Thermally conductive sheet and method for producing same

Abstract

To provide a thermally conductive sheet having a low thermal resistance value, excellent tackiness, initial adhesiveness, adhesiveness after being held at a high temperature, and adhesiveness after a heat cycle.SOLUTION: A first region of 500 μm * 50 μm and a second region of 500 μm * 50 μ m, wherein an atomic concentration (a2) of a carbon atom contained in the second region is higher than an atomic concentration (a1) of a carbon atom contained in the first region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Known thermally conductive sheets that have thermal conductivity and adhesion to an adherend include thermally conductive sheets that contain a composition containing graphite particles oriented in the thickness direction of the thermally conductive sheet and an organic polymer compound (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2008 / 053843 Brochure [Patent Document 2] Patent Publication No. 2017-141443 Summary of the Invention [Problem to be solved by the invention]

[0005] The thermally conductive sheets described in Patent Documents 1 and 2 have a certain level of thermal conductivity and adhesion. Meanwhile, in recent years, high-performance CPUs and GPUs have been used in, for example, servers, supercomputers, and automotive ECUs (electronic control units). As the amount of information processed increases and processing speeds improve, chip temperatures tend to rise. Because chip temperature increases can cause a decrease in performance of CPUs, GPUs, and other devices, more efficient heat dissipation is required, even in high-temperature environments. To accommodate such applications, thermally conductive sheets with even lower thermal resistance than conventional ones are required. Furthermore, to enhance adhesion to the adherend, thermally conductive sheets must be resistant to peeling when temporarily attached to the adherend. Furthermore, thermally conductive sheets may be maintained in a high-temperature environment or in a state where they are repeatedly subjected to low and high temperatures while attached to the adherend. Therefore, in addition to initial adhesion to the adherend, the thermally conductive sheets must also have excellent adhesion after high-temperature exposure and after heat cycles.

[0006] Therefore, one aspect of the present invention aims to provide a thermally conductive sheet having low thermal resistance, excellent tackiness, initial adhesion, adhesion after being held at high temperatures, and adhesion after heat cycling. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a thermally conductive sheet according to one embodiment of the present invention is a thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and when a first region of 500 μm×50 μm and a second region of 500 μm×50 μm are defined on the surface, at least one pair of the first region and the second region satisfies the relationship that the following (a2) is higher than the following (a1): (a1) the atomic concentration of carbon atoms contained in the first region (a2) The atomic concentration of carbon atoms contained in the second region.

[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 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 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. [Effects of the Invention]

[0009] According to one aspect of the present invention, a thermally conductive sheet having low thermal resistance, excellent tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycles can be provided, and therefore the thermally conductive sheet can be preferably used in applications requiring efficient heat dissipation. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows the results of mapping the surface of the thermally conductive sheet obtained in Example 1 by SEM-EDX, where 1001 indicates the results of identifying carbon, and 1002 is an SEM image of the surface. [Figure 2] FIG. 2 is an enlarged view of 1002 in FIG. 1, showing a state in which a 500 μm×50 μm area (area 1) and a 500 μm×50 μm area (area 2) are set on the surface. [Figure 3] 10 shows the results of mapping the surface of the thermally conductive sheet obtained in Example 3 by SEM-EDX, where 1003 indicates the results of identifying carbon, and 1004 is an SEM image of the surface. [Figure 4] FIG. 10 is a diagram showing a state in which a 500 μm×50 μm area (area 1) and a 500 μm×50 μm area (area 2) are set on the surface of the thermally conductive sheet obtained in Example 3. [Figure 5] 10 is a diagram showing the results of mapping the surface of the thermal conductive sheet according to Comparative Example 1 by SEM-EDX, where 1005 shows the results of identifying carbon, and 1006 is an SEM image of the surface. [Figure 6] 5, showing a state in which areas 1 and 2 are set at positions that roughly correspond to areas 1 and 2 shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0012] [1. Thermal Conduction Sheet] A thermally conductive sheet according to one embodiment of the present invention is a thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and when a first region of 500 μm×50 μm and a second region of 500 μm×50 μm are defined on the surface, at least one pair of the first region and the second region satisfies the relationship that the following (a2) is higher than the following (a1): (a1) the atomic concentration of carbon atoms contained in the first region (a2) The atomic concentration of carbon atoms contained in the second region.

[0013] The present inventors defined a first region and a second region, each measuring 500 μm × 50 μm, on the surface of a thermally conductive sheet and performed elemental analysis using an energy dispersive X-ray analyzer (SEM-EDX) attached to a scanning electron microscope (SEM). The results showed that the surface of a thermally conductive sheet according to one embodiment of the present invention (hereinafter also referred to as the thermally conductive sheet of the present invention) contained a first region with a low atomic concentration of carbon atoms and a second region with a higher atomic concentration of carbon atoms than the first region. In contrast, in conventionally known thermally conductive sheets, no bias was observed in the atomic concentration of carbon atoms between the first and second regions, regardless of how the first and second regions were defined. The present inventors then discovered that the thermally conductive sheet of the present invention has lower thermal resistance, superior tackiness, initial adhesion, adhesion after high-temperature exposure, and adhesion after heat cycling than conventionally known thermally conductive sheets, leading to the completion of the present invention.

[0014] The first and second regions can be determined by observing the surface of the thermally conductive sheet of the present invention using, for example, an SEM. The region with a higher atomic concentration of carbon atoms is designated as the second region, and the region with a lower atomic concentration is designated as the first region. The thermally conductive sheet of the present invention may have at least one pair of first and second regions that satisfy the relationship that (a2) is higher than (a1). For example, suppose that two 500 × 50 μm regions determined by observing the surface of a thermally conductive sheet do not satisfy the requirement that (a2) is higher than (a1). Even in this case, if, for example, two other 500 × 50 μm regions are defined on the surface and the requirement is satisfied, the thermally conductive sheet falls within the scope of the present invention.

[0015] Furthermore, the first and second regions are not limited to a single set. For example, if the first and second regions set on the surface satisfy the above requirement, two other 500 × 50 μm regions set in an area other than the first and second regions may also satisfy the above requirement.

[0016] The first and second regions that satisfy the above requirements can be determined, for example, based on differences in appearance found when the surface is observed with an SEM. This point will be explained below with reference to Figures 1 to 6.

[0017] 1 shows the results of SEM-EDX mapping of the surface of the thermally conductive sheet obtained in Example 1, which will be described later. 1001 shows the results of identifying carbon, and 1002 is an SEM image of the surface.

[0018] In 1001 and 1002, four regions that appear darker than the surrounding area are observed at approximately equal intervals vertically. The surface state of the thermally conductive sheet of the present invention is not limited to that shown in Fig. 1 , but the thermally conductive sheet of the present invention has regions that are clearly distinguishable from other regions in appearance, as shown in 1001 and 1002, for example. As a result of elemental analysis by the present inventors, it was revealed that the atomic concentration of carbon atoms is high in regions other than the regions that appear darker than the surrounding area shown in 1001 and 1002, and that the atomic concentration of carbon atoms is low in the regions that appear darker than the surrounding area.

[0019] Figure 2 is an enlarged view of 1002 in Figure 1. As shown in Figure 2, the surface of the thermal conductive sheet is observed using an SEM to set a first region of 500 μm × 50 μm and a second region of 500 μm × 50 μm. In this case, it can be confirmed by, for example, SEM-EDX that (a2) is higher than (a1). "Area 1" shown in Figure 2 corresponds to the first region, and "Area 2" corresponds to the second region.

[0020] FIG. 3 shows the results of SEM-EDX mapping of the surface of the thermal conductive sheet obtained in Example 3 (described later). Reference numeral 1003 indicates the results of carbon identification, and reference numeral 1004 indicates an SEM image of the surface. FIG. 4 is an enlarged view of reference numeral 1004 in FIG. 3, showing the surface divided into a 500 μm × 50 μm area (area 1) and a 500 μm × 50 μm area (area 2). In this case, as in FIGS. 1 and 2, regions that appear darker than the surrounding area are observed in 1003 and 1004. The carbon atom concentration is higher in the regions other than these regions, while the carbon atom concentration is lower in the regions that appear darker than the surrounding area. Therefore, by defining the first and second regions, for example, as shown in FIG. 4, it can be confirmed that (a2) is higher than (a1).

[0021] On the other hand, FIG. 5 shows the results of mapping the surface of the thermal conductive sheet obtained in Comparative Example 1, which will be described later, by SEM-EDX. 1005 shows the results of identifying carbon, and 1006 is an SEM image of the surface. FIG. 6 is an enlarged view of 1006 in FIG. 5, showing areas 1 and 2 set at positions roughly corresponding to areas 1 and 2 shown in FIG. 2. In this case, as shown in FIGS. 5 and 6, no areas that appeared darker than the surrounding area, as seen in FIG. 1, etc., were observed. Furthermore, no matter how the first and second areas were set, it was not possible to confirm that (a2) was higher than (a1).

