Thermally conductive sheet

Abstract

To provide a thermally conductive sheet excellent in temporary sticking property and adhesiveness in addition to thermal conductivity.SOLUTION: A thermally conductive sheet comprising a composition containing graphitized particles (A) and an organic polymer compound (B), wherein the graphitized particles (A) are oriented in a thickness direction of the thermally conductive sheet, at least one of a tensile strength in an X direction and a tensile strength in a Y direction is less than 0. 8MPa, and a ratio of the tensile strength in the X direction to the tensile strength in the Y direction is more than 2.2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive sheet. [Background technology]

[0002] Conventionally, a technology for suppressing temperature rise by attaching a heat sink to a heat-generating body such as an electronic component is known. When using such a heat sink, a thermally conductive sheet-like member (thermal conduction sheet) is used to efficiently transfer heat from the heat-generating body to the heat sink. In addition, the thermal conduction sheet is also required to have adhesion to the adherend.

[0003] Known thermally conductive sheets that have thermal conductivity and adhesion to an adherend include thermally conductive sheets that contain a composition containing graphite particles oriented in the thickness direction of the thermally conductive sheet and an organic polymer compound (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-016528 [Patent Document 2] Japanese Patent Publication No. 2023-151582 [Patent Document 3] International Publication No. 2023 / 157617 Brochure [Patent Document 4] Japanese Patent Publication No. 2020-55893 [Patent Document 5] Japanese Patent Application Publication No. 2022-129990 [Patent Document 6] Japanese Patent Application Publication No. 2023-49931 Summary of the Invention [Problem to be solved by the invention]

[0005] The thermally conductive sheets described in Patent Documents 1 to 6 have a certain level of thermal conductivity and adhesion. Meanwhile, in recent years, for example, high-performance CPUs and GPUs have been used in servers, supercomputers, and automotive ECUs (electronic control units), and as the amount of information processed increases and processing speeds improve, chip temperatures tend to rise. Because chip temperature increases can cause a decrease in CPU performance, more efficient heat dissipation is required, even in high-temperature environments. To accommodate such applications, thermally conductive sheets with lower thermal resistance and higher thermal conductivity than conventional ones are required. Furthermore, thermally conductive sheets are typically stored adhered to a backing, and when temporarily attached to a substrate, they are peeled off the backing and temporarily attached to the substrate. However, conventional thermally conductive sheets, such as those described in Patent Documents 1 to 5, have room for improvement in terms of ease of removal from the backing and ease of attachment to the substrate, i.e., temporary attachment. Furthermore, the conventional thermal conductive sheets have room for improvement in terms of adhesion to the adherend, for example, adhesion to the heat generating element and the heat radiator when the sheets are heated and attached to the heat generating element and the heat radiator.

[0006] Therefore, an object of one aspect of the present invention is to provide a thermally conductive sheet that is excellent not only in thermal conductivity but also in temporary attachment property and adhesion property. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a thermally conductive sheet according to one embodiment of the present invention is a thermally conductive sheet comprising a composition containing graphite particles (A) and (B), the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, At least one of the tensile strength in the X direction and the tensile strength in the Y direction is less than 0.8 MPa, and This is a thermally conductive sheet in which the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction) is more than 2.2 times. [Effects of the Invention]

[0008] According to one aspect of the present invention, a thermally conductive sheet can be provided that has excellent thermal conductivity, temporary attachment properties, and adhesion properties, and can therefore be suitably used in applications that require efficient heat dissipation. DETAILED DESCRIPTION OF THE INVENTION

[0009] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0010] [1. Thermal Conduction Sheet] A thermally conductive sheet according to one embodiment of the present invention is a thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and at least one of the tensile strength in the X direction and the tensile strength in the Y direction is less than 0.8 MPa, and the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in X direction / tensile strength in Y direction) is more than 2.2 times.

[0011] [1-1. Tensile strength] In a thermal conduction sheet according to one embodiment of the present invention, at least one of the tensile strength in the X direction and the tensile strength in the Y direction is less than 0.8 MPa, and the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction) is more than 2.2 times.

[0012] In this specification, the "X direction" refers to the in-plane direction in which the thermal conductivity is highest when measured on the main surface of the thermal conductive sheet, and the "Y direction" refers to the in-plane direction perpendicular to the X direction. Furthermore, in this specification, the "main surface" refers to at least one surface of the thermal conductive sheet.

[0013] Furthermore, a thermally conductive sheet manufactured by a manufacturing method including a step of slicing a cross section of a laminate formed by stacking primary sheets, as described below, may have a striped pattern corresponding to the laminate structure of the primary sheets. When a thermally conductive sheet according to an embodiment of the present invention has the striped pattern, the X direction is typically perpendicular to the stacking direction of the laminate, specifically, parallel to the striped pattern and corresponding to the horizontal plane of the primary sheets. On the other hand, when a thermally conductive sheet according to an embodiment of the present invention has the striped pattern, the Y direction is typically the same as the stacking direction of the laminate, specifically, perpendicular to the striped pattern and corresponding to the thickness direction of the primary sheets, i.e., the stacking direction of the primary sheets.

[0014] In this specification, "tensile strength in the X direction" is also referred to as "tensile strength (X)," "tensile strength in the Y direction" is also referred to as "tensile strength (Y)," and "the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction)" is also referred to as "tensile strength ratio." Furthermore, in this specification, the feature of the thermal conductive sheet according to one embodiment of the present invention, that "at least one of the tensile strength (X) and the tensile strength (Y) is less than 0.8 MPa, and the tensile strength ratio is more than 2.2 times," is also referred to as "feature A."

[0015] When a thermally conductive sheet is temporarily attached or heated to be attached to an adherend, stress is applied to the thermally conductive sheet. Furthermore, when an environmental test is performed in which the thermally conductive sheet is attached to an adherend and maintained at a high temperature or exposed to high and low temperatures continuously, the materials constituting the thermally conductive sheet and the adherend expand and contract due to changes in temperature and humidity. In other words, the dimensions of the materials change during the environmental test. These dimensional changes also apply stress to the thermally conductive sheet.

[0016] In essence, a thermally conductive sheet having Feature A means that it has low tensile strength in one of the X and Y directions. A thermally conductive sheet with low tensile strength in one direction can release the applied stress to the side with the lower tensile strength, improving temporary adhesion and adhesion to the substrate. As a result, the thermally conductive sheet according to one embodiment of the present invention has excellent temporary adhesion and adhesion.

[0017] Furthermore, in the thermally conductive sheet according to one embodiment of the present invention, the graphite particles (A) are oriented in the thickness direction, which gives the thermally conductive sheet excellent thermal conductivity (low thermal resistance). The thermally conductive sheet having Feature A has a tensile strength ratio of more than 2.2 times, and high tensile strength in one direction, which prevents significant deformation when laminated, and maintains the orientation of the graphite in the thickness direction. As a result, the thermally conductive sheet according to one embodiment of the present invention has excellent thermal conductivity (low thermal resistance).

[0018] As described above, the thermally conductive sheet according to one embodiment of the present invention has the effect of being excellent not only in thermal conductivity but also in temporary attachment property and adhesion property.

[0019] In this specification, "adhesion" refers not only to the adhesion when the thermally conductive sheet is attached to the adherend, i.e., initial adhesion, but also to adhesion after high-temperature exposure and adhesion after heat cycles. Here, "adhesion after high-temperature exposure" refers to the adhesion between the thermally conductive sheet and the adherend when the thermally conductive sheet is attached to the adherend and held in a high-temperature environment while in close contact with the adherend. Furthermore, "adhesion after heat cycles" refers to the adhesion between the thermally conductive sheet and the adherend when the thermally conductive sheet is attached to the adherend and held in a high-temperature environment while in a high-temperature environment while in close contact with the adherend.

[0020] A large tensile strength ratio means a large difference in tensile strength between the X and Y directions. In this case, the aforementioned stress is more likely to move and escape in the direction of lower tensile strength. Therefore, a larger tensile strength ratio improves the temporary attachment and adhesion of the thermal conductive sheet according to one embodiment of the present invention. From this perspective, in one embodiment of the present invention, the lower limit of the tensile strength ratio is greater than 2.2 times, preferably 3.0 times or more, and more preferably 3.4 times or more.

[0021] On the other hand, by having the tensile strength ratio be equal to or less than a predetermined value, it is possible to preferably prevent a decrease in the accuracy of temporary attachment due to large dimensional changes in the X and Y directions when temporarily attached. Furthermore, by having the tensile strength ratio be equal to or less than a predetermined value, it is possible to preferably prevent the thermal conductive sheet from being damaged on the side with lower tensile strength due to the attachment force when heated and attached, thereby further improving adhesion. Furthermore, in the environmental test, it is possible to preferably prevent the thermal conductive sheet from being damaged on the side with lower tensile strength due to dimensional changes in the material caused by changes in temperature and humidity, thereby further improving adhesion.

[0022] As described above, in the thermal conductive sheet according to one embodiment of the present invention, the tensile strength ratio is a predetermined value or less, thereby enabling the temporary attachment property and adhesion property to be further improved. From this viewpoint, in one embodiment of the present invention, the upper limit of the tensile strength ratio is preferably 10.0 times or less, more preferably 7.0 times or less, and even more preferably 6.0 times or less.

[0023] In a thermal conductive sheet according to one embodiment of the present invention, the tensile strength ratio is more than 2.2 times, so the tensile strength (Y) is smaller than the tensile strength (X). Furthermore, at least one of the tensile strength (Y) and the tensile strength (Y) is less than 0.80 MPa. Therefore, in one embodiment of the present invention, the tensile strength (Y) is less than 0.80 MPa.

[0024] In one embodiment of the present invention, when the tensile strength (Y) is low, the tensile strength ratio increases, making it easier to release the aforementioned stress in the Y direction where the tensile strength is low. Therefore, it is believed that the temporary attachment property and adhesion of the thermal conductive sheet according to one embodiment of the present invention are further improved. From this perspective, in one embodiment of the present invention, the tensile strength (Y) is preferably less than 0.50 MPa, more preferably less than 0.30 MPa, and even more preferably 0.25 MPa or less. On the other hand, in terms of the strength of the thermal conductive sheet itself, the tensile strength (Y) is preferably a predetermined value or greater. Specifically, the tensile strength (Y) is preferably 0.05 MPa or greater, more preferably 0.10 MPa or greater, and even more preferably 0.12 MPa or greater.

