Method for producing thermally conductive sheet

Abstract

To produce a heat conductive sheet excellent in heat conductivity, temporary sticking property and adhesion.SOLUTION: A method for producing a thermally conductive sheet, the method comprising a primary sheet-forming step of forming a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet shape to obtain a primary sheet, a laminate forming step of laminating a plurality of the primary sheets while applying pressure to reduce the thickness of the primary sheets to obtain a laminate, and a slicing step of slicing a laminate cross section of the laminate.SELECTED DRAWING: None

Description

[Technical Field]

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

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

[0003] A method for producing a thermally conductive sheet having thermal conductivity and adhesiveness is known, which includes a step of stacking primary sheets containing graphite particles and an organic polymer compound to form a laminate, and a step of slicing the laminate to obtain a thermally conductive sheet (Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5381102 [Patent Document 2] Patent No. 6341303 [Patent Document 3] Patent No. 6881429 [Patent Document 4] Japanese Patent Publication No. 2023-016528 Summary of the Invention [Problem to be solved by the invention]

[0005] Recently, there has been a demand for improved thermal conductivity of thermally conductive sheets. One known method for improving the thermal conductivity of thermally conductive sheets is to reduce the thickness of the thermally conductive sheet. However, thin thermally conductive sheets manufactured by conventional manufacturing methods such as those described in Patent Documents 1 to 4 often have holes, i.e., areas that cannot come into contact with the adherend, which can reduce the temporary attachment and adhesion of the sheet to the adherend.

[0006] In view of the above, the present invention aims to provide a method for manufacturing a thermally conductive sheet that improves the thermal conductivity of the thermally conductive sheet and improves the adhesion of the thermally conductive sheet to an adherend without reducing the thickness, and that can prevent a decrease in adhesion even when the thickness is reduced. In other words, the object of the present invention is to improve the thermal conductivity, temporary adhesion, and adhesion of the manufactured thermally conductive sheet, and to manufacture a thermally conductive sheet that is excellent in thermal conductivity, temporary adhesion, and adhesion. [Means for solving the problem]

[0007] 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 mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet; a laminate forming step of stacking a plurality of the primary sheets while applying pressure to the primary sheets so as to reduce their thickness, thereby obtaining a laminate of the primary sheets; and a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet. [Effects of the Invention]

[0008] According to one aspect of the present invention, a thermally conductive sheet having excellent thermal conductivity, temporary attachment properties, and adhesiveness can be produced. [Brief explanation of the drawings]

[0009] [Figure 1]1 shows an XRD profile obtained by measuring the X-ray diffraction intensity of the surface of the primary sheet obtained in Example 1 using a two-dimensional X-ray diffractometer (XRD). [Figure 2] 1 is an SEM image of the surface of the thermally conductive sheet obtained in Example 1, which was observed and mapped using SEM-EDX. [Figure 3] 1 is an image showing the results of identifying carbon obtained by observing and mapping the surface of the thermally conductive sheet obtained in Example 1 using SEM-EDX. [Figure 4] This is an enlarged view of the SEM image shown in Figure 2, showing how a 500 μm x 50 μm area (area 1) that includes an area that appears darker than the surrounding area and a 500 μm x 50 μm area (area 2) that does not include an area that appears darker than the surrounding area are set on the surface. 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. Manufacturing method of thermal conductive sheet 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 mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet; a laminate forming step of stacking a plurality of the primary sheets while applying pressure to reduce the thickness of 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.

[0012] Hereinafter, the method for manufacturing a thermally conductive sheet according to one embodiment of the present invention will be referred to as "the manufacturing method." Furthermore, the thermally conductive sheet manufactured by this manufacturing method will be referred to as "the thermally conductive sheet." Each step of this manufacturing method will be described in detail below.

[0013] 1-1. Primary sheet forming process The present production method includes a primary sheet forming step of forming a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet.

[0014] A conventional method for forming a primary sheet involves melt-kneading graphite particles (A), an organic polymer compound (B), and, if necessary, additives without adding a solvent, and then forming the resulting kneaded mixture into a sheet to obtain a primary sheet. The present inventors have confirmed that there is no difference in carbon concentration on the surface of a thermally conductive sheet manufactured using a primary sheet obtained by this method.

[0015] Therefore, the present inventors conducted extensive research and produced a primary sheet using a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent, rather than by melt-kneading without adding a solvent. As a result, they found that by subjecting the primary sheet to the laminate-forming step and the slicing step, a thermally conductive sheet having a difference in carbon concentration can be obtained. In other words, this thermally conductive sheet is a thermally conductive sheet having a difference in carbon concentration.

[0016] Here, a thermally conductive sheet having a difference in carbon concentration essentially means that it has a portion with a high content of graphite particles (A) and a portion with a high content of organic polymer compound (B). Therefore, according to this production method, it is possible to produce a thermally conductive sheet in which the presence of the portion with a high content of graphite particles (A) favorably improves thermal conductivity, and the presence of the portion with a high content of organic polymer compound (B) favorably improves temporary attachment and adhesion to an adherend.

[0017] Furthermore, when primary sheets obtained by a conventional method are laminated under pressure to reduce the thickness in the laminate formation step described below, the present inventors have confirmed that some of the graphite particles (A) contained in the primary sheets are lost, resulting in a decrease in their particle size. In such cases, the thermal conductivity of the produced thermal conductive sheet may decrease due to the decrease in the particle size of the graphite particles (A).

[0018] On the other hand, in the primary sheet formation step of the present production method, even when pressure is applied to reduce the thickness, a primary sheet is formed that has an internal structure that can suitably prevent a decrease in particle size due to the loss of the graphite particles (A) or that has enough capacity to reduce the degree of such decrease. Therefore, according to the present production method, a decrease in the thermal conductivity of the thermal conductive sheet due to a decrease in the particle size of the graphite particles (A) can be suitably prevented or the degree of such decrease can be suitably reduced, and as a result, a thermal conductive sheet with suitably improved thermal conductivity can be produced.

[0019] While the reason for the difference in carbon concentration that results from using the mixture is unclear, it is believed that the degree of dispersion of the graphite particles (A) and the organic polymer compound (B) varies between the interior and surface of the primary sheet depending on the solvent, and that this variation is reflected in the laminate. Furthermore, it is believed that the organic polymer compound (B) migrates to the surface of the primary sheet during the heating and solvent drying process after coating the solution containing the graphite particles (A) and the organic polymer compound (B), resulting in the presence of areas with a low carbon concentration after lamination. Furthermore, it is believed that the organic polymer compound (B) may have seeped out to the interface between the primary sheets during pressing in the laminate formation process. Furthermore, it is also unclear why the mixture allows the formation of a primary sheet with the internal structure having the aforementioned clearance. However, it is believed that the reason for this is that the degree of dispersion of the graphite particles (A) and the organic polymer compound (B) varies between the interior and surface of the primary sheet, resulting in the formation of the internal structure having the aforementioned clearance in the primary sheet. However, the present invention is not limited to such speculation.

[0020] (Graphite particles (A)) By providing a mixture containing graphite particles (A) in the primary sheet forming step, the present manufacturing method can produce a thermally conductive sheet containing graphite particles (A). Here, the thermally conductive graphite particles (A) are dispersed in the thermally conductive sheet. This improves the thermal conductivity of the thermally conductive sheet, thereby reducing the thermal resistance of the thermally conductive sheet.

[0021] The graphite particles (A) used in the primary sheet forming step may be spherical or non-spherical in shape. The graphite particles (A) are preferably non-spherical in shape, because the graphite particles are easily oriented, thereby improving the thermal conductivity in the orientation direction and thereby reducing the thermal resistance of the thermally conductive sheet in the orientation direction. The graphite particles (A) may be of one type, or two or more types may be used in combination.

[0022] 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 flake-like shape; an ellipsoidal shape; an acicular shape; a rod-like shape; a fibrous shape; or an irregular shape. Among these, the shape of the non-spherical graphite particles (A) facilitates orientation and maintains interparticle contact, thereby further improving thermal conductivity in the orientation direction. From the viewpoint of further reducing the thermal resistance of the present thermal conductive sheet in the orientation direction, it is more preferable that the shape of the non-spherical graphite particles (A) be a plate-like shape such as a scale-like or thin flake-like shape.

[0023] 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.

[0024] For "non-spherical" graphite particles (A), the aspect ratio refers to the ratio of the maximum length of the graphite particles (A) to the minimum length (maximum length / minimum length). For example, if the shape is plate-like, the minimum length of the graphite particles (A) is the thickness, and the aspect ratio is the ratio of the maximum length to the thickness (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.

