Thermally conductive composite silicone rubber sheet

Abstract

The present invention is a thermally conductive composite silicone rubber sheet characterized by comprising a thermally conductive silicone rubber sheet and a thermally softening silicone gel layer that is disposed on one or both surfaces of the thermally conductive silicone rubber sheet, has a thickness of 5-100 μm, and has an absolute viscosity of 5-1,000 Pa·s at 70°C. The thermally conductive composite silicone rubber sheet is also characterized in that the tack force of the thermally softening silicone gel layer, as measured by a constant-pressure insertion method using a solder paste tackiness tester, is 0.098 N or more. This makes it possible to provide a thermally conductive composite silicone rubber sheet which has low thermal resistance, is capable of exhibiting tackiness by instantaneous contact, and has excellent storage properties due to a suppressed decrease in tack force during storage.

Description

Thermally conductive composite silicone rubber sheet

[0001] This invention relates to a thermally conductive composite silicone rubber sheet.

[0002] As electrical and electronic devices become smaller and more highly integrated, the effects of heat generated by electrical and electronic components such as power semiconductors and memory are becoming more serious than ever before. When heat accumulates in electrical and electronic components, their temperature rises, potentially causing malfunctions or failures. To prevent such problems, many heat dissipation methods and heat dissipation materials have been proposed to efficiently dissipate the heat generated by electrical and electronic components to cooling materials such as heat sinks.

[0003] Conventionally, in electrical and electronic equipment, heat sinks made of metal plates with high thermal conductivity, such as aluminum or copper, have been used to suppress the temperature rise of components during operation. Heat sinks conduct heat generated from the components and release that heat from their surface due to the temperature difference with the surrounding air.

[0004] If the heat-generating element and the heat sink are placed in direct contact, air will be present at the interface, hindering heat conduction. Therefore, the heat sink must be in close contact with the element. Due to differences in height and tolerances during assembly, flexible and thermally conductive sheets or greases are used.

[0005] Compared to grease, thermal conductive sheets offer superior handling advantages, and thermal conductive sheets, formed from thermally conductive resins, are used in a variety of fields.

[0006] Furthermore, particularly in the automotive sector, long-term reliability is required over a wide temperature range, from around -40°C, the lowest temperature in cold regions, to high temperatures of 150°C or more, the temperature of heat-generating components. In addition, properties such as flame retardancy and electrical insulation are often required. Silicone is suitable as a resin that satisfies all of these properties, and thermally conductive silicone sheets, which are compounded with silicone and thermally conductive fillers, are used. In particular, a well-known type is one in which a highly filled, high-hardness silicone rubber layer is reinforced with a cloth-like reinforcing material such as glass cloth (Patent Document 1). This type of heat dissipation sheet is very useful because the hardness of the rubber layer allows it to handle heat conduction while also ensuring insulation. However, because heat dissipation sheets have almost no surface tack, mounting and fixing them to heat-generating components has been extremely difficult.

[0007] To improve the workability of mounting and fixing, heat dissipation sheets are commercially available in which an adhesive layer is provided on one or both sides of a high-hardness, thermally conductive silicone rubber sheet, and the adhesive layer surface is further protected with a release protective sheet such as release paper. However, because the adhesive used in these sheets does not have thermal conductivity, the overall thermal conductivity of the composite product is low, and in many cases, the desired heat dissipation performance cannot be obtained.

[0008] Furthermore, a heat dissipation sheet is disclosed in which a low-hardness thermally conductive silicone rubber layer is laminated onto a high-hardness thermally conductive silicone rubber sheet reinforced with the aforementioned reinforcing material (Patent Document 2). However, in the case of this composite type of heat dissipation sheet, due to manufacturing problems, it is not possible to obtain one with an overall thickness of less than 0.45 mm. Therefore, even if the low-hardness silicone rubber layer itself has good high thermal conductivity, a thin composite product cannot be obtained as a whole, resulting in the disadvantage of high thermal resistance. Thus, adhesive strength and thermal conductivity are inversely related, and a method for imparting adhesive strength without sacrificing thermal conductivity as much as possible has been needed for many years.

[0009] Patent Document 3 proposes a thermally conductive composite silicone rubber sheet that achieves both adhesive strength, heat dissipation performance, and long-term reliability by providing a thermo-softening silicone resin layer with a thickness of 0.5 to 10 μm. However, in order to sufficiently adhere the thermally conductive silicone rubber sheet and prevent peeling or falling from the adherend, a process of pressing it for several seconds to tens of seconds during application was essential. To shorten these assembly processes, it was essential to improve the tack force, which is generally expressed as adhesiveness that manifests upon instantaneous contact. Furthermore, when such a thermo-softening silicone resin layer is laminated onto a thermally conductive silicone rubber sheet, there was a problem that the tack force of the adhesive layer decreased over time. This decrease in tack force was more pronounced during high-temperature storage, and the need for refrigerated storage or refrigerated transport to maintain the tack force was a problem.

[0010] JP-A-56-161140 JP-A-06-155517 JP-A 2020-203457

[0011] This invention has been made in view of these circumstances, and aims to provide a thermally conductive composite silicone rubber sheet that has low thermal resistance, can exhibit tackiness upon instantaneous contact, and has excellent storage properties because the reduction in tackiness during storage is suppressed.

[0012] To solve the above problems, the present invention provides a thermally conductive composite silicone rubber sheet comprising a thermally conductive silicone rubber sheet and a thermo-softening silicone gel layer disposed on one or both sides of the thermally conductive silicone rubber sheet, having a thickness of 5 to 100 μm and an absolute viscosity of 5 to 1,000 Pa·s at 70°C, wherein the tack force of the thermo-softening silicone gel layer, measured using a constant pressure penetration method with a solder paste adhesion tester, is 0.098 N or more.

[0013] A thermally conductive composite silicone rubber sheet having such a thermo-softening silicone gel layer can exhibit excellent adhesion upon instantaneous contact, and because the migration of components from the thermo-softening silicone gel layer to the silicone rubber component of the thermo-conductive silicone rubber sheet is suppressed, the decrease in adhesive strength during storage is suppressed. Even if thermo-softening occurs during high-temperature storage, the components remain in the cross-linked structure, thus suppressing the decrease in adhesive strength.

[0014] Furthermore, because such a thermo-softening silicone gel layer is thermo-soft, it can be made into a thin film during mounting, resulting in good adhesion to the substrate. As a result, it is possible to minimize the increase in thermal resistance, which was a trade-off for imparting tackiness.

[0015] Furthermore, in the present invention, it is preferable that the thermosoftening silicone gel layer comprises a thermosoftening silicone gel and a thermally conductive filler.

[0016] With such a thermo-softening silicone gel layer, it is possible to suppress the increase in thermal resistance even when the film thickness is relatively thick.

[0017] Furthermore, in this invention, the thermal resistance of the thermosoftening silicone gel layer measured at a temperature of 50°C and a pressure of 0.69 MPa using a TIM-Tester (manufactured by Analystech) compliant with ASTM D 5470 is 0.5 cm². ２ - Preferably, it is kW or less.

[0018] Such a thermo-softening silicone gel layer minimizes the increase in thermal resistance when tackiness is imparted to a thermally conductive composite silicone rubber sheet.

