JP6705329B2 - Composite sheet and thermocompression bonding method - Google Patents

Description

The present invention relates to a composite sheet and a thermocompression bonding method, and more particularly to a composite sheet containing a fluororesin and a carbon material and a thermocompression bonding method using the composite sheet.

In recent years, a sheet-shaped member (composite sheet) made of a composite material having functionality such as thermal conductivity has been used for various purposes.

On the other hand, a thermocompression bonding method is known as a method of joining and adhering the same or different materials. In the thermocompression bonding method, for example, the materials can be heat-welded by applying heat and pressure at a temperature equal to or lower than the melting point of the material to be joined/bonded. It is also possible to apply a low melting point adhesive between the materials to be joined/bonded and apply heat and pressure at a temperature equal to or lower than the melting point of the materials to heat-weld the materials with high adhesion. .. Then, in the thermocompression bonding method, normally, between the heating device and the fixture, the materials optionally sandwiched with an adhesive are laminated and arranged, and heating and pressurization are performed from the heating device side facing one material. While performing, the adhesive is melted while transferring heat to the fixing device side where the other material is fixed, and the materials are heat-welded with high adhesion.

Here, the fixture is made of metal, and when the material and the metal fixture are directly contacted with each other, heat is favorably transferred from the material to the fixture due to the high thermal conductivity that metal usually has, for example, There is an advantage that it is possible to prevent the material from being discolored and melted due to excessive heat during thermocompression bonding. However, for example, when the hardness of the material is lower than that of the metal and vibration energy such as ultrasonic waves is used as the heat source of the heating device, generally, when the material and the metal fixture are directly contacted with each other, the material has higher hardness. Repeated collisions with the fixtures it has during thermocompression bonding can cause scratches or other damage to the surface of the material. Therefore, in order to reduce such damage to the material, a thermocompression bonding sheet may be interposed between the material and the fixture. A resin material such as plastic is usually preferably used as a material having a hardness lower than that of metal.
On the other hand, when the thermal conductivity of the thermocompression bonding sheet itself is low, heat is not sufficiently radiated from the material to the fixture through the thermocompression bonding sheet, and discoloration or melting may occur on the surface of the material. is there.
Therefore, the thermocompression bonding sheet used for thermocompression bonding of materials may have high thermal conductivity and appropriate hardness that can reduce the collision between the material and the fixture while promoting heat dissipation from the materials. It has been demanded. Further, the thermocompression bonding sheet is also required to have excellent durability capable of withstanding repeated thermocompression bonding. When materials are thermocompression-bonded using such a thermocompression-bonding sheet, it is also required to prevent scratches on the surface of the materials and perform good thermocompression bonding.

For example, in Patent Document 1, as the thermocompression bonding sheet, there is a heat conductive filler composed of a component (A) made of organopolysiloxane and a ground powder of metallic silicon, a ground powder of crystalline silicon dioxide or a ground powder of aluminum oxide ( It proposes a silicone rubber sheet containing component B) and component (C) made of carbon black powder for imparting heat resistance and antistatic properties. The silicone rubber sheet of Patent Document 1 exhibits high strength and thermal conductivity of about 0.8 W/m·K.
Further, from the viewpoint of increasing the thermal conductivity of the sheet, Patent Documents 2 to 3 disclose a thermal conductive sheet containing an acrylic acid ester copolymer resin, scale-like expanded graphite powder and the like. And in the heat conductive sheet of patent documents 2-3, heat conductivity is raised, adjusting Asker C hardness.
Further, from the viewpoint of enhancing the durability of the sheet, for example, as disclosed in Patent Document 4, in a heat conductive sheet containing flake graphite and a binder resin, it is possible to use polytetrafluoroethylene as the binder resin. Conceivable.

Japanese Patent No. 5058938 Japanese Patent No. 5381102 Japanese Patent No. 5316254 Japanese Patent No. 5185582

However, from the viewpoint of promoting heat dissipation while suppressing damage caused on the material surface when applying vibration and heating, such as thermocompression bonding using ultrasonic waves, the hardness and heat of the silicone rubber sheet of Patent Document 1 There was room for improvement in conductivity.
Moreover, in the heat conductive sheets of Patent Documents 2 to 3, there is room for improvement in durability when the heat conductive sheet is used as, for example, a thermocompression bonding sheet.
Further, the heat conductive sheet of Patent Document 4 using polytetrafluoroethylene generally has very high hardness, and there is room for improvement in terms of achieving an appropriate hardness that can mitigate the collision between the material and the fixture. there were.

Therefore, an object of the present invention is to provide a composite sheet which has appropriate hardness, high thermal conductivity and excellent durability, and is useful for thermocompression bonding.
Another object of the present invention is to provide a thermocompression bonding method which is excellent in the scratch resistance of the surface of the material to be thermocompression bonded.

The present inventors have earnestly studied to achieve the above object. Then, the present inventors produce a composite sheet having a predetermined hardness and thermal conductivity using a predetermined resin and a carbon material, thereby arranging appropriate hardness, high thermal conductivity, and excellent durability in parallel. , It was found that a composite sheet useful for thermocompression bonding can be obtained. Further, the present inventors have found that by using such a composite sheet arranged at a predetermined position, it is possible to satisfactorily thermocompression-bond materials together while preventing scratches on the surface of the material. Completed the invention.

That is, an object of the present invention is to advantageously solve the above-mentioned problems, and a composite sheet of the present invention is a sheet containing a fluororesin and a carbon material, and has an Asker C hardness of more than 40 at 25°C. It is 70 or less, and the thermal conductivity in the thickness direction is 15 W/m·K or more. As described above, when the composite sheet contains the fluororesin and the carbon material and has the hardness within the above-mentioned predetermined range and the thermal conductivity equal to or more than the above lower limit, it exhibits appropriate hardness, high thermal conductivity and excellent durability. However, it can be favorably used in thermocompression bonding.
In the present invention, "Asker C hardness" (hereinafter sometimes simply referred to as "hardness") is based on the Asker C method of the Japan Rubber Association standard (SRIS 0101), and the temperature is measured using a hardness meter. It can be measured at 25°C.
Further, in the present invention, the “thermal conductivity” can be measured by the method described in the examples of the present specification.

Moreover, the composite sheet of the present invention preferably has a thickness of less than 1.3 mm. If the thickness is less than the above upper limit, the deformation amount of the composite sheet against pressure is limited, so that the strength against pressure is exhibited, and for example, the composite sheet can be better used as a thermocompression-bonding sheet. Is.

Further, in the composite sheet of the present invention, it is preferable that the carbon material contains a particulate carbon material. This is because if the composite sheet contains the particulate carbon material, the composite sheet will have better hardness and thermal conductivity, and can be used more favorably during thermocompression bonding.
In the present invention, the “particulate carbon material” refers to a carbon material having an aspect ratio (major axis/minor axis) of 1 or more and 10 or less. Further, the "aspect ratio of the particulate carbon material" is obtained by observing a cross section in the thickness direction of the composite sheet with a SEM (scanning electron microscope), and regarding any 50 particulate carbon materials, the maximum diameter (major axis), It can be determined by measuring the particle diameter (minor axis) in the direction orthogonal to the maximum diameter and calculating the average value of the ratio of the major axis and the minor axis (major axis/minor axis).

Further, in the composite sheet of the present invention, the carbon material preferably contains a fibrous carbon material. This is because if the composite sheet contains the fibrous carbon material, the hardness and thermal conductivity of the composite sheet will be further improved, and the composite sheet can be used even better during thermocompression bonding. Further, when the particulate carbon material and the fibrous carbon material are used together as the carbon material, it is possible to prevent the particulate carbon material from falling off the composite sheet.
In the present invention, the “fibrous carbon material” refers to a carbon material having an aspect ratio (major axis/minor axis) of more than 10. The “aspect ratio of fibrous carbon material” is the maximum diameter (major axis) of any 50 fibrous carbon materials obtained by observing a cross section in the thickness direction of the composite sheet with a SEM (scanning electron microscope). It can be determined by measuring the particle diameter (minor axis) in the direction orthogonal to the maximum diameter and calculating the average value of the ratio of the major axis and the minor axis (major axis/minor axis).

Further, in the composite sheet of the present invention, the content ratio of the carbon material is preferably 70% by mass or less based on 100% by mass of the total content of the fluororesin and the carbon material. This is because if the content ratio of the carbon material in the composite sheet is at most the above upper limit, the flexibility can be more easily adjusted by imparting flexibility to the composite sheet, and the composite sheet can be used more favorably during thermocompression bonding. ..

Further, the present invention is intended to advantageously solve the above problems, the thermocompression bonding method of the present invention, between the heating device and the fixture, the first material and the second material A method of thermocompression bonding, step A in which a laminate having the first material and the second material and any one of the composite sheets described above are arranged between the heating device and the fixture, Heating the laminated body by using the heating device, and thermocompression-bonding the first material and the second material, and in the step A, the composite sheet is the fixture and the It is characterized in that it is interposed between the laminates. As described above, when the steps A and B are performed while the composite sheet is arranged at a predetermined position, the hardness of the material to be thermocompression bonded is lower than the hardness of the fixing tool, and the material is vibrated and heated. Even in the case where the materials are present, the materials can be satisfactorily thermocompression bonded while realizing excellent scratch resistance of the material surfaces.

