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

Abstract

To provide a heat-conductive sheet that exhibits high graphite bondability and superior adhesion to an adherend.SOLUTION: A heat-conductive sheet of the present invention includes a composition containing graphite particles (A) and an organic polymer compound (B) comprising an acrylic acid ester resin containing a carboxyl group in an amount of 0.010-0.410 mmol / g or less, the graphite particles (A) being oriented in a thickness direction.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] Conventionally, a technology for preventing or reducing temperature rise by attaching a heat sink to a heat-generating body such as an electronic component has been 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 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] Japanese Patent Publication No. 2010-132856 [Patent Document 3] Japanese Patent Publication No. 2011-184663 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional thermal conductive sheets containing compositions containing graphite particles and organic polymer compounds, such as the thermal conductive sheets described in Patent Documents 1 to 3, have room for improvement in terms of graphite binding ability and adhesion to the adherend.

[0006] Therefore, an object of one aspect of the present invention is to provide a thermally conductive sheet that is excellent in graphite binding property and adhesion to an adherend. [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 including 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, the organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, The content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less.

[0008] In order to solve the above-mentioned problems, a method for producing a thermally conductive sheet according to one embodiment of the present invention includes a primary sheet forming step of forming a composition containing graphite particles (A) and an organic polymer compound (B) 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 organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, The content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less. [Effects of the Invention]

[0009] According to one aspect of the present invention, a thermally conductive sheet having excellent graphite binding properties and adhesion to an adherend can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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)."

[0011] [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) and an organic polymer compound (B), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, the organic polymer compound (B) comprises an acrylic acid ester resin having a carboxyl group, and the content of the carboxyl group in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less.

[0012] [1-1. Composition containing graphite particles (A) and organic polymer compound (B)] (Graphite particles (A)) The thermally conductive sheet of the present invention comprises a composition containing graphite particles (A) and an organic polymer compound (B). 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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).

[0018] 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.

[0019] 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.

[0020] 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.).

[0021] 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.

[0022] (Organic polymer compound (B)) The composition contains an organic polymer compound (B), which functions as a binder and improves the flexibility of the thermally conductive sheet, thereby enabling the heat-generating body and the heat-dissipating body to be well adhered to each other via the thermally conductive sheet.

[0023] The organic polymer compound (B) contains an acrylic ester resin having a carboxyl group (-COOH group). The organic polymer compound (B) may contain one type of acrylic ester resin having a carboxyl group, or may contain two or more types of acrylic ester resins having a carboxyl group. Therefore, the organic polymer compound (B) contains a carboxyl group.

[0024] In the thermally conductive sheet of the present invention, the content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less.

[0025] When the content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) (hereinafter also referred to as the "carboxyl group content of the present invention") is 0.010 mmol / g or more, the graphite binding property of the thermal conductive sheet can be improved. This is thought to be because the carboxyl groups in the organic polymer compound (B) interact with the graphite particles (A) and function as a binder that binds multiple graphite particles (A). Therefore, the thermal conductive sheet of the present invention has excellent graphite binding property.

[0026] As mentioned above, graphite binding strength is improved by using an organic polymer compound (B) having a carboxyl group as the organic polymer compound. However, it has been found that thermally conductive sheets obtained by laminating sheets formed from a composition containing graphite particles (A) and an organic polymer compound (B) having a carboxyl group may have poor adhesion to an adherend. The inventors have discovered that this is because the thermally conductive sheet is usually applied while being heated, and during use, heat is applied from the heat-generating body that is the adherend, causing water absorbed by the heat to be discharged to the outside, resulting in a change in shape. After extensive investigation, they have found that a thermally conductive sheet with excellent adhesion to an adherend can be achieved by setting the content of carboxyl groups in the organic polymer compound (B) to a predetermined amount or less relative to the total weight of the organic polymer compound (B). This is thought to be because, when the carboxyl group content in the thermal conductive sheet is excessively high, the carboxyl groups react easily with water molecules, causing the thermal conductive sheet to be highly hygroscopic and absorbing a large amount of water from the air. In this case, the amount of water discharged is large, which increases the degree of deformation. As a result, gaps are formed between the thermal conductive sheet and the adherend, and adhesion to the adherend tends to decrease. The thermal conductive sheet of the present invention has a carboxyl group content of 0.410 mmol / g or less, and the carboxyl group content is not excessively high, so it also has excellent adhesion to the adherend.