[0019] Furthermore, in the present invention, it is preferable that the silicone rubber component of the thermally conductive silicone rubber sheet consists of dimethylsiloxane units.

[0020] Such a thermally conductive silicone rubber sheet can suppress the diffusion of diphenylsiloxy group-containing organopolysiloxane contained in the thermosoftening silicone gel layer.

[0021] Furthermore, in the present invention, it is preferable that the thermally conductive silicone rubber sheet contains glass cloth and / or a plastic film.

[0022] If the material contains glass cloth, it will have superior strength, and if it contains plastic film, it will have even better electrical insulation properties.

[0023] Furthermore, in the present invention, it is preferable that the Type A hardness of the thermally conductive silicone rubber sheet, as measured by the method described in JIS K6253:2012, is 50 to 100.

[0024] With such a thermally conductive silicone rubber sheet, it is possible to suppress the instability of insulation caused by changes in thickness due to the fixing pressure of screws and clips when mounting the thermally conductive composite silicone rubber sheet, and to suppress cracking of the sheet when folded or bent.

[0025] Furthermore, in the present invention, it is preferable that the thermosoftening silicone gel layer contains phenyl silicone gel.

[0026] With such a heat-softening silicone gel layer, component migration between it and the heat-conductive silicone rubber sheet is suppressed, thus improving storage and transportability.

[0027] Furthermore, in the present invention, it is preferable that the thermosoftening silicone gel layer is a cured product of a thermosoftening thermally conductive silicone composition containing the following components (A) to (E): (A) Having two or more alkenyl groups in one molecule and having a kinematic viscosity of 100 to 100,000 mm at 25°C ２ / s and R' １ SiO ３／２ Phenyl-modified organopolysiloxane (in the formula R') that does not contain units (T units) １is a substituted or unsubstituted monovalent hydrocarbon group.): 100 parts by mass, (B) an organohydrogenpolysiloxane having at least two hydrosilyl groups at the molecular chain ends: an amount such that the molar number of hydrosilyl groups in the component (B) is 0.1 to 3 moles with respect to 1 mole of the alkenyl group in the component (A), (C) an organopolysiloxane having a hydrolyzable functional group, and one or more selected from alkoxysilane compounds represented by the following general formula (2): 10 to 1,000 parts by mass, R ３ ｂ R ４ ｃ Si(OR ５ ) ４－ｂ－ｃ (2) (In the formula, R ３ is independently an alkyl group having 6 to 15 carbon atoms, R ４ is independently a monovalent hydrocarbon group having 1 to 15 carbon atoms, R ５ is independently an alkyl group having 1 to 6 carbon atoms, b is an integer of 1 to 3, c is an integer of 0 to 2, provided that b + c is an integer of 1 to 3.) (D) One or more thermally conductive fillers selected from the group consisting of metals, metal oxides, metal hydroxides, and metal nitrides: an amount of 10 to 97% by mass based on the whole composition, and (E) a platinum group metal catalyst: 0.01 to 1,000 ppm on a mass basis in terms of platinum group metal atoms with respect to the mass of the component (A).

[0028] If the above thermoplastic silicone gel layer is a cured product of such a thermoplastic thermally conductive silicone composition, stable desired tack force, thermoplasticity, and storage stability can be obtained.

[0029] At this time, it is preferable that the organopolysiloxane having a hydrolyzable functional group in the component (C) is represented by the following general formula (1). (In the formula, R １ is independently an aromatic hydrocarbon group having 6 to 10 carbon atoms or independently an alkyl group having 1 to 10 carbon atoms, R ２ is an alkyl group having 1 to 4 carbon atoms. a is 2 or 3, and n is an integer of 2 ≤ n ≤ 60. However, it contains 1% or more of an aromatic hydrocarbon group having 6 to 10 carbon atoms.)

[0030] A thermo-softening, thermally conductive silicone composition containing such component (C) allows for stable dispersion of the thermally conductive filler within the silicone.

[0031] Furthermore, it is preferable that the heat-softening, heat-conductive silicone composition further contains, as component (F), 1 to 500 parts by mass of a non-reactive phenyl-modified organopolysiloxane per 100 parts by mass of component (A).

[0032] With such a thermo-softening, thermally conductive silicone composition, the thermo-softening silicone gel layer can be softened, making it possible to control the adhesive strength.

[0033] As described above, the thermally conductive composite silicone rubber sheet of the present invention can exhibit adhesiveness upon instantaneous contact while minimizing the increase in thermal resistance. For example, when mounted at the interface between a heating element and a cooling element, it can adhere to the substrate simply by contacting it, thus shortening process time and significantly improving production efficiency. Furthermore, it has good storage and transportability, and the decrease in adhesive strength is suppressed even after high-temperature storage, making it possible to store and transport it at room temperature.

[0034] As described above, there was a need to develop a thermally conductive composite silicone rubber sheet that has low thermal resistance, can exhibit tackiness upon instantaneous contact, and has excellent storage properties due to suppressed reduction in tackiness during storage.

[0035] As a result of diligent research into the above-mentioned problems, the present inventors have discovered that a thermally conductive composite silicone rubber sheet comprising a thermally conductive silicone rubber sheet and a thermally softening silicone gel layer disposed on one or both sides of the thermally conductive silicone rubber sheet, having a thickness of 5 to 100 μm and an absolute viscosity of 10 to 1,000 Pa·s at 70°C, and having a tack force of 0.098 N or more, can exhibit tackiness upon instantaneous contact, has low thermal resistance, and has good storage and transportability, thus completing the present invention.

[0036] In other words, the present invention relates to a thermally conductive composite silicone rubber sheet comprising a thermally conductive silicone rubber sheet and a thermo-softening silicone gel layer disposed on one or both sides of the thermally conductive silicone rubber sheet, having a thickness of 5 to 100 μm and an absolute viscosity of 5 to 1,000 Pa·s at 70°C, wherein the tack force of the thermo-softening silicone gel layer, measured using a constant-pressure penetration method with a solder paste adhesion tester, is 0.098 N or more.

[0037] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0038] [Thermally conductive composite silicone rubber sheet] The thermally conductive composite silicone rubber sheet of the present invention comprises a thermally conductive silicone rubber sheet and a thermo-softening silicone gel layer, wherein the tack force of the thermo-softening silicone gel layer is 0.098 N or more.

[0039] [Thermally Conductive Silicone Rubber Sheet] The thermally conductive silicone rubber sheet of the present invention is, for example, obtained by adding a thermally conductive filler and a curing agent to a silicone polymer, kneading the resulting thermally conductive silicone rubber composition, molding it into a sheet by any method, and curing it. However, the thermally conductive silicone rubber sheet of the present invention is not particularly limited as long as it is a thermally conductive silicone rubber sheet.

[0040] The mixing is preferably carried out by a mixing method that has shear force, such as a planetary mixer, kneader, or double-roll mixer, but is not particularly limited. The method for molding the thermally conductive silicone rubber composition into a sheet includes, but is not particularly limited, calendering, coating molding, extrusion molding, etc.