Further, in the thermocompression bonding method of the present invention, it is preferable that the heating device is an ultrasonic oscillator. This is because if ultrasonic waves are used as a heat source in thermocompression bonding, heat can be efficiently transmitted to the material that is the object to be thermocompressed, and the materials can be thermocompression bonded better.

Advantageous Effects of Invention According to the present invention, it is possible to provide a composite sheet that has appropriate hardness, high thermal conductivity and excellent durability, and is useful for thermocompression bonding.
Further, according to the present invention, it is possible to provide a thermocompression bonding method which is excellent in the scratch resistance of the surface of the material to be thermocompression bonded.

Hereinafter, embodiments of the present invention will be described in detail.
The composite sheet of the present invention can be used as a thermocompression bonding sheet to be interposed between a material and a fixture in a thermocompression bonding method in which materials are joined and adhered to each other using a heating device and a fixture. Specifically, the composite sheet of the present invention is, for example, between the heating device and the fixture, when the first material and the second material are thermocompression-bonded via an optional adhesive, the heating device and It can be preferably used as a thermocompression-bonding sheet interposed between a fixture and a laminate having a first material, an optional adhesive and a second material, which is arranged between the fixtures. .. In other words, the composite sheet of the present invention can be used in the structure of, for example, a heating device/a laminate having a first material, a second material and an optional adhesive/a sheet for thermocompression bonding/a fixture, It can be suitably used as a pressure-bonding sheet. The composite sheet of the present invention is not limited to the above use. For example, the composite sheet of the present invention can be used as a heat conductive sheet arranged between a heat source such as a semiconductor element and a heat dissipation member such as a heat sink.
The composite sheet of the present invention is not particularly limited as long as it contains a fluororesin and a carbon material and has a predetermined hardness and thermal conductivity, and can be manufactured by any method.
Further, the thermocompression bonding method of the present invention can be carried out, for example, by interposing the composite sheet of the present invention between the material that is the object to be thermocompression bonded and the fixture.

(Composite sheet)
The composite sheet of the present invention is characterized by containing a fluororesin and a carbon material and having a hardness within a predetermined range and a thermal conductivity of a predetermined value or more in the thickness direction. If the composite sheet does not contain a fluororesin, for example, the repeated durability when the composite sheet is used as a thermocompression bonding sheet cannot be sufficiently obtained. If the composite sheet does not contain a carbon material and/or does not have a thermal conductivity higher than a predetermined value, the composite sheet cannot exhibit excellent heat dissipation, and for example, the composite sheet is used for thermocompression bonding. When it is used as a sheet, it is impossible to improve heat dissipation from the material that is the object to be heat-pressed and prevent discoloration of the material surface. Furthermore, if the hardness of the composite sheet is too high and exceeds a predetermined value, for example, when it is used as a thermocompression-bonding sheet when thermocompressing materials having a hardness lower than that of the fixture by heating with vibration, the composite sheet is fixed. It is not possible to prevent damage to the material surface due to collision with the tool. In addition, if the hardness of the composite sheet is too low and lower than a predetermined value, the composite sheet becomes excessively soft, and for example, when the composite sheet is used as a thermocompression-bonding sheet, the composite sheet is formed on the surface of the material to be thermocompression bonded. There is a risk that it will melt and adhere to contaminate.

<Fluorine resin>
Here, the fluororesin is not particularly limited, and examples thereof include a thermoplastic fluororesin that is solid under normal temperature and normal pressure, such as an elastomer obtained by polymerizing a fluorine-containing monomer; a thermoplastic fluororesin that is liquid under normal temperature and normal pressure. Resin; and the like. Also, these fluororesins may be used alone or in combination of two or more, but while ensuring durability, impart flexibility to the composite sheet to obtain a more appropriate hardness. From the viewpoint of adjusting, it is preferable to use a liquid thermoplastic fluororesin at least under normal temperature and normal pressure, and it is more preferable to use a solid thermoplastic fluororesin under normal temperature and normal pressure and a liquid thermoplastic fluororesin under normal temperature and normal pressure in combination. preferable.
In addition, in this specification, "normal temperature" refers to 23° C., and "normal pressure" refers to 1 atm (absolute pressure).
In addition, in the present invention, rubber and elastomer are included in “resin”.

[Thermoplastic fluororesin that is solid under normal temperature and pressure]
More specifically, as the thermoplastic fluororesin that is solid at room temperature and atmospheric pressure, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene -Ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer Coalescence, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, acrylic modified product of polytetrafluoroethylene, ester modified product of polytetrafluoroethylene, epoxy modified product of polytetrafluoroethylene and silane of polytetrafluoroethylene Examples include modified products.
Among these, from the viewpoint of processability, as the solid thermoplastic fluororesin at room temperature and normal pressure, polytetrafluoroethylene, an acrylic modified product of polytetrafluoroethylene, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene A fluoride-hexafluoropropylene-tetrafluoroethylene copolymer is preferred. Moreover, these may be used individually by 1 type and may use 2 or more types together.

Examples of commercially available thermoplastic fluororesin that is solid at room temperature and atmospheric pressure include Daiel (registered trademark) G-300 series/G-700 series/G-7000 series (polyol vulcanization/vinylidene) manufactured by Daikin Industries, Ltd. Fluoride-hexafluoropropylene binary copolymer), DAIEL G-550 series/G-600 series (polyol vulcanization/vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer), DAIEL G -800 series (peroxide vulcanization/vinylidene fluoride-hexafluoropropylene binary copolymer), Daier G-900 series (peroxide vulcanization/vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer) Polymer); KYNAR (registered trademark) series (vinylidene fluoride based fluororesin), KYNAR FLEX (registered trademark) series (vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer) manufactured by ALKEMA; And so on.

[Thermoplastic fluororesin that is liquid at normal temperature and pressure]
Examples of commercially available thermoplastic fluororesins that are liquid at room temperature and normal pressure include Daiel (registered trademark) G-101 (binary fluororubber) manufactured by Daikin Industries, Ltd., and the like.
The viscosity of the liquid thermoplastic fluororesin at room temperature and normal pressure is not particularly limited in terms of good kneadability, fluidity, crosslinking reactivity, and excellent moldability. , 500 mPa·s to 30,000 mPa·s, and more preferably 550 mPa·s to 25,000 mPa·s.
In the present specification, the “viscosity” can be measured using a viscometer under the conditions of a temperature of 105° C. and an atmosphere of 1 atm and a rotation speed of 6 rpm.

[Mixing ratio]
In addition, the compounding ratio when using both a thermoplastic fluororesin that is solid under normal temperature and normal pressure and a thermoplastic fluororesin that is liquid under normal temperature and normal pressure (thermoplastic fluororesin that is solid under normal temperature and normal pressure: thermoplastic under normal temperature and normal pressure) The mass ratio of the fluororesin is preferably 30 or more and 70 or less, more preferably 40 or more and 60 or less, more preferably 80 or less and 20 or more, and 70 or less and 30 or more. It is more preferable that it is 60 or less: 40 or more. If the compounding ratio of the solid thermoplastic fluororesin at room temperature and atmospheric pressure is at least the above lower limit and the compounding ratio of the liquid thermoplastic fluororesin at room temperature and atmospheric pressure is at most the above upper limit, for example, a composite sheet as a thermocompression bonding sheet This is because it is possible to improve moderate hardness and repeated durability without excessively softening. Further, if the mixing ratio of the liquid thermoplastic fluororesin under normal temperature and normal pressure is not less than the above lower limit and the mixing ratio of the solid thermoplastic fluororesin under normal temperature and normal pressure is not more than the above upper limit, for example, as a thermocompression-bonding sheet. This is because, while ensuring the repeated durability of the composite sheet, it is possible to obtain an appropriate hardness that can prevent the surface of the material that is the object to be thermocompression bonded from being damaged by vibration or the like accompanying thermocompression bonding.

[Content ratio of fluororesin]
The content ratio of the fluororesin in the composite sheet is preferably 30% by mass or more, and more preferably 40% by mass or more, based on 100% by mass of the total content of the fluororesin and the carbon material described later. It is preferably 80% by mass or less, and more preferably 70% by mass or less. When the content ratio of the fluororesin is not less than the above lower limit, for example, the repeating durability when the composite sheet is used as a thermocompression bonding sheet is further improved, and heat resistance, oil resistance and chemical resistance are also improved. is there. In addition, since the flexibility of the composite sheet is increased, for example, when the composite sheet is used as a thermocompression-bonding sheet, it is possible to prevent the surface of the material, which is a thermocompression-bonded object, from being damaged by vibrations and the like accompanying the thermocompression bonding. This is because the hardness can be easily adjusted. When the content ratio of the fluororesin is less than 30% by mass, the thermal conductivity of the composite sheet itself is improved as follows, but the force for retaining the carbon material described later in the composite sheet becomes weak, and therefore, for example, particles The powder of the carbon material such as the particulate carbon material is dropped.
Further, when the content ratio of the fluororesin is not more than the above upper limit, the thermal conductivity of the composite sheet is further improved, and, for example, when the composite sheet is used as a thermocompression bonding sheet, it is This is because the surface can be prevented from being contaminated by the composite sheet melted by heating.