[0022] The first and second regions are set to 500 μm in length and 50 μm in width because if the regions are made too wide, it becomes difficult to set a region that satisfies the requirement that "the (a2) is higher than the (a1)."

[0023] The first region preferably includes more areas that appear darker than the surrounding area, and most preferably includes only areas that appear darker than the surrounding area. Conversely, the (a2) preferably includes fewer areas that appear darker than the surrounding area, and most preferably does not include any areas that appear darker than the surrounding area. This is because the more areas that appear darker than the surrounding area are included in the first region, the more likely the thermal conductive sheet is to satisfy the requirement that "the (a2) is higher than the (a1)," and the more likely it is to achieve the above-mentioned effect.

[0024] In this way, the thermal conductive sheet of the present invention has a difference in atomic concentration of carbon atoms between the first region and the second region. The inventors have found that by including the first region and the second region in a single thermal conductive sheet, the thermal conductive sheet has excellent thermal resistance, tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling.

[0025] The second region has a higher atomic concentration of carbon atoms than the first region. This is thought to be because the second region contains more graphite particles (A) than the first region. Therefore, the second region is thought to mainly contribute to the reduction of thermal resistance and tackiness (reducing tackiness) derived from the graphite particles (A).

[0026] On the other hand, the present inventors have found that the first region has a lower atomic concentration of carbon atoms than the second region and a higher atomic concentration of oxygen atoms than the second region. That is, the first region is considered to be a region containing many oxygen atoms derived from the organic polymer compound (B). Therefore, the first region is considered to mainly contribute to the exhibiting of tackiness (improving tackiness), initial adhesion, adhesion after high temperature retention, and adhesion after heat cycling derived from the organic polymer compound (B).

[0027] It can be confirmed, for example, by mapping analysis using SEM-EDX that the atomic concentration of carbon atoms in the second region is higher than that in the first region, and that the atomic concentration of oxygen atoms in the first region is higher than that in the second region.

[0028] As described above, the thermally conductive sheet according to one embodiment of the present invention has a region that primarily contributes to reducing thermal resistance and a region that primarily contributes to exhibiting tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycles. Therefore, although the exact reason is unclear, it is believed that the thermally conductive sheet can clearly exhibit low thermal resistance, tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycles, all independently of each other. Specifically, the thermally conductive sheet can exhibit, for example, the following effects (a) to (d).

[0029] (a) The thermal conductive sheet of the present invention can reduce the thermal resistance value due to the presence of the second region.

[0030] (b) The thermally conductive sheet of the present invention is easily peeled off from the backing sheet due to the presence of the first region.

[0031] (c) The thermally conductive sheet of the present invention is easily temporarily attached to a heat generating element due to the presence of the first region.

[0032] (d) Due to the presence of the first region, the thermally conductive sheet of the present invention has excellent initial adhesion when heated and attached to a heat generating element and a heat sink, adhesion after being maintained at high temperatures, and adhesion after a heat cycle, thereby enabling the sheet to effectively transport heat from the heat generating element to the heat sink.

[0033] As a method for producing the thermally conductive sheet of the present invention, for example, a method for producing a thermally conductive sheet according to one embodiment of the present invention, which will be described later, can be mentioned.

[0034] In the thermally conductive sheet of the present invention, the value obtained by dividing the (a2) by the (a1) is preferably 1.01 or more.

[0035] In the thermally conductive sheet having such a configuration, the above value is 1.01 or more, and therefore it is clear that more graphite particles (A) are present in the second region than in the first region. Therefore, the effects (a) to (d) can be more efficiently achieved. From this viewpoint, the value is more preferably 1.05 or more, and even more preferably 1.07 or more.

[0036] On the other hand, if a single thermally conductive sheet has multiple regions with extremely different compositions, there is a possibility that the thermally conductive sheet will have different hardness depending on the region, etc. Therefore, the upper limit of the value obtained by dividing (a2) by (a1) is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.5 or less.

[0037] The specific numerical value of the atomic number concentration can be determined by performing area analysis of the first and second regions using SEM-EDX and semi-quantitative analysis using the ZAF method. Specific analysis conditions will be described later in the Examples. Then, by dividing the atomic number concentration (a2) of carbon atoms contained in the second region by the atomic number concentration (a1) of carbon atoms contained in the first region, it can be confirmed that the value is 1.01 or more.

[0038] As a method for producing a thermally conductive sheet having the above value of 1.01 or more, for example, there can be mentioned a method for producing a thermally conductive sheet according to one embodiment of the present invention, which will be described later.

[0039] In the thermally conductive sheet of the present invention, the difference between the (a2) and the (a1) is preferably 1 atom % or more.

[0040] In the thermally conductive sheet having this configuration, the difference is 1 atom % or more, so it is clear that more graphite particles (A) are present in the second region than in the first region. Therefore, the effects (a) to (d) can be more efficiently achieved. From this viewpoint, the difference is more preferably 2 atom % or more, more preferably 3 atom % or more, even more preferably 5 atom % or more, and particularly preferably 7 atom % or more.

[0041] On the other hand, if a single thermally conductive sheet has multiple regions with extremely different compositions, this may cause inconveniences such as differences in the hardness of the thermally conductive sheet depending on the region. Therefore, the difference is preferably 30 atom% or less, more preferably 25 atom% or less, and even more preferably 20 atom% or less.

[0042] The difference can be determined by performing area analysis of the first region and the second region by SEM-EDX, obtaining the atomic concentration of carbon atoms by semi-quantitative analysis using the ZAF method, and subtracting (a1) from (a2).

[0043] The atomic concentration (a1) of carbon atoms contained in the first region is preferably 60 to 98 atom %, more preferably 65 to 97 atom %, because this allows the thermal resistance value to be reduced.

[0044] The atomic concentration (a2) of carbon atoms contained in the second region is preferably 65 to 99 atom %, more preferably 70 to 98 atom %, because this can improve tackiness, adhesion, adhesion after high temperature retention, and adhesion after heat cycles.

[0045] As a method for producing a thermally conductive sheet in which the difference is 1 atom % or more, for example, there can be mentioned a method for producing a thermally conductive sheet according to one embodiment of the present invention, which will be described later.

[0046] In the thermal conductive sheet of the present invention, it is preferable that (a2) is measured for one of the strips constituting the thermal conductive sheet, and (a1) is measured between the one strip and another adjacent strip.

[0047] As described below, the thermally conductive sheet can be obtained by slicing the cross section of a laminate of primary sheets. Therefore, the thermally conductive sheet has an interface between one primary sheet constituting the thermally conductive sheet and another primary sheet adjacent to that primary sheet. Furthermore, the aforementioned area that appears darker than the surrounding area is formed around the interface.

[0048] Here, each primary sheet constituting the thermal conductive sheet is referred to as a "strip." The strip can be arbitrarily selected from the strips constituting the thermal conductive sheet. The (a2) is measured for the selected strip. As mentioned above, it is preferable that the second region for measuring the (a2) is set so as not to include the region that appears darker than the surrounding area, and therefore the second region may be set in this manner.

[0049] On the other hand, as mentioned above, it is preferable that the first region is set to include many areas that appear darker than the surrounding area. The areas that appear darker than the surrounding area are formed around the interface. Therefore, setting the first region between one strip and another adjacent strip more reliably sets the first region that includes areas that appear darker than the surrounding area than setting the first region only within the strip. Therefore, it is easier to confirm that the thermal conduction sheet satisfies the requirement that "(a2) is higher than (a1)."

[0050] The thermally conductive sheet is a thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), and it is preferable that the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet.

[0051] (Graphite particles (A)) By including the graphite particles (A) in the thermally conductive sheet, the thermally conductive graphite particles (A) are dispersed in the thermally conductive sheet, thereby improving the thermal conductivity of the thermally conductive sheet and thereby reducing the thermal resistance of the thermally conductive sheet.

[0052] 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.

[0053] The shape of the non-spherical graphite particles (A) is not particularly limited, and may be, for example, a plate-like shape such as a scale-like or thin plate-like shape; an ellipsoidal shape; a needle-like shape; a rod-like shape; a fiber-like shape; or an irregular shape. Among these, the shape of the non-spherical graphite particles (A) is more preferably a plate-like shape such as a scale-like or thin plate-like shape, from the viewpoint that the non-spherical graphite particles (A) are easily oriented and inter-particle contact is easily maintained, thereby further improving thermal conductivity in the orientation direction and thereby further reducing thermal resistance in the orientation direction.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] From the viewpoint of improving thermal conductivity in the orientation direction, the aspect ratio of the graphite particles (A) is preferably 20 or more, more preferably 40 or more, and even more preferably 70 or more. There is no particular upper limit, but it is usually 1000 or less. When the aspect ratio of the graphite particles (A) is 20 or more, by orienting the graphite particles (A) in the thickness direction of the thermal conductive sheet, the thermal conductivity in the thickness direction of the thermal conductive sheet can be further improved, and thus the thermal resistance in the thickness direction of the thermal conductive sheet can be further reduced, which is preferable.