[0027] Furthermore, the carboxyl groups interact with the substances that make up the surface of the adherend, contributing to the adhesion between the thermally conductive sheet and the adherend. Therefore, if the carboxyl group content of the present invention is 0.010 mmol / g or more, the tackiness of the thermally conductive sheet when it is adhered to the adherend can be improved. Therefore, the thermally conductive sheet of the present invention also has excellent tackiness.

[0028] From the viewpoint of further improving graphite binding properties, the carboxyl group content of the present invention is preferably 0.050 mmol / g or more, more preferably 0.090 mmol / g or more. Furthermore, the carboxyl group content of the present invention can also be expressed in the commonly used unit of "KOHmg / g" instead of the unit of "mmol / g." In this case, the carboxyl group content of the present invention is 0.56 KOHmg / g or more, preferably 2.81 KOHmg / g or more, more preferably 5.05 KOHmg / g or more.

[0029] From the viewpoint of further improving the adhesion to the adherend, the carboxyl group content of the present invention is preferably 0.380 mmol / g or less, more preferably 0.350 mmol / g or less. When the carboxyl group content of the present invention is expressed in units of "KOHmg / g", it is 23.00 KOHmg / g or less, preferably 21.32 KOHmg / g or less, more preferably 19.64 KOHmg / g or less.

[0030] To convert from mmol / g to mg / g of KOH, multiply mmol / g by 56.1056 mg / mmol.

[0031] The method for measuring the carboxyl group content of 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 organic polymer compound (B) is extracted from the thermally conductive sheet, and the total weight (unit: g) of the extracted organic polymer compound (B) is measured. (2) 1 The amount of carboxyl groups (unit: mmol) in the organic polymer compound (B) extracted in step (1) is measured using 1H NMR or the like. (3) The carboxyl group content (unit: mmol / g) of the present invention is calculated by dividing the carboxyl group content (number of moles) in the organic polymer compound (B) measured in the step (2) by the total weight of the organic polymer compound (B) measured in the step (1).

[0032] In addition, when the weight average molecular weights of all polymers contained in the organic polymer compound (B), the content of the monomer having a carboxyl group in all the constituent monomers, and the content ratio of each polymer are known, the carboxyl group content of the present invention can also be calculated based on these.

[0033] The content of the acrylic ester resin having a carboxyl group 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 35% by weight or more, and particularly preferably 40% by weight or more. The content of the acrylic ester resin relative to the total weight of the organic polymer compound (B) can be, for example, 100% by weight, or may be 95% by weight or less, and preferably 90% by weight or less.

[0034] The organic polymer compound (B) may contain an organic polymer compound other than the acrylic ester resin having a carboxyl group.

[0035] 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.

[0036] Examples of the other organic polymer compounds include acrylic acid ester resins having no carboxyl groups, 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.

[0037] When the organic polymer compound (B) contains an epoxy resin as the other organic polymer compound, the content of the epoxy resin is preferably less than 6.5 parts by weight per 100 parts by weight of the acrylic ester resin having a carboxyl group.

[0038] The organic polymer compound (B) may be solid or liquid at room temperature. In this specification, "room temperature" refers to 20°C.

[0039] The acrylic ester resin having a carboxyl group preferably contains 50% by weight or more of repeating units derived from an acrylic monomer. The acrylic ester resin having a carboxyl group includes a polymer of a monomer component in which at least a portion of the constituent monomers has a carboxyl group and which contains one or more acrylic monomers. The acrylic ester resin having a carboxyl group also includes a copolymer in which at least a portion of the constituent monomers has a carboxyl group and an acrylic monomer with another monomer. 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 (b2) include (meth)acrylic esters having an ester having 1 to 10 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0040] Examples of the other monomer (b3) include acrylonitrile, glycidyl methacrylate, and 2-chloroethyl vinyl ether. The other monomer 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.

