Thermally conductive composite silicone rubber sheet

Abstract

To provide a thermally conductive composite silicone rubber sheet that can express adhesiveness by instantaneous contact while suppressing oil bleeding.SOLUTION: A thermally conductive composite silicone rubber sheet has a thermally conductive silicone rubber sheet, and a thermosoftening silicone resin layer which is arranged for one side or both sides of the thermally conductive silicone rubber sheet, has a thickness of 0.5 to 10 μm, and absolute viscosity of 10 to 700 Pa s at 70°C, where the thermosoftening silicone resin layer consists of (A) thermosoftening silicone resin in which a ratio of phenyl group to the number of all substituents directly connected to a silicon atom is 20 mol% or more: 75 to 95 mass%, and (B) diphenylsiloxy group-containing organopolysiloxane expressed by a specific structure: 5 to 25 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive composite silicone rubber sheet that is used for heat dissipation, for example, by being placed between a heat-generating component and a heat-dissipating component in an electronic device. [Background technology]

[0002] Conventionally, heat sinks made of metal plates with high thermal conductivity, such as aluminum or copper, have been used in electronic devices to suppress temperature increases in semiconductors during operation. Electrical insulation must be maintained between the semiconductor and the heat sink, and it is known that both insulation and thermal conductivity can be achieved by using a thermally conductive silicone rubber sheet, which is made by filling a polymer such as silicone with a thermally conductive filler to give it thermal conductivity.

[0003] Furthermore, when mounting a thermally conductive silicone rubber sheet between a heat-generating element such as a semiconductor and a cooling plate such as a heat sink, the sheet is secured in place using screws or spring clips. However, due to process issues during mounting, adhesiveness is required on at least one side of the thermally conductive silicone rubber sheet. This is because the mounting location of the thermally conductive silicone rubber sheet must be aligned during mounting. Without an adhesive layer, the sheet may be misaligned from the desired mounting location. Furthermore, due to mounting process circumstances, the thermally conductive silicone rubber sheet may need to be attached vertically.

[0004] Applying an adhesive layer to a thermally conductive silicone rubber sheet is a known technique, and applying an adhesive layer has been used to address the mounting process (Patent Documents 1, 2, and 3). However, the adhesive layer applied to conventional thermally conductive silicone rubber sheets is approximately 10 to 50 μm thick, significantly reducing thermal conductivity due to its thickness. While thinning the adhesive layer to improve thermal conductivity does improve thermal conductivity, it also reduces adhesive strength. While adding thermal conductivity to the adhesive layer itself is an alternative approach, adding a thermally conductive filler to the adhesive layer would also reduce adhesive strength. Therefore, increasing the thickness of the adhesive layer is considered a way to ensure adhesive strength, but doing so sacrifices thermal conductivity. Thus, adhesive strength and thermal conductivity are in a tradeoff relationship, and a method for adding adhesive strength without sacrificing thermal conductivity has long been needed.

[0005] Patent Document 4 proposes a thermally conductive composite silicone rubber sheet that combines adhesive strength, heat dissipation performance, and long-term reliability by providing a 0.5-10 μm thick heat-softening silicone resin layer. However, to ensure sufficient adhesion of the thermally conductive silicone rubber sheet and prevent it from peeling or falling off the adherend, a pressure-bonding step for several to several tens of seconds is essential when attaching the sheet. To shorten these assembly steps, it is essential to improve tack, which is generally expressed as the adhesiveness that appears with momentary contact. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-193598 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-193491 [Patent Document 3] International Publication No. 2018 / 070351 [Patent Document 4] Japanese Patent Publication No. 2020-203457 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and aims to provide a thermally conductive composite silicone rubber sheet in which a heat-softening silicone resin layer is provided on one or both sides of a thermally conductive silicone rubber sheet, which is capable of exhibiting adhesiveness with instantaneous contact while suppressing oil bleeding. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a heat-conductive silicone rubber sheet, a heat-softening silicone resin layer disposed on one or both sides of the heat-conductive silicone rubber sheet, the layer having a thickness of 0.5 to 10 μm and an absolute viscosity at 70°C of 10 to 700 Pa·s; A thermally conductive composite silicone rubber sheet having The heat-softenable silicone resin layer is (A) a thermosoftening silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms is 20 mol % or more: 75 to 95 mass %; and (B) 5 to 25 mass% of a diphenylsiloxy group-containing organopolysiloxane represented by the following formula (1): [ka] (In the formula, m is an integer of 3 to 5, and n is an integer of 5 to 12.) The present invention provides a thermally conductive composite silicone rubber sheet comprising:

