Heat-conductive sheet and method for producing heat-conductive sheet

Abstract

To provide a heat-conductive sheet that exhibits superior tack properties after being held at a high temperature.SOLUTION: The problem is solved by a heat-conductive sheet including a composition containing graphite particles (A), an acrylic acid ester resin (B), and an antioxidant (C), in which the graphite particles (A) are oriented in a thickness direction and the acrylic acid ester resin (B) has a functional group.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] A conventional technique 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. Furthermore, the thermal conduction sheet is required to have flexibility so that it can adhere closely to the adherend.

[0003] Known thermally conductive sheets that have high thermal conductivity and flexibility that allows them to adhere closely to an adherend include thermally conductive sheets that contain a composition that contains graphite particles oriented in the thickness direction of the thermally conductive sheet and an organic polymer compound (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2008 / 053843 Brochure [Patent Document 2] Patent Publication No. 2010-132856 [Patent Document 3] Patent Publication No. 2011-184663 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, when a thermally conductive sheet is actually used, the thermally conductive sheet may be maintained in a high-temperature environment while adhered to an adherend. Therefore, the thermally conductive sheet needs to maintain its adhesive strength even when maintained in a high-temperature environment. Therefore, the thermally conductive sheet is also required to have excellent tackiness after being maintained at a high temperature, which corresponds to the adhesive strength when maintained in a high-temperature environment.

[0006] However, conventional thermally conductive sheets containing compositions containing graphite particles and organic polymer compounds, such as the thermally conductive sheets described in Patent Documents 1 to 3, have room for improvement in terms of the tackiness after being held at high temperatures.

[0007] Therefore, an object of one aspect of the present invention is to provide a thermally conductive sheet that has excellent tackiness even after being kept at high temperatures. [Means for solving the problem]

[0008] 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 including a composition containing graphite particles (A), an acrylic acid ester-based resin (B), and an antioxidant (C), the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, The acrylic ester resin (B) is a thermally conductive sheet having a functional group.

[0009] In order to solve the above-mentioned problems, a method for producing a thermal conductive sheet according to one embodiment of the present invention includes a primary sheet forming step of forming a composition containing graphite particles (A), an acrylic acid ester-based resin (B), and an antioxidant (C) 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 laminating the primary sheets to obtain a laminate of primary sheets; a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet, The acrylic ester resin (B) has a functional group, and this is a method for producing a thermally conductive sheet. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a thermally conductive sheet that has excellent tackiness even after being kept at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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)."

[0012] [1. Thermal Conduction Sheet] A thermally conductive sheet according to one embodiment of the present invention (hereinafter also referred to as "thermally conductive sheet of the present invention") is a thermally conductive sheet comprising a composition containing graphite particles (A), an acrylic ester-based resin (B), and an antioxidant (C), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and the acrylic ester-based resin (B) has functional groups.

[0013] [1-1. Composition containing graphite particles (A), acrylic ester resin (B), and antioxidant (C)] (Graphite particles (A)) The thermally conductive sheet of the present invention comprises a composition containing graphite particles (A), an acrylic ester resin (B), and an antioxidant (C). By including the graphite particles (A) in the thermally conductive sheet, the thermal conductivity of the thermally conductive sheet can be improved because the thermally conductive graphite particles (A) are dispersed in the thermally conductive sheet, thereby reducing the thermal resistance of the thermally conductive sheet.

[0014] 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.

[0015] 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 which a plate-like shape such as a scale-like or thin plate-like shape is more preferable. When the non-spherical graphite particles (A) have a plate-like shape, the graphite particles (A) are easily oriented and inter-particle contact is easily maintained, which makes it possible to further improve thermal conductivity in the orientation direction and thereby further reduce thermal resistance in the orientation direction.

[0016] 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.

[0017] 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.

[0018] 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).

[0019] 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.

[0020] The sulfur content of the graphite particles (A) is preferably 1.0 wt % or less, more preferably 0.7 wt % or less, and even more preferably 0.5 wt % or less. By making the sulfur content 1.0 wt % or less, corrosion of electronic components in contact with the thermal conductive sheet, which is caused by sulfur contained as an impurity in the graphite particles (A) leaching out as an acid, can be suitably prevented.

[0021] 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.).

[0022] 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.

[0023] (Acrylate ester resin (B)) The composition contains an acrylic ester resin (B) having a functional group.

[0024] The acrylic ester resin (B) functions as a binder, improves the flexibility of the thermally conductive sheet, and enables the heat generating element and the heat dissipating element to be well adhered to each other via the thermally conductive sheet. The acrylic ester resin (B) is not particularly limited as long as it is an acrylic ester resin (B) having a functional group, and may consist of one type of acrylic ester resin or a mixture of two or more types of acrylic ester resins.

[0025] The functional group has the function of binding multiple graphite particles (A) together, and therefore exerts the effect of binding multiple graphite particles (A). Therefore, since the acrylic ester resin (B) has 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 of the present invention and the adherend is also improved.

[0026] 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, for example, one or more 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 (B) using NMR or the like.

[0027] In one embodiment of the present invention, when the content of the functional group relative to the total weight of the acrylic ester resin (B) is high, the graphite particles (A) are more suitably bound to each other via the acrylic ester resin (B) in the thermal conductive sheet of the present invention. As a result, the graphite binding property of the thermal conductive sheet of the present invention is further improved. Hereinafter, the content of the functional group relative to the total weight of the acrylic ester resin (B) is referred to as the "functional group content of the present invention."

