Thermally conductive sheet and manufacturing method thereof

Abstract

To provide a thermally conductive sheet having higher thermal conductivity.SOLUTION: A thermally conductive sheet includes a scaly filler, a fibrous filler, and a non-anisotropic filler in a polymer matrix, and the long axis direction of the scale-like surface of the scaly filler and the fiber axis direction of the fibrous filler are oriented in the same direction in the thickness direction, and the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermally conductive sheet and a method for producing the same. [Background technology]

[0002] In electronic devices such as computers, automobile parts, and mobile phones, heat sinks and other heat dissipators are commonly used to dissipate heat generated from heat generating bodies such as semiconductor elements and machine parts. It is known that a thermally conductive sheet is disposed between the heat generating body and the heat dissipator in order to increase the efficiency of heat transfer to the heat dissipator.

[0003] A thermally conductive sheet generally contains a polymer matrix and a thermally conductive filler dispersed in the polymer matrix. In addition, the thermally conductive sheet may have an anisotropic filler, such as a thermally conductive fiber, oriented in one direction to enhance thermal conductivity in a specific direction.

[0004] Known examples of thermally conductive sheets in which anisotropic fillers are oriented in one direction include thermally conductive sheets in which thermally conductive fibers are oriented in a fixed direction by applying magnetic field lines to a highly thermally conductive composition in which thermally conductive fibers and non-fibrous thermally conductive fillers are dispersed in a polymer matrix (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-146057 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in recent years, as electronic devices become smaller and more powerful, the amount of heat generated is increasing, and there is a demand for thermally conductive sheets with higher thermal conductivity than that of the thermally conductive sheet of Patent Document 1. In addition, although the thermally conductive sheet of Patent Document 1 exhibits good thermal conductivity in its thickness direction, it is unclear whether it will be able to fully meet the high performance that will be required in the future.

[0007] In view of the above, an object of the present invention is to provide a thermally conductive sheet having higher thermal conductivity. [Means for solving the problem]

[0008] In the present invention, we attempted to further improve thermal conductivity by including a scaly filler and a fibrous filler in a polymer matrix and orienting the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the same direction. However, when a scaly filler is included, the viscosity of the material increases, and it was sometimes difficult to orient the material using a magnetic field as in Patent Document 1. Therefore, we found that the above problem could be solved by adopting flow orientation as the orientation method and setting the content of the scaly filler within a specified range, and thus completed the present invention. That is, the present invention provides the following [1] to

[10] .

[0009] [1] A thermally conductive sheet containing a scaly filler and a fibrous filler in a polymer matrix, wherein the long axis direction of the scale-like surface of the scaly filler and the fiber axis direction of the fibrous filler are oriented in the same direction, and the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more. [2] The thermally conductive sheet according to [1], wherein the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 65 / 35 to 95 / 5. [3] A thermal conductive sheet according to [1] or [2], in which the thickness direction is defined as a first direction, a direction perpendicular to the first direction is defined as a second direction, and a direction perpendicular to the first and second directions is defined as a third direction, the thermal conductivity in the first direction is 11 W / mK or more. [4] The thermally conductive sheet according to any one of [1] to [3], wherein the flaky filler is flaky graphite powder. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the fibrous filler is carbon fiber. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the normal direction of the scale-like filler to the scale surfaces is aligned in a predetermined direction. [7] A thermally conductive sheet according to any one of [1] to [6], which comprises a plurality of unit layers, each of which contains the scaly filler and the fibrous filler and is laminated in one direction along the surface direction of the sheet. [8] A method for manufacturing a thermally conductive sheet containing a scaly filler and a fibrous filler in a polymer matrix, the method comprising: a mixture preparation step of preparing a mixture containing a resin that is a precursor of the polymer matrix, a scaly filler, and a fibrous filler; and an orientation treatment step of orienting the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the same direction by a flow orientation treatment when forming the mixture into a predetermined shape. [9] A method for manufacturing a thermally conductive sheet containing a scaly filler and a fibrous filler in a polymer matrix, the method comprising the steps of: a mixture preparation step of preparing a mixture containing a resin that is a precursor of the polymer matrix, a scaly filler, and a fibrous filler; an orientation treatment step of orienting the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the same direction by a flow orientation treatment when forming the mixture into a sheet; a step of preparing a plurality of primary sheets obtained through the orientation treatment step, stacking the plurality of primary sheets to form a laminated block; and a cutting step of cutting the laminated block into sheets along the stacking direction.

[10] The method for producing a thermally conductive sheet according to [8] or [9], wherein the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more. Effect of the Invention

[0010] According to the present invention, it is possible to provide a thermally conductive sheet having higher thermal conductivity. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic perspective view showing a thermally conductive sheet according to an embodiment. [Diagram 2] FIG. 2 is a schematic perspective view showing an example of a method for producing a thermally conductive sheet according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the thermally conductive sheet according to the embodiment of the present invention (the present embodiment) will be described in detail. The thermally conductive sheet of this embodiment contains a scaly filler and a fibrous filler in a polymer matrix, and the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler are oriented in the same direction. By being oriented in the same direction, for example, when they are oriented in the thickness direction of the sheet, the thermal conductivity in the thickness direction can be increased. In addition, by the presence of the scaly filler between one fibrous filler and another fibrous filler, a heat conduction path is well formed, and higher thermal conductivity can be obtained.

[0013] Incidentally, a resin composition containing a fibrous filler and a scale-like filler is more likely to thicken than a resin composition containing only a fibrous filler or a resin composition containing a fibrous filler and a spherical filler. Because of the high viscosity of such a resin composition, it is difficult to orient the long axis direction of the scale-like filler and the fiber axis direction of the fibrous filler in the same direction by magnetic field orientation. Therefore, in the present invention, by adopting flow orientation to orient the long axis direction of the scale-like filler and the fiber axis direction of the fibrous filler in the same direction and setting the mass ratio of the scale-like filler and the fibrous filler (scale-like filler / fibrous filler) to 55 / 45 or more, higher thermal conductivity has been successfully achieved.

[0014] In other words, describing this embodiment from another perspective, it is a thermally conductive sheet containing a scaly filler and a fibrous filler in a polymer matrix, in which the long axis direction of the scale-like surface of the scaly filler and the fiber axis direction of the fibrous filler are oriented in the same direction by flow orientation treatment, and the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more. In addition, "the mass ratio of the scaly filler to the fibrous filler (flake filler / fibrous filler) is 55 / 45 or more" means that the mass ratio of the scaly filler is the same as or greater than 55 / 45.

[0015] An example of the thermally conductive sheet of this embodiment is shown in Fig. 1. The thermally conductive sheet 10 in Fig. 1 contains a scale-like filler 12 and a fibrous filler 13 in a polymer matrix 11, and the long axis direction of the scale surface of the scale-like filler 12 and the fiber axis direction of the fibrous filler 13 are oriented in the same direction, specifically, in the thickness direction (first direction). The thermally conductive sheet 10 is made of a plurality of unit layers 14 by a manufacturing method described later, and each unit layer 14 contains the scale-like filler 12 and the fibrous filler 13 and is laminated in one direction along the surface direction of the sheet 10 (a direction perpendicular to the first direction: a third direction).

