Method for manufacturing graphene dispersion and adhesive sheet

Abstract

The present invention provides a graphene dispersion and adhesive sheet manufacturing method that exhibits excellent thermal conductivity and retention, and does not require organic solvents. [Solution] A graphene dispersion containing an emulsion-based adhesive resin and graphene having a two-dimensional structure. The emulsion-based adhesive resin is preferably an acrylic adhesive resin. The graphene dispersion preferably has particle size distribution peaks in the range of particle diameters of 0.01 μm or more and 1 μm or less, and in the range of particle diameters of 5 μm or more and 100 μm or less, in a volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution measurement. Furthermore, the cumulative particle diameter D50 is preferably 5 μm or more and 20 μm or less.

Description

Technical Field

[0001] The present invention relates to a graphene dispersion liquid and a method for manufacturing an adhesive sheet using the same.

Background Art

[0002] Conventionally, in electronic devices such as semiconductor devices such as thermoelectric conversion devices, photoelectric conversion devices, and large-scale integrated circuits, a heat dissipation material having thermal conductivity has been used to release the generated heat. For example, as a method for efficiently dissipating heat generated from an electronic device to the outside, a heat dissipation sheet having excellent thermal conductivity is provided between the electronic device and the heat sink, or a heat dissipation grease is interposed.

[0003] As an example of the heat dissipation sheet as described above, it is disclosed in Patent Document 1. The heat dissipation sheet of Patent Document 1 is manufactured by applying a coating liquid of a heat dissipation material containing an adhesive resin, an inorganic filler, a curing agent, and a solvent to a release sheet or a base material and drying it. As the inorganic filler, plate-like inorganic particles made of aluminum, silver, copper, boron nitride, graphite, etc., and spherical inorganic particles made of silica, alumina, graphite, etc. are disclosed.

[0004] Also, as an example of the heat dissipation grease as described above, it is disclosed in Patent Document 2. In the heat dissipation grease of Patent Document 2, aluminum, boron nitride, graphite, magnesium oxide, alumina, and aluminum nitride are used as the heat conduction filler to be blended.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] However, conventional heat dissipation sheets sometimes fail to provide the desired thermal conductivity. When inorganic fillers are heavily filled into conventional heat dissipation sheets to achieve high thermal conductivity, the surface roughness increases, making it difficult for tack to develop, resulting in problems such as a loss of adhesiveness when attaching to the substrate. In addition, heavy filling of inorganic fillers reduces the flexibility of the heat dissipation sheet, preventing it from adequately conforming to and adhering to electronic devices and heat sinks, which can lead to reduced thermal conductivity between components.

[0007] On the other hand, conventional thermal greases have poor holding power, which can cause the fixing between electronic devices and heat sinks to shift.

[0008] In recent years, environmental issues have become a major concern, and when manufacturing adhesive sheets, it is preferable to use water as a solvent or diluent rather than organic solvents.

[0009] This invention has been made in view of the above circumstances, and aims to provide a graphene dispersion and adhesive sheet manufacturing method that is excellent in thermal conductivity and retention, and does not require organic solvents. [Means for solving the problem]

[0010] To achieve the above objective, firstly, the present invention provides a graphene dispersion containing an emulsion-type adhesive resin and graphene having a two-dimensional structure (Invention 1).

[0011] According to the graphene dispersion of the above invention (Invention 1), by having the above configuration, it is possible to manufacture an adhesive sheet (adhesive layer) with excellent thermal conductivity and holding power without requiring an organic solvent.

[0012] In the above invention (Invention 1), it is preferable that the emulsion-based adhesive resin is an acrylic-based adhesive resin (Invention 2).

[0013] In the above inventions (Inventions 1 and 2), it is preferable that the volume-based particle size distribution curve measured by the laser diffraction / scattering particle size distribution measurement method has particle size distribution peaks in the range of particle diameters from 0.01 μm to 1 μm, and in the range of particle diameters from 5 μm to 100 μm (Invention 3).

[0014] In the above inventions (Inventions 1 to 3), it is preferable that the cumulative particle size D50 is 5 μm or more and 20 μm or less (Invention 4).

[0015] In the above inventions (Inventions 1 to 4), it is preferable that the content of graphene having a two-dimensional structure is 5 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the adhesive resin (Invention 5).

[0016] Secondly, the present invention provides a method for producing an adhesive sheet, characterized by preparing a graphene dispersion containing an emulsion-type adhesive resin and graphene having a two-dimensional structure, applying the graphene dispersion to a desired object, and drying it to form an adhesive layer (Invention 6).

[0017] In the above invention (Invention 6), it is preferable that the emulsion-based adhesive resin is an acrylic-based adhesive resin (Invention 7).

[0018] In the above inventions (Inventions 6 and 7), it is preferable that the content of graphene having a two-dimensional structure in the graphene dispersion is 5 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the adhesive resin (Invention 8).

[0019] In the above inventions (inventions 6 to 8), it is preferable to prepare the graphene dispersion by mixing the graphene having the two-dimensional structure with the emulsion-type adhesive resin and performing a dispersion treatment, and then mixing water and performing another dispersion treatment (invention 9).

[0020] In the above inventions (Inventions 6 to 9), it is preferable that the particle size distribution of the graphene dispersion liquid has particle size distribution peaks in the range where the particle diameter is 0.01 μm or more and 1 μm or less, and in the range where the particle diameter is 5 μm or more and 100 μm or less in the volume-based particle size distribution curve measured by the laser diffraction / scattering type particle size distribution measurement method (Invention 10).