[0025] In one embodiment of the present invention, when the tensile strength (X) is low, the tensile strength ratio can be suitably controlled within a predetermined range or less, thereby further improving temporary adhesion and adhesion for the reasons described above. From this perspective, in one embodiment of the present invention, the tensile strength (X) is preferably less than 2.00 MPa, more preferably less than 1.00 MPa, and even more preferably less than 0.70 MPa. On the other hand, from the perspective of the strength of the thermal conductive sheet itself and of adjusting the tensile strength ratio to a preferred range of a predetermined amount or more to maintain temporary adhesion, adhesion, and the orientation of the graphite in the thickness direction while improving thermal conductivity, it is preferable that the tensile strength (X) be a predetermined value or more. Specifically, the tensile strength (X) is preferably 0.10 MPa or more, more preferably 0.30 MPa or more, and even more preferably 0.50 MPa or more.

[0026] In one embodiment of the present invention, the method for measuring the tensile strength (X) and the tensile strength (Y) is not particularly limited, and any known method for measuring tensile strength can be used, for example, the method described in the Examples can be used.

[0027] [1-2. Composition containing graphite particles (A) and organic polymer compound (B)] (Graphite particles (A)) In one embodiment of the present invention, the thermally conductive sheet contains graphite particles (A), and the thermally conductive graphite particles (A) are dispersed in the thermally conductive sheet, thereby improving the thermal conductivity of the thermally conductive sheet and thereby reducing the thermal resistance of the thermally conductive sheet.

[0028] The shape of the graphite particles (A) may be spherical or non-spherical. The heat conductive sheet preferably contains non-spherical graphite particles (A) because the graphite particles are easily oriented, which improves thermal conductivity in the orientation direction and thereby reduces thermal resistance in the orientation direction. The graphite particles (A) may be used alone or in combination of two or more types.

[0029] The shape of the non-spherical graphite particles (A) is not particularly limited, and may be, for example, a plate-like shape such as a scale-like or thin plate-like shape; an ellipsoidal shape; a needle-like shape; a rod-like shape; a fiber-like shape; or an irregular shape. Among these, the shape of the non-spherical graphite particles (A) is more preferably a plate-like shape such as a scale-like or thin plate-like shape, from the viewpoint that the non-spherical graphite particles (A) are easily oriented and inter-particle contact is easily maintained, thereby further improving thermal conductivity in the orientation direction and thereby further reducing thermal resistance in the orientation direction.

[0030] In this specification, "spherical" refers to a true sphere or ellipsoid with an aspect ratio of 1.0 to 1.5, in other words, a true sphere with an aspect ratio of 1.0 or an ellipsoid with an aspect ratio of more than 1.0 but not more than 1.5, and does not necessarily have to be a true sphere. When the graphite particles (A) are "spherical," the aspect ratio refers to the ratio expressed as the major axis / minor axis. Furthermore, "non-spherical" refers to a shape other than the aforementioned "spherical," i.e., a shape with an aspect ratio exceeding 1.5. Furthermore, "ellipsoidal" refers to an ellipsoid shape formed by rotating an ellipse, such as a rugby ball.

[0031] In "non-spherical" graphite particles (A), the aspect ratio means the ratio of the maximum length to the minimum length of the graphite particles (A) (maximum length / minimum length), and for example, in the case of a plate-like shape, it is the ratio of the maximum length to the thickness of the graphite particles (A) (maximum length / thickness). The aspect ratio can be determined by observing a sufficient number of graphite particles (A) (e.g., 10 or more) with a scanning electron microscope, calculating the major axis / minor axis or the maximum length / minimum length of each graphite particle (A), and averaging these values.

[0032] When two or more types of graphite particles (A) are used, the aspect ratio is an average aspect ratio calculated as a weighted average of the aspect ratios of the respective graphite particles (A).

[0033] From the viewpoint of improving thermal conductivity in the orientation direction, the aspect ratio of the graphite particles (A) is preferably 20 or more, more preferably 40 or more, and even more preferably 70 or more. There is no particular upper limit, but it is usually 1000 or less. When the aspect ratio of the graphite particles (A) is 20 or more, by orienting the graphite particles (A) in the thickness direction of the thermal conductive sheet, the thermal conductivity in the thickness direction of the thermal conductive sheet can be further improved, and thus the thermal resistance in the thickness direction of the thermal conductive sheet can be further reduced, which is preferable.

[0034] Examples of the graphite particles (A) used in one embodiment of the present invention include particles such as flake graphite, flaky graphite, amorphous graphite, artificial graphite, exfoliated graphite, acid-treated graphite, expanded graphite, and carbon fiber flakes.

[0035] The average particle size of the graphite particles (A) is preferably 20 μm to 1000 μm, more preferably 30 μm to 500 μm, and particularly preferably 40 μm to 240 μm. Here, the average particle size of the graphite particles (A) is a value determined by a laser diffraction / scattering particle size distribution analyzer (LA-920 manufactured by Horiba, Ltd.).

[0036] When the average particle size of the graphite particles (A) is 20 μm or more, the graphite particles (A) are oriented in a desired direction in the heat conductive sheet, and a good heat transfer path is easily formed. Furthermore, when the upper limit of the average particle size of the graphite particles (A) is within the above-mentioned range, the graphite particles are exposed on the surface of the heat conductive sheet, and when the sheet comes into contact with a heating element, the heat transfer from the heating element to the heat conductive sheet can be improved.

[0037] When the graphite particles (A) are plate-like, their average thickness is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm, and particularly preferably 0.3 μm to 3 μm. Here, the average thickness of the graphite particles (A) can be determined by observing a sufficient number (e.g., 10 or more) of graphite particles (A) with an ultra-high resolution scanning electron microscope (S-4800 manufactured by Hitachi, Ltd.), calculating the thickness of each graphite particle (A), and averaging these values.

[0038] If the lower limit of the average thickness of the graphite particles (A) is within the above-mentioned range, the heat transport amount per particle increases, and good heat transfer paths are easily formed. Also, if the upper limit of the average thickness of the graphite particles (A) is within the above-mentioned range, the number of graphite particles (A) per unit weight increases, and the graphite particles (A) interfere with each other, aligning them in the desired direction, and good heat transfer paths are easily formed.

[0039] In the thermally conductive sheet according to one embodiment of the present invention, when the degree of orientation of the graphite particles (A) is relatively high, the graphite particles (A) are suitably oriented in the thickness direction of the thermally conductive sheet, and as a result, the thermal resistance of the thermally conductive sheet is reduced and superior thermal conductivity is exhibited.

[0040] On the other hand, when the degree of orientation of the graphite particles (A) in the thermally conductive sheet is relatively low, the orientation of the graphite particles (A) is somewhat disordered. Therefore, when the degree of orientation of the graphite particles (A) is relatively low, the thermally conductive sheet is more likely to conform to the adherend when force is applied during the temporary attachment. Furthermore, when the degree of orientation of the graphite particles (A) is relatively low, force is also applied when the thermally conductive sheet is heated and attached to an adherend such as a heating element or a radiator, and the thermally conductive sheet is more likely to conform to the adherend. As described above, when the degree of orientation of the graphite particles (A) in the thermally conductive sheet is relatively low, better temporary attachment properties and better adhesion are exhibited.

[0041] Examples of indicators representing the degree of orientation of the graphite particles (A) include the (110) plane orientation degree and the (002) plane orientation degree of the graphite particles, which are calculated by the Lotgering method using an X-ray diffraction profile. Hereinafter, the "(110) plane orientation degree of the graphite particles calculated by the Lotgering method using an X-ray diffraction profile" will be simply referred to as the "(110) plane orientation degree of the graphite particles." Furthermore, the "(002) plane orientation degree of the graphite particles calculated by the Lotgering method using an X-ray diffraction profile" will be simply referred to as the "(002) plane orientation degree of the graphite particles." The method for obtaining the X-ray diffraction profile is not particularly limited and may be a method using a commercially available X-ray diffractometer, more specifically, the method described in the Examples. The method for calculating the (110) plane orientation degree and the (002) plane orientation degree of the graphite particles is not particularly limited and may be, for example, the method described in the Examples.

[0042] From the viewpoint of achieving the above-mentioned superior thermal conductivity, the degree of orientation of the (110) plane of the graphite particles is preferably 0.010 or more, more preferably 0.020 or more, and even more preferably 0.032 or more. Furthermore, from the viewpoint of achieving the above-mentioned superior temporary attachment property and superior adhesion property, the degree of orientation of the (110) plane of the graphite particles is preferably less than 0.081, more preferably less than 0.065, and even more preferably less than 0.045.

[0043] From the viewpoint of achieving the above-mentioned superior thermal conductivity, the degree of orientation of the (002) plane of the graphite particles is preferably −0.10 or more, more preferably 0.00 or more, and even more preferably 0.10 or more. Furthermore, from the viewpoint of achieving the above-mentioned superior temporary attachment property and superior adhesion property, the degree of orientation of the (002) plane of the graphite particles is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less.

[0044] Another index representing the degree of orientation of the graphite particles (A) is, for example, the degree of orientation of the graphite particles calculated by the following formula (1) using an X-ray diffraction profile. Hereinafter, "the degree of orientation of the graphite particles calculated by the following formula (1) using an X-ray diffraction profile" will also be referred to as "degree of orientation A of the graphite particles." Orientation of graphite particles = {sum of vertical counts + (sum of diagonal counts / 2)} / horizontal counts (1) (In formula (1), the vertical count sum is the sum of the (100) plane orientation degree and the (110) plane orientation degree, the diagonal count sum is the sum of the (101) plane orientation degree and the (112) plane orientation degree, and the horizontal count is the (002) plane orientation degree.) The method for obtaining the X-ray diffraction profile may be the same as the method for obtaining the X-ray diffraction profile used to calculate the (110) plane orientation degree of graphite particles. The method for measuring each orientation degree in formula (1) using the X-ray diffraction profile and calculating the vertical count sum, diagonal count sum, and horizontal count sum using each orientation degree is not particularly limited, and the method described in the Examples can be adopted.

[0045] From the viewpoint of achieving the above-mentioned superior thermal conductivity, the degree of orientation A of the graphite particles is preferably 0.10 or more, more preferably 0.15 or more, and even more preferably 0.20 or more. Also, from the viewpoint of achieving the above-mentioned superior temporary attachment property and superior adhesion property, the degree of orientation A of the graphite particles is preferably less than 0.37, more preferably less than 0.33, and even more preferably less than 0.30.