[0058] 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.

[0059] 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.).

[0060] 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.

[0061] When the graphite particles (A) are plate-like, their average thickness is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm, and particularly preferably 0.3 μm to 3 μm. Here, the average thickness of the graphite particles (A) can be determined by observing a sufficient number (e.g., 10 or more) of graphite particles (A) with an ultra-high resolution scanning electron microscope (S-4800 manufactured by Hitachi, Ltd.), calculating the thickness of each graphite particle (A), and averaging these values.

[0062] If the lower limit of the average thickness of the graphite particles (A) is within the above-mentioned range, the heat transport amount per particle increases, and good heat transfer paths are easily formed. Also, if the upper limit of the average thickness of the graphite particles (A) is within the above-mentioned range, the number of graphite particles (A) per unit weight increases, and the graphite particles (A) interfere with each other, aligning them in the desired direction, and good heat transfer paths are easily formed.

[0063] (Organic polymer compound (B)) The organic polymer compound (B) functions as a binder, improves the flexibility of the heat conductive sheet, and enables the heat generating element and the heat radiating element to be well adhered to each other via the heat conductive sheet.

[0064] 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.

[0065] 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.

[0066] The organic polymer compound (B) may be solid or liquid at room temperature. In this specification, "room temperature" refers to 20°C.

[0067] 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.

[0068] The content of the organic polymer compound (B) relative to the total weight of the thermally conductive sheet is preferably 10% by weight or more, more preferably 15% by weight or more, and even more preferably 20% by weight or more. When the content of the organic polymer compound (B) is 10% by weight or more, the flexibility of the thermally conductive sheet is improved, and the heat-generating body and the heat-dissipating body can be well adhered to each other via the thermally conductive sheet.

[0069] 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.

[0070] <Acrylate ester resin> The organic polymer compound (B) preferably contains an acrylic ester resin. The use of the acrylic ester resin has the advantage of providing a thermally conductive sheet that is adhesive and elastic enough to restore its thickness. The acrylic ester resin may be used alone or in combination of two or more.

[0071] 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.

[0072] 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.

[0073] A more preferred example of the acrylic ester resin is an acrylic ester resin containing either or both of butyl acrylate and 2-ethylhexyl acrylate as monomers, the total amount of which is 50 wt % or more based on the total amount of monomer components. This acrylic ester resin is preferred because it is easy to achieve high flexibility, has excellent chemical stability and processability, and is easy to control adhesiveness. Furthermore, incorporating a crosslinked structure into the acrylic ester resin without impairing flexibility is preferred in terms of long-term adhesion retention and film strength. The crosslinked structure can be incorporated, for example, by reacting a polymer having a hydroxyl group with a compound having an isocyanate group. Alternatively, the crosslinked structure can be incorporated, for example, by reacting a polymer having a carboxyl group with a compound having an epoxy group.

[0074] 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.

[0075] The Tg of the acrylic ester resin is preferably −35° C. or lower, more preferably −50° C. or lower, and even more preferably −60° C. or lower. When the Tg of the acrylic ester resin is −35° C. or lower, the acrylic ester resin becomes more likely to flow when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic ester resin is not particularly limited and is, for example, −150° C. or higher. The “Tg” described in this specification can be calculated, for example, by the method described in the Examples.

[0076] 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.

[0077] In this specification, "room temperature" means 20°C, and "normal pressure" means 1 atm. In other words, the acrylic ester resin is preferably an acrylic ester resin having a melting point of 20°C or lower. The "melting point" described in this specification refers to the melting point under normal pressure (1 atm). In addition, in this specification, "being liquid" means that the resin flows when the container, such as a bottle or a can, is tilted while the resin is held in the container at room temperature (20°C). The resin may also be a block resin.

[0078] The weight-average molecular weight of the acrylic ester resin is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 250,000 or more. Because the weight-average molecular weight of the acrylic ester resin is as high as 50,000 or more, the acrylic ester resin is less likely to flow when the press plate is released after the hot press during lamination, or when an external force is applied to the thermal conductive sheet after lamination. This allows for even greater adhesion between the thermal conductive sheet and the adherend.

[0079] The weight-average molecular weight of the acrylic ester resin is preferably 3 million or less, more preferably 2 million or less, and even more preferably 1.5 million or less. When the weight-average molecular weight of the acrylic ester resin is 3 million or less, the acrylic ester resin becomes more fluid when the thermal conductive sheet is attached using a hot press. This improves the wettability of the thermal conductive sheet with the attached adherend, thereby increasing the adhesion between the thermal conductive sheet and the adherend.

[0080] 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.

[0081] 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.

[0082] 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 composition into a sheet, and as a result, it is possible to more easily provide a thermally conductive sheet containing the composition. Furthermore, the functional group may interact with a substance that constitutes the surface of an adherend, contributing to the adhesion between the thermally conductive sheet and the adherend. In this case, it is believed that the adhesion between the thermally conductive sheet and the adherend is also improved.

[0083] 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.

[0084] 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.

[0085] In one embodiment of the present invention, when the content of the functional group relative to the total weight of the acrylic ester resin is high, the graphite particles (A) are more suitably bound to each other via the acrylic ester resin in the thermal conductive sheet. As a result, the graphite binding property of the thermal conductive sheet is further improved. Hereinafter, the content of the functional group relative to the total weight of the acrylic ester resin is referred to as the "functional group content C." The functional group content C is the sum of the functional group content A and the functional group content B described below.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] To convert from mmol / g to mg / g of KOH, multiply mmol / g by 56.1056 mg / mmol.

[0091] 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).

[0092] (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.

[0093] (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.

[0094] (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).

[0095] Furthermore, when the weight-average molecular weights of all polymers contained in the acrylic ester 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.

[0096] 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.

[0097] <Acrylic resin with functional groups> The glass transition temperature (Tg) of the acrylic resin having the functional group is preferably −35°C or lower, more preferably −50°C or lower, and even more preferably −60°C or lower. When the Tg of the acrylic resin having the functional group is −35°C or lower, the acrylic ester resin becomes more fluid when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the Tg of the acrylic resin having the functional group is not particularly limited, and is, for example, −150°C or higher.

[0098] The weight-average molecular weight of the acrylic resin having a functional group is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. The weight-average molecular weight of the acrylic resin having a functional group is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. By adjusting the weight-average molecular weight of the acrylic resin having a functional group to fall within the aforementioned preferred range, the weight-average molecular weight of the acrylic ester resin can be suitably controlled within the aforementioned preferred range. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the acrylic resin having a functional group is preferably 1.0 to 10.0.

[0099] The acrylic resin having the functional group may be solid or liquid at room temperature and pressure, and is preferably liquid. In other words, the acrylic resin having the functional group is preferably an acrylic resin having a melting point of 20°C or less.

[0100] The acrylic resin having a functional group preferably contains 50% by weight or more of repeating units derived from an acrylic monomer. The acrylic resin having a functional group includes a polymer of monomer components in which at least a portion of the constituent monomers has the functional group and which contains one or more acrylic monomers. The acrylic resin having a functional group also includes a copolymer of an acrylic monomer and another monomer in which at least a portion of the constituent monomers has the functional group. The acrylic monomer and the other monomer can be the acrylic monomer and the other monomer described above as monomers that can constitute the acrylic ester resin.

[0101] The ratio of the weight of the monomer having a functional group to the weight of all monomers constituting the acrylic resin having a functional group is preferably 0.1 to 5.2 wt%, more preferably 0.3 to 4.0 wt%. Furthermore, the ratio of the amount of the monomer having a functional group to the amount of all monomers constituting the acrylic resin having a functional group is preferably 0.1 mol% to 5.0 mol%, more preferably 0.3 mol% to 4.0 mol%. Adjusting the ratio within the aforementioned range is preferable for suitably controlling the content of the functional group in the acrylic resin having a functional group within the range described below. The monomer having a functional group may be any of the monomers having a functional group described above as a monomer capable of constituting the acrylic ester resin. Hereinafter, the content of the functional group relative to the weight of the acrylic resin having a functional group is referred to as the "functional group content A."

[0102] From the viewpoint of further improving the graphite binding property, the content A of the functional group is preferably 0.010 mmol / g or more, and more preferably 0.050 mmol / g or more, based on the total weight of the acrylic resin having the functional group.

