JP2019108496A - Thermal conductive sheet and production method thereof - Google Patents

Abstract

To provide a thermal conductive sheet having high insulation reliability.SOLUTION: The thermal conductive sheet comprises a resin and an insulating filler, where the particle size distribution curve of the insulating filler on a volume basis has at least one peak in a particle size range of 133 μm to 890 μm.SELECTED DRAWING: None

Description

  The present invention relates to a heat conductive sheet and a method of manufacturing the same.

  2. Description of the Related Art In recent years, electronic components such as plasma display panels (PDPs) and integrated circuit (IC) chips have an increased amount of heat generation as their performance is enhanced. As a result, in electronic devices using electronic components, it is necessary to take measures against functional failure due to temperature rise of the electronic components.

  As measures against functional failure due to temperature rise of electronic components, generally, a method is adopted in which heat dissipation is promoted by attaching a heat sink such as a metal heat sink, a heat dissipation plate, a heat dissipation fin to a heat generating element such as an electronic component. ing. And when using a heat sink, in order to efficiently transfer heat from a heat generating body to a heat sink, a heat radiating member such as a sheet-like member (heat conductive sheet) having a high thermal conductivity is usually interposed The heat generating body and the heat radiating body are in close contact with each other.

  In the past, studies have been made to improve the characteristics of the heat conductive sheet as a heat dissipation member. For example, Patent Document 1 discloses high thermal conductivity by dispersing plate-like boron nitride particles having a predetermined average particle diameter in a predetermined resin so as to be oriented in the long axis direction with respect to the sheet thickness direction. A method of producing a thermally conductive sheet having a property is described.

  Further, for example, in Patent Document 2, in order to obtain a thermally conductive sheet excellent in thermal conductivity, secondary aggregation particles formed by aggregating primary particles of boron nitride are used as a high thermal conductivity inorganic filler. Has been proposed.

  Furthermore, for example, Patent Document 3 includes a composite particle containing a resin, a particulate carbon material, and a fibrous carbon nanostructure, and in which the fibrous carbon nanostructure is unevenly distributed in the surface layer portion. It has been proposed to obtain a sheet excellent in thermal conductivity by pressure molding.

WO 2010/047278 WO 2009/041300 JP, 2017-88792, A

  Here, the heat conductive sheet is also required to have less variation in insulation performance between the sheets, that is, excellent in insulation reliability. However, the heat conductive sheet according to the said patent documents 1-3 was inadequate by the point of insulation reliability.

  Then, an object of this invention is to provide the manufacturing method of the heat conductive sheet which can manufacture the heat conductive sheet with high insulation reliability, and this heat conductive sheet favorably.

  The present inventors diligently studied to achieve the above object. And this inventor discovers newly that the insulation reliability of a heat conductive sheet can be notably improved by mix | blending the heat conductive sheet with the insulation filler which has a particle size distribution curve of a predetermined | prescribed volume reference | standard. Completed.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the thermally conductive sheet of the present invention contains a resin and an insulating filler, and the volume-based particle size distribution curve of the insulating filler is particles. It is characterized in that it has at least one peak in the range of a diameter of 133 μm or more and 890 μm or less. As described above, when the particle size distribution curve based on volume is taken in the heat conduction sheet, the heat conduction is performed by including the insulating filler which exhibits at least one peak in the range of the particle diameter of 133 μm or more and 890 μm or less. The insulation reliability of the sheet can be enhanced.
Here, the “volume-based particle size distribution” of the insulating filler is measured, for example, using a laser diffraction method using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, type “LA-960”). It can be done. The “volume-based particle size distribution curve” refers to a curve in which the particle diameter measured according to the above is taken on the horizontal axis (unit: μm) and the frequency of volume-converted particles is taken on the vertical axis (unit:%). The term "peak" refers to a convex inflection point in the particle size distribution curve, and includes not only a peak exhibiting a distinct convexity, but also a peak exhibiting a so-called shoulder.

  Here, in the heat conductive sheet of the present invention, the frequency of the insulating filler present in the particle diameter range of 133 μm to 890 μm is preferably 1% by volume to 30% by volume of the entire insulating filler. When the frequency of the insulating filler present in the particle diameter range of 133 μm to 890 μm contained in the heat conductive sheet is 1% by volume to 30% by volume of the entire insulating filler, the insulation reliability of the heat conductive sheet is further enhanced. be able to.

  In the heat conductive sheet according to the present invention, preferably, the particle size distribution curve further has at least one peak in a range of a particle diameter of more than 0 μm and less than 133 μm. If the frequency distribution curve of the insulating filler contained in the heat conductive sheet further has at least one peak in the range of the particle diameter of more than 0 μm and less than 133 μm, the thermal conductivity of the heat conductive sheet can be enhanced.

  Moreover, it is preferable that the frequency of the insulation filler which exists in the range whose particle diameter is less than 133 micrometers is 70 volume% or more and 99 volume% or less of the whole insulation filler. If the frequency of the insulating filler present in the range of particle diameter less than 133 μm contained in the heat conductive sheet is 70% by volume or more and 99% by volume or less of the whole insulating filler, the thermal conductivity and insulation reliability of the heat conductive sheet are further increased. It can be enhanced in a well-balanced manner.