[0046] (Organic polymer compound (B)) In the thermally conductive sheet according to one embodiment of the present invention, the organic polymer compound (B) functions as a binder and also improves the flexibility of the thermally conductive sheet, thereby enabling good adhesion between the heat generating element and the heat dissipating element via the thermally conductive sheet.

[0047] The organic polymer compound (B) is not particularly limited, and any organic polymer compound that is normally used in a heat conductive sheet can be used.

[0048] Examples of the organic polymer compound (B) include acrylic ester resins, resins having a main chain consisting of repeating siloxane bonds (silicone resins), resins having rubber elasticity at room temperature (elastomer resins), epoxy resins, fluororesins, polyolefins, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyacetal, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, polyphenylene ether, modified polyphenylene ether, aliphatic polyamides, aromatic polyamides, polyamideimide, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, polyurethane, liquid crystal polymers, and ionomers. These may be used alone or in combination.

[0049] The organic polymer compound (B) may be solid or liquid at room temperature. In this specification, "room temperature" refers to 20°C.

[0050] The Tg and weight-average molecular weight of the organic polymer compound (B) are preferably in the same ranges as the preferred ranges of the Tg and weight-average molecular weight of the acrylate ester resin described below, thereby providing the thermally conductive sheet with the same effects as when the Tg and weight-average molecular weight of the acrylate ester resin are in the preferred ranges.

[0051] The content of the organic polymer compound (B) relative to the total weight of the thermally conductive sheet is preferably 10% by weight or more, more preferably 15% by weight or more, and even more preferably 20% by weight or more. When the content of the organic polymer compound (B) is 10% by weight or more, the flexibility of the thermally conductive sheet is improved, and the heat-generating body and the heat-dissipating body can be well adhered to each other via the thermally conductive sheet.

[0052] The content of the organic polymer compound (B) relative to the total weight of the heat conductive sheet is preferably 60% by weight or less, more preferably 50% by weight or less, and even more preferably 40% by weight or less.

[0053] (Acrylate ester resin) The organic polymer compound (B) preferably contains an acrylic ester resin. The use of the acrylic ester resin has the advantage of providing a thermally conductive sheet that is adhesive and elastic enough to restore its thickness. The acrylic ester resin may be used alone or in combination of two or more.

[0054] The acrylic ester resin includes a polymer of a monomer component containing one or more acrylic monomers selected from (meth)acrylic acid and (meth)acrylic esters, and a copolymer of the acrylic monomer with another monomer. In this specification, "(meth)acrylic" includes both "methacrylic" and "acrylic." Examples of the (meth)acrylic ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0055] Examples of the other monomers include acrylonitrile, glycidyl methacrylate, and 2-chloroethyl vinyl ether. Acrylic rubber can be obtained by copolymerizing a (meth)acrylic acid ester with acrylonitrile, 2-chloroethyl vinyl ether, or the like. Acrylic rubber is also classified as an elastomer resin, which will be described later, but in this specification, acrylic rubber is considered to be included in acrylic acid ester-based resins.

[0056] A more preferred example of the acrylic ester resin is an acrylic ester resin containing either or both of butyl acrylate and 2-ethylhexyl acrylate as monomers, the total amount of which is 50 wt % or more based on the total amount of monomer components. This acrylic ester resin is preferred because it is easy to achieve high flexibility, has excellent chemical stability and processability, and is easy to control adhesiveness. Furthermore, incorporating a crosslinked structure into the acrylic ester resin without impairing flexibility is preferred in terms of long-term adhesion retention and film strength. The crosslinked structure can be incorporated, for example, by reacting a polymer having a hydroxyl group with a compound having an isocyanate group. Alternatively, the crosslinked structure can be incorporated, for example, by reacting a polymer having a carboxyl group with a compound having an epoxy group.

[0057] The content of the acrylic ester resin relative to the total weight of the organic polymer compound (B) is preferably 15% by weight or more, more preferably 20% by weight or more, even more preferably 25% by weight or more, and particularly preferably 30% by weight or more. The content of the acrylic ester resin relative to the total weight of the organic polymer compound (B) may be, for example, 100% by weight.

[0058] The Tg of the acrylic ester resin is preferably −35° C. or lower, more preferably −50° C. or lower, and even more preferably −60° C. or lower. When the Tg of the acrylic ester resin is −35° C. or lower, the acrylic ester resin becomes more likely to flow when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic ester resin is not particularly limited and is, for example, −150° C. or higher. The “Tg” described in this specification can be calculated, for example, by the method described in the Examples.

[0059] The acrylic ester resin may be solid or liquid at room temperature and normal pressure, and is preferably liquid at room temperature and normal pressure.

[0060] In this specification, "room temperature" means 20°C, and "normal pressure" means 1 atm. In other words, the acrylic ester resin is preferably an acrylic ester resin having a melting point of 20°C or lower. The "melting point" described in this specification refers to the melting point under normal pressure (1 atm). In addition, in this specification, "being liquid" means that the resin flows when the container, such as a bottle or a can, is tilted while the resin is held in the container at room temperature (20°C). The resin may also be a block resin.

[0061] The weight-average molecular weight of the acrylic ester resin is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 250,000 or more. Because the weight-average molecular weight of the acrylic ester resin is as high as 50,000 or more, the acrylic ester resin is less likely to flow when the press plate is released after the hot press during lamination, or when an external force is applied to the thermal conductive sheet after lamination. This allows for even greater adhesion between the thermal conductive sheet and the adherend.

[0062] The weight-average molecular weight of the acrylic ester resin is preferably 3 million or less, more preferably 2 million or less, and even more preferably 1.5 million or less. When the weight-average molecular weight of the acrylic ester resin is 3 million or less, the acrylic ester resin becomes more fluid when the thermal conductive sheet is attached using a hot press. This improves the wettability of the thermal conductive sheet with the attached adherend, thereby increasing the adhesion between the thermal conductive sheet and the adherend.

[0063] The weight average molecular weight described in this specification can be measured, for example, by gel permeation chromatography of the object to be measured using a calibration curve of standard polystyrene.

[0064] The organic polymer compound preferably includes an acrylate resin having a functional group. In this specification, the term "acrylate resin having a functional group" means that the acrylate resin includes a polymer of monomer components including a monomer having a functional group.

[0065] The functional group has the function of binding a plurality of the graphite particles (A). Therefore, by providing the acrylic ester resin with the functional group, the composition can be formed into a sheet, and as a result, a thermally conductive sheet containing the composition can be provided. In addition, the functional group may interact with a substance constituting the surface of an adherend, contributing to the adhesion between the thermally conductive sheet and the adherend. In this case, it is believed that the adhesion between the thermally conductive sheet and the adherend is also improved.

[0066] The type of the functional group is not particularly limited as long as it has the function of binding multiple graphite particles (A). The functional group may be one type or two or more types. The functional group may be, for example, one or more types selected from a hydroxyl group, a carboxyl group, and an epoxy group, preferably a hydroxyl group and / or a carboxyl group, and more preferably a hydroxyl group. The type of the functional group can be identified by known methods, such as structural analysis of the acrylic ester resin using NMR or the like.

[0067] The monomer having a functional group is not particularly limited, and preferred examples include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-1-methyl (meth)acrylate, acrylic acid, methacrylic acid, glycidyl (meth)acrylate, etc. Among these, it is more preferred that the monomer having a functional group contains 2-ethylhexyl acrylate, in other words, that the acrylic ester resin contains a copolymer containing 2-ethylhexyl acrylate as a monomer.

[0068] In one embodiment of the present invention, when the content of the functional group relative to the total weight of the acrylic ester resin is high, the graphite particles (A) are more suitably bound to each other via the acrylic ester resin in the thermal conductive sheet. As a result, the graphite binding property of the thermal conductive sheet is further improved. Hereinafter, the content of the functional group relative to the total weight of the acrylic ester resin is referred to as the "functional group content C." The functional group content C is the sum of the functional group content A and the functional group content B described below.

[0069] The preferred range of the functional group content C is 0.001 mmol / g or more and 0.410 mmol / g or less. The preferred range of the functional group content C can vary depending on the type of the functional group and the type of the graphite particles (A). For example, when the functional group is one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group, from the viewpoint of further improving graphite binding, the functional group content C is preferably 0.001 mmol / g or more, more preferably 0.010 mmol / g or more, and even more preferably 0.090 mmol / g or more. The functional group content can also be expressed in the commonly used unit "mg KOH / g" in addition to the unit "mmol / g." Specifically, for example, when the functional group is one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group, the content C of the functional group is preferably 0.056 KOHmg / g or more, more preferably 0.56 KOHmg / g or more, and even more preferably 5.05 KOHmg / g or more.

[0070] Furthermore, the functional groups can also typically form bonds with water molecules. Therefore, when the functional group content C is within a predetermined range, the affinity of the acrylic ester resin for water is reduced, thereby reducing its moisture absorption. As a result, the moisture absorption of the thermal conductive sheet is controlled within a suitable range, resulting in improved adhesion after high-temperature storage.

[0071] For example, when the functional group is a hydroxyl group, from the viewpoint of further improving the adhesion after the high-temperature holding, the content C of the functional group is preferably 0.371 mmol / g or less, more preferably 0.340 mmol / g or less, and even more preferably 0.300 mmol / g or less. Furthermore, when the functional group is a hydroxyl group and the content C of the functional group is expressed in units of "KOHmg / g", it is preferably 20.76 KOHmg / g or less, more preferably 19.08 KOHmg / g or less, and even more preferably 16.83 KOHmg / g or less.

[0072] For example, when the functional group is a carboxyl group, from the viewpoint of further improving the adhesion after the high-temperature holding, the content C of the functional group is preferably 0.410 mmol / g or less, more preferably 0.360 mmol / g or less, and even more preferably 0.300 mmol / g or less. Furthermore, when the functional group is a carboxyl group and the content C of the functional group is expressed in units of "KOHmg / g", it is preferably 23.00 KOHmg / g or less, more preferably 20.20 KOHmg / g or less, and even more preferably 16.83 KOHmg / g or less.

[0073] To convert from mmol / g to mg / g of KOH, multiply mmol / g by 56.1056 mg / mmol.

[0074] The method for measuring the content C of functional groups is not particularly limited, and examples thereof include a method including the following steps (1) to (3). (1) Using a known method, the acrylic ester resin is extracted from the thermally conductive sheet, and the weight (unit: g) of the entire extracted acrylic ester resin is measured. (2)H 1 The amount of the functional group (unit: mmol) in the acrylic ester resin extracted in step (1) is measured using NMR or the like. (3) The amount of the functional group in the acrylate resin measured in step (2) is divided by the weight of the entire acrylate resin measured in step (1) to calculate the content of the functional group (unit: mmol / g).