[0028] The preferred range of the content of the functional group of the present invention is preferably 0.010 mmol / g or more from the viewpoint of further improving graphite binding ability. Furthermore, the preferred range of the content of the functional group of the present invention may vary depending on the type of the functional group and the type of the graphite particles (A). For example, when the functional group is a hydroxyl group or a carboxyl group, the content of the functional group of the present invention is preferably 0.010 mmol / g or more, more preferably 0.050 mmol / g or more, and even more preferably 0.090 mmol / g or more from the viewpoint of further improving graphite binding ability. Furthermore, the content of the functional group of the present invention can also be expressed in the commonly used unit "KOHmg / g" in addition to the unit "mmol / g." Specifically, for example, when the functional group is a hydroxyl group or a carboxyl group, the content of the functional group of the present invention is preferably 0.56 KOHmg / g or more, more preferably 2.81 KOHmg / g or more, and even more preferably 5.05 KOHmg / g or more.

[0029] Furthermore, the functional groups can usually form bonds with water molecules. Therefore, if the content of the functional groups of the present invention is excessively high, the hygroscopicity of the thermally conductive sheet of the present invention will be excessively high. Here, when heat is applied during use, the thermally conductive sheet changes shape, which can result in a decrease in adhesion to the adherend. The inventors have discovered that this is caused by a change in shape due to the water absorbed in the thermally conductive sheet being expelled to the outside by heat. If the hygroscopicity of the thermally conductive sheet is excessively high, the amount of water expelled will be large, resulting in a greater degree of deformation, and as a result, the tendency for adhesion to the adherend to decrease will become greater.

[0030] Therefore, from the viewpoint of preventing a decrease in adhesion to the adherend due to the large degree of deformation and improving adhesion to the adherend during use, it is preferable to control the content of the functional group of the present invention to a range not exceeding a predetermined amount.

[0031] Specifically, the preferred range of the content of the functional group of the present invention is preferably 0.410 mmol / g or less from the viewpoint of improving the adhesion. Furthermore, for example, when the functional group is a hydroxyl group, the content of the functional group of the present invention 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 from the viewpoint of improving the adhesion. Furthermore, when the functional group is a hydroxyl group and the content of the functional group of the present invention 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.

[0032] For example, when the functional group is a carboxyl group, from the viewpoint of improving the adhesion, the content of the functional group of the present invention 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. When the functional group is a hydroxyl group and the content of the functional group of the present invention 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.

[0033] To convert from mmol / g to mg / g of KOH, multiply mmol / g by 56.1056 mg / mmol.

[0034] The method for measuring the content of functional groups in the present invention 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 (B) is extracted from the thermally conductive sheet, and the total weight (unit: g) of the extracted acrylic ester resin (B) is measured. (2)H 1 The amount of the functional group (unit: mmol) in the acrylic ester resin (B) extracted in step (1) is measured using NMR or the like. (3) The content (number of moles) of the functional group in the acrylate ester resin (B) measured in the step (2) is divided by the total weight of the acrylate ester resin (B) measured in the step (1) to calculate the content (unit: mmol / g) of the functional group of the present invention.

[0035] Furthermore, when the weight-average molecular weights of all polymers contained in the acrylic ester-based resin (B), the content of the monomer having the functional group in all the constituent monomers, and the content ratio of each polymer are known, the content of the functional group in the present invention can also be calculated based on these.

[0036] The acrylic ester resin (B) may be solid or liquid at room temperature.

[0037] The acrylic ester resin (B) preferably contains 50% by weight or more of repeating units derived from acrylic monomers. The acrylic ester resin (B) includes a polymer of monomer components containing one or more acrylic monomers, at least some of which have the functional group. The acrylic ester resin (B) also includes a copolymer of an acrylic monomer with another monomer, at least some of which have the functional group. The acrylic monomer is one or more monomers selected from (meth)acrylic acid and (meth)acrylic esters. Herein, "(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.

[0038] Examples of the other monomer include acrylonitrile and 2-chloroethyl vinyl ether. The other monomer (b3) may be one type or two or more types. Incidentally, an acrylic rubber can be obtained by copolymerizing a (meth)acrylic acid ester with acrylonitrile and 2-chloroethyl vinyl ether. In this specification, the acrylic rubber is included in the acrylic acid ester resin.

[0039] The ratio of the weight of the monomer having a functional group to the weight of all monomers constituting the acrylic ester resin (B) is preferably 0.1 to 5.2% by weight, more preferably 0.3 to 4.0% by weight. Furthermore, the ratio of the amount of the monomer having a functional group to the amount of all monomers constituting the acrylic ester resin is preferably 0.1 to 5.0 mol%, more preferably 0.3 to 4.0 mol%. Adjusting this ratio within the aforementioned range is preferred in terms of suitably controlling the content of the functional group within the aforementioned range in the present invention.

[0040] 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, and glycidyl (meth)acrylate. 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 is a copolymer containing 2-ethylhexyl acrylate as a monomer. The monomer having a functional group may be one type or two or more types.

[0041] The acrylic ester resin (B) may be a random copolymer or a block copolymer, but a random copolymer is preferred because it is readily available. The structure of the acrylic ester resin (B) may be linear or branched, but a linear structure is preferred because it is readily available.

[0042] The weight-average molecular weight of the acrylic ester resin (B) is preferably 100,000 or more, more preferably 300,000 or more, even more preferably 500,000 or more, and particularly preferably 550,000 or more. The weight-average molecular weight of the acrylic ester resin (B) is as high as 100,000 or more, so that the acrylic ester resin (B) 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 of the present invention after lamination. This allows for even greater adhesion of the thermal conductive sheet of the present invention to the adherend.

[0043] The weight-average molecular weight of the acrylic ester resin (B) is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. When the weight-average molecular weight of the acrylic ester resin (B) is 3,000,000 or less, the acrylic ester resin (B) becomes more fluid when the thermal conductive sheet of the present invention is attached using a hot press. This can further improve the wettability of the thermal conductive sheet of the present invention with the attached adherend, thereby further increasing the adhesion to the adherend.

[0044] The weight average molecular weight can be measured, for example, by gel permeation chromatography of the acrylic acid ester resin (B) using a calibration curve of standard polystyrene.