  Further, in the heat conductive sheet of the present invention, it is preferable that the insulating filler having a particle diameter of 133 μm or more and 890 μm or less contains secondary particles. If the insulating filler having a particle diameter of 133 μm or more and 890 μm or less contained in the heat conductive sheet contains secondary particles, the insulation reliability of the heat conductive sheet can be further enhanced. In the present specification, “secondary particles” means aggregates or aggregates of primary particles which are unit particles.

  Further, in the heat conductive sheet of the present invention, it is preferable that the insulating filler having a particle diameter of less than 133 μm contains primary particles. If the insulating filler having a particle diameter of less than 133 μm contained in the heat conductive sheet contains primary particles, the thermal conductivity of the heat conductive sheet can be further enhanced.

Here, the present invention aims to solve the above-mentioned problems advantageously, and the method for producing a thermally conductive sheet of the present invention comprises a composition containing a resin and an insulation having a volume average particle diameter of 133 μm or more. A sheet material preparation step of preparing a sheet material by mixing with the filler B, a step of pressing the sheet material to form it into a sheet to obtain a pre-heat conduction sheet, and a plurality of the pre-heat conduction sheets in the thickness direction Or laminating or winding the pre-heat conductive sheet to obtain a laminated body, slicing the laminated body at an angle of 45 ° or less with respect to the laminating direction, and heat conductive sheet Obtaining the step of Excellent insulation reliability by using a pre-heat conductive sheet obtained by pressure forming a sheet material obtained by mixing an insulating filler having a volume average particle diameter of 133 μm or more with the pulverized composition. The heat conductive sheet can be manufactured well.
In addition, the volume average particle diameter of the insulating filler B can be measured according to the method described in the example using a laser diffraction / scattering type particle size distribution measuring apparatus (manufactured by Horiba, type "LA-960"). .

  Further, the method for producing a thermally conductive sheet of the present invention is characterized by further including pulverizing the insulating filler A and the resin together to obtain a pulverized composition in preparing the composition containing the resin. By manufacturing the heat conductive sheet through the pulverizing step of pulverizing the resin and the insulating filler together, it is possible to efficiently manufacture a heat conductive sheet which is further excellent in insulation reliability and thermal conductivity.

  Further, in the method of manufacturing a heat conductive sheet according to the present invention, preferably, the insulating filler A is primary particles, and the insulating filler B is secondary particles. According to the manufacturing method using such specific particles, it is possible to efficiently manufacture a heat conductive sheet which is further excellent in insulation reliability and thermal conductivity.

  ADVANTAGE OF THE INVENTION According to this invention, the heat conductive sheet with high insulation reliability and the manufacturing method which can manufacture such a heat conductive sheet favorably can be provided.

It is a figure explaining 1 process in manufacturing the heat conductive sheet according to this invention.

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 sandwiching it between a heat generating body and a heat radiating body when attaching the heat radiating body to the heat generating body. That is, the heat conduction sheet of the present invention can constitute a heat dissipation device as a heat dissipation member together with a heat dissipation body such as a heat sink, a heat dissipation plate, and a heat dissipation fin. In particular, since the heat conductive sheet of the present invention is excellent in insulation reliability, it can be particularly suitably used when the heat generator is an electronic device.
And the heat conductive sheet of the present invention is particularly limited as long as the volume based particle size distribution curve of the insulating filler contained in the insulating sheet has at least one peak in the range of particle diameter 133 μm or more and 890 μm or less Although it can manufacture according to any manufacturing method, it can manufacture favorably according to the manufacturing method of the heat conductive sheet of this invention mentioned later.

(Heat conduction sheet)
The heat conductive sheet of the present invention contains a resin and an insulating filler. Furthermore, the heat conductive sheet of the present invention is characterized in that the volume-based particle size distribution curve of the insulating filler has at least one peak in the range of particle diameter of 133 μm or more and 890 μm or less. Here, the heat conductive sheet of the present invention may optionally contain other components other than the resin and the insulating filler. The heat conductive sheet of the present invention is excellent in insulation reliability because the volume-based particle size distribution curve of the insulating filler contained in the heat conductive sheet has at least one peak in the range of particle diameters of 133 μm to 890 μm. The reason is not clear, but is presumed to be as follows. First, one of the causes of loss of insulation reliability of the heat conductive sheet is that the heat conductive sheet is pressed in the thickness direction, whereby the heat conductive sheet is crushed in the thickness direction to form a conductive path. . Here, the heat conductive sheet of the present invention has a peak of frequency distribution in the range of the relatively large particle diameter as described above for the contained insulating filler. Such a large particle size insulating filler exhibits a function like a "pillar" when the heat conductive sheet is pressed in the thickness direction, effectively suppressing the heat conductive sheet from collapsing in the thickness direction, and conducting It is assumed that it can inhibit the formation of paths. It is inferred that the heat conductive sheet of the present invention is excellent in insulation reliability by such a mechanism.

<Resin>
As resin contained in the heat conductive sheet of this invention, arbitrary resin according to the use of a sheet can be used. Specifically, as the resin, at least one of a resin that is liquid at normal temperature and normal pressure and a resin that is solid at normal temperature and normal pressure can be used. In the present specification, “normal temperature” refers to 23 ° C., and “normal pressure” refers to 1 atm (absolute pressure).