[0075] Furthermore, when the weight-average molecular weights of all polymers contained in the acrylic ester-based resin, the content of the monomer having the functional group in all the constituent monomers, and the content ratio of each polymer are known, the functional group content C can also be calculated based on these.

[0076] The acrylic ester resin more preferably contains an acrylic resin and / or an acrylic block copolymer having functional groups. In particular, the organic polymer compound (B) preferably contains an acrylic resin or an acrylic block copolymer having functional groups, and more preferably contains an acrylic resin and an acrylic block copolymer having functional groups. The acrylic resin having functional groups may consist of an acrylic resin having one type of functional group, or may be a mixture of acrylic resins having two or more types of functional groups. The acrylic block copolymer may consist of one type of acrylic block copolymer, or may be a mixture of two or more types of acrylic block copolymers.

[0077] <Acrylic resin with functional groups> The glass transition temperature (Tg) of the acrylic resin having the functional group is preferably −35°C or lower, more preferably −50°C or lower, and even more preferably −60°C or lower. When the Tg of the acrylic resin having the functional group is −35°C or lower, the acrylic ester resin becomes more fluid when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic resin having the functional group is not particularly limited, and is, for example, −150°C or higher.

[0078] The weight-average molecular weight of the acrylic resin having a functional group is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. The weight-average molecular weight of the acrylic resin having a functional group is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. By adjusting the weight-average molecular weight of the acrylic resin having a functional group to fall within the aforementioned preferred range, the weight-average molecular weight of the acrylic ester resin can be suitably controlled within the aforementioned preferred range. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the acrylic resin having a functional group is preferably 1.0 to 10.0.

[0079] The acrylic resin having the functional group may be solid or liquid at room temperature and pressure, and is preferably liquid. In other words, the acrylic resin having the functional group is preferably an acrylic resin having a melting point of 20°C or less.

[0080] The acrylic resin having a functional group preferably contains 50% by weight or more of repeating units derived from an acrylic monomer. The acrylic resin having a functional group contains a polymer of monomer components in which at least a portion of the constituent monomers has the functional group and which contains one or more acrylic monomers. The acrylic monomer and other monomers can be the acrylic monomers and other monomers described above as monomers that can constitute the acrylic ester resin.

[0081] The ratio of the weight of the functional group-containing monomer to the weight of all monomers constituting the functional group-containing acrylic resin is preferably 0.1 to 5.2 wt%, more preferably 0.3 to 4.0 wt%. Furthermore, the ratio of the amount of the functional group-containing monomer to the amount of all monomers constituting the functional group-containing acrylic resin is preferably 0.1 mol% to 5.0 mol%, more preferably 0.3 mol% to 4.0 mol%. Adjusting this ratio within the range described below is preferable in terms of suitably controlling the content of the functional group in the functional group-containing acrylic resin within the aforementioned range. The functional group-containing monomer may be any of the monomers described above as monomers capable of constituting the acrylic ester-based resin. Hereinafter, the content of the functional group relative to the weight of the functional group-containing acrylic resin will be referred to as the "functional group content A."

[0082] From the viewpoint of further improving the graphite binding property, the content A of the functional group is preferably 0.010 mmol / g or more, and more preferably 0.050 mmol / g or more, based on the total weight of the acrylic resin having the functional group.

[0083] Furthermore, when the thermally conductive sheet is maintained in a high-temperature environment and heated, the water absorbed by the heat is expelled, causing the sheet's shape to change, potentially resulting in poor adhesion to the adherend after the high-temperature exposure. Specifically, a thermally conductive sheet containing a highly hygroscopic acrylate ester resin is thought to absorb a large amount of water from the air. In this case, the large amount of water expelled increases the degree of deformation, resulting in gaps between the thermally conductive sheet and the adherend, potentially reducing adhesion to the adherend. Furthermore, it is believed that a thermally conductive sheet with excellent adhesion to the adherend after high-temperature exposure can be achieved when the acrylate ester resin is poorly water-soluble.

[0084] In one embodiment of the present invention, when the content A of functional groups is low, the functional groups can react with ordinary water molecules (HO), which reduces the affinity of the acrylic ester resin for water and reduces its hygroscopicity. As a result, the hygroscopicity of the thermally conductive sheet is controlled within a suitable range, resulting in improved adhesion after being maintained at high temperatures.

[0085] Specifically, for example, when the functional group is a hydroxyl group, from the viewpoint of improving the adhesion after being kept at high temperature, the content A of the functional group is preferably 0.371 mmol / g or less, more preferably 0.340 mmol / g or less, and even more preferably 0.300 mmol / g or less, relative to the weight of the entire acrylic resin having the functional group.

[0086] Furthermore, for example, when the functional group is a carboxyl group, from the viewpoint of improving the adhesion, the content A of the functional group is preferably 0.410 mmol / g or less, more preferably 0.360 mmol / g or less, and even more preferably 0.300 mmol / g or less, relative to the total weight of the acrylic resin having the functional group.

[0087] By keeping the functional group content A within the above range, it is possible to suitably control the functional group content C within a preferred range. Note that, as a method for measuring the functional group content A, for example, the same method as the method for measuring the functional group content C can be mentioned, except that the target is an acrylic resin having the functional groups.

[0088] The acrylic resin having the functional group may be a random copolymer or a block copolymer, but a random copolymer is preferred because it is more readily available.The structure of the acrylic resin having the functional group may be either linear or branched, but a linear structure is preferred because it is more readily available.

[0089] <Acrylic block copolymer> The acrylic block copolymer has a block structure and therefore has a Tg at both low and high temperatures. Because the acrylic block copolymer has a Tg at low temperatures, a thermally conductive sheet containing the acrylic block copolymer remains soft even at low temperatures. Therefore, the thermally conductive sheet containing the acrylic block copolymer can maintain adhesion even when exposed to low temperatures. Furthermore, because the acrylic block copolymer has a Tg at high temperatures, the thermally conductive sheet containing the acrylic block copolymer does not become too soft even at high temperatures and remains elastic. Therefore, the thermally conductive sheet containing the acrylic block copolymer can maintain adhesion even when exposed to high temperatures. Therefore, the thermally conductive sheet exhibits excellent adhesion even after being held at high temperatures.

[0090] The low-temperature Tg of the acrylic block copolymer is preferably −35°C or lower, more preferably −50°C or lower. When the low-temperature Tg of the acrylic block copolymer is −35°C or lower, the acrylic ester resin becomes more fluid when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the low-temperature Tg of the acrylic block copolymer is not particularly limited, and is, for example, −150°C or higher, preferably −55°C or higher.

[0091] The lower limit of the high-temperature Tg of the acrylic block copolymer is preferably 100° C. or higher, more preferably 102° C. or higher. The upper limit of the high-temperature Tg of the acrylic block copolymer is preferably 120° C. or lower, more preferably 118° C. or lower. When the high-temperature Tg is within the above-mentioned range, the thermal conductive sheet can be more effectively prevented from becoming excessively soft at high temperatures and can more effectively maintain its elasticity at high temperatures, resulting in improved adhesion after being held at high temperatures.

[0092] The weight-average molecular weight of the acrylic block copolymer is preferably 10,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. The weight-average molecular weight of the acrylic block copolymer is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. By adjusting the weight-average molecular weight of the acrylic block copolymer within the above-mentioned preferred range, the weight-average molecular weight of the acrylic ester resin can be suitably controlled within the preferred range described below. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the acrylic block copolymer is preferably 1.0 to 2.0.

[0093] The acrylic block copolymer may be solid or liquid at room temperature and normal pressure, and is preferably liquid. In other words, the acrylic block copolymer preferably has a melting point of 20° C. or lower.

[0094] The acrylic block copolymer preferably contains 50% by weight or more of repeating units derived from an acrylic monomer. The acrylic block copolymer includes a copolymer of a monomer component containing two or more types of acrylic monomers. The acrylic block copolymer also includes a copolymer of one or more types of acrylic monomers and one or more types of other monomers. The acrylic monomers and other monomers may be the acrylic monomers and other monomers described above as monomers that can constitute the acrylic ester resin.

[0095] The acrylic block copolymer is a block copolymer. Here, the term "block copolymer" refers to a polymer in which the majority of the main chain, preferably the entire main chain, is a polymer in which blocks having two or more different chemical structures are linked together. The blocks are composed of repeating units derived from two or more monomers. The majority of the main chain refers to a portion composed of repeating units derived from, for example, 95% or more, preferably 97% or more of the total number of repeating units derived from the monomers constituting the main chain.

[0096] Examples of the block structure of the acrylic block copolymer include diblock (A-B), triblock (A-B-A or A-B-C), and tetrablock (A-B-A-B or A-B-C-D, etc.), and from the viewpoint of improving adhesion at high temperatures, A-B-A triblock copolymers are preferred.

[0097] The repeating units constituting the A block of the A-B-A triblock copolymer are preferably those derived from a monomer such as methyl methacrylate, which gives a homopolymer Tg of 100 to 120°C or higher. The repeating units constituting the B block are preferably those derived from a monomer such as butyl acrylate or 2-ethylhexyl acrylate, which gives a homopolymer Tg of -60 to -40°C or lower. Preferred examples of the A-B-A triblock copolymer include poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate), poly(methyl methacrylate)-poly(2-ethylhexyl acrylate)-poly(methyl methacrylate), and poly(methyl methacrylate)-random poly(butyl acrylate, 2-ethylhexyl acrylate)-poly(methyl methacrylate).

[0098] The weight ratio of each block of the ABA triblock copolymer is preferably A / B / A=1-25 / 98-50 / 1-25, and the weight average molecular weight of the ABA triblock copolymer is preferably 10,000 to 3,000,000.

[0099] The acrylic block copolymer may have a functional group. The type of the functional group is not particularly limited and may be, for example, one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group. A hydroxyl group and / or a carboxyl group is preferred, and a hydroxyl group is more preferred. Meanwhile, the functional group typically reacts with water molecules (HO). Therefore, when the content of the functional group is low, or preferably when the acrylic block copolymer does not have the functional group, the affinity of the acrylic ester resin with water decreases, resulting in reduced moisture absorption. As a result, similar to when the functional group content A is low, the moisture absorption of the thermally conductive sheet is controlled within a suitable range, resulting in improved adhesion after high-temperature storage. From the above perspective, a low content of functional groups in the acrylic block copolymer is preferred.