[0009] In a heat-conductive composite silicone rubber sheet having such a heat-softening silicone resin layer, the silicone rubber component of the heat-conductive silicone rubber sheet and the resin component (component (A)) of the heat-softening silicone resin layer are not too compatible, so the resin component of the heat-softening silicone resin layer disperses throughout the heat-conductive silicone rubber sheet, preventing a decrease in adhesive strength during storage. This allows adhesiveness to be achieved with just a momentary contact. Furthermore, the diphenylsiloxy group-containing organopolysiloxane (component (B)) is properly retained within the resin layer, preventing oil bleeding to the outside.

[0010] The component (A) is represented by the following formula (2) or (3): D p T φ q D Vi r (2) (where D is the dimethylsiloxane unit: (CH3)2SiO 2 / 2 represents T φ is the phenylsiloxane unit: (C6H5)SiO 3 / 2 represents D Vi is the methylvinylsiloxane unit: (CH3)(CH2=CH)SiO 2 / 2 where p, q, and r satisfy the molar ratio (p+r) / q = 0.25 to 4.0, and the molar ratio (p+r) / r = 1.0 to 4.0. M L D p T φ q D Vi r (3) (where M is a trimethylsiloxane unit: (CH3)3SiO 1 / 2 represents D, T φ and D Vi are as described above, and p, q, r, and L satisfy the following: (p+r) / q (molar ratio) = 0.25 to 4.0, (p+r) / r (molar ratio) = 1.0 to 4.0, and L / (p+r) (molar ratio) = 0.001 to 0.1. Preferably, the silicone resin is a heat-softenable silicone resin represented by the formula:

[0011] If the thermosoftening silicone resin of component (A) is one of the above, it will be possible to achieve superior adhesiveness with only a momentary contact.

[0012] The tack strength of the heat-softening silicone resin layer measured by the probe tack test according to ASTM D2979 is 2.0 N / cm 2 It is preferable that this is equal to or greater than this.

[0013] Tack strength: 2.0N / cm 2 If the adhesive strength is more than this, it is possible to fix the adhesive to the adherend without applying additional pressure.

[0014] The silicone rubber component of the thermally conductive silicone rubber sheet preferably comprises a dimethylsiloxane unit.

[0015] Thus, the heat-conductive silicone rubber sheet preferably contains a silicone rubber component consisting of dimethylsiloxane units, i.e., is preferably dimethylsilicone rubber. Such a material can inhibit the diffusion of the diphenylsiloxy group-containing organopolysiloxane, which is component (B) of the heat-softening silicone resin layer.

[0016] The heat-conductive silicone rubber sheet preferably contains glass cloth and / or a plastic film.

[0017] If the sheet contains glass cloth, it will have excellent strength, and if it contains plastic film, it will have even better electrical insulation properties.

[0018] In this case, it is preferable that the Type A hardness of the thermally conductive silicone rubber sheet is 50 to 100 as measured by the method described in JIS K6253:2012.

[0019] Within this range, thickness changes and cracks in the thermally conductive silicone rubber sheet can be suppressed, and stable insulation properties can be maintained. [Effects of the Invention]

[0020] As described above, the thermally conductive composite silicone rubber sheet of the present invention can exhibit adhesiveness with just a momentary contact while suppressing oil bleeding. For example, when mounted at the interface between a heating element and a cooling member, the sheet can adhere to the substrate simply by contacting it, thereby shortening processing time and significantly improving production efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0021] As described above, there has been a need for the development of a thermally conductive composite silicone rubber sheet that has an adhesive layer on one or both sides of the thermally conductive silicone rubber sheet, which can exhibit adhesiveness upon momentary contact while suppressing oil bleeding.