[0103] Furthermore, when the thermally conductive sheet is maintained in a high-temperature environment and heated, the water absorbed by the heat is expelled, causing the sheet's shape to change, potentially resulting in poor adhesion to the adherend after the high-temperature exposure. Specifically, a thermally conductive sheet containing a highly hygroscopic acrylate ester resin is thought to absorb a large amount of water from the air. In this case, the large amount of water expelled increases the degree of deformation, resulting in gaps between the thermally conductive sheet and the adherend, potentially reducing adhesion to the adherend. Furthermore, it is believed that a thermally conductive sheet with excellent adhesion to the adherend after high-temperature exposure can be achieved when the acrylate ester resin is poorly water-soluble.

[0104] In one embodiment of the present invention, when the content A of functional groups is low, the functional groups can react with ordinary water molecules (HO), which reduces the affinity of the acrylic ester resin for water and reduces its hygroscopicity. As a result, the hygroscopicity of the thermally conductive sheet is controlled within a suitable range, resulting in improved adhesion after being held at high temperatures.

[0105] Specifically, for example, when the functional group is a hydroxyl group, from the viewpoint of improving the adhesion after being kept at high temperature, the content A of the functional group is preferably 0.371 mmol / g or less, more preferably 0.340 mmol / g or less, and even more preferably 0.300 mmol / g or less, relative to the weight of the entire acrylic resin having the functional group.

[0106] Furthermore, for example, when the functional group is a carboxyl group, from the viewpoint of improving the adhesion, the content A of the functional group is preferably 0.410 mmol / g or less, more preferably 0.360 mmol / g or less, and even more preferably 0.300 mmol / g or less, relative to the total weight of the acrylic resin having the functional group.

[0107] By setting the functional group content A within these ranges, the functional group content C can be suitably controlled within a preferred range. Note that, as a method for measuring the functional group content A, for example, the same method as the method for measuring the functional group content C can be used, except that the target is an acrylic resin having the functional groups.

[0108] The acrylic resin having the functional group may be a random copolymer or a block copolymer, but a random copolymer is preferred because it is more readily available.The structure of the acrylic resin having the functional group may be either linear or branched, but a linear structure is preferred because it is more readily available.

[0109] <Acrylic block copolymer> The acrylic block copolymer has a block structure and therefore has a Tg at both low and high temperatures. Because the acrylic block copolymer has a Tg at low temperatures, a thermally conductive sheet containing the acrylic block copolymer remains soft even at low temperatures. Therefore, the thermally conductive sheet containing the acrylic block copolymer can maintain adhesion even when exposed to low temperatures. Furthermore, because the acrylic block copolymer has a Tg at high temperatures, the thermally conductive sheet containing the acrylic block copolymer does not become too soft even at high temperatures and remains elastic. Therefore, the thermally conductive sheet containing the acrylic block copolymer can maintain adhesion even when exposed to high temperatures. Therefore, the thermally conductive sheet exhibits excellent adhesion even after being held at high temperatures.

[0110] The low-temperature Tg of the acrylic block copolymer is preferably −35°C or lower, more preferably −50°C or lower. When the low-temperature Tg of the acrylic block copolymer is −35°C or lower, the acrylic ester resin becomes more fluid when the thermally conductive sheet is attached using a hot press. This can further improve the wettability of the thermally conductive sheet with the attached adherend, thereby further increasing the adhesion to the adherend. The lower limit of the low-temperature Tg of the acrylic block copolymer is not particularly limited, and is, for example, −150°C or higher, preferably −55°C or higher.

[0111] The lower limit of the high-temperature Tg of the acrylic block copolymer is preferably 100° C. or higher, more preferably 102° C. or higher. The upper limit of the high-temperature Tg of the acrylic block copolymer is preferably 120° C. or lower, more preferably 118° C. or lower. When the high-temperature Tg is within the above-mentioned range, the thermal conductive sheet can be more effectively prevented from becoming excessively soft at high temperatures and can more effectively maintain its elasticity at high temperatures, resulting in improved adhesion after being held at high temperatures.

[0112] The weight-average molecular weight of the acrylic block copolymer is preferably 10,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. The weight-average molecular weight of the acrylic block copolymer is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. By adjusting the weight-average molecular weight of the acrylic block copolymer within the above-mentioned preferred range, the weight-average molecular weight of the acrylic ester resin can be suitably controlled within the preferred range described below. The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the acrylic block copolymer is preferably 1.0 to 2.0.

[0113] The acrylic block copolymer may be solid or liquid at room temperature and pressure, and is preferably liquid. In other words, the acrylic block copolymer preferably has a melting point of 20° C. or lower.

[0114] The acrylic block copolymer preferably contains 50% by weight or more of repeating units derived from an acrylic monomer. The acrylic block copolymer includes a copolymer of a monomer component containing two or more types of acrylic monomers. The acrylic block copolymer also includes a copolymer of one or more types of acrylic monomers and one or more types of other monomers. The acrylic monomers and other monomers may be the acrylic monomers and other monomers described above as monomers that can constitute the acrylic ester resin.

[0115] The acrylic block copolymer is a block copolymer. Here, the term "block copolymer" refers to a polymer in which the majority of the main chain, preferably the entire main chain, is a polymer in which blocks having two or more different chemical structures are linked together. The blocks are composed of repeating units derived from two or more monomers. The majority of the main chain refers to a portion composed of repeating units derived from, for example, 95% or more, preferably 97% or more of the total number of repeating units derived from the monomers constituting the main chain.

[0116] Examples of the block structure of the acrylic block copolymer include diblock (AB), triblock (A-B-A or A-B-C), and tetrablock (A-B-A-B or A-B-C-D, etc.), and from the viewpoint of improving adhesion at high temperatures, A-B-A triblock copolymers are preferred.

[0117] The repeating units constituting the A block of the A-B-A triblock copolymer are preferably those derived from a monomer such as methyl methacrylate, which gives a homopolymer Tg of 100 to 120°C or higher. The repeating units constituting the B block are preferably those derived from a monomer such as butyl acrylate or 2-ethylhexyl acrylate, which gives a homopolymer Tg of -60 to -40°C or lower. Preferred examples of the A-B-A triblock copolymer include poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate), poly(methyl methacrylate)-poly(2-ethylhexyl acrylate)-poly(methyl methacrylate), and poly(methyl methacrylate)-random poly(butyl acrylate, 2-ethylhexyl acrylate)-poly(methyl methacrylate).

[0118] The weight ratio of each block of the ABA triblock copolymer is preferably A / B / A=1-25 / 98-50 / 1-25, and the weight average molecular weight of the ABA triblock copolymer is preferably 10,000 to 3,000,000.

[0119] The acrylic block copolymer may have a functional group. The type of the functional group is not particularly limited and may be, for example, one or more selected from a hydroxyl group, a carboxyl group, and an epoxy group. A hydroxyl group and / or a carboxyl group is preferred, and a hydroxyl group is more preferred. Meanwhile, the functional group typically reacts with water molecules (HO). Therefore, when the content of the functional group is low, or preferably when the acrylic block copolymer does not have the functional group, the affinity of the acrylic ester resin with water decreases, resulting in reduced moisture absorption. As a result, similar to when the functional group content A is low, the moisture absorption of the thermally conductive sheet is controlled within a suitable range, resulting in improved adhesion after high-temperature storage. From the above perspective, a low content of functional groups in the acrylic block copolymer is preferred.

[0120] Hereinafter, the content of functional groups relative to the weight of the acrylic block copolymer will be referred to as the "functional group content B." Specifically, the functional group content B is preferably 0.020 mmol / g or less, more preferably less than 0.010 mmol / g, relative to the total weight of the acrylic block copolymer. It is particularly preferable that the functional group content B is 0 mmol / g, i.e., the acrylic block copolymer does not contain the functional group. The functional group content B can be measured, for example, by the same method as the above-mentioned method for measuring the functional group content C, except that the acrylic block copolymer is the target.

[0121] Furthermore, the acrylic block copolymer with fewer functional groups has high heat resistance, and its structure is more stable against heat. Therefore, the acrylic block copolymer with fewer functional groups is less likely to generate radicals when heated than an acrylic block copolymer with a higher functional group content. Therefore, when the functional group content B is low, the acrylic ester resin generates fewer radicals when heated than when the functional group content B is high. Therefore, in a thermally conductive sheet containing the acrylic ester resin, the chain reaction is less likely to proceed when the functional group content B is low. As a result, when the functional group content B is low, the tackiness of the acrylic ester resin is less likely to decrease when heat is applied, and the thermally conductive sheet has better tackiness after being kept at high temperatures.