<Other resins>
In addition to the fluororesin, the composite sheet of the present invention may further contain any other resin other than the fluororesin as long as the object of the present invention is not impaired.
When the composite sheet further contains other resin, the content ratio of the other resin is 10 mass% or less in the total 100 mass% of all the resins (fluorine resin and other resin) contained in the composite sheet. Is preferred, 5% by mass or less is more preferred, and 1% by mass or less is even more preferred.

<Carbon material>
The carbon material is not particularly limited, and a known carbon material can be used. Specifically, a particulate carbon material, a fibrous carbon material, or the like can be used as the carbon material. The particulate carbon material and the fibrous carbon material may be used alone or in combination of both, but at least from the viewpoint of easily increasing the thermal conductivity of the composite sheet, at least It is preferable to use a particulate carbon material. That is, it is preferable that the carbon material contains at least a particulate carbon material. In addition, it is more preferable to use the particulate carbon material and the fibrous carbon material in combination from the viewpoint of preventing the particulate carbon material from falling off from the composite sheet while further improving the thermal conductivity of the composite sheet. That is, it is more preferable that the carbon material further contains a fibrous carbon material in addition to the particulate carbon material.

[Content ratio of carbon material]
The content ratio of the carbon material in the composite sheet is preferably 20% by mass or more, and more preferably 30% by mass or more, based on 100% by mass of the total content of the fluororesin and the carbon material described above. It is preferably 70% by mass or less, and more preferably 60% by mass or less. When the content ratio of the carbon material in the composite sheet is at least the above lower limit, the carbon material is better oriented in the composite sheet and the carbon materials come into contact with each other to form a good heat transfer path. As a result, the composite sheet can exhibit higher thermal conductivity. Further, if the content ratio of the carbon material is not more than the above upper limit, the hardness can be more easily adjusted by imparting flexibility to the composite sheet.

[Particulate carbon material]
The particulate carbon material is not particularly limited, and examples thereof include artificial graphite, flake graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite, and other graphite; carbon black; Can be used. These may be used alone or in combination of two or more.
Of these, expanded graphite is preferably used as the particulate carbon material. This is because the use of expanded graphite can further improve the thermal conductivity of the composite sheet.
In the present invention, the aspect ratio (major axis/minor axis) of the particulate carbon material contained in the composite sheet is usually 1 or more and 10 or less, and preferably 1 or more and 5 or less. In the present invention, the “aspect ratio” is the maximum diameter (major axis) and maximum of any 50 particulate carbon materials obtained by observing a cross section in the thickness direction of the composite sheet with a SEM (scanning electron microscope). It can be determined by measuring the particle diameter (short diameter) in the direction orthogonal to the diameter and calculating the average value of the ratio of the long diameter to the short diameter (long diameter/short diameter).

[[Expanded graphite]]
Here, the expanded graphite that can be preferably used as the particulate carbon material is, for example, expandable graphite obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like, and then heat-expanded to obtain fine graphite. Can be obtained. Examples of the expanded graphite compounded in the composite sheet of the present invention include EC1500, EC1000, EC500, EC300, EC100, EC50 (all are trade names) manufactured by Ito Graphite Industry Co., Ltd.

[[Particle size of particulate carbon material]]
The volume-based mode diameter of the particulate carbon material in the composite sheet is preferably 100 μm or more, more preferably 150 μm or more, and preferably 300 μm or less. If the particle diameter of the particulate carbon material is not less than the above lower limit, the particulate carbon materials contact each other in the composite sheet to form a good heat transfer path, so that the composite sheet can exhibit higher thermal conductivity. Because you can. Further, if the particle diameter of the particulate carbon material is not more than the above upper limit, the hardness can be adjusted more easily by imparting flexibility to the composite sheet.
In the present invention, the “volume-based mode diameter” can be measured using, for example, a laser diffraction/scattering particle size distribution measuring device. To measure the volume-based mode diameter of the particulate carbon material contained in the composite sheet, specifically, the composite sheet is dissolved in a methyl ethyl ketone solvent to obtain a suspension containing the particulate carbon material. Then, the particle diameter of the particulate carbon material contained in the obtained suspension was measured, and a particle diameter distribution curve was obtained in which the horizontal axis represents the particle diameter and the vertical axis represents the abundance ratio (volume basis) of the particulate carbon material. By obtaining the particle diameter, the particle diameter at the maximum value of the particle diameter distribution curve can be obtained as the volume-based mode diameter.

[[Particulate carbon material content]]
The content ratio of the particulate carbon material in the carbon material is preferably more than 0% by mass, more preferably 80% by mass or more, further preferably 90% by mass or more, and 99.5%. The content is more preferably not less than 100% by mass, more preferably not more than 100% by mass, and preferably not more than 99.9% by mass. When the content ratio of the particulate carbon material in the carbon material is at least the above lower limit, the particulate carbon material is better oriented in the composite sheet, and the particulate carbon materials come into contact with each other to form a good heat transfer path. To do. As a result, the composite sheet can exhibit higher thermal conductivity. Further, if the content ratio of the particulate carbon material is 99.9 mass% or less, it is possible to prevent the particulate carbon material from falling off the composite sheet.

[Fibrous carbon material]
In the composite sheet of the present invention, the carbon material preferably contains a fibrous carbon material, and it is more preferable to use a fibrous carbon material together with the above-mentioned particulate carbon material.
Here, the fibrous carbon material is not particularly limited, and for example, carbon nanotubes, vapor grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof can be used. .. These may be used alone or in combination of two or more.
And, by containing a fibrous carbon material in the composite sheet of the present invention, it is possible to further improve the thermal conductivity of the composite sheet, and to prevent the powder of the particulate carbon material from falling off when used in combination with the particulate carbon material. It can be prevented more. The reason why the powdery carbon material can be prevented from falling off by blending the fibrous carbon material is not clear. However, the fibrous carbon material forms a three-dimensional network structure to improve thermal conductivity. It is presumed that this is because the desorption of the particulate carbon material is prevented while increasing the strength and strength.

Among the above, as the fibrous carbon material, fibrous carbon nanostructures such as carbon nanotubes are preferably used, and fibrous carbon nanostructures containing carbon nanotubes are more preferably used. This is because the use of fibrous carbon nanostructures such as carbon nanotubes can further improve the thermal conductivity and strength of the composite sheet of the present invention.

[[Fibrous carbon nanostructure containing carbon nanotubes]]
Here, the fibrous carbon nanostructure containing carbon nanotubes, which can be preferably used as the fibrous carbon material, may be composed of only carbon nanotubes (hereinafter, may be referred to as “CNT”). Alternatively, it may be a mixture of CNT and a fibrous carbon nanostructure other than CNT.
The CNTs in the fibrous carbon nanostructure are not particularly limited, and single-walled carbon nanotubes and/or multi-walled carbon nanotubes can be used. Nanotubes are preferable, and single-walled carbon nanotubes are more preferable. This is because the use of single-walled carbon nanotubes can further improve the thermal conductivity and strength of the composite sheet, as compared with the case where multi-walled carbon nanotubes are used.

Further, as a fibrous carbon nanostructure containing CNTs, the ratio (3σ/Av) of the value (3σ) obtained by multiplying the standard deviation (σ) of the diameter by 3 with respect to the average diameter (Av) is more than 0.20. It is preferable to use a carbon nanostructure of less than 0.60, more preferably to use a carbon nanostructure having 3σ/Av of more than 0.25, and to use a carbon nanostructure of 3σ/Av of more than 0.50. More preferably. If a fibrous carbon nanostructure containing CNTs with 3σ/Av of more than 0.20 and less than 0.60 is used, the thermal conductivity and strength of the composite sheet can be improved even if the amount of the carbon nanostructure is small. This is because it can be sufficiently increased. Therefore, it is possible to suppress an increase in hardness of the composite sheet (that is, a decrease in flexibility) by blending the fibrous carbon nanostructure containing CNT, and to sufficiently improve the thermal conductivity and the appropriate hardness of the composite sheet. This is because they can be placed side by side at a high level.
The “average diameter of the fibrous carbon nanostructure (Av)” and the “standard deviation of the diameter of the fibrous carbon nanostructure (σ: sample standard deviation)” were measured using a transmission electron microscope. The diameter (outer diameter) of 100 randomly selected fibrous carbon nanostructures can be measured and obtained. Then, the average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures containing CNTs are adjusted by changing the manufacturing method and the manufacturing conditions of the fibrous carbon nanostructures containing CNTs. Alternatively, it may be adjusted by combining a plurality of fibrous carbon nanostructures containing CNT obtained by different production methods.