[0016] In addition, as shown in FIG. 1, when the thickness direction is the first direction, the direction perpendicular to the first direction is the second direction, and the direction perpendicular to the first and second directions is the third direction, the first direction is the same as the long axis direction of the scale surface of the scale-like filler 12 and the fiber axis direction of the fibrous filler 13, so that high thermal conductivity is exhibited. Specifically, the thermal conductivity is preferably 8 W / mK or more, more preferably 11 W / mK or more, even more preferably 13 W / mK or more, and particularly preferably 16 W / mK or more. The thermal conductivity is measured by a method conforming to ASTM D5470-06.

[0017] In addition, in the second direction, the short axis direction of the scale surface of the scale-like filler 12 and the fiber width direction of the fibrous filler 13 are oriented in the same direction, so high thermal conductivity is also exhibited in this direction. In other words, the thermally conductive sheet shown in Fig. 1 is a two-way thermally conductive sheet that exhibits high thermal conductivity in both the first and second directions. The thermal conductivity in the second direction is preferably 3 W / mK or more, more preferably 4 W / mK or more, and even more preferably 6 W / mK or more.

[0018] Hereinafter, each material constituting the thermally conductive sheet according to this embodiment will be described. (polymer matrix) The polymer matrix is ​​a member that holds the scaly filler and the fibrous filler, and is preferably made of a soft rubber-like elastic body. The polymer matrix is ​​formed from a resin that is its precursor. In order to incorporate the scaly filler and the fibrous filler in an oriented state into the polymer matrix, it is required that the resin has fluidity during the orientation process. For example, if the resin that is the precursor of the polymer matrix is ​​a thermoplastic resin, the scaly filler and the fibrous filler can be oriented in a heated and plasticized state. In addition, if the resin is a reactive liquid resin, the scaly filler and the fibrous filler can be oriented before curing, and the resin can be cured while maintaining that state to obtain a cured product in which the scaly filler and the fibrous filler are oriented. The former has a relatively high viscosity, and if plasticized to a low viscosity, the resin may be thermally deteriorated, so it is preferable to adopt the latter resin.

[0019] As the reactive liquid resin, it is preferable to use a rubber or gel that is liquid before the reaction and hardens under a predetermined condition to form a crosslinked structure. The crosslinked structure refers to a structure in which at least a part of the polymer is crosslinked three-dimensionally to form a hardened body that does not melt when heated. In addition, since a mixed composition is prepared by adding a scaly filler and a fibrous filler to a liquid resin and orienting them in the liquid resin with fluidity, it is preferable that the viscosity is low and that the resin has the property of being hardenable under a predetermined condition after orientation.

[0020] Examples of the curing method of such reactive liquid resins include thermosetting and photosetting, but since they contain a large amount of scaly filler and fibrous filler that block light, it is preferable to use thermosetting rubber or gel. More specifically, examples include silicone resin, urethane rubber that utilizes the reaction of polyol and isocyanate, and acrylic rubber that utilizes the radical reaction or cationic reaction of acrylate, but it is preferable to use silicone resin.

[0021] Silicone resin is not particularly limited as long as it is organopolysiloxane, but it is preferable to use curable silicone resin. When silicone resin is curable, it is obtained by curing a curable silicone composition. Silicone resin may be an addition reaction type or other types may be used. When silicone resin is an addition reaction type, it is preferable that curable silicone composition is composed of a silicone compound as a main component and a curing agent that cures the main component.

[0022] The silicone compound used as the base agent is preferably an alkenyl group-containing organopolysiloxane, and specific examples include vinyl group-containing organopolysiloxanes such as vinyl group-containing polydimethylsiloxane, vinyl group-containing polyphenylmethylsiloxane, vinyl group-containing dimethylsiloxane-diphenylsiloxane copolymer, vinyl group-containing dimethylsiloxane-phenylmethylsiloxane copolymer, and vinyl group-containing dimethylsiloxane-diethylsiloxane copolymer.

[0023] The curing agent is not particularly limited as long as it can cure the silicone compound, which is the main component, but organohydrogenpolysiloxane, which is an organopolysiloxane having two or more hydrosilyl groups (SiH), is preferred. The hardness of the primary sheet, which will be described later, can be adjusted by appropriately adjusting the number of hydrosilyl groups, the molecular weight, and the blending ratio of the curing agent to the base agent. Specifically, the hardness of the primary sheet can be reduced by using a curing agent with fewer hydrosilyl groups per molecule or a large molecular weight, or by reducing the blending ratio of the curing agent to the base agent.

[0024] The content of the resin, which is a precursor of the polymer matrix, is preferably 15 to 50% by volume, and more preferably 25 to 45% by volume, based on the total volume of the thermally conductive sheet, expressed in volume % (filling rate).

[0025] In the thermally conductive sheet 10 shown in Fig. 1, adjacent unit layers 14, 14 are bonded to each other, but it is preferable that each unit layer 14 is directly fixed to the adjacent unit layer 14. In other words, it is preferable that adjacent unit layers 14, 14 are directly bonded to each other without using a material other than the unit layers, such as an adhesive. With this configuration, when a silicone resin is preferably used as the resin that is the precursor of the matrix, for example, the silicone resin of each unit layer 14 is bonded to each other.

[0026] Generally, it is difficult to bond silicone resins together with a high adhesive strength, but in this embodiment, as described below, the bonding surfaces of the unit layers 14 are activated by irradiating them with VUV light, so that adjacent unit layers 14, 14 are bonded together with a relatively high adhesive strength. Therefore, peeling does not occur at the interface between the unit layers 14. In addition, since the unit layers 14, 14 are bonded together without the use of another member or curing, the flexibility of the thermally conductive sheet 10 is not lost.

[0027] (scaly filler) The scaly filler preferably has an aspect ratio of 3 or more, more preferably 6-50, and even more preferably 8-15, from the viewpoint of facilitating orientation in the thickness direction of the sheet and enhancing thermal conductivity. The aspect ratio means the length in the major axis direction / thickness of the scale surface of the scaly filler.

[0028] The average particle size (average major axis length) of the scaly filler is preferably 10 to 400 μm, more preferably 15 to 300 μm. Also, 20 to 200 μm is particularly preferable. By setting the average particle size to 10 μm or more, the fillers in the thermal conductive sheet can easily come into contact with each other, a heat transfer path is secured, and the thermal conductivity of the thermal conductive sheet is improved. On the other hand, by setting the average particle size to 400 μm or less, the bulk of the scaly filler is reduced, making it possible to achieve high packing in the matrix. The average particle size of the scaly filler can be calculated by observing it under a microscope and taking the length in the long axis direction as the diameter. More specifically, the long axis lengths of 50 random scaly fillers can be measured using an electron microscope, optical microscope, or X-ray CT scanner, and the average value (arithmetic mean value) can be used as the average particle size. Similarly, the thickness of the scaly filler can be measured using an electron microscope, an optical microscope, or an X-ray CT device.

[0029] Examples of the scaly filler include scaly carbon powder, scaly silicon carbide powder, scaly aluminum nitride powder, scaly boron nitride powder, scaly aluminum oxide powder, etc. Among these, scaly graphite powder is preferred. In flake graphite powder, the crystal planes of graphite are aligned in the in-plane direction of the flake surface, and the flake surface has high thermal conductivity in the in-plane direction. Therefore, by aligning the flake surface in a specific direction, the thermal conductivity in a specific direction can be increased. The flake graphite powder preferably has a high degree of graphitization.

