JPWO2018225468A1 - Method for producing sheet containing anisotropic filler - Google Patents

Abstract

A step of forming a film of ink containing an anisotropic filler and a resin on a support, and a step of applying vibration having a frequency of 5 kHz or more to the film while the film is flowable, A method for producing a sheet containing an anisotropic filler.

Description

  The present invention relates to a method for producing an anisotropic filler-containing sheet, that is, a sheet containing an anisotropic filler having an anisotropic particle shape (having a diameter different depending on the direction) and a resin.

Anisotropic fillers having anisotropic particle shape often have anisotropy in their physical properties, and utilizing such properties, sheets containing anisotropic filler and resin are used in various applications. I have.
As a typical example, one direction (specifically, the major axis direction (plane direction)) is the other direction (specifically, the minor axis direction (thickness direction)), such as flaky hexagonal boron nitride. A heat conductive sheet using an anisotropic filler having a higher heat conductivity than that of (a) is known. In such a heat conductive sheet, the anisotropic filler is oriented such that the major axis direction is parallel to the direction in which thermal conductivity is required (that is, the thickness direction of the sheet) (hereinafter, referred to as “vertical orientation”). In some cases.).
However, when a composition containing an anisotropic filler and a resin serving as a binder is simply applied in a sheet shape using a doctor blade or the like, the major axis direction of each particle is oriented parallel to the surface direction of the sheet (hereinafter, “horizontal direction”). Orientation).), A sheet having high thermal conductivity cannot be obtained.

In this regard, Patent Document 1 discloses that a boron nitride particle is agglomerated into particles that are quasi-isotropic with respect to thermal conductivity (agglomerated particles), and a thermal conductive sheet is manufactured using the particles. ing.
However, this method requires the preparation of aggregated particles. In addition, voids cannot be avoided in the aggregated particles, but if voids are present in the sheet, their thermal conductivity will be reduced. A heat conductive sheet having a sufficiently high conductivity cannot be obtained.

In addition, Non-Patent Document 1 discloses that a paste containing hexagonal boron nitride particles and a resin is dropped using a discharge nozzle to form one-point potting, and this potting is repeatedly formed to form an aggregate. Discloses that a sheet in which hexagonal boron nitride particles are longitudinally oriented is prepared. Further, Patent Document 2 discloses that after stacking primary sheets in which the major axis direction of the hexagonal boron nitride particles is oriented in parallel to the plane direction to obtain a laminate, 0 to the normal line emerging from the primary sheet surface. It is disclosed that a sheet in which hexagonal boron nitride particles are longitudinally oriented is prepared by slicing the laminate at ３０30 degrees.
However, these methods have complicated sheet manufacturing methods and have problems in mass productivity.

JP 2015-6980 A JP 2012-38763 A

"2) Development of heat sink material with controlled orientation of ceramic particles", Saga Ceramic Technology Center 2013 report, pp. 9-13

  In view of the above problems, an object of the present invention is to efficiently produce an anisotropic filler-containing sheet in which anisotropic fillers are vertically oriented as much as possible by a simple method.

  The present inventors apply high-frequency vibration to a film (layer) containing an anisotropic filler and a resin while the film (layer) containing the anisotropic filler has fluidity (that is, while the film (flowable) can flow). It has been found that the anisotropic filler (primary particles) rearranges randomly, and as a result, the ratio of those vertically oriented increases, and the present invention has been completed using such knowledge.

That is, the present invention is as follows.
[1] forming a film of an ink containing an anisotropic filler and a resin on a support, and applying a vibration having a frequency of 5 kHz or more to the film while the film is flowable;
A method for producing a sheet containing an anisotropic filler.
[2] The method for producing an anisotropic filler-containing sheet according to [1], wherein the frequency of the vibration is 10 to 1000 kHz.
[3] The method for producing an anisotropic filler-containing sheet according to [1] or [2], wherein the average longest diameter of the anisotropic filler is 0.5 μm to 200 μm.
[4] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [3], wherein the aspect ratio of the anisotropic filler is 2 or more.
[5] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [4], wherein the anisotropic filler includes scaly boron nitride particles.
[6] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [5], wherein the anisotropic filler includes hexagonal boron nitride particles.
[7] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [6], wherein a volume ratio of the anisotropic filler in the film is 10 to 90% by volume.
[8] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [7], wherein the resin contains a thermosetting resin.
[9] The method for producing an anisotropic filler-containing sheet according to any one of [1] to [8], further comprising a step of pressing the film.