As the fibrous carbon nanostructure containing CNT, the diameter measured as described above is plotted on the horizontal axis and the frequency is plotted on the vertical axis, and a normal distribution is obtained when approximated by Gaussian. Things are usually used.

Further, the fibrous carbon nanostructure containing CNT preferably has a peak of Radial Breathing Mode (RBM) when evaluated using Raman spectroscopy. It should be noted that RBM does not exist in the Raman spectrum of the fibrous carbon nanostructure composed of only multi-walled carbon nanotubes of three or more layers.

The fibrous carbon nanostructure containing CNTs preferably has a ratio of G band peak intensity to D band peak intensity (G/D ratio) in the Raman spectrum of 1.0 or more and 20 or less. When the G/D ratio is 1.0 or more and 20 or less, the thermal conductivity and strength of the composite sheet can be sufficiently increased even if the amount of the fibrous carbon nanostructure is small. Therefore, it is possible to prevent the flexibility of the composite sheet from being significantly reduced by the blending of the fibrous carbon nanostructure, and to arrange the thermal conductivity and the appropriate hardness of the composite sheet at a sufficiently high level.

Further, the average diameter (Av) of the fibrous carbon nanostructure containing CNT is preferably 0.5 nm or more, more preferably 1 nm or more, preferably 15 nm or less, and 10 nm or less. More preferably, This is because if the average diameter (Av) of the fibrous carbon nanostructures is 0.5 nm or more, aggregation of the fibrous carbon nanostructures can be suppressed and the dispersibility of the carbon nanostructures can be enhanced. .. Also, if the average diameter (Av) of the fibrous carbon nanostructure is 15 nm or less, the thermal conductivity and strength of the composite sheet can be sufficiently increased.

Further, in the fibrous carbon nanostructure containing CNT, the average length of the structure at the time of synthesis is preferably 100 μm or more and 5000 μm or less. Since the longer the length of the structure during synthesis is, the more easily the CNT is damaged or broken during dispersion, the average length of the structure during synthesis is preferably 5000 μm or less.

Furthermore, the BET specific surface area of the fibrous carbon nanostructure containing CNT is preferably 600 m ² /g or more, more preferably 800 m ² /g or more, and 2500 m ² /g or less. It is more preferably 1200 m ² /g or less. Furthermore, when the CNTs in the fibrous carbon nanostructure are mainly open, the BET specific surface area is preferably 1300 m ² /g or more. This is because if the BET specific surface area of the fibrous carbon nanostructure containing CNTs is 600 m ² /g or more, the thermal conductivity and strength of the composite sheet can be sufficiently increased. When the BET specific surface area of the fibrous carbon nanostructure containing CNT is 2500 m ² /g or less, the aggregation of the fibrous carbon nanostructure is suppressed to enhance the dispersibility of CNT in the composite sheet. Because you can.
In addition, in this invention, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

Furthermore, the fibrous carbon nanostructure containing CNTs is, according to the supergrowth method described later, collected on a base material having a catalyst layer for growing carbon nanotubes on the surface and oriented in a direction substantially perpendicular to the base material. Although it is obtained as a body (oriented aggregate), the mass density of the fibrous carbon nanostructure as the aggregate is preferably 0.002 g/cm ³ or more and 0.2 g/cm ³ or less. When the mass density is 0.2 g/cm ³ or less, the fibrous carbon nanostructures are weakly bound to each other, so that the fibrous carbon nanostructures can be uniformly dispersed in the composite sheet. When the mass density is 0.002 g/cm ³ or more, the integrity of the fibrous carbon nanostructure can be improved and the fibrous carbon nanostructure can be prevented from being loosened, which facilitates handling.

The fibrous carbon nanostructure containing CNTs having the above-described properties is obtained by, for example, supplying a raw material compound and a carrier gas onto a base material having a catalyst layer for producing carbon nanotubes on the surface thereof and chemically vaporizing it. When CNTs are synthesized by the phase growth method (CVD method), a small amount of an oxidant (catalyst activating substance) is present in the system to dramatically improve the catalytic activity of the catalyst layer (super growth method). ; International Publication No. 2006/011655), and can be efficiently produced. Note that, hereinafter, the carbon nanotube obtained by the super growth method may be referred to as “SGCNT”.

Here, the fibrous carbon nanostructure containing CNTs produced by the super growth method may be composed only of SGCNT, or in addition to SGCNT, for example, other non-cylindrical carbon nanostructures or the like. Carbon nanostructures may be included.

[[Properties of fibrous carbon material]]
The average fiber diameter of the fibrous carbon material that can be contained in the composite sheet is preferably 1 nm or more, more preferably 3 nm or more, preferably 2 μm or less, and more preferably 1 μm or less. preferable. This is because if the average fiber diameter of the fibrous carbon material is within the above range, the thermal conductivity, appropriate hardness and strength of the composite sheet can be juxtaposed at a sufficiently high level.

In addition, in this invention, "average fiber diameter" is the SEM (scanning electron microscope) or TEM (transmission electron microscope) of the cross section in the thickness direction of the composite sheet. It can be determined by measuring the fiber diameter and calculating the number average value of the measured fiber diameters. In particular, when the fiber diameter is small, it is preferable to observe the same cross section with a TEM (transmission electron microscope).

[[Content ratio of fibrous carbon material]]
The content ratio of the fibrous carbon material in the carbon material can be 0% by mass, preferably 0.1% by mass or more, preferably less than 100% by mass, and 20% by mass or less. Is more preferable, 10% by mass or less is more preferable, and 0.5% by mass or less is still more preferable. When the content ratio of the fibrous carbon material in the carbon material is at least the above lower limit, it is possible to sufficiently improve the thermal conductivity and strength of the composite sheet, and the particulate carbon material when used in combination with the particulate carbon material. This is because it is possible to sufficiently prevent the powder from falling off. Further, if the content ratio of the fibrous carbon material is not more than the above upper limit, the hardness of the composite sheet is excessively increased by blending the fibrous carbon material (that is, flexibility is excessively reduced), and This is because, for example, when the composite sheet of the present invention is used as a sheet for thermocompression bonding between materials, it is possible to sufficiently prevent the surface of the material from being damaged.

<Additive>
If necessary, the composite sheet of the present invention can be mixed with known additives that can be used for forming the composite sheet. The additive that can be added to the composite sheet is not particularly limited, and examples thereof include plasticizers such as fatty acid esters such as sebacic acid esters; flame retardants such as red phosphorus flame retardants and phosphoric acid ester flame retardants; Toughness improving agents such as urethane acrylates; moisture absorbing agents such as calcium oxide and magnesium oxide; silane coupling agents, titanium coupling agents, adhesion improving agents such as acid anhydrides; nonionic surfactants, fluorochemical surfactants, etc. And the like; an ion trap agent such as an inorganic ion exchanger; and the like.
Further, a known cross-linking agent and/or a polymerization initiator may be added within a range not impairing the object of the present invention.

Among the above, from the viewpoint of easily adjusting the hardness of the composite sheet, it is preferable to add a fatty acid ester as the plasticizer, and it is more preferable to add a sebacate ester.

<Hardness>
The composite sheet of the present invention needs to have an Asker C hardness at 25° C. of more than 40 and 70 or less. Further, the Asker C hardness at 25° C. of the composite sheet of the present invention is preferably 43 or more, more preferably 50 or more, and preferably 69 or less. When the hardness of the composite sheet is above the lower limit, it imparts physical strength to the composite sheet and, for example, when the composite sheet of the present invention is used as a sheet for thermocompression bonding, it is subjected to thermocompression bonding due to heating and pressing. It is possible to prevent the components of the composite sheet from adhering to and contaminating the surface of the physical material. Further, when the hardness of the composite sheet is not more than the above upper limit, it gives flexibility to the composite sheet and, for example, when the composite sheet of the present invention is used as a sheet for thermocompression bonding, a material having a hardness lower than that of the fixture. It is possible to prevent the material surface from being damaged by the collision between the fixing tool and the fixing tool.

Incidentally, it is not clear that the components of the composite sheet adhere to the surface of the material that is the object to be thermocompression bonded, but the resin component in the composite sheet that has been subjected to heat and pressure during thermocompression bonding is dissolved, etc. It is inferred that it leaks out from the surface of and is attached to the material surface as an attached matter. Such an adhered substance is usually in the form of an irregular surface, and the long axis of the irregular surface is often 2 mm or more. Then, since the gloss on the surface of the composite sheet that is contaminated with the adhered matter is different from that of the normal surface that is not contaminated with the adhered matter, the adhered matter on the surface of the composite sheet can be visually observed. ..

When using the composite sheet of the present invention as a thermocompression-bonding sheet to be interposed between a fixture and a material having a hardness lower than that of the fixture, when utilizing vibration energy such as ultrasonic waves as a heat source, The hardness of the composite sheet is preferably at least lower than the hardness of the fixture in order to favorably prevent damage to the surface of the material that is the object to be thermocompression bonded.