[0041] The ratio by weight of the monomer having a carboxyl group to the weight of all monomers constituting all polymeric compounds (polymers) contained in the organic polymer compound (B) is preferably 0.1 wt% to 5.2 wt%, more preferably 0.3 wt% to 4.0 wt%. Furthermore, the ratio by moles of the monomer having a carboxyl group to the moles of all monomers constituting all polymeric compounds (polymers) contained in the organic polymer compound (B) is preferably 0.1 mol% to 5.2 mol%, more preferably 0.3 mol% to 4.0 mol%. Adjusting this ratio within the aforementioned range is preferred in terms of suitably controlling the carboxyl group content of the present invention within the aforementioned range.

[0042] The ratio of the weight of the carboxyl group-containing monomer to the weight of all monomers constituting the carboxyl group-containing acrylic ester resin contained in the organic polymer compound (B) is preferably 0.1 wt% to 5.2 wt%, more preferably 0.3 wt% to 4.0 wt%. The ratio of the amount (molar number) of the carboxyl group-containing monomer to the amount (molar number) of all monomers constituting the carboxyl group-containing acrylic ester resin contained in the organic polymer compound (B) is preferably 0.1 mol% to 5.2 mol%, more preferably 0.3 mol% to 4.0 mol%. Adjusting this ratio within the above range is preferred in terms of suitably controlling the carboxyl group content of the present invention within the above range.

[0043] The monomer (b1) having a carboxyl group is not particularly limited, and preferred examples include acrylic acid and methacrylic acid. The monomer (b1) having a carboxyl group may be one type or two or more types.

[0044] The weight ratio ((b1) / (b2) / (b3)) of the carboxyl group-containing monomer (b1), the (meth)acrylic acid ester (b2), and the other monomer (b3) is preferably 0.1 to 5.2 / 99.9 to 79.8 / 0 to 15. The weight ratio ((b1) / (b2) / (b3)) may be, for example, within the ranges of 5 to 15 / 95 to 60 / 0 to 25.

[0045] The acrylic ester resin having a carboxyl group may be a random copolymer or a block copolymer, but a random copolymer is preferred because it is more readily available.

[0046] The structure of the acrylic ester resin having a carboxyl group may be either linear or branched, but linear structures are preferred because they are more readily available.

[0047] The organic polymer compound (B) is preferably one that is soluble in an organic solvent.

[0048] The carboxyl group-containing acrylic ester resin may or may not contain a crosslinked structure as long as it does not impair flexibility. The inclusion of a crosslinked structure is preferable in terms of long-term adhesion retention and film strength. The crosslinked structure can be incorporated, for example, by reacting a polymer having an -OH group with a compound having an isocyanate group. Alternatively, the crosslinked structure can be incorporated, for example, by reacting a polymer having a -COOH group with a compound having an epoxy group. However, when reacting a polymer having a -COOH group with a compound having an epoxy group, the -COOH group is consumed in the reaction. Therefore, in such cases, care must be taken to ensure that the carboxyl group content does not decrease to less than 0.01 mmol / g. Hereinafter, compounds capable of reacting with functional groups such as -OH groups and -COOH groups in the organic polymer compound (B), such as the isocyanate group-containing compound and the epoxy group-containing compound, to form a crosslinked structure are referred to as "crosslinking agents." When the "crosslinking agent" is used, the amount used is preferably less than 5 parts by weight per 100 parts by weight of the organic polymer compound (B).

[0049] The weight-average molecular weight of the organic polymer compound (B) is preferably 100,000 or more, more preferably 400,000 or more, and even more preferably 600,000 or more. Because the weight-average molecular weight of the organic polymer compound (B) is as high as 100,000 or more, the organic polymer compound (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 thermally conductive sheet of the present invention after lamination. This allows for even greater adhesion of the thermally conductive sheet of the present invention to the adherend.

[0050] The weight-average molecular weight of the organic polymer compound (B) 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 organic polymer compound (B) is 3 million or less, the organic polymer compound (B) becomes more likely to flow during application using a hot press. This can further improve the wettability of the thermally conductive sheet of the present invention with the adherend to which it is applied, thereby further increasing the adhesion to the adherend.