The resin which is liquid at normal temperature and normal pressure includes a thermoplastic resin which is liquid at normal temperature and normal pressure and a thermosetting resin which is liquid at normal temperature and normal pressure.
And as a thermoplastic resin of a liquid under normal temperature normal pressure, an acrylic resin, an epoxy resin, a silicone resin, a fluorine resin etc. are mentioned, for example.
Moreover, as a thermosetting resin which is liquid at normal temperature and normal pressure, for example, natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; Butyl rubber; Halogenated butyl rubber; Polyisobutylene rubber; Epoxy resin; Polyimide resin; Bismaleimide resin; Benzocyclobutene resin; Phenolic resin; Unsaturated polyester; Diallyl phthalate resin; Polyimide silicone resin; Polyurethane; Thermosetting polyphenylene ether; Type modified polyphenylene ether; and the like.

Moreover, as a resin solid at normal temperature normal pressure, a thermoplastic resin solid at normal temperature normal pressure and a thermosetting resin solid at normal temperature normal pressure can be mentioned.
And as a thermoplastic resin solid at normal temperature and normal pressure, for example, poly (2-ethylhexyl acrylate), a copolymer of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or ester thereof, polyacrylic acid or Acrylic resin such as ester; silicone resin; fluoro resin; polyethylene; polypropylene; ethylene-propylene copolymer; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymer; polyvinyl alcohol Polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymer; acrylonitrile-butadiene-styrene copolymer (A S resin); styrene-butadiene block copolymer or its hydrogenated product; styrene-isoprene block copolymer or its hydrogenated product; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; Polycarbonate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether nitrile, polyether ketone, poly ketone, polyurethane, liquid crystal polymer, ionomer, and the like.
Moreover, as a thermosetting resin which is solid at normal temperature and pressure, for example, natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; Butyl rubber; Halogenated butyl rubber; Polyisobutylene rubber; Epoxy resin; Polyimide resin; Bismaleimide resin; Benzocyclobutene resin; Phenolic resin; Unsaturated polyester; Diallyl phthalate resin; Polyimide silicone resin; Polyurethane; Thermosetting polyphenylene ether; Type modified polyphenylene ether; and the like.

  In addition, the resin mentioned above may be used individually by 1 type, and may use 2 or more types together.

<Insulation filler>
The insulating filler is a component that can contribute to improving the insulation reliability of the heat conductive sheet. And in the thermally conductive sheet of the present invention, the volume-based particle size distribution curve of the insulating filler contained in the thermally conductive sheet has a particle diameter of at least 133 μm to 890 μm (hereinafter also referred to as “particle diameter range β”) It is necessary to have one peak. Furthermore, from the viewpoint of enhancing the thermal conductivity of the thermally conductive sheet, in the thermally conductive sheet of the present invention, the volume-based particle size distribution curve of the insulating filler contained in the thermally conductive sheet is in the range of , And “particle size range α”) preferably further have at least one peak. The volume-based particle size distribution curve of the insulating filler may have at least one peak within the particle diameter range β, and may have a plurality of peaks. In addition, the volume-based particle size distribution curve of the insulating filler may have a plurality of peaks within the particle diameter range α. Furthermore, the volume-based particle size distribution curve of the insulating filler does not have a peak on the larger particle diameter side than the particle diameter range β. In other words, in the volume-based particle size distribution curve of the insulating filler contained in the heat conductive sheet, the peak present in the particle size range β is the peak with the largest particle size.

[Position of peak on particle size range β side]
At least one peak present in the particle size range β preferably has a particle size in the range of 150 μm to 450 μm, more preferably in the range of 150 μm to 350 μm, and in the range of 150 μm to 250 μm. It is further preferred that If the position of at least one peak present in the particle diameter range β is within the above particle diameter range, the insulation reliability and the thermal conductivity of the heat conductive sheet can be enhanced in a well-balanced manner. In the case where there are a plurality of peaks in the particle size range β, it is preferable that at least the peak with the largest frequency value falls within the above-mentioned preferable particle size range, and all the plurality of peaks are It is more preferred to fall within the preferred particle size range.

[Particle size range α]
The particle size range α may be in the range of more than 0 μm and less than 133 μm. If the volume-based particle size distribution curve of the insulating filler further has at least one peak in the particle size range α, the thermal conductivity of the thermally conductive sheet is high.

[Volume-based particle size distribution]
The volume-based particle size distribution is not particularly limited as long as it has at least one peak in the above-described particle size range β, and may be any aspect. Here, the frequency of the insulating filler present in the particle diameter range β is preferably 1% by volume or more of the whole insulating filler, preferably 30% by volume or less, and more preferably 10% by volume or less More preferably, it is 5% by volume or less. If the frequency of the insulating filler contained in the particle diameter range β is equal to or more than the above lower limit, the insulation reliability of the heat conductive sheet can be further improved, and if it is equal to or less than the above upper limit, the heat resistance of the heat conductive sheet Can be suppressed from being excessively increased to enhance the thermal conductivity of the thermally conductive sheet.

  The frequency of the insulating filler present in the particle diameter range α is preferably 70% by volume or more of the whole insulating filler, more preferably 90% by volume or more, and still more preferably 95% by volume or more And 99% by volume or less. If the frequency of the insulating filler present in the particle diameter range α is the above lower limit or more, the thermal conductivity of the thermal conductive sheet can be enhanced, and if it is the above upper limit or less, the thermal conductivity of the thermal conductive sheet It can be further improved.