<Thermal conductivity>
Further, the composite sheet of the present invention needs to have a thermal conductivity in the thickness direction of 15 W/m·K or more at 25°C. The thermal conductivity in the thickness direction of the composite sheet of the present invention at 25° C. is preferably 20 W/m·K or more, more preferably 25 W/m·K or more. If the thermal conductivity is at least the above lower limit, the thermal conductivity as a composite sheet is sufficiently high, for example, when the composite sheet of the present invention is used as a thermocompression bonding sheet, from a material that is a thermocompression bonded product. The heat dissipation can be improved to prevent discoloration and dissolution of the material surface. In other words, when the thermal conductivity is less than the above lower limit, for example, when the composite sheet of the present invention is used as a thermocompression bonding sheet, the heat from the heat source is There is a risk of discoloration, dissolution, etc. on the material surface because the material surface is excessively heated by being retained in the space.

<Thickness>
Furthermore, the composite sheet of the present invention preferably has a thickness of less than 1.3 mm, more preferably 1.0 mm or less, and more preferably more than 0.3 mm. When the thickness of the composite sheet is less than the above upper limit, it is possible to realize appropriate flexibility and appropriate strength by thinning the composite sheet, and therefore it can be better used as a thermocompression bonding sheet. If the composite sheet has an excessively large thickness, for example, when the composite sheet is used as a thermocompression bonding sheet, the deformation width of the composite sheet due to the pressure applied in the thermocompression bonding becomes large. When the deformation width of the composite sheet is large, the friction that can occur between the surface of the composite sheet and the surface of the material that is the object to be thermocompression-bonded is also large. Therefore, in thermocompression bonding, the resin component in the composite sheet is more likely to be contaminated by adhering to the material between the composite sheet and the material that have undergone greater friction as well as heating.
Further, if the thickness of the composite sheet exceeds the above lower limit, the composite sheet is more excellent in durability as a thermocompression bonding sheet without making the composite sheet excessively thin. Specifically, if the thickness of the composite sheet is 0.3 mm or less, the composite sheet is too thin to withstand the impact when repeatedly used as a thermocompression bonding sheet. On the other hand, it has been confirmed that if the thickness of the composite sheet is more than 0.3 mm, the composite sheet does not break under normal conditions even when used as a thermocompression bonding sheet at least 10 times.

<Moonie viscosity>
Furthermore, the composite sheet of the present invention preferably has a Mooney viscosity (ML ₁₊₄ , 100° C.) of 100 or less, more preferably 50 or less, further preferably 25 or less, and 15 or less. It is particularly preferable that it is 5 or more, more preferably 9 or more. When the Mooney viscosity of the composite sheet is at least the above lower limit, for example, when the composite sheet of the present invention is used as a thermocompression-bonding sheet, the composite sheet is formed on the surface of the material to be thermocompression-bonded with heating and pressurization. This is because it is possible to further prevent the components of (3) from adhering and contaminating. Further, when the hardness of the composite sheet is not more than the above upper limit, it gives flexibility to the composite sheet and, for example, when the composite sheet of the present invention is used as a sheet for thermocompression bonding, a material having a hardness lower than that of the fixture. This is because it is possible to further prevent the surface of the material from being damaged due to the collision between the material and the fixture.
In the present invention, the “Moonie viscosity (ML ₁₊₄ , 100°C)” can be measured at a temperature of 100°C according to JIS K6383.

<Manufacturing method>
The composite sheet described above is not particularly limited, and for example, a step of pressurizing a composite material containing a fluororesin and a carbon material into a sheet shape to obtain a pre-composite sheet (pre-composite sheet forming step), A step of stacking a plurality of pre-composite sheets in the thickness direction or folding or winding the pre-composite sheet to obtain a laminated body (laminate forming step), and the obtained laminated body in the laminating direction. It can be manufactured by a manufacturing method including a step of slicing the composite sheet at an angle of 45° or less (slicing step).

[Pre-composite sheet molding process]
In the pre-composite sheet forming step, a pre-composite sheet can be obtained by pressurizing a composite material containing a fluororesin and a carbon material and optionally further containing an additive to form a sheet. The composite material containing the fluororesin and the carbon material may be prepared and prepared by any method, or a commercially available product may be purchased and prepared.

[[Preparation of composite material]]
When preparing the composite material, the fluororesin and the carbon material and any additives can be prepared by stirring and mixing. Then, as the fluororesin, the carbon material and the additive, those described above as the fluororesin, the carbon material and the additive which can be contained in the composite sheet of the present invention can be used.

Incidentally, when a resin such as a fluororesin contained in the composite sheet is a crosslinkable resin, a precomposite sheet may be formed using a composite material containing the crosslinkable resin, or a crosslinkable resin. A cross-linkable resin may be contained in the composite sheet by forming a pre-composite sheet using a composite material containing a cross-linking agent and crosslinking the cross-linkable resin after the pre-composite sheet molding step.

The stirring and mixing can be performed using a known mixing device such as a kneader, a roll, a Henschel mixer, a Hobart mixer, a high speed mixer, and a twin-screw kneader without any particular limitation. The stirring and mixing may be performed in the presence of a solvent such as ethyl acetate or methyl ethyl ketone. The stirring and mixing conditions can be appropriately set, for example, with reference to the examples described below. The stirring and mixing temperature can be set to, for example, 5°C or higher and 150°C or lower.

[[Molding of composite material]]
The composite material prepared as described above may be defoamed and crushed, and then pressed to form a sheet. When a solvent is used during mixing, it is preferable to remove the solvent and then form into a sheet. For example, if defoaming is performed using vacuum defoaming, the solvent is removed at the same time as defoaming. be able to.

Here, the composite material is not particularly limited as long as it is a molding method in which a pressure is applied, and can be formed into a sheet by using a known molding method such as press molding, roll molding or extrusion molding. Above all, the composite material is preferably formed into a sheet shape by roll forming, and more preferably formed into a sheet shape by being passed between rolls in a state of being sandwiched between protective films. The protective film is not particularly limited, and a release polyethylene terephthalate (PET) film having excellent releasability, a sandblasted polyethylene terephthalate film, or the like can be used. The roll temperature can be set to 5°C or higher and 150°C.

In the pre-composite sheet formed by pressing the composite material into a sheet shape, the carbon material is mainly arranged in the in-plane direction, and it is speculated that the thermal conductivity in the in-plane direction of the pre-composite sheet is improved. Further, when the carbon material contains a fibrous carbon material, the fibrous carbon material is oriented in the pre-composite sheet, and it is presumed that the thermal conductivity of the pre-composite sheet is further improved.

The thickness of the pre-composite sheet is not particularly limited and may be, for example, 0.05 mm or more and 2 mm or less. Further, from the viewpoint of further improving the thermal conductivity of the composite sheet, the thickness of the pre-composite sheet is preferably 0.10 mm or more, and preferably 0.80 mm or less.

[Laminate formation process]
In the laminate forming step, a plurality of pre-composite sheets obtained in the pre-composite sheet forming step may be laminated in the thickness direction, or the pre-composite sheet may be folded or wound to obtain a laminate. Here, the formation of the laminate by folding the pre-composite sheet is not particularly limited, and can be performed by folding the pre-composite sheet with a constant width using a folding machine. The formation of the laminate by winding the pre-composite sheet is not particularly limited, and may be performed by winding the pre-composite sheet around an axis parallel to the lateral direction or the longitudinal direction of the pre-composite sheet. it can.

Here, normally, in the laminate obtained in the laminate forming step, the adhesive force between the surfaces of the pre-composite sheets is sufficiently obtained by the pressure when laminating the pre-composite sheets and the pressure when folding or winding the pre-composite sheets. Be done. However, when the adhesive strength is insufficient or when it is necessary to sufficiently suppress delamination of the laminate, the laminate forming step may be performed with the surface of the pre-composite sheet slightly dissolved with a solvent. Then, the laminate forming step may be performed in a state in which an adhesive is applied to the surface of the pre-composite sheet or in a state in which an adhesive layer is provided on the surface of the pre-composite sheet.

The solvent used for dissolving the surface of the pre-composite sheet is not particularly limited, and a known solvent capable of dissolving the resin component contained in the pre-composite sheet can be used.

The adhesive applied to the surface of the pre-composite sheet is not particularly limited, and a commercially available adhesive or tacky resin can be used. Among them, as the adhesive, it is preferable to use a resin having the same composition as the resin component contained in the pre-composite sheet. The thickness of the adhesive applied to the surface of the pre-composite sheet can be, for example, 10 μm or more and 1000 μm or less.
Further, the adhesive layer provided on the surface of the pre-composite sheet is not particularly limited, and a double-sided tape or the like can be used.

From the viewpoint of suppressing delamination, the obtained laminate may be pressed at 20° C. or higher and 100° C. or lower for 1 to 30 minutes while being pressed at a pressure of 0.05 MPa or higher and 1.0 MPa or lower in the stacking direction. preferable.