[0025] 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).

[0026] From the viewpoint of improving thermal conductivity in the orientation direction, the aspect ratio of the graphite particles (A) is preferably 10 or more, more preferably 20 or more, even more preferably 40 or more, and particularly preferably 70 or more. There is no particular upper limit, but it is usually 1000 or less. When the aspect ratio of the graphite particles (A) is 10 or more, by orienting the graphite particles (A) in the thickness direction of the thermal conductive sheet, the thermal conductivity in the thickness direction of the thermal conductive sheet can be further improved, and thus the thermal resistance in the thickness direction of the thermal conductive sheet can be further reduced, which is preferable.

[0027] The upper limit of the average value of the minor axis or minimum length of the graphite particles (A) is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. When the average value of the minor axis or minimum length of the graphite particles (A) is a small value of 5 μm or less, the density of the primary sheet obtained in the primary sheet forming step can be controlled to a lower value. As a result, in this production method, by subjecting a primary sheet with a lower density to the laminate forming step described below, the graphite particles (A) can be more suitably oriented during lamination, thereby producing a thermally conductive sheet with improved thermal conductivity. On the other hand, the lower limit of the average value of the minor axis or minimum length of the graphite particles (A) is not particularly limited and can be, for example, 0.005 μm or more.

[0028] Examples of the graphite particles (A) include particles such as flake graphite, flaky graphite, amorphous graphite, artificial graphite, exfoliated graphite, acid-treated graphite, expanded graphite, and carbon fiber flakes.

[0029] The lower limit of the average particle size of the graphite particles (A) is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more, of the thickness of the thermally conductive sheet. The upper limit of the average particle size of the graphite particles (A) is preferably 100% or less, more preferably 95% or less, and even more preferably 90% or less. Specifically, 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, of the thickness of the thermally conductive sheet. The average particle size of the graphite particles (A) is a value determined using a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.). The thickness of the thermally conductive sheet is measured by a known method, for example, the method described in the Examples.

[0030] When the average particle size of the graphite particles (A) is 50% or more of the thickness of the thermally conductive sheet, the graphite particles (A) are oriented in the desired direction in the thermally conductive sheet, making it easier to form a good heat transfer path. 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 thermally conductive sheet, which improves the heat transfer from the heating element to the thermally conductive sheet when it comes into contact with the heating element.

[0031] (Organic polymer compound (B)) By providing a mixture containing the organic polymer compound (B) in the primary sheet forming step, the present manufacturing method can produce a thermally conductive sheet containing the organic polymer compound (B). Here, in this thermally conductive sheet, the organic polymer compound (B) functions as a binder and also improves the flexibility of the thermally conductive sheet. Therefore, this thermally conductive sheet can provide good adhesion between the heat generating element and the heat dissipating element.

[0032] The organic polymer compound (B) is not particularly limited, and any organic polymer compound that is normally used in a heat conductive sheet can be used.

[0033] Examples of the organic polymer compound (B) include acrylic ester resins, resins having a main chain consisting of repeating siloxane bonds (silicone resins), resins having rubber elasticity at room temperature (elastomer resins), epoxy resins, fluororesins, polyolefins, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyacetal, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, polyphenylene ether, modified polyphenylene ether, aliphatic polyamides, aromatic polyamides, polyamideimide, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, polyurethane, liquid crystal polymers, and ionomers. These may be used alone or in combination.

[0034] The organic polymer compound (B) may be solid or liquid at room temperature. In this specification, "room temperature" refers to 20°C.

[0035] The Tg and weight-average molecular weight of the organic polymer compound (B) are preferably in the same ranges as the preferred ranges of the Tg and weight-average molecular weight of the acrylate ester resin described below, thereby providing the thermally conductive sheet with the same effects as when the Tg and weight-average molecular weight of the acrylate ester resin are in the preferred ranges.

[0036] <Acrylate ester resin> The organic polymer compound (B) preferably contains an acrylic ester resin, and the acrylic ester resin may be used alone or in combination of two or more.

[0037] The acrylic ester resin includes a polymer of a monomer component containing one or more acrylic monomers selected from (meth)acrylic acid and (meth)acrylic esters, and a copolymer of the acrylic monomer with another monomer. In this specification, "(meth)acrylic" includes both "methacrylic" and "acrylic." Examples of the (meth)acrylic ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0038] Examples of the other monomers include acrylonitrile, glycidyl methacrylate, and 2-chloroethyl vinyl ether. Acrylic rubber can be obtained by copolymerizing a (meth)acrylic acid ester with acrylonitrile, 2-chloroethyl vinyl ether, or the like. Acrylic rubber is also classified as an elastomer resin, which will be described later, but in this specification, acrylic rubber is considered to be included in acrylic acid ester-based resins.

[0039] A more preferred example of the acrylic ester resin is an acrylic ester resin containing either or both of butyl acrylate and 2-ethylhexyl acrylate as monomers, with the total amount of these monomers being 50 wt% or more based on the total amount of monomer components. This acrylic ester resin is preferred because it allows the thermal conductive sheet to easily achieve high flexibility, excellent chemical stability and processability, and easy control of adhesiveness. Furthermore, incorporating a crosslinked structure into the acrylic ester resin without impairing flexibility is preferred in terms of the long-term adhesion retention and film strength of the thermal conductive sheet. The crosslinked structure can be incorporated, for example, by reacting a polymer having a hydroxyl group with a compound having an isocyanate group. Alternatively, the crosslinked structure can be incorporated, for example, by reacting a polymer having a carboxyl group with a compound having an epoxy group.

[0040] The content of the acrylic ester resin relative to the total weight of the organic polymer compound (B) is preferably 15% by weight or more, more preferably 20% by weight or more, even more preferably 25% by weight or more, and particularly preferably 30% by weight or more. The content of the acrylic ester resin relative to the total weight of the organic polymer compound (B) may be, for example, 100% by weight.

[0041] The Tg of the acrylic ester resin is preferably −35°C or lower, more preferably −50°C or lower, and even more preferably −60°C or lower. When the Tg of the acrylic ester resin is −35°C or lower, the acrylic ester resin becomes more fluid when the thermal conductive sheet is attached using a hot press. This can further improve the wettability of the thermal conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic ester resin is not particularly limited and is, for example, −150°C or higher. The “Tg” described in this specification can be calculated, for example, by the method described in the Examples.

[0042] The acrylic ester resin may be solid or liquid at room temperature and normal pressure, and is preferably liquid at room temperature and normal pressure.

[0043] In this specification, "normal pressure" means 1 atm. In other words, the acrylic ester resin is preferably an acrylic ester resin having a melting point of 20°C or lower. The "melting point" described in this specification is the melting point under normal pressure (1 atm). In addition, in this specification, "being liquid" means that the resin flows when the container, such as a bottle or a can, containing the resin at room temperature (20°C) is tilted. In addition, the resin may be a block resin.

[0044] The weight-average molecular weight of the acrylic ester resin is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 250,000 or more. Because the weight-average molecular weight of the acrylic ester resin is as high as 50,000 or more, the acrylic ester resin is less likely to flow when the press plate is released after the heat press during lamination, or when external force is applied after lamination. This allows for increased adhesion of the thermally conductive sheet to the adherend.

[0045] The weight-average molecular weight of the acrylic ester resin is preferably 3 million or less, more preferably 2 million or less, and even more preferably 1.5 million or less. When the weight-average molecular weight of the acrylic ester resin is 3 million or less, the acrylic ester resin becomes more fluid when the thermal conductive sheet is attached using a hot press. This improves the wettability of the thermal conductive sheet with the attached adherend, thereby increasing the adhesion to the adherend.

[0046] The weight average molecular weight described in this specification can be measured, for example, by gel permeation chromatography of the object to be measured using a calibration curve of standard polystyrene.

[0047] The organic polymer compound preferably includes an acrylate resin having a functional group. In this specification, the term "acrylate resin having a functional group" means that the acrylate resin includes a polymer of monomer components including a monomer having a functional group.

[0048] The functional group functions to bond a plurality of the graphite particles (A). Therefore, the presence of the functional group in the acrylic ester resin makes it easier to form the mixture into a sheet, thereby making it easier to provide the present thermally conductive sheet containing the mixture. Furthermore, the functional group may interact with a substance that constitutes the surface of an adherend, contributing to the adhesion between the present thermally conductive sheet and the adherend. In this case, it is believed that the adhesion between the present thermally conductive sheet and the adherend is also improved.