[0041] The curing mode of the above-mentioned thermally conductive silicone rubber composition is not particularly limited, but examples include addition-cured silicone rubber by hydrosilylation reaction, peroxide-cured silicone rubber by peroxide catalyst, and condensation-cured silicone rubber by condensation reaction with silanol, etc. Among these, addition-cured or peroxide-cured silicone rubber is preferred in terms of the time required for curing.

[0042] Furthermore, the above-mentioned silicone polymer can be arbitrarily selected depending on the desired physical properties of the cured product, but it is preferable that the silicone polymer be a dimethyl silicone polymer in which all substituents other than reaction sites such as alkenyl groups, hydrosilyl groups, and hydroxyl groups, among the substituents directly attached to the silicon atoms of the silicone polymer, are methyl groups. In other words, it is preferable that the silicone rubber component of the thermally conductive silicone rubber sheet consists of dimethylsiloxane units. Such a silicone polymer is preferable because it can suppress the diffusion of diphenylsiloxy group-containing organopolysiloxane contained in the thermosoftening silicone gel layer described later.

[0043] The thermal conductivity of the thermally conductive silicone rubber sheet is preferably 0.8 W / mK or higher, and more preferably 1.2 W / mK or higher. A thermal conductivity of 0.8 W / mK or higher is sufficient to adequately transfer heat from the heat-generating element to the cooling area. There is no particular upper limit to the thermal conductivity; however, if it can be molded into a sheet, a higher thermal conductivity is preferable because it allows for more efficient transfer of heat from the heat-generating element to the cooling area.

[0044] The thickness of the thermally conductive silicone rubber sheet is preferably between 0.08 mm and 1.2 mm. A thickness of 0.08 mm or more ensures sufficient insulation. A thickness of 1.2 mm or less ensures insulation while also allowing sufficient heat from the heat-generating element to be transferred to the cooling area.

[0045] The thermally conductive silicone rubber sheet may contain glass cloth and / or plastic film. For example, materials such as glass cloth may be included to provide a reinforcing effect, or plastic film may be included to provide an insulating effect. For example, the thermally conductive silicone rubber sheet may consist of two silicone rubber layers and an intermediate layer interposed between them, and the above-mentioned material may be included in the intermediate layer.

[0046] If the material contains glass cloth, it will have superior strength. Furthermore, if it contains plastic film, it will have even better electrical insulation properties.

[0047] It is preferable that the Type A hardness of the above-mentioned thermally conductive silicone rubber sheet, as measured by the method described in JIS K6253:2012, is 50 to 100. In particular, it is preferable that the hardness of the thermally conductive silicone rubber sheet containing glass cloth and / or plastic film is 50 or more and 100 or less in Type A hardness as measured by the method described in JIS K6253:2012. If the Type A hardness is 50 or more, it is possible to suppress the instability of insulation caused by changes in thickness due to the fixing pressure of screws and clips when mounting the thermally conductive composite silicone rubber sheet. Furthermore, if the Type A hardness is 100 or less, it is possible to suppress cracking of the sheet when bending or folding.

[0048] Various thermally conductive silicone rubber sheets are already available on the market, including TC-20CG (manufactured by Shin-Etsu Chemical Co., Ltd.), TC-30BG (manufactured by Shin-Etsu Chemical Co., Ltd.), TC-15TAP-2 (manufactured by Shin-Etsu Chemical Co., Ltd.), TC-20TAG-8 (manufactured by Shin-Etsu Chemical Co., Ltd.), TC-20TA-1 (manufactured by Shin-Etsu Chemical Co., Ltd.), TC-20TAG-2 (manufactured by Shin-Etsu Chemical Co., Ltd.), and TC-20TAP-2 (manufactured by Shin-Etsu Chemical Co., Ltd.). These are merely examples and not the only products available.

[0049] [Thermo-softening silicone gel layer] The thermo-softening silicone gel layer contains thermo-softening silicone gel. Thermo-softening means that when heated from room temperature (25°C), it becomes less viscous and more fluid. In other words, when a thermo-conductive composite silicone rubber sheet, which has a thermo-softening silicone gel layer laminated as an adhesive layer on a thermo-conductive silicone rubber sheet, is mounted, for example, at the interface between a heating element and a cooling element, the thermo-softening silicone gel layer softens and becomes fluid due to the heat from the heating element, improving the contact state with the adherend and suppressing the increase in thermal resistance. In addition, because it is a gel, it has adhesive properties and can adhere to the adherend simply by contact when mounted at the interface between the heating element and the cooling element.

[0050] The absolute viscosity of the thermosoftening silicone gel layer at 70°C is between 5 Pa·s and 1,000 Pa·s. If the absolute viscosity of the thermosoftening silicone gel layer at 70°C is higher than 1,000 Pa·s, it becomes difficult to adequately fill the voids with the adherend, and if it is lower than 5 Pa·s, the fluidity is too high, which may lead to leakage.

[0051] The absolute viscosity can be measured using the HAAKE RotoVisco 1 rotational viscometer. Specifically, a sample of silicone resin is placed between two horizontally positioned discs, one above and one below a vertical central axis: a lower flat disc (20 mm in diameter) and an upper cone-shaped disc (20 mm in diameter, cone angle 2°, trunk 0.1 mm). The flat disc is fixed, and the cone-shaped disc is rotated around the central axis at a speed of 10 s. －１ It can be measured by rotating it.

[0052] The thickness of the thermo-softening silicone gel layer is 5 to 100 μm, preferably 10 to 50 μm. If it is thinner than 5 μm, it cannot conform to the unevenness of the adherend surface and sufficient adhesion cannot be obtained. If it is thicker than 100 μm, the thermal resistance of the thermally conductive composite silicone rubber sheet becomes too high.

[0053] The tack force of the thermosoftening silicone gel layer of the thermally conductive composite silicone rubber sheet of the present invention is 0.098 N or more, preferably 0.196 N or more, and more preferably 0.294 N or more, as measured by a constant pressure penetration method. If the tack force is less than 0.098 N, sufficient tack force cannot be obtained when in contact with the adherend, resulting in displacement or falling. The upper limit of the tack force is not particularly limited, but it can be, for example, 2.94 N or less.

[0054] The tack force was measured using a solder paste adhesion tester. In this method, the tack force can be measured from the load required to peel off a fixed thermally conductive composite silicone rubber sheet by bringing a probe into contact with the softening silicone gel layer.

[0055] It is preferable that the thermosoftening silicone gel layer of the thermally conductive composite silicone rubber sheet of the present invention contains a thermosoftening silicone gel and a thermoconductor filler. When the thermosoftening silicone gel layer contains a thermosoftening silicone gel and a thermoconductor filler, the increase in thermal resistance can be suppressed even when the film thickness is relatively thick.

[0056] The thermal resistance of the thermosoftening silicone gel layer of the thermally conductive composite silicone rubber sheet is 0.5 cm². ２ - Preferably less than or equal to kW, and more preferably 0.4 cm ２ - It is less than or equal to K / W, and more preferably 0.3 cm ２ • It is less than kW. The thermal resistance is 0.5 cm². ２ - If the value is below K / W, the increase in thermal resistance when tackiness is imparted to the thermally conductive composite silicone rubber sheet can be minimized. There is no particular limit to the lower limit, but for example, 0.01 cm ２ - Can be set to kW or higher.