[0051] The weight-average molecular weight of the carboxyl-containing acrylic ester resin is preferably 100,000 or more, more preferably 400,000 or more, and even more preferably 600,000 or more. Because the weight-average molecular weight of the carboxyl-containing acrylic ester resin is as high as 100,000 or more, the organic polymer compound (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 thermally conductive sheet of the present invention after lamination. This allows for even greater adhesion of the thermally conductive sheet of the present invention to the adherend.

[0052] The weight-average molecular weight of the carboxyl-containing acrylic ester resin 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 carboxyl-containing acrylic ester resin is 3,000,000 or less, the organic polymer compound (B) becomes more fluid when the thermally conductive sheet of the present invention is applied using a hot press. This further improves the wettability of the thermally conductive sheet of the present invention with the adherend to which it is applied, thereby further increasing the adhesion to the adherend.

[0053] The weight average molecular weight can be measured, for example, by gel permeation chromatography of the organic polymer compound (B) or the acrylic acid ester resin having a carboxyl group, using a calibration curve of standard polystyrene.

[0054] The molecular weight distribution (weight average molecular weight / number average molecular weight) of the acrylic ester resin having a carboxyl group is preferably 1.0 to 10.0.

[0055] The glass transition temperature (Tg) of the organic polymer compound (B) is preferably 0°C or lower, more preferably -30°C or lower, and even more preferably -60°C or lower. When the Tg of the organic polymer compound (B) is 0°C or lower, the organic polymer compound (B) becomes more fluid when the thermally conductive sheet of the present invention is attached using a hot press. This can further improve the wettability of the thermally 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 organic polymer compound (B) is not particularly limited, and is, for example, -150°C or higher.

[0056] The glass transition temperature (Tg) of the carboxyl group-containing acrylic ester resin is preferably 0°C or lower, more preferably -30°C or lower, and even more preferably -60°C or lower. When the Tg of the carboxyl group-containing acrylic ester resin is 0°C or lower, the organic polymer compound (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 carboxyl group-containing acrylic ester resin is not particularly limited, and is, for example, -150°C or higher.

[0057] The Tg can be calculated, for example, by the method described in the Examples.

[0058] (composition) In one embodiment of the present invention, the composition containing graphite particles (A) and an organic polymer compound (B) may optionally contain additives such as a curing agent, a flame retardant, an antioxidant, a heat stabilizer, a colorant, an antistatic agent, a tackifier, and a filler other than the graphite particles (A). In the process of producing a thermally conductive sheet, the graphite particles (A), the organic polymer compound (B), and the additives 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 the like, i.e., the composition contained in the final thermally conductive sheet.

[0059] Examples of the flame retardant include bromine-based flame retardants, phosphorus-based flame retardants, and inorganic flame retardants. The flame retardant may be one type or two or more types. The content of the flame retardant is preferably 1 to 300 parts by weight per 100 parts by weight of the organic polymer compound (B).

[0060] The curing agent is not particularly limited, and examples thereof include bisphenol-type epoxy, biphenyl-type epoxy, stilbene-type epoxy, naphthalene-type epoxy, etc. The curing agent may be one type or two or more types.

[0061] [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.

[0062] (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.

[0063] 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).

[0064] 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.

[0065] (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.

[0066] 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.

[0067] The sulfur content of the thermally conductive sheet of the present invention is preferably 0.30 wt% or less, more preferably 0.25 wt% or less, even more preferably 0.20 wt% or less, and particularly preferably 0.10 wt% or less, based on the total weight of the thermally conductive sheet. Herein, the sulfur content of the thermally conductive sheet refers to the sulfur content measured by the method described in the Examples. A sulfur content of 0.30 wt% or less of the thermally conductive sheet can more suitably reduce the hygroscopicity of the thermally conductive sheet, thereby further improving adhesion to the adherend. The lower the sulfur content of the thermally conductive sheet, the better. While not particularly limited, the lower limit is, for example, 0.01 wt% or more.

[0068] 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.

[0069] 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 60.0 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.

[0070] The content of the organic polymer compound (B) in the thermally conductive sheet of the present invention 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 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 thermally conductive sheet.

[0071] 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.