[0021] In the above inventions (Inventions 6 to 10), it is preferable that the cumulative particle diameter D50 of the graphene dispersion liquid is 5 μm or more and 20 μm or less (Invention 11).

[0022] In the above inventions (Inventions 6 to 11), it is preferable that the thermal conductivity of the adhesive layer is 0.5 W / m·K or more (Invention 12).

[0023] In the above inventions (Inventions 6 to 12), as the holding power of the adhesive sheet conforming to JIS Z0237:2009, the adherend is made of stainless steel, the pasting area is 25 mm × 25 mm, the temperature during the test is 40 °C, a load of 9.8 N is applied, and the time until the adhesive sheet falls is preferably 70,000 seconds or more (Invention 13).

Effects of the Invention

[0024] According to the method for producing the graphene dispersion liquid and the adhesive sheet according to the present invention, an adhesive sheet excellent in thermal conductivity and holding power can be produced without using an organic solvent.

Brief Description of the Drawings

[0025] [Figure 1] It is a cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view of a heat dissipation device according to an embodiment of the present invention. [Figure 3] It is a volume-based particle size distribution curve measured by the laser diffraction / scattering type particle size distribution measurement method of the graphene dispersion liquid of Example 5. [Figure 4]This is the volume-based particle size distribution curve of the graphene dispersion of Example 7, measured by the laser diffraction / scattering particle size distribution method. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below. [Graphene dispersion] A graphene dispersion according to one embodiment of the present invention contains an emulsion-type adhesive resin and graphene having a two-dimensional structure.

[0027] The graphene dispersion according to this embodiment, having the above configuration, can produce an adhesive sheet (adhesive layer) with excellent thermal conductivity and retention while eliminating the need for organic solvents.

[0028] The graphene having a two-dimensional structure in this embodiment has a planar structure that extends in two dimensions, making it easy for graphene particles to come into contact with each other and for heat conduction paths to be easily formed in the graphene dispersion. Furthermore, the graphene having a two-dimensional structure has a very high thermal conductivity in the planar direction, of about 3000 W / m·K. In addition, graphene has a low specific gravity of about 2.25 compared to conventional inorganic fillers such as metals, metal oxides, and nitride compounds, and is less prone to settling. Therefore, even if the content of the graphene having the two-dimensional structure is not large, the adhesive layer obtained using the graphene dispersion according to this embodiment will have excellent thermal conductivity.

[0029] Furthermore, since the graphene dispersion according to this embodiment contains an emulsion-based adhesive resin, an organic solvent is not required. Moreover, the adhesive obtained using the graphene dispersion according to this embodiment has higher cohesive force than an adhesive in which graphene having a two-dimensional structure is blended with an organic solvent-based adhesive resin, and thus has higher holding power even without the use of a crosslinking agent. It is believed that the emulsion-based adhesive resin has high holding power because, when dried to form a sheet, the emulsion particles fuse together to form a strong film. Due to this high holding power, the adhesive layer obtained using the graphene dispersion according to this embodiment can sufficiently fix a heat source such as an electronic device to a heat dissipation member such as a heat sink, and can suppress their displacement.

[0030] 1. Each ingredient (1) Emulsion-based adhesive resin The type of emulsion-based adhesive resin in the graphene dispersion according to this embodiment is not particularly limited, and examples include acrylic, vinyl acetate, ethylene-vinyl acetate, urethane, and rubber-based resins. Among these, acrylic adhesive resins are preferred because they easily provide the desired holding power. The acrylic adhesive resin may be either a crosslinked or non-crosslinked type, but a non-crosslinked type is preferred because the graphene dispersion according to this embodiment provides sufficient cohesive force and holding power even without a crosslinking agent.

[0031] As an acrylic adhesive resin, (meth)acrylic acid ester polymers obtained by polymerizing (meth)acrylic acid ester monomers are preferred. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the concept of "polymer" is also included in the concept of "polymer."

[0032] The (meth)acrylic acid ester polymer used as an adhesive resin preferably contains an alkyl (meth)acrylic acid ester as a monomer unit constituting the polymer. This allows the resulting graphene dispersion to exhibit good adhesive properties. The alkyl group may be linear, branched, or cyclic.

[0033] From the viewpoint of adhesiveness, alkyl (meth)acrylate esters with 1 to 20 carbon atoms in the alkyl group are preferred. Examples of alkyl (meth)acrylate esters with 1 to 20 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

[0034] Among the above, alkyl (meth)acrylates with 1 to 9 C1 of the alkyl group are more preferred, alkyl (meth)acrylates with 1 to 6 C1 of the alkyl group are particularly preferred, and alkyl (meth)acrylates with 1 to 4 C1 of the alkyl group are even more preferred, from the viewpoint of imparting good tackiness and dispersibility of graphene having a two-dimensional structure. These may be used individually or in combination of two or more.

[0035] The (meth)acrylic acid ester polymer preferably contains 40% by mass or more of alkyl (meth)acrylic acid ester as monomer units, more preferably 55% by mass or more, particularly preferably 50% by mass or more, and even more preferably 80% by mass or more, from the viewpoint of imparting good tackiness and dispersibility of graphene having a two-dimensional structure. The upper limit of the content is not particularly limited and may be 100% by mass, or 99.9% by mass or less if other monomers are blended.