[0049] The type of the functional group is not particularly limited as long as it has the function of binding multiple graphite particles (A). The functional group may be one type or two or more types. The functional group may be, for example, one or more types selected from a hydroxyl group, a carboxyl group, and an epoxy group, preferably a hydroxyl group and / or a carboxyl group, and more preferably a hydroxyl group. The type of functional group can be identified by known methods, such as structural analysis of the acrylic ester resin using NMR or the like.

[0050] The monomer having a functional group is not particularly limited, and preferred examples include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-1-methyl (meth)acrylate, acrylic acid, methacrylic acid, glycidyl (meth)acrylate, etc. Among these, it is more preferred that the monomer having a functional group contains 2-ethylhexyl acrylate, in other words, that the acrylic ester resin contains a copolymer containing 2-ethylhexyl acrylate as a monomer.

[0051] In one embodiment of the present invention, when the content of the functional groups relative to the total weight of the acrylic ester resin is high, the graphite particles (A) in the thermal conductive sheet are more suitably bound together via the acrylic ester resin. As a result, the graphite binding property of the thermal conductive sheet is further improved. Hereinafter, the content of the functional groups relative to the total weight of the acrylic ester resin is referred to as the "functional group content C." The functional group content C is the sum of the functional group content A and the functional group content B described below.

[0052] The preferred range of the functional group content C is 0.001 mmol / g or more and 0.410 mmol / g or less. The preferred range of the functional group content C can vary depending on the type of the functional group and the type of the graphite particles (A). For example, when the functional group is one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group, from the viewpoint of further improving graphite binding, the functional group content C is preferably 0.001 mmol / g or more, more preferably 0.010 mmol / g or more, and even more preferably 0.090 mmol / g or more. The functional group content can also be expressed in the commonly used unit "mg KOH / g" in addition to the unit "mmol / g." Specifically, for example, when the functional group is one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group, the content C of the functional group is preferably 0.056 KOHmg / g or more, more preferably 0.56 KOHmg / g or more, and even more preferably 5.05 KOHmg / g or more.

[0053] Furthermore, the functional groups can also typically form bonds with water molecules. Therefore, when the functional group content C is within a predetermined range, the affinity of the acrylic ester resin for water is reduced, thereby reducing its moisture absorption. As a result, the moisture absorption of the thermal conductive sheet is controlled within a suitable range, resulting in improved adhesion after high-temperature storage.

[0054] For example, when the functional group is a hydroxyl group, from the viewpoint of further improving the adhesion after the high-temperature holding, the content C of the functional group is preferably 0.371 mmol / g or less, more preferably 0.340 mmol / g or less, and even more preferably 0.300 mmol / g or less. Furthermore, when the functional group is a hydroxyl group and the content C of the functional group is expressed in units of "KOHmg / g", it is preferably 20.76 KOHmg / g or less, more preferably 19.08 KOHmg / g or less, and even more preferably 16.83 KOHmg / g or less.

[0055] For example, when the functional group is a carboxyl group, from the viewpoint of further improving the adhesion after the high-temperature holding, the content C of the functional group is preferably 0.410 mmol / g or less, more preferably 0.360 mmol / g or less, and even more preferably 0.300 mmol / g or less. Furthermore, when the functional group is a carboxyl group and the content C of the functional group is expressed in units of "KOHmg / g", it is preferably 23.00 KOHmg / g or less, more preferably 20.20 KOHmg / g or less, and even more preferably 16.83 KOHmg / g or less.

[0056] To convert from mmol / g to mg / g of KOH, multiply mmol / g by 56.1056 mg / mmol.

[0057] The method for measuring the content C of functional groups is not particularly limited, and examples thereof include a method including the following steps (1) to (3). (1) Using a known method, the acrylic ester resin is extracted from the thermally conductive sheet, and the weight (unit: g) of the entire extracted acrylic ester resin is measured. (2)H 1 The amount of the functional group (unit: mmol) in the acrylic ester resin extracted in step (1) is measured using NMR or the like. (3) The amount of the functional group in the acrylate resin measured in step (2) is divided by the weight of the entire acrylate resin measured in step (1) to calculate the content of the functional group (unit: mmol / g).

[0058] Furthermore, when the weight-average molecular weights of all polymers contained in the acrylic ester-based resin, the content of the monomer having the functional group in all the constituent monomers, and the content ratio of each polymer are known, the functional group content C can also be calculated based on these.

[0059] The acrylic ester resin more preferably includes an acrylic resin having a functional group and an acrylic block copolymer. The acrylic resin having a functional group may be composed of an acrylic resin having one type of functional group, or may be a mixture of acrylic resins having two or more types of functional groups. The acrylic block copolymer may be composed of one type of acrylic block copolymer, or may be a mixture of two or more types of acrylic block copolymers.

[0060] (solvent) The mixture used in the primary sheet formation process contains a solvent. The solvent is not particularly limited, and examples include aromatic hydrocarbon solvents such as toluene and xylene; ester-based solvents such as ethyl acetate and butyl acetate; ketone-based solvents such as methyl ethyl ketone and methyl isobutyl ketone (MIBK); and cellosolve-based solvents such as butyl cellosolve, phenyl cellosolve, and dimethyl cellosolve. The amount of solvent is preferably such that the solids content of the mixture, i.e., the total concentration of the graphite particles (A), the organic polymer compound (B), and the additives described below, falls within the preferred ranges described below. A solvent amount of 10 to 40 wt % is preferred, and a solvent amount of 20 to 40 wt % is more preferred. When a primary sheet is produced at this concentration, adequate spacing is created between the graphite particles, improving particle orientation during sheet production and lamination pressing. This is preferred.

[0061] (mixture) In one embodiment of the present invention, the solids concentration of the mixture is preferably 10% by weight or more and 40% by weight or less, more preferably 10% by weight or more and 37% by weight or less, and even more preferably 15% by weight or more and 35% by weight or less, based on the total weight of the mixture. Adjusting the solids concentration of the mixture within the aforementioned preferred ranges creates an appropriate amount of space between the graphite particles, improving particle orientation during sheet production and lamination pressing, which is preferable because it further improves the thermal conductivity of the heat conductive sheet. The solids consist of the graphite particles (A), the organic polymer compound (B), and optionally the additives described below.

[0062] In one embodiment of the present invention, the lower limit of the content of the graphite particles (A) is preferably greater than 50 wt %, more preferably 50.1 wt % or more, and even more preferably 50.3 wt % or more, based on the total weight of the solid content of the mixture. A content of the graphite particles (A) greater than 50 wt % based on the total weight of the solid content of the mixture is preferred because the thermal conductive sheet exhibits improved thermal conductivity. Furthermore, the upper limit of the content of the graphite particles (A) in the mixture is preferably 65 wt % or less, more preferably 60 wt % or more, and even more preferably 55 wt % or more, based on the total weight of the solid content of the mixture. A content of the graphite particles (A) of 65 wt % or less is preferred because the flexibility and adhesion of the thermal conductive sheet can be further improved.

[0063] In one embodiment of the present invention, the content of the organic polymer compound (B) in the mixture is preferably 35% by weight or more but less than 50% by weight, more preferably 40% by weight or more but less than 49.9% by weight, and even more preferably 45% by weight or more but less than 49.7% by weight, based on the total weight of the mixture. A content of the organic polymer compound (B) of 35% by weight or more is preferable because it improves the flexibility of the thermally conductive sheet and enables good adhesion between the heat generating element and the heat dissipating element via the thermally conductive sheet. Furthermore, a higher content of the organic polymer compound (B) within the range of less than 50% by weight is preferable because it allows the graphite particles (A) to be more effectively fixed and improves adhesion to the semiconductor and / or spreader.

[0064] The mixture may contain additives such as plasticizers, flame retardants, antioxidants, heat stabilizers, colorants, antistatic agents, tackifiers, and fillers other than the graphite particles (A), as needed. The plasticizer may be, for example, polybutene or a phosphorus-based flame retardant. By incorporating polybutene and / or a phosphorus-based flame retardant into the thermally conductive sheet, the wettability with the silicone and / or spreader is improved, thereby reducing thermal resistance. The flame retardant may be, for example, a phosphorus-based flame retardant. The phosphorus-based flame retardant has the function of suppressing the combustion of the resin.

[0065] When the mixture 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 total weight of the solid content of the mixture.

