Silicone composition

Abstract

To provide a silicone composition that retains fluidity, is excellent in treatment, is excellent in heat dissipation, further excellent in durability / reliability under high temperature or high temperature and high humidity condition even when a thermally conductive filler is highly filled in order to impart excellent insulation and thermal conductivity.SOLUTION: A silicone composition comprises (A) Organopolysiloxane represented by the following general formula (1): 50-100 pts.mass, (B) Organopolysiloxane represented by the following average composition formula (2) R3cSiO(4-c) / 2 (2): 0-50 pts.mass, (C) α-aluminum oxide powder having a hexagonal close-packed lattice crystal structure composed of polyhedra having 8 or more faces, and (D) a silicone composition containing zinc oxide powder having an average particle diameter of 0.01 μm or more and less than 3 μm, where the thermal conductivity is 4.0 W / m K or more and less than 7.0 W / m K in the hot disk method according to ISO 22007-2, and the viscosity is 5-800 Pa s when the rotation speed is measured at 10 rpm by a spiral viscometer at 25°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a silicone composition.

Background Art

[0002] Many electronic components generate heat during use. Therefore, in order to make these electronic components function properly, it is necessary to remove heat from these electronic components. In particular, integrated circuit elements such as CPUs used in personal computers have an increasing amount of heat generation due to the increase in the operating frequency, and heat countermeasures have become an important issue.

[0003] Many methods have been proposed as means for removing this heat. In particular, for electronic components with a large amount of heat generation, a method has been proposed in which a heat conductive material such as a heat conductive grease composition or a heat conductive sheet is interposed between the electronic component and a member such as a heat sink to release heat. However, it has not been satisfactory for heat dissipation in locations where the specification thicknesses are significantly different (see Patent Document 1).

[0004] In addition, as such a heat conductive material, a heat dissipation grease composition based on silicone oil and blended with zinc oxide or alumina powder has been proposed, but the heat resistance at 200°C has been unsatisfactory (see Patent Documents 2 and 3).

[0005] To improve thermal conductivity, Patent Document 1 proposes a thixotropic thermal conductive material using aluminum nitride powder, comprising at least one selected from a liquid organosilicon carrier, silica fiber, dendritic zinc oxide, flaky aluminum nitride, and flaky boron nitride. Patent Document 4 proposes a silicone grease composition obtained by blending spherical hexagonal aluminum nitride powder of a certain particle size range with a specific organopolysiloxane. Patent Document 5 proposes a thermal conductive silicone grease composition combining fine-grained aluminum nitride powder and coarse-grained aluminum nitride powder. Patent Document 6 proposes a thermal conductive silicone grease composition combining aluminum nitride powder and zinc oxide powder. Patent Document 7 proposes a thermal conductive grease composition using aluminum nitride powder surface-treated with organosilane, but all were unsatisfactory in terms of durability and reliability. Patent Document 8 proposes a thermal conductive silicone composition containing silicone resin, diamond, zinc oxide, and a dispersant, but its post-heat resistance properties were particularly unsatisfactory.

[0006] Furthermore, metals are materials with high thermal conductivity and can be used in areas of electronic components where insulation is not required. Patent document 9 proposes a thermally conductive grease composition obtained by mixing metallic aluminum powder with a base oil such as silicone oil, but it was unsatisfactory because it lacked insulating properties. Recently, all thermally conductive materials and thermally conductive grease compositions have become insufficient for the heat generated by integrated circuit elements such as CPUs.

[0007] As can be seen from Maxwell and Blagemann's theoretical formulas, the thermal conductivity of a material obtained by compounding a thermally conductive filler with silicone oil is almost independent of the thermal conductivity of the thermally conductive filler when the volume fraction of the thermally conductive filler is 0.6 or less. Only when the volume fraction exceeds 0.6 does the thermal conductivity of the thermally conductive filler begin to be affected. In other words, to increase the thermal conductivity of a thermally conductive grease composition, it is important to first determine how high the amount of thermally conductive filler can be filled, and how high the thermal conductivity of the filler can be used. However, high filling reduces the fluidity of the thermally conductive grease composition, leading to problems such as poor workability (dispensability, screen printability), making it impractical for use. Furthermore, the reduced fluidity prevents it from following the fine irregularities on the surface of electronic components and heat sinks, resulting in increased contact thermal resistance.

[0008] To date, studies have been conducted to incorporate alkoxy-group-containing organopolysiloxanes into thermal conductive materials to significantly improve dispersibility by treating the surface of the thermal conductive filler, with the aim of achieving high filler capacity and obtaining thermally conductive materials with good fluidity (see Patent Documents 10 and 11). However, these treatment agents have the drawback of degrading under high temperature and high humidity conditions through hydrolysis, etc., which induces deterioration of the performance of the thermal conductive material.

[0009] Therefore, thermally conductive silicone grease compositions have been proposed that suppress the performance degradation of thermally conductive materials even under high temperature and high humidity conditions. However, although there are specifications for the average particle size of the thermally conductive filler, there are no specifications for the shape of the thermally conductive filler, the amount of hydroxyl groups, or the coarseness of the particles, and these have not been satisfactory, especially for applications where insulation is required (Patent Document 12).

[0010] Japanese Patent Publication No. 5755977 (Patent Document 13) proposes a high thermal conductivity resin composition that combines spherical aluminum oxide powder with a specific average sphericity, specific hydroxyl group content, and average particle diameter of 10 to 50 μm, and aluminum oxide powder with an average particle diameter of 0.3 to 1 μm, with specified blending ratios and volume ratios for each type of aluminum oxide. However, although it is stated that the average particle diameter of the spherical aluminum oxide powder is up to 50 μm, there are no specifications regarding the range of coarse particle size or content. Therefore, when attempting to apply the high thermal conductivity resin composition to a thin film of 50 μm or less, there was a problem of insufficient thermal resistance.