[0036] The (meth)acrylic acid ester polymer used as an adhesive resin may further contain other monomers as monomers constituting the polymer. Examples of such other monomers include reactive functional group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and acrylic acid; alkoxyalkyl (meth)acrylate esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; non-crosslinked acrylamides such as acrylamide and methacrylamide; non-crosslinked (meth)acrylic acid esters having tertiary amino groups such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate; vinyl acetate; and styrene. These may be used individually or in combination of two or more.

[0037] The polymerization mode of the (meth)acrylic acid ester polymer may be random polymer or block polymer.

[0038] The weight-average molecular weight of the (meth)acrylic acid ester polymer is preferably 30,000 to 1,500,000, more preferably 50,000 to 1,000,000, and particularly preferably 100,000 to 500,000. Having the weight-average molecular weight within this range improves the dispersibility of two-dimensional graphene in the graphene dispersion and enhances its retention capacity. The weight-average molecular weights used herein are values ​​calculated on a standard polystyrene basis by gel permeation chromatography (GPC).

[0039] The graphene dispersion according to this embodiment may contain one of the above-mentioned (meth)acrylic acid ester polymers, or it may contain two or more. Furthermore, the graphene dispersion according to this embodiment may contain another (meth)acrylic acid ester polymer along with the above-mentioned (meth)acrylic acid ester polymer.

[0040] Here, the emulsion-type adhesive resin is a state in which the adhesive resin as a solid component is dispersed in water. The solid content concentration of the emulsion-type adhesive resin before compounding is preferably 5 to 80% by mass, particularly preferably 10 to 70% by mass, and even more preferably 15 to 60% by mass.

[0041] The cumulative particle size D50 of emulsion particles in an emulsion-based adhesive resin is preferably 50 to 600 nm, particularly preferably 150 to 550 nm, and even more preferably 250 to 450 nm. When the lower limit of the cumulative particle size D50 is as described above, an adhesive with thermal conductivity is more easily obtained, and when the upper limit of the cumulative particle size D50 is as described above, the emulsion particles become more stable. The average particle size of the emulsion particles can be controlled by the type and concentration of emulsifier added during polymerization, the concentration of the polymerization initiator, etc. Here, the average particle size of the emulsion particles is based on the volume-based median diameter value obtained by measuring with a laser diffraction / scattering particle size distribution analyzer.

[0042] (2) Graphene having a two-dimensional structure The graphene dispersion according to this embodiment contains graphene having a two-dimensional structure. Graphene is a two-dimensional compound consisting of a single atom, having a two-dimensional structure in which carbon atoms are regularly arranged in a hexagonal pattern. In this specification, "graphene having a two-dimensional structure" may be multilayered, and preferably has a thickness of 1 / 10 or less of the shortest length in plan view. In this specification, graphene also includes graphene produced by thinly peeling (cleaving) graphite.

[0043] As described above, graphene having a two-dimensional structure may be single-layered or multi-layered. In the case of multi-layered graphene, there are usually between 2 and 1,000 layers. The planar shape of graphene having a two-dimensional structure is not particularly limited.

[0044] The graphene having a two-dimensional structure in this embodiment is preferably graphene having a two-dimensional crystalline structure because it has superior thermal conductivity. Here, "graphene having a two-dimensional crystalline structure" refers to graphene having structural periodicity in the two-dimensional direction and having layers with a thickness of one atom, and consisting only of such layers, or having such layers stacked from two to several hundred layers by van de Waals forces. In such "graphene having a two-dimensional crystalline structure", experimentally, a clear crystal peak can be obtained from its periodic structure by wide-angle X-ray diffraction (WAXD) measurement. Furthermore, in the case of multiple stacked layers, a crystal peak attributed to the periodic structure in the stacking thickness direction can also be obtained.

[0045] When a graphene dispersion (or adhesive layer composed of it) containing graphene having a two-dimensional crystalline structure is measured by X-ray diffraction using a CuKα source (wavelength 0.15418 nm), it is preferable that peaks are detected at 2θ positions of 26.6° and 42.4°. The diffraction peaks at 2θ positions of 26.6° and 42.4° are interlayer and in-plane crystalline peaks of graphene, and the detection of peaks at these positions indicates that the graphene has a crystalline structure.

[0046] There are no particular limitations on the method for producing graphene having a two-dimensional structure, but examples include physically cleaving graphite or cleaving oxidized graphite to form a single layer (graphene oxide) and then reducing it to produce graphene (reduced graphene oxide (RGO)). Among these, graphene obtained by physically cleaving graphite is preferred because it has a good two-dimensional crystal structure and therefore superior thermal conductivity.

[0047] The average particle size of graphene having a two-dimensional structure is preferably 0.5 μm or more, more preferably 1.0 μm or more, particularly preferably 3.0 μm or more, and even more preferably 5.0 μm or more. This makes it easier for each graphene to come into contact with each other, and facilitates the formation of heat conduction paths, so that the characteristics of the two-dimensional structure function and the graphene dispersion has superior thermal conductivity. Furthermore, the average particle size of graphene having a two-dimensional structure is preferably 30 μm or less, particularly preferably 20 μm or less, and even more preferably 15 μm or less. This maintains the dispersion state in other materials such as solvents and adhesive resins, suppresses segregation which prevents the formation of heat conduction paths, and results in superior thermal conductivity.