[0066] Examples of the anti-aging agent include phenolic anti-aging agents and amine anti-aging agents, etc. The amount of the anti-aging agent to be added is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8 parts by weight, per 100 parts by weight of the total weight of the organic polymer compound (B).

[0067] The content of the graphite particles (A), the organic polymer compound (B), and the additives relative to the total weight of the solid content of the mixture may be the same as the content of the graphite particles (A), the organic polymer compound (B), and the additives relative to the total weight of the thermal conductive sheet.

[0068] (Method of forming primary sheet) The primary sheet forming step is preferably a step of forming a primary sheet by coating the mixture. This step is called a scraping method, in which the mixture is poured into a mold, scraped off, and dried to obtain a primary sheet. This method is preferred because it is easy to obtain a thermally conductive sheet with a carbon concentration difference on the surface. In this step, the solvent is removed.

[0069] The primary sheet forming step is preferably a step of forming a primary sheet by coating the mixture and then drying it. According to this configuration, since drying is performed separately after coating, the solvent can be further removed. Therefore, a thermal conductive sheet with minimal residual solvent can be obtained. Examples of coating methods include the scraping method described above, and examples of drying methods include air drying.

[0070] The thickness of the composition when formed into a sheet, i.e., the thickness of the primary sheet obtained in the primary sheet forming step, is preferably more than 20 times, and more preferably 20 to 100 times, the average particle diameter of the graphite particles (A). A thickness within the above range is preferred because a high-strength sheet can be obtained and the graphite is more likely to be oriented after lamination pressing. It is also preferred because a thermally conductive sheet having a carbon concentration difference on the surface can be easily obtained.

[0071] (Physical properties of primary sheet) The upper limit of the density of the primary sheet obtained in the primary sheet forming step is preferably 1.2 g / cm 3 or less, more preferably 1.0 g / cm 3 or less, and more preferably 0.5 g / cm 3 The density of the primary sheet is 1.2 g / cm or less. 3When the density of the primary sheet is a low value below this, the graphite particles (A) can be more suitably oriented during lamination by subjecting the primary sheet with a lower density to the laminate formation step described below, thereby producing a thermally conductive sheet with improved thermal conductivity. Furthermore, during lamination, the sheets are easily compressed, making it possible to remove air contained within and between the sheets, thereby producing a thermally conductive sheet with no or few holes. Furthermore, the lower limit of the density of the primary sheet is not particularly limited, and can be, for example, 0.1 g / cm. 3 The density of the primary sheet can be controlled, for example, by adjusting the mixture used and the amount of its solids content, as well as the thickness of the primary sheet.

[0072] The upper limit of the tensile strength of the primary sheet obtained in the primary sheet forming step is preferably 0.5 MPa or less, more preferably 0.4 MPa or less, and even more preferably 0.3 MPa or less. When the tensile strength of the primary sheet is a small value of 0.5 MPa or less, the sheet is easily compressed during lamination, making it possible to remove air trapped inside and between the sheets, resulting in a thermally conductive sheet with no or few holes. Furthermore, in terms of the strength of the primary sheet and the thermally conductive sheet, the lower limit of the tensile strength of the primary sheet is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, and even more preferably 0.03 MPa or more. The method for measuring the tensile strength of the primary sheet is not particularly limited, and any known method for measuring tensile strength can be used, such as the method described in the Examples.

[0073] When the degree of orientation of the graphite particles (A) in the primary sheet obtained in the primary sheet forming step is relatively low, the degree of orientation of the graphite particles (A) in the present thermal conductive sheet is also relatively low, and the orientation of the graphite particles (A) is somewhat disordered. Here, when the orientation of the graphite particles (A) in the present thermal conductive sheet is somewhat disordered, force is applied during temporary attachment and when the thermal conductive sheet is attached to an adherend, and at that time the thermal conductive sheet is more likely to conform to the adherend. As described above, when the degree of orientation of the graphite particles (A) in the primary sheet is relatively low, the present manufacturing method can manufacture a thermal conductive sheet that exhibits better temporary attachment properties and better adhesion.

[0074] On the other hand, when the degree of orientation of the graphite particles (A) in the primary sheet is relatively high, the degree of orientation of the graphite particles (A) in the present thermal conductive sheet is also relatively high, and the graphite particles (A) are preferably oriented in the thickness direction of the present thermal conductive sheet. As a result, the present thermal conductive sheet has reduced thermal resistance and exhibits superior thermal conductivity. As described above, when the degree of orientation of the graphite particles (A) in the primary sheet is relatively high, the present manufacturing method can produce a present thermal conductive sheet exhibiting superior thermal conductivity.

[0075] Furthermore, an example of an index representing the degree of in-plane orientation of the graphite particles (A) in the primary sheet is the ratio of the maximum value to the minimum value of the (002) of the graphite particles in a β profile obtained by measuring the X-ray diffraction intensity of the surface of the primary sheet using a two-dimensional X-ray diffractometer (XRD), extracting the (002) peak of the graphite particles (A) from the XRD profile, and plotting the intensity distribution in the circumferential direction. Hereinafter, the ratio of the maximum value to the minimum value of the (002) of the graphite particles in the β profile is also referred to as the "degree of in-plane orientation of the (002) of the graphite particles." The method for obtaining the XRD profile is not particularly limited and may be a method using a commercially available X-ray diffractometer, and more specifically, may be a method described in the Examples. The method for calculating the "degree of in-plane orientation of the (002) of the graphite particles" from the XRD profile may be, for example, a method described in the Examples.

[0076] From the viewpoint of being able to produce a thermally conductive sheet exhibiting the above-mentioned superior temporary adhesion and superior adhesion, the "degree of in-plane orientation of the (002) graphite particles" in the primary sheet is preferably 4.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. Furthermore, from the viewpoint of being able to produce a thermally conductive sheet exhibiting the above-mentioned superior thermal conductivity, the lower limit of the "degree of in-plane orientation of the (002) graphite particles" in the primary sheet is preferably 1.0 or more.

[0077] 1-2. Laminate formation process This manufacturing method includes a laminate formation step in which multiple primary sheets are stacked while being pressed to reduce the thickness of the primary sheets to obtain a laminate of primary sheets. Here, the primary sheets that make up the laminate have been pressed to reduce their thickness, and are thinner than the primary sheets obtained in the primary sheet formation step, and their internal structure has also changed. Hereinafter, the primary sheets that make up the laminate will also be referred to as "primary sheets after pressing" to distinguish them from the primary sheets obtained in the primary sheet formation step. Furthermore, the primary sheets obtained in the primary sheet formation step will also be referred to as "primary sheets before pressing."

[0078] In the laminate formation step, the pre-pressurized primary sheet is pressed to reduce its thickness, changing into a pressurized primary sheet. During this process, the pressure increases the degree of orientation of the graphite particles (A) in the pre-pressurized primary sheet, and the degree of orientation of the graphite particles (A) is improved in the pressurized primary sheet. Therefore, the graphite particles (A) in the pressurized primary sheet also have a high degree of orientation, and therefore the graphite particles (A) in this thermally conductive sheet also have a high degree of orientation, resulting in excellent thermal conductivity.

[0079] Furthermore, the holes (voids) in the primary sheet before pressure are closed by the pressure, reducing their size, number, or disappearing. As a result, the primary sheet after pressure has no holes, or, if holes exist, they are small in size and / or few in number. Therefore, the present thermally conductive sheet also has no holes, or, if holes exist, they are small in size and / or few in number. As a result, the present thermally conductive sheet prevents or reduces a decrease in adhesion with the adherend caused by the holes, i.e., the occurrence of areas that cannot make contact with the adherend.

[0080] From the above and the items described in the section [1. Manufacturing method of thermal conductive sheet], it can be understood that this manufacturing method can manufacture a thermal conductive sheet that has excellent thermal conductivity, temporary application properties, and adhesion properties.

[0081] (Lamination method) In the laminate formation step, the method for stacking multiple primary sheets is not particularly limited, and examples thereof include a method of stacking multiple primary sheets and a method of folding a primary sheet. When stacking the primary sheets, it is preferable to stack them so that the orientation of the graphite particles (A) in the sheet plane is aligned. The stacking may also be performed under appropriate heating. The temperature at that time is not particularly limited, and is, for example, 20°C to 200°C. The number of primary sheets stacked in the laminate formation step is not particularly limited, as long as it is multiple, i.e., two or more. The upper limit of the number of primary sheets stacked is not particularly limited and can be selected appropriately depending on the size in the planar direction of the thermal conductive sheet to be manufactured. The upper limit of the number of primary sheets stacked may be, for example, 50 or less.