[0011] Furthermore, while the republished Patent Publication No. 2002-092693 (Patent Document 14) proposes a thermally conductive silicone composition using alumina powder with an average particle size of 0.1 to 100 μm, it does not specify the thermal conductivity or viscosity. Moreover, although a mixture of spherical alumina powder with an average particle size of 5 to 50 μm (excluding 5 μm) and spherical or irregularly shaped alumina powder with an average particle size of 0.1 to 5 μm is used, and a thermally conductive silicone composition is proposed with specified blending ratios and weight ratios of aluminum oxide, there are no specifications for the average sphericity or hydroxyl group content of the spherical alumina with a larger average particle size, nor are there any specifications regarding the range or content of coarse particle size, and this also has the same problem as Patent Document 14 in terms of thermal resistance being insufficient.

[0012] Therefore, although Japanese Patent Publication No. 6866877 (Patent Document 15) found that a silicone composition containing α-aluminum oxide powder having a hexagonal close-packed lattice crystal structure consisting of polyhedra with defined average particle diameter and coarse particle content could be improved in terms of thermal resistance by reducing contact thermal resistance, further improvement in thermal conductivity was desired. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 56-28264 [Patent Document 2] Special Publication No. 52-33272 [Patent Document 3] Special Publication No. 59-52195 [Patent Document 4] Japanese Patent Application Publication No. 2-153995 [Patent Document 5] Japanese Patent Application Publication No. 3-14873 [Patent Document 6] Japanese Patent Application Publication No. 10-110179 [Patent Document 7] Japanese Patent Publication No. 2000-63872 [Patent Document 8] Japanese Patent Publication No. 2002-30217 [Patent Document 9] Japanese Patent Publication No. 2000-63873 [Patent Document 10] Japanese Patent Publication No. 2004-262972 [Patent Document 11] Japanese Patent Publication No. 2005-162975 [Patent Document 12] Patent No. 4933094 [Patent Document 13] Patent No. 5755977 [Patent Document 14] Republished Gazette No. 2002-092693 [Patent Document 15] Patent No. 6866877 [Overview of the project] [Problems that the invention aims to solve]

[0014] The present invention has been made in view of the above circumstances, and aims to provide a silicone composition that maintains fluidity, is easy to handle, has excellent heat dissipation performance, and is also durable and reliable under high temperature or high temperature and high humidity conditions, even when a high concentration of thermal conductive filler is used to impart excellent insulating and thermal conductivity properties. [Means for solving the problem]

[0015] As a result of diligent research to achieve the above objectives, the inventors have found that a silicone composition containing α-aluminum oxide having a polyhedral shape with a defined average particle diameter and coarse particle content has excellent insulating properties and thermal conductivity, as well as good fluidity, making it easy to handle. Furthermore, it conforms to fine irregularities, reducing contact thermal resistance, resulting in a silicone composition with excellent heat dissipation performance and low thermal resistance. In addition, it exhibits excellent durability under high temperature or high temperature and high humidity conditions, thereby improving reliability during mounting. Based on these findings, the inventors have come to the present invention.

[0016] Accordingly, the present invention provides the following silicone compositions. 1. (A) General formula (1): [ka] (In the formula, R 1 R is an unsubstituted or substituted monovalent hydrocarbon group, 2 (where a is an integer between 5 and 100, and b is an integer between 1 and 3.) It is expressed as such, and the kinematic viscosity at 25°C is 10 to 10,000 mm². 2 / s organopolysiloxane: 50-100 parts by mass, (B) The following average composition formula (2): R 3 c SiO (4-c) / 2 (2) (In the formula, R 3 (Each is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, where c is a number between 1.8 and 2.2.) The kinematic viscosity at 25°C, as shown by [formula], is 10 to 100,000 mm². 2 Organopolysiloxane in / s: 0-50 parts by mass (However, the total amount of component (A) and component (B) must be 100 parts by mass.) (C) α-aluminum oxide powder having a hexagonal close-packed crystal structure composed of polyhedra with 8 or more faces, wherein when the maximum particle diameter parallel to the hexagonal lattice plane of the hexagonal close-packed lattice is D and the particle diameter perpendicular to the hexagonal lattice plane is H, the particle shape has a D / H ratio of 0.3 or more and 30 or less, the average particle diameter is 7 to 30 μm, and the proportion of coarse particles at 50 μm or more in the laser diffraction particle size distribution is 1 mass% or less of the whole, and the purity is 99% or more of α-aluminum oxide powder, (D) Zinc oxide powder having an average particle diameter of 0.01 μm or more and less than 3 μm, and the proportion of coarse particles at 10 μm or more in the laser diffraction particle size distribution is 1 mass% or less of the whole of component (D), (However, the blending ratio of component (C) and component (D) is 5:5 to 9.5:0.5 by mass ratio, and the total blending amount of (C) and (D) is 75 to 85% by volume.) A silicone composition containing the above, having a thermal conductivity of 4.0 W / m·K or more and less than 7.0 W / m·K in the hot disk method conforming to ISO 22007-2, and a viscosity at 25°C of 5 to 800 Pa·s when measured at a rotational speed of 10 rpm by a spiral viscometer. 2. The thermal resistance at 25°C measured by the laser flash method is 11 mm 2 ·K / W or less of the silicone composition according to 1. 3. After leaving in an atmosphere of 130°C / 85%RH for 96 hours, the thermal resistance at 25°C measured by the laser flash method is 11 mm 2 ·K / W or less of the silicone composition according to 1 or 2. 4. After thermal degradation at 200°C for 100 hours, the viscosity at 25°C when measured at a rotational speed of 10 rpm by a spiral viscometer is 1,000 Pa·s or less of the silicone composition according to any one of 1 to 3. 5. Further, (E) a volatile solvent capable of dispersing or dissolving the above components (A) and (B): the silicone composition according to any one of 1 to 4 containing 100 parts by mass or less with respect to 100 parts by mass of the total amount of components (A) and (B). 6. Further, (F) the following general formula (3): R 4 d R5 e Si(OR 6 ) 4-d-e (3) (In the formula, R 4 Each of these is an alkyl group having 9 to 15 carbon atoms, and R 5 Each of these is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and R 6 Each of the following is an alkyl group having 1 to 6 carbon atoms, d is an integer from 1 to 3, e is an integer from 0 to 2, provided that d+e is an integer from 1 to 3.) An alkoxysilane represented by 0.1 to 50 parts by mass per 100 parts by mass of the total amount of component (A) and component (B), wherein component (C) and component (D) are surface-treated with component (F), according to any one of 1 to 5. 7. Volume resistivity is 1 × 10⁻⁶ 9 A silicone composition according to any one of 1 to 6, wherein the value is Ω·cm or greater. [Effects of the Invention]