[0022] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that a thermally conductive composite silicone rubber sheet having a thermally softenable silicone resin layer on one or both sides thereof, the thermally softenable silicone resin layer comprising (A) 75 to 95 mass% of a thermosoftenable silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms is 20 mol% or more, and (B) 5 to 25 mass% of a diphenylsiloxy group-containing organopolysiloxane represented by the above formula (1), and having a thickness of 0.5 to 10 μm and an absolute viscosity at 70°C of 10 to 700 Pa s, can suppress oil-bleeding and exhibit adhesion upon momentary contact, thereby completing the present invention.

[0023] That is, the present invention provides a heat-conductive silicone rubber sheet, a heat-softening silicone resin layer disposed on one or both sides of the heat-conductive silicone rubber sheet, the layer having a thickness of 0.5 to 10 μm and an absolute viscosity at 70°C of 10 to 700 Pa·s; A thermally conductive composite silicone rubber sheet having The heat-softenable silicone resin layer is (A) a thermosoftening silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms is 20 mol % or more: 75 to 95 mass %; and (B) 5 to 25 mass% of a diphenylsiloxy group-containing organopolysiloxane represented by the following formula (1): [ka] (In the formula, m is an integer of 3 to 5, and n is an integer of 5 to 12.) The thermally conductive composite silicone rubber sheet is characterized by comprising:

[0024] In the thermally conductive composite silicone rubber sheet of the present invention, the silicone rubber component of the thermally conductive silicone rubber sheet and the resin component (component (A)) of the heat-softening silicone resin layer are not too compatible, so the resin component of the heat-softening silicone resin layer disperses throughout the thermally conductive silicone rubber sheet, preventing a decrease in adhesive strength during storage. This allows adhesiveness to be achieved with just a momentary contact. Furthermore, the diphenylsiloxy group-containing organopolysiloxane (component (B)) is properly retained within the resin layer, preventing oil bleeding to the outside.

[0025] The present invention will be described in detail below, but the present invention is not limited thereto.

[0026] [Thermal conductive silicone rubber sheet] The thermally conductive silicone rubber sheet included in the thermally conductive composite silicone rubber sheet of the present invention is, for example, a thermally conductive silicone rubber composition obtained by adding a thermally conductive filler and a curing agent to a silicone polymer, kneading the mixture, molding the resulting mixture into a sheet by any method, and curing the resulting mixture. However, the thermally conductive silicone rubber sheet included in the thermally conductive composite silicone rubber sheet of the present invention is not particularly limited as long as it is a thermally conductive silicone rubber sheet.

[0027] The kneading is preferably carried out by a kneading method that generates shear force, such as a planetary mixer, kneader, or two-roll mill, but is not particularly limited.Methods for molding the thermally conductive silicone rubber composition into a sheet include, but are not particularly limited to, calendar molding, coating molding, and extrusion molding.

[0028] The curing form of the thermally conductive silicone rubber composition is not particularly limited, but examples include addition-cured silicone rubbers cured by a hydrosilylation reaction, peroxide-cured silicone rubbers cured by a peroxide catalyst, and condensation-cured silicone rubbers cured by a condensation reaction of silanol, etc. Among these, addition-cured or peroxide-cured silicone rubbers are preferred in terms of the time required for curing.

[0029] The silicone polymer can be selected arbitrarily depending on the desired physical properties of the cured product, but is preferably a dimethylsilicone polymer in which all of the substituents directly bonded to the silicon atoms of the silicone polymer, except for reactive sites such as alkenyl groups, hydrosilyl groups, and hydroxyl groups, are methyl groups. In other words, the silicone rubber component of the thermally conductive silicone rubber sheet is preferably composed of dimethylsiloxane units. Such a silicone polymer is preferred because it can suppress the diffusion of the diphenylsiloxy group-containing organopolysiloxane contained in the heat-softenable silicone resin layer described below.

[0030] 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 can sufficiently transfer heat from the heating element to the cooling area. There is no particular upper limit to the thermal conductivity, and as long as it can be molded into a sheet, a higher thermal conductivity is preferred because it allows for more efficient transfer of heat from the heating element to the cooling area.

[0031] The thickness of the thermally conductive silicone rubber sheet is preferably between 0.08 mm and 1.2 mm. If it is 0.08 mm or more, sufficient insulation can be ensured. If it is 1.2 mm or less, insulation can be ensured and heat from the heating element can be sufficiently transferred to the cooling area.