[0082] In one embodiment of the present invention, it is preferred that the primary sheets are planar, and that in the laminate formation step, the planar primary sheets are laminated in the normal direction of the plane to obtain the laminate.

[0083] (Pressure method) In one embodiment of the present invention, the mode of pressurization in the laminate formation step is not particularly limited, and may be a single pressurization or multiple pressurizations. More specifically, pressurization may be applied after each pre-pressurized primary sheet is laminated, after each multiple sheets are laminated, or after all pre-pressurized primary sheets are laminated, or a combination of these. A preferred example is a method in which pressurization is applied after each single or multiple pre-pressurized primary sheet is laminated, and after all primary sheets are laminated.

[0084] The pressurizing method in the laminate formation step is not particularly limited as long as it is a method that can apply pressure so as to reduce the thickness of the primary sheet before pressing, and any known pressurizing method can be used, for example, the method described in the examples can be used.

[0085] In one embodiment of the present invention, in the laminate formation step, the primary sheet is pressed so that its thickness is preferably 95% or less, more preferably 70% or less, and even more preferably 50% or less, of the thickness of the primary sheet before pressing, taken as 100%. The above means that in the laminate formation step, the primary sheet is pressed so that its thickness after pressing is equal to or less than the aforementioned preferred upper limit. By pressing the primary sheet so that its thickness after pressing is equal to or less than the aforementioned preferred upper limit, the degree of orientation of the graphite particles (A) in the primary sheet after pressing and in the present thermal conductive sheet is suitably improved, and as a result, the present production method can produce a present thermal conductive sheet with superior thermal conductivity.

[0086] On the other hand, if the thickness of the primary sheet after pressing is excessively thinned in the laminate formation process, the graphite particles (A) in the primary sheet before pressing may be partially damaged by the pressurization, resulting in a decrease in their particle diameter. In this case, the thermal conductivity of the thermal conductive sheet may be reduced due to the reduction in the particle diameter of the graphite particles (A). Therefore, from the viewpoint of preventing or reducing the degree of reduction in the thermal conductivity of the thermal conductive sheet due to the reduction in the particle diameter of the graphite particles (A), it is preferable to apply the pressurization so as to maintain the thickness of the primary sheet after pressing at a predetermined value or more. From the above viewpoint, specifically, in the laminate formation process, the primary sheet is pressed so that its thickness is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more, based on the thickness of the primary sheet before pressing (defined as 100%). The above means that in the laminate formation process, the primary sheet is pressed so that its thickness after pressing is equal to or greater than the above-mentioned preferable lower limit.

[0087] In one embodiment of the present invention, the lower limit of the pressure applied when pressing the primary sheet in the laminate forming step is preferably 1 kg / cm 2 More preferably, it is 5 kg / cm or more. 2 More preferably, it is 10 kg / cm 2 When the pressure is equal to or greater than the aforementioned preferable lower limit, the thickness of the primary sheet after pressing can be suitably controlled to a range equal to or less than the aforementioned preferable upper limit, and as a result, the present manufacturing method can produce a thermally conductive sheet with superior thermal conductivity.

[0088] In one embodiment of the present invention, the upper limit of the pressure applied when pressing the primary sheet in the laminate forming step is preferably 100 kg / cm 2 More preferably, it is 70 kg / cm or less. 2 More preferably, it is 50 kg / cm or less. 2When the pressure is equal to or less than the above-mentioned preferable upper limit, the thickness of the primary sheet after pressing can be suitably controlled to a range equal to or greater than the above-mentioned preferable lower limit, and as a result, a decrease in the thermal conductivity of the thermally conductive sheet due to a decrease in the particle size of the graphite particles (A) can be suitably prevented.

[0089] When the pressing is carried out in a plurality of steps, it is preferable that the pressure applied to the primary sheet after pressing and / or during pressing in each step is within the above-mentioned preferred range.

[0090] [1-3. Slicing process] The present manufacturing method includes a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet.

[0091] The angle at which the cross section of the primary sheet laminate is sliced ​​in the slicing step is not particularly limited. The angle is preferably 45° or less, more preferably 0 to 30°, and even more preferably 0 to 15°, relative to the lamination direction of the cross section of the primary sheet laminate. By slicing at an angle of 45° or less relative to the lamination direction in the slicing step, a thermally conductive sheet with excellent thermal conductivity can be obtained.

[0092] The method for slicing the laminate of primary sheets is not particularly limited, and examples thereof include a multi-blade method, a laser processing method, a water jet method, and a knife processing method.

[0093] In one embodiment of the present invention, the slicing step slices the cross-section of the laminate so that the thickness of the resulting thermally conductive sheet is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 110 μm or less. By slicing the cross-section of the laminate so that the thickness of the resulting thermally conductive sheet is 150 μm or less, the thermal resistance of the thermally conductive sheet can be further reduced, resulting in a thermally conductive sheet with superior thermal conductivity. In another embodiment of the present invention, the slicing step slices the cross-section of the laminate so that the thickness of the resulting thermally conductive sheet is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more. By slicing the cross-section of the laminate so that the thickness of the resulting thermally conductive sheet is 30 μm or more, the thermally conductive sheet can be produced with superior temporary attachment properties and superior adhesion. The thickness of the thermally conductive sheet obtained in the slicing step refers to the thickness of the actual thermally conductive sheet.

[0094] [1-4. Physical properties of this thermal conductive sheet] In one embodiment of the present invention, unlike conventional manufacturing methods, the graphite particles (A) contained in this thermal conductive sheet are not partially damaged or only slightly damaged during each step of this manufacturing method. Therefore, a decrease in the average particle size of the graphite particles (A) due to the damage is also suitably prevented or the degree of the decrease is reduced. As a result, a decrease in the thermal conductivity of the thermal conductive sheet due to a decrease in the average particle size during the manufacturing process of the thermal conductive sheet is suitably prevented or the degree of the decrease in thermal conductivity is suitably reduced, thereby enabling the manufacture of a thermal conductive sheet with suitably improved thermal conductivity.

[0095] In view of the above, in one embodiment of the present invention, the average particle size of the graphite particles (A) eluted from the thermally conductive sheet using an eluent is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more of the thickness of the thermally conductive sheet. The eluent can be any eluent selected from those that dissolve the organic polymer compound (B) and, if the thermally conductive sheet contains additives, the additives, but do not dissolve the graphite particles (A). The eluent is not particularly limited and may be, for example, methyl ethyl ketone. The average particle size, like the average particle size of the graphite particles (A) used in the primary sheet formation step, is a value determined using a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.).

[0096] In one embodiment of the present invention, in an XRD profile obtained by measuring the X-ray diffraction intensity of the surface of the thermally conductive sheet using a two-dimensional X-ray diffractometer (XRD), the half-width of the peak representing the (002) plane of the graphite particles (A) is preferably 45° to 63°, more preferably 46° to 62°, and even more preferably 47° to 61°. When the half-width of the peak is within the above-mentioned preferred range, the thermally conductive sheet has lower thermal resistance, i.e., better thermal conductivity, better temporary application properties, and better adhesion properties. The method for measuring the half-width of the peak is not particularly limited, and for example, the method described in the examples can be adopted.

[0097] <Summary> An embodiment of the present invention includes the following configuration. [1] a primary sheet forming step of forming a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet; a laminate forming step of stacking a plurality of the primary sheets while applying pressure to the primary sheets so as to reduce their thickness, thereby obtaining a laminate of the primary sheets; a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet. [2] A method for manufacturing a thermal conductive sheet according to [1], wherein in the laminate formation process, the primary sheet is pressed so that its thickness is 95% or less, assuming that the thickness of the primary sheet before pressing is 100%. [3] The density of the primary sheet obtained in the primary sheet forming step is 1.2 g / cm 3 A method for producing a thermal conductive sheet according to [1] or [2], which is as follows: [4] The method for producing a thermal conductive sheet according to any one of [1] to [3], wherein the thickness of the primary sheet obtained in the primary sheet forming step is more than 20 times the average particle diameter of the graphite particles (A). [5] The method for producing a thermally conductive sheet according to any one of [1] to [4], wherein the primary sheets are planar, and in the laminate formation step, the planar primary sheets are laminated in the direction normal to the plane to obtain a laminate. [6] The method for producing a thermal conductive sheet according to any one of [1] to [5], wherein the solid content of the mixture is 10% by weight or more and 40% by weight or less, based on the total weight of the mixture. [7] In the laminate forming step, the pressure applied when pressing the primary sheet is 1 kg / cm 2 The method for producing a thermally conductive sheet according to any one of [1] to [6] above. [8] The method for producing a thermal conductive sheet according to any one of [1] to [7], wherein the mixture contains more than 50% by weight of the graphite particles (A) based on the total weight of the solid content of the mixture. [9] The method for producing a thermally conductive sheet according to any one of [1] to [8], wherein the average minor axis or minimum length of the graphite particles (A) is 5 μm or less.

