WO2016185688A1 - Heat transfer sheet and method for manufacturing same - Google Patents

Abstract

The purpose of the present invention is to provide a heat transfer sheet having exceptional flame retardancy and durability. This heat transfer sheet contains a fluororesin and expanded graphite, and exhibits thickness-direction thermal conductivity of 20 W/m•K or higher. In addition, this method for manufacturing a heat transfer sheet includes: a step for pressurizing a composition containing a fluororesin and expanded graphite, forming the composition into the form of a sheet, and obtaining a pre-heat-transfer sheet; a step for laminating a plurality of the pre-heat-transfer sheets in the thickness direction, or folding or winding the pre-heat-transfer sheet, to obtain a laminated body; and a step for slicing the laminated body at an angle equal to or less than 45° relative to the lamination direction, and obtaining a heat transfer sheet.

Description

Thermal conductive sheet and manufacturing method thereof

The present invention relates to a heat conductive sheet and a method for producing the heat conductive sheet.

In recent years, electronic parts such as a plasma display panel (PDP) and an integrated circuit (IC) chip have increased in calorific value as performance is improved. As a result, in electronic devices using electronic components, it is necessary to take measures against functional failures due to temperature rise of the electronic components.

Here, in general, as a countermeasure against functional failure due to a temperature rise, a method of promoting heat dissipation by attaching a heat sink such as a metal heat sink, a heat sink, or a heat sink to a heat generator such as an electronic component is adopted. ing. And when using a heat radiator, in order to transfer heat efficiently from a heat generating body to a heat sink, a heat generating body, a heat sink, and a heat conductive sheet through a sheet-like member (heat conductive sheet) with high heat conductivity. Are in close contact. Therefore, the heat conductive sheet used by being sandwiched between the heat generator and the heat radiator is required to have high thermal conductivity and high flexibility.

Therefore, for example, in Patent Document 1, as a heat conductive sheet excellent in thermal conductivity and flexibility, the glass transition temperature (Tg) is an acrylate copolymer having a temperature of 50 ° C. or less, and a scaly, oval or rod-like shape, Formed using a composition containing graphite particles in which the six-membered ring surface in the crystal is oriented in the plane direction of the scale, the long axis direction of the ellipsoid or the long axis direction of the rod, and the phosphate ester flame retardant A heat conductive sheet in which graphite particles are oriented in the thickness direction has been proposed.

International Publication No. 2008/053843

Here, in recent years, from the viewpoint of safety and the like, the thermal conductive sheet is also required to have high flame resistance and excellent durability in addition to high thermal conductivity and flexibility. However, the conventional heat conductive sheet described in Patent Document 1 or the like is not sufficient in flame retardancy and durability.

Then, an object of this invention is to provide the heat conductive sheet excellent in a flame retardance and durability.
Moreover, an object of this invention is to provide the manufacturing method of the heat conductive sheet which can manufacture efficiently the heat conductive sheet excellent in a flame retardance and durability.

The present inventors have intensively studied to achieve the above object. The inventors have found that a heat conductive sheet formed using a composition containing a fluororesin and expanded graphite is excellent in both flame retardancy and durability, and completed the present invention. .

That is, this invention aims at solving the said subject advantageously, The heat conductive sheet of this invention contains a fluororesin and expanded graphite, and the heat conductivity of the thickness direction is 20 W /. It is more than m · K. Thus, if a fluororesin and expanded graphite are contained, a heat conductive sheet excellent in flame retardancy and durability can be obtained. Moreover, if the heat conductivity of the thickness direction is 20 W / m * K or more, it can be used favorably as a heat conductive sheet.
In the present invention, the “thermal conductivity in the thickness direction” refers to the thermal diffusivity α (m ² / s) in the thickness direction of the heat conductive sheet, the constant pressure specific heat Cp (J / g · K), and the specific gravity ρ (g / m ³ ), the following formula (I):
Thermal conductivity in thickness direction λ (W / m · K) = α × Cp × ρ (I)
It can be obtained more. Here, "thermal diffusivity" can be measured using a thermophysical property measuring device, "constant pressure specific heat" can be measured using a differential scanning calorimeter, and "specific gravity" can be measured using an automatic hydrometer. Can be measured.

Here, the heat conductive sheet of the present invention preferably contains 110 parts by mass or more of the expanded graphite per 100 parts by mass of the fluororesin. When the content ratio of the expanded graphite is 110 parts by mass or more per 100 parts by mass of the fluororesin, a heat conductive sheet in which flame retardancy, durability, and heat conductivity are juxtaposed at a sufficiently high level can be obtained.

Moreover, it is preferable that the heat conductive sheet of the present invention further contains an adhesive resin. If an adhesive resin is contained, a heat conductive sheet can be favorably formed.

Furthermore, the heat conductive sheet of the present invention preferably further contains a phosphate ester flame retardant. If a phosphate ester flame retardant is contained, the heat conductive sheet can be formed satisfactorily, and the flame retardance of the heat conductive sheet can be further improved.

And it is preferable that the heat conductive sheet of this invention further contains a fibrous carbon material. When the fibrous carbon material is contained, the heat conductive sheet can be formed satisfactorily and the flame retardancy, durability and heat conductivity of the heat conductive sheet can be juxtaposed at a sufficiently high level. Moreover, if a fibrous carbon material is blended, the expanded graphite can be prevented from falling off.

Another object of the present invention is to advantageously solve the above-mentioned problems, and a method for producing a heat conductive sheet according to the present invention is a method in which a composition containing a fluororesin and expanded graphite is pressed to form a sheet. Forming a pre-heat conductive sheet, and stacking a plurality of the pre-heat conductive sheets in the thickness direction, or folding or winding the pre-heat conductive sheet to obtain a laminate, and And slicing the laminated body at an angle of 45 ° or less with respect to the laminating direction to obtain a heat conductive sheet. Thus, if a laminate comprising a pre-heat conductive sheet formed by pressurizing a composition containing a fluororesin and expanded graphite is sliced at an angle of 45 ° or less with respect to the lamination direction, flame retardancy and durability are achieved. It is possible to easily manufacture a heat conductive sheet that is excellent in properties and heat conductivity.

According to the present invention, it is possible to provide a heat conductive sheet excellent in flame retardancy and durability and an efficient manufacturing method thereof.

