JP2018203857A - Thermally conductive sheet - Google Patents

Abstract

To provide a thermally conductive sheet which suppresses occurrence of siloxane gas and secures good resistance to pump out property, and can exhibit excellent thermal conductivity under comparatively low sandwiching pressure.SOLUTION: A thermally conductive sheet contains a fluorine resin and a thermally conductive filler containing boron nitride particles, and has a heat resistance value at 0.05 MPA pressurization of 0.90°C/W or less. The fluorine resin preferably contains a fluorine resin that is liquid under normal temperature and normal pressure.SELECTED DRAWING: None

Description

  The present invention relates to a heat conductive sheet.

  In recent years, electronic components such as plasma display panels (PDP) and integrated circuit (IC) chips have increased in heat generation 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.

  As countermeasures against functional failures due to temperature rise of electronic components, generally, a method of promoting heat dissipation by attaching a heat sink such as a metal heat sink, heat sink, heat sink or the like to a heat generator such as an electronic component is adopted. ing. And when using a radiator, in order to efficiently transfer heat from the heating element to the radiator, a heat radiating member such as a sheet-like member (heat conduction sheet) having a high thermal conductivity is usually interposed. The heating element and the radiator are in close contact with each other.

  And examination which improves the characteristic of the heat conductive sheet as a heat radiating member conventionally is made | formed. For example, in Patent Document 1, plate-like boron nitride particles having a predetermined average particle diameter are dispersed in a predetermined resin such as a silicone resin so as to be oriented in the major axis direction with respect to the sheet thickness direction. A method for producing a heat conductive sheet having not only high heat conductivity but also excellent flexibility is described. And according to patent document 1, in the manufacture of a heat conductive sheet, while including the phosphate ester flame retardant, the flame retardance of the said heat conductive sheet can be improved and a softness | flexibility can be improved further.

Patent No. 5882581

  Here, when the heat conductive sheet of Patent Document 1 is sandwiched between a heat generator and a heat radiator, outgas may be generated from the heat conductive sheet. Specifically, when a silicone resin is used as the resin, the silicone resin may be decomposed due to heat from the heating element to generate siloxane gas. Outgas such as siloxane gas causes problems such as contact failure, and contributes to a decrease in performance of electronic components.

In particular, in recent years, when sandwiched between adherends such as a heating element and a radiator, the pressure applied to the heat conductive sheet (hereinafter sometimes referred to as “clamping pressure”) is 0.08 MPa or less. There is a case where a heat conductive sheet is used at a relatively low pressure, and there is a demand for a heat conductive sheet that exhibits excellent heat conductivity even when used at such a relatively low clamping pressure.
For such a problem, for example, the heat conduction sheet is given high flexibility to improve the adhesion between the heat dissipation member and the adherend, and the heat resistance value of the heat conduction sheet under pressure by being sandwiched is set. It is conceivable to reduce it.
However, when the flexibility of the heat conductive sheet is increased by using the method described in Patent Document 1 described above, the heat conductive sheet such as a phosphate ester-based flame retardant is caused by the clamping pressure and the heat from the heating element. There was a problem that the component of the liquid dripped (pumped out) outside the adherend.
That is, the conventional heat conductive sheet described in Patent Document 1 or the like suppresses the generation of siloxane gas and suppresses pump-out (that is, ensures good pump-out resistance), and has a relatively low clamping pressure. There was room for improvement in terms of exhibiting excellent thermal conductivity when used in the above.

Therefore, the present invention provides a heat conductive sheet that suppresses the generation of siloxane gas, ensures good pump-out resistance, and can exhibit excellent heat conductivity under a relatively low clamping pressure. For the purpose.
In the present invention, “relatively low clamping pressure” means that the clamping pressure is 0.08 MPa or less (absolute pressure).

  The inventor has intensively studied to achieve the above object. And if this inventor uses a fluororesin and the boron nitride particle | grains as a heat conductive filler, and if a heat conductive sheet is formed so that heat resistance value may become below a predetermined value, the cause of siloxane gas generation | occurrence | production Even without using a silicone resin, the heat conductive sheet can be made to exhibit excellent heat conductivity under a relatively low clamping pressure, and in addition, the pump-out can be well suppressed, and the present invention Was completed.

That is, this invention aims at solving the said subject advantageously, The heat conductive sheet of this invention contains a fluororesin and the heat conductive filler containing a boron nitride particle, 0 A thermal resistance value under a pressure of 0.05 MPa is 0.90 ° C./W or less. Thus, if it is a thermal conductive sheet containing at least a fluororesin and boron nitride particles and having a low thermal resistance value of not more than the predetermined value under a pressure of 0.05 MPa, generation of siloxane gas is suppressed, and In addition, while ensuring good pump-out resistance, excellent thermal conductivity can be exhibited when used at a relatively low clamping pressure. Therefore, for example, when the heat conductive sheet of the present invention is attached between the heat generating body and the heat radiating body, when the clamping pressure is relatively low, the generation of siloxane gas and the pump-out are suppressed well, Heat can be dissipated efficiently.
In the present invention, the “thermal resistance value” can be measured according to the method described in the examples of the present specification.

Here, in the heat conductive sheet of the present invention, the fluororesin preferably contains a fluororesin that is liquid at normal temperature and pressure. If a liquid fluororesin is used at room temperature and normal pressure, the thermal conductivity of the thermal conductive sheet under pressure due to being sandwiched (especially thermal conductivity under a relatively low clamping pressure) can be further improved. .
In the present invention, “normal temperature” refers to 23 ° C., and “normal pressure” refers to 1 atm (absolute pressure).