[10] The method for producing a thermally conductive sheet according to any one of [1] to [9], wherein the average particle size of the graphite particles (A) is 50% or more of the thickness of the thermally conductive sheet.

[11] The method for producing a thermally conductive sheet according to any one of [1] to

[10] , wherein the graphite particles (A) have an aspect ratio of 10 or more.

[12] The method for producing a thermally conductive sheet according to any one of [1] to

[11] , wherein the primary sheet obtained in the primary sheet forming step has a tensile strength of 0.5 MPa or less.

[13] The method for producing a thermal conductive sheet according to any one of [1] to

[12] , wherein the X-ray diffraction intensity of the surface of the primary sheet obtained in the primary sheet forming step is measured using a two-dimensional X-ray diffractometer (XRD), the (002) peak of the graphite particles (A) is extracted from the XRD profile obtained, and the intensity distribution in the circumferential direction is plotted, and the ratio of the maximum value to the minimum value of (002) of the graphite particles in the β profile is 4.0 or less.

[14] The method for producing a thermally conductive sheet according to any one of [1] to

[13] , wherein in the slicing step, the cross section of the laminate is sliced ​​so that the thickness of the resulting thermally conductive sheet is 150 μm or less.

[15] The method for producing a thermal conductive sheet according to any one of [1] to

[14] , wherein in an XRD profile obtained by measuring the X-ray diffraction intensity of the surface of the thermal conductive sheet using a two-dimensional X-ray diffractometer (XRD), the half-value width of the peak representing the (002) plane of the graphite particles (A) is 45° to 63°. [Example]

[0098] 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.

[0099] [Evaluation method] The evaluation methods used in the examples and comparative examples will be explained below.

[0100] <Thickness> The primary sheet or thermally conductive sheet before pressure application was cut into a 3 cm x 3 cm square to be used as an evaluation sample. The thickness of the evaluation sample was measured at four corner points and one central point using a micrometer manufactured by Mitutoyo Corporation, and the average of the obtained measurements was used as the thickness of the primary sheet or thermally conductive sheet before pressure application. Here, the "central point" refers to the position where two diagonal lines intersect when a diagonal line is drawn from the four corner points to the measurement point located diagonally opposite the corner point.

[0101] The thickness of the primary sheet stack was measured using the same method as for the thickness of the primary sheet or thermally conductive sheet. The thickness of the stack was then divided by the number of primary sheets constituting the stack to calculate the thickness of the primary sheets constituting the stack, i.e., the thickness of the primary sheets after pressurization. The ratio of the thickness of the primary sheets after pressurization to the thickness of the primary sheets before pressurization, which was taken as 100%, was then calculated.

[0102] <Density of primary sheet before pressing> The density of the primary sheet before pressing was calculated by dividing the weight of the primary sheet before pressing by the volume. The product of the thickness and area of ​​the primary sheet before pressing was calculated, and the calculated value was used as the volume of the primary sheet before pressing.

[0103] <Tensile strength of primary sheet before pressure> The primary sheet before pressure was punched out using a No. 2 dumbbell in accordance with JIS K6251 to prepare test pieces. Using a tensile tester (Instron, Model 5565, small universal testing machine), the test piece was pinched at 1 cm from both ends and pulled at a temperature of 23°C in a direction perpendicular to the normal line extending from the surface of the test piece at a pulling rate of 500 mm / min to measure the breaking strength (tensile strength). The breaking strength (tensile strength) was measured in two directions, the scraping direction and the direction perpendicular to the scraping direction, during the preparation of the primary sheet, and the average value was taken as the tensile strength of the primary sheet before pressure.

[0104] <(002) In-plane Orientation of Graphite Particles in the Primary Sheet Before Pressing> Using a two-dimensional X-ray diffractometer (XRD) (Nano-Viewer small-angle scattering measurement device manufactured by Rigaku Corporation) with respect to the surface of the primary sheet before pressurization, the X-ray diffraction intensity was measured under the conditions shown in the following <XRD measurement conditions> to obtain an XRD profile. The peak of (002) of the graphite particles (A) (2θ = 26 to 29°) was extracted, and the intensity distribution in the circumferential direction was plotted to obtain a β profile. Among the β profiles, the in-plane orientation degree of (002) of the graphite particles (A) was calculated by dividing the maximum value by the minimum value. The XRD profile obtained for the primary sheet before pressurization described in Example 1 is shown in FIG. 1. <XRD Measurement Conditions> Tube target: CuKα ray, output: 40 kV - 30 mA, Slit: 1st slit: 0.2 mm, 2nd slit: 0.1 mm, 3rd slit: 0.25 mm, Measurement method: Transmission method, Detector: PILATUS - 100K, Exposure time: 30 minutes (10 minutes × 3 times), Camera length: 67 mm.

[0105] <Average Particle Diameter of Graphite Particles (A)> The average particle diameter of the graphite particles (A) before use, which were used in Examples and Comparative Examples, was measured using a laser diffraction / scattering particle size distribution measuring device (LA - 920 manufactured by Horiba, Ltd.).

[0106] Also, from the heat conduction sheet, using methyl ethyl ketone as an eluent, the graphite particles (A) contained in the heat conduction sheet were eluted. The average particle diameter of the eluted graphite particles (A) was measured using a laser diffraction / scattering particle size distribution measuring device (LA - 920 manufactured by Horiba, Ltd.). The measured average particle diameter of the eluted graphite particles (A) was defined as the "average particle diameter of the graphite particles (A) eluted from the heat conduction sheet".

[0107] <Presence or Absence of Holes> Light was applied from the back surface of the heat conduction sheet, and it was visually confirmed whether there were holes in the heat conduction sheet.

[0108] <Presence or absence of parts with different carbon contents> As the SEM, an ultra-high resolution scanning electron microscope (ULTRAplus manufactured by Carl Zeiss) was used, and as the energy dispersive X-ray analyzer (EDX), QUANTAX XFlash 5010 manufactured by Bruker AXS attached to the SEM was used to observe and map the surface of the heat conduction sheet. From the obtained images, specifically, the SEM image and the image showing the result of carbon identification, the distribution of the atomic number concentration of carbon atoms was observed to confirm whether there are parts with different carbon contents. The observation conditions by SEM and the analysis conditions by EDX were as follows. The SEM image of the surface obtained by observing and mapping the surface of the heat conduction sheet obtained in Example 1 using the SEM attached with the EDX, that is, SEM-EDX, is shown in Fig. 2, and the image showing the result of carbon identification is shown in Fig. 3.

[0109] <Observation conditions by SEM> Acceleration voltage: 5 kV Detector: SE2 (chamber type secondary electron detector) <Analysis conditions by EDX> Acceleration voltage: 10 kV (element mapping at low magnification), 5 kV (element mapping and area analysis at high magnification) Analysis method: ZAF method.

[0110] <Carbon atomic number concentration and oxygen atomic number concentration> The surfaces of the heat conduction sheet and the comparative heat conduction sheet according to an embodiment of the present invention were subjected to elemental mapping to confirm the in-plane distribution of elements. Next, area analysis and semi-quantification by the ZAF method were performed on the heat conduction sheet according to an embodiment of the present invention. As the object of area analysis, as shown in FIG. 4, in the image observed by SEM, a 500 μm × 50 μm area (area 1) including a region that appears darker than the surroundings and a 500 μm × 50 μm area (area 2) not including a region that appears darker than the surroundings were set. By the ZAF method, the atomic number concentration of carbon and the atomic number concentration of oxygen in area 1 and area 2 were determined. Thereafter, "atomic number concentration of carbon atoms in area 2 (a2) (atom%) - atomic number concentration of carbon atoms in area 1 (a1) (atom%)" was calculated.