[0017] The silicone composition of the present invention possesses excellent insulating properties while maintaining good thermal conductivity, and its excellent fluidity ensures superior workability. Furthermore, it exhibits excellent adhesion to heat-generating electronic components and heat-dissipating components, thereby reducing contact thermal resistance and enabling low thermal resistance. In other words, by interposing the silicone composition of the present invention between heat-generating electronic components and heat-dissipating components, heat generated from the heat-generating electronic components can be efficiently dissipated to the heat-dissipating components. Moreover, the silicone composition of the present invention exhibits excellent durability under high temperatures or high temperature and high humidity conditions, providing extremely good reliability when used, for example, for heat dissipation in general power supplies and electronic devices, and for heat dissipation of integrated circuit elements such as LSIs and CPUs used in electronic devices such as personal computers and digital video disc drives. Therefore, the low thermal resistance silicone composition of the present invention can significantly improve the stability and lifespan of heat-generating electronic components and electronic devices using them. [Modes for carrying out the invention]

[0018] The present invention will be described in detail below. [(A) component] (A) Component is given by the following general formula (1): [ka] (In the formula, R 1 R is an unsubstituted or substituted monovalent hydrocarbon group, 2 (where a is an integer between 5 and 100, and b is an integer between 1 and 3.) It is expressed as such, and the kinematic viscosity at 25°C is 10 to 10,000 mm². 2 It is an organopolysiloxane of type / s, and can be used alone or in combination of two or more types.

[0019] Component (A) maintains the fluidity of the composition and provides good handling properties to the composition, even when the thermally conductive fillers of components (C) and (D) are densely packed into the composition to obtain a thermally conductive silicone composition.

[0020] The above R 1 The group is independently an unsubstituted or substituted monovalent hydrocarbon group, preferably having 1 to 18 carbon atoms, and more preferably 1 to 10 carbon atoms. Specifically, examples include linear alkyl groups, branched alkyl groups, cyclic alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups. Examples of linear alkyl groups include methyl, ethyl, propyl, hexyl, and octyl groups. Examples of branched alkyl groups include isopropyl, isobutyl, tert-butyl, and 2-ethylhexyl groups. Examples of cyclic alkyl groups include cyclopentyl and cyclohexyl groups. Examples of alkenyl groups include vinyl and allyl groups. Examples of aryl groups include phenyl and tolyl groups. Examples of aralkyl groups include 2-phenylethyl and 2-methyl-2-phenylethyl groups. Examples of alkyl halides include 3,3,3-trifluoropropyl group, 2-(nonafluorobutyl)ethyl group, and 2-(heptadecafluorooctyl)ethyl group.1 Preferably, it is a methyl group or a phenyl group.

[0021] The above, R 2 R is independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group. The number of carbon atoms is preferably 1 to 18, and more preferably 1 to 10. Examples of alkyl groups include R 1 Examples of linear alkyl groups, branched alkyl groups, cyclic alkyl groups, etc., similar to those exemplified above, are also included. Examples of alkenyl groups include R 1 Examples similar to those given for the above can be cited. Examples of alkoxyalkyl groups include methoxyethyl group and methoxypropyl group. Examples of acyl groups include acetyl group and octanoyl group. R 2 It is preferable that the group is an alkyl group, and more preferably a methyl group or an ethyl group.

[0022] a is an integer between 5 and 100, preferably between 5 and 50, and more preferably between 5 and 30. b is an integer between 1 and 3, preferably 3.

[0023] (A) The kinematic viscosity of component at 25°C is 10 to 10,000 mm². 2 / s, 10~5,000mm 2 / s is preferable. The kinematic viscosity is 10 mm 2 If the kinematic viscosity is less than 10,000 mmHg, oil bleeding will occur from the resulting silicone composition. 2 If the value exceeds / s, the resulting silicone composition will have poor fluidity. In this invention, the kinematic viscosity of component (A) is the value obtained at 25°C using an Ostwald viscometer.

[0024] The amount of component (A) is in the range of 50 to 100 parts by mass, preferably 55 to 95 parts by mass. However, the total amount of component (A) and component (B), described later, is 100 parts by mass. When the amount is within this range, the silicone composition is more likely to maintain good fluidity and workability. In addition, it is easier to fill the silicone composition with the thermally conductive fillers component (C) and component (D), described later. Note that if the amount of component (A) is less than 50 parts by mass, it will not be possible to fill the composition with the thermally conductive fillers component (C) and component (D) to a high degree.

[0025] (A) Suitable specific examples of component include the following: [ka]

[0026] [(B) Component] Component (B) of the present invention has the following average composition formula (2): R 3 c SiO (4-c) / 2 (2) (In the formula, R 3 (Each is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, where c is a number between 1.8 and 2.2.) The kinematic viscosity at 25°C, as shown by [formula], is 10 to 100,000 mm². 2 It is an organopolysiloxane of type / s, which can be used alone or in combination of two or more types. Component (B) is used to impart properties such as viscosity modifier and tackifier to the silicone composition of the present invention.

[0027] The above R 3 R is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, preferably with 1 to 10 carbon atoms. 3Examples include alkyl groups such as methyl, ethyl, propyl, hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl and allyl groups; aryl groups such as phenyl and tolyl groups; aralkyl groups such as 2-phenylethyl and 2-methyl-2-phenylethyl groups; and halogenated hydrocarbon groups such as 3,3,3-trifluoropropyl, 2-(perfluorobutyl)ethyl, 2-(perfluorooctyl)ethyl, and p-chlorophenyl groups. Among these, methyl, phenyl, and alkyl groups having 6 to 18 carbon atoms are preferred, with methyl and phenyl groups being more preferred.