[0057] The thermal resistance was measured using a TIM-Tester (manufactured by Analystech) compliant with ASTM D 5470, at a measurement temperature of 50°C and a pressure of 0.69 MPa.

[0058] It is preferable that the thermo-softening silicone gel layer of the thermally conductive composite silicone rubber sheet contains phenyl silicone gel. With such a thermo-softening silicone gel layer, component migration between it and the thermally conductive silicone rubber sheet is suppressed, thus improving storage and transportability.

[0059] More specifically, it is preferable that the thermosoftening silicone gel layer is a cured product of a thermosoftening thermally conductive silicone composition containing the following components (A) to (E).

[0060] [Thermo-softening, thermally conductive silicone composition] The above thermo-softening, thermally conductive silicone composition contains the following components (A) to (E), and may optionally contain (F) a non-reactive phenyl-modified organopolysiloxane or other components. (A) Having two or more alkenyl groups in one molecule, with a kinematic viscosity of 100 to 100,000 mm at 25°C ２ / s and R' １ SiO ３／２ Phenyl-modified organopolysiloxane (in the formula R') that does not contain units (T units) １ (A) is a substituted or unsubstituted monovalent hydrocarbon group. (A): 100 parts by mass, (B) an organohydrogenpolysiloxane having at least two hydrosilyl groups at the molecular chain ends: in an amount such that the number of moles of hydrosilyl groups in component (B) is 0.1 to 3 moles per mole of alkenyl groups in component (A), (C) one or more selected from organopolysiloxanes having hydrolyzable functional groups and alkoxysilane compounds represented by the following general formula (2): 10 to 1,000 parts by mass, R ３ ｂ R ４ ｃ Si ( OR ５ ) ４－ｂ－ｃ (2) (wherein, R ３ R is an alkyl group having 6 to 15 carbon atoms, ４ R is an independent monovalent hydrocarbon group having 1 to 15 carbon atoms. ５(A) is an alkyl group having 1 to 6 carbon atoms independently, b is an integer from 1 to 3, c is an integer from 0 to 2, except that b + c is an integer from 1 to 3. (D) One or more thermally conductive fillers selected from the group consisting of metals, metal oxides, metal hydroxides, and metal nitrides: in an amount of 10 to 97% by mass of the whole composition, and (E) Platinum group metal catalyst: 0.01 to 1,000 ppm on a mass basis converted to platinum group metal atoms relative to the mass of component (A).

[0061] If the above-mentioned thermosoftening silicone gel layer is a cured product of such a thermosoftening, thermally conductive silicone composition, then the desired tack strength, thermosoftening properties, and storage properties can be obtained stably.

[0062] [(A) Phenyl-modified organopolysiloxane] Component (A) has two or more alkenyl groups in the molecule, preferably 2 to 10, more preferably 2 to 5, and has a kinematic viscosity of 100 to 100,000 mm at 25°C. ２ It is a phenyl-modified organopolysiloxane with a s property. The main chain is preferably composed of diorganosiloxane units, and is preferably a linear organopolysiloxane.

[0063] The alkenyl group is preferably an alkenyl group having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms. Examples include vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl groups. The vinyl group is particularly preferred. The alkenyl group may be bonded to a silicon atom at the end of the molecular chain, a silicon atom in the middle of the molecular chain, or both.

[0064] Furthermore, the phenyl-modified organopolysiloxane of component (A) above preferably has 0.0000001 to 0.005 mol / g, and more preferably 0.00001 to 0.005 mol / g, of alkenyl groups per molecule.

[0065] Furthermore, component (A) has a phenyl group, and preferably the amount of phenyl groups in one molecule is such that the number of siloxane units containing a phenyl group per total siloxane unit is 5 to 100%. If the amount of phenyl groups in one molecule is within the above range relative to the total siloxane units, the thermal softening properties of the thermally softened thermal conductive silicone composition and the cured product will be good.

[0066] Furthermore, the phenyl group may be contained in either the terminal or side chain, but it is preferable that the phenyl group be contained only in the side chain.

[0067] Furthermore, from the viewpoint of viscosity, groups other than the alkenyl group and phenyl group are preferably alkyl groups having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms. Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group, etc. It is also possible to use alkyl groups in which some of the hydrogen atoms are substituted with halogen atoms. Methyl groups are particularly preferred as alkyl groups.

[0068] Furthermore, the phenyl-modified organopolysiloxane of component (A) above has a kinematic viscosity of 100 to 100,000 mm at 25°C. ２ The kinematic viscosity is / s. In this invention, the kinematic viscosity is the value measured by an Ostwald viscometer as described in JIS Z8803:2011. The kinematic viscosity is preferably 300 to 20,000 mm². ２ / s, and more preferably 500 to 10,000 mm ２ It is / s. The kinematic viscosity is 100 mm ２ A value of 1 / s or higher is preferable because it ensures a sufficient phenyl modification rate. Also, a kinematic viscosity of 100,000 mm² is preferable. ２ A value of / s or less is preferable because it facilitates the handling of the thermosoftening, thermally conductive silicone composition.

[0069] The phenyl-modified organopolysiloxane of component (A) above may be used alone or in combination of two or more types.

[0070] [(B) Organohydrogenpolysiloxane] Component (B) is an organohydrogenpolysiloxane having at least two hydrosilyl groups at the ends of its molecular chain. Preferably, it is an organohydrogenpolysiloxane having two hydrosilyl groups at the ends of its molecular chain and preferably 0 to 10, more preferably 0 to 4, hydrosilyl groups in its side chain. Preferably, there is one hydrosilyl group at each of the two ends of the molecular chain.

[0071] Component (B) can be used if it can undergo an addition reaction with the alkenyl group of component (A) in the presence of the platinum group metal catalyst (E) described later to form a sylalkylene structure.

[0072] The above organohydrogenpolysiloxane is not particularly limited in its molecular structure as long as it has the above properties, and examples include linear structures, branched structures, or linear structures having a partially branched or cyclic structure. A linear structure is preferred.

[0073] The above organohydrogen polysiloxane preferably has a kinematic viscosity of 1 to 1,000 mm at 25°C. ２ / s, more preferably 10-100 mm ２ The kinematic viscosity is 1 mm². ２ If the temperature is 1 / s or higher, the physical properties of the thermosoftening, thermally conductive silicone composition will be good, and 1,000 mm ２ If the value is less than or equal to / s, the extensibility of the thermosoftening, thermally conductive silicone composition will be sufficient.

[0074] The organic group bonded to the silicon atom of the above organohydrogenpolysiloxane preferably includes a monovalent aromatic hydrocarbon group having 6 to 10 carbon atoms, and preferably does not include groups that have hydrosilylation reactivity, such as alkenyl groups or alkynyl groups.

[0075] Furthermore, groups other than the monovalent aromatic hydrocarbon group are preferably alkyl groups, more preferably alkyl groups having 1 to 12 carbon atoms, and more preferably alkyl groups having 1 to 10 carbon atoms. Examples include methyl groups, ethyl groups, propyl groups, butyl groups, hexyl groups, and dodecyl groups. It is also possible to use alkyl groups in which some of the hydrogen atoms are substituted with halogen atoms. Among these, the methyl group is preferred.