[0111] <Half-value width of the peak representing the (002) plane of the graphite particles (A)> Using a two-dimensional X-ray diffractometer (XRD) (Nano-Viewer small-angle scattering measurement device manufactured by Rigaku Corporation) for the surface of the heat conduction sheet, the X-ray diffraction intensity was measured under the conditions shown in the following <XRD measurement conditions> to obtain an XRD profile. The peak located in the range of 2θ = 24° to 29° in the obtained XRD profile was regarded as the peak representing the (002) plane of the graphite particles (A), and its half-value width was measured. <XRD measurement conditions> Tube target: CuKα ray, Output: 40 kV - 30 mA, Slit: 1st slit: 0.4 mm, 2nd slit: 0.2 mm, 3rd slit: 0.45 mm, Measurement method: Transmission method, Detector: HyPix-3000, Exposure time: 15 minutes, Camera length: 62 mm, Probe diameter: Approximately 1 mmφ.

[0112] <Thermal resistance value> The heat conduction sheet was cut out into a 1 cm × 1 cm square to obtain an evaluation sample. For the evaluation sample, the thermal resistance value of the heat conduction sheet (cm 2The thermal resistance (K / W) was measured at a sample temperature of 50°C and a pressure of 0.5 MPa using a thermal resistance measuring device (Hitachi Technology and Services, Ltd., Resin Material Thermal Resistance Measuring Device).

[0113] The thermal resistance of the thermal conductive sheet was evaluated according to the following criteria: A (Excellent): The thermal resistance of the thermal conductive sheet is 0.080cm 2 If it is less than K / W. B (Good): The thermal resistance of the thermal conductive sheet is 0.080 cm 2 K / W super, 0.10cm 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.

[0114] <Temporary adhesion> The temporary adhesion of the thermal conductive sheet is evaluated by peeling off a 40 x 40 mm thermal conductive sheet from the separator and attaching it to a 50 x 50 mm silicon wafer. Excellent temporary adhesion means the following: The thermal conductive sheet can be easily peeled off from the separator and fixed onto the silicon wafer with precision. The thermal conductive sheet will not come off even when the silicon wafer is transported or turned upside down, and any air trapped between the silicon wafer and the thermal conductive sheet can be easily released.

[0115] The evaluation criteria are as follows: A: (Excellent) Easy to peel off from the separator, easy to stick to the silicon wafer, and less likely to trap air. B: (Good) Easy to peel off from the separator, easy to stick to the silicon wafer (slightly light), and does not trap air. C: (Poor) It is difficult to peel off from the separator and sticks too much to the silicon wafer, causing air to get trapped. Or it peels off too much from the separator and does not stick to the silicon wafer.

[0116] <Initial adhesion> Silicon (50 x 50 x 0.7 mm), thermally conductive sheet (40 x 40 x 0.11 mm), and spreader (nickel-plated copper: 50 x 50 x 2 mm) were stacked in this order and placed in a heat press. The heat press then bonded the silicon, thermally conductive sheet, and spreader together in this order at 150°C and 100 kg. This resulted in a laminate for adhesion measurement. An ultrasonic imaging device (Hitachi Power Solutions, product name: FineSAT) was then used to measure the contact area between the thermally conductive sheet and the adherend (silicon and spreader) in the laminate for adhesion measurement.

[0117] 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.

[0118] <Adhesion after high temperature exposure> A laminate for adhesion measurement was obtained using the same method as described in the <Initial Adhesion> section above. The laminate for adhesion measurement was then placed in an oven, and the atmosphere inside the heating furnace was heated to 150°C and maintained at this temperature for 100 hours. The laminate for adhesion measurement was then removed from the heating furnace, and the adhesion area between the thermally conductive sheet and the adherend (silicon and spreader) in the laminate for adhesion measurement was measured. Based on the adhesion area, adhesion after high-temperature maintenance was evaluated using the same criteria as those for evaluating initial adhesion described in the <Initial Adhesion> section above.

[0119] <Adhesion after heat cycle> Except for the following points, the adhesion after the heat cycle was evaluated by the same method as that described in the above section <Adhesion after high temperature retention>. The adhesion after the heat cycle was evaluated according to the same criteria as those for the initial adhesion described in the above section <Initial adhesion>. The laminate for adhesion measurement was placed in a heat shock tester (manufacturer: Hitachi Appliances, Inc., product name: ES-56L). The ambient temperature inside the heat cycle tester was then raised to 120°C, then lowered to -40°C, and then raised again to 120°C, and this heat cycle was repeated 500 times.

[0120] [Example 1] <Preparation of composition solution> The materials shown below were mixed and stirred for 10 minutes using a planetary centrifugal mixer to obtain a composition solution. The solids concentration of the composition solution was 30.0 wt %. The composition solution corresponds to the "mixture containing graphite particles (A), an organic polymer compound (B), and a solvent" in this production method. As graphite particles (A), 115.42 g (50.5 parts by weight) of flake graphite powder (average particle size: 73 μm, thickness: 0.80 μm, aspect ratio: 91, sulfur content: 1.0 wt % or less); 388.54 g of a 15 wt % toluene / ethyl acetate solution of an acrylic resin (weight average molecular weight: 900,000, Tg: -60°C, content of hydroxyl groups as functional groups: 0.116 mmol / g, 6.5 KOH mg / g, liquid at room temperature) as an acrylic resin having functional groups (58.28 g (25.5 parts by weight) as the acrylic resin having functional groups); As the acrylic block copolymer, 129.49 g of a 15 wt % toluene / ethyl acetate solution of an acrylic block copolymer (weight average molecular weight: 56,000, Tg: hard segment 100 to 120°C, soft segment -50 to -40°C, no functional groups, liquid at room temperature): (19.42 g (8.5 parts by weight) of the acrylic block copolymer without functional groups); · 22.86 g of tackifier (hydrogenated petroleum resin: softening point 90°C); · 11.43 g of plasticizer (polybutene: weight average molecular weight 3700); · Antiaging agent (amine-based antiaging agent: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine) 1.14 g; Toluene: Toluene was used in an amount such that the solid content concentration of the composition solution was 30.0% by weight.

[0121] <Preparation of primary sheet> The obtained composition solution was spread on a polyethylene terephthalate film whose surface had been treated with a release agent in a 2 mm thick mold, and any portion thicker than 2 mm was scraped off. The film was then dried at 120°C for 20 minutes or more, and the dried sheet was peeled off to obtain a 2 mm thick primary sheet. This procedure was repeated three times to produce three primary sheets. These primary sheets correspond to the primary sheets before pressure application.

[0122] The contents of the graphite particles, the acrylic ester resin, and the antioxidant relative to the total weight of the composition contained in the primary sheet correspond to the contents of the composition contained in the final thermal conductive sheet, i.e., relative to the total weight of the final thermal conductive sheet.

[0123] <Preparation of laminate> The three obtained primary sheets were each cut into a size of 2.4 cm x 6.4 cm, and placed in a container with an internal volume of 2.5 cm x 6.5 cm x 7.5 cm height. Each time a sheet was stacked, it was pressed at room temperature at a pressure of 2.5 MPa, and the stacking and pressing were repeated. Next, the stacked product was heated at 120°C for 15 minutes, and then pressed at 2.5 MPa (25.5 kg / cm). 2 ) to obtain a laminate of 2.5 cm × 6.5 cm × 6.5 cm. The pressing was carried out so that the thickness of the primary sheets constituting the laminate after pressing was 0.5 mm, i.e., 25% of the thickness of the primary sheets before pressing, which was taken as 100%.

[0124] <Making a thermal conductive sheet> The cross section of the resulting laminate was sliced ​​at an angle of 45 degrees to the lamination direction to produce a thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick.

[0125] [Example 2] When producing the laminate, the same operation as in Example 1 was carried out except that instead of pressing every time one primary sheet was laminated, pressing was carried out every five primary sheets, and a thermally conductive sheet measuring 6.5 cm in length, 6.5 cm in width, and 110 μm in thickness was produced. Note that in Example 2 as well, pressing when producing the laminate was carried out so that the thickness of the primary sheets after pressing was 0.5 mm, that is, 25% of the thickness of the primary sheets before pressing, which is taken as 100%.

[0126] [Example 3] The same operations as in Example 1 were carried out to produce a thermally conductive sheet measuring 6.5 cm in length, 6.5 cm in width, and 110 μm in thickness, except that when producing the laminate, instead of pressing every time one primary sheet was laminated, pressing was carried out every 10 primary sheets. Note that in Example 3 as well, pressing was carried out to produce a laminate such that the thickness of the primary sheets after pressing was 0.5 mm, that is, 25% of the thickness of the primary sheets before pressing, which is taken as 100%.