[0100] Hereinafter, the content of functional groups relative to the weight of the acrylic block copolymer will be referred to as the "functional group content B." Specifically, the functional group content B is preferably 0.020 mmol / g or less, more preferably less than 0.010 mmol / g, relative to the total weight of the acrylic block copolymer. It is particularly preferable that the functional group content B is 0 mmol / g, i.e., the acrylic block copolymer does not contain the functional group. The functional group content B can be measured, for example, by the same method as the above-mentioned method for measuring the functional group content C, except that the acrylic block copolymer is the target.

[0101] Furthermore, the acrylic block copolymer with fewer functional groups has high heat resistance, and its structure is more stable against heat. Therefore, the acrylic block copolymer with fewer functional groups is less likely to generate radicals when heated than an acrylic block copolymer with a higher functional group content. Therefore, when the functional group content B is low, the acrylic ester resin generates fewer radicals when heated than when the functional group content B is high. Therefore, in a thermally conductive sheet containing the acrylic ester resin, the chain reaction is less likely to proceed when the functional group content B is low. As a result, when the functional group content B is low, the tackiness of the acrylic ester resin is less likely to decrease when heat is applied, and the thermally conductive sheet has better tackiness after being kept at high temperatures.

[0102] Hereinafter, the ratio of the weight of the acrylic resin having the functional group to the weight of the acrylic block copolymer in the acrylic ester resin (acrylic resin having functional group / acrylic block copolymer) will be referred to as "ratio A." When ratio A is equal to or greater than a predetermined value, it means that the content of the acrylic resin having the functional group and the functional group in the acrylic ester resin is suitably high. In this case, the graphite binding property of the thermal conductive sheet is further improved due to the presence of the functional group. From the viewpoint of further improving the graphite binding property of the thermal conductive sheet, ratio A is preferably equal to or greater than 0.02, more preferably equal to or greater than 0.05, and even more preferably equal to or greater than 0.1.

[0103] The ratio A being equal to or less than a predetermined value means that the content of the acrylic block copolymer in the acrylic ester resin is suitably high. In this case, the presence of the acrylic block copolymer further improves the adhesion of the thermally conductive sheet after being held at high temperatures. From the viewpoint of further improving the adhesion of the thermally conductive sheet after being held at high temperatures, the ratio A is preferably equal to or less than 50, more preferably equal to or less than 25, and even more preferably equal to or less than 10.

[0104] From the viewpoint of achieving a balanced improvement in the graphite binding property of the thermal conductive sheet and the adhesion after being held at high temperatures, the ratio A is preferably within the above-mentioned range, more preferably 1.2 to 8, and particularly preferably 1.5 to 5.

[0105] (composition) The composition may optionally contain additives such as plasticizers, flame retardants, antioxidants, heat stabilizers, colorants, antistatic agents, tackifiers, and fillers other than the graphite particles (A). The composition preferably contains an antioxidant and / or a tackifier. The inclusion of the additives in the composition means that the thermally conductive sheet of the present invention further contains the additives. In a method for producing a thermally conductive sheet according to one embodiment of the present invention, described below, a primary sheet is formed using a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent. In this specification, the term "composition" does not refer to the mixture, but rather to the composition after the solvent has been removed by drying or other methods, i.e., the composition contained in the final thermally conductive sheet.

[0106] The plasticizer may be, for example, polybutene or a phosphorus-based flame retardant. By including polybutene and / or a phosphorus-based flame retardant in the thermal conductive sheet, the wettability with the silicone and / or spreader is improved, thereby reducing thermal resistance. The flame retardant may be, for example, a phosphorus-based flame retardant. The phosphorus-based flame retardant has the function of suppressing the combustion of the resin.

[0107] In one embodiment of the present invention, when the composition contains a plasticizer, the content thereof is preferably 20 wt % or less based on the total weight of the solid content of the composition, which corresponds to the total weight of the thermal conductive sheet according to one embodiment of the present invention.

[0108] Examples of the anti-aging agent include phenolic anti-aging agents and amine anti-aging agents, etc. The amount of the anti-aging agent to be added is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8 parts by weight, per 100 parts by weight of the total weight of the organic polymer compound (B).

[0109] In one embodiment of the present invention, the content of the graphite particles (A) in the composition is preferably 30% by weight to 80% by weight, more preferably 35% by weight to 75% by weight, and even more preferably 40% by weight to 70% by weight, based on the total weight of the composition. A content of the graphite particles (A) of 30% by weight or more is preferred because sufficient thermal conductivity is exhibited. Furthermore, a content of the graphite particles (A) of 80% by weight or less is preferred because excellent flexibility and adhesion are achieved.

[0110] In one embodiment of the present invention, the content of the organic polymer compound (B) in the composition is preferably 10% by weight to 60% by weight, more preferably 15% by weight to 50% by weight, and even more preferably 20% by weight to 40% by weight, based on the total weight of the composition. A content of the organic polymer compound (B) of 10% by weight or more is preferable because it improves the flexibility of the thermally conductive sheet and enables good adhesion between the heat generating element and the heat dissipating element via the thermally conductive sheet. Furthermore, a higher content of the organic polymer compound (B) within the range of 60% by weight or less is preferable because it allows the graphite particles (A) to be more effectively fixed and improves adhesion to the semiconductor and spreader.

[0111] [1-3. Thermal Conduction Sheet] (Orientation of graphite particles (A)) The graphite particles (A) are oriented in the thickness direction of the thermal conductive sheet. If the graphite particles (A) are oriented in the thickness direction of the thermal conductive sheet, the thermal conductivity in the thickness direction of the orientation can be improved, thereby reducing the thermal resistance in the thickness direction of the orientation, which is preferable. Note that, as long as the thermal conductivity can be improved in the thickness direction of the orientation, it is not necessary for all of the graphite particles (A) contained in the thermal conductive sheet to be oriented in the thickness direction of the thermal conductive sheet.

[0112] The phrase "graphite particles (A) are oriented in the thickness direction of the heat conductive sheet" means that the angle of the 6-membered carbon ring plane in the crystal of the graphite particle (A) relative to the sheet surface of the heat conductive sheet is greater than 45°. This angle is more preferably 50° or greater, even more preferably 70° or greater, and particularly preferably 80° or greater. The term "angle of the 6-membered carbon ring plane relative to the sheet surface of the heat conductive sheet" refers to the smaller angle except when the angle between the two is 90°. Here, in the graphite particles (A), the 6-membered carbon ring plane in the crystal of the graphite particle (A) is oriented in the plane direction of the scales and flakes in the case of plate-like graphite particles (A) such as scales and flakes, and in the long axis direction of the particles in the case of graphite particles (A) having an ellipsoidal, acicular, rod-like, fibrous, or irregular shape. The long axis of the graphite particle (A) coincides with the maximum length of the graphite particle (A).

[0113] The angle of the 6-membered carbon ring plane in the crystal of the graphite particle (A) relative to the sheet plane, which is the surface of the heat conductive sheet, can be measured by observing a cross section of the heat conductive sheet in the thickness direction using a scanning electron microscope. First, a thin film slice is prepared from the central portion of the heat conductive sheet in the thickness direction. Then, the graphite particles (A) in the thin film slice are observed using a scanning electron microscope, and the angle between the major axis of any 20 graphite particles (A) and the sheet plane can be measured. In this specification, the angles of 45°, 50°, 70°, 80°, or more mentioned above mean that the average of the values ​​measured as above is equal to or greater than that angle. Note that when the angle between the major axis of the graphite particle (A) and the sheet plane exceeds 90°, the supplementary angle is used as the measured value.

[0114] (Physical properties of thermal conductive sheets, etc.) The thermal resistance of the thermally conductive sheet according to one embodiment of the present invention is preferably 0.20°C / W or less, more preferably 0.12°C / W or less, even more preferably 0.10°C / W or less, and particularly preferably 0.085°C / W or less. Here, in this specification, thermal resistance refers to thermal conduction in the thickness direction of the thermally conductive sheet, and is the thermal resistance value measured by the method described in the Examples. If the thermal resistance is 0.20°C / W or less, the thermally conductive sheet has excellent thermal conductivity and excellent heat dissipation characteristics when interposed between a heat generating body and a heat dissipating body to form a heat dissipation device. The lower the thermal resistance, the better.

[0115] The thickness of the thermally conductive sheet according to one embodiment of the present invention is preferably 500 μm or less, more preferably 200 μm or less, even more preferably 140 μm or less, even more preferably 100 μm, even more preferably 95 μm or less, and particularly preferably 80 μm or less. Herein, the "thickness of the thermally conductive sheet" refers to the thickness measured by the method described in the Examples. A thermally conductive sheet having a thickness of 500 μm or less is preferable because it can be attached to a heat-generating body such as an electronic component even in a narrow space. The lower limit of the thickness of the thermally conductive sheet is not particularly limited as long as it functions as a thermally conductive sheet, but is preferably 3 μm or more, and more preferably 5 μm or more.

[0116] The hardness at 20°C of the thermally conductive sheet according to one embodiment of the present invention is preferably 65 or more, more preferably 70 or more, even more preferably 75 or more, and particularly preferably 80 or more. Herein, the "hardness at 20°C of the thermally conductive sheet" refers to the hardness measured by the method described in the Examples. A thermally conductive sheet having a hardness at 20°C of 65 or more is preferable because the thermally conductive sheet is sufficiently hard and can therefore be sliced ​​to a thin thickness. Furthermore, the hardness at 20°C of the thermally conductive sheet is preferably 95 or less, more preferably 90 or less, and even more preferably 88 or less. A thermally conductive sheet having a hardness at 20°C of 95 or less can be sufficiently adhered to the components it contacts. Therefore, heat can be efficiently transferred and thermal stress can be sufficiently alleviated.

[0117] The hardness at 70°C of the thermally conductive sheet according to one embodiment of the present invention is preferably greater than 60, more preferably greater than 63, and even more preferably greater than 65. In this specification, the "hardness at 70°C of the thermally conductive sheet" refers to the hardness measured by the method described in the Examples. A thermally conductive sheet having a hardness at 70°C of greater than 60 is preferable because the thermally conductive sheet is sufficiently hard and can therefore be sliced ​​to a thin thickness. Furthermore, the hardness at 70°C of the thermally conductive sheet is preferably 90 or less, more preferably 85 or less, and even more preferably 83 or less. A thermally conductive sheet having a hardness at 70°C of 90 or less can be sufficiently adhered to the components it contacts. This allows for efficient heat transfer and sufficient thermal stress relief.