[0028] The above value c is a number between 1.8 and 2.2, and preferably between 1.9 and 2.1, from the viewpoint of the viscosity required for the composition of the present invention, as a silicone composition with low thermal resistance.

[0029] The kinematic viscosity of component (B) at 25°C is 10 to 100,000 mm². 2 / s, 10~10,000mm 2 It is preferable that the kinematic viscosity is 10 mm² / s. 2 If the kinematic viscosity is less than 100,000 mmHg, liquid separation and oil bleeding will occur from the resulting silicone composition. 2 If the viscosity exceeds / s, the resulting silicone composition will have poor fluidity, leading to problems with workability. Note that the kinematic viscosity of component (B) is also the value obtained at 25°C using an Ostwald viscometer.

[0030] (B) Specific examples of component (B) include the following: [ka]

[0031] The amount of component (B) is 0 to 50 parts by mass, with 5 to 45 parts by mass being more preferable (however, the total amount of components (A) and (B) mentioned above is 100 parts by mass). Component (B) may also be omitted. When the amount is within this range, the silicone composition maintains good fluidity and workability, and it is easy to fill the composition with the thermally conductive fillers components (C) and (D) described later. On the other hand, if the amount of component (B) exceeds 50 parts by mass, it becomes impossible to fill the silicone composition with the thermally conductive fillers components (C) and (D) to a high degree.

[0032] [(C) component] Component (C) of the present invention is an α-aluminum oxide powder having a hexagonal close-packed lattice crystal structure consisting of 8 or more polyhedra, wherein the particle shape has a D / H ratio of 0.3 to 30, where D is the maximum particle diameter parallel to the hexagonal lattice planes and H is the particle diameter perpendicular to the hexagonal lattice planes, the average particle diameter is 7 to 30 μm, the proportion of coarse particles in the laser diffraction particle size distribution of 50 μm or more is 1% by mass or less of the total, and the purity is 99% or more. This α-aluminum oxide powder can be used alone or in combination of two or more types.

[0033] The aluminum oxide of component (C) has a hexagonal close-packed lattice crystal structure consisting of 8 or more polyhedra, but octahedrons to icosahedrons are preferred, and it is preferable that it is α-aluminum oxide having a crystal structure substantially composed of 8 and / or 16 faces. The crystal structure can be confirmed with the image diffraction apparatus shown below.

[0034] In the present invention, the particle shape of component (C) is such that the D / H ratio is in the range of 0.3 to 30, where D is the maximum particle diameter parallel to the hexagonal lattice plane and H is the particle diameter perpendicular to the hexagonal lattice plane of the α-aluminum oxide powder having a hexagonal close-packed lattice structure. The D / H ratio can be measured by importing particle images captured with a scanning electron microscope into an image analysis device, for example, a JEOL product called "JSM-7500F," as follows: That is, the maximum particle diameter parallel to the hexagonal lattice plane of the particles is measured from the photograph as D, and the particle diameter perpendicular to the hexagonal lattice plane as H. The D / H ratio of 10 arbitrary particles obtained in this way is determined, and the average value is taken as D / H. In the present invention, a D / H ratio in the range of 0.3 to 5 is preferred. If the D / H ratio is less than 0.3, the packing ability into the resin deteriorates, contact between particles decreases, and the thermal resistance increases due to the increased inter-particle contact thermal resistance. Furthermore, when the D / H ratio of component (C) exceeds 30, contact between particles increases significantly, the surface irregularities of the silicone composition become larger, the interfacial thermal resistance increases, and the thermal resistance becomes higher.

[0035] The average particle size (primary and / or secondary particle size) of component (C) is 7 to 30 μm by volume, preferably 10 to 25 μm. When the average particle size is within this range, the bulk density of component (C) tends to be high and the specific surface area tends to be low, making it easy to densely fill component (C) in the silicone composition of the present invention. If the average particle size is less than 7 μm, it becomes difficult to achieve the thermal conductivity desired in the present invention. On the other hand, if the average particle size exceeds 30 μm, oil separation may easily occur, causing the thermal resistance to deteriorate over time.

[0036] If the proportion of coarse particles above 50 μm in the laser diffraction particle size distribution is 1% by mass or less of the total (C) component, the desired thermal resistance and high thermal conductivity can be achieved simultaneously. On the other hand, if the proportion of coarse particles above 50 μm exceeds 1% by mass of the total (C) component, the thickness may not reach 60 μm or less, and the desired thermal resistance tends not to be achieved. The proportion of such coarse particles is preferably 0.5% by mass or less of the total (C) component.

[0037] The average particle size of component (C) in this invention, based on volume, can be measured, for example, using a Shimadzu Corporation "Laser Diffraction Particle Size Distribution Analyzer SALD-2300". For the evaluation sample, 5g of the thermal conductive powder to be measured is added to 50mL of pure water in a glass beaker, stirred with a spatula, and then dispersed in an ultrasonic cleaner for 10 minutes. The dispersed thermal conductive powder solution is added drop by drop to the sampler section of the analyzer using a dropper, and the sample is allowed to stabilize until the absorbance can be measured. Measurement is then performed once the absorbance has stabilized. The laser diffraction particle size distribution analyzer calculates the particle size distribution from the light intensity distribution data of the diffracted / scattered light from the particles detected by the sensor. The average particle size is obtained by multiplying the measured particle size by the relative particle amount (difference %) and dividing by the total relative particle amount (100%). The average particle size is the average diameter of the particles. For example, the proportion of coarse particles larger than 50μm in component (C) can also be easily confirmed from the overall particle size distribution. Furthermore, two or more types with different average particle sizes may be used in combination, as long as they do not impair the effects of the present invention.

[0038] The purity of component (C) is 99% or higher, preferably 99.5% or higher. If the purity is lower than this, the thermal resistance will increase. In this invention, the purity of component (C) is measured by atomic absorption spectroscopy based on JIS K 1410. The blending ratio of component (C) is as described later.