[0122] Hereinafter, the ratio of the weight of the acrylic resin having the functional group to the weight of the acrylic block copolymer in the acrylic ester resin (acrylic resin having functional group / acrylic block copolymer) will be referred to as "ratio A." When ratio A is equal to or greater than a predetermined value, it means that the content of the acrylic resin having the functional group and the functional group in the acrylic ester resin is suitably high. In this case, the graphite binding property of the thermal conductive sheet is further improved due to the presence of the functional group. From the viewpoint of further improving the graphite binding property of the thermal conductive sheet, ratio A is preferably 0.02 or more, more preferably 0.05 or more, and even more preferably 0.1 or more.

[0123] The ratio A being equal to or less than a predetermined value means that the content of the acrylic block copolymer in the acrylic ester resin is suitably high. In this case, the presence of the acrylic block copolymer further improves the adhesion of the thermally conductive sheet after being held at high temperatures. From the viewpoint of further improving the adhesion of the thermally conductive sheet after being held at high temperatures, the ratio A is preferably equal to or less than 50, more preferably equal to or less than 25, and even more preferably equal to or less than 10.

[0124] From the viewpoint of achieving a balanced improvement in the graphite binding property of the thermal conductive sheet and the adhesion after being held at high temperatures, the ratio A is preferably within the above-mentioned range, more preferably 1.2 to 8, and particularly preferably 1.5 to 5.

[0125] (composition) In one embodiment of the present invention, the content of the graphite particles (A) in the composition is preferably 30% by weight to 80% by weight, more preferably 35% by weight to 75% by weight, and even more preferably 40% by weight to 70% by weight, based on the total weight of the composition. A content of the graphite particles (A) of 30% by weight or more is preferred because sufficient thermal conductivity is exhibited. Furthermore, a content of the graphite particles (A) of 80% by weight or less is preferred because excellent flexibility and adhesion are achieved.

[0126] When the content of the graphite particles (A) is within the above range, the ratio of the graphite particles (A) to the organic polymer compound (B) in the composition is more preferable for satisfying the requirement that "the (a2) is higher than the (a1)," which makes it easier to produce the thermal conductive sheet of the present invention.

[0127] In one embodiment of the present invention, the content of the organic polymer compound (B) in the composition is preferably 10% by weight to 60% by weight, more preferably 15% by weight to 50% by weight, and even more preferably 20% by weight to 40% by weight, based on the total weight of the composition. A content of the organic polymer compound (B) of 10% by weight or more is preferable because it improves the flexibility of the thermally conductive sheet and enables good adhesion between the heat generating element and the heat dissipating element via the thermally conductive sheet. Furthermore, a higher content of the organic polymer compound (B) within the range of 60% by weight or less is preferable because it allows the graphite particles (A) to be more effectively fixed and improves adhesion to the semiconductor and spreader.

[0128] The composition 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 thermal conductive sheet, the wettability with the silicone and / or spreader is improved, thereby reducing thermal resistance. The flame retardant may be, for example, a phosphorus-based flame retardant. The phosphorus-based flame retardant has the function of suppressing the combustion of the resin.

[0129] In a method for producing a thermally conductive sheet according to one embodiment of the present invention, which will be described later, a primary sheet is formed using a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent. In this specification, the term "composition" does not refer to the mixture, but rather to the composition obtained after the solvent has been removed by drying or the like, i.e., the composition contained in the final conductive sheet.

[0130] When the thermal conductive sheet contains the additive, the content of the additive is not particularly limited as long as it does not impair the effects of the present invention. A preferred content of the additive is, for example, 50 wt % or less based on the weight of the thermal conductive sheet.

[0131] 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).

[0132] The contents of the graphite particles (A), the organic polymer compound (B), and the additives in the thermally conductive sheet may be the same as the contents of the graphite particles (A), the organic polymer compound (B), and the additives relative to the weight of the entire composition.

[0133] (Orientation of graphite particles (A)) In the thermally conductive sheet, the graphite particles (A) are preferably oriented in the thickness direction of the thermally conductive sheet. In this case, the thermal conductivity of the thermally conductive sheet is improved in the thickness direction in which the graphite particles (A) are oriented, thereby reducing the thermal resistance in the thickness direction in which the graphite particles (A) are oriented. Note that in the thermally conductive sheet, it is not necessary for all of the graphite particles (A) to be oriented in the thickness direction of the thermally conductive sheet. In the thermally conductive sheet, it is sufficient that at least a portion of the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and the thermal conductivity can be improved in the thickness direction in which they are oriented.

[0134] The phrase "graphite particles (A) are oriented in the thickness direction of the heat conductive sheet" means that the angle of the six-membered carbon ring plane in the crystal of the graphite particle (A) relative to the sheet surface of the heat conductive sheet is greater than 45°. This angle is more preferably 50° or greater, even more preferably 70° or greater, and particularly preferably 80° or greater. The term "angle of the six-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 six-membered carbon ring plane in the crystal of the graphite particle (A) is oriented in the plane direction of the scales and flakes in the case of plate-like graphite particles (A) such as scales and flakes, and in the long axis direction of the particles in the case of graphite particles (A) having an ellipsoidal, acicular, rod-like, fibrous, or irregular shape. The long axis of the graphite particle (A) coincides with the maximum length of the graphite particle (A).

[0135] 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.

[0136] (Physical properties of thermal conductive sheets, etc.) The thermal resistance of the thermal conductive sheet according to one embodiment of the present invention is 0.20 cm 2 K / W or less is preferable, and 0.12 cm 2 K / W or less is more preferable, and 0.10 cm 2 K / W or less is more preferable, and 0.085 cm 2It is particularly preferable that the thermal resistance is 0.20 cm / W or less. Here, in this specification, the thermal resistance is the thermal conduction in the thickness direction of the thermal conductive sheet, and is the thermal resistance value measured by the method described in the Examples. 2 If the thermal resistance is 100 K / 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 dissipating device. The lower the thermal resistance, the more preferable.

[0137] The thickness of the thermally conductive sheet according to one embodiment of the present invention is preferably 500 μm or less, more preferably 200 μm or less, even more preferably 140 μm or less, even more preferably 100 μm, even more preferably 95 μm or less, and particularly preferably 80 μm or less. Herein, the "thickness of the thermally conductive sheet" refers to the thickness measured by the method described in the Examples. A thermally conductive sheet having a thickness of 500 μm or less is preferable because it can be attached to a heat-generating body such as an electronic component even in a narrow space. The lower limit of the thickness of the thermally conductive sheet is not particularly limited as long as it functions as a thermally conductive sheet, but is preferably 3 μm or more, and more preferably 5 μm or more.

[0138] The sulfur content of the thermally conductive sheet according to one embodiment 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. Here, in this specification, 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 is preferable because it is less likely to corrode electronic components in contact with the thermally conductive sheet. The lower the sulfur content of the thermally conductive sheet, the better, and although there are no particular limitations, the lower limit is, for example, 0.01 wt% or more.

[0139] The hardness at 20°C of the thermally conductive sheet according to one embodiment of the present invention is preferably 65 or more, more preferably 70 or more, even more preferably 75 or more, and particularly preferably 80 or more. Herein, the "hardness at 20°C of the thermally conductive sheet" refers to the hardness measured by the method described in the Examples. A thermally conductive sheet having a hardness at 20°C of 65 or more is preferable because the thermally conductive sheet is sufficiently hard and can therefore be sliced ​​to a thin thickness. Furthermore, the hardness at 20°C of the thermally conductive sheet is preferably 95 or less, more preferably 90 or less, and even more preferably 88 or less. A thermally conductive sheet having a hardness at 20°C of 95 or less can be sufficiently adhered to the components it contacts. Therefore, heat can be efficiently transferred and thermal stress can be sufficiently alleviated.

[0140] The hardness at 70°C of the thermally conductive sheet according to one embodiment of the present invention is preferably greater than 60, more preferably greater than 63, and even more preferably greater than 65. In this specification, the "hardness at 70°C of the thermally conductive sheet" refers to the hardness measured by the method described in the Examples. A thermally conductive sheet having a hardness at 70°C of greater than 60 is preferable because the thermally conductive sheet is sufficiently hard and can therefore be sliced ​​to a thin thickness. Furthermore, the hardness at 70°C of the thermally conductive sheet is preferably 90 or less, more preferably 85 or less, and even more preferably 83 or less. A thermally conductive sheet having a hardness at 70°C of 90 or less can be sufficiently adhered to the components it contacts. This allows for efficient heat transfer and sufficient thermal stress relief.

[0141] The tackiness of the thermally conductive sheet according to one embodiment of the present invention can be evaluated by a numerical value (unit: N·mm) representing the tackiness measured by the method described in the Examples. The tackiness of the thermally conductive sheet is preferably 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 may be, for example, less than 5.0 N·mm.