[0030] (fibrous filler) From the viewpoint of easily orienting the fiber axis direction in the thickness direction of the sheet and thereby enhancing thermal conductivity, the fibrous filler preferably has an aspect ratio of 4 or more, more preferably 7 to 100, and even more preferably 15 to 50. The aspect ratio means the length in the fiber axial direction of a fibrous filler (fiber length) / fiber diameter.

[0031] The average fiber length of the fibrous filler is preferably 20 to 500 μm, more preferably 80 to 400 μm. When the average fiber length is 20 μm or more, the fillers in the thermally conductive sheet are in proper contact with each other, a heat transfer path is secured, and the thermal conductivity of the thermally conductive sheet is improved. On the other hand, when the average fiber length is 500 μm or less, the bulk of the fibrous filler is reduced, allowing for high packing. In addition, even if a conductive fibrous filler is used, the conductivity of the thermally conductive sheet is prevented from becoming higher than necessary. The average fiber length can be calculated by observing the fibrous filler under a microscope. For example, the fiber lengths of 50 arbitrary fibrous fillers separated by dissolving the matrix component of the thermally conductive sheet can be measured using an electron microscope or optical microscope, and the average value (arithmetic mean value) can be used as the average fiber length. In this case, a large shear is not applied so as not to crush the fibers. In addition, if it is difficult to separate the fibrous filler from the thermally conductive sheet, the fiber length of the fibrous filler can be measured using an X-ray CT device, and the average fiber length can be calculated. Similarly, the diameter of the fibrous filler can be measured using an electron microscope, an optical microscope, or an X-ray CT device. In the present invention, "arbitrary" refers to something selected at random.

[0032] Examples of the fibrous filler include carbon fiber, metal fiber, ceramic fiber, polyparaphenylene benzoxazole fiber, etc. Among these, carbon fiber is preferable. As the carbon fiber, graphitized carbon fiber is preferable. In graphitized carbon fiber, the crystal planes of graphite are arranged in the fiber axis direction, and the graphitized carbon fiber has high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axis direction in a specific direction, the thermal conductivity in a specific direction can be increased. As the graphitized carbon fiber, one having a high degree of graphitization is preferable.

[0033] As the graphitized carbon material such as the graphitized carbon fiber described above, the following raw materials can be graphitized. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile) and pitch can be mentioned, but it is preferable to use graphitized mesophase pitch, polyimide, and polybenzazole, which have a particularly high degree of graphitization. For example, by using mesophase pitch, the pitch is oriented in the fiber axis direction due to its anisotropy in the spinning process described later, and graphitized carbon fiber having excellent thermal conductivity in the fiber axis direction can be obtained. The use of mesophase pitch in graphitized carbon fiber is not particularly limited as long as it can be spun, and mesophase pitch may be used alone or in combination with other raw materials. However, it is most preferable to use mesophase pitch alone, that is, graphitized carbon fiber containing 100% mesophase pitch, from the viewpoints of high thermal conductivity, spinnability, and stability of quality.

[0034] The graphitized carbon fiber may be one which has been subjected to spinning, infusibility and carbonization in sequence, pulverized or cut to a predetermined particle size, and then graphitized, or one which has been pulverized or cut after carbonization and then graphitized. When pulverization or cutting is performed before graphitization, the newly exposed surface due to pulverization is more likely to undergo condensation polymerization and cyclization reactions during the graphitization process, and therefore it is possible to obtain graphitized carbon fiber with a higher degree of graphitization and further improved thermal conductivity. On the other hand, when spun carbon fiber is graphitized and then pulverized, the graphitized carbon fiber is easy to pulverize because it is hard, and carbon fiber powder with a relatively narrow fiber length distribution can be obtained by pulverization for a short period of time.

[0035] Here, the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more, preferably 60 / 40 to 95 / 5, and more preferably 65 / 45 to 90 / 10, as described above. If the mass ratio is less than 55 / 45, the thermal conductivity in the thickness direction may not be sufficiently increased. Even if the normal direction of the scaly filler is aligned, the thermal conductivity in the second direction is low.

[0036] The total content of the scaly filler and fibrous filler in the thermal conductive sheet is preferably 10 to 500 parts by mass, more preferably 50 to 350 parts by mass, per 100 parts by mass of the resin that is the precursor of the matrix. Moreover, the total content is preferably 2 to 40 volume %, more preferably 8 to 30 volume %, based on the total amount of the thermal conductive sheet, when expressed as a filling rate based on volume (volume filling rate). By making the total content 10 parts by mass or more, it becomes easier to increase thermal conductivity, and by making it 500 parts by mass or less, the viscosity of the liquid composition described below tends to be appropriate, resulting in good orientation of each filler.

[0037] The thermal conductivity of the scaly filler and fibrous filler along the anisotropic direction (i.e., the long axis direction, the fiber axis direction) is generally, but not limited to, 30 W / m K or more, and preferably 100 W / m K or more. The upper limit of the thermal conductivity is, but not limited to, for example, 2000 W / m K or less. The method for measuring the thermal conductivity is the laser flash method.

[0038] In addition, the scaly filler and the fibrous filler may be conductive or insulating. If the scaly filler and the fibrous filler have insulating properties, the insulation in the thickness direction of the thermal conductive sheet can be increased, so that the thermal conductive sheet can be suitably used in electrical devices. In the present invention, being conductive means, for example, a volume resistivity of 1×10 9 In addition, insulation means a material with a volume resistivity of, for example, 1×10 9 This refers to a resistance exceeding Ω·cm.

[0039] The scale-like filler and the fibrous filler may be used alone or in combination of two or more. For example, at least two fillers having different average particle diameters or average fiber lengths may be used as the scale-like filler or the fibrous filler. When fillers of different sizes are used, the smaller fillers are inserted between the relatively larger fillers, so that the fillers can be densely packed in the matrix and the heat conduction efficiency can be improved.

[0040] In the example shown in FIG. 1, the scale-like filler 12 and the fibrous filler 13 are oriented in the thickness direction (first direction) of the thermally conductive sheet in each unit layer 14. The thickness direction orientation of the scale-like filler 12 and the fibrous filler 13 will be described more specifically. First, the scale-like filler 12 refers to a state in which the ratio of the number of scale-like fillers whose scale surface forms an angle of less than 30° with the long axis direction with respect to the thickness direction of the thermally conductive sheet 10 exceeds 50% with respect to the total amount of the scale-like filler, and this ratio can be preferably greater than 80%. In other words, the ratio of the number of scale-like fillers whose scale surface forms an angle of less than 30° with the normal direction of the long axis direction with respect to the sheet surface of the thermally conductive sheet exceeds 50% with respect to the total amount of the scale-like filler, and this ratio preferably exceeds 80%. In addition, the fibrous filler 13 means that the proportion of the number of fibrous fillers whose major axis forms an angle of less than 30° with respect to the thickness direction of the thermally conductive sheet 10 exceeds 50% of the total amount of fibrous filler, and this proportion preferably exceeds 80%. From the viewpoint of increasing thermal conductivity, the orientation directions of the scaly filler 12 and the fibrous filler 13 are preferably such that the angle between the fiber axis direction of the fibrous filler and the thickness direction, or the angle between the long axis direction of the scale surface, is 0° or more and less than 5°. On the other hand, the inclination may be in the range of 5° or more and less than 30°, so that the load when the thermally conductive sheet 10 is compressed can be reduced. These angles are the average values ​​of the orientation angles of a certain number of scaly fillers 12 or fibrous fillers 13 (for example, 50 pieces of any scaly fillers 12 or fibrous fillers 13).