Hereinafter, embodiments of the present invention will be described in detail.
The heat conductive sheet of the present invention can be used, for example, by being sandwiched between a heat generator and a heat radiator when the heat radiator is attached to the heat generator. That is, the heat conductive sheet of this invention can comprise a heat radiating device with heat sinks, such as a heat sink, a heat sink, and a heat radiating fin. And the heat conductive sheet of this invention can be manufactured, for example using the manufacturing method of the heat conductive sheet of this invention.

(Heat conduction sheet)
The heat conductive sheet of the present invention contains a fluororesin and expanded graphite, and optionally further contains a fibrous carbon material, a particulate carbon material other than the expanded graphite, an additive, and the like. Moreover, the heat conductive sheet of this invention is 20 W / m * K or more in the heat conductivity of the thickness direction. And since the heat conductive sheet of this invention contains the fluororesin and expanded graphite, it is excellent in a flame retardance and durability. Moreover, since the heat conductivity sheet of the present invention has a heat conductivity in the thickness direction of 20 W / m · K or more and can efficiently transfer heat in the thickness direction, for example, between the heating element and the heat dissipation element. It can be used satisfactorily as a heat conductive sheet used by being sandwiched.

<Fluorine resin>
The fluororesin is not particularly limited. For example, 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, vinylidene fluoride -Tetrafluoroethylene-hexafluoropropylene copolymer, acrylic modified product of polytetrafluoroethylene, ester modified product of polytetrafluoroethylene, polytetrafluoroethylene Epoxy-modified products of alkylene and silane-modified product of polytetrafluoroethylene, and the like. Among these, from the viewpoint of processability, as the fluororesin, polytetrafluoroethylene, polytetrafluoroethylene modified acrylic, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene- A hexafluoropropylene copolymer is preferred.
In the present invention, rubber and elastomer are included in “resin”.

Here, the fluororesin constitutes a matrix resin of the heat conductive sheet and also functions as a binder for binding expanded graphite and the like in the heat conductive sheet. And it is preferable that content of a fluororesin is 35 to 50 mass% in a heat conductive sheet. If the content of the fluororesin is 35% by mass or more, the expanded graphite can be bound well to form a heat conductive sheet, and the heat conductive sheet has sufficient flame retardancy and durability. Can be increased. Moreover, if content of a fluororesin is 50 mass% or less, while being able to fully improve the heat conductivity of a heat conductive sheet, the hardness of a heat conductive sheet will raise (namely, a softness | flexibility will fall). Can be suppressed.

<Expanded graphite>
The expanded graphite contained in the heat conductive sheet of the present invention is obtained by, for example, expanding the expanded graphite obtained by chemically treating graphite such as scale-like graphite with sulfuric acid or the like, and then reducing the size. Obtainable. Examples of expanded graphite include EC1500, EC1000, EC500, EC300, EC100, and EC50 (all trade names) manufactured by Ito Graphite Industries.

Here, the average particle size of the expanded graphite contained in the heat conductive sheet is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 500 μm or less, and 250 μm or less. More preferably. This is because if the average particle diameter of the expanded graphite is within the above range, the thermal conductivity of the thermal conductive sheet can be further improved.
Further, the aspect ratio (major axis / minor axis) of the expanded graphite contained in the heat conductive sheet is preferably 1 or more and 10 or less, and more preferably 1 or more and 5 or less.

In the present invention, the “average particle diameter” refers to a cross section in the thickness direction of the heat conductive sheet observed with a SEM (scanning electron microscope), and the maximum diameter (major diameter) of any 50 expanded graphites is measured. It can obtain | require by calculating the number average value of the measured major axis. Further, in the present invention, the “aspect ratio” refers to a cross section in the thickness direction of the heat conductive sheet observed with an SEM (scanning electron microscope), and for any 50 expanded graphites, the maximum diameter (major diameter) and the maximum It can be determined by measuring the particle diameter (minor axis) in the direction perpendicular to the diameter and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis).

In the heat conductive sheet, the expanded graphite content is preferably 110 parts by mass or more, more preferably 130 parts by mass or more, and 150 parts by mass or less per 100 parts by mass of the fluororesin. Is preferable, and it is more preferable that it is 140 mass parts or less. If content of the expanded graphite per 100 mass parts of fluororesins is 110 mass parts or more, the heat conductivity of a heat conductive sheet can fully be improved. Moreover, if content of the expanded graphite per 100 mass parts of fluororesins is 150 mass parts or less, while being able to form a heat conductive sheet favorably, the durability of a heat conductive sheet can fully be improved. . Further, the heat conduction sheet is provided with a sufficiently high level of heat conductivity, flame retardancy, durability and flexibility by suppressing the increase in the hardness (that is, the flexibility is lowered) of the heat conduction sheet. Can be obtained.

<Fibrous carbon material>
The fibrous carbon material arbitrarily blended in the heat conductive sheet of the present invention is not particularly limited, and examples thereof include carbon nanotubes, vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and Those cut pieces can be used. These may be used individually by 1 type and may use 2 or more types together.
And if a fibrous carbon material is contained in a heat conductive sheet, the flame retardance, durability, and heat conductivity of a heat conductive sheet can be juxtaposed at a sufficiently high level. Moreover, while being able to form a heat conductive sheet favorably, powder fall-off of expanded graphite and the particulate carbon material mentioned later can also be prevented. The reason why the heat conductive sheet can be satisfactorily formed by blending the fibrous carbon material and the powdered powder of the expanded graphite and the particulate carbon material can be prevented is not clear, but the fiber This is presumably because the formation of the three-dimensional network structure of the carbonaceous material prevents detachment of the expanded graphite and the particulate carbon material while improving the thermal conductivity and durability.

Here, among the above, as the fibrous carbon material, a fibrous carbon nanostructure such as a carbon nanotube is preferably used, and a fibrous carbon nanostructure including a carbon nanotube is more preferably used. This is because the use of fibrous carbon nanostructures such as carbon nanotubes can further improve the thermal conductivity and durability of the thermal conductive sheet.

[Fibrous carbon nanostructures containing carbon nanotubes]
Here, the fibrous carbon nanostructure containing carbon nanotubes that can be suitably used as the fibrous carbon material may be composed only of carbon nanotubes (hereinafter sometimes referred to as “CNT”). Alternatively, a mixture of CNT and a fibrous carbon nanostructure other than CNT may be used.
The CNT in the fibrous carbon nanostructure is 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 if single-walled carbon nanotubes are used, the thermal conductivity and durability of the thermal conductive sheet can be further improved as compared with the case where multi-walled carbon nanotubes are used.