[0048] Furthermore, the thickness of the graphene having a two-dimensional structure is preferably 500 nm or less, more preferably 300 nm or less, particularly preferably 200 nm or less, and even more preferably 100 nm or less. This ensures that the flexibility of the graphene dispersion (and the adhesive layer composed of it) is well maintained. On the other hand, the lower limit of the thickness of the graphene having a two-dimensional structure is not particularly limited, but is usually 0.7 nm or more, preferably 5.0 nm or more, particularly preferably 10 nm or more, and even more preferably 15 nm or more, from the viewpoint of thermal conductivity.

[0049] The content of graphene having a two-dimensional structure is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, particularly preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of adhesive resin. The lower limit of the graphene content is as described above, which makes it easier for each graphene to come into contact with each other and for heat conduction paths to be formed, resulting in superior thermal conductivity.

[0050] Furthermore, the content of graphene having a two-dimensional structure is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, particularly preferably 100 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of adhesive resin. In this embodiment, by using graphene having a two-dimensional structure, the desired thermal conductivity can be obtained even with a relatively small content as described above. Furthermore, as the content of the adhesive resin increases relatively, the holding power becomes even better.

[0051] (3) Various additives The graphene dispersion according to this embodiment may optionally contain crosslinking agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters, rust inhibitors, flame retardants, and the like. In addition to graphene having a two-dimensional structure, the graphene dispersion according to this embodiment may also contain conventional thermally conductive fillers such as aluminum, boron nitride, graphite, magnesium oxide, alumina, and aluminum nitride.

[0052] (4)Water The graphene dispersion according to this embodiment contains water as a dispersion medium. The solid content concentration of the graphene dispersion according to this embodiment is preferably 5 to 40% by mass, particularly preferably 10 to 35% by mass, and even more preferably 20 to 30% by mass. This allows for the maintenance of a good dispersion state and easily achieves a viscosity suitable for coating.

[0053] 2. Preparation of graphene dispersion The graphene dispersion according to this embodiment can be prepared by conventional methods. Specifically, it can be prepared by sequentially blending and mixing an emulsion-type adhesive resin, graphene having a two-dimensional structure, and optionally water, additives, etc., while subjecting them to dispersion treatment.

[0054] Preferred methods for compounding each component include (1) a method in which graphene having a two-dimensional structure is compounded with an emulsion-type adhesive resin and dispersed, and then water is compounded and dispersed; and (2) a method in which graphene having a two-dimensional structure is compounded with water and dispersed, and then an emulsion-type adhesive resin is compounded and dispersed. Among these, compounding method (1) is preferred. According to this compounding method, emulsion aggregation is less likely to occur, the graphene having a two-dimensional structure is uniformly dispersed, and the graphene is less likely to aggregate, resulting in a higher thermal conductivity of the resulting adhesive layer.

[0055] The dispersion treatment of the above mixture can be carried out using conventionally known methods, such as using known kneaders and dispersers like homogenizers, bead mills, ball mills, jet mills, dispersers, mixers, kneaders, and ultrasonic dispersers. The dispersion treatment can be carried out using a single device or a combination of two or more devices.

[0056] Among the above, it is preferable to perform the dispersion treatment using a disperser, mixer, jet mill, or ultrasonic disperser, as this suppresses the significant decrease in thermal conductivity caused by excessive crushing of graphene, suppresses the aggregation of graphene, and allows for uniform dispersion of the graphene in the mixture. When performing the dispersion treatment of the above mixture using a disperser, it is preferable to stir the mixture at a rotation speed of 500 to 5000 rpm for 1 minute to 30 minutes, and more preferably at a rotation speed of 1000 to 4000 rpm for 3 minutes to 10 minutes.

[0057] 3. Physical properties (1) Particle size distribution peak In the graphene dispersion according to this embodiment, it is preferable that the volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution measurement method has particle size distribution peaks in the range of particle diameters from 0.01 to 1 μm and in the range of particle diameters from 5 to 100 μm. It is preferable that there is no particle size distribution peak (peak B) in the range of particle diameters greater than 100 μm, but if such a particle size distribution peak is present, it is preferable that the particle size distribution peak (peak B) is lower than the particle size distribution peak (peak A) in the range of particle diameters from 5 to 100 μm. Specifically, the height of peak B is preferably 95% or less of the height of peak A, more preferably 90% or less, particularly preferably 80% or less, and even more preferably 75% or less. This ensures that the graphene having a two-dimensional structure is uniformly dispersed without aggregation, resulting in a higher thermal conductivity of the resulting adhesive layer. Such a particle size distribution can be obtained by the compounding method described in (1) above.

[0058] (2) Cumulative particle diameter D50 In the graphene dispersion according to this embodiment, the cumulative particle size D50 is preferably 5 to 20 μm, more preferably 6 to 15 μm, and particularly preferably 7 to 12 μm. This ensures that the graphene having a two-dimensional structure is uniformly dispersed, resulting in a higher thermal conductivity of the resulting adhesive layer. Such a cumulative particle size D50 can be obtained by the compounding method described in (1) above.

[0059] [Adhesive sheet] An adhesive sheet according to one embodiment of the present invention comprises at least an adhesive layer, the adhesive layer being formed using the graphene dispersion according to the above embodiment.