In the laminate obtained by laminating, folding or winding the pre-composite sheets, the carbon material such as the particulate carbon material and/or the fibrous carbon material is arranged in a direction substantially orthogonal to the laminating direction. Inferred.

[Slicing process]
In the slicing step, the laminated body obtained in the laminated body forming step can be sliced at an angle of 45° or less with respect to the laminating direction to obtain a composite sheet including sliced pieces of the laminated body. Here, the method for slicing the laminate 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. Among them, the knife processing method is preferable because it is easy to make the thickness of the composite sheet uniform. The shape of the knife used in the knife processing method may be single-edged, double-edged, or asymmetrical, but single-edged is preferable from the viewpoint of achieving thickness accuracy. Further, the cutting tool when slicing the laminate is not particularly limited, a smooth board surface having a slit, and a slicing member having a blade portion protruding from the slit portion (for example, a sharp blade is provided. Canna or slicer) can be used.

From the viewpoint of increasing the thermal conductivity of the composite sheet, the angle at which the laminate is sliced is preferably 30° or less with respect to the laminating direction, and more preferably 15° or less with respect to the laminating direction. It is preferable that the angle is approximately 0° with respect to the stacking direction (that is, the direction is along the stacking direction).

Further, from the viewpoint of easily slicing the laminate, the temperature of the laminate during slicing is preferably −20° C. or higher and 40° C. or lower, and more preferably 10° C. or higher and 30° C. or lower. Furthermore, for the same reason, it is preferable to slice the laminated body while slicing while applying a pressure in a direction perpendicular to the laminating direction, and a pressure of 0.1 MPa or more and 0.5 MPa or less in the direction perpendicular to the laminating direction. It is more preferable to slice while loading. In the composite sheet thus obtained, it is assumed that the carbon material such as the particulate carbon material and/or the fibrous carbon material is arranged in the thickness direction.

(Thermo-compression method)
In the thermocompression bonding method of the present invention, the first material and the second material are thermocompression bonded between the heating device and the fixture. Specifically, in the thermocompression bonding method of the present invention, a laminate having the first material and the second material and any one of the composite sheets described above are provided at predetermined positions between the heating device and the fixture. It includes a step A of arranging in a relationship, and a step B of heating the laminate using a heating device to thermocompress the first material and the second material.
In the thermocompression bonding method of the present invention, since the steps A and B are performed using the composite sheet of the present invention, the hardness of the material to be thermocompression bonded is lower than the hardness of the fixture, and the material is Even if the material is vibrated and heated, it is possible to prevent the material surface, particularly the material surface on the side fixed to the fixture via the composite sheet, from being scratched. In addition, it is possible to prevent adhesion and contamination of the surface of the material. Further, even if the material to be thermocompression-bonded has insufficient thermal conductivity, heat can be satisfactorily transferred from the heating device to the fixture, and discoloration and dissolution of the material surface can be prevented. And since the composite sheet can endure repeated thermocompression bonding, it is excellent in workability.

<Process A>
In step A, a laminate having the first material and the second material, which are the objects to be heat-bonded, and one of the above-described composite sheets are arranged with a predetermined positional relationship between the heating device and the fixture. To do.

[Placement method]
Here, in step A, when the laminate having the first material and the second material and any one of the composite sheets described above are arranged between the heating device and the fixture, the composite sheet is attached to the fixture and It is necessary to interpose between the laminates. In other words, in step A, the heating device/the laminate having the first material and the second material/the composite sheet/the fixture are arranged in that order. At this time, in the laminated body, the first material may be arranged on the heating device side and the second material may be arranged on the fixture side, or the second material may be arranged on the heating device side and the first material may be fixed. It may be arranged on the tool side so that the first material and the second material face both sides of the heating device side and the fixing device side (that is, the direction in which the stacking direction of the laminate and the heating device and the fixing device are connected. May be arranged so that and are substantially orthogonal to each other. Further, an adhesive may be optionally further arranged between the first material and the second material of the laminated body.

[First material and second material]
Here, the first material and the second material can be arbitrary materials to be pressure-bonded. Further, the first material and the second material may be the same material or different materials, may have the same shape and/or size, and may have different shapes. And/or may have a size.
The materials of the first material and the second material are not particularly limited, and examples thereof include metals and resins. Furthermore, for example, when the first material and/or the second material is fixed to the fixture and thermocompression bonding is performed, the material of the first material and the second material is more than the constituent material of the fixture. Also, a material having a low hardness can be mentioned, a resin is preferable, and a synthetic resin such as plastic is more preferable.

[Heating device]
The heating device is not particularly limited as long as it can apply heat to the material to be thermocompression bonded, and a known heating device can be used. Examples of the heat source used by the known heating device include those that generate vibrational energy such as sound waves such as ultrasonic waves and electromagnetic waves such as microwaves and infrared rays; ordinary heating wires such as nichrome wires; and the like. Among them, from the viewpoint of efficiently transmitting heat, as the heat source, those that generate vibration energy are preferable, and ultrasonic waves are more preferable. That is, it is preferable to use an ultrasonic oscillator as the heating device.
The heating device is not particularly limited, and may function as a pressurizing device that pressurizes the material to be thermocompressed in thermocompression bonding. Further, the heating device may function as a fixture for fixing the material to be thermocompression-bonded without any particular limitation. For example, if a known ultrasonic oscillator is used as the heating device, the laminated body including the first material and the second material is fixed together with other fixing tools, and heating and heating are performed while transmitting vibration to the fixed material. Pressure can be applied simultaneously.

[Fixture]
The fixture is not particularly limited as long as it can be fixed to heat and press the material to be thermocompression-bonded, and known fixtures, for example, jigs, plates having jigs and pedestals can be mentioned. .. The material of the fixture includes metal and resin, but is usually made of metal.

<Process B>
Then, in step B, the laminate is heated using a heating device to thermocompress the first material and the second material. As the heating device used in step B, the same device as the heating device described above can be used. Further, for example, when an ultrasonic oscillator is used as the heating device, conditions for heating and pressurizing such as ultrasonic frequency, ultrasonic treatment time, output, press pressure and the like can be appropriately selected.

Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.
Then, in Examples and Comparative Examples, the Asker C hardness, the thermal conductivity and the powder falling prevention property of the composite sheet; the synthetic resin material when the composite sheet is used as a thermocompression bonding sheet for thermocompression bonding of synthetic resin materials The surface scratch resistance, the composite sheet adhesion prevention property to the surface of the synthetic resin material, and the repeated durability of the composite sheet were measured or evaluated according to the following methods.

<Asker C hardness>
The Asker C hardness of the composite sheet was based on the Asker C method of the Japan Rubber Association standard (SRIS 0101) and was measured using a hardness meter in an environment at a temperature of 25°C.
Specifically, in Example 1, Example 4, and Comparative Examples 1 and 2, the obtained composite sheets were cut into a size of 30 mm in length×50 mm in width×1.0 mm in thickness and 30 sheets were stacked. Further, in Examples 2 to 3, 60 sheets were cut and cut into a size of 30 mm length×50 mm width×0.5 mm thickness. Then, the laminated composite sheets were allowed to stand in a thermostatic chamber kept at a temperature of 25° C. for 48 hours or more to obtain a test body. Next, the damper height was adjusted so that the pointer was 95 to 98, and the test body and the damper were made to collide. Then, the Asker C hardness of the test body 60 seconds after the collision was measured twice using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ"), and the average value of the measurement results was adopted. did. Generally, the smaller the Asker C hardness, the higher the flexibility.

<Thermal conductivity>
For the composite sheet, the thermal diffusivity α (m ² /s) in the thickness direction, the constant pressure specific heat Cp (J/g·K) and the density ρ (g/m ³ ) were measured by the following methods. The temperature for various measurements was 25°C.
[Thermal diffusivity]
The measurement was performed using a thermophysical property measuring device (product name "Thermo Wave Analyzer TA35" manufactured by Bethel Co., Ltd.).
[Constant pressure specific heat]
Using a differential scanning calorimeter (manufactured by Rigaku, product name “DSC8230”), specific heat was measured under a temperature rising condition of 10° C./min.
[Density of composite sheet]
The measurement was performed using an automatic hydrometer (manufactured by Toyo Seiki Co., Ltd., trade name "DENSIMTER-H").
Then, using the obtained measured value, the following formula (I):
λ=α×Cp×ρ (I)
The thermal conductivity λ (W/m·K) in the thickness direction of the composite sheet at 25° C. was determined from the above.