[0118] The temporary adhesion property of the thermally conductive sheet according to one embodiment of the present invention can be evaluated by peeling off a 40 x 40 mm thermally conductive sheet from the separator and attaching it to a 50 x 50 mm silicon wafer. The fact that the thermally conductive sheet has excellent temporary adhesion property means the following: The thermal conductive sheet can be easily peeled off from the separator and fixed onto the silicon wafer with precision. The thermal conductive sheet will not peel off even when the silicon wafer is transported or turned upside down, and any air trapped between the silicon wafer and the thermal conductive sheet can be easily removed.

[0119] The initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling of a thermal conductive sheet according to one embodiment of the present invention can be evaluated using the methods described in the examples below, and it is preferable that the evaluation results in all cases be A or B according to the criteria described in the examples below.

[0120] [1-4. Manufacturing method of thermal conductive sheet] The method for producing a thermally conductive sheet according to one embodiment of the present invention is not particularly limited, as long as it is a method that can produce a thermally conductive sheet whose tensile strength (X) and tensile strength (Y) are controlled within a range that satisfies characteristic A. Examples of the production method include a primary sheet forming step of forming a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet in which the graphite particles (A) are oriented in a direction parallel to the sheet surface, a laminate forming step of stacking the primary sheets to obtain a laminate of primary sheets, and a slicing step of slicing the laminate cross section of the primary sheet laminate to obtain a thermally conductive sheet.

[0121] By adopting the above-described configuration, the manufacturing method can control the tensile strength (X) and the tensile strength (Y) within a suitable range, and can manufacture a thermally conductive sheet according to one embodiment of the present invention.

[0122] (Primary sheet forming process) In the primary sheet forming step, a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent is formed into a sheet to obtain a primary sheet in which the graphite particles (A) are oriented in a direction parallel to the sheet surface.

[0123] Here, the graphite particles (A), the organic polymer compound (B), and the composition containing the graphite particles (A) and the organic polymer compound (B) are as described above in [1-2.].

[0124] A conventional primary sheet forming process involves melt-kneading graphite particles (A), an organic polymer compound (B), and, if necessary, the aforementioned additives without the addition of a solvent, and then forming the resulting mixture into a sheet to obtain a primary sheet. The present inventors have found that the tensile strength (X) and tensile strength (Y) of a thermally conductive sheet produced using a primary sheet obtained by this method are not controlled within a range satisfying Feature A. Therefore, after extensive research, the present inventors produced a primary sheet using a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent, rather than melt-kneading without the addition of a solvent. As a result, they found that by subjecting the primary sheet to the laminate-forming process and slicing process, a thermally conductive sheet according to one embodiment of the present invention can be obtained, in which the tensile strength (X) and tensile strength (Y) are controlled within a range satisfying Feature A.

[0125] It is not clear why the use of the mixture controls the tensile strength (X) and tensile strength (Y) to a range that satisfies characteristic A. However, it is thought that the reason is that the degree of dispersion of the graphite particles (A) and the organic polymer compound (B) changes between the interior and surface of the primary sheet depending on the solvent, and this change is reflected in the laminate. However, the present invention is not limited to such speculation.

[0126] Examples of the solvent include aromatic hydrocarbon solvents such as toluene and xylene; ester-based solvents such as ethyl acetate and butyl acetate; ketone-based solvents such as methyl ethyl ketone and methyl isobutyl ketone (MIBK); and cellosolve-based solvents such as butyl cellosolve, phenyl cellosolve, and dimethyl cellosolve. The amount of solvent is preferably such that the total concentration of the graphite particles (A), organic polymer compound (B), and additives is 10 to 50% by weight, more preferably 20 to 40% by weight. This concentration is preferred because, when a primary sheet is produced at this concentration, adequate spaces are formed between the graphite particles, improving particle orientation during sheet production and lamination pressing.

[0127] The primary sheet forming step is preferably a step of forming a primary sheet by coating. This step is also called a solvent casting method, in which the mixture is poured into a mold and dried to obtain a primary sheet. This method is preferred because it allows the tensile strength (X) and tensile strength (Y) to be suitably controlled within a range that satisfies characteristic A. In this step, the solvent is removed.

[0128] When the composition is formed into a sheet, the thickness thereof is preferably at least 20 times, and more preferably 20 to 100 times, the average value of the maximum length or major axis of the graphite particles (A). A thickness within the above range is preferable because a sheet with high strength can be obtained.

[0129] (Laminate formation process) The laminate formation step is a step of laminating the primary sheets to obtain a laminate of the primary sheets. The method of laminating the primary sheets is not particularly limited, and examples thereof include a method of laminating a plurality of primary sheets and a method of folding a primary sheet. When laminating the primary sheets, it is preferable to laminate them with the orientation of the graphite particles (A) aligned in the plane of the sheets.

[0130] The pressure to be applied when stacking the primary sheets is not particularly limited, but is adjusted so that the pressure is weak enough to prevent the sliced ​​surfaces from being crushed in the subsequent slicing step, but strong enough to ensure good adhesion between the primary sheets. Furthermore, the stacking may be carried out under appropriate heating.

[0131] The pressure when laminating the primary sheets may be applied each time a primary sheet is laminated, or may be applied after laminating multiple sheets, or may be applied after laminating all of the primary sheets. A preferred example is a method in which pressure is applied each time a primary sheet or multiple sheets are laminated, and also after laminating all of the primary sheets. In such a case, the pressure and temperature applied each time a primary sheet or multiple sheets are laminated are not particularly limited, but for example, the pressure may be 1 kgf / cm 2 ~100kgf / cm 2 The temperature is 20° C. to 200° C. The pressure and temperature to be applied after all the primary sheets are laminated are not particularly limited. For example, the pressure may be 1 kgf / cm 2 ~100kgf / cm 2 and the temperature is 20℃ to 200℃.

[0132] (Slicing process) In the slicing step, the cross section of the primary sheet laminate is sliced ​​to obtain a thermally conductive sheet. The angle at which the cross section of the primary sheet laminate is sliced ​​is not particularly limited, but more preferably, the cross section of the primary sheet laminate is sliced ​​at an angle of 45° or less with respect to the stacking direction, even more preferably at an angle of 0 to 30°, and particularly preferably at an angle of 0 to 15° to obtain a thermally conductive sheet. By slicing at an angle of 45° or less with respect to the stacking direction, a thermally conductive sheet with excellent thermal conductivity can be obtained.

[0133] The method for slicing the laminate of primary sheets is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, and a knife processing method.

[0134] <Summary> An embodiment of the present invention includes the following configuration. [1] A thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, At least one of the tensile strength in the X direction and the tensile strength in the Y direction is less than 0.8 MPa, and A thermal conductive sheet in which the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction) is more than 2.2 times. [2] The thermal conductive sheet according to [1], wherein the degree of orientation of the (110) plane of the graphite particles calculated by the Lotgering method using an X-ray diffraction profile is 0.010 or more and less than 0.081. [3] The thermal conductive sheet according to [1] or [2], wherein the degree of orientation of the (110) plane of the graphite particles calculated by the Lotgering method using an X-ray diffraction profile is 0.010 or more and less than 0.045. [4] The thermal conductive sheet according to any one of [1] to [3], wherein the degree of orientation of the (002) plane of the graphite particles calculated by the Lotgering method using an X-ray diffraction profile is -0.10 or more and 0.40 or less. [5] The thermal conductive sheet according to any one of [1] to [4], wherein the degree of orientation of the graphite particles calculated by the following formula (1) using an X-ray diffraction profile is 0.10 or more and less than 0.37. Orientation of graphite particles = {sum of vertical counts + (sum of diagonal counts / 2)} / horizontal counts (1) (In formula (1), the vertical count sum is the sum of the (100) plane orientation degree and the (110) plane orientation degree, the diagonal count sum is the sum of the (101) plane orientation degree and the (112) plane orientation degree, and the horizontal count is the (002) plane orientation degree.) [6] The thermally conductive sheet according to any one of [1] to [5], wherein the organic polymer compound (B) includes an acrylic resin having a functional group. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the organic polymer compound (B) includes an acrylic block copolymer. [8] The thermally conductive sheet according to any one of [1] to [7], further comprising a tackifier. [9] The thermally conductive sheet according to any one of [1] to [8], further comprising 20% ​​by weight or less of a plasticizer based on the total weight of the thermally conductive sheet.

[10] The thermally conductive sheet according to any one of [1] to [9], further comprising an antioxidant. [Example]

[0135] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these.

[0136] [Evaluation method] The evaluation methods used in the examples and comparative examples will be explained below.

[0137] <Thickness> The thermally conductive sheet was cut into a 3 cm x 3 cm square to prepare an evaluation sample. The thickness of the evaluation sample was measured at four corners and one central point using a micrometer manufactured by Mitutoyo Corporation, and the average of the measurements was used as the thickness of the thermally conductive sheet. Here, the "central point" refers to the intersection of two diagonal lines drawn from the four corners to the measurement points located diagonally opposite each other.

[0138] <Tensile strength (X), tensile strength (Y), tensile strength ratio> Test pieces were prepared by punching out the thermally conductive sheet in the X and Y directions to a size of 50 mm x 20 mm. A tensile test in the X direction was performed on the obtained test pieces using a small universal testing machine (Instron, product name: Model 5565) by pulling them in the X direction at a chuck distance of 30 mm and a pulling speed of 20 mm / min. The maximum strength (N) during the X direction tensile test was divided by the thickness (mm) of the test piece to calculate the tensile strength of the thermally conductive sheet in the X direction, i.e., tensile strength (X).

[0139] A tensile test in the Y direction was carried out in the same manner as the tensile test in the X direction, except that the direction in which the thermal conductive sheet was pulled was changed to the Y direction. As in the calculation of the tensile strength (X), the maximum strength (N) during the tensile test in the Y direction was divided by the thickness (mm) of the test piece to calculate the tensile strength of the thermal conductive sheet in the Y direction, i.e., the tensile strength (Y).

[0140] The calculated tensile strength (X) and tensile strength (Y) were used to calculate the ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction), i.e., the tensile strength ratio.

[0141] In the above-mentioned tensile test, the direction perpendicular to the stacking direction of the laminates prepared in Examples 1 to 4 and Comparative Example 1 described below was defined as the X direction of the thermal conductive sheet, and the direction perpendicular to the X direction, i.e., the direction coinciding with the stacking direction of the laminate, was defined as the Y direction.