According to the present invention, a coating film of an ink containing an anisotropic filler and a resin is formed, and only by applying high-frequency vibration to the coating film, the lateral orientation of the anisotropic filler is prevented, and the anisotropic filler is randomly dispersed. Oriented or longitudinally oriented sheets can be efficiently produced by a simple method.
Therefore, according to the present invention, a heat conductive sheet having high heat conductivity can be efficiently manufactured by a simple method.

4 is an FE-SEM image of a cross section of the anisotropic filler-containing sheet (C sheet) obtained in Example 2. 4 is an FE-SEM image of a cross section of the anisotropic filler-containing sheet (C sheet) obtained in Comparative Example 1.

  Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in more detail. However, the present invention is not limited to these, and various modifications may be made without departing from the gist thereof. Deformation is possible.

The method of the present embodiment includes a step of forming a coating film of an ink containing an anisotropic filler and a resin on a support.
In the present embodiment, the anisotropic filler is a particle having an anisotropic shape (different in diameter depending on the direction), for example, an inorganic compound such as carbon, an inorganic oxide, an inorganic nitride, an inorganic carbide, a resin, or the like. And specific examples thereof include metal oxides such as boron nitride, aluminum nitride, aluminum oxide, zinc oxide, silicon carbide, and aluminum hydroxide, metal nitrides, metal carbides, metal hydroxides; metals and alloys; graphite, Carbon materials such as graphite and diamond; fibrous, acicular, scaly, whisker-like particles made of high thermal conductive resin and the like.
Among them, hexagonal boron nitride particles are preferable from the viewpoint of thermal conductivity, and examples of the shape include flat, scale-like, plate-like, linear, flat, granular, fibrous, and whisker-like shapes. It is preferably in the form of a scale, a plate or a line, more preferably in the form of a scale or a plate, and particularly preferably in the form of a scale.
In the present embodiment, only one type of anisotropic filler may be used, or two or more types of anisotropic filler may be contained as long as the effects of the present invention are not impaired. For example, boron nitride particles and other anisotropic fillers can be used in combination.

  When the anisotropic filler is in the form of a flake or a plate, the aspect ratio (the ratio of the longest diameter to the thickness) is not limited, but is preferably 2 or more, more preferably 5 or more, and 10 or more. More preferably, it is the above. Although there is no upper limit on the aspect ratio, it is usually 1,000 or less.

Further, when the sheet containing an anisotropic filler is used as a heat conductive sheet, particularly when it is incorporated in a heat-generating electronic component or the like, it may be used at a high temperature of 180 ° C or higher. Even in the use under such a high temperature of 180 ° C. or higher, the average longest diameter of the anisotropic filler is set to be longer than that of the sheet in order to extend the life of the peripheral members and secure reliability such as high thermal conductivity and withstand voltage characteristics. Is preferably or less, more preferably or less.
If the average longest diameter exceeds half the thickness of the sheet, anisotropic fillers protrude from the sheet surface, deteriorating the surface shape of the sheet, and deteriorating the adhesion when producing a laminated sheet with other members. However, the withstand voltage characteristics may be reduced.
On the other hand, when the average longest diameter of the anisotropic filler is too small, the probability that the heat conduction path is connected from the top to the bottom in the thickness direction of the heat conduction sheet decreases, and the heat conductivity in the thickness direction of the heat conduction sheet is insufficient. It may be.
From the above viewpoints, although there is no limitation on the particle size of the anisotropic filler, the average longest diameter is preferably 0.1 to 500 μm, more preferably 0.5 to 200 μm, and 1 to 100 μm Is particularly preferred.
Even in the case where the material has the above-described average longest diameter, there may be a case where the number is so large that it does not affect the average longest diameter in the raw material. Therefore, in the present embodiment, it is preferable to use the anisotropic filler after previously removing a material having a particle size equal to or larger than a predetermined value from a raw material using a sieve or the like.