In addition, the fibrous carbon nanostructure containing CNT has a ratio (3σ / Av) of a 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 a carbon nanostructure with 3σ / Av exceeding 0.25, and a carbon nanostructure with 3σ / Av exceeding 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 durability of the thermal conductive sheet can be achieved even with a small amount of carbon nanostructure. The sex can be enhanced sufficiently. Therefore, the heat conductivity, flame retardancy, durability, and flexibility are suppressed by suppressing the increase in the hardness of the heat conductive sheet (that is, the decrease in flexibility) by blending the fibrous carbon nanostructure containing CNT. It is possible to obtain a heat conductive sheet in which the properties are juxtaposed at a sufficiently high level.
“Average diameter (Av) of fibrous carbon nanostructure” and “standard deviation of diameter of fibrous carbon nanostructure (σ: sample standard deviation)” are measured using a transmission electron microscope, respectively. It can be determined by measuring the diameter (outer diameter) of 100 randomly selected fibrous carbon nanostructures. And the average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructure containing CNT are adjusted by changing the manufacturing method and manufacturing conditions of the fibrous carbon nanostructure containing CNT. Alternatively, it may be adjusted by combining a plurality of types of fibrous carbon nanostructures containing CNTs obtained by different production methods.

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

Furthermore, the fibrous carbon nanostructure containing CNTs preferably has a peak of Radial Breathing Mode (RBM) when evaluated using Raman spectroscopy. Note that there is no RBM in the Raman spectrum of a fibrous carbon nanostructure composed of only three or more multi-walled carbon nanotubes.

In addition, the fibrous carbon nanostructure containing CNTs preferably has a G-band peak intensity ratio (G / D ratio) of 1 to 20 in the Raman spectrum. When the G / D ratio is 1 or more and 20 or less, the thermal conductivity and durability of the thermal conductive sheet can be sufficiently enhanced even if the blending amount of the fibrous carbon nanostructure is small. Therefore, the increase in the hardness of the heat conductive sheet (that is, the decrease in flexibility) is suppressed by blending the fibrous carbon nanostructure, and the thermal conductivity, flame retardancy, durability and flexibility are sufficient. It is possible to obtain a heat conductive sheet arranged side by side at a high level.

Furthermore, the average diameter (Av) of the fibrous carbon nanostructure containing CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, preferably 15 nm or less, and preferably 10 nm or less. More preferably it is. When the average diameter (Av) of the fibrous carbon nanostructure is 0.5 nm or more, aggregation of the fibrous carbon nanostructure can be suppressed and the dispersibility of the carbon nanostructure can be improved. Moreover, if the average diameter (Av) of a fibrous carbon nanostructure is 15 nm or less, the heat conductivity and durability of a heat conductive sheet can fully be improved.

Further, the fibrous carbon nanostructure containing CNTs preferably has an average length of the structure at the time of synthesis of 100 μm or more and 5000 μm or less. Note that, as the length of the structure at the time of synthesis increases, damage such as breakage or cutting occurs more easily at the time of dispersion. Therefore, the average length of the structure at the time of synthesis is preferably 5000 μm or less.

Further, the BET specific surface area of the fibrous carbon nanostructure containing CNTs is preferably 600 m ² / g or more, more preferably 800 m ² / g or more, and 2500 m ² / g or less. Preferably, it is 1200 m ² / g or less. Furthermore, when the CNT in the fibrous carbon nanostructure is mainly opened, the BET specific surface area is preferably 1300 m ² / g or more. If the BET specific surface area of the fibrous carbon nanostructure containing CNTs is 600 m ² / g or more, the thermal conductivity and durability of the thermal conductive sheet can be sufficiently enhanced. Moreover, if 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 and the dispersibility of the CNT in the heat conductive sheet is increased. be able to.
In the present invention, the “BET specific surface area” refers to a nitrogen adsorption specific surface area measured using the BET method.

Furthermore, the fibrous carbon nanostructure containing CNTs is an aggregate oriented in a direction substantially perpendicular to the base material on the base material having a catalyst layer for carbon nanotube growth on the surface according to the super growth method described later. Although obtained as a body (aligned 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. If the mass density is 0.2 g / cm ³ or less, since the bonds between the fibrous carbon nanostructures are weakened, the fibrous carbon nanostructures can be uniformly dispersed in the heat conductive sheet. Further, if the mass density is 0.002 g / cm ³ or more, the integrity of the fibrous carbon nanostructure can be improved, and the handling can be facilitated because it can be prevented from being broken.

The fibrous carbon nanostructure containing CNTs having the above-described properties can be obtained by, for example, supplying a raw material compound and a carrier gas onto a substrate having a catalyst layer for producing carbon nanotubes on the surface, When synthesizing CNTs by the phase growth method (CVD method), a method of dramatically improving the catalytic activity of the catalyst layer by making a small amount of oxidizing agent (catalyst activation material) present in the system (super growth method) According to International Publication No. 2006/011655). Hereinafter, the carbon nanotube obtained by the super growth method may be referred to as “SGCNT”.
Here, the fibrous carbon nanostructure containing CNT produced by the super-growth method may be composed only of SGCNT, and in addition to SGCNT, other carbon nanostructures such as non-cylindrical carbon nanostructures may be used. Carbon nanostructures may be included.

[Properties of fibrous carbon material]
And the average fiber diameter of the fibrous carbon material contained in a heat conductive 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, durability and flexibility of the thermal conductive sheet can be juxtaposed at a sufficiently high level. Here, the aspect ratio of the fibrous carbon material preferably exceeds 10.

In the present invention, the “average fiber diameter” is measured by observing a cross section in the thickness direction of the heat conductive sheet with an SEM (scanning electron microscope), measuring the fiber diameter of any 50 fibrous carbon materials. It can obtain | require by calculating the number average value of the made fiber diameter. In addition, when a fiber diameter is small, the same cross section is observed with TEM (transmission electron microscope), and an average fiber diameter can be calculated | required with the same method.