[0032] The thermally conductive silicone rubber sheet may contain glass cloth and / or plastic film. For example, glass cloth may be added for reinforcement, or plastic film may be added for insulation. For example, the thermally conductive silicone rubber sheet may contain two silicone rubber layers and an intermediate layer between them, and the intermediate layer may contain the above-mentioned material.

[0033] If the sheet contains glass cloth, it will have excellent strength, and if it contains plastic film, it will have even better electrical insulation properties.

[0034] The thermally conductive silicone rubber sheet containing the glass cloth and / or plastic film preferably has a Type A hardness of 50 to 100, as measured by the method described in JIS K6253:2012. A Type A hardness of 50 or more can prevent instability in insulation due to changes in thickness caused by the fixing pressure of screws or clips when the thermally conductive composite silicone rubber sheet is mounted. Furthermore, a Type A hardness of 100 or less can prevent the sheet from cracking due to folding or bending.

[0035] Various thermally conductive silicone rubber sheets are already available on the market, including TC-20CG (Shin-Etsu Chemical Co., Ltd.), TC-30BG (Shin-Etsu Chemical Co., Ltd.), TC-15TAP-2 (Shin-Etsu Chemical Co., Ltd.), TC-20TAG-8 (Shin-Etsu Chemical Co., Ltd.), TC-20TA-1 (Shin-Etsu Chemical Co., Ltd.), TC-20TAG-2 (Shin-Etsu Chemical Co., Ltd.), TC-20TAP-2 (Shin-Etsu Chemical Co., Ltd.), etc. These are merely examples and are not intended to be limiting.

[0036] [Thermosoftening silicone resin layer] The thermosoftenable silicone resin layer contains a thermosoftenable silicone resin (component (A)). Thermosoftening means that the material is solid at room temperature (25°C) but becomes fluid when heated. In other words, when a thermally conductive composite silicone rubber sheet, in which a thermosoftenable silicone resin layer is laminated as an adhesive layer on a thermally conductive silicone rubber sheet, is mounted, for example, at the interface between a heating element and a cooling element, the heat from the heating element softens the thermosoftenable silicone resin layer, making it fluid, improving contact with the adherend and increasing thermal conductivity.

[0037] More specifically, the heat-softenable silicone resin layer comprises the following components (A) and (B): (A) 75 to 95 mass% of a thermosoftenable silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms (hereinafter sometimes referred to as the phenyl modification rate) is 20 mol% or more; and (B) 5 to 25 mass% of a diphenylsiloxy group-containing organopolysiloxane represented by the following formula (1): [ka] (In the formula, m is an integer of 3 to 5, and n is an integer of 5 to 12.) The thermosoftening silicone resin layer has an absolute viscosity at 70°C of 10 to 700 Pa·s.

[0038] The phenyl modification rate of component (A) is 20 mol % or more, and preferably 30 to 70 mol %. If the phenyl modification rate is 20 mol % or more, the compatibility between the heat-conductive silicone rubber component mainly composed of dimethylsiloxane units and the resin component of the heat-softening silicone resin layer does not become too high, and diffusion of the resin component of the heat-softening silicone resin layer into the heat-conductive silicone rubber sheet can be suppressed.

[0039] The heat-softenable silicone resin of component (A) is preferably a silicone polymer having a specific composition of bifunctional structural units (D units) and trifunctional structural units (T units), as well as monofunctional structural units (M units), as shown in formula (2) or (3) below.

[0040] D p T φ q D Vi r (2) (where D is a dimethylsiloxane unit (i.e., (CH3)2SiO 2 / 2 ) and T φ is a phenylsiloxane unit (i.e., (C6H5)SiO 3 / 2 ) and D Vi is a methylvinylsiloxane unit (i.e., (CH3)(CH2=CH)SiO 2 / 2 ) where p, q, and r satisfy the molar ratio (p+r) / q = 0.25 to 4.0, and the molar ratio (p+r) / r = 1.0 to 4.0.