[0045] The molecular weight distribution (weight average molecular weight / number average molecular weight) of the acrylic ester resin having a functional group is preferably 1.0 to 10.0.

[0046] The glass transition temperature (Tg) of the acrylic ester resin (B) is preferably −40°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 having a hydroxyl group is −40°C or lower, the acrylic ester resin (B) becomes more fluid when the thermal conductive sheet of the present invention is attached using a hot press. This can further improve the wettability of the thermal conductive sheet of the present invention with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic ester resin having a hydroxyl group is not particularly limited, and is, for example, −150°C or higher.

[0047] The Tg can be calculated, for example, by the method described in the Examples.

[0048] (Anti-aging agent (C)) The composition contains an antioxidant (C). Here, "aging" refers to the deterioration of the properties of an object over time. For objects containing organic polymer compounds such as acrylate resins, such as the thermal conductive sheet of the present invention, an agent capable of preventing the aging of the organic polymer compounds is generally used as the antioxidant (C). Therefore, the "antiaging agent" in one embodiment of the present invention is an agent capable of preventing the aging of organic polymer compounds.

[0049] Specifically, the aging of organic polymer compounds is believed to be caused by radicals generated from the organic polymer compounds due to various factors, which then initiate chain reactions that cause the organic polymer compounds to decompose and / or oxidize. The antioxidant (C) is an agent that inhibits the progression of the chain reactions and prevents the aging of the organic polymer compounds.

[0050] Known examples of the antioxidant (C) include agents that react preferentially with the radicals to stabilize them, thereby hindering the progression of the chain reaction. Examples of such antioxidants (C) include phenol-based antioxidants and amine-based antioxidants.

[0051] Here, thermally conductive sheets containing organic polymer compounds such as acrylate ester resins having functional groups may experience a decrease in tackiness when maintained at high temperatures. The inventors discovered that when the thermally conductive sheet is maintained at high temperatures, the applied heat generates radicals from the organic polymer compounds having functional groups, causing the chain reaction. The inventors also discovered that the decomposition and / or alteration of the organic polymer compounds due to the chain reaction is the cause of the decrease in tackiness when maintained at high temperatures. The inventors then discovered that the inclusion of the antioxidant in the composition can hinder the chain reaction and prevent the decrease in tackiness of the thermally conductive sheet when maintained at high temperatures. Based on the above, in one embodiment of the present invention, the inclusion of the antioxidant (C) in the composition can provide a thermally conductive sheet with excellent tackiness after being maintained at high temperatures.

[0052] The antioxidant (C) is not particularly limited as long as it has the function of interfering with the progress of the chain reaction. For example, examples of amine-based antioxidants include antioxidants having a secondary amino group, such as N-phenyl-1-naphthylamine, alkylated diphenylamine, octylated diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, p-(p-toluenesulfonylamido)diphenylamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-isopropyl-N'-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-p-phenylenediamine. For example, phenolic antioxidants include 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4,4',4''-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), 6,6'-di-tert-butyl-4,4'-butylidene-m-cresol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythritol. Examples of hindered phenol-based antioxidants include 3,9-bis{2-[3-(3-tert-butyl-4-hydroxyphenyl)propionate], 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenylmethyl)-2,4,6-trimethylbenzene.

[0053] The antioxidant (C) may be one type of antioxidant or a mixture of two or more types of antioxidants.

[0054] In the thermal conductive sheet of the present invention, the antioxidant (C) is preferably an amine-based antioxidant and / or a phenol-based antioxidant, and more preferably an amine-based antioxidant. Furthermore, in the thermal conductive sheet of the present invention, by adopting a suitable combination of the type of acrylic ester-based resin (B) and the type of antioxidant (C), properties such as tackiness after high-temperature retention can be further improved. Here, the type of acrylic ester-based resin (B) refers, for example, to the type of functional group contained in the acrylic ester-based resin (B). For example, from the viewpoint of more suitably improving tackiness after high-temperature retention, the following combinations of the type of functional group and the type of antioxidant shown in (1) and (2) below are suitable. (1) The functional group is a hydroxyl group and / or a carboxyl group, and the antioxidant (C) is an amine-based antioxidant. (2) The functional group is a hydroxyl group, and the antioxidant (C) is a phenol-based antioxidant.

[0055] (composition) In one embodiment of the present invention, the composition containing graphite particles (A), an acrylic ester-based resin (B), and an antioxidant (C) may contain an organic polymer compound other than the acrylic ester-based resin.

[0056] The other organic polymer compound is not particularly limited, and any organic polymer compound typically used in thermally conductive sheets can be used. The other organic polymer compound may be one type of resin or a mixture of two or more types of resins.

[0057] Hereinafter, an organic polymer compound comprising the acrylic acid ester resin (B) and optionally other organic polymer compounds will be referred to as a "mixed organic polymer compound."

[0058] The content of the acrylic ester resin (B) relative to the total weight of the mixed organic polymer compound 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 (B) relative to the total weight of the mixed organic polymer compound may be, for example, 100% by weight.

[0059] The Tg and weight-average molecular weight of the mixed organic polymer compound are preferably within the same ranges as the preferred ranges of the Tg and weight-average molecular weight of the acrylate ester resin (B) disclosed in the above section "(Acrylate ester resin (B))." When the Tg and weight-average molecular weight of the mixed organic polymer compound are within the above-mentioned ranges, the thermal conductive sheet of the present invention achieves the same effects as when the Tg and weight-average molecular weight of the acrylate ester resin (B) are within the preferred ranges.