<Prevention of falling powder>
A Kimwipe fully impregnated with cyclohexane was placed on top of the composite sheet. Further, a 2 kg weight was placed on the Kimwipe so that pressure was evenly applied. Then, 30 seconds after the weight was placed, the weight was removed, and the presence or absence of the substance adhered to the Kimwipe was visually confirmed, and the powder falling prevention property of the composite sheet was evaluated according to the following criteria. If no deposits are found on the Kimwipe, it indicates that the composite sheet has an excellent powder falling prevention property.
○: No deposit on Kimwipe ×: Some deposit on Kimwipe

<Prevention of scratches on the surface of synthetic resin material>
Synthetic resin materials A and B were prepared as the first material and the second material to be adhered to each other. Here, each of the synthetic resin materials A and B was made of polypropylene, and was molded in the same star shape (size that fits in a circle having a diameter of 6 cm). Next, 0.20 g of an adhesive made of acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS resin) is applied between the synthetic resin materials A and B to bond the synthetic resin materials A and B together. It was laminated via the agent. At this time, the adhesive was in a solid state at room temperature, and the synthetic resin materials A and B were not adhered by the adhesive.
Subsequently, the obtained laminated body of synthetic resin material A/adhesive/synthetic resin material B was fixed to an ultrasonic welding machine (manufactured by Herman Ultrasonics, product name “HiQ VARIO”) via a composite sheet. The ultrasonic welding machine was equipped with an ultrasonic oscillator as a heating device and a fixture. Specifically, on the lower side of the ultrasonic welding machine, there is a pedestal having a metal jig as a fixture, and on the upper side of the ultrasonic welding machine, a horn that generates ultrasonic waves is attached as a heating device. The laminated body is fixed between the pedestal and the horn so that the synthetic resin material A is on the upper side (side facing the horn) and the synthetic resin material B is on the lower side (side fixed to the pedestal). did. When fixing, the obtained composite sheet was interposed between the side of the synthetic resin material B and the pedestal in the laminate. That is, from the upper side, a horn (ultrasonic oscillator) as a heating device/a synthetic resin material A as a first material/an adhesive/a synthetic resin material B as a second material/a composite sheet as a thermocompression bonding sheet/ The laminated body was fixed to the ultrasonic welding machine in the order of a pedestal having a metal jig as a fixture.
Subsequently, the synthetic resin materials A and B are thermocompression bonded by irradiating the synthetic resin material A side with ultrasonic waves from the upper horn and transmitting the heat generated from the vibration energy of the ultrasonic waves to dissolve the adhesive. It was Here, the synthetic resin material A and the horn were in contact with each other while the ultrasonic wave was being applied. The conditions of thermocompression bonding by ultrasonic irradiation were as follows: press pressure: 180 N/mm ² , ultrasonic frequency: 30 kHz, ultrasonic treatment time: about 5 seconds, output: 1800 W.
Then, after the synthetic resin materials A and B are heat-welded as described above, the laminated body is removed from the ultrasonic welding machine and fixed to the surface of the laminated body on the synthetic resin material B side, that is, the pedestal via the composite sheet. The surface condition on the side that had been abraded was visually observed, and the scratch resistance of the surface of the synthetic resin material was evaluated according to the following criteria. As a sheet for thermocompression bonding, the composite sheet has an appropriate hardness that prevents the surface of the synthetic resin material from being damaged by collision with the pedestal during thermocompression bonding so that no scratch is observed on the surface of the synthetic resin material. Demonstrate usefulness.
Here, in the present evaluation standard, the “scratch” means a damaged portion having a size of 1 mm or more in the plane direction of the surface of the synthetic resin material B that was fixed to the pedestal via the composite sheet. Refers to. The "scratch" may be, for example, any linear shape, a state in which the surface layer of the synthetic resin material B is cut off as a surface of a certain range, or the like, shape, state, or the like. Further, the “scratch” refers to a damaged portion that can be visually confirmed, and for example, a damaged portion of a minute level that cannot be distinguished without using a microscope such as an electron microscope does not correspond.
In the thermocompression bonding, if the composite sheet is not interposed between the synthetic resin material B and the pedestal, the synthetic resin material B also vibrates due to the vibration of the ultrasonic waves and causes friction with the pedestal. It was confirmed that scratches were generated on the surface of B.
○: The surface of the synthetic resin material is not scratched ×: The surface of the synthetic resin material is scratched

<Prevention of adhesion of synthetic resin material to surface>
The synthetic resin materials A and B were thermocompression bonded by the same procedure as the method for evaluating the surface scratch resistance of the synthetic resin material.
Then, the laminated body was removed from the ultrasonic welding machine, and the surface state of the synthetic resin material B side of the laminated body, that is, the surface state fixed to the pedestal via the composite sheet was visually observed, and the following criteria The synthetic resin material was evaluated for its adhesion prevention property to the surface. It is useful as a sheet for thermocompression bonding, having a suitable hardness to prevent the composite sheet from adhering to and staining the surface of the synthetic resin material during thermocompression bonding, so that no adhered matter is observed on the surface of the synthetic resin material. Indicates that.
Here, in the present evaluation criteria, the "adhered matter" refers to an article that can be visually confirmed in an arbitrary shape, state, etc., for example, a minute level object that cannot be distinguished without using a microscope such as an electron microscope. Not applicable.
○: No deposit on the surface of the synthetic resin material ×: There is deposit on the surface of the synthetic resin material

<Repeat durability>
When the synthetic resin materials A and B are thermocompression bonded by the same procedure as the method for evaluating the surface scratch resistance of the synthetic resin material, the composite sheet after being repeatedly used 20 times as a thermocompression bonding sheet Was visually observed, and the repeated durability of the composite sheet was evaluated according to the following criteria.
In this evaluation standard, the term “crack” refers to a crevice having a length of 3 mm or more in the plane direction of at least one surface of the composite sheet. Further, in this evaluation standard, “breakage” refers to a state in which a crack further progresses in the thickness direction of the composite sheet and penetrates from one surface to the other surface of the composite sheet. Further, the “crack” refers to a crack that can be visually confirmed, and for example, a minute level crack that cannot be discriminated without using a microscope such as an electron microscope does not apply.
◯: No crack and tear on the surface of the composite sheet ×: Crack and/or tear on the surface of the composite sheet

(Example 1)
<Preparation of fibrous carbon nanostructure containing CNT>
A fibrous carbon nanostructure containing SGCNT was obtained by the super growth method as described in WO 2006/011655.
The obtained fibrous carbon nanostructure had a G/D ratio of 3.0, a BET specific surface area of 800 m ² /g, and a mass density of 0.03 g/cm ³ . The diameter of 100 randomly selected fibrous carbon nanostructures was measured using a transmission electron microscope. As a result, the average diameter (Av) was 3.3 nm, and the sample standard deviation (σ) was The value obtained by multiplying by 3 (3σ) was 1.9 nm, the ratio thereof (3σ/Av) was 0.58, and the average length was 100 μm. The obtained fibrous carbon nanostructure was mainly composed of single-walled CNTs (hereinafter, sometimes referred to as “SGCNT”).

<Preparation of fibrous carbon material>
[Preparation of dispersion]
400 mg of the fibrous carbon nanostructure obtained above as a fibrous carbon material was weighed out, mixed in 2 L of methyl ethyl ketone as a solvent, and stirred for 2 minutes with a homogenizer to obtain a crude dispersion liquid. Next, using a wet jet mill (manufactured by Tsuneko Co., Ltd., product name “JN-20”), the obtained crude dispersion was passed through a 0.5 mm channel of the wet jet mill at a pressure of 100 MPa for 2 cycles. Then, the fibrous carbon nanostructure was dispersed in methyl ethyl ketone. Then, a dispersion liquid having a solid content concentration of 0.20 mass% was obtained.
[Removal of solvent]
Thereafter, the dispersion liquid obtained above was filtered under reduced pressure using Kiriyama filter paper (No. 5A) to obtain a sheet-like easily dispersible aggregate as a fibrous carbon material.

<Pre-composite sheet molding process>
[Preparation of composite material]
40 parts of a thermoplastic fluororesin that is solid under normal temperature and normal pressure as a fluororesin (manufactured by Daikin Industries, Ltd., trade name "DAIEL G-704BP") and a thermoplastic fluororesin that is liquid under normal temperature and normal pressure (manufactured by Daikin Industries, Ltd., 45 parts of the product name "DAI-EL G-101") and 85 parts of expanded graphite (manufactured by Ito Graphite Industry Co., Ltd., product name "EC-50", average particle diameter: 250 μm) as a particulate carbon material, and fibers. 0.1 part of the easily dispersible aggregate of the fibrous carbon nanostructure obtained above as a particulate carbon material, and sebacic acid ester as a plasticizer (manufactured by Daihachi Chemical Industry Co., Ltd., trade name "DOS 5) and 5 parts with a Hobart mixer (manufactured by Kodaira Seisakusho Co., Ltd., product name "ACM-5LVT type", capacity: 5 L) in the presence of 100 parts of ethyl acetate as a solvent at room temperature for 5 minutes. Mixed. Next, the obtained stirred mixture was subjected to vacuum degassing for 30 minutes, and ethyl acetate was removed at the same time as defoaming to obtain a composite material containing a fluororesin, a particulate carbon material and a fibrous carbon material. Then, the obtained composite material was put into a wonder crush mill (manufactured by Osaka Chemical Co., Ltd., product name "D3V-10") and crushed for 10 seconds.
[Molding of composite material]
Then, 5 g of the crushed composite material was sandwiched by a sandblasted PET film (protective film) having a thickness of 50 μm, a roll gap of 550 μm, a roll temperature of 50° C., a roll linear pressure of 50 kg/cm, and a roll speed of 1 m/min. Was rolled and molded to obtain a pre-composite sheet having a thickness of 0.5 mm.