  Moreover, it is preferable that the heat conductive sheet of this invention is 10 mass% or more and 90 mass% or less of the ratio of the liquid fluororesin in the said fluororesin under the said normal temperature normal pressure. If the ratio of the liquid fluororesin in the fluororesin at room temperature and normal pressure is within the above-mentioned range, the heat resistance of the heat conducting sheet under pressure is ensured while being secured with better pump-out resistance. The conductivity (especially the thermal conductivity under a relatively low clamping pressure) can be further improved. In addition, the dielectric breakdown of the heat conductive sheet can be sufficiently suppressed (that is, the dielectric breakdown resistance can be ensured).

And it is preferable that the heat conductive sheet of this invention is 30 volume% or more and 75 volume% or less in the content rate of a heat conductive filler. If the content ratio of the heat conductive filler is within the above range, the heat conductivity of the heat conductive sheet under pressure due to being sandwiched is ensured while ensuring the formability when forming the heat conductive sheet (particularly, comparison) The thermal conductivity under a low clamping pressure can be further improved.
In the present invention, the “content ratio (volume%)” can be determined according to the method described in the examples of the present specification.

Here, the thermal conductive sheet of the present invention preferably has a thermal resistance value under 0.50 MPa pressure of less than 0.50 ° C./W. If it is a heat conductive sheet having a low thermal resistance value less than the predetermined value under 0.50 MPa pressure, it is excellent not only when used at a relatively low clamping pressure but also when used at a relatively high clamping pressure. High thermal conductivity can be exhibited.
In the present invention, the “relatively high clamping pressure” means that the clamping pressure is 0.30 MPa or more (absolute pressure).

  According to the present invention, there is provided a heat conductive sheet that suppresses generation of siloxane gas, ensures good pump-out resistance, and can exhibit excellent heat conductivity under a relatively low clamping pressure. be able to.

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 as a heat radiating member 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 by arbitrary methods, as long as it has the predetermined component and predetermined heat resistance value which are mentioned later.

(Heat conduction sheet)
The heat conductive sheet of this invention contains a fluororesin and the heat conductive filler containing a boron nitride particle. Here, the thermally conductive sheet of the present invention may optionally contain a thermally conductive filler other than boron nitride particles (hereinafter, may be abbreviated as “other thermally conductive filler”). Furthermore, the heat conductive sheet of the present invention may optionally contain other components such as resins other than fluororesin (hereinafter sometimes abbreviated as “other resins”) and additives. Further, the heat conductive sheet of the present invention has a heat resistance value of 0.90 ° C./W or less under a pressure of 0.05 MPa.
And the heat conductive sheet of the present invention contains at least fluororesin and boron nitride particles, and since the thermal resistance value under a pressure of 0.050 MPa is as low as the above predetermined value, generation of siloxane gas is suppressed, Further, for example, compared to the heat conductive sheet described in Patent Document 1 that ensures flexibility by using a large amount of a phosphoric ester-based flame retardant, pump-out is less likely to occur, and under a relatively low clamping pressure. Even if it is used in, it has excellent thermal conductivity. Accordingly, when the heat conductive sheet of the present invention is used in combination with a heat sink such as a heat sink, a heat sink, or a heat sink, the heat conductive sheet is sandwiched between the heat generator and the heat sink with a relatively low clamping pressure. Even if it is a case, heat can be effectively dissipated from the heating element through the heat conductive sheet. In addition, when the heat conductive sheet of the present invention is used by being sandwiched between adherends such as a heat generator and a heat radiator, it is possible to prevent performance degradation of electronic components due to generation of siloxane gas, and The adherend is not contaminated by pumping out and can be used for a long period of time.

<Fluorine resin>
The fluororesin constitutes a matrix resin of the heat conductive sheet and also functions as a binder for binding boron nitride particles and the like in the heat conductive sheet. A fluororesin is difficult to be decomposed at high temperatures (that is, excellent in heat resistance) and has sufficient flexibility, and is therefore preferable as a matrix resin for a heat conductive sheet. In addition, a fluororesin may be used individually by 1 type and may use 2 or more types together.
Here, the fluororesin can be classified according to its state at normal temperature and pressure. Specifically, the fluororesin can be classified into a liquid fluororesin that is liquid at normal temperature and pressure and a solid fluororesin that is solid at normal temperature and pressure.

<< Fluoropolymer liquid at normal temperature and pressure >>
By using a fluororesin that is liquid at normal temperature and pressure as a fluororesin, the flexibility of the thermal conductive sheet is increased, and the thermal conductivity of the thermal conductive sheet under pressure by being sandwiched (particularly, a relatively low clamping pressure) Underlying thermal conductivity) can be further improved.
Here, the fluororesin that is liquid under normal temperature and normal pressure is not particularly limited as long as it is a fluororesin that is liquid under normal temperature and normal pressure, and may be thermoplastic or thermosetting. Among these, from the viewpoint of improving the adhesion between the heat conductive sheet and the adherend when using the heat conductive sheet and radiating the heat from the heat generating element, a thermoplastic fluororesin that is liquid at normal temperature and normal pressure is preferable.