[0072] In one embodiment of the present invention, the content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) is preferably 0.0014 mmol / g or more, more preferably 0.01 mmol / g or more, and even more preferably 0.08 mmol / g or more. By having the content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) be 0.0014 mmol / g or more, graphite binding ability can be suitably improved.

[0073] The content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) is preferably 0.55 mmol / g or less, more preferably 0.40 mmol / g or less, and even more preferably 0.37 mmol / g or less. By having the content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) be 0.55 mmol / g or less, adhesion to an adherend can be suitably improved.

[0074] In one embodiment of the present invention, the weight ratio of the graphite particles (A) to the weight of the organic polymer compound (B) is preferably 3.0 or less, more preferably 2.0 or less, and the weight ratio of the graphite particles (A) to the weight of the organic polymer compound (B) is preferably 0.25 or more, more preferably 0.33 or more.

[0075] When the thermal conductive sheet of the present invention contains the tackifier, the content of the tackifier is not particularly limited as long as it does not impair the effects of the present invention. A preferred content of the tackifier is, for example, 40% by weight or less relative to the weight of the organic polymer compound (B).

[0076] When the thermal conductive sheet of the present invention contains the curing agent, the content of the curing agent is not particularly limited as long as it does not impair the effects of the present invention. A preferred content of the curing agent is, for example, 0.20 wt % or less based on the total weight of the thermal conductive sheet.

[0077] The contents of the graphite particles (A), the organic polymer compound (B), the sulfur, 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 organic polymer compound (B), the sulfur, and the additives in the composition relative to the weight of the entire composition.

[0078] 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, and even more preferably 84 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 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 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 bonded to a component by hot pressing, the graphite particles (A) contained in the thermally conductive sheet can maintain a state of being oriented in the thickness direction. Therefore, heat can be transferred well and thermal stress can be sufficiently relieved.

[0079] 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, deformation of the thermally conductive sheet is minimal when the thermally conductive sheet is 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.

[0080] 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.

[0081] When the tackiness of a thermally conductive sheet is 0.8 N·mm or more, the thermally conductive sheet can be positioned with high precision 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 the thermally conductive sheet is 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.

[0082] 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").

[0083] The production method of the present invention includes a primary sheet forming step of forming a composition containing graphite particles (A) and an organic polymer compound (B) 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, wherein the organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, and the content of the carboxyl group in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less.

[0084] (Primary sheet forming process) In the primary sheet forming step, a composition containing graphite particles (A) and an organic polymer compound (B) 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.

[0085] 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. Thermally conductive sheet].

[0086] 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).

[0087] (a) Graphite particles (A), an organic polymer compound (B), and, if necessary, the above-mentioned additives are mixed with or without the addition of a solvent to obtain a mixture.

[0088] (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.

[0089] 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), 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.

[0090] The method for mixing the graphite particles (A), the organic polymer compound (B), and, if necessary, the additives described above, with or without the addition of a solvent, is not particularly limited. For example, the organic polymer compound (B) is dissolved in a solvent, and then the graphite particles (A) and, if necessary, other additives are added and mixed. The mixing method is also not particularly limited, and mixing by stirring, roll kneading, kneader mixing, Brabender mixing, extruder mixing, etc. can be used.

[0091] The method for 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. When a solvent is used during mixing, the added solvent may be removed by drying or the like before or after forming the mixture into a sheet.

[0092] 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.

[0093] (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 so that the orientation of the graphite particles (A) in the sheet plane is the same.

[0094] 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.

[0095] 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 pressure is applied 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, and 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℃.

[0096] (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.

[0097] 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.