  The anisotropic filler may be primary particles in the ink, or may be in a state of aggregated particles (secondary particles) in which the primary particles are aggregated. However, in the case of aggregated particles, depending on the vibration application conditions (frequency, application time, etc.) in the high-frequency vibration application step, the rearrangement of the filler may not be sufficiently achieved, or voids may be formed in the finally obtained sheet. May remain. Therefore, as the anisotropic filler, it is preferable to use those existing in the state of primary particles.

The shape, particle size and aspect ratio of the anisotropic filler can be determined by observing the particles with an electron microscope.
Specifically, 200 or more particles are randomly selected from an image taken by a scanning electron microscope (SEM) (for example, FE-SEM-EDX (SU8220): manufactured by Hitachi High-Technologies Corporation), Judge from the shape.
The longest diameter is the length of the long side of the rectangle having the smallest area circumscribing the particles. In the case of a scaly or plate-like anisotropic filler, the longest diameter is determined by randomly selecting at least 200 particles whose plane direction is reflected.
In addition, the aspect ratio, from the image, randomly select the particles in which the plane direction is captured and the particles in which the thickness is captured, respectively, by 200 or more, and calculate the average value of the longest diameter and the thickness. It can be determined by calculating and calculating the ratio.

In the present embodiment, the volume ratio of the anisotropic filler in the film (ink) (the content of the anisotropic filler in the solid content) can be appropriately set depending on the application, for example, 10 to 90% by volume. The above can be considered.
If the content of the anisotropic filler is less than 10% by volume, desired properties (for example, thermal conductivity) may not be obtained due to too little anisotropic filler.
Conversely, if the content of the anisotropic filler exceeds 90% by volume, the sheet may be too brittle due to too much anisotropic filler, or the electrical insulation of the sheet may be reduced. In addition, the viscosity of the ink is increased, and it may be difficult to obtain a thin and flat sheet.
Here, the volume of the anisotropic filler is a value determined from the specific gravity of the material (compound) constituting the anisotropic filler and the mass of the anisotropic filler contained in the ink.

In the present embodiment, the resin contained in the ink is not limited. For example, a thermoplastic resin (eg, polyolefin, vinyl chloride resin, methyl methacrylate resin, nylon, fluororesin, etc.), a curable resin (eg, epoxy resin) Phenolic resins, urea resins, melamine resins, unsaturated polyester resins, silicon resins, etc.), synthetic rubbers and the like. Among them, a curable resin is preferable, and a thermosetting resin is particularly preferable.
In the present embodiment, the curable resin may be added to the uneven film in the form of a resin composition mixed with a curing agent or a curing catalyst, or may be added to a corresponding raw material (a precursor of a monomer, a dimer, an oligomer, or the like). ) May be added.

Examples of the thermosetting resin include polyimide resins such as polyimide resin, polyaminobismaleimide (polybismaleimide) resin, bismaleimide / triazine resin, polyamideimide resin, and polyetherimide resin; polybenzoxazole-based resin; polyether Resins; benzocyclobutene resins; silicone resins; epoxy resins such as phenolic epoxy resins and alcoholic epoxy resins.
Among them, epoxy resins, polyether resins, benzocyclobutene resins, and silicone resins are preferable because of their high thermal conductivity and good solubility in organic solvents, and epoxy resins are particularly preferable.
One of these resins may be used alone, or two or more thereof may be used in an optional combination and ratio.