[0060] In the thermal conductive sheet of the present invention, the content of the acrylic ester resin (B) is preferably 25% by weight or more, more preferably 30% by weight or more, and even more preferably 40% by weight or more, based on the weight of all organic components of the thermal conductive sheet. The content of the acrylic ester resin (B) may be 100% by weight or less, based on the weight of all organic components of the thermal conductive sheet. In this specification, the "weight of all organic components" refers to the total weight of the mixed organic polymer compound and, if the thermal conductive sheet of the present invention contains an additive made of an organic compound, the weight of the additive made of the organic compound.

[0061] The content of the antioxidant (C) in the thermal conductive sheet of the present invention is preferably 0.1 wt% or more, more preferably 0.2 wt% or more, and even more preferably 0.5 wt% or more, based on the weight of all organic components of the thermal conductive sheet. By controlling the content of the antioxidant to 0.1 wt% or more based on the weight of all organic components, the progress of the chain reaction can be suitably hindered, and as a result, the tackiness of the thermal conductive sheet of the present invention after being kept at high temperatures can be further improved.

[0062] The content of the antioxidant (C) is preferably 5 wt% or less, more preferably 3 wt% or less, and even more preferably 2 wt% or less, based on the weight of all organic components of the thermal conductive sheet. By controlling the content of the antioxidant (C) to 5 wt% or less, based on the weight of all organic components, it is possible to suitably prevent the properties of the thermal conductive sheet of the present invention from being impaired due to the inclusion of the antioxidant (C). More specifically, by controlling the content of the antioxidant (C) to 5 wt% or less, based on the weight of all organic components of the thermal conductive sheet, it is possible to reduce the amount of water and / or solvent absorbed by the thermal conductive sheet of the present invention.

[0063] The composition may contain additives such as plasticizers, flame retardants, heat stabilizers, colorants, antistatic agents, tackifiers, and fillers other than the graphite particles (A), as needed. The additives may include additives made from the organic compounds described above. The plasticizer may be, for example, polybutene or a phosphorus-based flame retardant. The inclusion of polybutene and / or a phosphorus-based flame retardant in the thermal conductive sheet of the present invention improves wettability with silicone and / or a spreader, 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 resin combustion. The inclusion of the additive in the composition means that the thermal conductive sheet of the present invention further contains the additive. In the manufacturing process of a thermal conductive sheet, the graphite particles (A), the acrylic ester resin (B), and the additive may be mixed with a solvent to form a primary sheet. However, in this specification, the term "composition" refers to the composition after the solvent has been removed by drying or other methods, i.e., the composition contained in the final thermal conductive sheet.

[0064] When the thermal conductive sheet of the present invention contains the additive, the content of the additive is not particularly limited as long as it does not impair the effects of the present invention. A preferred content of the additive is, for example, 50 wt % or less based on the weight of the thermal conductive sheet of the present invention.

[0065] [1-2. Thermal Conduction Sheet] The thermally conductive sheet of the present invention contains the composition, and the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet.

[0066] (Orientation of graphite particles (A)) In the thermally conductive sheet of the present invention, the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, thereby improving thermal conductivity in the thickness direction along the orientation, and thereby reducing thermal resistance in the thickness direction along the orientation. It is not necessary for all of the graphite particles (A) contained in the thermally conductive sheet to be oriented in the thickness direction of the thermally conductive sheet. In the thermally conductive sheet of the present invention, it is sufficient for at least a portion of the graphite particles (A) to be oriented in the thickness direction of the thermally conductive sheet, and thermal conductivity can be improved in the thickness direction along the orientation.

[0067] The graphite particles (A) being 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 particles (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 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 particles (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 particles (A) coincides with the maximum length of the graphite particles (A).

[0068] 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.

[0069] (Physical properties of thermal conductive sheets, etc.) The thermal resistance of the thermally conductive sheet of the present invention is preferably 0.10°C / W or less, more preferably 0.09°C / W or less, even more preferably 0.085°C / W or less, and particularly preferably 0.082°C / W or less. Herein, thermal resistance refers to the 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 0.10°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.

[0070] The thickness of the thermally conductive sheet of the present invention is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 140 μm or less, even more preferably 110 μm or less, 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 300 μm or less or 200 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 10 μm or more, and more preferably 20 μm or more.

[0071] The content of the graphite particles (A) in the thermal conductive sheet of the present invention relative to the total weight of the thermal conductive sheet is preferably 40.0 wt% or more, more preferably 45.0 wt% or more, even more preferably 47.5 wt% or more, and even more preferably 50.0 wt% or more. When the content of the graphite particles (A) is 40.0 wt% or more or 45.0 wt% or more, the thermal conductive sheet of the present invention preferably exhibits sufficient thermal conductivity.

[0072] The content of the graphite particles (A) relative to the total weight of the thermal conductive sheet is preferably 70.0 wt% or less, more preferably 65.0 wt% or less, and even more preferably 62.5 wt% or less. When the content of the graphite particles (A) is 70.0 wt% or less, the thermal conductive sheet of the present invention preferably exhibits sufficient flexibility and adhesion.

[0073] The content of the mixed organic polymer compound in the thermal conductive sheet of the present invention relative to the total weight of the thermal conductive sheet is preferably 10 wt % or more, more preferably 15 wt % or more, and even more preferably 20 wt % or more. When the content of the mixed organic polymer compound is 10 wt % or more, the flexibility of the thermal conductive sheet of the present invention is improved, and the heat-generating body and the heat-dissipating body can be well adhered to each other via the thermal conductive sheet.

[0074] The content of the mixed organic polymer compound relative to the total weight of the thermally 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.

[0075] The content of the antioxidant (C) in the thermal conductive sheet of the present invention is preferably 0.03% by weight or more, more preferably 0.1% by weight or more, and even more preferably 0.2% by weight or more, based on the total weight of the thermal conductive sheet. The content of the antioxidant (C) in the thermal conductive sheet is preferably 3% by weight or less, and more preferably 2% by weight or less, based on the total weight of the thermal conductive sheet.