[Content ratio of fibrous carbon material]
And as for a heat conductive sheet, it is preferable that content of fibrous carbon material is 0.05 mass part or more per 100 mass parts of fluororesins, and it is more preferable that it is 1.0 mass part or more. It is preferably 0 parts by mass or less, and more preferably 3.0 parts by mass or less. If content of the fibrous carbon material per 100 mass parts of fluororesins is 0.05 mass part or more, the heat conductivity and durability of a heat conductive sheet can fully be improved. Moreover, while being able to form a heat conductive sheet favorably, powder fall-off of expanded graphite and a particulate carbon material can be prevented. Further, if the content of the fibrous carbon material per 100 parts by mass of the fluororesin is 5.0 parts by mass or less, the hardness of the heat conductive sheet is increased by blending the fibrous carbon material (that is, the flexibility is decreased). ) Can be suppressed, and a heat conductive sheet in which heat conductivity, flame retardancy, durability and flexibility are juxtaposed at a sufficiently high level can be obtained.

<Particulate carbon material>
The particulate carbon material arbitrarily blended in the heat conductive sheet of the present invention is not particularly limited as long as it is a particulate carbon material other than expanded graphite. For example, artificial graphite, flake graphite, exfoliated It is possible to use graphite other than expanded graphite, such as graphite, natural graphite, acid-treated graphite, and expandable graphite; carbon black; These may be used individually by 1 type and may use 2 or more types together. Moreover, content of the particulate carbon material in a heat conductive sheet can be suitably adjusted according to content of expanded graphite.

<Additives>
If necessary, known additives that can be used for forming the heat conductive sheet can be blended in the heat conductive sheet. Additives that can be blended in the heat conductive sheet are not particularly limited, for example, adhesive resins; flame retardants such as red phosphorus flame retardants and phosphate ester flame retardants; plasticizers; calcium oxide, Hygroscopic agents such as magnesium oxide; Adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; Wettability improvers such as nonionic surfactants and fluorosurfactants; Inorganic ion exchangers, etc. Ion trapping agents; and the like.

Among the above-mentioned, it is preferable to mix an adhesive resin and / or a phosphate ester flame retardant into the heat conductive sheet. If an adhesive resin is blended with the heat conductive sheet, the heat conductive sheet can be formed satisfactorily. Moreover, if a phosphate ester flame retardant is blended in the heat conductive sheet, the heat conductive sheet can be favorably formed while further improving the flame retardancy of the heat conductive sheet.
The reason why the heat conductive sheet can be satisfactorily formed by adding an adhesive resin or a phosphate ester flame retardant is not clear, but an adhesive resin or a phosphate ester flame retardant was added. In this case, the composition used for the formation of the heat conductive sheet is imparted with tackiness, facilitating formation of the composition into a sheet, and detachment of expanded graphite and particulate carbon material from the formed heat conductive sheet. It is presumed that this is to prevent this.

[Adhesive resin]
Here, as the adhesive resin, a resin other than the above-described fluororesin can be used. Specifically, a known tackifier that does not contain a solvent can be used as the adhesive resin. Examples of tackifiers include rosin tackifiers, terpene tackifiers, and petroleum resin tackifiers. These may be used individually by 1 type and may use 2 or more types together.

Examples of rosin tackifiers include esters of rosin acid (main component: abietic acid) contained in pine ani and pine oil, glycerin and pentaerythritol, and their hydrogenated products. An average is mentioned. More specifically, examples of the rosin tackifier include gum rosin, tall oil rosin, wood rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, modified rosin, and rosin ester (rosin diol).

Also, examples of terpene tackifiers include those obtained by polymerizing terpene oil contained in pine or natural terpenes contained in orange peel. More specifically, examples of the terpene tackifier include terpene resins, aromatic modified terpene resins, terpene phenol resins, hydrogenated terpene resins, and the like.

Furthermore, examples of the petroleum resin tackifier include aliphatic, alicyclic and aromatic resins made from petroleum. More specifically, examples of petroleum resin tackifiers include C5 petroleum resins, C9 petroleum resins, copolymer petroleum resins, alicyclic saturated hydrocarbon resins, and styrene petroleum resins.

Among the above-mentioned, as the adhesive resin, rosin tackifier is preferable, and rosin ester is more preferable.

And as for a heat conductive sheet, it is preferable that content of adhesive resin is 3 mass parts or more per 100 mass parts of fluororesins, More preferably, it is 5 mass parts or more, It is 15 mass parts or less. Is preferable, and it is more preferable that it is 10 mass parts or less. If the content of the adhesive resin per 100 parts by mass of the fluororesin is 3 parts by mass or more, the composition used for the formation of the heat conductive sheet can be further easily formed, and the heat conductive sheet can be satisfactorily formed. Can do. Moreover, if content of the adhesive resin per 100 mass parts of fluororesins is 15 mass parts or less, the heat conductivity of a heat conductive sheet, a flame retardance, and durability can fully be improved.

[Phosphate ester flame retardant]
The phosphate ester flame retardant is not particularly limited, and examples thereof include aliphatic phosphate esters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate; triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trixylate. Aromatic phosphates such as nyl phosphate, cresyl-2,6-xylenyl phosphate, tris (t-butylated phenyl) phosphate, tris (isopropylated phenyl) phosphate, triaryl isopropylate; resorcinol bisdiphenyl phosphate , Aromatic condensed phosphate esters such as bisphenol A bis (diphenyl phosphate) and resorcinol bis-doxylenyl phosphate; and the like. These may be used individually by 1 type and may use 2 or more types together.

Among them, as the phosphate ester flame retardant, a phosphate ester flame retardant which is liquid at normal temperature and pressure, specifically, a phosphate ester flame retardant having a freezing point of 15 ° C. or lower and a boiling point of 120 ° C. or higher is preferable. If a phosphate ester-based flame retardant having a freezing point of 15 ° C. or lower and a boiling point of 120 ° C. or higher is used, the composition used for forming the heat conductive sheet is imparted with tackiness, and the composition can be easily formed into a sheet. . Moreover, the softness | flexibility of the formed heat conductive sheet improves.
Examples of the phosphate ester flame retardant having a freezing point of 15 ° C. or lower and a boiling point of 120 ° C. or higher include trimethyl phosphate, triethyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, cresyl-2,6- Examples include xylenyl phosphate, resorcinol bisdiphenyl phosphate, and bisphenol A bis (diphenyl phosphate).