[0039] [(D) component] Component (D) is zinc oxide powder having an average particle size of 0.01 μm or more and less than 3 μm, and the proportion of coarse particles in the laser diffraction particle size distribution of 10 μm or more is 1% by mass or less of the total. The zinc oxide powder of component (D) functions as a thermally conductive filler in the silicone composition of the present invention. Component (D) may be used alone or in combination of two or more types.

[0040] The average particle size of component (D) is 0.01 μm or more and less than 3 μm on a volume basis, preferably 0.01 to 2 μm, more preferably 0.01 to 1 μm, and even more preferably 0.01 to 0.5 μm. When the average particle size is within this range, the bulk density of component (D) tends to be high and the specific surface area tends to be low, making it easy to fill the silicone composition of the present invention with high density of component (D). If the average particle size is less than 0.01 μm, the packing ability into the resin deteriorates and the viscosity becomes significantly higher. On the other hand, if the average particle size exceeds 3 μm, oil separation proceeds easily.

[0041] Component (D) has a laser diffraction particle size distribution in which the proportion of coarse particles 10 μm or larger is 1 mass% or less of the total component (D), preferably 0.2 mass% or less. This range allows for both the desired thermal resistance and high thermal conductivity to be achieved. On the other hand, if the proportion of coarse particles 10 μm or larger exceeds 1 mass% of the total, the thickness may not be 20 μm or less, and the desired thermal resistance may not be achieved. The method for measuring the average particle size and the proportion of coarse particles of component (D) is the same as for component (C).

[0042] The shape of component (D) may be spherical, irregular, or a mixture thereof. In the present invention, component (D) may be irregular in shape if it is not spherical, for example, rod-shaped, needle-shaped, or disc-shaped, as long as it does not impair the effects of the present invention. Component (D) may be spherical or irregular in shape alone, or a combination of these. Component (D) is defined as spherical if its average sphericity is preferably 0.8 or higher, more preferably 0.9 or higher.

[0043] The average sphericity of component (D) can be measured by importing particle images captured with a scanning electron microscope into an image analysis device, such as the JEOL JSM-7500F, as follows: The projected area (X) and perimeter (Z) of the particle are measured from the photograph. If (Y) is the area of ​​a perfect circle corresponding to the perimeter (Z), then the sphericity of the particle can be expressed as X / Y. Therefore, assuming a perfect circle with the same perimeter (Z) as the sample particle, Z = 2πr and Y = πr 2(where r is the radius.) Therefore, Y = π × (Z / 2π) 2 Therefore, the sphericity of each particle is given by: Sphericity = X / Y = X × 4π / Z 2 It can be calculated as follows. The sphericity of 100 arbitrary particles obtained in this way was determined, and the average value was taken as the average sphericity.

[0044] Furthermore, the purity of component (D) is preferably 99.5% or higher, and particularly preferably 99.8% or higher from the viewpoint of impurities such as Pb and Cd. The method for measuring purity is the same as the method described for component (C).

[0045] The mixing ratio of component (D) to component (C) is 5:5 to 9.5:0.5 by mass ratio, with 6:4 to 9:1 being preferable. If the proportion of component (C) is less than 5 by mass ratio, the filler's packing ability will be poor. Conversely, if the proportion of component (C) exceeds 9.5 by mass ratio, it will be difficult to pack the filler densely, and the thermal conductivity will decrease.

[0046] The total amount of (C) and (D) in the silicone composition of the present invention, that is, the total content of the thermally conductive filler, is 75 to 85 volume percent of the total composition, and preferably 76 to 84 volume percent. If the total amount of (C) and (D) is less than 75 volume percent, the thermal conductivity of the silicone composition will be insufficient, and if it exceeds 85 volume percent, it will be difficult to fill with thermally conductive filler. In the present invention, the desired effect can be obtained even if the total amount of (C) and (D) is high.

[0047] [(E) component] The composition of the present invention may further contain, as component (E), a volatile solvent capable of dispersing or dissolving components (A) and (B). If the present invention further includes component (F), described later, in addition to components (A) and (B), it is preferable that component (F) is also a volatile solvent capable of dispersing or dissolving. Component (E) is not particularly limited as long as it can dissolve or disperse components (A) and (B), and optionally component (F). Component (E) can be used alone or in combination of two or more.

[0048] The thermal conductivity of a thermally conductive silicone composition is basically correlated with the filling rate of the thermally conductive filler; therefore, the more thermally conductive filler is added, the higher the thermal conductivity. However, naturally, increasing the amount of thermally conductive filler tends to increase the viscosity of the thermally conductive silicone composition itself, and the dilatancy of the composition when shear action is applied also tends to increase. In particular, in screen printing, when squeegeeing a thermally conductive silicone composition, if dilatancy is strongly expressed in the thermally conductive silicone composition, the fluidity of the thermally conductive silicone composition is temporarily strongly suppressed, which can prevent the thermally conductive silicone composition from passing through the screen mask and screen mesh, resulting in extremely poor coating performance. Thus, conventionally, it has been difficult to easily and uniformly apply a thin layer of a highly thermally conductive silicone composition with a high concentration of thermally conductive filler to a heat sink or the like using screen printing. Even if the silicone composition of the present invention contains thermally conductive fillers (C) and (D) at a high filling rate, if it contains a volatile solvent (E), the viscosity tends to decrease rapidly and dilatancy is less likely to occur, resulting in good coatability, and it can be easily applied to heat sinks and the like by screen printing. After application, the contained (E) can be easily evaporated at room temperature or by actively heating. Therefore, in the present invention, a low thermal resistance silicone composition with a high filling rate of thermally conductive filler can be easily and uniformly thinly applied to heat sinks and the like by screen printing.

[0049] The boiling point of component (E) is preferably in the range of 80 to 260°C. When the boiling point is within this range, it is easier to prevent component (E) from rapidly volatilizing from the silicone composition during the coating process, thereby suppressing an increase in the viscosity of the silicone composition and ensuring sufficient coatability. Furthermore, since component (E) is less likely to remain in the silicone composition after the coating process, the heat dissipation characteristics tend to improve.