Examples of thermoplastic fluororesins that are liquid at normal temperature and pressure include, for example, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer, perfluoropropene oxide polymer, A tetrafluoroethylene-propylene-vinylidene fluoride copolymer may be mentioned.
Examples of commercially available thermoplastic fluororesins that are liquid at room temperature and normal pressure include, for example, Viton (registered trademark) LM manufactured by DuPont Co., Ltd., Daiel (registered trademark) G-101 (vinylidene) manufactured by Daikin Industries, Ltd. Fluoride-hexafluoropropylene copolymer), Dinion FC2210 manufactured by 3M Corporation, and SIFEL series manufactured by Shin-Etsu Chemical Co., Ltd.

The viscosity of the fluororesin that is liquid at normal temperature and normal pressure is not particularly limited, but from the viewpoint of good kneadability, fluidity, cross-linking reactivity, and excellent moldability, the viscosity at 80 ° C. (viscosity coefficient) ) Is preferably 500 P or more and 20000 P or less, and more preferably 1000 P or more and 10,000 P or less.
In the present invention, “viscosity (viscosity coefficient)” can be measured at a temperature of 80 ° C. using an E-type viscometer according to the method described in the examples of the present specification.

  Incidentally, the molecular weight of a fluororesin that is liquid under normal temperature and normal pressure is generally smaller than the molecular weight of a solid fluororesin under normal temperature and normal pressure described later. Therefore, for example, when the heat conductive sheet contains a fluororesin that is liquid at normal temperature and normal pressure and a fluororesin that is solid at normal temperature and normal pressure, the two different types obtained using gel permeation chromatography (GPC) are used. Of the two peaks, the low molecular weight peak usually refers to a liquid fluororesin at normal temperature and pressure, and the high molecular weight peak refers to a solid fluororesin at normal temperature and pressure.

<< Fluoropolymer that is solid at normal temperature and pressure >>
By using a solid fluororesin at room temperature and normal pressure as the fluororesin, it is possible to further enhance the pump-out resistance of the heat conductive sheet and to ensure the dielectric breakdown resistance of the heat conductive sheet.
Here, the fluororesin that is solid under normal temperature and normal pressure is not particularly limited as long as it is a fluororesin that is solid under normal temperature and normal pressure, and may be thermoplastic or thermosetting. Above all, from the viewpoint of ensuring good adhesion between the heat conductive sheet and the adherend while further enhancing the pump-out resistance of the heat conductive sheet when using the heat conductive sheet, the thermoplasticity of the solid at normal temperature and normal pressure A fluororesin is preferred.

  As the thermoplastic fluororesin that is solid at normal temperature and pressure, for example, a fluorine-containing monomer such as vinylidene fluoride fluororesin, tetrafluoroethylene-propylene fluororesin, tetrafluoroethylene-perfluorovinyl ether fluororesin, or the like is polymerized. Examples include elastomers obtained. More specifically, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychloro Trifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, Vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic modified product of polytetrafluoroethylene, ester modified product of polytetrafluoroethylene Epoxy-modified product of polytetrafluoroethylene and polytetrafluoroethylene silane modified product and the like. Among these, vinylidene fluoride-hexafluoropropylene copolymer is preferable from the viewpoint of processability.

  Moreover, as a commercially available thermoplastic fluororesin which is solid at normal temperature and normal pressure, for example, Daiel (registered trademark) G-912, G-700 series, Daiel G-550 series / G- manufactured by Daikin Industries, Ltd. 600 series, Daiel G-310; KYNAR (registered trademark) series, KYNAR FLEX (registered trademark) series manufactured by ALKEMA; Dyneon FC2211, FPO3600ULV manufactured by 3M; and the like.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the fluororesin that is solid at room temperature and normal pressure is preferably 3.5 or more, more preferably 10 or more, and further preferably 20 or more. Preferably, it is 120 or less, more preferably 100 or less, still more preferably 70 or less, still more preferably 50 or less, and particularly preferably 30 or less. If the Mooney viscosity of the solid fluororesin at room temperature and normal pressure is 10 or more, the pump-out resistance of the heat conductive sheet can be further improved. On the other hand, if the Mooney viscosity of the solid fluororesin at room temperature and normal pressure is 120 or less, the thermal conductivity of the thermal conductive sheet is increased by increasing the flexibility of the thermal conductive sheet (particularly, comparison) The thermal conductivity under a low clamping pressure can be further improved.
In the present invention, the “Mooney viscosity (ML _{1 + 4} , 100 ° C.)” can be measured at a temperature of 100 ° C. according to JIS K6300 according to the method described in the examples of the present specification.

<< Ratio of fluororesin that is liquid under normal temperature and normal pressure in fluororesin >>
The ratio of fluororesin that is liquid under normal temperature and normal pressure in the fluororesin (that is, liquid under normal temperature and normal pressure that occupies the total amount of fluororesin that is liquid under normal temperature and normal pressure and solid fluororesin under normal temperature and normal pressure) The ratio of the amount of the fluororesin) is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 40% by mass or more, and preferably 60% by mass or more. It is particularly preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, and particularly preferably 75% by mass or less. If the ratio of the fluororesin that is liquid at room temperature and normal pressure in the fluororesin is 10% by mass or more, the flexibility of the thermal conductive sheet is increased, and the thermal conductivity of the thermal conductive sheet under pressure by being sandwiched (particularly Can further improve the thermal conductivity under a relatively low clamping pressure. On the other hand, if the ratio of the liquid fluororesin in the fluororesin at room temperature and normal pressure is 90% by mass or less, the dielectric breakdown resistance of the heat conductive sheet can be improved and the pump-out resistance can be further improved.

<Thermal conductive filler>
A heat conductive filler is a component which can contribute to ensuring the heat conductivity of a heat conductive sheet. And the heat conductive sheet of this invention needs to contain a boron nitride particle as a heat conductive filler, and may contain another heat conductive filler arbitrarily.

