JP2002026202A - Heat conducting sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conducting sheet which has flexibility and following-up property to unevenness, can be formed thinly and has high thermal conductivity. SOLUTION: In this heat conducting sheet including binder resin and heat conducting filler dispersed in the binder resin, the binder resin is composed of thermoplastic resin, the heat conducting filler is composed of particles of inorganic filler which are orientated in the direction almost perpendicular to a surface of the sheet and have high thermal conductivity in the direction. After a plurality of primary sheets molded of kneaded material of the thermoplastic resin and the particles of the inorganic filler are laminated, an obtained laminate is sliced in the direction perpendicular to the lamination surface, and the heat conducting sheet is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conductive sheet, and more particularly, to a heat conductive sheet having high heat conductivity particularly in a direction perpendicular to the sheet surface and useful as a heat transfer medium for electronic parts and the like. Regarding the sheet. The invention also relates to a method for producing such a thermally conductive sheet.

[0002]

2. Description of the Related Art In recent years, removing heat from a heating element has become a problem in various fields. In particular, in various devices such as electronic devices and personal computers, for example, heat-generating electronic components (for example, IC chips) and other components (hereinafter, collectively referred to as “heat-generating components”) contained therein. Removing heat is an important issue. This is because, in various heat-generating components, as the temperature of the component increases, the probability that the component malfunctions tends to increase exponentially. In recent years, as heat-generating components have become smaller and smaller, and the processing speed has been increased, the demand for heat radiation characteristics has been further increased.

[0003] The heat released from the heat-generating component is usually transmitted to a heat radiator, for example, a heat sink, a heat radiating fin, a metal heat radiating plate, etc., through various heat conductive sheets, and is radiated there. Here, in order to obtain the maximum heat radiation effect, it is necessary that the heat conductive sheet to be used can sufficiently follow the surface of the heat-generating component or the heat radiator and has high heat conductivity. is there. In order to satisfy such a demand, many of the conventional heat conductive sheets contain a silicone rubber with a filler for improving heat conductivity. As the filler, for example, alumina, silica (quartz), boron nitride, magnesium oxide and the like are used. As a specific example, JP-A-56-837 discloses a heat radiation sheet containing an inorganic filler and a synthetic rubber such as silicone rubber as main components, wherein the inorganic filler comprises (A) boron nitride and (B)
A heat dissipation sheet comprising two components, alumina, silica, magnesia, zinc white and mica, is disclosed. Also, Japanese Patent Application Laid-Open No. 7-111300 discloses that 1 μm
There is disclosed an insulating and heat-dissipating sheet characterized in that a boron nitride powder having the above thickness is present in silicone rubber. In such a thermally conductive silicone rubber sheet, in order to obtain high thermal conductivity, it is necessary to add a large amount of a filler, and there is a problem that a processing machine is easily worn as a result of an increase in viscosity. In addition, the flexibility of the sheet is reduced, and the ability to follow the surface of the heat-generating component or the heat radiator is also deteriorated. Further, the amount of the filler added is limited, and it is difficult to obtain the desired thermal conductivity. That is, in the heat conductive sheet of the type described above, it is difficult to satisfy both softness and high heat conductivity at the same time, despite the high thermal conductivity of the filler itself used.

[0004] In recent years, attempts have been made to make the silicone rubber sheet softer in order to obtain high adhesion that can follow components having complicated shapes. For example, JP-A-10-189838 discloses that a condensation type gel such as a condensation-curable liquid silicone gel is used as a binder, and a silicone oil and
A heat conductive gel useful as a heat dissipation sheet, characterized by being added with a heat conductive filler such as boron nitride, silicon nitride, aluminum nitride, and magnesium oxide and being cured in a gel state at normal temperature, is disclosed. . However, in the case of this heat radiating sheet, although high adhesion is obtained, its thermal conductivity is about 0.8 to 1.1 W / m · k, and it is necessary to further increase it to meet recent demands. . However, when the filling rate of the thermally conductive filler is increased to obtain a high thermal conductivity, the plasticity of the gel composition is reduced, the workability is deteriorated, and further, the strength of the heat radiation sheet obtained after curing is reduced. The problem of lowering occurs.