[0050] Specific examples of component (E) include toluene, xylene, acetone, methyl ethyl ketone, cyclohexane, n-hexane, n-heptane, butanol, isopropanol (IPA), isoparaffinic solvents, and among these, isoparaffinic solvents are preferred from the viewpoint of safety, health, and workability, and isoparaffinic solvents with a boiling point of 80 to 260°C are particularly preferred.

[0051] When component (E) is added to the composition of the present invention, the amount added is preferably 100 parts by mass or less, and more preferably 75 parts by mass or less, relative to 100 parts by mass of the total of components (A) and (B). When the amount added is within this range, it is easier to suppress the rapid settling of components (C) and (D), and thus the shelf life of the silicone composition is easily improved. There is no particular lower limit to the amount of component (E) added, but from the viewpoint of the applicability of the silicone composition of the present invention, it is preferably 1 part by mass or more, and more preferably 5 parts by mass or more.

[0052] [(F) component] The composition of the present invention may further contain (F) alkoxysilane. Component (F) is given by the following general formula (3): R 4 d R 5 e Si(OR 6 ) 4-d-e (3) (In the formula, R 4 Each of these is an alkyl group having 9 to 15 carbon atoms, and R 5 Each of these is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and R 6 Each of these is an alkyl group having 1 to 6 carbon atoms, d is an integer from 1 to 3, and e is an integer from 0 to 2, where d+e is an integer from 1 to 3. This is an alkoxysilane represented by [formula]. Component (F) can be used alone or in combination of two or more.

[0053] Component (F) is both a wetter component and an additive that prevents deterioration of component (A) under high temperature and high humidity conditions. By treating the surface of the thermally conductive fillers (C) and (D) with component (F), the wettability of component (A) to components (C) and (D) can be further improved. As a result, component (F) assists in increasing the filler content of components (C) and (D). Furthermore, when used in combination with component (A), component (F) works to suppress contact between water vapor and component (A) under high temperature and high humidity conditions. Consequently, component (F) prevents deterioration of the performance of the silicone composition of the present invention due to deterioration of component (A) caused by hydrolysis or other factors under high temperature and high humidity conditions. Component (F) may be used alone or in combination of two or more types.

[0054] The above R 4 Each of these is an alkyl group having 9 to 15 carbon atoms, and specific examples include nonyl, decyl, dodecyl, tetradecyl, and pentadecyl groups. If the number of carbon atoms is less than 9, the wettability with the thermally conductive filler (components (C) and (D)) tends to be insufficient, and if it is greater than 15, component (F) tends to solidify at room temperature, making it inconvenient to handle, and the heat resistance and flame retardancy of the resulting composition tend to decrease.

[0055] The above R 5 Each of these is independently an unsubstituted or substituted saturated or unsaturated monovalent hydrocarbon group having 1 to 8 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, hexyl, and octyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl and allyl groups; aryl groups such as phenyl and tolyl groups; aralkyl groups such as 2-phenylethyl and 2-methyl-2-phenylethyl groups; and halogenated hydrocarbon groups such as 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and p-chlorophenyl groups, with methyl and ethyl groups being particularly preferred.

[0056] The above R 6Each of these is an alkyl group having 1 to 6 carbon atoms, and specific examples include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups, with methyl and ethyl groups being particularly preferred.

[0057] The above d is an integer between 1 and 3, preferably 1. The above e is an integer between 0 and 2. However, d+e is an integer between 1 and 3.

[0058] Specific examples of component (F) include the following: C 10 H 21 Si(OCH3)3, C 10 H 21 Si(OC2H5)3, C 12 H 25 Si(OCH3)3, C 12 H 25 Si(OC2H5)3, C 10 H 21 Si(CH3)(OCH3)2, C 10 H 21 Si(C6H5)(OCH3)2, C 10 H 21 Si(CH3)(OC2H5)2, C 10 H 21 Si(CH=CH2)(OCH3)2, C 10 H 21 Si(CH2CH2CF3)(OCH3)2

[0059] When component (F) is included, the amount is usually preferably 0.1 to 50 parts by mass, and more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the total of components (A) and (B). When the amount is within this range, the wetter effect and high temperature and high humidity resistance tend to increase in proportion to the amount included, making it economical. On the other hand, since component (F) is somewhat volatile, if a silicone composition containing component (F) is left in an open system, component (F) may evaporate from the silicone composition, causing the composition to gradually harden. When the amount of component (F) is within this range, it is easier to prevent this phenomenon.

[0060] When surface-treating components (C) and (D) with component (F), the treatment method can include a spray method using a fluid nozzle, a stirring method with shear force, a dry method using a ball mill or mixer, or a wet method using a water-based or organic solvent-based system. When using the stirring method, it is important to do so without damaging the spherical aluminum oxide powder. In the dry method, the system temperature or the drying temperature after treatment is appropriately determined according to the type of surface treatment agent, within a range where the surface treatment agent does not volatilize or decompose, but is generally between 80 and 180°C. Alternatively, a method can be adopted in which components (C) and (D) are heated and mixed together with components (A) and (B), then cooled, and component (F) is added and mixed.

[0061] [Other additives] The silicone composition of the present invention may further contain commonly used additives, fillers, etc., as optional components, provided that they do not impair the effects of the present invention. Specifically, fluorine-modified silicone surfactants; colorants such as carbon black, titanium dioxide, and red iron oxide; and flame retardants such as platinum catalysts, iron oxide, titanium dioxide, cerium oxide, and other metal oxides; and metal hydroxides may be added. Furthermore, fine silica powders such as settling silica and calcined silica, and thixotropic agents may be added as anti-settling agents for thermally conductive fillers at high temperatures. The amounts of these additives are appropriately selected within a normal range and without impairing the effects of the present invention.

[0062] [Preparation of composition] The silicone composition of the present invention is prepared by mixing the aforementioned components using mixing equipment such as a dough mixer (kneader), gate mixer, or planetary mixer. The silicone composition obtained in this way has significantly improved thermal conductivity, good workability, durability, and reliability.