  Here, the volume-based particle size distribution of the insulating filler contained in the heat conductive sheet may be, for example, appropriately selecting the volume average particle diameter of the insulating filler used when forming the heat conductive sheet, and the insulating filler It is possible to control based on appropriate selection of the timing of adding. More specifically, as described in detail in the method for producing a heat conductive sheet of the present invention described later, the sheet material is mixed with a composition containing a resin and an insulating filler satisfying a predetermined volume average particle diameter. After preparation, the sheet material is pressure-formed to obtain a sheet, so that the volume-based particle size distribution of the insulating filler contained in the obtained heat conductive sheet satisfies various conditions as described above. it can.

  The insulating filler includes primary particles which are unit particles and secondary particles which are aggregates or aggregates of such primary particles. In addition, "unit particles" may be determined based on a geometrical form etc. by enlarging observation of secondary particles which are aggregates or aggregates of primary particles using SEM (Scanning Electron Microscope) or the like. It is a particle that can be a constituent unit of an aggregate or aggregate. Although “aggregate” and “aggregate” are both common in that they are formed by a plurality of primary particles, in general, the aggregate is more pressure resistant than the aggregate (the shape when pressure is applied) High in nature). Therefore, from the viewpoint of enhancing the insulation reliability of the heat conductive sheet, it is preferable that the secondary particles present in the particle diameter range β be aggregates.

For example, when the insulating filler is a boron nitride particle, one particle (plate-like particle) forming a plate shape corresponds to a unit particle (that is, primary particle). In addition, the plate-like particles are aggregated to form flakes having a larger diameter, which corresponds to an aggregate which is a secondary particle. Furthermore, such plate-like particles are aggregated by chemical force, and particles having a shape closer to a sphere than flakes correspond to aggregates that are secondary particles.
Also, for example, when the insulating filler is aluminum nitride, one spherical particle (spherical particle) corresponds to a unit particle (that is, primary particle). The spherical or massive particles formed by the aggregation or agglomeration of such spherical particles correspond to aggregates or agglomerates which are secondary particles.

  Specifically, examples of the insulating filler include boron nitride particles, silicon carbide particles, alumina particles, zinc oxide particles, aluminum nitride particles, silicon nitride particles, and magnesium oxide particles. These may be used alone or in combination of two or more. Among them, as the insulating filler, aluminum nitride particles, boron nitride particles and silicon carbide particles are preferable, and boron nitride particles are more preferable.

Here, the boron nitride particles have, for example, hexagonal boron nitride particles (h-BN), cubic boron nitride particles (c-BN), wurtzite boron nitride particles (w-BN), and a rhombohedron depending on their crystal structure. It can be classified into crystallized boron nitride particles (r-BN) and turbulent structured boron nitride particles (t-BN). Among these, hexagonal boron nitride particles (h-BN) are preferable from the viewpoint of enhancing the thermal conductivity of the thermal conductive sheet.
As the boron nitride particles, boron nitride particles having only a single crystal structure may be used alone, or two or more types of boron nitride particles having crystal structures different from each other may be used in combination.

  The insulating filler having a particle diameter of 133 μm or more and 890 μm or less contained in the heat conductive sheet preferably contains secondary particles. More specifically, it is preferable that the insulating filler having a particle diameter of 133 μm or more and 890 μm or less contained in the heat conductive sheet is a secondary particle which is an aggregate of plate-like boron nitride particles. Furthermore, it is preferable that the insulation filler whose particle diameter contained in a heat conductive sheet is less than 133 micrometers contains primary particles. More specifically, it is preferable that the insulating filler having a particle diameter of less than 133 μm contained in the heat conductive sheet contains plate-like primary particles of boron nitride. Here, in the present specification, "containing secondary particles" means that 80% or more of the whole insulating filler having a particle diameter of 133 μm or more and 890 μm or less is a secondary particle. Similarly, “containing primary particles” means that 80% or more of the whole insulation filler having a particle diameter of less than 133 μm is primary particles.

[Content ratio]
And it is preferable that the content rate of the insulation filler in a heat conductive sheet is 30 volume% or more and 75 volume% or less. If the content ratio of the insulating filler is within the above range, the thermal conductivity and the insulation reliability of the thermally conductive sheet can be further enhanced.

<Other ingredients>
The heat conductive sheet of the present invention may optionally contain additives and the like in addition to the above-described resin and insulating filler.

  The additive is not particularly limited, and examples thereof include flame retardants, hygroscopic agents, surfactants and the like. One of these may be used alone, or two or more may be used in combination.

  In addition, carbon materials, such as a particulate-like carbon material and fibrous-like carbon material, may be contained in a general heat conductive sheet as a heat conductive filler. However, in the heat conductive sheet of the present invention, the content ratio of the thermally conductive filler such as carbon material in the heat conductive sheet is preferably 5 volume% or less, from the viewpoint of enhancing the insulation reliability, 1 volume %, More preferably 0.1% by volume, and particularly preferably 0% by volume, that is, it does not contain a thermally conductive filler.

<Properties of heat conductive sheet>
[Thermal resistance value]
The heat conductive sheet of the present invention preferably has a thermal resistance value of 1.20 ° C./W or less under a pressure of 0.05 MPa, and more preferably 0.90 ° C./W or less. Moreover, it is preferable that the heat resistance value under 0.50 MPa pressurization of the heat conductive sheet of this invention is 0.50 degrees C / W or less, and it is more preferable that it is 0.35 degrees C / W or less. The heat conductive sheet which has the heat resistance value under a predetermined pressurization condition is below the above-mentioned maximum is excellent in heat conductivity.
In addition, the heat resistance value of a heat conductive sheet can be controlled by adjusting the resin composition, the content rate of an insulation filler, etc. suitably, for example.