<< Boron nitride particles >>
Since boron nitride particles have high thermal conductivity, the thermal conductivity of the thermal conductive sheet under pressure due to being sandwiched (especially thermal conductivity under relatively low clamping pressure) should be sufficiently improved. Can do.
Here, the boron nitride particles contained in the heat conductive sheet of the present invention are, for example, hexagonal boron nitride particles (h-BN), cubic boron nitride particles (c-BN), wurtzite boron nitride depending on the crystal structure. The particles can be classified into particles (w-BN), rhombohedral boron nitride particles (r-BN), and turbostratic boron nitride particles (t-BN). Among these, hexagonal boron nitride particles (h-BN) are preferable from the viewpoint of imparting excellent heat conductivity to the heat conductive sheet.
As the boron nitride particles, boron nitride particles consisting of only a single crystal structure may be used alone, or two or more types of boron nitride particles having different crystal structures may be used in combination. In other words, the boron nitride particles contained in the heat conductive sheet of the present invention may be composed of a single crystal structure, or may be composed of two or more crystal structures. For example, the heat conductive sheet of the present invention may contain only hexagonal boron nitride particles as boron nitride particles, or may contain hexagonal boron nitride particles and cubic boron nitride particles.

  Further, the shape of the boron nitride particles in the heat conductive sheet is not particularly limited. For example, a plate, a spherical aggregate formed by aggregation of plate-like boron nitride particles, an irregular aggregate, or a granule formed by pulverization The shape is mentioned, A plate shape is preferable.

<< Other thermally conductive fillers >>
Other heat conductive fillers are not particularly limited as long as they are heat conductive fillers. Examples thereof include alumina particles, zinc oxide particles, aluminum nitride particles, silicon nitride particles, silicon carbide particles, magnesium oxide particles, and carbon materials such as particulate carbon materials and fibrous carbon materials. Here, as carbon materials, such as a particulate carbon material and a fibrous carbon material, the thing as described in Unexamined-Japanese-Patent No. 2017-43655 is mentioned, for example.
In addition, another heat conductive filler may be used individually by 1 type, and may use 2 or more types together.

<< content ratio >>
The content ratio of the heat conductive filler in the heat conductive sheet is preferably 30% by volume or more, more preferably 35% by volume or more, still more preferably 45% by volume or more, and 75% by volume. % Or less, more preferably 65% by volume or less, and still more preferably 55% by volume or less. If the content ratio of the thermal conductive filler is 30% by volume or more, the thermal conductivity of the thermal conductive sheet under pressure by being sandwiched (especially thermal conductivity under a relatively low clamping pressure) is sufficient. Can be secured. In addition, the pump-out resistance of the heat conductive sheet can be further improved. On the other hand, if the content rate of a heat conductive filler is 75 volume% or less, the moldability at the time of shape | molding a heat conductive sheet is securable.

  In addition, as a heat conductive filler, carbon materials, such as a particulate carbon material and a fibrous carbon material, can also be used as mentioned above. However, from the viewpoint of imparting electrical insulation to the heat conductive sheet, the content ratio of the carbon material in the heat conductive sheet is preferably 5% by volume or less, more preferably 3% by volume or less. More preferably, it is not more than volume%, particularly preferably not more than 0.1 volume%, and most preferably 0 volume%.

<Other ingredients>
The heat conductive sheet of the present invention may optionally contain other resins and additives in addition to the fluororesin and the heat conductive filler described above.

<< Other resins >>
As other resins, known resins such as acrylic resins, epoxy resins, and silicone resins can be used. These may be used individually by 1 type and may use 2 or more types together. From the viewpoint of ensuring the flexibility of the heat conductive sheet and sufficiently suppressing the generation of outgas such as siloxane gas, the ratio of the other resin in the total amount of the fluororesin and the other resin is 30 mass. %, Preferably 10% by mass or less, more preferably 5% by mass or less, particularly preferably 1% by mass or less, and most preferably 0% by mass. In other words, the ratio of the fluororesin to the total amount of the fluororesin and the other resin is preferably 70% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. More preferably, it is particularly preferably 99% by mass or more, and most preferably 100% by mass.

<< Additives >>
In addition, the additive that can be blended in the heat conductive sheet is not particularly limited. For example, a flame retardant such as a red phosphorus flame retardant and a phosphate ester flame retardant; a moisture absorbent; a silane coupling agent, and a titanium cup. Examples thereof include adhesion improvers such as ring agents and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine surfactants; and ion trapping agents such as inorganic ion exchangers. These may be used individually by 1 type and may use 2 or more types together.

Here, as described in Patent Document 1, if a phosphate ester flame retardant is blended in the heat conductive sheet, the flexibility of the heat conductive sheet can be easily increased. And if the flexibility of a heat conductive sheet becomes high, it is thought that the thermal resistance value of the heat conductive sheet under the pressurization by being pinched can be reduced.
However, when a liquid additive such as a phosphate ester flame retardant is blended in the heat conductive sheet, the pump-out resistance of the heat conductive sheet may be significantly lowered as the additive is blended.
On the other hand, the thermal conductive sheet of the present invention has a thermal conductivity (particularly, the thermal conductivity of the thermal conductive sheet under pressure by being sandwiched even when a liquid additive, particularly a phosphate ester flame retardant, is not blended. Can sufficiently improve the thermal conductivity under a relatively low clamping pressure.