On the other hand, a heat conductive sheet using hexagonal boron nitride (BN) particles as a heat conductive filler has been proposed. The thermal conductivity of BN particles having a layered crystal structure is about 30 times higher in the direction parallel to the layer (hereinafter referred to as the a-axis direction) than in the direction perpendicular to the layer (hereinafter referred to as the c-axis direction). Because it is expensive, this property is used. That is, in order to enhance the thermal conductivity of the thermally conductive sheet using the BN particles, various measures have been taken so that the a-axis of the BN particles is oriented in a direction perpendicular to the sheet surface.
For example, JP-A-3-151658 discloses a heat-dissipating sheet in which a thermally conductive filler (boron nitride) is distributed in a matrix resin, wherein the thermally conductive filler is erected in the thickness direction. A heat dissipation sheet characterized by being oriented in a state is disclosed. This heat dissipation sheet can be manufactured by, for example, extruding a kneaded product of a matrix resin and a thermally conductive filler to obtain an elastic body, slicing the elastic body, and further pressing and vulcanizing. Japanese Patent Application Laid-Open No. 5-65347 discloses that, when a material for forming an anisotropic heat conductive sheet containing a liquid matrix resin and a heat conductive filler (boron nitride) as main components is formed in a sheet shape, 1 kV / mm or more. A method for producing an anisotropic heat conductive sheet, characterized in that a direct current voltage is applied to orient the heat conductive filler in the thickness direction of the sheet. Also, Japanese Patent Application Laid-Open No. H8-244094 discloses that a kneaded product containing resin and / or rubber and flaky particles (boron nitride) is extruded into a plurality of strip-shaped plastics while they are assembled with a lip to form a sheet. A method of manufacturing a heat-dissipating sheet characterized by post-curing or curing while forming into a sheet is disclosed. Further, JP-A-11-19948 discloses that a rubber green sheet containing boron nitride powder is formed, a plurality of the green sheets are laminated and cured by vulcanization, and then cut to a desired thickness in the laminating direction, or A method for manufacturing a heat radiating member for an electronic component, which comprises laminating a plurality of sheets, cutting the laminate in a desired thickness in a laminating direction, and vulcanizing and curing the laminate is disclosed. Furthermore, Japanese Patent Laid-Open No.
No. 1-77795 discloses that a rubber kneaded product containing an addition-reaction-type liquid silicone and boron nitride powder is passed through a mold having a plurality of slits to continuously extrude a plurality of strip-shaped sheets. And slicing the combined object perpendicular to its thickness direction,
A method for producing a heat-dissipating rubber sheet characterized by curing them is disclosed. However, in the heat conductive sheet using these BN particles, a soft binder resin such as silicone rubber or silicone gel is used.
In the method described in Japanese Patent Application Laid-Open No. 1-1948, that is, a method of obtaining a sheet by slicing a block-shaped product, as the thickness of the sheet decreases, the cut-out sheet expands and deforms, or becomes uniform. Problems such as the inability to obtain a thick sheet occur. Further, once the silicone rubber has been crosslinked, its cured product cannot be reused, and thus expensive BN particles cannot be effectively used.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve many of the problems of the prior art as described above, and to have flexibility and follow special shapes such as irregularities and curved surfaces. An object of the present invention is to provide a heat conductive sheet that can be formed thin and has high heat conductivity at the same time. Another object of the present invention is to provide a method for producing such a heat conductive sheet.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned objects, and as a result, when producing a heat conductive sheet, a heat conductive filler was contained in the binder resin in the sheet surface. It has been found that it is effective to orient substantially vertically, and the present invention has been completed. That is, the present invention provides a heat conductive sheet including a binder resin and a heat conductive filler dispersed in the binder resin, wherein the binder resin is made of a thermoplastic resin, and The conductive filler is oriented in a direction substantially perpendicular to the plane of the thermally conductive sheet, is a particle of the inorganic filler having a high thermal conductivity in that direction, and wherein the thermally conductive sheet is After laminating a plurality of primary sheets formed from a kneaded product of thermoplastic resin and the particles of the inorganic filler, it was formed by slicing the obtained laminate in a direction perpendicular to the lamination plane. A heat conductive sheet characterized by the above.