And as for a heat conductive sheet, it is preferable that content of a phosphate ester type flame retardant is 3 mass parts or more per 100 mass parts of fluororesins, It is more preferable that it is 5 mass parts or more, 40 mass parts or less It is preferable that it is 30 mass parts or less. If the content of the phosphate ester flame retardant per 100 parts by mass of the fluororesin is 3 parts by mass or more, it becomes easier to form a composition used for forming the heat conductive sheet, and the heat conductive sheet is improved. Can be formed. Furthermore, the flame retardance and flexibility of the heat conductive sheet can be sufficiently enhanced. Moreover, if content of the phosphate ester flame retardant per 100 mass parts of fluororesins is 40 mass parts or less, the heat conductivity and durability of a heat conductive sheet can fully be improved. Furthermore, bleeding of the phosphate ester flame retardant from the heat conductive sheet can also be suppressed.

In addition to the above-described components, the heat conductive sheet of the present invention may contain an adhesive or an adhesive layer used when manufacturing the heat conductive sheet.

<Properties of thermal conductive sheet>
And the heat conductive sheet of this invention is not specifically limited, It is preferable to have the following properties.

[Thermal conductivity]
The thermal conductivity sheet needs to have a thermal conductivity in the thickness direction of 20 W / m · K or higher at 25 ° C., preferably 30 W / m · K or higher, and 40 W / m · K or higher. More preferably, it is more preferably 45 W / m · K or more, and particularly preferably 50 W / m · K or more. If the thermal conductivity in the thickness direction is 20 W / m · K or more, for example, when sandwiched between a heating element and a radiator, heat can be efficiently transferred from the heating element to the radiator. .

[hardness]
The heat conductive sheet preferably has an Asker C hardness of 90 or less, more preferably 88 or less. If the Asker C hardness is 90 or less, for example, when used by being sandwiched between a heating element and a heat dissipation body, excellent flexibility can be exhibited, and the heating element and the heat dissipation element can be adhered well.
In the present invention, the “Asker C hardness” can be measured at a temperature of 23 ° C. using a hardness meter in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS).

[Thickness]
In addition, the thickness of a heat conductive sheet becomes like this. Preferably it is 0.1 mm or more and 10 mm or less.

(Method for producing heat conductive sheet)
And the heat conductive sheet mentioned above is not specifically limited, For example, the process (pre heat conductive sheet shaping | molding process) of forming a pre heat conductive sheet using the composition containing a fluororesin and expanded graphite, And it can manufacture through the process (laminate formation process) which forms a laminated body using the obtained pre heat conductive sheet, and the process (slicing process) which slices a laminated body.
Hereinafter, each step will be specifically described.

<Pre-heat conductive sheet molding process>
In the pre-heat conductive sheet molding step, it contains a fluororesin and expanded graphite, and optionally a fibrous carbon material, a particulate carbon material other than expanded graphite, an adhesive resin, a phosphate ester flame retardant, etc. A composition further containing these additives is pressed into a sheet shape to obtain a pre-heat conductive sheet.

[Composition]
Here, the composition can be prepared by mixing the fluororesin and the expanded graphite and the above-described optional components (fibrous carbon material, particulate carbon material, additive). And as fluororesin, expanded graphite, fibrous carbon material, particulate carbon material and additive, fluororesin, expanded graphite, fibrous carbon material, particulate carbon material which can be included in the heat conductive sheet of the present invention And what was mentioned above as an additive can be used.

Further, the mixing of the above-described components is not particularly limited, and can be performed using a known mixing apparatus such as a kneader, a roll, or a mixer. Mixing may be performed in the presence of a solvent such as an organic solvent. And mixing time can be made into 5 minutes or more and 60 minutes or less, for example. Also, the mixing temperature can be, for example, 5 ° C. or more and 150 ° C. or less.

Of the components described above, the fibrous carbon material is particularly prone to agglomerate and has low dispersibility. Therefore, when mixed with other components such as fluororesin and expanded graphite as they are, it is excellent in the composition. Difficult to disperse. On the other hand, when the fibrous carbon material is mixed with other components such as fluororesin and expanded graphite in the state of dispersion dispersed in a solvent (dispersion medium), the occurrence of aggregation can be suppressed. In the case of mixing in this state, a large amount of solvent is used when the solid content is solidified after mixing to obtain a composition, and therefore the amount of the solvent used for preparing the composition may increase. Therefore, when a fibrous carbon material is blended in the composition used to form the pre-heat conductive sheet, the fibrous carbon material is a solvent from a dispersion obtained by dispersing the fibrous carbon material in a solvent (dispersion medium). It is preferable to mix with other components in the state of an aggregate (easily dispersible aggregate) of fibrous carbon materials obtained by removing. The aggregate of the fibrous carbon material obtained by removing the solvent from the dispersion of the fibrous carbon material is composed of the fibrous carbon material once dispersed in the solvent, and the fibrous carbon material before being dispersed in the solvent. Since the dispersibility is superior to that of the above-mentioned aggregate, it becomes an easily dispersible aggregate with high dispersibility. Therefore, mixing easily dispersible aggregates with other components such as fluororesin and expanded graphite effectively disperses the fibrous carbon material in the composition efficiently without using a large amount of solvent. Can be made.

Here, as the dispersion of the fibrous carbon material, for example, a coarse dispersion obtained by adding the fibrous carbon material to the solvent is subjected to a dispersion treatment that provides a cavitation effect or a dispersion treatment that obtains a crushing effect. Can be obtained. In addition, the dispersion process which can obtain a cavitation effect is a dispersion method using a shock wave generated when a vacuum bubble generated in water bursts when high energy is applied to a liquid. Specific examples of the dispersion treatment that can provide a cavitation effect include dispersion treatment using an ultrasonic homogenizer, dispersion treatment using a jet mill, and dispersion treatment using a high shear stirrer. In addition, the dispersion treatment that provides the crushing effect is to apply shear force to the coarse dispersion liquid to crush and disperse the aggregates of the fibrous carbon material, and further to apply a back pressure to the coarse dispersion liquid. This is a dispersion method in which the fibrous carbon material is uniformly dispersed in a solvent while suppressing generation. And the dispersion | distribution process from which a crushing effect is acquired can be performed using a commercially available dispersion | distribution system (For example, product name "BERYU SYSTEM PRO" (product made from a beautiful grain) etc.).

The solvent can be removed from the dispersion using a known solvent removal method such as drying or filtration. From the viewpoint of removing the solvent quickly and efficiently, filtration such as vacuum filtration is used. It is preferable to carry out.

[Molding of composition]
The composition prepared as described above can be defoamed and crushed arbitrarily, and then pressed to form a sheet. In addition, when a solvent is used at the time of mixing, it is preferable to form the sheet after removing the solvent. For example, if defoaming is performed using vacuum defoaming, the solvent is simultaneously removed at the time of defoaming. be able to.