<Method for forming heat conductive sheet>
The heat conductive sheet of the present invention is not particularly limited, and is formed through a pre-heat conductive sheet forming step, a laminate forming step, a slicing step, and the like according to the method described in International Publication No. 2016/185688, for example. Can do.

<< Pre-heat conductive sheet molding process >>
In the pre-heat conductive sheet forming step, a pre-heat conductive sheet is formed by pressurizing a composition containing a fluororesin and a heat conductive filler containing boron nitride particles and optionally containing other components to form a sheet. obtain.

[Composition]
Here, the composition can be prepared by mixing a fluororesin, boron nitride particles, and the above-described optional components (other heat conductive fillers, other resins, additives, and the like).
Moreover, the mixing of the above-described components is not particularly limited, and can be performed using a known mixing device 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.

[Molding of composition]
And after defoaming and crushing arbitrarily, the composition prepared as mentioned above can be shape | molded in a sheet form by pressurization (primary pressurization).
Here, the composition is not particularly limited as long as it is a molding method in which pressure is applied, and can be molded into a sheet using a known molding method such as press molding, rolling molding, or extrusion molding. 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, it does not specifically limit, The polyethylene terephthalate (PET) film etc. which performed the sandblast process can be used. The roll temperature can be 5 ° C. or more and 150 ° C.

[Pre-heat conductive sheet]
And the thickness of the pre heat conductive sheet formed by pressing a composition and shape | molding in a sheet form is not specifically limited, For example, it can be 0.05 mm or more and 2 mm or less.

<< 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, in the laminate obtained in the laminate formation step, when the adhesion between the surfaces of the pre-heat conductive sheet is further increased and the delamination of the laminate is sufficiently suppressed, the surface of the pre-heat conductive sheet is The laminate formation process may be performed in a state slightly dissolved in a solvent, or the laminate is formed in a state where an adhesive is applied to the surface of the pre-heat conduction sheet or an adhesive layer is provided on the surface of the pre-heat conduction sheet. A process may be performed and the laminated body which laminated | stacked the pre heat conductive sheet may be further heat-pressed (secondary pressurization) in the lamination direction.

  In addition, from the viewpoint of efficiently suppressing delamination, it is preferable to secondarily press the obtained laminate in the lamination direction. And it does not specifically limit as conditions of secondary pressurization, It can be 10 seconds-30 minutes at the pressure of 0.05 Mpa or more and 0.5 Mpa or less in the lamination direction, and the temperature of 80 to 170 degreeC.

<< 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.

  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).

  From the viewpoint of easily slicing the laminate, the temperature of the laminate when slicing is preferably -20 ° C or higher and 30 ° C or lower. 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.

<Properties of thermal conductive sheet>
<< Thermal resistance value >>
The heat conductive sheet of the present invention needs to have a heat resistance value of 0.90 ° C./W or less under a pressure of 0.05 MPa. The thermal resistance value of the heat conductive sheet of the present invention under a pressure of 0.05 MPa is preferably 0.70 ° C./W or less, more preferably 0.55 ° C./W or less, and More preferably, it is 40 ° C./W or less. If a heat conductive sheet is produced using the above-mentioned predetermined components so that the thermal resistance value under a pressure of 0.05 MPa is 0.90 ° C./W or less, the heat resistance is reduced when used at a relatively low clamping pressure. The conductive sheet can surely exhibit excellent thermal conductivity.
The thermal resistance value of the heat conductive sheet of the present invention under a pressure of 0.50 MPa is preferably less than 0.50 ° C./W, more preferably 0.40 ° C./W or less, and 0.30 More preferably, it is not more than ° C / W. If the heat conductive sheet is manufactured using the above-mentioned predetermined components so that the thermal resistance value under 0.50 MPa pressure is less than 0.50 ° C./W, it can be used only at the time of use at a relatively low clamping pressure. In addition, even when used at a relatively high clamping pressure, excellent thermal conductivity can be exhibited. Note that the thermal resistance value of the thermal conductive sheet is, for example, at normal temperature and normal pressure in the fluororesin. It can prepare by adjusting suitably the ratio of a liquid fluororesin, the content rate of a heat conductive filler, etc.

<< Thickness >>
Further, the heat conductive sheet of the present invention preferably has a thickness of 0.50 mm or less, more preferably 0.40 mm or less, further preferably 0.25 mm or less, and 0.05 mm or more. be able to. If the thickness is as thin as 0.50 mm or less, for example, even when the heat conductive sheet is interposed between the adherends with a relatively low clamping pressure, the heat conductive sheet follows the shape of the adherend better. Therefore, the heat conductivity of the heat conductive sheet can be further improved. On the other hand, if the thickness is 0.05 mm or more, the heat conductive sheet is not excessively thinned, and the strength and handling properties of the heat conductive sheet can be ensured.

<< Hardness >>
In the heat conductive sheet of the present invention, the Asker C hardness at 25 ° C. is preferably 40 or more, more preferably 45 or more, preferably 80 or less, and preferably 70 or less. More preferred. If hardness is 40 or more, the pump-out resistance of a heat conductive sheet can further be improved. On the other hand, if the hardness of the heat conductive sheet is 80 or less, the flexibility increases, so that the heat conductivity of the heat conductive sheet under pressure by being sandwiched (particularly, the heat conductivity under a relatively low pinching pressure). ) Can be further improved.
In the present invention, the “Asker C hardness” can be measured using a hardness meter in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS 0101).