<Laminate formation process>
Then, the obtained pre-composite sheet was cut into a length of 60 mm×width of 60 mm×thickness of 0.5 mm, and 120 sheets of double-sided tape were laminated in the thickness direction of the pre-composite sheet to obtain a laminate having a thickness of about 60 mm.

<Slicing process>
After that, while pressing the laminated cross-section of the obtained pre-composite sheet laminate with a pressure of 0.3 MPa, a slicer for woodworking (manufactured by Marunaka Iron Works Co., Ltd., product name "Super Finishing Planer Super Mechanical", slit Slice at an angle of 0 degree with respect to the laminating direction by using the protruding length of the blade portion from the portion: 0.11 mm (in other words, slicing in the direction normal to the main surface of the laminated pre-composite sheet) Then, a composite sheet having a length of 60 mm, a width of 60 mm, and a thickness of 1.0 mm was obtained.
And about the obtained composite sheet, the Asker C hardness, the thermal conductivity, and the powder falling prevention property were measured and evaluated according to the method described above. When the obtained composite sheet is used as a thermocompression-bonding sheet used for thermocompression bonding of synthetic resin materials to each other, according to the method described above, the scratch resistance of the surface of the synthetic resin material, the surface of the synthetic resin material The anti-adhesion property and the repeated durability of the composite sheet were observed and evaluated. The results are shown in Table 1.

(Example 2)
In manufacturing the composite sheet, a composite sheet was obtained in the same manner as in Example 1 except that the thickness of the composite sheet was changed to 0.5 mm by adjusting the protruding length of the blade portion from the slit portion.
And it measured like Example 1. The results are shown in Table 1.

(Example 3)
In preparing the composite material, the composite material was prepared as follows. Further, in the production of the composite sheet, a composite sheet was obtained in the same manner as in Example 1 except that the thickness of the composite sheet was changed to 0.5 mm by adjusting the protruding length of the blade portion from the slit portion.
And it measured like Example 1. The results are shown in Table 1.
<Preparation of composite material>
100 parts of a thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., trade name "Daiel G-101") which is liquid at room temperature and atmospheric pressure as a fluororesin, and expanded graphite as a particulate carbon material (Ito Graphite Industry Co., Ltd.) Manufactured by the trade name "EC-100", average particle diameter: 190 µm) in an amount of 50 parts by mass, and 0.1 as the easily dispersible aggregate of the fibrous carbon nanostructures obtained above as a fibrous carbon material. The mass part was put into a Hobart mixer (manufactured by Kodaira Seisakusho Co., Ltd., trade name "ACM-5LVT type", capacity: 5 L), the temperature was raised to and maintained at 80°C, and the mixture was stirred and mixed for 30 minutes. By the mixing and stirring, a composite material containing a fluororesin, a particulate carbon material and a fibrous carbon material was obtained. Then, the obtained composite material was put into a Wonder Crush Mill (Osaka Chemical Co., Ltd., product name "D3V-10") and crushed for 1 minute.

(Example 4)
In preparing the composite material, a composite sheet was obtained in the same manner as in Example 1 except that the fibrous carbon material was not used.
And it measured like Example 1. The results are shown in Table 1.

(Comparative Example 1)
In preparing the composite material, a composite sheet was obtained in the same manner as in Example 1 except that the composite material was prepared as follows.
And it measured like Example 1. The results are shown in Table 1.
<Preparation of composite material>
100 parts of non-crosslinking acrylic resin (manufactured by Sakai Chemical Industry Co., Ltd., trade name “U-LOCK 2004”) as other resin without using fluororesin, and expanded graphite (Ito graphite) Kogyo Co., Ltd., trade name "EC-50", average particle diameter: 250 μm) is 200 parts, and the easily dispersible aggregate of the fibrous carbon nanostructures obtained above as a fibrous carbon material is 0. 1 part was stirred and mixed at room temperature for 1 hour using a Hobart mixer (manufactured by Kodaira Seisakusho Co., Ltd., trade name "ACM-5LVT type", volume: 5L) in the presence of 20 parts of ethyl acetate as a solvent. .. Next, the obtained stirred mixture was subjected to vacuum defoaming for 1 hour, and ethyl acetate was removed at the same time as defoaming to obtain a composite material containing an acrylic resin, a particulate carbon material and a fibrous carbon material. Then, the obtained composite material was put into a Wonder Crush Mill (Osaka Chemical Co., Ltd., product name "D3V-10") and crushed for 1 minute.

(Comparative example 2)
In preparing the composite material, the amount of non-crosslinked acrylic resin was changed to 20 parts. In addition, 80 parts of 2-ethylhexyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 1.0 part of an organic peroxide thermal polymerization initiator (1,6-bis(t-butylperoxycarbonyloxy)hexane), and , A polyfunctional monomer as a cross-linking agent (Kyoeisha Chemical Co., Ltd., trade name "light acrylate PE-3A", pentaerythritol triacrylate: pentaerythritol tetraacrylate: pentaerythritol diacrylate in a ratio of 60:35:5. A composite material was prepared in the same manner as in Comparative Example 1 except that 1.0 part of (mixed in) was added. In Comparative Example 2, the obtained composite material was not crushed.
Further, in the molding of the composite material, 5 g of the composite material which has not been crushed is sandwiched by a sandblasted PET film (protective film) having a thickness of 50 μm, a roll gap of 550 μm, a roll temperature of 50° C., and a roll linear pressure of 50 kg/ cm and roll speed was 1 m/min. Furthermore, a composite sheet was obtained in the same manner as in Comparative Example 1 except that a pre-composite sheet having a thickness of 1.0 mm was obtained by reacting the roll-formed composite material in an environment of a temperature of 150° C. for 1 hour.
And it measured like Example 1. The results are shown in Table 1.

From Table 1, in the composite sheets of Examples 1 to 3 containing a fluororesin and a carbon material and having a predetermined appropriate hardness and high thermal conductivity, the composite sheets of Comparative Examples 1 and 2 containing no fluororesin were compared with each other. It can be seen that when the composite sheet is used as a thermocompression bonding sheet used for thermocompression bonding of synthetic resin materials to each other, it has excellent repeated durability.
Further, in Comparative Example 1 in which the hardness is less than or equal to a predetermined value, when the composite sheet is used as a thermocompression-bonding sheet used for thermocompression bonding of synthetic resin materials, as compared with Examples 1 to 3 having appropriate hardness within a predetermined range. In addition, it can be seen that the composite sheet adheres to the surface of the synthetic resin material and is inferior in adhesion prevention property.
Furthermore, in Comparative Example 2 in which the hardness is more than the predetermined value, when the composite sheet is used as a thermocompression bonding sheet used for thermocompression bonding of synthetic resin materials, as compared with Examples 1 to 3 having an appropriate hardness within a predetermined range. In addition, it can be seen that the surface of the synthetic resin material is scratched and the scratch resistance is poor.
As described above, in the thermocompression bonding method performed using the composite sheets of Examples 1 to 4, it is found that the surface of the synthetic resin material is excellent in scratch resistance and adhesion prevention, and the synthetic resins can be thermocompression bonded well. ..

According to the present invention, it is possible to provide a composite sheet which has high thermal conductivity, moderate hardness and excellent durability, and is useful for thermocompression bonding.
Further, according to the present invention, it is possible to provide a thermocompression bonding method which is excellent in the scratch resistance of the surface of the material to be thermocompression bonded.

Claims (7)

A sheet containing a fluororesin and a carbon material,
Asker C hardness at 25°C is more than 40 and 70 or less,
A composite sheet having a thermal conductivity in the thickness direction of 15 W/m·K or more. The composite sheet according to claim 1, having a thickness of less than 1.3 mm. The composite sheet according to claim 1, wherein the carbon material contains a particulate carbon material. The composite sheet according to claim 1, wherein the carbon material contains a fibrous carbon material. The composite sheet according to any one of claims 1 to 4, wherein a content ratio of the carbon material is 70% by mass or less based on a total content of 100% by mass of the fluororesin and the carbon material. A method of thermocompression bonding a first material and a second material between a heating device and a fixture, comprising:
Step A of arranging a laminate having the first material and the second material and the composite sheet according to any one of claims 1 to 5 between the heating device and the fixture.
Heating the laminate using the heating device, and thermocompression-bonding the first material and the second material,
In the step A, the thermocompression bonding method in which the composite sheet is interposed between the fixture and the laminate. The thermocompression bonding method according to claim 6, wherein the heating device is an ultrasonic oscillator.