[0041] Furthermore, it is preferable that the normal direction of the scale-like filler is aligned in a predetermined direction, specifically, it is preferable that it faces the third direction shown in Fig. 1. In this way, it is possible to obtain the above-mentioned two-way thermally conductive sheet having good thermal conductivity in the first direction and the second direction. To obtain a two-way thermally conductive sheet, the first method described later in the description of the manufacturing method may be adopted.

[0042] (non-anisotropic filler) In this embodiment, the matrix may contain a non-anisotropic filler other than the scaly filler and the fibrous filler. The non-anisotropic filler is a material that imparts thermal conductivity to the thermal conductive sheet together with the scaly filler and the fibrous filler. By containing the non-anisotropic filler, the filler is interposed between the oriented scaly filler and the fibrous filler, and a thermal conductive sheet with a higher thermal conductivity can be obtained. A non-anisotropic filler is a filler that has substantially no anisotropy in shape, and is a filler that does not orient in a predetermined direction even in an environment in which scaly fillers and fibrous fillers orient in a predetermined direction, such as under the action of shear force described below.

[0043] The aspect ratio of the non-anisotropic filler is preferably less than 2, and more preferably not more than 1.5. By making the aspect ratio less than 2, it is possible to prevent the viscosity of the liquid composition described below from increasing, and to achieve high filling.

[0044] The non-anisotropic filler may be conductive, but is preferably insulating, and in the thermally conductive sheet, the scaly filler, fibrous filler, and non-anisotropic filler are preferably insulating. If these are insulating, it becomes easier to further increase the insulation in the thickness direction of the thermally conductive sheet.

[0045] Examples of the non-anisotropic filler include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides, nitrides, carbides other than metals, etc. Examples of the shape of the non-anisotropic filler include spherical and amorphous powders. In the non-anisotropic filler, examples of metals include aluminum, copper, nickel, etc., examples of metal oxides include aluminum oxide, magnesium oxide, zinc oxide, etc., such as alumina, and examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Furthermore, examples of carbon materials include spherical graphite. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide. Among these, aluminum oxide and aluminum are preferred because they have high thermal conductivity and are readily available in spherical form, while aluminum hydroxide is preferred because it is readily available and can enhance the flame retardancy of the thermally conductive sheet. Examples of the non-anisotropic insulating filler include metal oxides, metal nitrides, metal hydroxides, and metal carbides, among those mentioned above, with aluminum oxide and aluminum hydroxide being particularly preferred. The non-anisotropic filler may be used alone or in combination of two or more of the above.

[0046] The average particle size of the non-anisotropic filler is preferably 0.1 to 50 μm, more preferably 0.5 to 35 μm. Also, it is particularly preferably 1 to 15 μm. By making the average particle size 50 μm or less, problems such as disturbance of the orientation of the scaly filler and fibrous filler are unlikely to occur. Also, by making the average particle size 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become larger than necessary, and even if a large amount is blended, the viscosity of the liquid composition is unlikely to increase, making it easy to highly fill the non-anisotropic filler. The average particle size of the non-anisotropic filler can be measured by observation using an electron microscope, etc. More specifically, like the measurements of the scaly filler and fibrous filler, the particle sizes of 50 random non-anisotropic fillers can be measured using an electron microscope, optical microscope, or X-ray CT scanner, and the average value (arithmetic mean value) can be used as the average particle size.

[0047] The content of the non-anisotropic filler in the thermally conductive sheet is preferably in the range of 50 to 1500 parts by mass, more preferably in the range of 200 to 800 parts by mass, relative to 100 parts by mass of the resin that is the precursor of the polymer matrix. By making it 50 parts by mass or more, the amount of the non-anisotropic filler present in the gaps between the scaly filler and the fibrous filler becomes a certain amount or more, and the thermal conductivity becomes good. On the other hand, by making it 1500 parts by mass or less, it is possible to obtain an effect of increasing the thermal conductivity according to the content, and the non-anisotropic filler does not inhibit the thermal conduction by the scaly filler and the fibrous filler. In addition, by making it within the range of 200 to 800 parts by mass, the thermal conductivity of the thermally conductive sheet is excellent, and the viscosity of the liquid composition is also suitable. The content of the non-anisotropic filler, expressed in volume %, is preferably 10 to 75 volume %, and more preferably 30 to 60 volume %, based on the total volume of the thermally conductive sheet. 1 have substantially the same composition. Therefore, the contents of the scale-like filler, fibrous filler, non-anisotropic filler, and resin that is a precursor of the polymer matrix in each unit layer are the same as those in the thermally conductive sheet, and the contents of the scale-like filler, fibrous filler, non-anisotropic filler, and resin that is a precursor of the polymer matrix in each unit layer are also as described above.

[0048] (Additional ingredients) In the thermally conductive sheet, various additives may be further blended into the polymer matrix within a range that does not impair the function of the thermally conductive sheet. Examples of the additives include at least one selected from dispersants, coupling agents, adhesives, flame retardants, antioxidants, colorants, and anti-settling agents. When the curable silicone composition is cured, an additive such as a curing catalyst that accelerates curing may be added. Examples of the curing catalyst include platinum-based catalysts.

[0049] (Other characteristics of thermal conductive sheets) The type E hardness of the thermally conductive sheet is, for example, 70 or less. When the type E hardness of the thermally conductive sheet is 70 or less, flexibility is ensured, and for example, the thermally conductive sheet has good conformability to a heat generating body and a heat dissipating body, and is likely to have good heat dissipation properties. From the viewpoint of improving flexibility and achieving excellent conformability, the type E hardness of the thermally conductive sheet is preferably 40 or less. More preferably, the type OO hardness is 50 or less. The lower limit of the hardness of the thermally conductive sheet is not particularly limited, but is, for example, 15 or more in type OO hardness, preferably 25 or more. In addition, it is particularly preferable that the type E hardness is 20 or more. The softer the hardness of the thermally conductive sheet, the smaller the stress on the heating element, the heat sink, or the substrate on which they are arranged when compressed, and it is preferable, but by setting the hardness to 15 or more in type OO hardness, the thermally conductive sheet can have a predetermined handleability. In particular, by setting the E hardness to 20 or more, it is possible to obtain a thermally conductive sheet with an excellent balance between handleability and softness. The above type E hardness and type OO hardness are values ​​measured using a prescribed durometer in accordance with the method specified in ASTM D2240-05.

[0050] In this embodiment, at least one of the scale-like filler and the fibrous filler is exposed on both sides of the thermally conductive sheet. At least one of the exposed scale-like filler and the fibrous filler may protrude from each of the two sides. When at least one of the scale-like filler and the fibrous filler is exposed on both sides of the thermally conductive sheet, the exposed surfaces become non-adhesive surfaces. When the thermally conductive sheet is cut with a blade as described below, both sides become cut surfaces, so that usually at least one of the scale-like filler and the fibrous filler is exposed on both sides. However, either one or both of the two surfaces may be an adhesive surface without exposing the scale-like filler and the fibrous filler.