In the present embodiment, the ink may contain a solvent or a dispersion medium as necessary. In particular, when a thermosetting resin is used as the resin, it is preferable to include a solvent or a dispersion medium.
The type of the solvent (dispersion medium) is not particularly limited, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl cellosolve, and cyclopentanone; aromatic hydrocarbons such as toluene and xylene; and cyclohexane and cyclopentane. Cycloalkanes; alcohols such as methanol, ethanol and n-butyl alcohol; esters such as ethyl acetate, propyl acetate and butyl acetate; amides such as dimethylformamide; and organic solvents such as propylene glycol monomethyl ether and acetate thereof. Can be One kind of the solvent may be used alone, or two or more kinds may be used in combination.
During the film formation and during the application of the high-frequency vibration, the viscosity of the ink is adjusted to be constant, and after the application of the high-frequency vibration, from the viewpoint of quickly drying the ink, a solvent whose evaporation rate is 4.5 times or less that of butyl acetate is used. Preferably, it is used. If the evaporation rate is too high, a large amount of the solvent evaporates during film formation or high-frequency vibration application, and the viscosity of the ink changes. On the other hand, if the evaporation rate is too slow, drying of the solvent becomes difficult and drying at a high temperature for a long time is required.When such drying is performed, the curing proceeds when a thermosetting resin is used as the resin. I will. From such a viewpoint, it is more preferable to use a solvent 0.05 to 4.5 times the evaporation rate of butyl acetate.
The content of the solvent (dispersion medium) is not limited, and can be appropriately determined in consideration of, for example, the viscosity of the ink, and is usually about 10 to 50% by mass of the ink. When the amount of the solvent is insufficient, it is difficult to form a film having a uniform thickness, and the film surface may be uneven. Conversely, when the amount of the solvent is excessive, the orientation retention of the anisotropic filler in the film after the application of high-frequency vibration may be poor.

In the present embodiment, in addition to the anisotropic filler, the resin, and the solvent / dispersion medium, the ink may further contain various additives conventionally used depending on the application and the like.
Examples of such additives include, for example, a coupling agent for improving the adhesiveness between the anisotropic filler and the resin, the above-described curing agent and curing catalyst, a resin curing accelerator, a viscosity modifier, and a dispersing agent. Examples include a stabilizer, a surfactant, an emulsifier, a low-elasticity agent, a diluent, an antifoaming agent, and an ion trapping agent. Each of these may be used alone or in combination of two or more in any combination and ratio.

As the coupling agent, those generally used for surface treatment of an anisotropic filler can be suitably used, and the type thereof is not particularly limited. Specifically, aminosilanes such as γ-aminopropyltriethoxysilane and N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane, β- (3,4 -Epoxysilanes such as epoxycyclohexyl) ethyltrimethoxysilane; vinylsilanes such as γ-methacryloxypropyltrimethoxysilane and vinyl-tri (β-methoxyethoxy) silane; N-β- (N-vinylbenzylaminoethyl)- Cationic silanes such as γ-aminopropyltrimethoxysilane hydrochloride; and silane coupling agents such as phenylsilane.
These silane coupling agents can be used alone or in combination of two or more.
Although depending on the surface area of the anisotropic filler, the coupling agent is preferably added in an amount of 0.01 to 10% by mass, more preferably 1 to 2% by mass, based on the anisotropic filler.
The coupling agent can be added to the anisotropic filler in advance, and the method is not limited.For example, the coupling agent stock solution is uniformly dispersed in the anisotropic filler that is rapidly stirred by a stirrer. And a wet method in which an anisotropic filler is immersed in a dilute solution of a coupling agent and stirred.

The viscosity of the ink is not limited, and may be, for example, 0.1 to 100 Pa · s, and may be 5 to 20 Pa · s.
The method of preparing the ink is not particularly limited, and the components may be mixed. At that time, in order to uniformly mix the components, known processes such as stirring, mixing, and kneading can be performed.