[0142] When the tackiness of the thermally conductive sheet is 0.8 N·mm or more, the thermally conductive sheet can be positioned accurately when temporarily attached to an adherend. Furthermore, even if the adherend is moved while temporarily attached, it does not shift position. Therefore, better adhesion can be achieved when hot-pressing. Furthermore, when the tackiness of the thermally conductive sheet is less than 5.0 N·mm, air easily escapes between the thermally conductive sheet and the adherend when temporarily attached to the adherend. Furthermore, when the thermally conductive sheet and the adherend are bonded together by hot-pressing, air trapped between the thermally conductive sheet and the adherend is easily escaped. Therefore, in the thermally conductive sheet of the present invention, a tackiness of less than 5.0 N·mm allows the thermally conductive sheet to be more sufficiently adhered to the components it contacts.

[0143] The temporary adhesion property of the thermally conductive sheet according to one embodiment of the present invention can be evaluated by peeling off a 40 x 40 mm thermally conductive sheet from the separator and attaching it to a 50 x 50 mm silicon wafer. The fact that the thermally conductive sheet has excellent temporary adhesion property means the following: The thermal conductive sheet can be easily peeled off from the separator and fixed onto the silicon wafer with precision. The thermal conductive sheet will not peel off even when the silicon wafer is transported or turned upside down, and any air trapped between the silicon wafer and the thermal conductive sheet can be easily removed.

[0144] The initial adhesion of the thermally conductive sheet according to one embodiment of the present invention is the adhesion when the thermally conductive sheet and the adherend are bonded together, and can be measured by the method described in the Examples below. If the adhesion is not excellent when the thermally conductive sheet and the adherend are bonded together, it is impossible to expect adhesion after high temperature exposure and after heat cycling, as described below. Therefore, the thermally conductive sheet must first have sufficient initial adhesion. The initial adhesion can be measured by the method described in the Examples below, and it is preferable that the evaluation in the Examples be A or B.

[0145] The adhesion of a thermally conductive sheet according to one embodiment of the present invention after high temperature exposure refers to the adhesion between the thermally conductive sheet and the adherend when the sheet is exposed to a high temperature environment. The thermally conductive sheet may be exposed to a high temperature environment while attached to the adherend. Therefore, the thermally conductive sheet preferably has excellent adhesion after high temperature exposure. The adhesion after high temperature exposure can be measured by the method described in the examples, and the evaluation in the examples is preferably A or B.

[0146] The adhesion after heat cycle of a thermally conductive sheet according to one embodiment of the present invention is the adhesion between the thermally conductive sheet and the adherend when the sheet is maintained in an environment where low and high temperatures are repeatedly changed. The thermally conductive sheet may be maintained in a state where low and high temperatures are repeatedly changed while adhered to the adherend. Therefore, it is preferable that the thermally conductive sheet has excellent adhesion after heat cycle. The adhesion after heat cycle can be measured by the method described in the examples, and it is preferable that the evaluation described in the examples is A or B.

[0147] 2. 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 the primary sheets to obtain a laminate of primary sheets; and a slicing step of slicing the cross section of the laminate of primary sheets to obtain a thermally conductive sheet.

[0148] The manufacturing method according to the present invention can produce a thermally conductive sheet having low thermal resistance, excellent tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling.

[0149] (Primary sheet forming process) In the primary sheet forming step, a mixture containing graphite particles (A), an organic polymer compound (B), and a solvent is formed into a sheet to obtain a primary sheet.

[0150] 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.].

[0151] A conventional method for forming a primary sheet involves melt-kneading graphite particles (A), an organic polymer compound (B), and, if necessary, the additives described above, 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.

[0152] 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 of the present invention having a difference in carbon concentration can be obtained.

[0153] Although the reason why the carbon concentration difference occurs when the mixture is used is unclear, it is thought 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. It is also thought that after the solution containing the graphite particles (A) and the organic polymer compound (B) is applied, the solution is heated and the organic polymer compound (B) migrates to the surface layer of the primary sheet during the process of drying the solvent, resulting in the presence of areas with a low carbon concentration after lamination. It is also thought that the organic polymer compound (B) may have seeped out to the interface between the primary sheets during pressing in the laminate formation process. However, the present invention is not limited to such speculation.

[0154] Examples of the solvent include aromatic hydrocarbon solvents such as toluene and xylene; ester-based solvents such as ethyl acetate and butyl acetate; ketone-based solvents such as methyl ethyl ketone and methyl isobutyl ketone (MIBK); and cellosolve-based solvents such as butyl cellosolve, phenyl cellosolve, and dimethyl cellosolve. The amount of solvent is preferably such that the total concentration of the graphite particles (A), organic polymer compound (B), and additives is 10 to 50% by weight, more preferably 20 to 40% by weight. This concentration is preferred because, when a primary sheet is produced at this concentration, adequate spaces are formed between the graphite particles, improving particle orientation during sheet production and lamination pressing.

[0155] The primary sheet forming step is preferably a step of forming a primary sheet by coating the mixture. This step is also called a scraping method, in which the mixture is poured into a mold 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.

[0156] 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, the solvent can be further removed by performing a separate drying step after coating. Therefore, a thermally conductive sheet with minimal residual solvent can be obtained. Examples of coating methods include the aforementioned scraping method, and examples of drying methods include air drying or heating in an oven.

[0157] When the composition is molded into a sheet, the thickness 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 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.

[0158] (Laminate formation process) The laminate formation step is a step of laminating the primary sheets to obtain a laminate of the primary sheets. The method of laminating the primary sheets is not particularly limited, and examples thereof include a method of laminating a plurality of primary sheets and a method of folding a primary sheet. When laminating the primary sheets, it is preferable to laminate them with the orientation of the graphite particles (A) aligned in the plane of the sheets.

[0159] The pressure to be applied when stacking the primary sheets is not particularly limited, but is adjusted so that the pressure is weak enough to prevent the sliced ​​surfaces from being crushed in the subsequent slicing step, but strong enough to ensure good adhesion between the primary sheets. Furthermore, the stacking may be carried out under appropriate heating.

[0160] The pressure when laminating the primary sheets may be applied each time a primary sheet is laminated, or may be applied after laminating multiple sheets, or may be applied after laminating all of the primary sheets. A preferred example is a method in which pressure is applied each time a primary sheet or multiple sheets are laminated, and also after laminating all of the primary sheets. In such a case, the pressure and temperature applied each time a primary sheet or multiple sheets are laminated are not particularly limited, but for example, the pressure may be 1 kgf / cm 2 ~100kgf / cm 2 The temperature is 20° C. to 200° C. The pressure and temperature to be applied after all the primary sheets are laminated are not particularly limited. For example, the pressure may be 1 kgf / cm 2 ~100kgf / cm 2 and the temperature is 20℃ to 200℃.

[0161] (Slicing process) In the slicing step, the cross section of the primary sheet laminate is sliced ​​to obtain a thermally conductive sheet. The angle at which the cross section of the primary sheet laminate is sliced ​​is not particularly limited, but more preferably, the cross section of the primary sheet laminate is sliced ​​at an angle of 45° or less with respect to the stacking direction, even more preferably at an angle of 0 to 30°, and particularly preferably at an angle of 0 to 15° to obtain a thermally conductive sheet. By slicing at an angle of 45° or less with respect to the stacking direction, a thermally conductive sheet with excellent thermal conductivity can be obtained.

[0162] 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.

[0163] The thermal conductive sheet of the present invention can be obtained by the method for producing a thermal conductive sheet according to one embodiment of the present invention, which includes the above steps.

[0164] <Summary> An embodiment of the present invention includes the following configuration.

[0165] [1] A thermally conductive sheet comprising a composition containing graphite particles (A) and an organic polymer compound (B), wherein the graphite particles (A) are oriented in the thickness direction of the thermally conductive sheet, and when a first region of 500 μm × 50 μm and a second region of 500 μm × 50 μm are defined on the surface, at least one pair of the first region and the second region satisfies the relationship that the following (a2) is higher than the following (a1): (a1) the atomic concentration of carbon atoms contained in the first region (a2) The atomic concentration of carbon atoms contained in the second region.

[0166] [2] The thermal conductive sheet according to [1], wherein the value obtained by dividing (a2) by (a1) is 1.01 or more.

[0167] [3] The thermal conductive sheet according to [1] or [2], wherein the difference between (a2) and (a1) is 1 atom % or more.

[0168] [4] A thermal conduction sheet according to any one of [1] to [3], wherein (a2) is measured for one of the strips constituting the thermal conduction sheet, and (a1) is measured between the one strip and another adjacent strip.

[0169] [5] The thermally conductive sheet according to any one of [1] to [4], wherein the organic polymer compound (B) is an acrylic ester resin having a functional group.

