% of a Q-branched alkenyl-functional polyorganosiloxane having at least three terminal alkenyl groups per molecule and having a viscosity of 25 millipascal seconds to 2000 millipascal seconds as measured at 25 °C using a glass capillary Cannon-Fenske type viscometer in accordance with ASTM D445-21; (B1) A silyl-hydride-functional polyorganosiloxane crosslinker 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 polyorganosiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) in the range of 0.2 to 0.35; (C) 90 wt% or more of a thermally conductive filler; (D) A filler treatment agent; and (E) A platinum-based hydrosilylation reaction catalyst; (II) Thermally curing the additive obtained in step (I) to form a pre-cured composite material; and (III) Mixing the pre-cured composite material obtained in step (II) with a silyl-hydride-functional polyorganosiloxane crosslinker (B2) containing at least two silyl-hydride groups per molecule; thereby obtaining the curable thermally conductive composition; wherein the total molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride-functional polyorganosiloxane crosslinkers (B1) and (B2) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; wherein the weight percentages are relative to the weight of the curable thermally conductive composition.

2. The method according to claim 1, the method further comprising adding (F) an inhibitor, (E') an additional platinum-based hydrosilylation reaction catalyst or a mixture thereof in step (III) or after step (III).

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

4. The method according to any one of claims 1 to 3, wherein the molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride-functional polyorganosiloxane crosslinker (B1) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is in the range of 0.22 to 0.

28.

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

6. The method according to any one of claims 1 to 5, wherein the crosslinkers (B1) and (B2) each independently have an average chemical structure (IV): R bb (3-h) H h SiO-(HR bb SiO) e -(R bb 2SiO) f -SiH h' R bb (3-h') (IV) wherein R bb is independently selected, at each occurrence, from alkyl groups having 1 to 6 carbon atoms and phenyl; the subscripts h and h' are each independently selected, at each occurrence, from values in the range of zero to 3, provided that the combination of e, h and h' is at least 2; the subscript e is from zero to 30; and the subscript f is from 5 to 200.

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

8. A curable thermally conductive composition, the curable thermally conductive composition comprising an admixture of a pre-cured composite material and a (B2) silyl-hydride functional polysiloxane crosslinker, the crosslinker containing at least two silyl-hydride groups per molecule; wherein the pre-cured composite material comprises component (C); component (D); and a hydrosilylation reaction product of components (A), (B1), and (E): (A) 3% to 10% by weight of a Q-branched alkenyl-functional polyorganosiloxane having at least three terminal alkenyl groups per molecule and having a viscosity of 25 millipascal seconds to 2000 millipascal seconds as measured at 25 °C using a glass capillary Cannon-Fenske type viscometer in accordance with ASTM D445-21; (B1) A silyl-hydride functional polysiloxane crosslinker containing at least two silyl-hydride groups per molecule and present in a concentration to provide 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 0.2 to 0.35; (C) 90% by weight or more of a thermally conductive filler; (D) A filler treatment agent; and (E) A platinum-based hydrosilylation catalyst; wherein the total molar ratio of silicon-bonded hydrogen atoms in the silyl-hydride functional polysiloxanes crosslinkers (B1) and (B2) to alkenyl groups in the Q-branched alkenyl-functional polyorganosiloxane (A) is greater than 0.45; wherein the weight percentages are relative to the weight of the curable thermally conductive composition; wherein the curable thermally conductive composition has an extrusion rate of 15 g / min or greater and an oil bleeding degree of no more than 10% after aging for 5 days at 25 °C and 2 days at 125 °C, and cures into a material having a thermal conductivity of greater than 3.0 W / (m·K) according to ISO 22007-2 using a hot disk.

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

10. The method according to claim 9, wherein the application of the curable thermally conductive composition comprises dispensing the curable thermally conductive composition.

Images