[0098] <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, the organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, A thermally conductive sheet, wherein the content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less. [2] The thermally conductive sheet according to [1], wherein the organic polymer compound (B) has a weight average molecular weight of 100,000 or more. [3] The thermally conductive sheet according to [1] or [2], wherein the glass transition temperature (Tg) of the organic polymer compound (B) is 0°C or lower. [4] The thermally conductive sheet according to any one of [1] to [3], wherein the content of the curing agent relative to the total weight of the thermally conductive sheet is 0.20% by weight or less. [5] The thermally conductive sheet according to any one of [1] to [4], wherein the sulfur content relative to the total weight of the thermally conductive sheet is 0.30% by weight or less. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the content of the graphite particles (A) relative to the total weight of the thermally conductive sheet is 40.0% by weight or more and 70.0% by weight or less. [7] The thermally conductive sheet according to any one of [1] to [6], wherein the content of the organic polymer compound (B) relative to the total weight of the thermally conductive sheet is 10% by weight or more and 60% by weight or less. [8] The thermal conductive sheet according to any one of [1] to [7], wherein the content of the acrylic acid ester resin having a carboxyl group relative to the total weight of the organic polymer compound (B) is 40% by weight or more and 90% by weight or less. [9] The thermally conductive sheet according to any one of [1] to [8], which contains 1 to 300 parts by weight of a flame retardant per 100 parts by weight of the organic polymer compound (B).

[10] The thermal conductive sheet according to any one of [1] to [9], wherein the content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) is 0.0014 mmol / g or more and 0.55 mmol / g or less.

[11] a primary sheet forming step of forming a composition containing graphite particles (A) and an organic polymer compound (B) 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 organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, the content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less; The method for producing a thermally conductive sheet, wherein the organic polymer compound (B) has a weight average molecular weight of 30,000 or more.

[12] A method for producing a thermal conductive sheet according to

[11] , wherein the primary sheet forming step is a step of forming a primary sheet by coating.

[0099] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0100] 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.

[0101] 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.

[0102] [Methods for measuring physical properties, etc.] The evaluation methods used in the examples and comparative examples will be explained below.

[0103] <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 organic polymer compound (B) used in the examples.

[0104] <Carboxyl group content of the present invention> (Identification of each monomer constituting the organic polymer compound (B)) Using a pyrolysis GC / MS measurement device (manufacturer: Japan Analytical Industry Co., Ltd., product name: JCI-22), the organic polymer compound (B) used in the examples was pyrolyzed into each of its constituent monomers, and the type of each monomer was identified by gas chromatography.

[0105] ( 1 HNMR analysis) The organic polymer compound (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 intensity of the peaks derived from each of the monomers in the HNMR spectrum, the proportion (mmol / g) of the monomer having a carboxyl group contained in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) was calculated. Here, since the amount of the monomer having a carboxyl group and the amount of the carboxyl group are the same, the calculated proportion was taken as the content of the carboxyl group in the present invention.

[0106] <Glass transition temperature (Tg)> The organic polymer compound (B) used in the examples was a copolymer of an acrylic ester resin having a carboxyl group, and therefore its glass transition temperature (Tg) was calculated using the FOX formula shown in the following formula (3). n A 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. <Graphite adhesion> After producing the laminates of the Examples and Comparative Examples described below, the laminates were sliced ​​and the state of the laminates was visually inspected, and the graphite binding properties of the thermal conductive sheets were evaluated according to the following criteria. A (excellent): After the laminate was produced, when the laminate was sliced, the shape of the laminate was maintained and the laminate layer could be sliced. B (good): After the laminate was produced, when the laminate was sliced, the shape of the laminate was deformed, but the laminate layers could be sliced. C (bad): The rectangular parallelepiped shape cannot be maintained immediately after the laminate is produced, or the shape of the laminate is lost when the laminate is sliced ​​after production, making it impossible to slice the laminate layer.

[0107] <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.

[0108] <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. 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 Science and Technology of Japan (SRIS). The hardness at 20°C was measured by adjusting the temperature so that the temperature measured with a surface thermometer of the evaluation sample was 20°C. The hardness at 70°C was measured by heating the evaluation sample so that the temperature measured with a surface thermometer of the evaluation sample was 70°C.

[0109] 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.

[0110] 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, under 63 C (bad): 60 or less.

[0111] <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.

[0112] 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 0.080cm2 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 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.

[0113] <Tackiness> The 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 tackiness was evaluated using a probe with a diameter of 7 mm 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.

[0114] <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.

[0115] The 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.