[0127] [Example 4] The same operations as in Example 1 were carried out to produce a thermally conductive sheet measuring 6.5 cm in length, 6.5 cm in width, and 110 μm in thickness, except that in the production of the primary sheet, a mold was provided so that the coating thickness would be 3 mm instead of 2 mm. In Example 3, the primary sheet was 3 mm thick before pressurization. The press used to produce the laminate was applied so that the thickness of the primary sheet after pressurization would be 0.75 mm, that is, 25% of the thickness of the primary sheet before pressurization, which was taken as 100%.

[0128] [Example 5] A thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick was produced by the same procedures as in Example 1, except that (i) the amount of toluene used in preparing the composition solution was changed to an amount such that the solids concentration of the composition solution would be 20.0 wt %, (ii) when creating the laminate, instead of pressing each primary sheet, pressing was performed every five primary sheets, and (iii) the pressing method was changed so that the thickness of the primary sheet after pressing was 0.33 mm, that is, 17% of the thickness of the primary sheet before pressing, which was 100%.

[0129] [Comparative Example 1] <Preparation of Composition> A composition was obtained by melt-kneading, under heating, 120 g of flake-shaped expanded graphite powder (average particle size: 250 μm, thickness: 5 μm, aspect ratio: 50, sulfur content: 1.5 wt % or more) as graphite particles (A), 54 g of an acrylic ester resin (weight-average molecular weight: 1.2 million, Tg: -37°C, containing OH groups as functional groups) as organic polymer compound (B), and 66 g of an aromatic condensed phosphate ester (CR-741, manufactured by Daihachi Chemical Industry Co., Ltd.).

[0130] <Preparation of primary sheet> A portion of the resulting composition (240 g) was taken, rolled into a block, sandwiched between PTFE films, and pressed using a press with a 10 cm x 20 cm tool surface at a tool temperature of 170°C to obtain a primary sheet with a thickness of 2 mm. This operation was repeated to produce 12 primary sheets. These primary sheets correspond to the primary sheets before pressing.

[0131] <Preparation of laminate> All of the obtained primary sheets were cut into pieces of 2.4 cm x 6.4 cm, and stacked in a container with an internal volume of 2.5 cm x 6.5 cm x 7.5 cm (height) to obtain a pre-pressurized laminate. The obtained pre-pressurized laminate was heated at 120°C for 15 minutes and then subjected to a pressure of 2.5 MPa (25.5 kg / cm). 2) to obtain a laminate of 2.5 cm × 6.5 cm × 6.5 cm. The pressing was performed so that the thickness of the primary sheets constituting the laminate after pressing was 2.00 mm, that is, 100% of the thickness of the primary sheets before pressing.

[0132] <Preparation of comparative thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at an angle of 45 degrees to the lamination direction to produce a comparative thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick.

[0133] [Evaluation of thermal conductive sheets] The physical properties of the thermally conductive sheets obtained in Examples 1 to 5 and the comparative thermally conductive sheet obtained in Comparative Example 1 were measured using the evaluation methods described above, and the results are shown in Table 1. The "compressibility" in Table 1 refers to the aforementioned "proportion of the thickness of the primary sheet after pressing, assuming that the thickness of the primary sheet before pressing is 100%." ​​The "number of stacked sheets before pressing" in Table 1 indicates how many primary sheets before pressing were stacked together during laminate formation, and "all at once" in Comparative Example 1 means that one pressing was performed after all the primary sheets before pressing were stacked. The "half-width" in Table 1 refers to the aforementioned "half-width of the peak representing the (002) plane of the graphite particles (A)." The "(a2)-(a1)" in Table 1 refers to the aforementioned "atomic concentration of carbon atoms in area 2 (a2) (atom%) - atomic concentration of carbon atoms in area 1 (a1) (atom%)." The "average particle size of graphite particles (A)" in Table 1 means the "average particle size of graphite particles (A) eluted from the thermally conductive sheet" described above.

[0134] [Table 1]

[0135] From the descriptions of Examples 1 to 5 and Table 1, it can be seen that the manufacturing methods of the thermally conductive sheets in Examples 1 to 5 included the following steps. A primary sheet forming step in which a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent is formed into a sheet to obtain a primary sheet. A laminate forming step in which a plurality of the primary sheets are laminated while being pressed so as to reduce the thickness of the primary sheets, thereby obtaining 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.

[0136] Therefore, the manufacturing methods of the thermally conductive sheets in Examples 1 to 5 correspond to the present manufacturing method.

[0137] On the other hand, Comparative Example 1 does not use a solvent and therefore does not correspond to the present production method.

[0138] As shown in Table 1, the thermally conductive sheets described in Examples 1 to 5 have lower thermal resistance and better thermal conductivity than the comparative thermally conductive sheet described in Comparative Example 1, and also have better temporary application properties, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling, resulting in better adhesion.

[0139] Therefore, it was found that this manufacturing method can produce a thermally conductive sheet that is excellent in thermal conductivity, temporary attachment property, and adhesiveness.

[0140] In addition, from the descriptions in FIGS. 1 to 4, it was found that the primary sheet described in Example 1 had no in-plane orientation. [Industrial Applicability]

[0141] The method for manufacturing a thermally conductive sheet according to one embodiment of the present invention can produce a thermally conductive sheet that has both excellent thermal conductivity and adhesion. Therefore, the method for manufacturing a thermally conductive sheet according to one embodiment of the present invention can be preferably used to manufacture products that utilize a thermally conductive sheet and require the thermally conductive sheet to have excellent thermal conductivity and adhesion. Examples of such products include electronic components that include wiring boards and semiconductor packages.

Claims

1. a primary sheet forming step of forming a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent into a sheet to obtain a primary sheet; a laminate forming step of stacking a plurality of the primary sheets while applying pressure to the primary sheets so as to reduce their thickness, thereby obtaining a laminate of the primary sheets; a slicing step of slicing the cross section of the laminate of the primary sheets to obtain a thermally conductive sheet.

2. The method for manufacturing a thermal conductive sheet according to claim 1, wherein in the laminate formation process, the primary sheet is pressed so that its thickness is 95% or less, assuming that the thickness of the primary sheet before pressing is 100%.

3. The density of the primary sheet obtained in the primary sheet forming step is 1.2 g / cm ３ The method for producing a thermal conductive sheet according to claim 1 or 2, wherein:

4. 3. The method for producing a thermal conductive sheet according to claim 1, wherein the thickness of the primary sheet obtained in the primary sheet forming step is more than 20 times the average particle diameter of the graphite particles (A).

5. The method for producing a thermally conductive sheet according to claim 1 or 2, wherein the primary sheets are planar, and in the laminate formation step, the planar primary sheets are laminated in a direction normal to the plane to obtain the laminate.

6. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the solid content of the mixture is 10% by weight or more and 40% by weight or less, based on the total weight of the mixture.

7. In the laminate forming step, the pressure applied when pressing the primary sheet is 1 kg / cm ２ The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the method is as described above.

8. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the mixture contains more than 50% by weight of the graphite particles (A) based on the total weight of the solid content of the mixture.

9. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the graphite particles (A) have an average minor axis or minimum length of 5 μm or less.

10. 3. The method for producing a thermal conductive sheet according to claim 1, wherein the average particle size of the graphite particles (A) is 50% or more of the thickness of the thermal conductive sheet.

11. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the graphite particles (A) have an aspect ratio of 10 or more.

12. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the primary sheet obtained in the primary sheet forming step has a tensile strength of 0.5 MPa or less.

13. 3. The method for producing a thermal conductive sheet according to claim 1 or 2, wherein the X-ray diffraction intensity of the surface of the primary sheet obtained in the primary sheet forming step is measured using a two-dimensional X-ray diffractometer (XRD), the (002) peak of the graphite particles (A) is extracted from the XRD profile obtained, and the intensity distribution in the circumferential direction is plotted, and the ratio of the maximum value to the minimum value of (002) of the graphite particles in the β profile is obtained is 4.0 or less.

14. The method for producing a thermally conductive sheet according to claim 1 or 2, wherein in the slicing step, the cross section of the laminate is sliced ​​so that the thickness of the resulting thermally conductive sheet is 150 μm or less.

15. 3. The method for producing a thermal conductive sheet according to claim 1, wherein the half width of a peak representing the (002) plane of the graphite particles (A) in an XRD profile obtained by measuring the X-ray diffraction intensity of the surface of the thermal conductive sheet using a two-dimensional X-ray diffractometer (XRD) is 45 ° to 63 °.

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