[0076] The contents of the graphite particles (A), the mixed organic polymer compound, the antioxidant (C), and the additives in the thermal conductive sheet of the present invention may be the same as the contents of the graphite particles (A), the mixed organic polymer compound, the antioxidant (C), and the additives in the composition relative to the weight of the entire composition.

[0077] In this specification, the hardness of the thermally conductive sheet of the present invention is substituted by the value of the laminate before slicing. The hardness at 20°C of the thermally conductive sheet of the present invention is preferably 75 or more, more preferably 80 or more, even more preferably 84 or more, and particularly preferably 86 or more. Here, in this specification, 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 75 or more is preferable because the thermally conductive sheet is sufficiently hard and therefore can be sliced ​​to a thin thickness. Furthermore, the hardness at 20°C of the thermally conductive sheet is preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less. If the hardness at 20°C of the thermally conductive sheet is 95 or less, when the thermally conductive sheet is bonded to a component by hot pressing, the thermally conductive sheet undergoes little deformation and can be sufficiently adhered to the component it contacts. Furthermore, when the thermally conductive sheet is laminated by hot pressing, the graphite particles (A) contained in the thermally conductive sheet can maintain a state of being oriented in the thickness direction, thereby enabling efficient heat transfer and sufficient relaxation of thermal stress.

[0078] The hardness at 70°C of the thermally conductive sheet of the present invention is preferably greater than 60, more preferably greater than 63, and even more preferably greater than 65. Herein, 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 80 or less, more preferably 78 or less, and even more preferably 75 or less. When the thermally conductive sheet has a hardness at 70°C of 80 or less, the thermally conductive sheet undergoes minimal deformation when bonded to a component by hot pressing, allowing the thermally conductive sheet to be sufficiently adhered to the component. Furthermore, when the thermally conductive sheet is bonded to a component by hot pressing, the graphite particles (A) contained in the thermally conductive sheet can maintain a state oriented in the thickness direction. Therefore, heat can be efficiently transferred and thermal stress can be sufficiently alleviated.

[0079] In this specification, the tackiness of a thermally conductive sheet can be evaluated by a numerical value (unit: N·mm) representing the tackiness measured by the method described in the Examples. The thermally conductive sheet of the present invention preferably has a tackiness of 0.8 N·mm or more, more preferably 1.0 N·mm or more, and even more preferably 1.2 N·mm or more. The upper limit of the tackiness is not particularly limited and can be, for example, less than 5.0 N·mm.

[0080] When the tackiness of a thermally conductive sheet is 0.8 N·mm or more, the thermally conductive sheet can be positioned accurately when temporarily attached to an adherend. Furthermore, even if the adherend is moved while temporarily attached, it does not shift position. Therefore, when the thermally conductive sheet of the present invention has a tackiness of 0.8 N·mm or more, it can exhibit better adhesion when hot-pressed. Furthermore, when the tackiness of a thermally conductive sheet is less than 5.0 N·mm, air easily escapes between the thermally conductive sheet and the adherend when temporarily attached to the adherend. Furthermore, when the thermally conductive sheet and the adherend are bonded together by hot-pressing, air trapped between the thermally conductive sheet and the adherend easily escapes. Therefore, when the thermally conductive sheet of the present invention has a tackiness of less than 5.0 N·mm, the thermally conductive sheet of the present invention can be more sufficiently adhered to the components it contacts.

[0081] 2. Manufacturing method of thermal conductive sheet The method for manufacturing the thermal conductive sheet of the present invention is not particularly limited as long as it is a method that can manufacture the above-mentioned thermal conductive sheet, and examples thereof include the method for manufacturing a thermal conductive sheet according to one embodiment of the present invention described below (hereinafter referred to as the "manufacturing method of the present invention").

[0082] The production method of the present invention includes a primary sheet forming step of forming a composition containing graphite particles (A), an acrylic ester-based resin (B), and an antioxidant (C) 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 primary sheet laminate; and a slicing step of slicing the laminate cross section of the primary sheet laminate to obtain a thermally conductive sheet, wherein the acrylic ester-based resin (B) has a functional group.

[0083] (Primary sheet forming process) In the primary sheet forming step, a composition containing graphite particles (A), an acrylic acid ester resin (B), and an antioxidant (C) 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.

[0084] Here, the graphite particles (A), the acrylic ester-based resin (B), the antioxidant (C), and the composition containing the graphite particles (A), the acrylic ester-based resin (B), and the antioxidant (C) are as described above in [1. Thermal Conductive Sheet].

[0085] Examples of a method for forming the composition into a sheet to obtain a primary sheet in which the graphite particles (A) are oriented in a direction parallel to the sheet surface include the following methods (a) and (b). (a) Graphite particles (A), acrylic ester resin (B), antioxidant (C), and, if necessary, the other organic polymer compounds and additives are mixed with or without the addition of a solvent to obtain a mixture. In other words, graphite particles (A), the mixed organic polymer compounds, antioxidant (C), and, if necessary, the additives are mixed with or without the addition of a solvent to obtain a mixture. (b) The mixture obtained in (a) is formed into a sheet to prepare a primary sheet in which the graphite particles (A) are oriented in a direction approximately parallel to the main surface.

[0086] 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 solvent may be a single solvent or a mixture of two or more solvents. The amount of solvent is preferably such that the total concentration of the graphite particles (A), the mixed organic polymer compound, and the 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.

[0087] The method for mixing the graphite particles (A), the mixed organic polymer compound, and, if necessary, the additives described above, with or without the addition of a solvent is not particularly limited.

[0088] The method for subsequently forming the resulting mixture into a sheet is not particularly limited, and examples thereof include methods for producing a primary sheet by rolling, press molding, extrusion molding, or coating.

[0089] 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.

[0090] (Laminate formation process) The laminate forming 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.