[0170] [6] The thermally conductive sheet according to any one of [1] to [5], wherein the content of the graphite particles (A) in the composition is 30 to 80% by weight based on the total weight of the composition.

[0171] [7] A method for producing a thermally conductive sheet, 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 to obtain a primary sheet; 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.

[0172] [8] The method for manufacturing a thermal conductive sheet according to [7], wherein the primary sheet forming step is a step of forming a primary sheet by applying the mixture.

[0173] [9] A method for producing a thermal conductive sheet according to [7] or [8], wherein the primary sheet forming step is a step of forming a primary sheet by applying the mixture and then drying it.

[0174] 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]

[0175] Hereinafter, an 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 thereto.

[0176] 〔Evaluation Method〕 Each evaluation method in the Examples and Comparative Examples will be described below.

[0177] <Atomic Number Concentration of Carbon Atoms and Atomic Number Concentration of Oxygen Atoms> As the SEM, an ultra-high resolution scanning electron microscope (ULTRAplus manufactured by Carl Zeiss) was used, and as the EDX, QUANTAX XFlash 5010 manufactured by Bruker AXS attached to the SEM was used. The observation conditions by SEM and the analysis conditions by EDX were as follows.

[0178] <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.

[0179] The surfaces of the heat conduction sheet according to an embodiment of the present invention and the comparative heat conduction sheet were subjected to element mapping to confirm the in-plane distribution of elements. Next, for the heat conduction sheet according to an embodiment of the present invention, area analysis and semi-quantification by the ZAF method were performed. As the target of area analysis, 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.

[0180] <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.

[0181] <Graphite adhesion> The laminates produced in the Examples and Comparative Examples were sliced ​​and the state of the laminates was visually inspected, and the graphite binding properties of the thermally conductive sheets were evaluated according to the following criteria. A (excellent): The shape of the laminate is maintained and the laminate can be sliced. B (good): The shape of the laminate is deformed, but the laminate can be sliced. C (bad): The rectangular parallelepiped shape cannot be maintained immediately after the laminate is produced, or the laminate loses its shape when it is sliced ​​after production, making it impossible to slice the laminate.

[0182] <Sulfur content> The sulfur content (wt %) of the thermally conductive sheet was determined by elemental analysis using a scanning X-ray fluorescence analyzer (ZSX PrimusIII+ manufactured by Rigaku Corporation).

[0183] The sulfur content of the thermal conductive sheet was evaluated according to the following criteria: A (excellent): 0.10% by weight or less B (Good): More than 0.10% by weight, less than 0.30% by weight C (defective): More than 0.30% by weight.

[0184] <Hardness> The hardness of the thermally conductive sheet was evaluated by measuring the center of a cross section (6.5 x 6.5 cm) of a laminate (pre-sliced) consisting of the thermally conductive sheet. The laminate was obtained by the procedure described in the "Laminate Preparation" section below, but before the procedure described in the "Thermal Conduction Sheet Preparation" section below. Specifically, the hardness of the center of the cross section of the evaluation sample was measured using a hardness tester (ASKER CL-150LJ manufactured by Kobunshi Keiki Co., Ltd.) in accordance with the Asker C method of the Society of Rubber Industry Standards of Japan (SRIS). The hardness at 20°C is measured at 20°C, and the hardness at 70°C is measured at 70°C.

[0185] 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.

[0186] 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.

[0187] <Thermal resistance value> The thermal conductive sheet was cut into a 1 cm x 1 cm square to prepare a sample for evaluation. The thermal resistance value (cm 2 The thermal resistance (K / W) was measured at a sample temperature of 50°C and a pressure of 0.5 MPa using a thermal resistance measuring device (Hitachi Technology and Services, Ltd., Resin Material Thermal Resistance Measuring Device).

[0188] The thermal resistance of the thermal conductive sheet was evaluated according to the following criteria: A (Excellent): The thermal resistance of the thermal conductive sheet is 0.080cm 2 If it is less than K / W. B (Good): The thermal resistance of the thermal conductive sheet is 0.080 cm 2 K / W super, 0.10cm 2If it is less than K / W. C (bad): The thermal resistance of the thermal conductive sheet is 0.10 cm 2 If it is over K / W.

[0189] <Tackiness> The tackiness of the thermal conductive sheet was evaluated by measuring a numerical value representing the tackiness using a texture analyzer (manufactured by Eiko Seiki Co., Ltd., product name: TA.XTplus100C) at 25°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. Tackiness A: Integrated value of tackiness A (excellent): The value representing tackiness A is greater than 3.0 N·mm and less than 5.0 N·mm. B (Good): The value representing tackiness A is greater than 0.7 N·mm and less than 3.0 N·mm. C (poor): The value representing tackiness A is 0.7 N·mm or less or 5.0 N·mm or more. Tackiness B: Peak strength of tackiness A (excellent): The value representing the tackiness B is greater than 9.50N and less than 16.00N. B (good): The value representing the tackiness B is greater than 1.40N and equal to or less than 9.50N. C (bad): The value representing the tackiness B is 1.40N or less or 16.00N or more.

[0190] <30% compressive strength> The thermal conductive sheet was evaluated at 23°C using a small universal testing machine (Instron, product name: Model 5565) for its compressive modulus of 0.03 MPa, compressive modulus of 0.10 MPa, and compressive strain of 0.14 MPa. Specifically, the sample size was 15 x 15 x 2 mm. The evaluation sample was made by stacking 15 x 15 mm thermal conductive sheets to a thickness of 2 mm. 12.5 μm polyimide film was sandwiched on the top and bottom of the evaluation sample. The thickness of the polyimide film was subtracted from the analysis. The measurement method used was the crosshead travel method (with instrument compliance correction), and the 30% compressive strength was evaluated at a test speed of 1.0 mm / min.

[0191] The criteria for evaluation of 30% compressive strength are as follows: A: (Excellent) Over 2.00 MPa B: (Good) Over 1.00MPa, 2.00MPa or less C: (Poor) 1.00MPa or less.

[0192] <Compressive modulus and compressive strain at 150℃> The thermal conductive sheet was evaluated for compressive modulus of 0.03 MPa, compressive modulus of 0.10 MPa, and compressive strain of 0.14 MPa using a universal testing machine (Instron, product name: Model 1185) at 150°C. Specifically, the sample size was 14 mm in diameter. 12.5 μm polyimide films were sandwiched between the top and bottom of the evaluation sample. The thickness of the polyimide films was subtracted from the analysis. The crosshead travel method (with instrument compliance correction) was used for the measurement, and the compressive modulus and compressive strain were evaluated at a test speed of 0.1 mm / min.

[0193] The evaluation criteria for the compressive elastic modulus at 150°C and 0.03 MPa are as follows: A: (Excellent) Over 0.60, 1.20 or less B: (Good) Over 1.20, under 1.65 C: (Poor) 0.60 or less and 1.65 or more.

[0194] The evaluation criteria for the compressive elastic modulus at 150°C and 0.10 MPa are as follows: A: (Excellent) Over 1.40 MPa, less than 2.50 MPa B: (Good) 2.50 MPa or more, less than 3.40 MPa C: (Poor) 1.40 MPa or less and 3.40 MPa or more.

[0195] The evaluation criteria for compressive strain at 150°C and 0.14 MPa are as follows: A: (Excellent) Over 11.0% and under 36.0% B: (Good) More than 5.0% · Less than 11.0 C: (Poor) 5.0% or less and 36.0% or more.

[0196] <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.

[0197] 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.

[0198] <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.

[0199] 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.

[0200] <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.

[0201] <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.

[0202] 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" described in [2. Method for producing a thermal conductive sheet] above. 125.71 g of flake graphite powder (average particle size: 73 μm, thickness: 0.80 μm, aspect ratio: 91, sulfur content: 1.0 wt.% or less) as graphite particles (A); 336.76 g of a 15 wt % toluene / ethyl acetate solution of an acrylic resin (weight average molecular weight: 900,000, Tg: -60°C, hydroxyl group content as the functional group: 0.116 mmol / g, 6.5 KOH mg / g, liquid at room temperature) as an acrylic resin having functional groups (50.51 g as the acrylic resin having functional groups); As the acrylic block copolymer, 112.76 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): 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): acrylic block copolymer (16.91 g as no functional group acrylic block copolymer); · 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 of the composition solution became 30.0% by weight. Ta.

[0203] <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.

[0204] 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 are determined by the following formula: That is, it corresponds to the content relative to the total weight of the finally obtained thermally conductive sheet.

[0205] <Preparation of laminate> Each of the three primary sheets was cut into a 2.4cm x 6.4cm size and placed in a container with a volume of 2.5cm x 6.5cm x 7.5cm high. Five sheets were stacked together and pressed at room temperature at a pressure of 400kg or more until the final thickness after pressing was 6.5cm or more. The stacked sheets were then heated at 120°C for 15 minutes and pressed at a pressure of 400kg or more to obtain a 2.5cm x 6.5cm x 6.5cm laminate.