[0008] Here, the "primary sheet" is a sheet obtained by kneading particles of a thermoplastic resin and an inorganic filler by a method described later, and the flat inorganic filler is applied to the surface of the sheet. It refers to one that is oriented in a substantially parallel state. Further, the present invention is a method for producing a thermally conductive sheet containing a binder resin and a thermally conductive filler dispersed in the binder resin, wherein the thermoplastic resin as the binder resin, Molding the kneaded material containing particles of the heat conductive filler, to produce a primary sheet in which the particles of the inorganic filler are oriented in a direction substantially parallel to the main surface,
A plurality of the primary sheets are laminated to a predetermined thickness, and the obtained laminate is sliced in a direction perpendicular to a lamination surface thereof, and is oriented in a direction substantially perpendicular to the surface of the heat conductive sheet. And a method of manufacturing a heat conductive sheet provided with particles of an inorganic filler having high heat conductivity in that direction.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The heat conductive sheet according to the present invention and the method for producing the same can be implemented in various forms within the scope of the present invention. Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The heat conductive sheet of the present invention is basically configured to include a binder resin and a heat conductive filler dispersed in the binder resin, similarly to the conventional heat conductive sheet, , Binder resin and the kind of the heat conductive filler, and the method of manufacturing the sheet are distinguished from the conventional heat conductive sheet.

Referring to FIG. 1, the heat conductive sheet 10 of the present invention includes at least a binder resin 1 and a heat conductive filler 2 dispersed in the binder resin. In this heat conductive sheet 10,
(1) The binder resin 1 is made of a thermoplastic resin,
(2) The thermally conductive filler 2 in the binder resin 1 is oriented in a direction substantially perpendicular to the main surface 10a of the thermally conductive sheet 10, and is made of an inorganic filler having high thermal conductivity in that direction. Particles, and (3) heat conductive sheet 10
After laminating a plurality of primary sheets formed from a kneaded material containing at least particles of a thermoplastic resin as a binder resin 1 and particles of an inorganic filler as a thermally conductive filler 2, the obtained laminate is It is formed by slicing in a direction perpendicular to the lamination surface.

More specifically, the resin used as the binder resin in the heat conductive sheet of the present invention should be of such a degree that it is thermoplastic and does not adversely affect the manufacturing process of the heat conductive sheet at room temperature. Hard and, in particular, as will be described in detail below, hard enough not to reduce the productivity when the laminate of the primary sheet is formed into a sheet in the slicing process, even when a large amount of the thermally conductive filler is mixed (for example, Even when boron nitride particles are mixed in a volume fraction of 30 parts or more with respect to 100 parts of the binder resin, as long as the sheet can be easily formed by extrusion molding,
There is no particular limitation. In particular, a thermoplastic resin that can absorb a plasticizer in the state of the sheet obtained after the slicing step and can arbitrarily adjust the softness of the heat conductive sheet can be advantageously used as the binder resin.

Suitable thermoplastic resins are not limited to those listed below, but include, for example, synthetic rubber resins (copolymer rubbers) represented by SIS, SBS, SEBS, SEPS and the like. Or an acrylic resin. If necessary, a resin such as a polyolefin resin may be used as the binder resin instead of or in combination with the acrylic resin. These thermoplastic resins may be used alone or in combination of two or more.