[0051] The thickness of the thermally conductive sheet is appropriately changed depending on the shape and use of the electronic device in which the thermally conductive sheet is mounted. The thickness of the thermally conductive sheet is not particularly limited, but may be in the range of 0.1 to 5 mm, for example. The thickness of each unit layer is not particularly limited, but is preferably 0.1 to 5.0 mm, and more preferably 0.3 to 3.0 mm. The thickness of the unit layer is the length 14L corresponding to the third direction in FIG.

[0052] The thermally conductive sheet according to the present embodiment is used inside electronic devices. Specifically, the thermally conductive sheet is interposed between a heat generating body and a heat sink, and transfers heat generated by the heat generating body to the heat sink by thermal conduction, and dissipates the heat from the heat sink. Here, examples of the heat generating body include various electronic components used inside electronic devices, such as a CPU, a power amplifier, and a power supply. Examples of the heat sink include a heat sink, a heat pump, and a metal housing of an electronic device. The thermally conductive sheet is used by being in close contact with the heat generating body and the heat sink on both sides, respectively, and being compressed.

[0053] <Method of manufacturing thermally conductive sheet> The method for producing a thermally conductive sheet of the present invention is a method for producing a thermally conductive sheet containing a scaly filler and a fibrous filler in a polymer matrix, and includes a mixture preparation step of preparing a mixture containing a resin that is a precursor of the polymer matrix, a scaly filler, and a fibrous filler, and an orientation treatment step of orienting the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the same direction by flow orientation treatment when forming the mixture into a predetermined shape. In this production method, flow orientation is used to orient the long axis direction of the scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the same direction, so that the desired orientation state can be obtained more reliably than with magnetic field orientation. The above-mentioned "predetermined shape" refers to a specific shape such as a sheet shape, a column shape, etc. From the viewpoint of obtaining high thermal conductivity, the mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is preferably 55 / 45 or more.

[0054] Preferred embodiments of the method for producing the thermally conductive sheet include the following first to eighth methods.

[0055] (First Method) The first method is a method for producing a thermally conductive sheet, which includes a step of orienting the long axis direction of the scale-like surface of the scale-like filler and the fiber axis direction of the fibrous filler in the same direction by a flow orientation process when forming the mixture into a sheet, preparing multiple primary sheets obtained through this orientation process, stacking the multiple primary sheets to form a laminated block, and a cutting step of cutting the laminated block into sheets along the stacking direction.

[0056] (Second Method) In the second method, the mixture is molded into a plate shape by extrusion molding, injection molding, or press molding while orienting the scaly filler and fibrous filler, the molded plate is rolled around the axis along the orientation direction of the scaly filler and fibrous filler, and the molded body thus obtained is surrounded by an elastic body.Then, the heat conductive sheet is cut along a plane perpendicular to the axis of the roll to obtain a plate-shaped heat conductive sheet.

[0057] (Third Method) In the third method, the mixture is molded into a plate shape by extrusion molding, injection molding, or press molding while orienting the scaly filler and fibrous filler, the molded plate is cut into a plurality of plates along the orientation direction of the scaly filler and fibrous filler, and the plurality of cut plates are stacked with the above orientation direction aligned. The obtained molded body is surrounded by an elastic body, and cut along a plane perpendicular to the orientation direction to obtain a plate-shaped thermally conductive sheet.

[0058] (Fourth Method) The fourth method is a method for producing a thermally conductive sheet in which, when the mixture is formed into a sheet shape by a flow orientation process, the long axis direction of the scale-like filler and the fiber axis direction of the fibrous filler are oriented in the same direction, and the mixture is passed through an orientation section and a compression section provided in a molding die to produce a thermally conductive sheet. Specifically, the mixture is passed through a die having a plurality of structures to perform orientation molding. The mixture is passed through a plurality of slits or a circular or polygonal flow path provided in the die to orient the scale-like filler and fibrous filler mixed in the mixture in the thickness direction of the sheet, and then passed through a compression area provided in the configured die to mold the mixture without disturbing the orientation state of the anisotropic inorganic particles, and then extruded as a block from the die outlet. The molded body is cured by a method suitable for the resin, and then cut in the width direction of the sheet to produce a thermally conductive sheet.

[0059] (5th method) In the fifth method, the mixture is first extruded by an extruder to form a thin and columnar provisional molded body in which the scale-like filler and the fibrous filler are oriented along the extrusion direction, and then a plurality of the provisional molded bodies are aligned so as to be adjacent to each other in a direction perpendicular to the longitudinal direction, and a laminate is obtained in which the aligned provisional molded bodies are arranged in a direction approximately perpendicular to the alignment direction. The laminate is cured to form a final molded body in which the provisional molded bodies constituting the laminate are integrated together. The final molded body is then cut to a predetermined size in a direction perpendicular to the longitudinal direction of the provisional molded body to form a thermally conductive sheet.

[0060] (6th method) In the sixth method, first, a pressure is applied to the mixture to prepare a primary sheet with the orientation direction of the scale-like filler and the fibrous filler being approximately parallel to the main surface. The primary sheets are stacked to form a laminate. The laminate is sliced ​​at an angle of 5 to 40° to the normal line coming out of the primary sheet surface to form a sheet, and a thermally conductive sheet is formed in which the surface direction of the scale-like filler is inclined in the range of 5 to 40° to the surface of the thermally conductive sheet, or the laminate is sliced ​​at an angle approximately perpendicular to the normal line coming out of the primary sheet surface to form a sheet, and then the sliced ​​sheet is roll-pressed to form a thermally conductive sheet in which the surface direction of the scale-like filler is inclined in the range of 5 to 40° to the surface of the thermally conductive sheet.

[0061] (Seventh Method) In the seventh method, first, a pressure is applied to the mixture to prepare a primary sheet in which the orientation direction of the scale-like filler and the fibrous filler is oriented in a direction approximately parallel to the main surface. This primary sheet is wound around the orientation direction of the scale-like graphite to form a laminate. This laminate is sliced ​​at an angle of 5 to 40° to the normal line coming out of the primary sheet surface to form a sheet, and a thermally conductive sheet in which the surface direction of the scale-like graphite is oriented at an inclination in the range of 5 to 40° to the surface of the thermally conductive sheet is formed, or the laminate is sliced ​​at an angle approximately perpendicular to the normal line coming out of the primary sheet surface to form a sheet, and then the sliced ​​sheet is roll-pressed to form a thermally conductive sheet in which the surface direction of the scale-like graphite is oriented at an inclination in the range of 5 to 40° to the surface of the thermally conductive sheet.

[0062] (8th method) The eighth method is a method for manufacturing a thermally conductive sheet having a first gap of continuous vertical gap X and a second gap of vertical gap Y (where X < Y), in which the scaly filler and the fibrous filler are oriented in the thickness direction. Specifically, it includes a first step of passing a mixture through the first gap to obtain a resin molding precursor in which the scaly filler and the fibrous filler are oriented in the surface direction, and a second step of fusing the resin molding precursor that has passed through the first gap while folding it in a direction substantially perpendicular to the extrusion direction in the second gap to obtain a resin molded product. Here, the first gap is preferably 0.5 mm or more and 5.0 mm or less, and the second gap is preferably 2 to 20 times the first gap.