[0091] The pressure to be applied when stacking the primary sheets is not particularly limited, and may be 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 allow the primary sheets to be well bonded together. Furthermore, the stacking may be performed under appropriate heating.

[0092] The pressure applied when stacking the primary sheets may be applied after each primary sheet is stacked, after multiple sheets are stacked, or after all primary sheets are stacked. In such cases, the pressure and temperature applied after each primary sheet or multiple primary sheets are stacked and after all primary sheets are stacked are not particularly limited.

[0093] (Slicing process) In the slicing step, the cross section of the laminate of the primary sheets is sliced ​​to obtain a thermally conductive sheet. The angle at which the cross section of the laminate of the primary sheets is sliced ​​is not particularly limited.

[0094] 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, a knife processing method, and an ultrasonic processing method.

[0095] <Summary> An embodiment of the present invention includes the following configuration. [1] A thermally conductive sheet comprising a composition containing graphite particles (A), an acrylic acid ester resin (B), and an antioxidant (C), the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, The thermally conductive sheet, wherein the acrylic ester resin (B) has a functional group. [2] The thermally conductive sheet according to [1], wherein the antioxidant (C) is an amine-based antioxidant. [3] The antioxidant (C) is a phenolic antioxidant, and The thermal conductive sheet according to [1], wherein the functional group is a hydroxyl group. [4] The thermal conductive sheet according to [2], wherein the functional group is a hydroxyl group and / or a carboxyl group. [5] The thermal conductive sheet according to any one of [1] to [4], wherein the content of the antioxidant (C) is 0.1 wt % or more and 5 wt % or less, based on the weight of all organic components of the thermal conductive sheet. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the content of the acrylic ester resin (B) is 25% by weight or more based on the weight of all organic components of the thermally conductive sheet. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the acrylic ester resin (B) has a glass transition temperature (Tg) of −40° C. or lower. [8] The thermally conductive sheet according to any one of [1] to [7], wherein the acrylic ester resin (B) has a weight average molecular weight of 550,000 or more. [9] a primary sheet forming step of forming a composition containing graphite particles (A), an acrylic acid ester resin (B), and an antioxidant (C) 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 laminating the primary sheets to obtain a laminate of primary sheets; a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet, The method for producing a thermally conductive sheet, wherein the acrylic ester resin (B) has a functional group.

[10] The method for producing a thermal conductive sheet according to [9], wherein the primary sheet forming step is a step of forming a primary sheet by coating. [Example]

[0096] 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.

[0097] The following evaluations and production of the thermally conductive sheets were carried out at room temperature (20° C.) and atmospheric pressure (1 atm) unless otherwise specified.

[0098] [Methods for measuring physical properties, etc.] The evaluation methods used in the examples and comparative examples will be explained below.

[0099] <Weight average molecular weight: GPC (gel permeation chromatography) analysis> GPC equipment (manufacturer: Tosoh, product name: HLC-8420, column: TSKgelGMH XL x2+TSKgelG3000H XL +TSKgelG2000H XL GPC analysis was carried out using tetrahydrofuran (THF) as an eluent to measure the weight average molecular weight (Mw) of the acrylic acid ester resin (B) used in the examples.

[0100] <Content of Functional Groups in the Present Invention> (Identification of each monomer constituting the acrylic ester resin (B)) Using a pyrolysis GC / MS measurement device (manufacturer: Japan Analytical Industry Co., Ltd., product name: JCI-22), the acrylic acid ester resin (B) used in the examples was pyrolyzed into each of its constituent monomers, and the type of each monomer was identified by gas chromatography.

[0101] ( 1 HNMR analysis) The acrylic ester resin (B) was dissolved in deuterated chloroform (CDCl) to prepare a sample for NMR measurement. The sample for NMR measurement was analyzed using an NMR measurement device (manufacturer: Bruker, product name: AVA700). 1 HNMR measurement was performed. 1 H NMR spectra were obtained. 1 Based on the peak intensities of the peaks derived from each of the monomers in the HNMR spectrum, the proportion (mmol / g) of the monomer having a functional group contained in the acrylate ester resin (B) relative to the total weight of the acrylate ester resin (B) was calculated. Here, since the amount of the monomer having a functional group and the amount of the functional group are the same, the calculated proportion was taken as the content of the functional group in the present invention.

[0102] <Glass transition temperature (Tg)> Since the acrylic ester resin (B) used in the examples was a copolymer, its glass transition temperature (Tg) was calculated using the FOX formula shown in the following formula (3). Note that Tg1, Tg2, Tg nA known value was used as the (1 / Tg)=(C1 / Tg1)+(C2 / Tg2)+...(C n / Tg n )··(3) (In formula (3), Tg1, Tg2,...Tg n are the Tg of the homopolymers (homopolymers) made up of each monomer that makes up the copolymer. Also, C1, C2...C n is the weight ratio of each monomer to the total weight of the monomers. <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.

[0103] <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 the laminate, which consisted of only the thermally conductive sheet. 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 was measured by adjusting the temperature of the evaluation sample so that the temperature measured with a surface thermometer was 20°C, and the hardness at 70°C was measured by heating the evaluation sample so that the temperature measured with a surface thermometer was 70°C.

[0104] 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.

[0105] The hardness of the thermal conductive sheet at 70°C was evaluated according to the following criteria: A (Excellent): Over 63 B (Good): Over 60, 63 or less C (bad): 60 or less.

[0106] <Thermal resistance> The thermal conductive sheet was cut into a 1 cm x 1 cm square to be used as an evaluation sample. The thermal resistance value [cm 2 K / W] was measured using a thermal resistance measuring device (Hitachi Technology and Services, Ltd., Resin Material Thermal Resistance Measuring Device) at a sample temperature of 50°C and a pressure of 0.5 MPa.

[0107] 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 0.082 cm 2 If it is less than K / W. B (Good): The thermal resistance of the thermal conductive sheet is 0.082 cm 2 K / W super, 0.10cm 2 If 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.