[0142] <(110) plane orientation of graphite particles> The thermally conductive sheet was cut into approximately 15 mm squares, and measurements were performed using wide-angle X-ray diffraction with the streaks perpendicular to the X-ray incidence direction. The X-ray diffraction intensity was measured on the surface of the thermally conductive sheet using an X-ray diffractometer (manufactured by Bruker, product name: D8 ADVANCE) under the following conditions: scan range: 20 to 90°, step size: 0.0153°, voltage: 40 kV, current: 40 mA, and an XRD profile was obtained. From the obtained XRD profile, the degree of orientation of the (110) plane of the graphite particles was calculated according to the Lotgering method. Specifically, the Lotgering factor f related to the degree of orientation of the (110) plane of the graphite particles was calculated according to the following procedure. 110 The Lotgering factor f 110 was calculated using the peak intensity of the X-ray diffracted from the target crystal plane according to the following formula (2). f 110 =(ρ-ρ0) / (1-ρ0) (2) Here, ρ0 in equation (2) was calculated using the X-ray diffraction intensity (I0) of the non-oriented sample. Specifically, ρ0 was calculated using the following equation (3) as the ratio of the total diffraction intensity of the (110) plane (ΣI0((110) plane)) to the sum of all diffraction intensities in the non-oriented sample (ΣI0(hkl)). Graphite particles have a shape that makes them easy to orient, so even powder particles tend to orient when filling the sample. Therefore, in this study, we decided to use the peak intensity ratio of the ICSD data calculated from the crystal structure as the X-ray diffraction intensity of the non-oriented sample. ρ0=ΣI0((110) plane) / ΣI0(hkl) (3) The value of ρ in equation (2) was calculated using the X-ray diffraction intensity (I) of the oriented sample (thermal conductive sheet). Specifically, ρ was calculated using the following equation (4) as the ratio of the total diffraction intensity of the (110) plane (ΣI((110) plane)) to the total diffraction intensity of the primary sheet (ΣI(hkl)). ρ=ΣI((110) plane) / ΣI(hkl) (4) In the above, the diffraction intensity refers to the peak height of the target oriented plane in the XRD profile. In the case of the (110) plane orientation, the diffraction intensity refers to the peak height at 2θ=77°, which corresponds to the (110) plane.

[0143] <(002) plane orientation of graphite particles> The (002) plane orientation degree of the graphite particles was calculated according to the Lotgering method from the same XRD profile as that used to calculate the (110) plane orientation degree of the graphite particles. Specifically, the Lotgering factor f 002 The Lotgering factor f 002 was calculated using the peak intensity of the X-ray diffracted from the target crystal plane according to the following formula (2'). f 002 =(ρ´-ρ0´) / (1-ρ0´) (2´) Here, ρ0' in equation (2') was calculated using the X-ray diffraction intensity (I0) of the non-oriented sample. Specifically, ρ0' was calculated using the following equation (3') as the ratio of the sum of the diffraction intensities of the (002) plane (ΣI0((002) plane)) to the sum of all diffraction intensities in the non-oriented sample (ΣI0(hkl)). As with the calculation of the degree of orientation of the (110) plane of graphite particles, the peak intensity ratio of the ICSD data calculated from the crystal structure was used for the X-ray diffraction intensity of the non-oriented sample. ρ0´=ΣI0((002) plane) / ΣI0(hkl) (3´) The ρ in formula (2') was calculated using the X-ray diffraction intensity (I) of the oriented sample (thermal conductive sheet). Specifically, ρ was calculated using formula (4') below as the ratio of the sum of the diffraction intensities of the (002) plane (ΣI((002) plane)) to the sum of all diffraction intensities in the primary sheet (ΣI(hkl)). ρ´=ΣI((002) plane) / ΣI(hkl) (4´) In the above, the diffraction intensity means the peak height of the target oriented plane in the XRD profile. In the case of the (002) plane orientation, the diffraction intensity means the peak height at 2θ=25.5 to 27.5° corresponding to the (002) plane.

[0144] <Graphite particle orientation degree A> The thermal conductive sheet was cut into 12 mm diameter specimens, which were then rotated and measured using wide-angle X-ray diffraction. The X-ray diffraction intensity of the surface was measured using an X-ray diffractometer (Bruker, product name: D8 ADVANCE) under conditions of a scan range of 20 to 90°, a step size of 0.0153°, a sample rotation of 30 rpm, a voltage of 40 kV, and a current of 40 mA, to obtain an XRD profile. In the obtained XRD profile, the peak intensity of the peak located in the 2θ range of 41.0 to 43.0° was defined as the (100) plane orientation, and the peak intensity of the peak located in the 2θ range of 76.5 to 78.5° was defined as the (110) plane orientation. Furthermore, in the XRD profile, the peak intensity of the peak located in the 2θ range of 43.5 to 45.5° was defined as the (101) plane orientation, and the peak intensity of the peak located in the 2θ range of 81.5 to 83.5° was defined as the (112) plane orientation. Furthermore, in the XRD profile, the peak intensity of the peak located in the range of 2θ=25.5 to 27.5° was taken as the degree of orientation in the (002) plane.

[0145] Using each of the above-mentioned degrees of orientation, the degree of orientation of the graphite particles, that is, the degree of orientation A of the graphite particles, was calculated by the following formula (1). Orientation of graphite particles = {sum of vertical counts + (sum of diagonal counts / 2)} / horizontal counts (1) (In formula (1), the vertical count sum is the sum of the (100) plane orientation degree and the (110) plane orientation degree, the diagonal count sum is the sum of the (101) plane orientation degree and the (112) plane orientation degree, and the horizontal count is the (002) plane orientation degree.) <Hardness> The hardness of the thermally conductive sheet was evaluated by measuring the center of a cross section (6.5 x 6.5 cm) of a laminate (pre-sliced) consisting of the thermally conductive sheet. The laminate was obtained by the procedure described in the "Laminate Preparation" section below, but before the procedure described in the "Thermal Conduction Sheet Preparation" section below. Specifically, the hardness of the center of the cross section of the evaluation sample was measured using a hardness tester (ASKER CL-150LJ manufactured by Kobunshi Keiki Co., Ltd.) in accordance with the Asker C method of the Society of Rubber Industry Standards of Japan (SRIS). The hardness at 20°C is measured at 20°C, and the hardness at 70°C is measured at 70°C.

[0146] The hardness of the thermally conductive sheet at 20°C was evaluated according to the following criteria: A (Excellent): 84 or above B (Good): 80 or above, less than 84 C (poor): Less than 80.

[0147] The hardness of the thermal conductive sheet at 70°C was evaluated according to the following criteria: A (Excellent): Over 63 B (Good): 80 or above, less than 84 C (bad): 60 or less.

[0148] <Thermal resistance value> The thermal conductive sheet was cut into a 1 cm x 1 cm square to prepare a sample for evaluation. The thermal resistance value (cm 2 The thermal resistance (K / W) was measured at a sample temperature of 50°C and a pressure of 0.5 MPa using a thermal resistance measuring device (Hitachi Technology and Services, Ltd., Resin Material Thermal Resistance Measuring Device).

[0149] The thermal resistance of the thermal conductive sheet was evaluated according to the following criteria: A (Excellent): The thermal resistance of the thermal conductive sheet is 0.080cm 2 If it is less than K / W. B (Good): The thermal resistance of the thermal conductive sheet is 0.080 cm 2 K / W super, 0.10cm 2If it is less than K / W. C (bad): The thermal resistance of the thermal conductive sheet is 0.10 cm 2 If it is over K / W.

[0150] <Temporary adhesion> The temporary adhesion of the thermal conductive sheet is evaluated by peeling off a 40 x 40 mm thermal conductive sheet from the separator and attaching it to a 50 x 50 mm silicon wafer. Excellent temporary adhesion means the following: The thermal conductive sheet can be easily peeled off from the separator and fixed onto the silicon wafer with precision. The thermal conductive sheet will not come off even when the silicon wafer is transported or turned upside down, and any air trapped between the silicon wafer and the thermal conductive sheet can be easily released.

[0151] The evaluation criteria are as follows: A: (Excellent) Easy to peel off from the separator, easy to stick to the silicon wafer, and less likely to trap air. B: (Good) Easy to peel off from the separator, easy to stick to the silicon wafer (slightly light), and does not trap air. C: (Poor) It is difficult to peel off from the separator and sticks too much to the silicon wafer, causing air to get trapped. Or it peels off too much from the separator and does not stick to the silicon wafer.

[0152] <Initial adhesion> Silicon (50 x 50 x 0.7 mm), thermally conductive sheet (40 x 40 x 0.11 mm), and spreader (nickel-plated copper: 50 x 50 x 2 mm) were stacked in this order and placed in a heat press. The heat press then bonded the silicon, thermally conductive sheet, and spreader together in this order at 150°C and 100 kg. This resulted in a laminate for adhesion measurement. An ultrasonic imaging device (Hitachi Power Solutions, product name: FineSAT) was then used to measure the contact area between the thermally conductive sheet and the adherend (silicon and spreader) in the laminate for adhesion measurement.

[0153] The initial adhesion of the thermal conductive sheet was evaluated according to the following criteria: A (excellent): The contact area is 95% or more of the total area of ​​the surface of the thermal conductive sheet that is bonded to the adherend. B (Good): The contact area is 90% or more and less than 95% of the total area of ​​the surface of the thermal conductive sheet that is bonded to the adherend. C (Poor): The contact area is less than 90% of the total area of ​​the surface of the thermal conductive sheet that is bonded to the adherend.

[0154] <Adhesion after high temperature exposure> A laminate for adhesion measurement was obtained using the same method as described in the <Initial Adhesion> section above. The laminate for adhesion measurement was then placed in a heating furnace, and the atmosphere inside the furnace was heated to 150°C and maintained at this temperature for 500 hours. The laminate for adhesion measurement was then removed from the heating furnace, and the adhesion area between the thermally conductive sheet and the adherend (silicon and spreader) in the laminate for adhesion measurement was measured. Based on the adhesion area, adhesion after high-temperature maintenance was evaluated using the same criteria as those for evaluating initial adhesion described in the <Initial Adhesion> section above.