[0041] M L D p T φ q D Vi r (3) (where M is a trimethylsiloxane unit (i.e., (CH3)3SiO 1 / 2 ) and D, T φ and D Vi are as described above, and p, q, r, and L satisfy the following: (p+r) / q (molar ratio) = 0.25 to 4.0, (p+r) / r (molar ratio) = 1.0 to 4.0, and L / (p+r) (molar ratio) = 0.001 to 0.1.

[0042] The heat-softening silicone resin may be used alone or in combination of two or more types.

[0043] The heat-softenable silicone resin layer contains, as component (B), a diphenylsiloxy group-containing organopolysiloxane represented by the following formula (1). [ka]

[0044] In the formula (1), m is an integer of 3 to 5, preferably an integer of 4 to 5. n is an integer of 5 to 12, preferably an integer of 6 to 12. m+n is preferably in the range of 8 to 17, more preferably in the range of 10 to 15.

[0045] This diphenylsiloxy group-containing organopolysiloxane can be present in the softening silicone resin layer without causing oil bleeding, and allows the softening silicone resin layer to maintain its tackiness for a long period of time.

[0046] The content of (B) diphenylsiloxy group-containing organopolysiloxane in the heat-softenable silicone resin layer is 5 to 25% by mass of the entire heat-softenable silicone resin layer, and preferably 10 to 20% by mass. If the content of diphenylsiloxy group-containing organopolysiloxane is less than 5% by mass, it is difficult to obtain sufficient tackiness, and if it is more than 25% by mass, there is a possibility of oil bleeding from the heat-softenable silicone resin layer.

[0047] The absolute viscosity of the heat-softening silicone resin layer at 70°C is between 10 and 700 Pa·s. If the absolute viscosity of the heat-softening silicone resin layer at 70°C is higher than 700 Pa·s, it will be difficult to fully fill the gaps between the layer and the adherend, and if it is lower than 10 Pa·s, the fluidity will be too high and there is a risk of it flowing out.

[0048] The absolute viscosity can be measured using a HAAKE RotoVisco 1 rotational viscometer. Specifically, two disks are arranged horizontally above and below a vertical central axis. The lower disk is a flat disk (20 mm in diameter) and the upper disk is a cone-shaped disk (20 mm in diameter, 2° cone angle, 0.1 mm trunk). The sample silicone resin is sandwiched between these two disks, and the flat disk is fixed in place. The central axis is used as the axis of rotation, and the cone-shaped disk is rotated around it at a speed of 10 s. -1 It can be rotated and measured.

[0049] The thickness of the heat-softening silicone resin layer is 0.5 to 10 μm, preferably 1 to 5 μm. If it is thinner than 0.5 μm, it will not be able to conform to the irregularities on the adherend surface and will not provide sufficient adhesion. If it is thicker than 10 μm, the thermal resistance of the heat-conductive composite silicone rubber sheet will increase.

[0050] The tack strength of the softening silicone rubber resin layer of the thermally conductive composite silicone rubber sheet is 2.0N / cm 2 It is preferably equal to or greater than 2.5 N / cm 2 or more, and more preferably 3.0 N / cm 2 That's it. Tack strength is 2.0N / cm 2 If the adhesive strength is above this, sufficient tackiness can be obtained when the adhesive is brought into contact with an adherend, and displacement or dropping can be prevented.

[0051] Tack strength can be measured using the probe tack test method in accordance with ASTM D2979. With this method, a stainless steel probe is brought into contact with the softening silicone rubber resin layer of a fixed thermally conductive composite silicone rubber sheet, and the tack strength can be measured from the maximum load required to peel it off. [Example]

[0052] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0053] [Thermal conductive silicone rubber sheet] For the thermally conductive silicone rubber sheet, either 1 or 2 below was used. 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 0.2 mm, thermal conductivity 2.0 W / mK, Type A hardness 88, peroxide curing) 2. Dimethyl silicone rubber glass cloth reinforced thermally conductive silicone rubber sheet (product name: TC-20TAG-3, manufactured by Shin-Etsu Chemical Co., Ltd., thickness 0.2 mm, thermal conductivity 3.0 W / mK, Type A hardness 88, peroxide curing)

[0054] [Thermosoftening silicone resin layer] To an 85% xylene solution of (Component A) (Component A) of the following formula (4), (Component B-1) (Component B) of the following formula (5) or (Component B-2) of the following formula (6) was added, charged into a planetary mixer, and stirred at room temperature for 30 minutes to obtain a heat-softening silicone resin composition. This composition was applied to one side of a heat-conductive silicone rubber sheet using a comma coater, and then dried at 80°C for 10 minutes to remove the xylene, forming a heat-softening silicone resin layer. Tables 1 and 2 show the ratios of (Component A) to (Component B-1) or (Component B-2) in the heat-softening silicone resin layer for each Example and Comparative Example.