[Thickness and structure]
Moreover, the thickness of the heat conductive sheet of this invention may be 0.05 mm or more and 0.50 mm or less, for example. Furthermore, the heat conductive sheet preferably has a structure in which strips including a resin and an insulating filler are joined in parallel from the viewpoint of enhancing the thermal conductivity. In particular, in the case where the insulating filler, for example, boron nitride particles which are the plate-like particles or their aggregates or aggregates described above is contained, the boron nitride particles are in the long axis direction with respect to the thickness direction of the heat conduction sheet. It is preferable to be oriented. It is because thermal conductivity can be improved favorably.

[Insulation reliability]
The insulation reliability of the heat conductive sheet can be evaluated by the method described in the examples. More specifically, according to the method described in the examples, the withstand voltage test value of the heat conductive sheet is measured using n samples, and among the respective withstand voltage test values obtained for n samples, It is preferable that the lowest value (hereinafter, also referred to as "the lower limit value of the withstand voltage test") is high. For example, the lower limit value of the withstand voltage test is obtained even if the average value of the withstand voltage test values obtained by preparing and measuring n samples for each of two types of heat conductive sheets is the same. It can be said that the higher the heat conductive sheet, the higher the insulation reliability as the heat conductive sheet. In the heat conductive sheet of the present invention, as described above, the insulating filler having a large particle diameter exhibits a function like a "pillar" when the heat conductive sheet is pressed in the thickness direction, so the insulation performance is stabilized. Insulation reliability is high because it can be

  Specifically, the lower limit of the withstand voltage test measured on n (for example, n = 5) samples of the heat conductive sheet is preferably 1.00 kV / mm or more, and 1.30 kV / mm or more Is more preferred. The heat conductive sheet which has a withstand voltage test lower limit is more than the said lower limit is excellent in insulation reliability.

(Method of manufacturing heat conductive sheet)
The method for producing a thermally conductive sheet of the present invention comprises preparing a sheet material by mixing a composition containing a resin and an insulating filler B having a volume average particle diameter of 133 μm or more to prepare a sheet material (hereinafter referred to as “sheet material preparation Step) and pressing the sheet material to form it into a sheet to obtain a pre-heat conductive sheet (hereinafter also referred to as "pre-heat conductive sheet forming step"), and the pre-heat conductive sheet in the thickness direction Step of laminating a plurality of sheets, or folding or winding a pre-heat conductive sheet to obtain a laminate (hereinafter also referred to as “laminate forming step”), and 45 ° of the laminate to the laminating direction Slicing at the following angle to obtain a heat conductive sheet (hereinafter also referred to as "slicing step"). According to the method for producing a heat conductive sheet of the present invention including the above steps (hereinafter, also referred to as “the method for producing the present invention”), the above-described heat conductive sheet of the present invention can be favorably formed. Furthermore, in the production method of the present invention, the step of obtaining the “composition containing a resin” according to the above by pulverizing the insulating filler A and the resin together in the former stage of the sheet material preparation step (hereinafter referred to as “preparation step”) Is preferred to include.

[Preparation process]
In the preparation step, in the preparation step, the insulating filler A and the resin are pulverized together to obtain a “composition containing a resin”. Here, the “composition containing resin” may be “composite particles” in which the insulating filler A and the pulverized product of the resin are complexed. More specifically, in the preparation step, after kneading the resin and the insulating filler A, the resulting kneaded product is pulverized and optionally classified to obtain composite particles. The kneading method is not particularly limited, and any kneader such as a kneader, a roller, or a Banbury mixer can be used. Kneading may be performed in the presence of a solvent using a kneader such as a Hobart mixer or a high speed mixer, for example. And when using a solvent at the time of kneading | mixing, it is preferable to grind | pulverize, after removing a solvent. The kneaded material can be ground using a known grinder such as a cutter mill, a hammer mill, a roll mill, a ball mill, a jet mill and the like. And classification of particles obtained by grinding a kneaded material can be performed using a known classifier such as a sieve, a centrifugal classifier or the like.

In addition, various resin listed by the item of <resin> can be used as resin.
Moreover, as the insulation filler A, various insulation fillers listed in the item of <insulation filler> can be used. Here, the volume average particle diameter of the insulating filler A is not particularly limited, and may be, for example, 0.1 μm or more and 1000 μm or less. In addition, it is preferable that the volume average particle diameter of the insulation filler A is 10 micrometers or more and 500 micrometers or less from a viewpoint of improving the heat conductivity of a heat conductive sheet. The insulating filler A may be crushed together with the resin and contained in the heat conductive sheet in a reduced diameter state. Of course, depending on the pressure resistance and shear resistance of the material employed as the insulating filler A, it may be contained in the heat conductive sheet in the same size and shape as the material stage without reducing the diameter.
In addition, the volume average particle diameter of the insulating filler A can be measured according to the method described in the example using a laser diffraction / scattering type particle size distribution measuring apparatus (manufactured by Horiba, type "LA-960"). .