<< Withstand voltage test value >>
The heat conductive sheet of the present invention preferably has a withstand voltage test value of 1.0 kV / mm or more, more preferably 2.0 kV / mm or more, and 3.0 kV / mm or more. Is more preferable. If a withstand voltage test value is 1.0 kV / mm or more, the dielectric breakdown of a heat conductive sheet can fully be suppressed.
In the present invention, the “withstand voltage test value” can be measured according to the method described in the examples of the present specification.

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 the examples and comparative examples, the viscosity of the resin that is liquid at normal temperature and pressure; the Mooney viscosity of the resin that is solid at normal temperature and pressure; the content of the heat conductive filler in the heat conductive sheet; the thickness of the heat conductive sheet; Pump-out property, thermal resistance value, dielectric breakdown resistance, Asker C hardness, and siloxane gas generation were measured or evaluated according to the following methods, respectively.

<Viscosity of liquid resin under normal temperature and normal pressure>
The viscosity (viscosity coefficient: P) of the liquid resin at room temperature and normal pressure was measured using an E-type viscometer (manufactured by BROOKFIELD, apparatus name “BROOKFIELD DIGITAL VISCOMETER MODEL DV-II Pro”) at a temperature of 80 ° C. .

<Mooney viscosity of solid resin at normal temperature and pressure>
The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the resin solid at normal temperature and normal pressure is 100 according to JIS-K6300 using Mooney viscometer (manufactured by Shimadzu Corporation, product name “MOONEY VISCOMETER SMV-202”). Measured at ° C. Generally, the lower the Mooney viscosity of a solid resin at room temperature and normal pressure, the higher the flexibility.

<Content ratio of heat conductive filler>
The theoretical value in the volume fraction was used for the content ratio of the heat conductive filler in the heat conductive sheet. Specifically, the volume (cm ³ ) is determined from the density (g / cm ³ ) and the blending amount (g) for each component of the resin, the heat conductive filler, and the additive contained in the heat conductive sheet. It calculated and calculated | required the content rate of the heat conductive filler in a heat conductive sheet by the volume fraction (volume%).

<Thickness>
The thickness of the heat conductive sheet was measured using a film thickness meter (manufactured by Mitutoyo, product name “Digimatic Indicator ID-C112XBS”). And the average value (micrometer) of the value measured about five arbitrary places on the heat conductive sheet surface was made into the thickness of a heat conductive sheet.

<Pump-out resistance>
The pump-out resistance of the heat conductive sheet was evaluated as follows.
That is, two copper foils (coarse copper foils) each having a 50 mm square copper plate and a rough surface on one side were prepared. On one copper plate, a rough copper foil was disposed so that the rough surface was on top, and a heat conductive sheet cut into a size of 10 mm × 10 mm square was disposed at a substantially central portion on the rough surface side of the rough copper foil. Subsequently, the other rough copper foil is arranged on the arranged heat conductive sheet so that the rough surface is on the bottom, and the other copper plate is arranged on the rough copper foil, so that the heat conductive sheet becomes the coarse copper foil. A laminate composed of copper plate / coarse copper foil / heat conductive sheet / coarse copper foil / copper plate sandwiched between copper surfaces and a copper plate was obtained as a test piece. Next, a 500 g weight was placed on the obtained test piece, placed in a thermostatic bath at a temperature of 150 ° C., and stored for 72 hours. At this time, the pressure applied to the heat conductive sheet sandwiched between the copper plate and the rough copper foil was 0.05 MPa. And after 72-hour storage, the copper plate and rough copper foil of a test piece were peeled off from the heat conductive sheet, and the presence or absence of the "stain" spread on the rough surface of two rough copper foils was confirmed visually. When “stain” was present, the average value (mm) of the maximum diameter of the outline of the “stain” was measured. Note that the “stain” was formed so as to extend substantially concentrically, and it was possible to approximate a circle or an ellipse. And it evaluated according to the following references | standards.
When the presence of “stain” cannot be confirmed by visual observation, it indicates that the heat conductive sheet is extremely excellent in pump-out resistance. Further, when the presence of “stain” can be confirmed, it indicates that the smaller the average value of the maximum diameter of the “stain”, the more excellent the heat conductive sheet is in the pump-out resistance. If the evaluation of the following heat conductive sheet is AA, A or B, it can be said that the pump-out resistance is relatively good.
AA: Presence of “stain” cannot be confirmed A: Average value of maximum diameter of “stain” exceeds 0 mm and less than 15 mm B: Average value of maximum diameter of “stain” is 15 mm or more and less than 25 mm C: Maximum diameter of “stain” The average value of 25mm or more

<Thermal resistance value>
The thermal resistance value of the heat conductive sheet was measured using a resin material thermal resistance tester (manufactured by Hitachi Technology & Service Co., Ltd., product name “C47108”). Here, a heat conductive sheet cut into a substantially square of 1 cm square is used as a sample, and a heat resistance value (° C./W) when a relatively low pressure of 0.05 MPa is applied at a sample temperature of 50 ° C. and a sample temperature of 50 At 0 ° C., the thermal resistance value (° C./W) was measured when 0.50 MPa, which is a relatively high pressure, was applied. The smaller the thermal resistance value, the more excellent the thermal conductivity of the heat conductive sheet, for example, it indicates that the heat dissipation characteristic is excellent when it is interposed between the heat generator and the heat radiator.