[0063] [Thermal conductivity] The thermal conductivity of the silicone composition of the present invention at 25°C is preferably 4.0 W / m·K or higher, more preferably 4.0 W / m·K or higher and less than 7.0 W / m·K, and even more preferably 4.5 to 6.5 W / m·K, according to the hot disk method in accordance with ISO 22007-2. By setting the thermal conductivity to less than 7 W / m·K, the coatability of the silicone composition is further improved. The thermal conductivity of the composition in the present invention can be measured using a thermal conductivity measuring device, such as the "TPS 2500 S" manufactured by Kyoto Electronics Corporation.

[0064] [viscosity] The viscosity of the silicone composition of the present invention at 25°C is 5 to 800 Pa·s, preferably 5 to 750 Pa·s, and more preferably 5 to 500 Pa·s, when measured at a rotation speed of 10 rpm using a spiral viscometer. When the viscosity is within this range, the resulting silicone composition tends to have good fluidity, which improves workability such as dispensability and screen printability, and makes it easier to apply the composition thinly to a substrate. The viscosity of the silicone composition of the present invention can be measured using a spiral viscometer, for example, a Malcolm Type PC-10AA.

[0065] The silicone composition of the present invention preferably has a viscosity of 1,000 Pa·s or less, more preferably 700 Pa·s or less, and even more preferably 500 Pa·s or less, measured at 25°C after thermal degradation using a dryer at 200°C for 100 hours, as described above. Having such a non-curing and thixotropic properties ensures the reliability of heat-generating electronic components.

[0066] [Thermal resistance] The thermal resistance of the silicone composition of the present invention, measured by laser flash method at 25°C, is 11 mm². 2 • Preferably less than kW, and 10 mm 2 A value of K / W or less is more preferable. With the configuration of the present invention, such a low thermal resistance silicone composition can be obtained.

[0067] The silicone composition of the present invention, after being left for 96 hours in a 130°C / 85%RH atmosphere, has a thermal resistance of 11 mm at 25°C, as measured by laser flash method. 2 • Preferably less than kW, and 10mm 2 It is more preferable that the thermal resistivity is less than or equal to kW. When this thermal resistivity is within this range, the silicone composition of the present invention can efficiently dissipate the heat generated from a heat-generating element to a heat-dissipating component, even when applied to such a element. The thermal resistance can be measured by the laser flash method in accordance with ASTM E 1461.

[0068] [Volume resistivity] The silicone composition of the present invention has a volume resistivity of 1 × 10⁻¹⁰ as measured by a method compliant with JIS K 6911. 9 Preferably, it is Ω·cm or more, and more preferably 1 × 10⁻⁶. 10 The density is Ω·cm or greater. Within this range, the silicone composition of the present invention can ensure better insulation.

[0069] [Uses of silicone compositions] The silicone composition of the present invention is applied to heat-generating elements and heat sinks. Examples of heat-generating elements include general power supplies; electronic devices such as power transistors, power modules, thermistors, thermocouples, and temperature sensors; and heat-generating electronic components such as integrated circuit elements like LSIs and CPUs. Examples of heat sinks include heat dissipation components such as heat spreaders and heat sinks; and heat pipes and heat sink plates. Application can be carried out, for example, by screen printing. Screen printing can be carried out, for example, using a metal mask or screen mesh. By applying the composition of the present invention interposed between the heat-generating element and the heat sink, heat can be efficiently conducted from the heat-generating element to the heat sink, thereby effectively removing heat from the heat-generating element. [Examples]

[0070] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0071] [Examples 1-5, Comparative Examples 1-4] The following components were prepared to create the silicone composition of the present invention. The kinematic viscosity is the value obtained at 25°C using an Ostwald viscometer. (A) component A-1: It is represented by the following formula, with a specific gravity (at 25°C) of 0.97 and a kinematic viscosity of 30 mm³. 2 / s organopolysiloxane [ka]

[0072] (B) Component B-1: Organopolysiloxane B-1: In the average composition formula (2), it is represented by the following formula with c=2.0, has a specific gravity (25℃) of 0.97, and a kinematic viscosity of 500 mmHg 2 / s organopolysiloxane [ka]

[0073] (C) Aluminum oxide powder (specific gravity 3.98) [Table 1]

[0074] The average particle size shown here was measured using a Shimadzu Corporation "SALD-2300 Laser Diffraction Particle Size Distribution Analyzer" and is a volume-based value calculated from the entire particle size distribution obtained by laser diffraction. The coarse particle content is the percentage of coarse particles 50 μm or larger relative to the entire particle size distribution obtained by laser diffraction.

[0075] (D) Zinc oxide powder (D-1) Amorphous zinc oxide powder (average particle size 0.27 μm, coarse particle content of 10 μm or larger is 0.1% by mass, specific gravity is 5.67) The average particle size shown here was measured using a Shimadzu Corporation "SALD-2300 Laser Diffraction Particle Size Distribution Analyzer" and is a volume-based value calculated from the entire particle size distribution obtained by laser diffraction. The coarse particle content is the proportion of 10 μm coarse particles in the entire particle size distribution obtained by laser diffraction.

[0076] A volatile solvent (specific gravity 0.79) capable of dispersing or dissolving components (E)(A-1), (B-1), and (F-1). E-1: Isoparaffinic solvent, boiling point 210-254℃: Isosol (registered trademark) 400 (product name, manufactured by ENEOS Corporation)

[0077] (F) Alkoxysilane F-1: An alkoxysilane represented by the following formula (specific gravity: 0.90) C 10 H 21 Si(OCH3)3

[0078] [Manufacturing method] The compositions of Examples 1-5 and Comparative Examples 1-4 were obtained by mixing components (A) to (D), and optionally components (E) and (F), as follows. Specifically, components (A) to (D) were weighed into a 5-liter planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.) in the composition ratios (parts by mass) shown in Tables 2 and 3, and mixed under reduced pressure at 150°C for 1 hour at a pressure of 30 mmHg or less. After that, the resulting mixture was cooled and mixed to room temperature. When adding components (E) and (F), components (E) and (F) were added to the cooled mixture in the proportions shown in Table 2 and mixed until uniform.

[0079] [Test Method] The properties of the obtained silicone composition were measured using the following test method. The results are shown in Tables 2 and 3.