[Sheet material preparation process]
In the sheet material preparation step, a sheet material is prepared by mixing a composition containing a resin (hereinafter also referred to as "composition (I)") and an insulating filler B having a volume average particle diameter of 133 μm or more. Here, “mixing” means mixing predetermined insulating filler B and composition (I) under non-shearing conditions. "Mixing" in this step means an operation different from "grinding", "kneading", etc. in the above preparation step, for example, insulation filler B and the composition in a non-shearing manner such as "shake" It refers to mixing with (I). In this "mixing", unlike "crushing" and "kneading" in the above preparation step, a strong shear force is not generated, so that the volume average particle size of the insulating filler B largely changes through before and after "mixing". There is no In addition, "the volume average particle diameter of the insulation filler B changes a lot" means that the volume average particle diameter after mixing is less than 30%, for example, assuming that the volume average particle diameter of the insulation filler B before mixing is 100%. It means that.

  The insulating filler B is not particularly limited as long as the volume average particle diameter is 133 μm or more, and various insulating fillers listed in the item of <insulating filler> can be used. Here, the volume average particle diameter of the insulating filler B is preferably 150 μm or more, more preferably 300 μm or more, preferably 1000 μm or less, and more preferably 900 μm or less. If the volume average particle diameter of the insulating filler B is equal to or more than the above lower limit value, the insulation reliability of the heat conductive sheet can be enhanced. Moreover, if the volume average particle diameter of the insulation filler B is below the said upper limit, the heat conductivity of a heat conductive sheet can be improved. In addition, the insulation filler B may be contained in a heat conductive sheet in the state which diameter-reduced slightly by receiving to the influence of pressurization etc. in a subsequent process. Of course, depending on the pressure resistance and shear resistance of the material employed as the insulating filler B, it may be contained in the heat conductive sheet in the same size and shape as the material stage without reducing the diameter or the like.

[Pre-heat conductive sheet forming process]
In the pre-heat conductive sheet forming step, the sheet material obtained in the above step is pressurized to be formed into a sheet to obtain a pre-heat conductive sheet. The method for forming into a sheet is not particularly limited, and known forming methods such as press forming, roll forming or extrusion may be used. Above all, as a method for forming into a sheet, rolling and forming is preferable. The thickness of the pre-heat conductive sheet is not particularly limited, and can be, for example, 0.05 mm or more and 2 mm or less.

[Laminate formation process]
In the laminate formation step, a plurality of the pre-heat conduction sheets obtained in the pre-heat conduction sheet formation step are stacked in the thickness direction, or the pre-heat conduction sheets are folded or wound to obtain a laminate. Here, in the laminate obtained in the laminate forming step, when the adhesion between the surfaces of the pre-heat conduction sheet is further enhanced to sufficiently suppress the delamination of the laminate, the surface of the pre-heat conduction sheet is used. The laminate forming step may be carried out in a state of being 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 conductive sheet or an adhesive layer is provided on the surface of the pre-heat conductive sheet. A process may be performed, and you may heat-press the laminated body which laminated the pre-heat-conduction sheet | seat further in the lamination direction (secondary pressure).

[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 thermally 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. Moreover, it does not specifically limit as a cutting tool at the time of slicing a laminated body, For example, it has fixing tools, such as a metal plate for pressing and fixing a laminated body in the lamination direction, and the cutting blade of a double-edged blade A slicer may be used, which is provided with a slicing member, and the laminated body is sliced by moving the cutting blade in the laminating direction while pressing the laminated body with the fixing tool.

  From the viewpoint of enhancing the thermal conductivity of the heat conductive sheet, it is preferable that the angle at which the laminate is sliced is approximately 0 ° with respect to the stacking direction (that is, a direction along the stacking direction). In addition, a heat conductive sheet having a structure in which strips including a resin and an insulating filler are connected in parallel is favorably manufactured by passing through the above-described [pre-heat conductive sheet forming step] to [slice step]. Can.

EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified.
And in an Example and a comparative example, volume average particle diameter of an insulation filler used for manufacture of a heat conduction sheet, volume-based particle size distribution of an insulation filler in a heat conduction sheet, heat resistance value of a heat conduction sheet, and heat conduction The withstand voltage test lower limit value of the sheet was measured according to the following method.

<Volume average particle diameter of insulating filler used for manufacturing of heat conductive sheet>
Various insulating fillers used in Examples and Comparative Examples are dispersed in methyl ethyl ketone solvent to obtain a suspension, which is suspended by a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, type "LA 960"). The particle size of the insulating filler contained in the liquid was measured. Then, the median diameter was obtained from the volume-based particle diameter distribution, and the “volume-average particle diameter of the insulating filler” was obtained.
<Volume-based particle size distribution of insulating filler in heat conductive sheet>
1 g of the heat conductive sheet obtained in Examples and Comparative Examples was placed in a methyl ethyl ketone solvent, and the resin component was dissolved to obtain a suspension in which the insulating filler contained in the sheet was separated and dispersed. Next, using the obtained suspension as a sample, the particle size of the insulating filler contained in the suspension was measured using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, type "LA 960"). did. Then, a particle size distribution curve is prepared with the obtained particle diameter as the horizontal axis and the frequency of volume-converted insulating filler as the vertical axis, and the particle diameter range (particle diameter range α) with particle diameter less than 133 μm and the particle diameter In the particle diameter range (particle diameter range β) of 133 μm or more and 890 μm or less, the total volume of the insulation filler contained in the particle diameter range of 0 μm or more and 890 μm or less is 100% by volume. %) Was calculated. Further, for all the examples, two peaks of the particle size distribution were confirmed, one for each of the particle diameter ranges α and β. Moreover, in Comparative Examples 1 and 2, one peak was confirmed in the particle diameter range α, and no peak was confirmed in the particle diameter range β.