In this embodiment, the film is formed on a support. The support preferably has a strength that holds the film and withstands high-frequency vibration, and has good releasability when peeled off later. Specific examples include a metal foil or a metal plate of copper or aluminum, a plastic film or a plastic plate, and the like.
The support may be peeled off after forming the sheet. In particular, when the support has characteristics that are not suitable for the use of the sheet (for example, when the sheet is a heat conductive sheet for an insulating layer of an electronic circuit, a conductive material such as a metal foil is used as the support. ), It is preferable to peel the support from the sheet. On the other hand, in the absence of the above-mentioned circumstances, the support does not necessarily have to be peeled off, and a laminate in which the support is finally left can be used as a sheet.
When the support is peeled from the sheet, there is no limitation on the timing of the peeling step, but it is preferable that the film be cured to some extent and become self-supporting.

In the present embodiment, the method of forming the above-described ink film on such a support is not limited, and for example, rolls such as gravure coating, roll coating, bar coating, die coating, dipping, and knife coating are used. Coating by various applicators such as various coatings, spray coating, blade coating, spin coating, and various printings such as screen printing. When the resin is a thermoplastic resin, it can be applied by melt coating such as hot melt coating.
In the manufacturing method of the present embodiment, since the anisotropic filler in the film is rearranged in the subsequent high-frequency vibration applying step, it is not necessary to consider the orientation state of the anisotropic filler determined at the time of film formation. The method for forming a coating film can be selected.
The thickness of the coating film can be appropriately determined according to the use and purpose, and can be, for example, 10 to 5000 μm.

The manufacturing method according to the present embodiment includes a step of applying vibration having a frequency of 5 kHz or more to the film, following the film forming step. According to the study of the present inventors, when high-frequency vibration is applied to the film, the anisotropic filler rearranges, even if it is supposed to be horizontally oriented, random orientation, furthermore, it may approach vertical orientation. found. Such rearrangement is presumed to be due to the action of a shock wave when a bubble generated by the cavitation phenomenon generated by the application of the high-frequency vibration pops, but the mechanism does not depend on this.
At this time, the film to be subjected to the vibration needs to be flowable, that is, liquid (liquid (including sol and gel)) so as to allow rearrangement of the anisotropic filler. .
When the ink does not contain a solvent or a dispersion medium and the resin is a thermoplastic resin (when the ink is a hot melt ink), the film is formed by melt coating. In this case, the film is formed after the film is formed. May be cooled and hardened (solidified). Therefore, in such a case, the film is kept in a flowable state in the high-frequency vibration applying step, for example, by heating the film to maintain a flowable state or by heating the cured film to return to a liquid state again. As in

There is no limitation on the method of applying high-frequency vibration to the coating film. For example, an ultrasonic generator can be used to apply vibration to the coating film via a support that holds the coating film.
The frequency of the vibration is 5 kHz or more, and there is no upper limit. For example, the frequency may be 10 to 1000 kHz or 15 to 1000 kHz.
The type of frequency used is not limited, and a vibration having a single frequency may be given, a vibration whose frequency changes over time may be used, and a plurality of vibrations having different frequencies may be used. Use in combination (sweep vibration) is also effective.
An appropriate frequency varies depending on the shape and size of the anisotropic filler. Generally, a lower frequency is suitable as the particle size of the filler is larger, and a higher frequency is suitable as the particle size is smaller. In other words, since the impact force of high-frequency vibration (ultrasonic waves) increases as the frequency decreases, when the frequency is increased, large anisotropic fillers tend to be randomly oriented. On the other hand, since the standing wave interval is narrower as the frequency is higher, lowering the frequency is effective for randomly aligning small anisotropic fillers.
The time for applying the high-frequency vibration is not limited, and can be appropriately determined depending on the frequency of the vibration and the film thickness, and can be, for example, 1 second to 300 seconds.