[0060] Figure 1 shows a specific configuration of an adhesive sheet as an example according to this embodiment. As shown in Figure 1, an adhesive sheet 1 according to one embodiment consists of two release sheets 12a and 12b, and an adhesive layer 11 sandwiched between the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. In this specification, the release surface of a release sheet refers to the surface of the release sheet that has release properties, and includes both surfaces that have undergone a release treatment and surfaces that exhibit release properties even without a release treatment.

[0061] 1. Each component 1-1. Adhesive layer The adhesive layer 11 in this embodiment is formed from the graphene dispersion according to the above-described embodiment.

[0062] 1-2. Release sheet The release sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

[0063] Examples of release sheets 12a and 12b include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. Crosslinked films of these may also be used. Furthermore, laminated films of these may also be used.

[0064] It is preferable that the release surfaces of the above-mentioned release sheets 12a and 12b (especially the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of release agents used in the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax-based release agents. Of the release sheets 12a and 12b, one release sheet may be a heavy-release type release sheet with a high release force, and the other release sheet may be a light-release type release sheet with a low release force.

[0065] There are no particular restrictions on the thickness of the release sheets 12a and 12b, but they are usually around 20 to 150 μm.

[0066] 2. Manufacturing of adhesive sheets To manufacture the adhesive sheet according to this embodiment, a graphene dispersion containing an emulsion-based adhesive resin and graphene having a two-dimensional structure is prepared, and the graphene dispersion is applied to a desired object (e.g., a release sheet or a substrate) and dried to form an adhesive layer. The method for preparing the graphene dispersion is as described above.

[0067] One example of manufacturing the adhesive sheet 1 involves coating the release surface of one release sheet 12a (or 12b) with a graphene dispersion. Next, the coating is dried (heated) to form an adhesive layer 11, and the release surface of the other release sheet 12b (or 12a) is placed on top of the adhesive layer 11.

[0068] Methods for coating with graphene dispersions include, for example, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0069] When the graphene dispersion is dried (heated), the water, which is the dispersion medium, evaporates, and an adhesive layer is formed. The drying conditions are preferably 80 to 120°C for 0.5 to 5 minutes, and particularly preferably 90 to 100°C for 1 to 2 minutes.

[0070] In contrast, conventional carbon fibers such as carbon nanotubes and carbon nanofibers, which are typical heat dissipation materials, have anisotropy in the longitudinal direction (one-dimensional) of the fiber. Therefore, in order to exhibit thermal conductivity, it was necessary to control the orientation by using them in combination with other particulate fillers or to align the orientation of the carbon fibers using a powerful magnetic field generator. In contrast, although graphene used in this embodiment is an anisotropic material, it has a two-dimensional planar structure, making it easy for graphene particles to come into contact with each other. As a result, the adhesive layer 11 obtained can exhibit excellent thermal conductivity without the need for special orientation treatment.

[0071] 3.Physical properties etc. (1) Thickness of the adhesive layer The thickness of the adhesive layer 11 (measured in accordance with JIS K7130) is preferably 2 μm or more as a lower limit, more preferably 5 μm or more, particularly preferably 10 μm or more, and even more preferably 20 μm or more, from the viewpoint of adhesiveness.

[0072] Furthermore, from the viewpoint of thermal conductivity, the thickness of the adhesive layer 11 is preferably 500 μm or less, more preferably 300 μm or less, particularly preferably 100 μm or less, and even more preferably 50 μm or less.

[0073] Here, when performing the orientation treatment described above on conventional carbon fibers such as carbon nanotubes and carbon nanofibers, space is required for the carbon fibers to move freely. To achieve this, when oriented in the direction of the heat dissipation sheet's film thickness, it is necessary to ensure a film thickness equal to or greater than the filler length, and generally, the film thickness was designed to be 0.5 to 2.0 mm. Furthermore, in methods of manufacturing heat dissipation sheets after orientation treatment, cutting is performed using slicers such as cutters and lasers, and due to the mechanism of the slicers, the sheet film thickness had to be 1 mm or more in order to manufacture stably.

[0074] In contrast, graphene, which has a two-dimensional structure, does not require special orientation treatment as described above. Therefore, the adhesive layer 11 in this embodiment can be formed even with a thin thickness as described above, and it is easy to make it a thicker film by lamination. In other words, in this embodiment, the thickness of the adhesive layer 11 can be easily controlled.

[0075] (2) Thermal conductivity The thermal conductivity of the adhesive layer 11 is preferably 0.1 W / m·K or higher, more preferably 0.2 W / m·K or higher, particularly preferably 1.5 W / m·K or higher, and even more preferably 2 W / m·K or higher. This means that the adhesive sheet 1 has excellent thermal conductivity. The adhesive sheet 1 according to this embodiment can achieve such high thermal conductivity by using graphene having a two-dimensional structure. The method for measuring thermal conductivity in this specification is as shown in the test examples described later.

[0076] (3) Holding power In this embodiment, the adhesive sheet 1, in accordance with JIS Z0237:2009, preferably has a holding power of 70,000 seconds or more when the adherend is stainless steel, the bonding area is 25 mm x 25 mm, the test temperature is 40°C, and a load of 9.8 N is applied. The adhesive layer 11 formed using the graphene dispersion in this embodiment has good cohesive force and can exhibit excellent holding power as described above.