[0076] The above organohydrogenpolysiloxanes may be used individually or in combination of two or more types.

[0077] The amount of organohydrogenpolysiloxane in component (B) is preferably such that the number of hydrosilyl groups in component (B) is 0.1 to 3 moles, more preferably 0.5 to 3 moles, and even more preferably 0.7 to 2 moles, per mole of alkenyl groups in component (A). If the amount of component (B) is above the lower limit, the addition reaction proceeds sufficiently and crosslinking is sufficient. If it is below the upper limit, the crosslinked structure tends to be uniform, and the long-term stability of the thermosoftening, thermally conductive silicone composition tends to be good.

[0078] [(C) Compounds having hydrolyzable functional groups] Component (C) is one or more selected from organopolysiloxanes having hydrolyzable functional groups and alkoxysilane compounds represented by the following general formula (2).

[0079] It is preferable that the organopolysiloxane having a hydrolyzable functional group of component (C) is represented by the following general formula (1). If a thermo-softening, thermally conductive silicone composition containing such component (C) is used, the thermally conductive filler can be stably dispersed in the silicone. (In the formula, R １ R is independently an aromatic hydrocarbon group having 6 to 10 carbon atoms, or independently an alkyl group having 1 to 10 carbon atoms. ２ (where a is an alkyl group having 1 to 4 carbon atoms; a is 2 or 3, and n is an integer between 2 and 60; provided that it contains 1% or more of an aromatic hydrocarbon group having 6 to 10 carbon atoms.)

[0080] In the above general formula (1), R １R is independently a monovalent aromatic hydrocarbon group having 6 to 10 carbon atoms, or independently an alkyl group having 1 to 10 carbon atoms. １ Specific examples include aryl groups such as phenyl, tolyl, xyl, and mesityl groups, and alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl, hexyl, octyl, nonyl, and decyl groups. Among these, phenyl and methyl groups are preferred from the viewpoint of ease of synthesis.

[0081] In the above general formula (1), R ２ R is an alkyl group having 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms. ２ Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, and tert-butyl groups. Among these, methyl and ethyl groups are particularly preferred from the viewpoint of hydrolysis of organopolysiloxanes having hydrolyzable functional groups. In addition, in the above general formula (1), a is an integer of 2 or 3, and is preferably 3.

[0082] In the above general formula (1), n ​​is an integer between 2 ≤ n ≤ 60, preferably 9 ≤ n ≤ 30, and more preferably 12 ≤ n ≤ 18. Within this range, it is preferable because it exhibits good compatibility with component (A), which is a phenyl-modified organopolysiloxane, and component (B), which is an organohydrogenpolysiloxane.

[0083] In the above general formula (1), the content of aromatic hydrocarbon groups having 6 to 10 carbon atoms is 1% or more, preferably 3% or more.

[0084] Alkoxysilane compounds are represented by the following general formula (2). ３ ｂ R ４ ｃ Si ( OR ５ ) ４－ｂ－ｃ (2) (wherein, R ３ R is an alkyl group having 6 to 15 carbon atoms, ４ R is an independent monovalent hydrocarbon group having 1 to 15 carbon atoms. ５(where b is an alkyl group having 1 to 6 carbon atoms, b is an integer from 1 to 3, c is an integer from 0 to 2, and b + c is an integer from 1 to 3.)

[0085] In the above general formula (2), R ３ Examples of alkyl groups having 6 to 15 carbon atoms represented by this R include hexyl, octyl, nonyl, decyl, dodecyl, and tetradecyl groups. ３ When the number of carbon atoms in the alkyl group represented by satisfies the range of 6 to 15, the wettability of component (A) is sufficiently improved, and handling becomes easier.

[0086] In the above general formula (2), R ４ Examples of monovalent hydrocarbon groups represented by include alkyl groups having 1 to 5 carbon atoms, preferably 1 to 3; aryl groups having 6 to 15 carbon atoms, preferably 6 to 12; and aralkyl groups having 7 to 15 carbon atoms, preferably 7 to 12. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and neopentyl groups. Examples of aryl groups include phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups. Examples of aralkyl groups include benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups. Among these, methyl, ethyl, propyl, and phenyl groups are preferred.

[0087] In the above general formula (2), R ５ Examples of alkyl groups having 1 to 6 carbon atoms represented by this formula include methyl, ethyl, propyl, butyl, and hexyl groups.

[0088] The amount of component (C) is preferably 10 to 1,000 parts by mass, and more preferably 10 to 500 parts by mass, per 100 parts by mass of component (A). If the amount is 10 parts by mass or more, the surface treatment of the thermal conductive filler will be sufficient, and the thermal conductive filler will be easily blended into the silicone. If the amount is 1,000 parts by mass or less, the cured product will have an appropriate hardness, and the thermo-softening silicone gel layer will not be damaged when the thermal conductive composite silicone rubber sheet is peeled off the release film.

[0089] [(D) Thermally conductive filler] Component (D) is one or more thermally conductive fillers selected from the group consisting of metals, metal oxides, metal hydroxides, and metal nitrides. Examples include aluminum, silver, alumina (aluminum oxide), zinc oxide, magnesium oxide, silicon dioxide, cerium oxide, iron oxide, aluminum hydroxide, cerium hydroxide, aluminum nitride, boron nitride, etc. These can be used individually or in appropriate combinations of two or more, and it is preferable that they are a combination of large particle components and small particle components.

[0090] The amount of component (D) is preferably 10 to 97% by mass of the total composition, more preferably 20 to 93% by mass, even more preferably 30 to 92% by mass, and particularly preferably 50 to 90% by mass. If the amount is 97% by mass or less, the viscosity of the thermosoftening thermally conductive silicone composition decreases, resulting in good processability. If the amount is 10% by mass or more, good thermal conductivity is achieved.

[0091] The average particle size of the large particle components is preferably in the range of 0.1 to 100 μm, and more preferably in the range of 1 to 75 μm. If it is 0.1 μm or larger, the viscosity of the resulting composition will not become too high and the processability will not decrease. If it is 100 μm or smaller, there is no risk of the resulting composition becoming non-uniform, or of oil bleeding or a decrease in compressibility.

[0092] Furthermore, the average particle size of the small particle components is preferably in the range of 0.01 μm or more and less than 10 μm, and more preferably in the range of 0.1 to 4 μm. If it is 0.01 μm or more, the viscosity of the resulting composition will not become too high and the processability will not decrease. On the other hand, if it is less than 10 μm, there is no risk of the resulting composition becoming non-uniform.

[0093] The ratio of large particles to small particles is not particularly limited, but a range of 9:1 to 1:9 (mass ratio) is preferred. Furthermore, the shape of the large and small particles is not particularly limited, and can be spherical, irregular, needle-shaped, etc. Irregular shape refers to any shape that has not undergone intentional spheroidizing treatment such as melting or granulation.

[0094] The average particle size of the thermally conductive filler can be determined, for example, as the volume-based average value (or median diameter) in particle size distribution measurement using laser diffraction.