[0108] <Initial tackiness> The initial tackiness of the thermal conductive sheet was evaluated by measuring a numerical value representing the tackiness of the thermal conductive sheet using a texture analyzer (manufactured by Eiko Seiki Co., Ltd., product name: TA.XTplus100C) at 20°C. Specifically, the initial tackiness was evaluated using a 7 mm diameter probe under the following conditions: test speed (before measurement): 0.5 mm / sec, (during measurement): 0.1 mm / sec, (return): 10 mm / sec, and an applied force of 40 N. A (excellent): The value representing the tackiness is greater than 2.0 N·mm and less than 5.0 N·mm. B (Good): The value representing the tackiness is greater than 0.7 N·mm and less than 2.0 N·mm. C (poor): The value representing the tackiness is 0.7 N·mm or less.

[0109] <Tackiness after high temperature storage> The thermally conductive sheet was placed in a heating furnace, and the atmosphere inside the furnace was heated to 150°C and maintained at this temperature for 100 hours. The thermally conductive sheet was then removed from the heating furnace, and the tackiness of the thermally conductive sheet was measured using the same method as described above in the "Initial Tackiness" section to evaluate the tackiness after high-temperature maintenance. The evaluation criteria for tackiness after high-temperature maintenance were the same as those for initial tackiness described above in the "Initial Tackiness" section.

[0110] <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.

[0111] 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.

[0112] [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 stirred mixture. The solid content of the composition solution was 30.0 wt %. Graphite particles: 120g of flake graphite powder (average particle size: 73μm, thickness: 0.80μm, aspect ratio: 91, sulfur content: 1.0% by weight or less); 356.4 g of a 15 wt % toluene / ethyl acetate solution of an acrylic ester resin (weight average molecular weight: 500,000, Tg: -36°C, containing a hydroxyl group as the functional group, the content of the functional group, i.e., the hydroxyl group, being 0.152 mmol / g and 8.5 KOHmg / g) as the acrylic ester resin (B) (53.5 g as the acrylic ester resin); Bisphenol A bis(diphenyl phosphate) as a flame retardant: 65.3g Antioxidant (C) (amine-based antioxidant: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine): 1.2g Toluene: Toluene was used in an amount such that the solid content concentration of the composition solution was 30.0% by weight.

[0113] <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.

[0114] The contents of the graphite particles, acrylate resin, flame retardant, and antioxidant (C) 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., the total weight of the final thermal conductive sheet. The weight of all organic components in the composition is the total weight of the acrylate resin, flame retardant, and antioxidant (C).

[0115] <Preparation of laminate> Each of the three primary sheets obtained was cut into a 2.4cm x 6.4cm piece and placed in a container with an internal volume of 2.5cm x 6.5cm x 7.5cm high. Every five sheets were stacked together and pressed at room temperature with a pressure of 400kg or more until the final thickness after pressing was 6.5cm or more. Next, the stacked sheets with a thickness of 6.5cm or more were heated at 120°C for 15 minutes and then pressed with a pressure of 400kg or more to obtain a 2.5cm x 6.5cm x 6.5cm laminate.

[0116] <Making a thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at a 45 degree angle to the lamination direction to produce a thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 100 μm thick, with graphite particles oriented in the thickness direction.

[0117] [Examples 2, 3, 5, and 6] Thermally conductive sheets were produced using the same procedures as in Example 1, except that the amounts of raw materials used were changed as shown in Table 1. In Examples 2, 3, 5, and 6, the amount of graphite particles used was 120 g, the same as in Example 1. The types of graphite particles, acrylic ester resin (B), antioxidant (C), and flame retardant were the same as in Example 1.

[0118] [Example 4] A thermally conductive sheet was produced by the same procedure as in Example 1, except that the type of antioxidant (C) was changed to a phenolic antioxidant: pentaerythritol tetrakis[3-[3,5-di(tert-butyl)-4-hydroxyphenyl]propionate].

[0119] [Example 7] A thermally conductive sheet was produced by the same procedure as in Example 1, except for the matters shown in (ix) to (xi) below. (ix) As the acrylic acid ester-based resin (B), instead of the 15 wt % toluene / ethyl acetate solution of the acrylic acid ester-based resin used in Example 1, a 15 wt % toluene / ethyl acetate solution of another acrylic acid ester-based resin having the properties described in Table 1 was used. (x) The amount of acrylic ester resin (B) used was changed to 376 g (56.4 g as acrylic ester resin). (xi) The amount of flame retardant used was changed to 62.2 g, and the amount of antioxidant (C) used was changed to 1.2 g.

[0120] [Example 8] A thermally conductive sheet was produced by the same procedure as in Example 1, except for the following points (xii) to (xiv). (xii) As the acrylic acid ester-based resin (B), instead of the 15 wt % toluene / ethyl acetate solution of the acrylic acid ester-based resin used in Example 1, a 15 wt % toluene / ethyl acetate solution of another acrylic acid ester-based resin having the properties described in Table 1 was used. (xiii) The amount of acrylic ester resin (B) used was changed to 520 g (78.0 g as acrylic ester resin). (xiv) The amount of flame retardant used was changed to 40.8 g, and the amount of antioxidant (C) used was changed to 1.2 g.

[0121] [Examples 9 to 11] A thermally conductive sheet was manufactured by the same procedure as in Example 1, except that, instead of the 15 wt % toluene / ethyl acetate solution of acrylic ester resin used in Example 1, another acrylic ester resin (a 15 wt % toluene / ethyl acetate solution of acrylic ester resin) having the properties shown in Table 1 was used as the acrylic ester resin (B).