[0077] [Heat dissipation device] As shown in Figure 2, the heat dissipation device 3 according to one embodiment of the present invention comprises a heat-generating member 31, a heat-transferring member 32, and an adhesive layer 11 provided between the heat-generating member 31 and the heat-transferring member 32.

[0078] In this embodiment, the adhesive layer 11 is preferably formed from the graphene dispersion according to the above-described embodiment, or is the adhesive layer 11 of the adhesive sheet 1 according to the above-described embodiment. The heat-generating member 31 and the heat-transferring member 32 are bonded together via the adhesive layer 11. Because this adhesive layer 11 contains graphene having a two-dimensional structure, it has excellent thermal conductivity and flexibly conforms to and adheres to the heat-generating member 31 and the heat-transferring member 32. Therefore, the heat generated by the heat-generating member 31 is efficiently conducted to the heat-transferring member 32 through the adhesive layer 11 and efficiently dissipated to the outside from the heat-transferring member 32.

[0079] In this embodiment, the heat-generating member 31 is a member that generates heat when performing a predetermined function, but whose temperature rise is required to be suppressed, or a member whose heat flow is required to be controlled in a specific direction. Examples of such heat-generating members 31 include semiconductor devices such as thermoelectric conversion devices, photoelectric conversion devices, and large-scale integrated circuits, electronic devices such as LED light-emitting elements, optical pickups, and power transistors, as well as various electronic devices such as mobile terminals and wearable terminals, batteries, motors, and engines.

[0080] In this embodiment, the heat transfer member 32 is a member that dissipates the heat it has received, or a member that transfers the heat it has received to another member. The heat transfer member 32 is preferably made of a material with high thermal conductivity, such as metals like aluminum, stainless steel, or copper, or of the form of graphite or carbon nanofiber. The form of the heat transfer member 32 is not particularly limited and may be any of the following: a substrate, a housing, a heat sink, a heat spreader, etc.

[0081] To manufacture the heat dissipation device 3, for example, one release sheet 12a (or 12b) is peeled off from the adhesive sheet 1, and one side of the exposed adhesive layer 11 is attached to the heat-generating member 31. Next, the other release sheet 12b (or 12a) is peeled off from the adhesive layer 11 provided on the heat-generating member 31, and the other side of the exposed adhesive layer 11 is attached to the heat-transferring member 32. Alternatively, one side of the adhesive layer 11 may be attached to the heat-transferring member 32, and then the heat-generating member 31 may be attached to the other side of the adhesive layer 11.

[0082] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it. Accordingly, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0083] For example, the release sheet 12a or release sheet 12b laminated on the adhesive sheet 1 in Figure 1 may be omitted.

[0084] Furthermore, the adhesive sheet according to the present invention may be formed by laminating a desired substrate, an adhesive layer 11, and a release sheet 12a (or 12b) in that order. The material constituting the substrate is not particularly limited and includes, for example, resin films, nonwoven fabrics, paper, graphite sheets, graphene sheets, metal substrates, etc., with resin films being commonly used. As the resin material constituting the resin film, for example, polyamides such as polyester, polyolefin, nylon 6, nylon 66, and partially aromatic polyamides, polyimides, polyamide-imides, polyetheretherketone, polyethersulfone, polyphenylene sulfide, polycarbonate, polyurethane, fluororesins such as ethylene-vinyl acetate copolymer and polytetrafluoroethylene, acrylic resins, polyacrylates, polystyrene, polyvinyl chloride, and polyvinylidene chloride can be used. The above resin film may be formed using a resin material containing one of these resins alone, or it may be formed using a resin material blended with two or more of these resins. The above resin film may be unstretched or stretched (for example, uniaxially stretched or biaxially stretched).

[0085] Furthermore, the shapes of the heat-generating element 31 and the heat-transferring element 32 in the thermal device 3 are not limited to those shown in Figure 2, but may be of various shapes. [Examples]

[0086] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0087] [Example 1] 100 parts by mass of emulsion-type adhesive resin (acrylic; manufactured by Toyo Chem Co., Ltd., product name "BPW6401") was mixed with 28 parts by mass (solids) of graphene having a two-dimensional structure (manufactured by ADEKA Corporation, product name "CNS-1A1") and subjected to dispersion treatment. Next, 203 parts by mass of water as a dispersion medium was mixed and subjected to dispersion treatment to obtain a graphene dispersion. The above dispersion treatments were carried out using a rotation-orbit mixer (manufactured by Thinky Co., Ltd., product name "ARE-400TWIN"), stirring for 5 minutes at a rotation speed of 1600 rpm and an orbital speed of 1600 rpm. The solids concentration of the obtained graphene dispersion was 27% by mass.

[0088] Further details regarding the emulsion-based adhesive resin and the graphene having the two-dimensional structure are as follows. • Emulsion-based adhesive resin: Manufactured by Toyo Chem Co., Ltd., product name "BPW6401", acrylic ester copolymer, solids content 57-59% by mass, cumulative particle size D50: approximately 400 nm • Graphene with a two-dimensional structure: ADEKA Corporation, product name "CNS-1A1", two-dimensional crystalline structure, average grain size 12 μm, thickness less than 50 nm, Raman peak intensity ratio D / G = 0.1, peaks detected at 2θ positions of 26.6° and 42.4° when measured by X-ray diffraction using a CuKα source (wavelength 0.15418 nm).