Here, the composition can be formed into a sheet using a known forming method such as press forming, rolling forming, or extrusion forming without particular limitation as long as it is a forming method in which pressure is applied. Among these, the composition is preferably formed into a sheet by rolling, and more preferably formed into a sheet by passing between rolls in a state of being sandwiched between protective films. In addition, as a protective film, the polyethylene terephthalate film etc. which performed the sandblast process etc. can be used, without being specifically limited. The roll temperature can be 5 ° C. or more and 150 ° C.

[Pre-heat conductive sheet]
And in the pre-heat conductive sheet formed by pressurizing the composition into a sheet shape, the expanded graphite, the particulate carbon material and the fibrous carbon material to be blended arbitrarily are arranged mainly in the in-plane direction, It is presumed that the thermal conductivity in the in-plane direction is improved.
In addition, the thickness of a pre heat conductive sheet is not specifically limited, For example, it can be 0.05 mm or more and 2 mm or less. From the viewpoint of further improving the thermal conductivity of the heat conductive sheet, the thickness of the pre-heat conductive sheet is preferably more than 20 times and not more than 5000 times the average particle diameter of the expanded graphite.

<Laminated body formation process>
In the laminated body forming step, a plurality of pre heat conductive sheets obtained in the pre heat conductive sheet forming step are laminated in the thickness direction, or the pre heat conductive sheets are folded or wound to obtain a laminate. Here, formation of the laminated body by folding of a pre heat conductive sheet is not specifically limited, It can carry out by folding a pre heat conductive sheet by fixed width using a folding machine. Further, the formation of the laminate by winding the pre-heat conductive sheet is not particularly limited, and by rolling the pre-heat conductive sheet around an axis parallel to the short direction or the long direction of the pre-heat conductive sheet It can be carried out.

Here, usually, in the laminate obtained in the laminate formation step, the adhesive force between the surfaces of the pre-heat conductive sheets depends on the pressure when laminating the pre-heat conductive sheets and the tensile force when folding or winding. Fully obtained. However, when the adhesive force 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-heat conductive sheet slightly dissolved with a solvent. Alternatively, the laminated body forming step may be performed in a state where an adhesive is applied to the surface of the pre-heat conductive sheet or a state where an adhesive layer is provided on the surface of the pre-heat conductive sheet.

In addition, as a solvent used when melt | dissolving the surface of a pre heat conductive sheet, it does not specifically limit, The known solvent which can melt | dissolve resin components, such as a fluororesin contained in the pre heat conductive sheet, is used. be able to. Among these, acetone is preferably used from the viewpoints of solubility and volatility.

Moreover, it does not specifically limit as an adhesive agent apply | coated to the surface of a pre heat conductive sheet, A commercially available adhesive agent and adhesive resin can be used. Among these, as the adhesive, it is preferable to use a resin having the same composition as the resin component such as a fluororesin contained in the pre-heat conductive sheet. And the thickness of the adhesive agent apply | coated to the surface of a pre heat conductive sheet can be 10 micrometers or more and 1000 micrometers or less, for example.
Furthermore, the adhesive layer provided on the surface of the pre-heat conductive sheet is not particularly limited, and a double-sided tape or the like can be used.
Here, the heat conductive filler may be mix | blended with the adhesive agent or the contact bonding layer in the range by which the heat conductive sheet obtained does not become hard too much.

From the viewpoint of suppressing delamination, the obtained laminate may be heated at 120 ° C. or more and 170 ° C. or less for 2 to 8 hours while being pressed at a pressure of 0.1 MPa or more and 0.5 MPa or less in the lamination direction. Good.

And in the laminate obtained by laminating, folding or winding the pre-heat conductive sheet, the expanded graphite and the arbitrarily mixed particulate carbon material and fibrous carbon material are arranged in a direction substantially perpendicular to the laminating direction. It is inferred that

<Slicing process>
In the slicing step, the laminated body obtained in the laminated body forming step is sliced at an angle of 45 ° or less with respect to the laminating direction to obtain a heat conductive sheet composed of 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. Especially, the knife processing method is preferable at the point which makes the thickness of a heat conductive sheet uniform. The cutting tool for slicing the laminate is not particularly limited, and includes a slice member (for example, a sharp blade) having a smooth board surface having a slit and a blade portion protruding from the slit portion. Canna and slicer) can be used.
And the heat conductive sheet obtained through the slicing step is usually a strip (laminated body) containing a fluororesin and expanded graphite and the above-mentioned optional components (fibrous carbon material, particulate carbon material, additive). The slice piece of the pre-heat-conductive sheet which has comprised was connected in parallel.

In addition, from the viewpoint of increasing the thermal conductivity of the heat conductive sheet, the angle at which the laminate is sliced is preferably 30 ° or less with respect to the stacking direction, and more preferably 15 ° or less with respect to the stacking direction. Preferably, it is approximately 0 ° with respect to the stacking direction (that is, the direction along the stacking direction).

Further, from the viewpoint of easily slicing the laminate, the temperature of the laminate when slicing is preferably −20 ° C. or more and 20 ° C. or less, and more preferably −10 ° C. or more and 0 ° C. or less. Furthermore, for the same reason, the laminated body to be sliced is preferably sliced while applying a pressure in a direction perpendicular to the lamination direction, and a pressure of 0.1 MPa to 0.5 MPa in the direction perpendicular to the lamination direction. It is more preferable to slice while loading.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the thermal conductivity, Asker C hardness, sheet formability, flame retardancy, and durability of the thermal conductive sheet were measured or evaluated using the following methods, respectively.