The present embodiment may further include a step of pressing the film in which the anisotropic filler has been rearranged as described above, whereby the voids contained in the film can be removed. If there are voids in the film, its thermal conductivity may decrease. Therefore, when the sheet is used as a heat conductive sheet, such a press is particularly effective.
The pressing conditions (pressure, temperature, time, atmosphere, etc.) at that time are not limited, and the arrangement of the anisotropic filler in the film is determined in consideration of the type of the anisotropic filler and the resin, the content of the filler in the film, and the like. Conditions may be appropriately determined so that the voids can be removed without affecting the air gap. The pressing pressure may be, for example, 0.01 to 20 MPa, and may be 10 Mpa or less, and usually 5 MPa or less is sufficient.
In addition, when the viscosity of the ink constituting the film is low and it is difficult to press as it is, prior to the pressing step, some or all of the solvent may be removed from the film, and the film may be semi-cured. . The method of removing the solvent at this time is not limited, and for example, a method such as vacuum drying and heat drying can be appropriately employed.

  The film formed as described above can be appropriately dried and / or cured as needed. In the case of curing, there is no limitation on the curing method, and the resin can be cured by heating or light irradiation depending on the type of the resin.

In the present embodiment, the thickness of the anisotropic filler-containing sheet may be appropriately determined according to the application, and may be, for example, 10 to 1000 μm.
When the anisotropic filler-containing sheet is a heat conductive sheet, the heat conductivity in the thickness direction of the sheet is. It is preferably at least 0 W / m · K, more preferably at least 7.0 W / m · K, even more preferably at least 10.0 W / m · K. There is no upper limit for the thermal conductivity, and a larger value is more preferable. According to the manufacturing method of the present embodiment, it is possible to manufacture such a heat conductive sheet having a high heat conductivity.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Methods for measuring the properties of the anisotropic filler-containing sheets produced in the examples and comparative examples are described below.
<Evaluation method for each characteristic>
(1) Thermal conductivity A test piece (10 mm × 10 mm × 1 mm thick) was cut out from the sheet (C sheet described later) obtained in each of the examples and comparative examples, and this test piece was subjected to heat conduction with a xenon flash analyzer LFA447 manufactured by NETZSCH. The thermal diffusivity of the test piece was measured with a laser flash using a rate meter.
Thermal diffusivity obtained as described above; density of sheet measured using a density measuring device (MS-DNY-43 manufactured by METTLER TOLEDO); and specific heat of each of boron nitride and resin (cured product) Specific heat of the sheet calculated from the mass ratio in these sheets (boron nitride: 0.81 J / g · K, resin: 0.80 J / g · K) (average value proportionally divided according to the mass ratio) From the product, the thermal conductivity (W / m · K) was calculated.
(2) Orientation intensity ratio The orientation of the boron nitride primary particles in the sheet is determined by the intensity of the I (002) diffraction line (2θ = 26.5 °) and the I (100) diffraction line (2θ) = 41.5 °) (I (002) / I (100)). However, what is evaluated by the X-ray diffraction method is the orientation of particles existing in a range near the surface of the sheet.
The thickness direction of the hexagonal boron nitride primary particles coincides with the crystallographic I (002) diffraction line, ie, the c-axis direction, and the in-plane direction coincides with the I (100) diffraction line, ie, the a-axis direction. When the boron nitride primary particles constituting the boron nitride particle aggregate have completely random orientation (non-oriented), (I (002) / I (100)) ≒ 6.7 (“JCPDS [powder X Line Diffraction Database] ", Crystal density value [Dx] of No. 34-0421 [BN]). The smaller (I (002) / I (100)) means that the a-axis direction of the hexagonal boron nitride particles is oriented in the thickness direction.
Specifically, a test piece (5 mm × 5 mm × 0.2 mm thick) was cut out from the sheets obtained in the examples and comparative examples, and a “fully automatic horizontal multipurpose X-ray diffractometer SmartLab” (manufactured by Rigaku Corporation, X X-rays are irradiated in the thickness direction of the test piece using a source: CuKα ray, tube voltage: 45 kV, tube current: 360 mA), and the intensity of I (002) diffraction line and I (100) diffraction line Was measured.