[0055] (Component A) Thermosoftening silicone resin D 25 T Φ 55 D Vi 20 (4) (Absolute viscosity at 70°C: 20 Pa·s)

[0056] (Component B-1) Diphenylsiloxy group-containing organopolysiloxane (phenyl content: 25 mol%) [ka]

[0057] (Component B-2) Dimethylpolysiloxane [ka]

[0058] [Examples 1 to 9] In Examples 1 to 9, a heat-softening silicone resin layer was formed on one side of heat-conductive silicone rubber sheet 1 or 2, with the content (ratio) of (component B-1) in the heat-softening silicone resin layer varying from 5 to 25 mass%, to obtain the heat-conductive composite silicone rubber sheets of Examples 1 to 9. Table 1 shows the ratios of (component A) and (component B-1) in the heat-softening silicone resin layer, as well as the thickness of the heat-softening silicone resin layer, for each of Examples 1 to 9.

[0059] [Comparative Examples 1 to 5] In Comparative Examples 1 and 2, a heat-softening silicone resin layer containing neither (Component B-1) nor (Component B-2) was formed on one side of the heat-conductive silicone rubber sheet 1 or 2, to obtain the heat-conductive composite silicone rubber sheets of Comparative Examples 1 and 2, respectively.

[0060] In addition, in Comparative Examples 3 and 4, a heat-softening silicone resin layer with a content of (Component B-1) of 30 mass% in the heat-softening silicone resin layer was formed on one side of the heat-conductive silicone rubber sheet 1 or 2, and the heat-conductive composite silicone rubber sheets of Comparative Examples 3 and 4 were obtained, respectively.

[0061] Furthermore, in Comparative Example 5, (Component B-1) was not added to the heat-softening silicone resin, but instead 10 mass% (Component B-2) was added to form a heat-softening silicone resin layer, and the heat-conductive composite silicone rubber sheet of Comparative Example 5 was obtained.

[0062] Table 2 shows the proportions of (Component A), (Component B-1) and (Component B-2) in the thermosoftening silicone resin layer, as well as the thickness of the thermosoftening silicone resin layer, for each of Comparative Examples 1 to 5.

[0063] [Evaluation method] [Thermal resistance measurement] The thermally conductive composite silicone rubber sheets of Examples 1 to 9 and Comparative Examples 1 to 5 obtained as described above were subjected to a TIM-Tester (manufactured by Analysistech) conforming to ASTM D 6470 at a measurement temperature of 50°C and a pressure of 0.69 N / mm 2was measured.

[0064] [Tackiness measurement] The tackiness of the heat-softened silicone resin layer of the thermally conductive composite silicone rubber sheets produced in Examples 1 to 9 and Comparative Examples 1 to 5 was measured at a measurement temperature of 25°C using a tackiness tester TK-1 (manufactured by Malcom) in accordance with ASTM D 2979.

[0065] [Oil bleeding check] A 100 μm polyethylene film was attached as a protective film to the heat-softening silicone resin layer of the thermally conductive composite silicone rubber sheets produced in Examples 1 to 9 and Comparative Examples 1 to 5, and the sheets were left to stand at 25° C. for 24 hours. The protective film was then peeled off, and the protective film side was visually inspected for any oil components adhering thereto.

[0066] [Absolute viscosity of heat-softening silicone resin layer] The absolute viscosity of the heat-softening silicone resin layer of the heat-conductive composite silicone rubber sheets produced in Examples 1 to 9 and Comparative Examples 1 to 5 was measured using a HAAKE RotoVisco 1 rotational viscometer.

[0067] The results of these measurements are shown in Tables 1 and 2.