[0116] [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); 360 g of a 15 wt % toluene / ethyl acetate solution of an acrylic ester resin (weight average molecular weight: 400,000, Tg: -40°C, containing a carboxyl group as a functional group, the carboxyl group content of the present invention being 0.010 mmol / g, 0.56 KOH mg / g) as an organic polymer compound (54.0 g as the acrylic ester resin), -Bisphenol A bis(diphenyl phosphate) as a flame retardant: 66.0g Toluene: Toluene was used in an amount such that the solid content concentration of the composition solution was 30.0% by weight.

[0117] <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.

[0118] The content of the graphite particles, the organic polymer compound, and the flame retardant relative to the total weight of the composition contained in the primary sheet corresponds to the content of the graphite particles, the organic polymer compound, and the flame retardant relative to the total weight of the composition contained in the final thermal conductive sheet, i.e., the content of the graphite particles, the organic polymer compound, and the flame retardant relative to the total weight of the final thermal conductive sheet.

[0119] <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.

[0120] <Making a thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at an angle of 45 degrees to the lamination direction (in other words, in the normal direction to the main surface of the laminated primary sheet), to produce a thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick, with graphite particles oriented in the thickness direction.

[0121] [Examples 2 to 7, Comparative Examples 1 to 3] A thermally conductive sheet was produced by the same procedure as in Example 1, except that a 15 wt % toluene / ethyl acetate solution of another acrylic ester resin having the properties shown in Table 1 was used as the organic polymer compound instead of the 15 wt % toluene / ethyl acetate solution of the acrylic ester resin used in Example 1. In Comparative Example 3, when the cross section of the laminate was sliced ​​at an angle of 45 degrees to the lamination direction, the shape of the laminate was distorted, making it impossible to slice the laminate layer, and a thermally conductive sheet could not be produced.

[0122] [Example 8] A thermally conductive sheet was produced by the same procedure as in Example 1, except for the following points (i) to (iii). (i) As the organic polymer compound, instead of the 15 wt % toluene / ethyl acetate solution of the acrylic ester resin used in Example 1, a 15 wt % toluene / ethyl acetate solution of another acrylic ester resin having the properties listed in Table 1 was used. (ii) The amount of organic polymer compound used was changed to 326 g (48.9 g as acrylic ester resin). (iii) The amount of flame retardant used was changed to 59.7g.

[0123] [Example 9] A thermally conductive sheet was produced by the same procedure as in Example 1, except for the following points (iv) to (vi). (iv) As the organic polymer compound, instead of the 15 wt % toluene / ethyl acetate solution of the acrylic ester resin used in Example 1, a 15 wt % toluene / ethyl acetate solution of another acrylic ester resin having the properties listed in Table 1 was used. (v) The amount of organic polymer compound used was changed to 295 g (44.2 g as acrylic ester resin). (vi) The amount of flame retardant used was changed to 54.0 g.

[0124] Comparative Example 4 A thermally conductive sheet was produced in the same manner as in Example 1 of Patent Document 2. In Comparative Example 4, a curing agent was used in addition to graphite particles, an organic polymer compound, and a flame retardant in preparing the composition solution.

[0125] Comparative Example 5 A thermally conductive sheet was produced by the same method as in Example 2 of Patent Document 2. In Comparative Example 5, the curing agent was also used in addition to the graphite particles, organic polymer compound, and flame retardant in preparing the composition solution.

[0126] [result] The properties of the organic polymer compound and the properties of the produced thermally conductive sheets measured by the above-mentioned methods in Examples 1 to 9 and Comparative Examples 1 to 5, as well as the blending ratios of the graphite particles, organic polymer compound, flame retardant, and curing agent, are shown in Table 1 below. In Table 1, the blending ratios refer to the content [wt %] relative to the weight of the entire thermally conductive sheet. Furthermore, "functional group amount a" refers to the carboxyl group content [mmol / g] of the present invention, and "functional group amount b" refers to the carboxyl group content [KOHmg / g] of the present invention. [Table 1] Furthermore, when the thermally conductive sheets produced in Examples 1 to 9 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.