[0095] [(E) Platinum Group Metal Catalyst] Component (E) is a platinum group metal catalyst that functions to promote the addition reaction of the components described above. Conventional platinum group metal catalysts used in addition reactions can be used. Examples include platinum-based, palladium-based, and rhodium-based catalysts, but platinum or platinum compounds, which are relatively easy to obtain, are preferred. Examples include elemental platinum, platinum black, chloroplatinic acid, platinum-olefin complexes, platinum-alcohol complexes, and platinum coordination compounds. A single platinum group metal catalyst or a combination of two or more may be used.

[0096] The amount of component (E) is preferably 0.01 to 1,000 ppm, and more preferably 10 to 1,000 ppm, based on the mass of platinum group metal atoms relative to the mass of component (A). If the amount of catalyst is above the lower limit, the catalytic effect can be obtained. If it is below the upper limit, it is preferable because it is more economical.

[0097] [(F) Non-reactive phenyl-modified organopolysiloxane] In addition to the above components, a non-reactive phenyl-modified organopolysiloxane that does not undergo hydrosilylation reactions with components (A) and (B) or condensation reactions with component (C) may be used. The molecular structure of the non-reactive phenyl-modified organopolysiloxane is not particularly limited as long as it has the above properties, and examples include a linear structure, a branched structure, or a linear structure having a partially branched or cyclic structure. A linear structure is preferred.

[0098] Furthermore, component (F) above has a phenyl group. The amount of phenyl groups in one molecule is preferably 10 to 100%, and more preferably 30% to 100%, of the number of siloxane units containing a phenyl group per side-chain siloxane unit. If the amount of phenyl groups in one molecule is 10% or more relative to the side-chain siloxane units, the change in viscosity at temperature of the thermo-softening, thermo-conductive silicone composition and the cured product is favorable.

[0099] Furthermore, from the viewpoint of viscosity, groups other than the phenyl group are preferably alkyl groups having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms. Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group, etc. It is also possible to use alkyl groups in which some of the hydrogen atoms are substituted with halogen atoms. Among alkyl groups, the methyl group is particularly preferred.

[0100] Furthermore, non-reactive phenyl-modified organopolysiloxanes have a kinematic viscosity of 100 to 100,000 mmHg at 25°C. ２ It is preferably / s, and more preferably 300 to 10,000 mm ２ / s, and more preferably 500 to 5,000 mm ２ It is / s. The kinematic viscosity is 100 mm ２ A value of 1 / s or higher is preferable because it indicates a sufficient phenyl modification rate. Also, a kinematic viscosity of 100,000 mm² is preferable. ２ A value of / s or less is preferable because it facilitates the handling of the thermosoftening, thermally conductive silicone composition.

[0101] The amount of component (F) is preferably 1 to 500 parts by mass, more preferably 1 to 100 parts by mass, and even more preferably 5 to 50 parts by mass, per 100 parts by mass of component (A). With such a blending amount, the thermosoftening silicone gel layer can be softened, making it possible to control the adhesive strength.

[0102] In other words, it is preferable that the heat-softening, heat-conductive silicone composition further contains, as component (F), 1 to 500 parts by mass of a non-reactive phenyl-modified organopolysiloxane per 100 parts by mass of component (A).

[0103] Component (F) may be used alone or in combination of two or more types.

[0104] [Other Components] Depending on the purpose and effects of the present invention, other components may be further added to the heat-softening, heat-conductive silicone composition of the present invention. For example, optional components such as hydrosilylation reaction regulators, heat-resistant improvers such as iron oxide, viscosity modifiers such as silica, and mold release agents may be added.

[0105] [Manufacturing Process for Thermoflexible Thermal Conductive Silicone Composition] The manufacturing method for the thermoflexible thermal conductive silicone composition according to the present invention will now be described. The manufacturing method for the thermoflexible thermal conductive silicone composition according to the present invention is not particularly limited.

[0106] One method of mixing the above-mentioned components (A) to (E), and component (F) and other components as needed, is to use a mixer such as a rotation / revolution type mixer (product name: Awatori Rentaro, manufactured by THINKY Co., Ltd.), Trimix, Twinmix, Planetary Mixer (all manufactured by Inoue Seisakusho Co., Ltd.), Ultra Mixer (Mizuho Industries Co., Ltd.), or Hibiscus Disper Mix (Tokushu Kika Kogyo Co., Ltd.). Alternatively, all components may be mixed at once, or one or more components may be mixed in several stages.

[0107] In the present invention, it is preferable to first mix components (A), (C), and (D) at room temperature, and then mix in components (B) and (E), and component (F) and other components if present. Heating may be performed if necessary.

[0108] [Manufacturing process for heat-softening, heat-conducting silicone cured product] The above heat-softening, heat-conducting silicone composition can be heated to a temperature of 40 to 180°C, preferably 60 to 150°C, and more preferably 80 to 120°C, by which component (A) and component (B) undergo a hydrosilylation reaction to obtain a cured product.

[0109] [Manufacturing Process for Thermally Conductive Composite Silicone Rubber Sheets] The manufacturing method for thermally conductive composite silicone rubber sheets according to the present invention will now be described. The manufacturing method for thermally conductive composite silicone rubber sheets according to the present invention is not particularly limited. For example, a thermally conductive composite silicone rubber sheet can be obtained by coating one or both sides of a thermally conductive silicone rubber sheet with a thin film of a silicone composition before curing and then curing it. The silicone composition may be diluted with a solvent or the like to improve its coatability, in which case it is preferable to add a drying step for solvent drying before the curing step. After curing, a release paper or release film may be provided on the thermo-softening silicone gel layer for the purpose of protection and improved handling.

[0110] In addition, a thin film of the uncured silicone composition can be applied to the release surface of release paper or release film, cured, and the exposed heat-softening silicone gel cured product can be laminated to one or both sides of a heat-conductive silicone rubber sheet. In this case, heat lamination is also effective in improving the adhesion between the heat-softening silicone gel cured product and the heat-conductive silicone rubber sheet.

[0111] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these. The Type A hardness was measured using the method described in JIS K6253:2012. The kinematic viscosity was measured using an Ostwald viscometer as described in JIS Z8803:2011.

[0112] [Thermally conductive silicone rubber sheet] For the thermally conductive silicone rubber sheet, either option 1 or 2 below was used.

[0113] 1. Dimethyl silicone rubber glass cloth reinforced thermal conductive silicone rubber sheet (product name: TC-20TAG-2, manufactured by Shin-Etsu Chemical Co., Ltd., thickness 200 μm, thermal conductivity 1.4 W / mK, Type A hardness 88, peroxide curing)

[0114] 2. Dimethyl silicone rubber glass cloth reinforced thermal conductive silicone rubber sheet (product name: TC-20TAG-8, manufactured by Shin-Etsu Chemical Co., Ltd., thickness 200 μm, thermal conductivity 4.0 W / mK, Type A hardness 84, peroxide curing)

[0115] [Thermoplastic silicone gel layer] (Preparation of thermoplastic silicone composition) The components (A) to (F) used in the following Examples and Comparative Examples are shown below. Here, Me represents a methyl group and Ph represents a phenyl group.