[0155] <Adhesion after heat cycle> Except for the following points, the adhesion after the heat cycle was evaluated by the same method as that described in the above section <Adhesion after high temperature retention>. The adhesion after the heat cycle was evaluated according to the same criteria as those for the initial adhesion described in the above section <Initial adhesion>. The laminate for adhesion measurement was placed in a heat shock tester (manufacturer: Hitachi Appliances, Inc., product name: ES-56L). The ambient temperature inside the heat cycle tester was then raised to 120°C, then lowered to -40°C, and then raised again to 120°C, and this heat cycle was repeated 500 times.

[0156] Example 1 <Preparation of composition solution> The raw materials shown below were mixed and stirred for 10 minutes using a planetary centrifugal mixer to obtain a composition solution. The solids concentration of the composition solution was 30.0% by weight. The composition solution corresponds to the "mixture containing graphite particles (A), an organic polymer compound (B), and a solvent" described in [2. Method for producing a thermal conductive sheet] above. The mixture of an acrylic resin and an acrylic block copolymer having the functional groups shown below corresponds to the organic polymer compound (B). 125.71 g of flake graphite powder (average particle size: 73 μm, thickness: 0.80 μm, aspect ratio: 91, sulfur content: 1.0 wt.% or less) as graphite particles (A); 336.76 g of a 15 wt % toluene / ethyl acetate solution of acrylic resin (weight average molecular weight: 900,000, Tg: -60°C, hydroxyl group content as the functional group: 0.116 mmol / g, 6.5 KOH mg / g, liquid at room temperature) as the acrylic resin having functional groups (50.51 g as the acrylic resin having functional groups); As an acrylic block copolymer, a 15 wt % toluene / ethyl acetate solution of an acrylic block copolymer (weight average molecular weight: 56,000, Tg: hard segment 100 to 120°C, soft segment -50 to -40°C, no functional groups, liquid at room temperature): 112.76 g (16.91 g as acrylic block copolymer without functional groups); Tackifier (hydrogenated petroleum resin: softening point 90°C): 22.86g; · Plasticizer (polybutene: weight average molecular weight 3700): 11.43g; Antiaging agent (amine-based antiaging agent: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine): 1.14g; Toluene: an amount that gives a solids concentration of the composition solution of 30.0% by weight.

[0157] <Preparation of primary sheet> The resulting composition solution was spread onto a polyethylene terephthalate film whose surface had been treated with a release agent, leaving a clearance so that the coating thickness was 2 mm. The film was then dried at 120°C for 20 minutes or more, and the dried sheet was peeled off to obtain a primary sheet with a thickness of 2 mm. This procedure was repeated three times to produce three primary sheets.

[0158] The contents of the graphite particles, the organic polymer compound (B), and the antioxidant relative to the total weight of the composition contained in the primary sheet correspond to the contents of the composition contained in the final thermal conductive sheet, i.e., relative to the total weight of the final thermal conductive sheet.

[0159] <Preparation of laminate> Each of the three primary sheets was cut into a 2.4cm x 6.4cm size and placed in a container with a volume of 2.5cm x 6.5cm x 7.5cm high. Five sheets were stacked together and pressed at room temperature at a pressure of 400kg or more until the final thickness after pressing was 6.5cm or more. The stacked sheets were then heated at 120°C for 15 minutes and pressed at a pressure of 400kg or more to obtain a 2.5cm x 6.5cm x 6.5cm laminate.

[0160] <Making a thermal conductive sheet> The cross section of the resulting laminate was sliced ​​at an angle of 45 degrees to the lamination direction to produce a thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick.

[0161] Examples 2 to 4 Thermally conductive sheets were produced in the same manner as in Example 1, except that the amounts of materials used in Example 1 were changed to the compounding ratios shown in Table 1. The thermally conductive sheets obtained in Examples 2 and 3 had a thickness of 110 μm, and the thermally conductive sheet obtained in Example 4 had a thickness of 75 μm.

[0162] Comparative Example 1 120 g of flake-shaped expanded graphite powder (average particle size: 250 μm, thickness: 5 μm, aspect ratio: 50, sulfur content: 1.5 wt % or more) as graphite particles (A), 54 g of acrylic ester resin (weight-average molecular weight: 1.2 million, Tg: -37°C, containing OH groups as functional groups) as organic polymer compound (B), and 66 g of aromatic condensed phosphate ester (CR-741, manufactured by Daihachi Chemical Industry Co., Ltd.) were melt-kneaded under heating.

[0163] <Preparation of primary sheet> A portion of the resulting composition (240 g) was taken, rolled into a block, sandwiched between PTFE films, and pressed using a press with a 10 cm × 20 cm tool surface at a tool pressure of 10 MPa and a tool temperature of 170°C to obtain a primary sheet with a thickness of 3 mm. This procedure was repeated to produce a large number of primary sheets.

[0164] <Preparation of laminate> The resulting primary sheets were each cut into a 2.4cm x 6.4cm size and placed in a container with an internal volume of 2.5cm x 6.5cm x 7.5cm (height). Five sheets were stacked together and pressed at room temperature at a pressure of 400kg or more until the final thickness after pressing was 6.5cm or more. The stacked sheets, which had reached a thickness of 6.5cm or more, were then heated at 120°C for 15 minutes and pressed at a pressure of 400kg or more to obtain a 2.5cm x 6.5cm x 6.5cm laminate.

[0165] <Preparation of comparative thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at a 45 degree angle to the lamination direction to produce a comparative thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 250 μm thick, with graphite particles oriented in the thickness direction.

[0166] [Evaluation of thermal conductive sheets] The physical properties of the thermally conductive sheets obtained in Examples 1 to 4 and the comparative thermally conductive sheet obtained in Comparative Example 1 were measured using the evaluation methods described above, and the results are shown in Table 1. In Table 1, the graphite particles (A) and plasticizer used in Examples 1 to 4 are each labeled "A." The graphite particles (A) and plasticizer used in Comparative Example 1 are each labeled "B." In Table 1, the acrylic resin used in Examples 1 to 4 as the acrylic resin having functional groups and the acrylic ester resin used in Comparative Example 1 are collectively referred to. In Table 1, the term "acrylic resin" is used, and the type of acrylic resin used in Examples 1 to 4 is labeled "A," and the type of acrylic resin used in Comparative Example 1 is labeled "B." The "blending ratio" is the ratio of the solid weight of the material used to the solid weight of all materials excluding the solvent. For example, the graphite blending ratio of "55.0" in Example 1 indicates that the ratio of the solid weight of the graphite particles (A) used in Example 1 to the solid weight of all materials excluding the solvent used in Example 1 is 55.0% by weight.

[0167] [Table 1]

[0168] Here, the thermally conductive sheets produced in Examples 1 to 4 were observed at 50 to 4000 magnifications using a scanning electron microscope (manufactured by Zeiss, product name: ULTRAplus), and it was confirmed that the graphite particles were oriented in the thickness direction of the thermally conductive sheet. Furthermore, as shown in Table 1, the thermally conductive sheets produced in Examples 1 to 4 had a tensile strength (Y) of less than 0.8 MPa and a tensile strength ratio of more than 2.2 times. On the other hand, the comparative thermally conductive sheet produced in Comparative Example 1 had a tensile strength ratio of 2.2 times or less.

[0169] Therefore, the thermally conductive sheets manufactured in Examples 1 to 4 correspond to a thermally conductive sheet according to one embodiment of the present invention, whereas the comparative thermally conductive sheet manufactured in Comparative Example 1 does not correspond to a thermally conductive sheet according to one embodiment of the present invention.

[0170] Furthermore, as shown in Table 1, the thermally conductive sheets produced in Examples 1 to 4 had lower thermal resistance and better thermal conductivity than the comparative thermally conductive sheet produced in Comparative Example 1. The thermally conductive sheets produced in Examples 1 to 4 were also superior to the comparative thermally conductive sheet produced in Comparative Example 1 in terms of temporary adhesion and adhesion, which are expressed as initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling.

[0171] From the above, it was found that the thermally conductive sheet according to one embodiment of the present invention is excellent not only in thermal conductivity but also in temporary attachment property and adhesion property. [Industrial Applicability]

[0172] The thermally conductive sheet according to one embodiment of the present invention has excellent thermal conductivity, temporary adhesion, and adhesiveness, and is therefore suitable for use in the manufacture of products that require excellent thermal conductivity, temporary adhesion, and adhesiveness, such as multilayer wiring boards and electronic components including semiconductor packages.

Claims

1. A thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), the graphite particles (A) are oriented in the thickness direction of the thermal conductive sheet, At least one of the tensile strength in the X direction and the tensile strength in the Y direction is less than 0.8 MPa, and A thermally conductive sheet having a ratio of the tensile strength in the X direction to the tensile strength in the Y direction (tensile strength in the X direction / tensile strength in the Y direction) of more than 2.2 times.

2. 2. The thermal conductive sheet according to claim 1, wherein the graphite particles have a (110) plane orientation degree of 0.010 or more and less than 0.081 as calculated by the Lotgering method using an X-ray diffraction profile.

3. 3. The thermal conductive sheet according to claim 1, wherein the graphite particles have a (110) plane orientation degree of 0.010 or more and less than 0.045, as calculated by the Lotgering method using an X-ray diffraction profile.

4. 3. The thermal conductive sheet according to claim 1, wherein the graphite particles have a (002) plane orientation degree calculated by the Lotgering method using an X-ray diffraction profile of -0.10 or more and 0.40 or less.

5. 3. The thermal conductive sheet according to claim 1, wherein the degree of orientation of the graphite particles calculated using an X-ray diffraction profile by the following formula (1) is 0.10 or more and less than 0.

37. Degree of orientation of graphite particles = {sum of vertical counts + (sum of diagonal counts / 2)} / horizontal count (1) (In formula (1), the vertical count sum is the sum of the (100) plane orientation degree and the (110) plane orientation degree, the diagonal count sum is the sum of the (101) plane orientation degree and the (112) plane orientation degree, and the horizontal count is the (002) plane orientation degree.)

6. The thermal conductive sheet according to claim 1 , wherein the organic polymer compound (B) includes an acrylic resin having a functional group.

7. The thermally conductive sheet according to claim 1 , wherein the organic polymer compound (B) includes an acrylic block copolymer.

8. The thermally conductive sheet according to claim 1 or 2, further comprising a tackifier.

9. 3. The thermal conductive sheet according to claim 1, further comprising 20% ​​by weight or less of a plasticizer based on the total weight of the thermal conductive sheet.

10. The thermally conductive sheet according to claim 1 or 2, further comprising an antioxidant.