[0122] [Comparative Examples 1 to 3] A thermally conductive sheet was produced by the same procedure as in Example 1, except for the following points (xv) to (xvii). (xv) As the acrylic acid ester-based resin (B), instead of the 15 wt % toluene / ethyl acetate solution of the acrylic acid ester-based resin used in Example 1, another acrylic acid ester-based resin (a 15 wt % toluene / ethyl acetate solution of the acrylic acid ester-based resin) having the properties described in Table 1 was used. (xvi) The amount of acrylic ester resin (B) used was changed to 360 g (54.0 g as acrylic ester resin). (xvii) The amount of flame retardant used was changed to 66.0 g, and the antioxidant (C) was not used.

[0123] [result] Table 1 below shows the properties of the acrylate ester resin (B) and the properties of the produced thermally conductive sheets measured by the above-mentioned methods in Examples 1 to 11 and Comparative Examples 1 to 3, as well as the blending ratios of the graphite particles, acrylate ester resin (B), flame retardant, and antioxidant (C), and the content of the antioxidant (C) relative to the weight of all organic components. In Table 1, the blending ratios refer to the content [wt %] relative to the weight of the entire thermally conductive sheet. Furthermore, "functional group content a" refers to the content [mmol / g] of the functional group, and "functional group content b" refers to the content [mg KOH / g] of the functional group. In Table 1, the "content of the acrylate ester resin (B) relative to the weight of all organic components" and the "content of the antioxidant relative to the weight of all organic components" are both referred to as "content in organic components."

[0124] [Table 1] TIFF2025168273000002.tif114170

[0125] Furthermore, when the thermally conductive sheets produced in Examples 1 to 11 were observed at 50 to 4000 magnifications using a scanning electron microscope (manufactured by Zeiss, product name: ULTRAplus), it was confirmed that the graphite particles were oriented in the thickness direction of the thermally conductive sheet.

[0126] From the descriptions of Examples 1 to 11 and the above-mentioned matters, it was found that the thermally conductive sheets produced in Examples 1 to 11 satisfied the following requirements and corresponded to the thermally conductive sheets of the present invention. The present invention includes a composition containing graphite particles (A), an acrylic ester resin (B), and an antioxidant (C). The graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet. The acrylic ester resin (B) has a functional group.

[0127] Furthermore, from the descriptions of Examples 1 to 11 and the above-mentioned matters, it was found that the manufacturing methods of the thermally conductive sheets described in Examples 1 to 9 correspond to the manufacturing methods of the present invention.

[0128] On the other hand, as described in Comparative Examples 1 to 3, no antioxidant (C) was used in Comparative Examples 1 to 3, and the thermally conductive sheets produced in Comparative Examples 1 to 3 did not contain the antioxidant (C). Therefore, the thermally conductive sheets produced in Comparative Examples 1 to 3 do not fall under the category of the thermally conductive sheet of the present invention. Furthermore, the manufacturing methods of the thermally conductive sheets described in Comparative Examples 1 to 3 do not fall under the category of the manufacturing method of the present invention.

[0129] As shown in Table 1, the thermally conductive sheets produced in Comparative Examples 1 to 3 had poor tackiness after being kept at high temperatures, while the thermally conductive sheets produced in Examples 1 to 11 had excellent tackiness after being kept at high temperatures.

[0130] Therefore, it was found that the thermally conductive sheet of the present invention has excellent tackiness after being kept at high temperatures. Furthermore, it was found that the manufacturing method of the present invention can produce a thermally conductive sheet of the present invention that has excellent tackiness after being kept at high temperatures. Therefore, it was found that one aspect of the present invention can provide a thermally conductive sheet that has excellent tackiness after being kept at high temperatures. [Industrial Applicability]

[0131] One embodiment of the present invention can be suitably used for producing a thermally conductive sheet that has excellent tackiness after being held at high temperatures, and for producing products that use the thermally conductive sheet, such as electronic components including multilayer wiring boards and semiconductor packages. Note that a thermally conductive sheet that has excellent tackiness after being held at high temperatures maintains its adhesiveness even when held in a high-temperature environment in a state where it is adhered to an adherend, and therefore can suitably maintain its adhered state with the adherend.

Claims

1. A thermally conductive sheet comprising a composition containing graphite particles (A), an acrylic acid ester-based resin (B), and an antioxidant (C), the graphite particles (A) are oriented in the thickness direction of the thermal conductive sheet, The thermally conductive sheet, wherein the acrylic ester resin (B) has a functional group.

2. The thermal conductive sheet according to claim 1 , wherein the antioxidant (C) is an amine-based antioxidant.

3. The antioxidant (C) is a phenol-based antioxidant, and The thermally conductive sheet according to claim 1 , wherein the functional group is a hydroxyl group.

4. The thermally conductive sheet according to claim 2 , wherein the functional group is a hydroxyl group and / or a carboxyl group.

5. 2. The thermal conductive sheet according to claim 1, wherein the content of the antioxidant is 0.1 wt % or more and 5.0 wt % or less based on the weight of all organic components of the thermal conductive sheet.

6. 2. The thermal conductive sheet according to claim 1, wherein the content of the acrylic ester resin (B) is 25% by weight or more based on the weight of all organic components of the thermal conductive sheet.

7. The thermal conductive sheet according to claim 1, wherein the acrylic ester resin (B) has a glass transition temperature (Tg) of −40° C. or lower.

8. The thermal conductive sheet according to claim 1 , wherein the acrylic ester resin (B) has a weight average molecular weight of 550,000 or more.

9. a primary sheet forming step of forming a composition containing graphite particles (A), an acrylic acid ester-based resin (B), and an antioxidant (C) 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 laminating the primary sheets to obtain a laminate of primary sheets; a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet, The method for producing a thermal conductive sheet, wherein the acrylic ester-based resin (B) has a functional group.

10. The method for producing a thermally conductive sheet according to claim 9 , wherein the primary sheet forming step is a step of forming the primary sheet by coating.

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