[0063] Among the above-described first to eighth methods, considering the production of a thermally conductive sheet as shown in FIG. 1, the first method is preferable. The first method will be described with reference to FIG. 2.

[0064] (Mixture preparation step, orientation treatment step) First, a mixture (liquid composition) containing a resin (for example, a curable silicone composition) that is a precursor of a polymer matrix, a scaly filler, and a fibrous filler is prepared. The liquid composition usually becomes a slurry. Appropriate additive components may be further mixed into the liquid composition as necessary. Here, for mixing the respective components constituting the liquid composition, for example, a known kneader, kneading roll, mixer, or the like may be used.

[0065] The viscosity of the liquid composition can be determined according to the means of sheet forming and the desired thickness of the sheet. When sheet forming is performed by coating the liquid composition on a substrate, the viscosity of the liquid composition is preferably 50 to 10,000 Pa·s. By setting the viscosity to 50 Pa·s or more, by applying a shearing force, it becomes easier to orient the major axis direction of one scaly surface of the scaly filler and the fiber axis direction of the fibrous filler in the surface direction of the primary sheet. Also, by setting it to 10,000 Pa·s or less, the coatability becomes good. The viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at a rotation speed of 10 rpm, and the measurement temperature is the temperature at the time of coating of the liquid composition.

[0066] For example, in the case of a curable silicone composition that is a liquid composition, it is usually liquid, and the above viscosity can be achieved by appropriately adjusting the molecular weight of each component (such as an alkenyl group-containing organopolysiloxane and an organohydrogenpolysiloxane) that constitutes the curable silicone composition. In addition, an organic solvent may be blended into the liquid composition as necessary to adjust the viscosity to the above range, but it is preferable not to blend an organic solvent.

[0067] Next, the liquid composition is formed into a sheet while applying a shear force, so that the long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler are oriented in a direction parallel to the sheet surface (i.e., in the plane direction). Here, the liquid composition may be applied to the substrate film, for example, by a coating applicator such as a bar coater or a doctor blade, or by extrusion molding or ejection from a nozzle, and such a method can apply a shear force along the coating direction of the liquid composition. By receiving this shear force, the long axis direction of the scale surface of the scale-like filler in the liquid composition and the fiber axis direction of the fibrous filler are oriented in the coating direction.

[0068] (Step of forming laminated blocks) Next, the liquid composition molded into a sheet shape is cured to obtain a primary sheet. In the primary sheet, as described above, the long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler are oriented along the surface direction. The liquid composition is cured by curing the curable silicone composition contained in the liquid composition. The liquid composition may be cured by heating, for example, at a temperature of about 50 to 150°C. The heating time is, for example, about 10 minutes to 3 hours. When a solvent is blended in the liquid composition, the solvent is preferably evaporated by heating during curing.

[0069] The thickness of the primary sheet obtained by curing is preferably in the range of 0.1 to 5.0 mm. By setting the thickness of the primary sheet within the above range, the scale-like filler and the fibrous filler can be appropriately oriented in the plane direction by shear force. Furthermore, by setting the thickness of the primary sheet to 0.1 mm or more, it can be easily peeled off from the base film. Furthermore, by setting the thickness of the primary sheet to 5.0 mm or less, the primary sheet is prevented from being deformed by its own weight. From these viewpoints, the thickness of the primary sheet is more preferably 0.3 to 3.0 mm.

[0070] The type OO hardness of the primary sheet is preferably 6 or more. By making it 6 or more, the primary sheet does not spread much even when pressure is applied when stacking the primary sheets, and a laminated block having a sufficient thickness can be produced. From this viewpoint, the type OO hardness of the primary sheet is more preferably 10 or more, and even more preferably 15 or more. From the viewpoint of ensuring the flexibility of the obtained thermally conductive sheet, the type E hardness of the primary sheet is preferably 70 or less, more preferably 40 or less, and further preferably 50 or less in type OO hardness.

[0071] (VUV irradiation process) Here, it is preferable to irradiate at least one surface of the cured primary sheet with VUV. VUV stands for vacuum ultraviolet ray, and refers to ultraviolet ray having a wavelength of 10 to 200 nm. Examples of the light source of VUV include an excimer Xe lamp and an excimer ArF lamp. The cured primary sheet contains silicone resin (organopolysiloxane) as described above, and when irradiated with VUV, the surface irradiated with VUV is activated. As described below, the primary sheet is overlapped with another primary sheet so that one activated surface becomes the overlapping surface, and the primary sheets are firmly bonded to each other. Although the principle is unclear, it is assumed that when silicone resin is irradiated with VUV, the C-Si bonds of the organopolysiloxane change to Si-O bonds such as Si-OH, and the primary sheets are firmly bonded together by these Si-O bonds. In other words, the primary sheets (unit layers 14, 14) are bonded together by bonds occurring between the organopolysiloxane molecules. The VUV irradiation conditions are not particularly limited as long as they can activate the surface of the primary sheet. For example, the integrated light amount is 5 to 100 mJ / cm 2 Preferably, the integrated light amount is 10 to 50 mJ / cm 2 It is recommended to irradiate VUV so that

[0072] Next, as shown in Figures 2(a) and (b), multiple primary sheets 21 are laminated so that the orientation direction of the long axis direction of the scale surface of the scale-like filler is the same as the orientation direction of the fiber axis direction of the fibrous filler. Here, as described above, it is sufficient that either one of the overlapping surfaces that contact each other of each primary sheet 21 has been irradiated with VUV in advance. By irradiating one surface with VUV, adjacent primary sheets 21, 21 are bonded to each other by the activated one surface. In addition, from the viewpoint of further improving adhesion, it is preferable that both overlapping surfaces are irradiated with VUV. That is, as shown in FIG. 2(a), the primary sheet 21 may be overlapped so that one surface 21A that has been irradiated with VUV is in contact with another primary sheet 21, and in this case, it is preferable that the other surface 21B of the other primary sheet 21 that is in contact with the one surface 21A is also irradiated with VUV.

[0073] Although the primary sheets 21 can be bonded simply by overlapping them as described above, to bond them more firmly, pressure may be applied in the lamination direction x of the primary sheets 21. The pressure should be such that the primary sheets 21 do not deform significantly, and can be applied using, for example, a roller or a press. As an example, when a roller is used, the pressure is preferably 0.3 to 3 kgf / 50 mm. The laminated primary sheets 21 may be appropriately heated, for example, when applying pressure, but since the primary sheets 21 activated by VUV irradiation can be bonded without heating, it is preferable not to heat the laminated primary sheets 21. Therefore, the temperature during pressing is, for example, 0 to 50°C, and preferably about 10 to 40°C.