<Dielectric breakdown resistance>
The dielectric breakdown resistance of the heat conductive sheet was evaluated by a withstand voltage test value measured using an in-oil test device (product name “TJ-20S” manufactured by Tama Denso Co., Ltd.). Specifically, a heat conductive sheet cut into a substantially 3 cm square was used as a sample, and the sample was immersed in silicone oil at 23 ° C. One minute after immersion, voltage application was started at a boosting rate of 0.6 kV / sec, and the voltage (kV) when the current flowing through the sample (detected current) reached 10 mA was measured. The withstand voltage test value (kV / mm) was obtained by dividing the obtained voltage (kV) value by the thickness (mm) of the heat conductive sheet as a sample. The larger the withstand voltage test value, the better the heat conductive sheet has the dielectric breakdown resistance.

<Asker C hardness>
Based on 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, 24 heat conductive sheet test pieces prepared in a size of width 30 mm × length 60 mm × thickness 0.5 mm were superposed and allowed to stand for 48 hours or more in a temperature-controlled room maintained at 23 ° C. Asker C hardness was measured using a sample. Then, the height of the damper is adjusted so that the pointer becomes 95 to 98, the hardness 20 seconds after the collision between the sample and the damper is measured five times, and the average value is defined as the Asker C hardness of the sample. .

<Siloxane gas generation>
The heat conductive sheet was cut into an arbitrary size to obtain a sheet piece, and a total of 1 g of the plurality of sheet pieces was measured and used as a sample. The sample was heated at 170 ° C. for 10 minutes using a headspace sampler (manufactured by JEOL, trade name “EQ-12031HSA”). The gas generated from the sample by heating was analyzed using a gas chromatograph / mass spectrometer (manufactured by JEOL, trade name “JMS-Q1000GC”) to confirm the presence or absence of siloxane gas generation. And it evaluated according to the following references | standards.
A: Generation of siloxane gas was not confirmed (that is, the amount of siloxane gas generated was below the detection limit).
B: Generation of siloxane gas was confirmed.

Example 1
<Preparation of composition>
Thermoplastic fluororesin that is liquid at room temperature and normal pressure (Daikin Industries, Ltd., trade name “DAIEL G-101”, viscosity (viscosity coefficient): 3300P) and 70 parts of thermoplastic fluororesin that is solid at room temperature and normal pressure (3M) Made by Japan Co., Ltd., trade name “Dinion FC2211,” Mooney viscosity: 27ML _{1 + 4} , 100 ° C., 30 parts, and boron nitride particles as a thermally conductive filler (product name “PT-110”, manufactured by Momentive Performance Materials) ”, 130 parts of a volume average particle diameter: 36 μm, hexagonal boron nitride particles) was stirred and mixed at a temperature of 150 ° C. for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the obtained mixture was put into a crusher and crushed for 10 seconds to obtain a composition.

<Formation of pre-heat conductive sheet>
Subsequently, 50 g of the obtained composition was sandwiched between sandblasted PET films (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 subjected to rolling forming (primary pressurization) to obtain a pre-heat conductive sheet having a thickness of 0.5 mm.

<Formation of laminate>
Subsequently, the obtained pre-heat conductive sheet was cut into a length of 150 mm × width of 150 mm × thickness of 0.5 mm, and 120 sheets were laminated in the thickness direction of the pre-heat conductive sheet, and further 3 at a temperature of 120 ° C. and a pressure of 0.1 MPa. By pressing (secondary pressing) in the laminating direction for a minute, a laminated body having a height of about 60 mm was obtained.

<Formation of heat conductive sheet>
Then, using a slicer for woodworking (manufactured by Marunaka Co., Ltd., trade name “Super-finished plane board super-mechanism S”) while pressing the laminated side surface of the secondary-pressurized laminate at a pressure of 0.3 MPa. Then, by slicing at an angle of 0 degrees with respect to the stacking direction (in other words, in the normal direction of the main surface of the stacked pre-heat conductive sheet), heat of 150 mm long × 60 mm wide × 0.15 mm thick is obtained. A conductive sheet was obtained.
And about the obtained heat conductive sheet, according to the above-mentioned method, thickness, pump-out resistance, thermal resistance value dielectric breakdown resistance, and Asker C hardness were measured and evaluated. The results are shown in Table 1.

(Example 2)
In the preparation of the composition, the amount of thermoplastic fluororesin that is liquid at room temperature and normal pressure (Daikin Industries, Ltd., trade name “DAIEL G-101”, viscosity (viscosity coefficient): 3300 P) is 50 parts at room temperature and normal pressure. The composition was the same as in Example 1 except that the amount of the solid thermoplastic fluororesin (manufactured by 3M Japan Co., Ltd., trade name “Dionion FC2211”, Mooney viscosity: 27ML _{1 + 4} , 100 ° C.) was changed to 50 parts. Product, pre-heat conductive sheet, laminate and heat conductive sheet were produced.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