(Example 1)
A sheet containing scaly boron nitride particles and a resin was prepared using the method of the present invention.
100 parts by mass of a triphenylmethane-type epoxy resin ("EPPN-501H" manufactured by Nippon Kayaku), 63 parts by mass of a curing agent (phenonovolac-based curing agent, "DL-92" manufactured by Meiwa Kasei), and a curing catalyst (2-phenylimidazole) , Manufactured by Shikoku Chemicals Co., Ltd.) to prepare a resin composition. The mixing ratio between the epoxy resin and the curing agent was such that the functional group of the epoxy resin / curing agent had an equivalent ratio of 1.0.
Next, 100 parts by mass of boron nitride primary particles having an average particle diameter of 45 μm (“PT110” manufactured by Momentive Performance) as an anisotropic filler, and 3-glycoxide propyltrimethoxylan (manufactured by Tokyo Chemical Industry Co., Ltd.) as a coupling agent. 1.5 parts by mass was added dropwise, and the mixture was stirred with a rotation revolution mixer (Sinky AR-100).
Subsequently, in 50 parts by mass of a solvent (methyl ethyl ketone), 39 parts by volume of the resin composition and a total of 50 parts by mass of 61% by volume of boron nitride primary particles to which the coupling agent was added were mixed to prepare an ink. .
This ink was applied on a support (copper foil) using an applicator (produced by Imoto Machinery Co., Ltd.) (gap: about 1.5 mm) to form a flat coating film. Subsequently, this was placed on an aluminum plate, and a vibrating element of an ultrasonic generator (Ultrasonic Homogenizer US-600T manufactured by Nippon Seiki Seisaku-sho, Ltd.) was applied to the aluminum plate, and the coating film was applied to the coating film via the aluminum plate and copper foil. Ultrasonic vibration was applied for a minute and then allowed to stand.
Next, the coating film was dried at 120 ° C. for 10 minutes to remove the solvent, thereby producing a semi-cured sheet (B sheet) (about 1.5 mm thick).
This was vacuum-pressed at 180 ° C. for 2 hours under the conditions of 10 MPa and cured, and finally the copper foil was peeled off to produce a sheet (C sheet) containing an anisotropic filler.

(Example 2)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 1 except that the press pressure at the time of vacuum pressing on the semi-cured sheet was changed to 5 MPa.
(Example 3)
In 50 parts by mass of a solvent (methyl ethyl ketone), 30 parts by volume of the resin composition and a total of 50 parts by mass of 70% by volume of the boron nitride primary particles added with the coupling agent were mixed to prepare an ink (ink solid). (A ratio of an anisotropic filler in the mixture was changed), and an anisotropic filler-containing sheet was produced in the same manner as in Example 1.
(Example 4)
An anisotropic filler-containing sheet was produced in the same manner as in Example 1 except that primary particles of boron nitride having an average particle diameter of 12 μm (“πBN-S03” manufactured by Tokuyama) were used as the anisotropic filler.
(Example 5)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 4, except that the pressure during the vacuum pressing of the semi-cured sheet was changed to 5 MPa.
(Example 6)
In 50 parts by mass of a solvent (methyl ethyl ketone), 30 parts by volume of the resin composition and a total of 50 parts by mass of 70% by volume of the boron nitride primary particles added with the coupling agent were mixed to prepare an ink (ink solid). (A ratio of an anisotropic filler in the mixture was changed), and an anisotropic filler-containing sheet was produced in the same manner as in Example 4.

(Comparative Example 1)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 1 except that ultrasonic vibration was not applied.
(Comparative Example 2)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 3 except that ultrasonic vibration was not applied.
(Comparative Example 3)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 4, except that ultrasonic vibration was not applied.
(Comparative Example 4)
An anisotropic filler-containing sheet was obtained in the same manner as in Example 6 except that ultrasonic vibration was not applied.
(Comparative Example 5)
An anisotropic filler-containing sheet was produced in the same manner as in Example 1, except that agglomerated boron nitride particles ("SGPS" manufactured by Denka) were used as the anisotropic filler, and that no ultrasonic vibration was applied.
(Comparative Example 6)
An anisotropic filler-containing sheet was produced in the same manner as in Example 3, except that aggregated boron nitride particles ("SGPS" manufactured by Denka) were used as the anisotropic filler, and that no ultrasonic vibration was applied.