[0116] Component (A) (A-1): Phenyl-modified organopolysiloxane having a kinematic viscosity of 2,000 mm ２ ·s －１

[0117] (A-2): Phenyl-modified organopolysiloxane having a kinematic viscosity of 700 mm ２ ·s －１

[0118] (A-3): Silicone resin represented by the following formula D ２５ T Φ ５５ D Ｖｉ ２０ However, D is Me ２ SiO ２／２ 、T Φ is PhSiO ３／２ 、D Ｖｉ is ViMeSiO ２／２

[0119] Component (B) (B-1): Phenyl-modified organohydrogenpolysiloxane having hydrosilyl groups at both ends of the molecular chain and having a kinematic viscosity of 4 mm ２ ·s －１

[0120] (B-2): Phenyl-modified organohydrogenpolysiloxane having hydrosilyl groups at both ends and side chains of the molecular chain and having a kinematic viscosity of 20 mm ２ ·s －１

[0121] (B-3): Phenyl-modified organohydrogenpolysiloxane having hydrosilyl groups in the side chain and having a kinematic viscosity of 20 mm ２ ·s －１

[0122] (C) Component (C-1): Hydrolyzable organopolysiloxane represented by the following formula (aromatic hydrocarbon group content: 8.3%)

[0123] (C-2): Decyltrimethoxysilane C represented by the following formula １０ H ２１ Si(OCH) ３ ) ３

[0124] (D) Component The average particle size of the thermally conductive filler in component (D) was measured using a particle size distribution analyzer MT3000II (manufactured by Microtrac-Bell Co., Ltd.). (D-1): Spherical aluminum oxide powder (average particle size: 3 μm) (D-2): Amorphous aluminum oxide powder (average particle size: 2 μm) (D-3): Amorphous zinc oxide powder (average particle size: 1 μm)

[0125] (E) Component: 5% 2-ethylhexanol chloroplatinate solution

[0126] (F) Component: Phenyl-modified organosiloxane represented by the following formula

[0127] [Manufacturing Method] The compositions of the examples and comparative examples were obtained by mixing components (A) to (F) of the thermosoftening silicone gel composition as follows. Components (A), (C), (D), and (F) were weighed out in a metal kettle in a planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.) in the composition ratio (parts by mass) shown in Table 1, and stirred at room temperature and 30 rpm for 1 hour. Then, component (E) was added and stirred at room temperature and 30 rpm for 30 minutes. Furthermore, component (B) was added and stirred at room temperature and 30 rpm for 20 minutes to obtain the composition.

[0128] Cured Thermoplastic Silicone Gel The obtained thermoplastic silicone gel composition was diluted with toluene to a solvent concentration of 20% by mass and applied to a 50 μm thick fluorine-treated peelable PET (product name FL1-01: manufactured by Takaline Corporation). After drying in an 80°C oven for 10 minutes, it was cured in a 120°C oven for 10 minutes to obtain a cured thermoplastic silicone gel. The physical properties of the prepared cured thermoplastic silicone gel are shown in Table 1.

[0129] A thermally conductive composite silicone rubber sheet was obtained by thermally pressing a heat-softening silicone gel cured material onto one side of a thermally conductive composite silicone rubber sheet 1 or 2. The composition and physical properties of the fabricated thermally conductive composite silicone rubber sheet are shown in Table 2.

[0130] [Evaluation Method] [Thickness] Measured using a Mitutoyo micrometer.

[0131] [Absolute viscosity of thermosoftening silicone gel cured product at 70°C] Measured using a HAAKE RotoVisco 1 rotational viscometer.

[0132] [Tack Force] The tack force of the thermosoftening silicone gel layer of a thermally conductive composite silicone rubber sheet was measured using a Takkinestester TK-1 (Malcolm Corporation) with a constant pressure immersion method at a measurement temperature of 25°C.

[0133] [Thermal Resistance Measurement] The thermal resistance of the thermally conductive silicone rubber sheet alone and the obtained thermally conductive composite silicone rubber sheet was measured using a TIM-Tester (manufactured by Analystech) in accordance with ASTM D 5470, under conditions of a measurement temperature of 50°C and a pressure of 0.69 MPa. The thermal resistance of the thermo-softening silicone gel layer was calculated by subtracting the thermal resistance of the thermally conductive silicone rubber sheet alone from the thermal resistance of the thermally conductive composite silicone rubber sheet.

[0134] In the table, the composition of each component is given in parts by mass.

[0135]

[0136] In Comparative Example 1, since silicone resin was used as the thermo-softening silicone gel layer, components contained in the silicone resin migrated from the thermo-softening silicone gel layer to the thermo-conductive silicone rubber sheet, resulting in a significant decrease in tack strength after storage at 40°C, reaching a value of less than 0.098 N.

[0137] As in Comparative Example 2, when a thermosoftening silicone gel layer with an absolute viscosity exceeding 1,000 Pa·s at 70°C was used, the tack force decreased significantly, and the thermosoftening silicone gel layer did not collapse during mounting, resulting in poor adhesion and a large increase in thermal resistance.

[0138] In Comparative Example 3, the thickness of the thermosoftening silicone gel layer exceeded 100 μm, making it less susceptible to crushing during mounting, and as a result, an increase in thermal resistance was observed.

[0139] On the other hand, the thermally conductive composite silicone rubber sheets of Examples 1 to 4 exhibited an initial tack force and a tack force of 0.098 N or higher after storage at 40°C, indicating that they are thermally conductive composite silicone rubber sheets with excellent mountability.

[0140] Furthermore, it can be seen that the thermally conductive composite silicone rubber sheets of Examples 1 to 4 have low thermal resistance in the thermosoftening silicone gel layer, and that the increase in the thermal resistance of the thermally conductive composite silicone rubber sheet is kept to a minimum. From this, it can be seen that the thermally conductive composite silicone rubber sheet in the present invention can be easily placed between a heating element and a cooling area, and can sufficiently transfer the heat from the heating element to the cooling area.