[0074] (cutting process) Next, as shown in FIG. 2(c), the laminated block 22 is cut by a blade 18 along the lamination direction x of the primary sheet 21 to obtain the thermally conductive sheet 10. In this case, the laminated block 22 is preferably cut in a direction perpendicular to the orientation direction of the long axis direction of the scale-like filler and the fiber axis direction of the fibrous filler. As the blade 18, for example, a double-edged or single-edged blade such as a razor blade or a cutter knife, a round blade, a wire blade, a saw blade, or the like can be used. The laminated block 22 is cut by the blade 18 by, for example, a method such as pushing, shearing, rotating, or sliding.

[0075] In the above manufacturing method, an example was described in which a curable silicone composition that is cured by heating was used as the raw material for the silicone resin, but the raw material for the silicone resin is not limited to one that has curability, and one that does not have curability may be used. In such a case, the liquid composition may be a mixture of silicone resin, scaly filler, fibrous filler, and other additive components that are mixed as necessary, diluted with an organic solvent. The liquid composition diluted with an organic solvent may be formed into a sheet and dried to form a primary sheet, and the primary sheet obtained by drying may be irradiated with VUV.

[0076] In the above description, the unit layers in the thermally conductive sheet have substantially the same composition, but the unit layers may have different compositions. The contents of the scale-like filler and the fibrous filler in each unit layer do not need to be the same, and the contents of the scale-like filler or the fibrous filler in some unit layers may be different from the contents of the scale-like filler or the fibrous filler in other unit layers. Also, the type of the scale-like filler or the fibrous filler in some unit layers may be different from the type of the scale-like filler or the fibrous filler in other unit layers.

[0077] As described above, the thermal conductivity of some unit layers may be made higher than that of other unit layers by appropriately adjusting the content and type of the scale-like filler or fibrous filler in each unit layer. In such a case, the unit layers with high thermal conductivity and the unit layers with low thermal conductivity may be arranged alternately, but they do not have to be arranged alternately.

[0078] Similarly, the conductivity of some unit layers may be lower than that of other unit layers. In such a case, the unit layers with high conductivity and the unit layers with low conductivity may be arranged alternately, but they do not have to be arranged alternately. By making the conductivity of some unit layers lower than that of the other unit layers, the conduction along the third direction (see FIG. 1) is hindered by the unit layers with low conductivity. Therefore, the conductivity in the third direction of the entire thermally conductive sheet is low, making it easier to ensure insulation. In order to make it easier to ensure insulation, it is preferable not to include a thermally conductive filler in the unit layers with low conductivity.

[0079] In addition, some of the multiple unit layers may be thermally conductive unit layers, and the other part may be optically transparent unit layers. The thermally conductive unit layers are layers containing a thermally conductive filler, preferably a scaly filler and a fibrous filler, and a non-anisotropic filler, as described above. On the other hand, the optically transparent unit layers may be layers that do not contain a thermally conductive filler. With this configuration, the entire thermally conductive sheet has a certain thermal conductivity and optical transparency along the thickness direction. The thermally conductive unit layers and the optically transparent unit layers may be arranged alternately, but do not need to be arranged alternately.

[0080] Of course, the configuration other than the conductive filler may be changed for each unit layer. For example, the type of silicone resin in some unit layers may be changed from the type of silicone resin in other unit layers. In addition, the presence or absence of an additive component in some unit layers, the type and amount of the additive component, etc. may be made different from those of other unit layers. For example, the hardness (type OO hardness) of some unit layers may be made different from the hardness of other unit layers by making at least a portion of the type or amount of silicone resin or the type or amount of thermally conductive filler of some unit layers different from that of other unit layers. EXAMPLES

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0082] In this example, the viscosity of the liquid composition (mixture) was measured by the following method, and the thermal conductivity of the thermally conductive sheet was evaluated. [Measurement of viscosity of liquid composition (mixture)] The viscosity of each liquid composition was measured using a viscometer (a rotational viscometer DV-E manufactured by BROOKFIELD) with a rotor of spindle SC4-14 at a rotation speed of 10 rpm and a measurement temperature of 25° C. The results are shown in Tables 1 and 2. [Thermal Conductivity] The thermal conductivity of the produced thermally conductive sheet in the thickness direction (first direction in FIG. 1) was measured according to a method in accordance with ASTM D5470-06. The thermal conductivity in the second and third directions in FIG. 1 was also measured according to a method in accordance with ASTM D5470-06. The results are shown in Tables 1 and 2. The thermal conductivity in the second direction is the thermal conductivity measured on a test piece (2 mm thick) cut from the laminated block of each example described below so that the second direction is the thickness direction, and the thermal conductivity in the third direction is the thermal conductivity measured on the primary sheet of each example (corresponding to primary sheet 21 in Figure 2, 2 mm thick). Also, the level of the thermal properties in the second direction as shown in FIG. 1 is shown as a percentage. Specifically, the calculation was performed using the following formula (1) so that the same as the first direction was "100%" and the same as the third direction was "0%". Thermal property level in the second direction = (λ2-λ3) / (λ1-λ3) Equation (1) λ1: Thermal conductivity in the first direction λ2: Thermal conductivity in the second direction λ3: Thermal conductivity in the third direction

[0083] [Example 1] As the curable silicone composition, an alkenyl group-containing organopolysiloxane (base agent) and a hydrogen organopolysiloxane (curing agent) (total of 100 parts by mass, volume filling rate of 40 volume%), 71.5 parts by mass (volume filling rate of 12 volume%) of scaly graphite powder (average long axis length 80 μm, aspect ratio 4-8, thermal conductivity 400 W / m·K) as a scaly filler, 58.5 parts by mass (volume filling rate of 10 volume%) of graphitized carbon fiber (average fiber length 100 μm, aspect ratio 10, thermal conductivity 500 W / m·K) as a fibrous filler, and 400 parts by mass (volume filling rate of 39 volume%) of aluminum oxide (spherical, average particle size 3 μm, aspect ratio 1.0) were mixed to obtain a slurry-like liquid composition (mixture). The viscosity of the liquid composition at 25°C was 245 Pa·s.

[0084] The liquid composition was applied in one direction on a polyethylene terephthalate (PET) substrate film at 25°C using a bar coater as an applicator. The long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler were oriented in the application direction, and the short axis was oriented in the normal direction to the application surface. Next, the applied liquid composition was heated at 120°C for 0.5 hours to harden the liquid composition, thereby obtaining a primary sheet with a thickness of 2 mm.

[0085] Both sides of each of the obtained primary sheets were irradiated with a VUV irradiation device (product name Excimer MINI, manufactured by Hamamatsu Photonics) at room temperature (25°C) in the atmosphere with an integrated light dose of 20 mJ / cm on the surface of the primary sheet. 2VUV was irradiated under the conditions of. Next, 100 sheets of the VUV-irradiated primary sheet were stacked and pressed with a roller at a pressure of 1.6 kgf / 50 mm in an environment of 25°C to obtain a laminated block. The obtained laminated block was sliced ​​with a cutter blade parallel to the stacking direction and perpendicular to the orientation direction of the long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler, to obtain a thermally conductive sheet with a thickness of each unit layer of 2 mm and a sheet thickness of 2 mm.