[0068] [Table 1]

[0069] [Table 2]

[0070] When no diphenylsiloxy group-containing organopolysiloxane was added as in Comparative Examples 1 and 2, the tack strength was 2.0 N / cm 2The results were as follows. On the other hand, when the diphenylsiloxy group-containing organopolysiloxane in the thermosoftenable silicone resin layer was greater than 25% by mass, as in Comparative Examples 3 and 4, the tackiness was high, but the diphenylsiloxy group-containing organopolysiloxane oil-bled from the resin layer and adhered to the protective film. The bled oil may cause contamination of electronic devices or contact failure. Furthermore, when dimethylpolysiloxane was added to a thermosoftenable silicone resin layer with a phenyl modification rate of 20 mol% or more, as in Comparative Example 5, compatibility was poor and oil adhesion to the protective film was observed even when the amount added was 10% by mass.

[0071] On the other hand, the thermally conductive composite silicone rubber sheets of Examples 1 to 9 had a compressive strength of 2.0 N / cm 2 While the above tackiness was exhibited, no oil adhesion to the protective film was observed.

[0072] From the above, it can be seen that a thermally conductive composite silicone rubber sheet with excellent tackiness while suppressing oil bleeding can be obtained by providing a 0.5 to 10 μm thick thermally softenable silicone resin layer on one or both sides of a thermally conductive silicone rubber sheet, the thermally softenable silicone resin containing 75 to 95 mass% of a thermosoftenable silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms is 20 mol% or more, and the thermally softenable silicone resin layer contains 5 to 25 mass% of a diphenylsiloxy group-containing organopolysiloxane, and has an absolute viscosity at 70°C of 10 to 700 Pa·s.

[0073] Furthermore, the thermally conductive composite silicone rubber sheets of Examples 1 to 9 had a thermal resistance of 2.0 cm 2 Since the value is less than 1.5K / W, it can be seen that by placing it between the heating element and the cooling part, the heat from the heating element can be sufficiently transferred to the cooling part.

[0074] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. a thermally conductive silicone rubber sheet; a heat-softening silicone resin layer disposed on one or both sides of the heat-conductive silicone rubber sheet, the layer having a thickness of 4 to 10 μm and an absolute viscosity at 70° C. of 10 to 700 Pa·s; A thermally conductive composite silicone rubber sheet having The heat-softenable silicone resin layer is (A) a thermosoftening silicone resin in which the ratio of phenyl groups to the total number of substituents directly bonded to silicon atoms is 20 mol % or more: 75 to 95 mass %; and (B) Diphenylsiloxy group-containing organopolysiloxane represented by the following formula (1): 5 to 25% by mass 【Chemistry 1】 (In the formula, m is an integer of 3 to 5, and n is an integer of 5 to 12.) A thermally conductive composite silicone rubber sheet comprising:

2. The component (A) is represented by the following formula (2): D ｐ T φ ｑ D Ｖｉ ｒ (2) (where D is a dimethylsiloxane unit: (CH ３ ) ２ SiO ２／２ represents T φ is a phenylsiloxane unit: (C ６ H ５ ) SiO ３／２ represents D Ｖｉ is a methylvinylsiloxane unit: (CH ３ ) (CH ２ =CH)SiO ２／２ where p, q, and r satisfy the molar ratio (p+r) / q = 0.25 to 4.0, and the molar ratio (p+r) / r = 1.0 to 4.

0.

2. The thermally conductive composite silicone rubber sheet according to claim 1, wherein the silicone rubber is a heat-softening silicone resin represented by the formula:

3. The tack strength of the heat-softening silicone resin layer measured by the probe tack test according to ASTM D2979 is 2.0 N / cm ２ 2. The thermally conductive composite silicone rubber sheet according to claim 1, wherein:

4. 2. The thermally conductive composite silicone rubber sheet according to claim 1, wherein the silicone rubber component of said thermally conductive silicone rubber sheet comprises a dimethylsiloxane unit.

5. 2. The thermally conductive composite silicone rubber sheet according to claim 1, wherein the thermally conductive silicone rubber sheet contains glass cloth and / or a plastic film.

6. The thermally conductive silicone rubber sheet according to claim 5, 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.

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