<Thermic resistance value of the heat conduction sheet>
The heat resistance value of the heat conduction sheet was measured using a resin material heat resistance tester (manufactured by Hitachi Technology & Services Co., Ltd.). Here, a heat conductive sheet cut into a square of 1 cm square is used as a sample, and a thermal resistance value (° C./W) when a relatively low pressure of 0.05 MPa is applied at a sample temperature of 50 ° C. The thermal resistance (° C./W) was measured when a relatively high pressure of 0.50 MPa was added at ° C. The smaller the thermal resistance value, the better the thermal conductivity of the thermal conductive sheet, and, for example, the better the heat dissipation characteristics when it is interposed between the heat generating body and the heat radiating body to form a heat dissipation device.

<Low-voltage test lower limit of heat conduction sheet>
The dielectric breakdown resistance of the heat conductive sheet was evaluated by a withstand voltage test value measured using an in-oil test apparatus (manufactured by Tama Densetsu Co., Ltd., product name "TJ-20S"). Specifically, a heat conductive sheet cut into an approximately 3 cm square was used as a sample, and the sample was immersed in silicone oil at 23 ° C. One minute after the immersion, application of voltage was started at a boosting rate of 0.6 kV / sec, and voltage (kV) was measured when the current (detection current) flowing to the sample became 10 mA. The withstand voltage test value (kV / mm) was obtained by dividing the value of the obtained voltage (kV) 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 is in the resistance to dielectric breakdown. The number n of the samples used for the measurement was 5 and the lowest value among the withstand voltage test values measured for the five samples was taken as the “withstand voltage test lower limit value”.

Example 1
<Preparation process>
Thermoplastic resin that is liquid at room temperature and normal pressure (80 parts of Daikin G-101, trade name "DAIEL G-101", viscosity (viscosity coefficient): 3300P) liquid, solid at room temperature and normal pressure 20 parts of a fluorine resin (manufactured by 3M Japan Co., Ltd., trade name "Dainion FC2211", Mooney viscosity: 27ML _{1 + 4} , 100 ° C), boron nitride particles (primary performance particles as insulating filler A (manufactured by Momentive Performance Materials Co., Ltd.) A trade name “PT-110”, volume average particle diameter: 51 μm, hexagonal boron nitride particles (195 parts) was stirred and mixed for 20 minutes at a temperature of 150 ° C. using a pressure kneader (manufactured by Nippon Spindle Co., Ltd.). Next, the obtained mixture is put into a crusher and broken for 10 seconds to obtain a composition (composition (I)) including composite particles in which the insulating filler A and the resin are complexed. The

<Sheet material preparation process>
Aggregated boron nitride particles which are secondary particles as insulating filler B (composition name “PT-670”, volume average particle diameter: 467 μm, hexagonal shape with respect to 290 g of the composition (I) 5 parts of agglomerates of crystallized boron nitride particles) were added, and the composition (I) and the insulating filler B were put in a bag and mixed by hand shaking until uniform. The conditions for shaking were: amplitude 50 cm, reciprocating shaking, shaking back and forth 30 times / minute, shaking time 2 minutes.

<Pre thermal conductive sheet forming process>
Next, 50 g of the composition obtained is sandwiched with a 50 μm thick sandblasted PET film (protective film), and the conditions for 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. The resultant was rolled and formed (primary pressure) to obtain a pre-heat conductive sheet having a thickness of 0.5 mm.

<Laminate formation process>
Subsequently, the obtained pre-heat conductive sheet is cut into 150 mm long × 150 mm wide × 0.5 mm thick, and 120 sheets are 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 laminate having a height of about 60 mm was obtained.

<Slicing process>
Then, leaving the length required for slicing, the entire top surface obtained was pressed with a metal plate, and a pressure of 0.1 MPa was applied from above to fix the laminate. In addition, fixation of the side of a laminated body and the back was not performed.
Next, the cutting blade 10 (double-edged, blade angle 2θ: 20 °, maximum thickness of the blade portion: 3.5 mm, material: super) in the press part of the servo press (made by EDM) Steel, Rockwell hardness: 91.5, silicon processing of blade surface: None, total length: 200 mm), slice speed 200 mm / sec, slice width 0.30 mm, stacking direction of laminated body (in other words, lamination) It sliced in the direction which corresponds to the normal line of the principal surface of the obtained pre heat conduction sheet, and obtained heat conduction sheet 30 of length 150 mm x width 60 mm x thickness 0.30 mm. The posture of the cutting blade at the time of slicing is such that the angle α shown in FIG. 1 is 10 °, and the extending direction of the blade surface 11 is parallel to the slice surface 21 of the laminate 20.
About the obtained heat conductive sheet, the heat resistance and the withstand voltage test lower limit were measured. The results are shown in Table 1. In addition, the content rate of the insulation filler in a heat conductive sheet was 61 volume%. In addition, 80% or more of the insulating filler in the particle diameter range α was primary particles, and the insulating filler in the particle diameter range β was approximately 100% of the secondary particles.