[0206] <Making a thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at a 45 degree angle to the lamination direction to produce a thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 110 μm thick, with graphite particles oriented in the thickness direction.

[0207] Examples 2 to 4 Thermally conductive sheets were produced in the same manner as in Example 1, except that the amounts of materials used in Example 1 were changed to the compounding ratios shown in Table 1. The thermally conductive sheets obtained in Examples 2 and 3 had a thickness of 110 μm, and the thermally conductive sheet obtained in Example 4 had a thickness of 75 μm.

[0208] Comparative Example 1 120 g of flake-shaped expanded graphite powder (average particle size: 250 μm, thickness: 5 μm, aspect ratio: 50, sulfur content: 1.5 wt % or more) as graphite particles (A), 54 g of acrylic ester resin (weight-average molecular weight: 1.2 million, Tg: -37°C, containing OH groups as functional groups) as organic polymer compound (B), and 66 g of aromatic condensed phosphate ester (CR-741, manufactured by Daihachi Chemical Industry Co., Ltd.) were melt-kneaded under heating.

[0209] <Preparation of primary sheet> A portion of the resulting composition (240 g) was taken, rolled into a block, sandwiched between PTFE films, and pressed using a press with a 10 cm × 20 cm tool surface at a tool pressure of 10 MPa and a tool temperature of 170°C to obtain a primary sheet with a thickness of 3 mm. This procedure was repeated to produce a large number of primary sheets.

[0210] <Preparation of laminate> The resulting primary sheets were each cut into a 2.4cm x 6.4cm size and placed in a container with an internal volume of 2.5cm x 6.5cm x 7.5cm (height). Five sheets were stacked together and pressed at room temperature at a pressure of 400kg or more until the final thickness after pressing was 6.5cm or more. The stacked sheets, which had reached a thickness of 6.5cm or more, were then heated at 120°C for 15 minutes and pressed at a pressure of 400kg or more to obtain a 2.5cm x 6.5cm x 6.5cm laminate.

[0211] <Preparation of comparative thermal conductive sheet> The cross section of the obtained laminate was sliced ​​at a 45 degree angle to the lamination direction to produce a comparative thermally conductive sheet measuring 6.5 cm long x 6.5 cm wide x 250 μm thick, with graphite particles oriented in the thickness direction.

[0212] [Evaluation of thermal conductive sheets] The physical properties of the thermally conductive sheets obtained in Examples 1 to 4 and the comparative thermally conductive sheet obtained in Comparative Example 1 were measured using the evaluation methods described above, and the results are shown in Table 1. In Table 1, the graphite particles (A), organic polymer compound (B), and plasticizer used in Examples 1 to 4 are each labeled "A." The graphite particles (A), organic polymer compound (B), and plasticizer used in Comparative Example 1 are each labeled "B." The "blending ratio" refers to the ratio of the solid weight of the material used to the solid weight of all materials excluding the solvent. For example, the graphite blending ratio of "55.0" in Example 1 indicates that the ratio of the solid weight of the graphite particles (A) used in Example 1 to the solid weight of all materials excluding the solvent used in Example 1 is 55.0 wt.%.

[0213] [Table 1]

[0214] As shown in Table 1, the thermally conductive sheets described in Examples 1 to 4 had lower thermal resistance values ​​and were significantly superior to Comparative Example 1. The thermally conductive sheets described in Examples 1 to 4 were also superior to Comparative Example 1 in terms of tackiness A and B, temporary adhesion, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling. Furthermore, the thermally conductive sheets described in Examples 1 to 4 were also superior to Comparative Example 1 in terms of graphite adhesion, sulfur content, hardness at 20°C and 70°C, 30% compressive strength, compressive modulus, and compressive strain.

[0215] The results shown in Table 1 reveal that the thermally conductive sheet according to one embodiment of the present invention has low thermal resistance, excellent tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling. It also reveals that the thermally conductive sheet has excellent properties in terms of graphite adhesion, sulfur content, hardness, compressive strength, compressive modulus, and compressive strain.

[0216] 1 shows the results of mapping the surface of the thermally conductive sheet obtained in Example 1 by SEM-EDX. 1001 shows the results of identifying carbon, and 1002 is an SEM image of the surface. In addition to carbon, nitrogen, oxygen, and silicon were also identified, but these are not shown in the figure.

[0217] FIG. 2 is an enlarged view of 1002 in FIG. 1, showing a state in which a 500 μm×50 μm area (area 1) and a 500 μm×50 μm area (area 2) are set on the surface.

[0218] 3 shows the results of mapping the surface of the thermal conductive sheet obtained in Example 3 by SEM-EDX. 1003 shows the results of identifying carbon, and 1004 is an SEM image of the surface. In addition to carbon, nitrogen, oxygen, and silicon were also identified, but these are not shown in the figure.

[0219] FIG. 4 is an enlarged view of 1004 in FIG. 3, showing a state in which a 500 μm×50 μm area (area 1) and a 500 μm×50 μm area (area 2) are set on the surface.

[0220] As shown by 1001 and 1002 in Fig. 1 and 1003 and 1004 in Fig. 3, areas that appeared darker than the surrounding area were clearly observed at approximately equal intervals in the thermally conductive sheets obtained in Examples 1 and 3. Note that the same mapping as in Figs. 1 and 3 was also performed on the thermally conductive sheets obtained in Examples 2 and 4, and similar results were obtained, but are not shown in the figures.

[0221] 5 shows the results of mapping the surface of the thermal conductive sheet according to Comparative Example 1 by SEM-EDX. 1005 shows the results of identifying carbon, and 1006 is an SEM image of the surface. In addition to carbon, nitrogen, oxygen, and silicon were also identified, but these are not shown in the figure.

[0222] FIG. 6 is an enlarged view of 1006 in FIG. 5, showing areas 1 and 2 set at positions roughly corresponding to areas 1 and 2 shown in FIG.

[0223] As shown in FIGS. 5 and 6, no area that appeared darker than the surrounding area was observed in the thermally conductive sheet according to Comparative Example 1.

[0224] As shown in Table 1, in the thermal conductive sheets of Examples 1 to 4, the carbon atom concentration in area 1 was lower than that in area 2, and the oxygen atom concentration in area 1 was higher than that in area 2. In other words, a significant difference in composition was observed between area 1 and area 2. On the other hand, as shown in Table 1, no difference in composition was observed between area 1 and area 2 in the thermal conductive sheet of Comparative Example 1.

[0225] In Table 1, the fact that (a2) is higher than (a1) corresponds to the fact that the thermally conductive sheets obtained in Examples 1 to 4 have better physical properties than the thermally conductive sheet obtained in Comparative Example 1. The same applies to (a2) / (a1) being 1.01 or more and (a2)-(a1) being 1 atom% or more. Therefore, it is believed that the thermally conductive sheet of the present invention exhibits excellent physical properties due to the difference in composition between Area 1 and Area 2, namely, the different carbon atom concentration and oxygen atom concentration between Area 1 and Area 2. [Industrial Applicability]

[0226] One embodiment of the present invention can be preferably used to manufacture a thermally conductive sheet that has low thermal resistance, excellent tackiness, initial adhesion, adhesion after high temperature exposure, and adhesion after heat cycling. Furthermore, one embodiment of the present invention can be preferably used to manufacture products that use the thermally conductive sheet, such as electronic components including wiring boards and 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, When a first region of 500 μm×50 μm and a second region of 500 μm×50 μm are set on the surface, A thermally conductive sheet, wherein at least one pair of the first region and the second region satisfies the relationship that the following (a2) is higher than the following (a1): (a1) the atomic concentration of carbon atoms contained in the first region (a2) The atomic concentration of carbon atoms contained in the second region.

2. The thermal conductive sheet according to claim 1 , wherein a value obtained by dividing (a2) by (a1) is 1.01 or more.

3. The thermal conductive sheet according to claim 1 , wherein the difference between (a2) and (a1) is 1 atom % or more.

4. The thermal conduction sheet according to claim 1, wherein (a2) is measured for one of the strips constituting the thermal conduction sheet, and (a1) is measured between the one strip and another adjacent strip.

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

6. 6. The thermal conductive sheet according to claim 1, wherein the content of the graphite particles (A) in the composition is 30 to 80% by weight, based on the total weight of the composition.

7. 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 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.

8. The method for producing a thermally conductive sheet according to claim 7 , wherein the primary sheet forming step is a step of forming the primary sheet by coating the mixture.

9. The method for producing a thermal conductive sheet according to claim 7 or 8, wherein the primary sheet forming step is a step of forming a primary sheet by applying the mixture and then drying it.

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