<Thermal conductivity>
About the heat conductive sheet, the thermal diffusivity α (m ² / s) in the thickness direction, the constant pressure specific heat Cp (J / g · K), and the specific gravity ρ (g / m ³ ) were measured by the following methods.
[Thermal diffusivity]
The thermal diffusivity at a temperature of 25 ° C. was measured using a thermophysical property measuring apparatus (product name “Thermo Wave Analyzer TA35” manufactured by Bethel Co., Ltd.).
[Specific pressure specific heat]
Using a differential scanning calorimeter (manufactured by Rigaku, product name “DSC8230”), the specific heat at a temperature of 25 ° C. was measured under a temperature rising condition of 10 ° C./min.
[specific gravity]
The measurement was performed using an automatic hydrometer (trade name “DENSIMTER-H” manufactured by Toyo Seiki Co., Ltd.).
And the following formula (I):
λ = α × Cp × ρ (I)
Further, the thermal conductivity λ (W / m · K) in the thickness direction of the thermal conductive sheet at a temperature of 25 ° C. was determined.
<Asker C hardness>
In accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), the hardness was measured at a temperature of 23 ° C. using a hardness meter (trade name “ASKER CL-150LJ” manufactured by Kobunshi Keiki Co., Ltd.).
Specifically, six heat conductive sheet test pieces prepared to have a size of width 30 mm × length 60 mm × thickness 1.0 mm were stacked and left in a temperature-controlled room maintained at 23 ° C. for 48 hours or more. Asker C hardness was measured using a sample. Then, the height of the damper was adjusted so that the pointer was 95 to 98, and the hardness 20 seconds after the sample and the damper collided was measured five times, and the average value was taken as the Asker C hardness of the sample. .
<Sheet formability>
The state of the pre-heat conductive sheet was visually confirmed, and sheet formability was evaluated according to the following criteria. It shows that the smaller the number of holes and breakage sites in the pre-heat conductive sheet, the easier the composition is made into a sheet, and the heat-conductive sheet can be favorably formed using the pre-heat conductive sheet.
○: Pre-heat conductive sheet has no holes of 1 mm or more and 1 mm or more breakage points ×: Pre-heat conduction sheet has 1 mm or more holes or 1 mm or more breakage sites <Flame Retardancy>
Five test pieces were prepared by cutting the heat conductive sheet into a size of width 10 mm × length 150 mm. Adjust the air and gas flow rate of the Bunsen burner to create a blue flame with a height of about 20 mm, and apply the Bunsen burner flame to the lower end of the vertically supported test piece (so that the flame and the test piece intersect about 10 mm). ) After holding for 10 seconds, the specimen and the Bunsen burner flame were released. After that, as soon as the flame of the test piece disappeared, the flame of the Bunsen burner was again applied to the test piece and held for another 10 seconds, and then the test piece and the flame of the Bunsen burner were separated. After completion of the first and second flame contact, the flaming and non-flaming combustion durations and the presence or absence of combustion drops (drip) were evaluated, and the flame retardancy was evaluated according to UL-94 (flame retardant standard).
That is, the flaming combustion duration after the end of the first and second flame contact, the total of the flammable combustion duration and the flameless combustion duration after the end of the second flame contact, Whether the flameless combustion duration corresponds to V-0 or V-2 of UL-94 (flame retardant standard) was determined based on the total duration of flameless combustion and the presence or absence of combustion drops (drip). Flame test was completed within 10 seconds after the first and second flame contact, and the total of the second and last flame-free combustion duration was within 30 seconds. The sum of the flaming and flameless burning durations of the pieces was within 50 seconds and there was no burning dripping was designated as V-0. In addition, the first and second flames were burned within 30 seconds after the end of the flame contact, and the total of the second flamed combustion duration and the flameless combustion duration was within 60 seconds, and 5 more The total of the flammable and non-flammable combustion durations of the test pieces was 250 seconds or less, and V-2 was the one where there was combustion dripping. Furthermore, all burned items were out of specification. If this evaluation satisfies the V-0 condition, it can be said that the flame retardancy is excellent.
<Durability>
A sample A was formed by forming a heat conductive sheet into a strip shape of 100 mm × 20 mm × 0.5 mm. And the test body A was heated at 200 degreeC in the thermostat for 3 hours. Specimen B was obtained by cooling specimen A taken out of the thermostat to room temperature in a 25 ° C. atmosphere.
And about the test body A and the test body B, the place of 0.5 cm from both ends of the test body is pinched using a tensile tester (manufactured by Nidec Sympo, small desk tester: FGS-TV), and the temperature is 25 ° C. The sample was pulled at a tensile speed of 30 mm / min, and the value when the most load was applied was measured as the breaking strength (tensile strength). And the thing which remove | divided the breaking strength of the test body B by the breaking strength of the test body A was made into the change rate (= breaking strength of the test body B / breaking strength of the test body A), and the following references | standards evaluated. Note that the closer the change rate is to 1.0, the smaller the change in breaking strength before and after heating, and the better the durability.
○: Change rate is 0.5 or more and 2.0 or less ×: Change rate is less than 0.5 or more than 2.0

(Preparation of fluororesin solution)
Fluorine rubber as a fluororesin (Daikin Kogyo Co., Ltd., Daiel-G912, ternary fluororubber made of vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer) is cut into rice grains with scissors and 60 g of methyl ethyl ketone The product was put into (made by Wako Pure Chemical Industries, Ltd.), stirred for 3 hours, and the piece of rubber that was visually invisible was used as a fluororesin solution.

(Preparation of fibrous carbon nanostructure A containing CNT)
A fibrous carbon nanostructure A containing SGCNT was obtained by the super-growth method according to the description in WO2006 / 011655.
The obtained fibrous carbon nanostructure A 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 . Moreover, as a result of measuring the diameter of 100 randomly selected fibrous carbon nanostructures A using a transmission electron microscope, the average diameter (Av) was 3.3 nm, and the sample standard deviation (σ) of the diameter (3σ) multiplied by 3 was 1.9 nm, the ratio (3σ / Av) was 0.58, and the average length was 100 μm. Moreover, the obtained fibrous carbon nanostructure A was mainly composed of single-walled CNTs.

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

(Adjustment of acrylic resin solution)
A reactor was charged with 100 parts of a monomer mixture composed of 94 parts of 2-ethylhexyl acrylate and 6 parts of acrylic acid, 0.03 part of 2,2′-azobisisobutyronitrile and 700 parts of ethyl acetate. After dissolving in nitrogen and purging with nitrogen, a polymerization reaction was carried out at 80 ° C. for 6 hours. The polymerization conversion rate was 97%. And the obtained polymer was dried under reduced pressure and ethyl acetate was evaporated, and the viscous solid acrylic resin was obtained. The weight average molecular weight (Mw) of the acrylic resin was 270000, and the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) was 3.1. The weight average molecular weight (Mw) and the number average molecular weight (Mn) were determined in terms of standard polystyrene by gel permeation chromatography using tetrahydrofuran as an eluent.
100 parts of methyl ethyl ketone was added to 100 parts of the obtained acrylic resin, and the mixture was stirred until it became uniform to obtain an acrylic resin solution.