[0089] The obtained graphene dispersion was applied using an applicator to the release surface of a release film (Lintec Corporation, product name "SP-PET3811(S)"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent. The dispersion was then heated at 100°C for 2 minutes to dry and form an adhesive layer. Subsequently, the release surface of another release film (Lintec Corporation, product name "SP-PET381031"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent, was bonded to this adhesive layer to create an adhesive sheet (release film / adhesive layer / release film) with an adhesive layer thickness of 30 μm.

[0090] [Examples 2-5] An adhesive sheet was prepared in the same manner as in Example 1, except that the amount of graphene with a two-dimensional structure and the amount of water were changed as shown in Table 1.

[0091] [Example 6] 48 parts by mass of two-dimensional graphene (ADEKA Corporation, product name "CNS-1A1") were mixed with 122 parts by mass of water as a dispersion medium and subjected to dispersion treatment. Next, 100 parts by mass of emulsion-type adhesive resin (acrylic type; Toyo Chem Co., Ltd., product name "BPW6401") were mixed and subjected to dispersion treatment to obtain a graphene dispersion. The above dispersion treatments were carried out using a rotation-orbit mixer (Thinky Co., Ltd., product name "ARE-400TWIN"), stirring for 5 minutes at a rotation speed of 1600 rpm and an orbital speed of 1600 rpm. The solid content concentration of the obtained graphene dispersion was 40% by mass.

[0092] Using the obtained graphene dispersion, an adhesive sheet was prepared in the same manner as in Example 1.

[0093] [Example 7] An adhesive sheet was prepared in the same manner as in Example 6, except that the amount of water used was changed as shown in Table 1.

[0094] Here, Figure 3 shows the volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution analysis (using the "Mastersizer 3000" manufactured by Malvern Panalytical, the same name used throughout this specification) for the graphene dispersion prepared in Example 5. The cumulative particle size D50 of this graphene dispersion was 9.34 μm. Furthermore, Figure 4 shows the volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution analysis for the graphene dispersion prepared in Example 7. The cumulative particle size D50 of this graphene dispersion was 12.9 μm.

[0095] [Comparative Example 1] An acrylic acid ester polymer was prepared by copolymerizing 80 parts by mass of 2-ethylhexyl acrylate and 20 parts by mass of 2-hydroxyethyl acrylate using a solution polymerization method.

[0096] 100 parts by mass (solid content) of the acrylic ester polymer obtained above was mixed with 83 parts by mass of graphene having a two-dimensional structure (manufactured by ADEKA, product name "CNS-1A1"), thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition.

[0097] The obtained adhesive composition coating solution was applied using an applicator to the release surface of a release film (Lintec Corporation, product name "SP-PET3811(S)"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent. The solution was then heated at 100°C for 2 minutes to dry and form an adhesive layer. Subsequently, the release surface of another release film (Lintec Corporation, product name "SP-PET381031"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent, was bonded to this adhesive layer to create an adhesive sheet (release film / adhesive layer / release film) with an adhesive layer thickness of 30 μm.

[0098] [Comparative Example 2] 100 parts by mass of latex resin (SBR type; manufactured by Nippon A&L Co., Ltd., product name "SR-100") was mixed with 52 parts by mass (solid content concentration) of graphene having a two-dimensional structure (manufactured by ADEKA Corporation, product name "CNS-1A1"), and then 256 parts by mass of water as a dispersion medium was added. Then, the mixture was dispersed using a disperser (manufactured by Primix Corporation, product name "Robomix") by stirring at 3000 rpm for 30 minutes to obtain a graphene dispersion. The solid content concentration of this graphene dispersion was 25% by mass.

[0099] Using the obtained graphene dispersion, an adhesive sheet was prepared in the same manner as in Example 1.

[0100] [Comparative Example 3] An emulsion-type adhesive resin (acrylic; manufactured by Toyo Chem Co., Ltd., product name "BPW6401") was applied with an applicator to the release surface of a release film (manufactured by Lintec Corporation, product name "SP-PET3811(S)"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent. The film was then heated at 100°C for 2 minutes to dry and form an adhesive layer. Subsequently, the release surface of another release film (manufactured by Lintec Corporation, product name "SP-PET381031"), which had one side of a polyethylene terephthalate film released with a silicone-based release agent, was laminated to this adhesive layer to produce an adhesive sheet (release film / adhesive layer / release film) with an adhesive layer thickness of 30 μm.

[0101] [Test Example 1] <Measurement of Thermal Conductivity> From the adhesive layers of the adhesive sheets prepared in the examples and comparative examples, square samples with sides of 5 mm were obtained. Using a thermal diffusivity / thermal conductivity measuring device (ai-phase mobile, manufactured by i-phase Corporation), the thermal conductivity (W / m·K) of the above samples (adhesive layers) was measured in accordance with ISO 22007-3 at an environment of 23°C and 50% RH. The results are shown in Table 1.