Example 3
In the preparation of the composition, an amount of a thermoplastic fluororesin that is liquid at room temperature and normal pressure (manufactured by Daikin Industries, Ltd., trade name “DAIEL G-101”, viscosity (viscosity coefficient): 3300 P) is 30 parts at room temperature and normal pressure. The composition was the same as in Example 1 except that the amount of the solid thermoplastic fluororesin (manufactured by 3M Japan Ltd., trade name “Dionion FC2211”, Mooney viscosity: 27ML _{1 + 4} , 100 ° C.) was changed to 70 parts. Product, pre-heat conductive sheet, laminate and heat conductive sheet were produced.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)
In the preparation of the composition, a thermoplastic fluororesin that is liquid at normal temperature and pressure is not used at room temperature and normal pressure, but is a thermoplastic fluororesin that is liquid at normal temperature and pressure (trade name “DAIEL G-101”, manufactured by Daikin Industries, Ltd.) Coefficient): A composition, a pre-heat conductive sheet, a laminate, and a heat conductive sheet were produced in the same manner as in Example 1 except that the amount of 3300P) was changed to 100 parts.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
In the preparation of the composition, a thermoplastic fluororesin that is liquid at room temperature and normal pressure is not used, and a thermoplastic fluororesin that is solid at room temperature and normal pressure (manufactured by 3M Japan Ltd., trade name “Dinion FC2211”, Mooney viscosity: 27 ML _{1 A} composition, a pre-heat conductive sheet, a laminate and a heat conductive sheet were produced in the same manner as in Example 1 except that the amount of ( ₊₄ , 100 ° C.) was changed to 100 parts.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)
In the formation of the heat conductive sheet, the composition, the pre-heat conductive sheet, the laminate, and the laminate were prepared in the same manner as in Example 1 except that the thickness of the sheet was adjusted to 0.30 mm and the heat conductive sheet was manufactured. A heat conductive sheet was produced.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 7)
In preparation of the composition, the amount of boron nitride particles (product name “PT-110”, volume average particle diameter: 36 μm, hexagonal boron nitride particles, manufactured by Momentive Performance Materials, Inc.) as a heat conductive filler is 70 parts. Except having changed, it carried out similarly to Example 1, and manufactured the composition, the pre heat conductive sheet, the laminated body, and the heat conductive sheet.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 8)
In the preparation of the composition, the amount of boron nitride particles (trade name “PT-110”, volume average particle diameter: 36 μm, hexagonal boron nitride particles, manufactured by Momentive Performance Materials, Inc.) as a thermally conductive filler is 250 parts. Except having changed, it carried out similarly to Example 1, and manufactured the composition, the pre heat conductive sheet, the laminated body, and the heat conductive sheet.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Except having used the composition prepared as follows, it carried out similarly to Example 1, and manufactured the composition, the pre heat conductive sheet, the laminated body, and the heat conductive sheet.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of composition>
Acrylate ester copolymer resin (manufactured by Nagase ChemteX Corporation, trade name “HTR-811DR”, butyl acrylate / ethyl acrylate / 2-hydroxyethyl methacrylate copolymer, weight average molecular weight: 420,000, glass transition temperature : 32.4 parts at −29.4 ° C. and boron nitride particles as thermal conductive filler (product name “PT-110”, manufactured by Momentive Performance Materials, Inc.), volume average particle diameter: 36 μm, hexagonal boron nitride particles ) 112.5 parts and 26.4 parts of phosphate ester flame retardant (manufactured by Daihachi Chemical Industry Co., Ltd., trade name “CR-741”) at a temperature of 120 ° C. Obtained.

(Comparative Example 2)
In the preparation of the composition, the amount of boron nitride particles (trade name “PT-110”, volume average particle diameter: 36 μm, hexagonal boron nitride particles, manufactured by Momentive Performance Materials, Inc.) as a thermally conductive filler is 50 parts. Except having changed, it carried out similarly to Example 1, and manufactured the composition, the pre heat conductive sheet, the laminated body, and the heat conductive sheet.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
In the preparation of the composition, a two-part curable liquid silicone resin (trade name “TSE-3062, manufactured by Momentive Co., Ltd.) was used without using a thermoplastic fluororesin that was solid at normal temperature and pressure and a liquid thermoplastic fluororesin at normal temperature and pressure. The composition, the pre-heat conductive sheet, the laminate and the heat conductive sheet were produced in the same manner as in Example 1 except that 100 parts of “A” and “B” were used in a mass ratio of 1: 1.
Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

From Table 1, the heat conductivity of Examples 1-8 which contains a fluororesin and the heat conductive filler containing boron nitride particle | grains, and the heat resistance value under 0.05 MPa pressurization is 0.90 degrees C / W or less. It can be seen that the sheet is suppressed in the generation of siloxane gas and has good pump-out resistance and high thermal conductivity under a relatively low clamping pressure.
On the other hand, while using only acrylic ester copolymer resin as resin, it turns out that the heat conductive sheet of the comparative example 1 which uses the phosphate ester type flame retardant is inferior to pump-out resistance. Moreover, it turns out that the heat conductive sheet of the comparative example 2 in which the thermal resistance value under 0.05 Mpa pressurization exceeds a predetermined value is inferior to the heat conductivity under a comparatively low clamping pressure. And it turns out that the siloxane gas will generate | occur | produce in the heat conductive sheet of the comparative example 3 which samples only a silicone resin as resin.

  According to the present invention, there is provided a heat conductive sheet that suppresses generation of siloxane gas, ensures good pump-out resistance, and can exhibit excellent heat conductivity under a relatively low clamping pressure. be able to.

Claims (5)

Including a fluororesin and a thermally conductive filler containing boron nitride particles,
The heat conductive sheet whose heat resistance value under 0.05MPa pressurization is 0.90 degrees C / W or less.   The heat conductive sheet according to claim 1, wherein the fluororesin contains a fluororesin that is liquid at normal temperature and pressure.   The heat conductive sheet according to claim 2, wherein a ratio of the liquid fluororesin in the fluororesin under the normal temperature and normal pressure is 10% by mass or more and 90% by mass or less.   The heat conductive sheet in any one of Claims 1-3 whose content rate of the said heat conductive filler is 30 volume% or more and 75 volume% or less.   The heat conductive sheet in any one of Claims 1-4 whose heat resistance value under 0.50 MPa pressurization is less than 0.50 degreeC / W.