[0127] From the above and the description in the "Amount of functional group a" column in Table 1, the thermally conductive sheets produced in Examples 1 to 9 correspond to the thermally conductive sheets of the present invention. Furthermore, from the description in Examples 1 to 9 and the description in the "Amount of functional group a" column in Table 1, the manufacturing methods for the thermally conductive sheets in Examples 1 to 9 correspond to the manufacturing methods of the present invention. On the other hand, the manufacturing methods for the thermally conductive sheets in Comparative Examples 1 to 5 do not correspond to the manufacturing methods of the present invention, and the manufactured thermally conductive sheets do not correspond to the thermally conductive sheets of the present invention.

[0128] As shown in Table 1, the thermally conductive sheets produced in Comparative Examples 1 to 5 were poor in either graphite binding or adhesion to the adherend, whereas the thermally conductive sheets produced in Examples 1 to 9 were excellent in both graphite binding and adhesion to the adherend.

[0129] Therefore, it was found that the thermally conductive sheet of the present invention has high graphite binding ability and excellent adhesion to the adherend. Furthermore, it was found that the manufacturing method of the present invention can manufacture a thermally conductive sheet of the present invention having high graphite binding ability and excellent adhesion to the adherend. Therefore, it was found that the present invention has the effect of providing a thermally conductive sheet having high graphite binding ability and excellent adhesion to the adherend.

[0130] The sulfur content of the graphite particles used in Examples 1 to 9 and Comparative Examples 1 to 3 was 1.0 wt % or less. On the other hand, the sulfur content of the graphite particles used in Comparative Examples 4 and 5 was greater than 3.0 wt %. It was also confirmed that the thermally conductive sheets described in Examples 1 to 9 and Comparative Examples 1 to 3 are less likely to corrode electronic components in contact with the thermally conductive sheets than the thermally conductive sheets described in Comparative Examples 4 and 5. [Industrial Applicability]

[0131] One embodiment of the present invention can be suitably used for producing a thermally conductive sheet that has high graphite binding properties and excellent adhesion to an adherend, and for producing products that use the thermally conductive sheet, such as multilayer wiring boards and electronic components that include 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, the organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, a thermally conductive sheet, wherein the content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) is 0.010 mmol / g or more and 0.410 mmol / g or less.

2. The thermal conductive sheet according to claim 1 , wherein the organic polymer compound (B) has a weight average molecular weight of 100,000 or more.

3. The thermal conductive sheet according to claim 1 or 2, wherein the organic polymer compound (B) has a glass transition temperature (Tg) of 0°C or lower.

4. 3. The thermal conductive sheet according to claim 1, wherein the content of the curing agent relative to the total weight of the thermal conductive sheet is 0.20% by weight or less.

5. 3. The thermal conductive sheet according to claim 1, wherein the sulfur content of the thermal conductive sheet is 0.30% by weight or less relative to the total weight of the thermal conductive sheet.

6. 3. The thermal conductive sheet according to claim 1, wherein the content of the graphite particles (A) relative to the total weight of the thermal conductive sheet is 40.0 wt % or more and 70.0 wt % or less.

7. 3. The thermal conductive sheet according to claim 1, wherein the content of said organic polymer compound (B) relative to the total weight of said thermal conductive sheet is 10% by weight or more and 60% by weight or less.

8. 3. The thermal conductive sheet according to claim 1, wherein the content of the acrylic ester resin having a carboxyl group relative to the total weight of the organic polymer compound (B) is 40% by weight or more and 90% by weight or less.

9. 3. The thermal conductive sheet according to claim 1, further comprising 1 to 300 parts by weight of a flame retardant per 100 parts by weight of the organic polymer compound (B).

10. 3. The thermal conductive sheet according to claim 1, wherein the content of carboxyl groups in the organic polymer compound (B) relative to the weight of the graphite particles (A) is 0.0014 mmol / g or more and 0.55 mmol / g or less.

11. a primary sheet forming step of forming a composition containing graphite particles (A) and an organic polymer compound (B) 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 organic polymer compound (B) contains an acrylic ester resin having a carboxyl group, a content of carboxyl groups in the organic polymer compound (B) relative to the total weight of the organic polymer compound (B) being 0.010 mmol / g or more and 0.410 mmol / g or less.

12. The method for producing a thermal conductive sheet according to claim 11 , wherein the primary sheet forming step is a step of forming the primary sheet by coating.

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