[0102] [Test Example 2] <Measurement of Holding Power> The adhesive layer of the adhesive sheets prepared in the examples and comparative examples was attached to a stainless steel (SUS) plate (SUS304, 360 grit polished) as the adherend. The area of ​​the adhesive layer attached to the stainless steel plate was 25 mm x 25 mm. The stainless steel plate with the adhesive sheet attached was left to stand for 15 minutes at 23°C and 50% RH, then placed in a creep tester and left to stand for another 15 minutes. Next, a load of 9.8 N was applied to the adhesive sheet at 40°C, and the time until the adhesive sheet fell (maximum 70,000 seconds) was measured according to the holding force measurement method of JIS Z0237:2009, and this was defined as the holding force (seconds) of the adhesive layer. The results are shown in Table 1.

[0103] [Test Example 3] <Evaluation of Adhesion> One of the release films from the adhesive sheets prepared in the examples and comparative examples was peeled off, and the exposed adhesive layer was attached to the easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET A4100", thickness: 100 μm) having an easy-adhesion layer. The resulting laminate was cut into 25 mm wide and 250 mm long pieces, which were used as measurement samples.

[0104] The other release film is peeled off from the above measurement sample, and the exposed adhesive layer is... The adhesive sheet was attached to the polished surface of a 600-grit stainless steel (SUS) plate and pressed down by rolling a 2kg rubber roller back and forth once. After standing for 24 hours in an environment of 23°C and 50%RH, the adhesive sheet was peeled off the SUS plate using a tensile testing machine (Orientec, Tensilon) under conditions of a peeling speed of 300 mm / min and a peeling angle of 180 degrees, and the adhesive strength (mN / 25mm) was measured. Measurements under conditions other than those described here were performed in accordance with JIS Z0237:2009.

[0105] Based on the adhesive strength measured above, the adhesive strength was evaluated. Specifically, the adhesive strength of Comparative Example 1, which used an acrylic ester polymer copolymerized by solution polymerization, was used as the baseline. A higher adhesive strength was marked with "○" and a lower adhesive strength with "×". The results are shown in Table 1.

[0106] [Table 1]

[0107] As can be seen from Table 1, the adhesive sheets produced in the examples had excellent thermal conductivity and holding power. Comparing Example 5 and Example 7, in which the mixing order of the emulsion-based adhesive resin and graphene was changed, Example 5 tended to have higher thermal conductivity. From the volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution measurement, Example 5 had a smaller particle size distribution peak in the range above 100 μm, confirming that emulsion aggregation is less likely to occur when mixing in the order of emulsion-based adhesive resin → graphene → water. [Industrial applicability]

[0108] The graphene dispersion and adhesive sheet according to the present invention can be suitably used, for example, to cool a heat-generating electronic device by interposing it between the electronic device and a heat-dissipating substrate or heat sink. [Explanation of symbols]

[0109] 1…Adhesive sheet 11…Adhesive layer 12a, 12b… Release sheets 3…Heat dissipation device 11…Adhesive layer 31… Heat-generating components 32… Heat transfer components

Claims

1. Emulsion-based adhesive resin, Graphene having a two-dimensional structure, A graphene dispersion containing [a specific ingredient / liquid].

2. The graphene dispersion according to claim 1, characterized in that the emulsion-based adhesive resin is an acrylic-based adhesive resin.

3. The graphene dispersion according to claim 1, characterized in that, in a volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution measurement, the graphene dispersion has particle size distribution peaks in the range of particle diameters of 0.01 μm or more and 1 μm or less, and in the range of particle diameters of 5 μm or more and 100 μm or less.

4. The graphene dispersion according to claim 1, characterized in that the cumulative particle size D50 is 5 μm or more and 20 μm or less.

5. The graphene dispersion according to claim 1, characterized in that the content of the graphene having the two-dimensional structure is 5 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the adhesive resin.

6. A graphene dispersion containing an emulsion-type adhesive resin and graphene having a two-dimensional structure is prepared. The graphene dispersion is applied to the desired object and dried to form an adhesive layer. A method for manufacturing an adhesive sheet, characterized by the following:

7. The method for producing an adhesive sheet according to claim 6, characterized in that the emulsion-based adhesive resin is an acrylic-based adhesive resin.

8. The method for producing an adhesive sheet according to claim 6, characterized in that the content of the graphene having a two-dimensional structure in the graphene dispersion is 5 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the adhesive resin.

9. The method for producing an adhesive sheet according to claim 6, characterized in that the graphene dispersion is prepared by mixing the graphene having the two-dimensional structure with the emulsion-based adhesive resin and performing a dispersion treatment, and then mixing water and performing another dispersion treatment.

10. The method for producing an adhesive sheet according to claim 6, characterized in that the particle size distribution of the graphene dispersion has particle size distribution peaks in the range of particle diameters of 0.01 μm or more and 1 μm or less, and in the range of particle diameters of 5 μm or more and 100 μm or less, in a volume-based particle size distribution curve measured by laser diffraction / scattering particle size distribution measurement method.

11. The method for producing an adhesive sheet according to claim 6, characterized in that the cumulative particle size D50 of the graphene dispersion is 5 μm or more and 20 μm or less.

12. The method for manufacturing an adhesive sheet according to claim 6, characterized in that the thermal conductivity of the adhesive layer is 0.5 W / m·K or more.

13. The method for manufacturing an adhesive sheet according to claim 6, characterized in that, as the holding force of the adhesive sheet in accordance with JIS Z0237:2009, the adherend is stainless steel, the bonding area is 25 mm x 25 mm, the test temperature is 40°C, and a load of 9.8 N is applied, the time until the adhesive sheet falls is 70,000 seconds or more.

Images