[0141] This specification includes the following embodiments: [1] A thermally conductive composite silicone rubber sheet comprising a thermally conductive silicone rubber sheet and a thermo-softening silicone gel layer disposed on one or both sides of the thermally conductive silicone rubber sheet, having a thickness of 5 to 100 μm and an absolute viscosity of 5 to 1,000 Pa·s at 70°C, wherein the tack force of the thermo-softening silicone gel layer measured by constant pressure penetration using a solder paste adhesion tester is 0.098 N or more. [2] The thermally conductive composite silicone rubber sheet according to [1], wherein the thermo-softening silicone gel layer comprises a thermo-softening silicone gel and a thermally conductive filler. [3] The thermal resistance of the thermo-softening silicone gel layer measured at a measurement temperature of 50°C and a pressure of 0.69 MPa using a TIM-Tester (manufactured by Analystech) conforming to ASTM D 5470 is 0.5 cm２ - The heat-conductive composite silicone rubber sheet according to [1] or [2] above, characterized by being K / W or less. [4]: The silicone rubber component of the heat-conductive silicone rubber sheet is composed of dimethylsiloxane units, and the heat-conductive composite silicone rubber sheet according to any one of [1] to [3] above is characterized in that. [5]: The heat-conductive silicone rubber sheet contains a glass cloth and / or a plastic film, and the heat-conductive composite silicone rubber sheet according to any one of [1] to [4] above is characterized in that. [6]: The heat-conductive composite silicone rubber sheet according to any one of [1] to [5] above, characterized in that the Type A hardness measured by the method described in JIS K6253:2012 of the heat-conductive silicone rubber sheet is 50 to 100. [7]: The heat-conductive composite silicone rubber sheet according to any one of [1] to [6] above, characterized in that the heat-softening silicone gel layer contains a phenyl silicone gel. [8]: The heat-conductive composite silicone rubber sheet according to any one of [1] to [7] above, characterized in that the heat-softening silicone gel layer is a cured product of a heat-softening heat-conductive silicone composition containing the following components (A) to (E). (A) A phenyl-modified organopolysiloxane having two or more alkenyl groups in one molecule, with a kinematic viscosity at 25°C of 100 to 100,000 mm ２ / s and not containing R’ １ SiO ３／２ units (T units) (where R’ １ is a substituted or unsubstituted monovalent hydrocarbon group.): 100 parts by mass, (B) An organohydrogenpolysiloxane having at least two hydrosilyl groups at the molecular chain ends, in an amount such that the molar number of hydrosilyl groups in component (B) is 0.1 to 3 moles per mole of the alkenyl group in component (A), (C) One or more selected from an organopolysiloxane having a hydrolyzable functional group and an alkoxysilane compound represented by the following general formula (2): 10 to 1,000 parts by mass, R ３ ｂ R ４ ｃ Si(OR ５ ) ４－ｂ－ｃ(2) (wherein, R ３ R is an alkyl group having 6 to 15 carbon atoms, ４ R is an independent monovalent hydrocarbon group having 1 to 15 carbon atoms. ５ (A) is an alkyl group having 1 to 6 carbon atoms independently, b is an integer from 1 to 3, and c is an integer from 0 to 2, provided that b + c is an integer from 1 to 3. (D) One or more thermally conductive fillers selected from the group consisting of metals, metal oxides, metal hydroxides, and metal nitrides: in an amount of 10 to 97% by mass of the whole composition, and (E) Platinum group metal catalyst: 0.01 to 1,000 ppm by mass on a basis converted to platinum group metal atoms with respect to the mass of component (A). [9]: The thermally conductive composite silicone rubber sheet of [8] above, characterized in that the organopolysiloxane having a hydrolyzable functional group of component (C) is represented by the following general formula (1). (In the formula, R １ R is independently an aromatic hydrocarbon group having 6 to 10 carbon atoms, or independently an alkyl group having 1 to 10 carbon atoms. ２ (a) is an alkyl group having 1 to 4 carbon atoms. a is 2 or 3, and n is an integer between 2 and n ≤ 60. (However, it contains 1% or more of an aromatic hydrocarbon group having 6 to 10 carbon atoms.)

[10] : The thermally conductive composite silicone rubber sheet according to [8] or [9] above, characterized in that the thermally softening thermally conductive silicone composition further contains, as component (F), 1 to 500 parts by mass of a non-reactive phenyl-modified organopolysiloxane per 100 parts by mass of component (A).

[0142] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A thermally conductive composite silicone rubber sheet comprising a thermally conductive silicone rubber sheet and a thermo-softening silicone gel layer disposed on one or both sides of the thermally conductive silicone rubber sheet, having a thickness of 5 to 100 μm and an absolute viscosity of 5 to 1,000 Pa·s at 70°C, wherein the tack force of the thermo-softening silicone gel layer, measured using a constant-pressure penetration method with a solder paste adhesion tester, is 0.098 N or more.

2. The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that the thermally softening silicone gel layer comprises a thermally softening silicone gel and a thermally conductive filler.

3. Using a TIM-Tester (manufactured by Analystech) compliant with ASTM D 5470, the thermal resistance of the thermosoftening silicone gel layer was measured at a measurement temperature of 50°C and a pressure of 0.69 MPa and was found to be 0.5 cm². ２ The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that it is less than or equal to K / W.

4. The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that the silicone rubber component of the thermally conductive silicone rubber sheet consists of dimethylsiloxane units.

5. The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that the thermally conductive silicone rubber sheet contains either glass cloth or plastic film, or both thereof.

6. The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that the Type A hardness of the thermally conductive silicone rubber sheet measured by the method described in JIS K6253:2012 is 50 to 100.

7. The thermally conductive composite silicone rubber sheet according to claim 1, characterized in that the thermosoftening silicone gel layer contains phenyl silicone gel.

8. The heat-conductive composite silicone rubber sheet according to any one of claims 1 to 7, wherein the thermoplastic silicone gel layer is a cured product of a thermoplastic heat-conductive silicone composition containing the following components (A) to (E). (A) A phenyl-modified organopolysiloxane having two or more alkenyl groups in one molecule and a kinematic viscosity at 25°C of 100 to 100,000 mm ２ / s and not containing R’ １ SiO ３／２ units (T units) (where R’ １ is a substituted or unsubstituted monovalent hydrocarbon group): 100 parts by mass, (B) An organohydrogenpolysiloxane having at least two hydrosilyl groups at the molecular chain terminals, in an amount such that the molar number of hydrosilyl groups in component (B) is 0.1 to 3 moles with respect to 1 mole of the alkenyl groups possessed by component (A), (C) One or more selected from an organopolysiloxane having a hydrolyzable functional group and an alkoxysilane compound represented by the following general formula (2): 10 to 1,000 parts by mass. R ３ ｂ R ４ ｃ Si(OR ５ ) ４－ｂ－ｃ (2) (In the formula, R ３ is independently an alkyl group having 6 to 15 carbon atoms, R ４ is independently a monovalent hydrocarbon group having 1 to 15 carbon atoms, R ５ is independently an alkyl group having 1 to 6 carbon atoms, b is an integer of 1 to 3, c is an integer of 0 to 2, provided that b + c is an integer of 1 to 3.) (D) One or more heat-conductive fillers selected from the group consisting of metals, metal oxides, metal hydroxides, and metal nitrides: in an amount of 10 to 97% by mass based on the whole composition, and (E) A platinum group metal catalyst: 0.01 to 1,000 ppm on a mass basis in terms of platinum group metal atoms with respect to the mass of component (A).

9. The thermally conductive composite silicone rubber sheet according to claim 8, characterized in that the organopolysiloxane having a hydrolyzable functional group of component (C) is represented by the following general formula (1). (In the formula, R １ R is independently an aromatic hydrocarbon group having 6 to 10 carbon atoms, or independently an alkyl group having 1 to 10 carbon atoms. ２ (where a is an alkyl group having 1 to 4 carbon atoms; a is 2 or 3, and n is an integer between 2 and 60; provided that it contains 1% or more of an aromatic hydrocarbon group having 6 to 10 carbon atoms.) 10. The thermally conductive composite silicone rubber sheet according to claim 8, characterized in that the thermally softening thermally conductive silicone composition further contains, as component (F), 1 to 500 parts by mass of a non-reactive phenyl-modified organopolysiloxane per 100 parts by mass of component (A).

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