(Example 1)
<Preparation of composition>
1 part of an easily dispersible aggregate of fibrous carbon nanostructure A as a fibrous carbon material, expanded graphite (trade name “EC-50” manufactured by Ito Graphite Industries Co., Ltd., average particle size: 250 μm) 130 parts, 190 parts of fluororesin solution (95 parts of solid content (fluororesin)), tack fire as an adhesive resin (trade name “KE-359”, manufactured by Arakawa Chemical Industries, Ltd.), super light rosin 5 parts of the ester was stirred and mixed for 1 hour using a Hobart mixer (manufactured by Kodaira Manufacturing Co., Ltd., trade name “ACM-5 LVT type”). The resulting mixture is vacuum degassed for 1 hour, and methyl ethyl ketone is removed simultaneously with degassing, and contains fibrous carbon nanostructure A, expanded graphite, fluororesin, and adhesive resin. A composition was obtained. And the obtained composition was thrown into the crusher and crushed for 10 seconds.
<Preparation of pre-heat conductive sheet>
Subsequently, 5 g of the crushed composition was sandwiched between 50 μm thick PET films (protective film) subjected to sandblast treatment, a roll gap of 330 μm, a roll temperature of 50 ° C., a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min. Roll forming was performed under conditions to obtain a pre-heat conductive sheet having a thickness of 0.3 mm.
And the sheet formability was evaluated using the obtained pre heat conductive sheet.
<Production of cylindrical body>
Then, after peeling off the protective film, a 12 μm thick double-sided tape (manufactured by Nichiban, trade name “Nai Stack”) is attached to one side of the obtained pre-heat conductive sheet, and pre-heat is applied around the 1 cm diameter metal rod. The conductive sheet was wound into a roll shape to obtain a cylindrical body (laminated body).
<Preparation of heat conductive sheet>
Then, the metal rod was extracted from the cylindrical body of the pre-heat conductive sheet and pressed at a pressure of 10 MPa from the surface direction of the pre-thermal conductive sheet, so that the cylindrical body was an elliptic cylinder. And the obtained elliptic cylinder (laminated body) is sliced woodworking slicer (manufactured by Marunaka Co., Ltd.) at an angle of 0 degrees with respect to the elliptical surface of the elliptical cylinder (that is, parallel to the elliptical surface). Then, the product was sliced with the trade name “Super-finished planer board super mechanism”, the protrusion length of the sword portion from the slit portion: 0.11 mm) to obtain an elliptical heat conductive sheet having a thickness of 0.5 mm.
And about the obtained heat conductive sheet, heat conductivity, Asker C hardness, a flame retardance, and durability were measured or evaluated. The results are shown in Table 1.

(Example 2)
When producing a cylindrical body using a pre-heat conductive sheet, acetone (made by Wako Pure Chemical Industries) is applied to one side of the obtained pre-heat conductive sheet without using a double-sided tape, and the surface of the pre-heat conductive sheet In the same manner as in Example 1 except that a cylindrical body was obtained by winding a pre-heat conductive sheet around a metal rod having a diameter of 1 cm in a state in which the resin component present in the resin was dissolved, in the same manner as in Example 1. Got. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
When preparing the composition, the amount of expanded graphite was changed to 120 parts, the amount of the fluororesin solution was changed to 160 parts (the solid content (fluororesin) was 80 parts), and the tackifier was replaced. An elliptical heat conductive sheet was obtained in the same manner as in Example 1 except that 20 parts of a phosphate ester flame retardant (trade name “PX-110”) was blended. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

Example 4
When preparing the composition, the compounding amount of expanded graphite is changed to 110 parts, the compounding amount of the fluororesin solution is changed to 200 parts (the solid content (fluororesin) is 100 parts), and tackifier is added. An elliptical heat conductive sheet was obtained in the same manner as Example 1 except that there was no. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
When preparing the composition, the compounding amount of the expanded graphite was changed to 110 parts, the compounding amount of the fluororesin solution was changed to 200 parts (the solid content (the fluororesin) was 100 parts), and the fibrous carbon nano An elliptical heat conductive sheet was obtained in the same manner as in Example 1 except that the easily dispersible aggregate of structure A and the tackifier were not blended. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
When preparing the composition, use 200 parts of an acrylic resin solution (solid content is 100 parts) instead of the fluororesin solution, and blend an easily dispersible aggregate of fibrous carbon nanostructure A and a tackifier. An elliptical heat conductive sheet was obtained in the same manner as Example 1 except that there was no. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
When preparing the composition, use 100 parts of an acrylic resin solution (50 parts in solid content) instead of the fluororesin solution, and blend an easily dispersible assembly of fibrous carbon nanostructure A and a tackifier. First, an elliptical heat conductive sheet was prepared in the same manner as in Example 1 except that 50 parts of a phosphate ester flame retardant (trade name “PX-110”) was blended. It was not possible to produce an elliptical heat conductive sheet.

From Table 1, the heat conductive sheets of Examples 1 to 5 containing fluororesin and expanded graphite are excellent in flame retardancy and durability as compared with the heat conductive sheet of Comparative Example 1 using an acrylic resin. I understand. In Comparative Example 2, a heat conductive sheet could not be produced.

According to the present invention, it is possible to provide a heat conductive sheet excellent in flame retardancy and durability and an efficient manufacturing method thereof.

Claims (6)

1. Including fluororesin and expanded graphite,
   A thermal conductive sheet having a thermal conductivity in the thickness direction of 20 W / m · K or more.
2. The heat conductive sheet according to claim 1, comprising 110 parts by mass or more of the expanded graphite per 100 parts by mass of the fluororesin.
3. The heat conductive sheet according to claim 1 or 2, further comprising an adhesive resin.
4. The heat conductive sheet according to any one of claims 1 to 3, further comprising a phosphate ester flame retardant.
5. The heat conductive sheet according to any one of claims 1 to 4, further comprising a fibrous carbon material.
6. Pressurizing a composition containing a fluororesin and expanded graphite to form a sheet, and obtaining a pre-heat conductive sheet;
   Laminating a plurality of the pre-heat conductive sheets in the thickness direction, or folding or winding the pre-heat conductive sheet to obtain a laminate; and
   Slicing the laminate at an angle of 45 ° or less with respect to the lamination direction to obtain a heat conductive sheet;
   The manufacturing method of the heat conductive sheet containing this.