[0086] (Examples 2 to 6, 8, Comparative Examples 1 to 4) The same procedure as in Example 1 was carried out, except that the blending ratio of the scaly filler and the fibrous filler was changed as shown in Tables 1 and 2. In Example 8 and Comparative Example 4, scaly graphite powder having an average major axis length of 40 μm (aspect ratio 3 to 6, thermal conductivity 400 W / m K) was used as the scaly filler. The viscosity of the liquid composition at 25°C in each of Examples 2 to 4 was 267 Pa·s or more. Moreover, Examples 5, 6, and Comparative Example 3 had a viscosity higher than 600 Pa·s. More specifically, empirically, when the viscosity exceeds 600 Pa·s, the sample is no longer able to follow the rotor, causing the rotor to spin freely, making it impossible to measure an appropriate viscosity, and therefore the viscosity is expressed as ">600 Pa·s." The obtained thermally conductive sheet had a thickness of 2 mm, and each unit layer had a thickness of 2 mm.

[0087] Example 7 The same procedure as in Example 1 was carried out, except that the scaly carbon powder was replaced with boron nitride powder (average major axis length 40 μm, aspect ratio 4 to 8, thermal conductivity 100 W / m·K). The obtained thermally conductive sheet had a thickness of 2 mm, and each unit layer had a thickness of 2 mm. The filling rate of the boron nitride powder was 51.4 vol%, the filling rate of the graphitized carbon fiber was 27.3 vol%, the filling rate of the silicone resin was 36 vol%, and the filling rate of the aluminum oxide was 36 vol%. The normal direction of the scaly surface of the boron nitride powder and the graphitized carbon fiber was oriented in the lamination direction. The viscosity of the liquid composition at 25°C was 325 Pa·s. The obtained thermally conductive sheet had a thickness of 2 mm, and each unit layer had a thickness of 500 μm.

[0088] Comparative Example 5 The same liquid composition as in Example 1 was poured into a block-shaped mold, and a magnetic field of 10 Tesla was applied in a magnetic field generator so that the graphitized carbon fiber and the scaly carbon powder were oriented in the vertical direction of the mold while vibrating the molding material in the mold. Then, the mold removed from the magnetic field generator was heated at 90°C for 60 minutes to react and harden the alkenyl group-containing organopolysiloxane and the hydrogen organopolysiloxane, and then the orientation block was removed from the mold. Then, the obtained orientation block was sliced ​​perpendicular to the orientation direction (first direction) with a cutter blade to obtain a thermally conductive sheet with a thickness of 2 mm. In addition, the test piece for measuring the thermal conductivity in the second direction was prepared by slicing in an arbitrary direction perpendicular to the first direction, and the test piece for measuring the thermal conductivity in the third direction was prepared by slicing at a cross section perpendicular to both the first direction and the second direction.

[0089] [Table 1] [Table 2]

[0090] Comparing Examples 1 to 6 and Comparative Examples 1 to 3, it was found that Examples 1 to 6, in which the ratio of scaly filler / fibrous filler was 55 / 45 or more, had higher thermal conductivity in the first direction than Comparative Examples 2 and 3, in which no graphitized carbon fiber and flake graphite powder were used in combination. In particular, excellent thermal conductivity was achieved when the ratio of scaly filler / fibrous filler was in the range of 60 / 40 to 95 / 5, and the thermal conductivity was maximized when the ratio was in the range of 65 / 35 to 90 / 10.

[0091] Comparing the viscosities of Examples 1 to 6 and Comparative Examples 2 and 3, it was found that the greater the proportion of the scaly filler, the higher the viscosity. On the other hand, since the high-viscosity Examples 4 and 5 also had high thermal conductivity, it was found that the thermally conductive sheet produced by flow orientation can orient the graphitized carbon fiber and flake graphite powder even in a formulation that results in high viscosity.

[0092] When the thermal conductivity in the second direction of Examples 1 to 6 and Comparative Examples 2 and 3 was compared, it was found that the greater the proportion of the scaly filler, the higher the thermal conductivity in the second direction.

[0093] The thermal conductivity of Example 7 was 13.5 W / mK. For example, it has better properties than Comparative Example 2, which used only a fibrous filler, and it was found that the thermal conductivity can be increased even when boron nitride is used.

[0094] Comparing Example 1 and Comparative Example 5, it was found that although the composition was the same, there was a large difference in the thermal conductivity in the first direction. These samples, in which the ratio of scale-like filler / fibrous filler was 55 / 45, had a high viscosity of 245 Pa s, and it is believed that the magnetic field orientation did not sufficiently align the long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler. [Explanation of symbols]

[0095] 10. Thermally conductive sheet 11 Matrix 12 Scaly filler 13 Fibrous fillers 14 Unit Layer

Claims

1. A thermally conductive sheet comprising a scale-like filler, a fibrous filler, and a non-anisotropic filler in a polymer matrix, The long axis direction of the scale surface of the scaly filler and the fiber axis direction of the fibrous filler are oriented in the same direction in the thickness direction, A thermally conductive sheet in which the mass ratio of a scaly filler to a fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more.

2. 2. The thermally conductive sheet according to claim 1, wherein the mass ratio of the scale-like filler to the fibrous filler (scale-like filler / fibrous filler) is 65 / 35 to 95 / 5.

3. A thermal conductive sheet as described in claim 1 or 2, wherein when the thickness direction is a first direction, a direction perpendicular to the first direction is a second direction, and a direction perpendicular to the first direction and the second direction is a third direction, the thermal conductivity in the first direction is 11 W / mK or more.

4. The thermally conductive sheet according to any one of claims 1 to 3, wherein the flaky filler contains at least one of flaky graphite powder and flaky boron nitride powder.

5. The thermally conductive sheet according to any one of claims 1 to 4, wherein the fibrous filler is carbon fiber.

6. 6. The thermally conductive sheet according to claim 1, wherein the normal direction of the scaly surfaces of the scaly filler is aligned in a predetermined direction.

7. The thermally conductive sheet according to any one of claims 1 to 6, which is composed of a plurality of unit layers, each of which contains the scale-like filler and the fibrous filler and is laminated in one direction along the surface direction of the sheet.

8. A method for producing a thermally conductive sheet containing a scale-like filler, a fibrous filler, and a non-anisotropic filler in a polymer matrix, comprising: a mixture preparation step of preparing a mixture containing a resin which is a precursor of a polymer matrix, a scale-like filler, and a fibrous filler; A method for manufacturing a thermally conductive sheet, which includes an orientation treatment process in which the long axis direction of the scale-like surface of the scale-like filler and the fiber axis direction of the fibrous filler are oriented in the same direction by a flow orientation treatment when the mixture is formed into a predetermined shape.

9. A method for producing a thermally conductive sheet containing a scale-like filler, a fibrous filler, and a non-anisotropic filler in a polymer matrix, comprising: a mixture preparation step of preparing a mixture containing a resin which is a precursor of a polymer matrix, a scale-like filler, and a fibrous filler; an orientation treatment step in which the mixture is formed into a sheet by a flow orientation treatment to orient the long axis direction of the scale surface of the scale-like filler and the fiber axis direction of the fibrous filler in the same direction; preparing a plurality of primary sheets obtained through the orientation treatment step, and laminating the plurality of primary sheets to form a laminated block; and a cutting step of cutting the laminated block into sheets along the lamination direction.

10. The method for producing a thermally conductive sheet according to claim 8 or 9, wherein a mass ratio of the scaly filler to the fibrous filler (scaly filler / fibrous filler) is 55 / 45 or more.

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