[0080] 〔viscosity〕 The obtained silicone composition was left in a constant temperature chamber at 25°C for 24 hours, and then its viscosity was measured at a rotation speed of 10 rpm using a viscometer (product name: spiral viscometer PC-10AA, manufactured by Malcolm Corporation).

[0081] [Viscosity after thermal degradation] The obtained silicone composition was subjected to thermal degradation using a dryer at 200°C for 100 hours, then left in a constant temperature chamber at 25°C for 24 hours, and measured in the same manner as above.

[0082] [Thermal conductivity] The procedure was performed according to the hot disk method compliant with ISO 22007-2. Two samples of the obtained silicone composition were prepared by wrapping them in kitchen wrap to prevent bubbles from entering. The thermal conductivity of the composition at 25°C was measured by placing these samples between the sensors of a thermal conductivity meter (product name: TPS-2500 S) manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0083] [Volume resistivity] Based on JIS K 6911, a test specimen was prepared with a sample thickness of 1 mm for measurement using the double-ring electrode method. 500 V was applied between the electrodes, and the volume resistivity was measured after 1 minute.

[0084] [Preparation of test specimens for measuring thickness and thermal resistance] A 40 μm thick composition was sandwiched between two circular aluminum plates, each 12.6 mm in diameter and 1 mm thick, and a test specimen was prepared by applying a pressure of 0.15 MPa at 25°C for 60 minutes.

[0085] [Thickness measurement] The thickness of the test specimen was measured using a micrometer (manufactured by Mitutoyo Corporation), and the thickness of the composition was calculated by subtracting the thickness of two aluminum plates that had been measured in advance.

[0086] [Measurement of thermal resistance] Using the above test specimen, the thermal resistance of the composition (unit: mm) was determined. 2 The thermal resistance (K / W) was measured at 25°C using a laser flash-based thermal resistance analyzer (Netch Corporation, xenon flash analyzer; LFA447 NanoFlash).

[0087] [Measurement of thermal resistance after being left in high temperature and high humidity conditions] After measuring the thermal resistance of the above test specimen, leave it in a 130°C / 85%RH atmosphere for 96 hours, and then measure the thermal resistance of the composition again (unit: mm). 2 The thermal resistance (K / W) was measured using the same thermal resistance meter.

[0088] [Table 2]

[0089] [Table 3]

Claims

1. (A) General formula (1) below: 【Chemistry 1】 (In the formula, R 1 R is independently an unsubstituted or substituted monovalent hydrocarbon group. 2 (where a is independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, a is an integer from 5 to 100, and b is an integer from 1 to 3.) It is expressed as such, and the kinematic viscosity at 25°C is 10 to 10,000 mm². 2 / s organopolysiloxane: 50 to 100 parts by mass, (B) The following average composition formula (2): R 3 c SiO (4-c) / 2 (2) (In the formula, R 3 (Each is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, where c is a number between 1.8 and 2.2.) The kinematic viscosity at 25°C, as shown by [formula], is between 10 and 100,000 mm². 2 / s organopolysiloxane: 0 to 50 parts by mass (However, the total amount of component (A) and component (B) must be 100 parts by mass.) (C) α-aluminum oxide powder having a hexagonal close-packed lattice crystal structure consisting of 8 or more polyhedra, wherein the particle shape has a D / H ratio of 0.3 or more and 30 or less, where D is the maximum particle diameter parallel to the hexagonal lattice planes of the hexagonal close-packed lattice and H is the particle diameter perpendicular to the hexagonal lattice planes, the average particle diameter is 7 to 30 μm, and the proportion of coarse particles in the laser diffraction particle size distribution of 50 μm or more is 1% by mass or less of the total, and the purity is 99% or more. (D) Zinc oxide powder having an average particle size of 0.01 μm or more and less than 3 μm, and the proportion of coarse particles in the laser diffraction particle size distribution of 10 μm or more being 1% by mass or less of the total component (D), (However, the mixing ratio of component (C) to component (D) is 5:5 to 9.5:0.5 by mass, and the total amount of (C) and (D) is 75 to 85% by volume.) A silicone composition containing the following, wherein the thermal conductivity is 4.0 W / m·K or more and less than 7.0 W / m·K in the hot disk method compliant with ISO 22007-2, and the viscosity at 25°C is 5 to 800 Pa·s when measured by a spiral viscometer at a rotation speed of 10 rpm.

2. The silicone composition according to claim 1, having a thermal resistance at 25°C measured by the laser flash method of 11 mm 2 ·K / W or less.

3. After being left for 96 hours in a 130°C / 85% RH atmosphere, the thermal resistance at 25°C, measured by laser flash method, was 11 mm². 2 The silicone composition according to claim 1, wherein the K / W is less than or equal to 1.

4. The silicone composition according to claim 1, wherein, after thermal degradation at 200°C for 100 hours, the viscosity at 25°C is 1,000 Pa·s or less when measured by a spiral viscometer at a rotation speed of 10 rpm.

5. Furthermore, the silicone composition according to claim 1 further comprises (E) a volatile solvent capable of dispersing or dissolving components (A) and (B): in an amount of 100 parts by mass or less per 100 parts by mass of the total amount of components (A) and (B).

6. Furthermore, (F) General formula (3) below: R 4 d R 5 e Si(OR 6 ) 4-d-e (3) (In the formula, R 4 Each of these is an alkyl group having 9 to 15 carbon atoms, and R 5 Each of these is independently an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms, R 6 The silicone composition according to claim 1, wherein each of the following is an alkyl group having 1 to 6 carbon atoms, d is an integer from 1 to 3, e is an integer from 0 to 2, and d + e is an integer from 1 to 3. The alkoxysilane represented by (A) is contained in an amount of 0.1 to 50 parts by mass per 100 parts by mass of the total amount of component (A) and component (B), and component (C) and component (D) are surface-treated with component (F).

7. Volume resistivity is 1 × 10⁻⁶ 9 A silicone composition according to any one of claims 1 to 6, wherein the size is Ω·cm or larger.

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