Table 1 shows the thermal conductivity and the orientation intensity ratio of boron nitride primary particles (I (002) / I (100)) of the anisotropic filler-containing sheets prepared in Examples 1 to 6 and Comparative Examples 1 to 6. Show.
In the sheets of Examples 1 and 2, the orientation intensity ratio I (002) / I (100) was smaller (compared to the case of random orientation) as compared with Comparative Example 1 manufactured using the same ink and without applying high-frequency vibration. (Close to theoretical 6.7), the thermal conductivity increased by a factor of about 2-3. In each of Examples 1 and 2 and Comparative Example 1, the orientation intensity ratio of the particles near the sheet surface evaluated by the X-ray diffraction method was higher after pressing (C sheet) than before pressing (B sheet). This is considered to be because some of the vertically oriented particles present near the sheet surface were pushed horizontally by the press plate, and the random orientation was maintained inside the sheet. Conceivable. In fact, from the SEM images of the cross sections of the sheet (C sheet) obtained in Example 2 and Comparative Example 1, the particles are horizontally oriented inside the sheet obtained without applying high frequency vibration. (Comparative Example 1, FIG. 2), it was confirmed that the particles were randomly oriented inside the sheet obtained by applying high-frequency vibration (Example 2, FIG. 1).
Similarly, the sheets of Examples 3 to 6 all have the thermal conductivity about twice higher than the corresponding ones (Comparative Examples 2 to 4) manufactured using the same ink and without applying high-frequency vibration. became.
Further, the sheet of Example 4 used aggregated boron nitride particles as an anisotropic filler, and had a higher orientation intensity ratio than the sheet of Comparative Example 5 produced in the same manner except that high frequency vibration was not applied. However, the porosity was low, resulting in high thermal conductivity.
Similarly, the sheet of Example 6 used aggregated boron nitride particles as an anisotropic filler, and had a higher orientation strength ratio than the sheet of Comparative Example 6 produced in the same manner except that high frequency vibration was not applied. Although large, the porosity was low, resulting in high thermal conductivity.

The anisotropic filler-containing sheet produced by the production method of the present invention can be used for various applications.
The anisotropic filler-containing sheet manufactured by the manufacturing method of the present invention can be used as a heat conductive sheet when a heat conductive substance is used as the anisotropic filler. For applications that require thermal conductivity and insulation (for example, materials for heat-dissipating insulating layers and adhesive layers in heat-generating electronic components such as circuit boards for power equipment and semiconductor power devices) ) Can be suitably used.

This application is based on Japanese Patent Application (No. 2017-114377) filed with the Japan Patent Office on June 9, 2017, the contents of which are incorporated herein by reference.

Claims (9)

Forming a film of an ink containing an anisotropic filler and a resin on a support, and applying a vibration having a frequency of 5 kHz or more to the film while the film is flowable;
A method for producing a sheet containing an anisotropic filler.   The method for producing an anisotropic filler-containing sheet according to claim 1, wherein the frequency of the vibration is 10 to 1000 kHz.   The method for producing an anisotropic filler-containing sheet according to claim 1, wherein an average longest diameter of the anisotropic filler is 0.5 μm to 200 μm.   The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 3, wherein an aspect ratio of the anisotropic filler is 2 or more.   The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 4, wherein the anisotropic filler includes scaly boron nitride particles.   The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 5, wherein the anisotropic filler includes hexagonal boron nitride particles.   The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 6, wherein a volume ratio of the anisotropic filler in the film is 10 to 90% by volume.   The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 7, wherein the resin includes a thermosetting resin. The method for producing an anisotropic filler-containing sheet according to any one of claims 1 to 8, further comprising a step of pressing the film.