(Examples 2 to 3)
The addition amount of primary particles as insulating filler A to be added in <preparation step> and the addition amount of secondary particles as insulating filler B to be added in <sheet material preparation step> were changed as shown in Table 1, respectively. Various operations and evaluations were performed in the same manner as in Example 1 except for the above. The results are shown in Table 1. In addition, 80% or more of the insulating filler in the particle diameter range α was primary particles, and the insulating filler in the particle diameter range β was approximately 100% of the secondary particles.

(Examples 4 to 6)
Secondary particles as insulating filler B to be added in <sheet material preparation step> are flaky boron nitride particles having a volume average particle diameter of 508 μm (trade name "Flakes 70/500" manufactured by 3M company, hexagonal boron nitride Changed to a collection of particles). Also, the addition amount of primary particles as insulating filler A to be added in <preparation step> and the addition amount of secondary particles as insulating filler B to be added in <sheet material preparation step> are as shown in Table 1 respectively. changed. Various operations and evaluations were performed in the same manner as in Example 1 except for these points. The results are shown in Table 1. In addition, 80% or more of the insulating filler in the particle diameter range α was primary particles, and the insulating filler in the particle diameter range β was approximately 100% of the secondary particles.

(Example 7)
As the insulating filler B to be added in the <sheet material preparation step>, silicon carbide (manufactured by Pacific Random Co., Ltd., trade name "NG-F46", volume average particle diameter: 350 μm) was used. In addition, the addition amounts of primary particles as insulating filler A to be added in <preparation step> and the addition amounts of silicon carbide as insulating filler B to be added in <sheet material preparation step> are changed as shown in Table 1 respectively. did. Various operations and evaluations were performed in the same manner as in Example 1 except for these points. The results are shown in Table 1.

(Comparative example 1)
The addition amount of primary particles as the insulating filler A added in <preparation step> was changed to 200 parts, and the insulating filler B was not added in <sheet material preparation step>. Various operations and evaluations were performed in the same manner as in Example 1 except for these points. The results are shown in Table 1.

(Comparative example 2)
200 parts of flake-like boron nitride particles (The 3M company make, brand name "Flakes 70/500, aggregate of hexagonal boron nitride particles") as insulation filler A added at <preparation process> Was used. Moreover, the insulation filler B was not added at <sheet material preparation process>. Various operations and evaluations were performed in the same manner as in Example 1 except for these points. The results are shown in Table 1.

From Table 1, the volume-based particle size distribution curve of the insulating filler contains at least one peak in the particle diameter range of 133 μm to 890 μm (particle size range β), including the resin and the insulating filler. The heat conductive sheet has a high withstand voltage test lower limit value and is found to be excellent in insulation reliability.
On the other hand, the heat conduction sheet of Comparative Examples 1 and 2 in which the volume-based particle size distribution curve of the insulation filler does not have a peak in the particle diameter range β has a low voltage test lower limit value, and it is understood that the insulation reliability is poor. .
In Example 7, the particle diameter corresponding to the peak detected in the particle diameter range β was 357 μm, which was measured for the insulating filler in the heat conductive sheet, and the insulating filler B was added in the sheet material preparation step. Slightly larger than the particle size of 350 μm. It is considered that the silicon carbide used in Example 7 hardly reduced in diameter in various processes, and mainly due to the measurement error in the particle diameter measurement method as described above.

  ADVANTAGE OF THE INVENTION According to this invention, the heat conductive sheet with high insulation reliability and the manufacturing method which can manufacture such a heat conductive sheet favorably can be provided.

DESCRIPTION OF SYMBOLS 10 cutting blade 11 blade surface 20 laminated body 21 slice surface 30 heat conductive sheet

Claims (9)

  A thermally conductive sheet, comprising a resin and an insulating filler, wherein the volume-based particle size distribution curve of the insulating filler has at least one peak within a range of a particle diameter of 133 μm to 890 μm.   The heat conductive sheet according to claim 1, wherein the frequency of the insulating filler present in the particle diameter range of 133 μm to 890 μm is 1% to 30% by volume of the whole insulating filler.   The heat conductive sheet according to claim 1 or 2, wherein the particle size distribution curve further has at least one peak in a range of particle diameter of more than 0 μm and less than 133 μm.   The heat conductive sheet according to any one of claims 1 to 3, wherein the frequency of the insulating filler present in the range of a particle diameter of less than 133 μm is 70% by volume or more and 99% by volume or less of the whole insulating filler.   The heat conductive sheet according to any one of claims 1 to 4, wherein the insulating filler having a particle diameter of 133 μm or more and 890 μm or less contains secondary particles.   The heat conductive sheet according to any one of claims 1 to 5, wherein the insulating filler having a particle size of less than 133 μm contains primary particles. A sheet material preparation step of preparing a sheet material by mixing a composition containing a resin and an insulation filler B having a volume average particle diameter of 133 μm or more;
Pressing the sheet material to form it into a sheet to obtain a pre-heat conductive sheet;
Obtaining a laminate by laminating a plurality of the pre-heat conduction sheets in the thickness direction or folding or winding the pre-heat conduction sheets;
Slicing the laminated body at an angle of 45 ° or less with respect to the laminating direction to obtain a heat conductive sheet;
A method of producing a thermally conductive sheet, comprising:   The method for producing a thermally conductive sheet according to claim 7, further comprising: grinding insulating filler A and the resin together to obtain a ground composition in preparing the composition containing the resin.   The manufacturing method of the heat conductive sheet of Claim 8 whose said insulation filler A is a primary particle and whose said insulation filler B is a secondary particle.

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