In order to improve the properties of the finally obtained heat conductive sheet, various methods are used for the binder resin described above or otherwise for the kneaded product of the binder resin and the heat conductive filler. It is preferable to mix various additives as necessary. For example, a plasticizer commonly used in this technical field can be added to adjust the softness of the heat conductive sheet. For example, when a synthetic rubber-based resin is used as a binder resin, paraffin-based oil, naphthenic-based oil, or the like can be suitably used as a plasticizer, and when an acrylic-based resin is used as a binder resin. For this, a phthalate or phosphate ester plasticizer can be suitably used. Such a plasticizer may be added alone, or two or more kinds may be mixed and added.

In order to impart durability to the heat conductive sheet, an antioxidant, an ultraviolet stabilizer, an ultraviolet absorber and the like may be added alone or in combination. It is preferable that a binder resin having excellent durability against deterioration due to oxidation or deterioration due to ultraviolet rays can be used instead of using such an additive.

Further, when a synthetic rubber-based resin is used as the binder resin, in the step of forming the kneaded material into a sheet by extrusion, it is necessary to adjust the workability of the extrusion or to adjust the hardness of the resin. For this purpose, various resins may be added. Suitable resins for this purpose are not limited to those listed below, but include aromatic petroleum resins, aliphatic petroleum resins, hydrogenated petroleum resins, cumarone.
Examples include indene resin and styrene resin. Among such resins, styrene-based resins, petroleum resins, and combinations thereof can be particularly preferably used because the hardness of the resin and the workability during extrusion molding can be appropriately adjusted. In addition, when these resins are used after hydrogenation, the weather resistance of the resins themselves is improved, so that they can be used more preferably.

On the other hand, when an acrylic resin is used as the binder resin, the type and amount of the monomer used as the starting material of such a resin are appropriately selected, or the molecular weight of the polymer is appropriately adjusted. By doing so, the processability during extrusion molding and the productivity of the sheet can be improved. In addition, a thermally conductive filler is previously contained in the polymerizable composition containing the starting material of the acrylic resin, and in that state, extruded before polymerization to form a sheet, and subsequently heated and cured. Thus, it is possible to obtain a primary sheet in which the thermally conductive filler is uniformly dispersed in the obtained acrylic resin.

Further, other usable additives include, for example, tackifiers, modifiers, heat stabilizers, and colorants such as pigments and dyes. In the heat conductive sheet of the present invention, as the heat conductive filler dispersed in the binder resin described above, various fillers generally used in the field of the heat conductive sheet can be used. Preferably, it is a particulate inorganic filler which is oriented in a direction substantially perpendicular to the plane of the heat conductive sheet by the process of the present invention and has high heat conductivity in that direction. As such an inorganic filler, there is preferably a particle of boron nitride (BN). As described above, the BN particles are hexagonal particles and have a layered crystal structure, and thus have a plate-like particle shape. This layered BN
In the particles, the thermal conductivity in the direction parallel to the layer (a-axis direction) is about 30 times that in the direction perpendicular to the layer (c-axis direction). Utilizing the above, a remarkably enhanced thermal conductivity is obtained. That is,
In the heat conductive sheet of the present invention, a plurality of molded products formed from a kneaded material containing particles of a thermoplastic resin and an inorganic filler, which will be described in detail below, due to its unique manufacturing process. After laminating the primary sheets, the resulting laminate is sliced in a direction perpendicular to the lamination plane, so that the BN particles are oriented in a direction perpendicular to the heat conductive sheet plane. , Thereby obtaining enhanced thermal conductivity. Such a selective orientation state of the BN particles can be understood from the schematic diagram of FIG.

Although the size of the plate-like BN particles can be widely varied depending on the constitution and thickness of the heat conductive sheet, the desired level of heat conductivity, and the like, usually, the length in the a-axis direction is not limited. By definition, it is in the range of about 1-100 μm, preferably in the range of about 5-70 μm. When the length of the BN particles is less than 1 μm, the surface area of the particles becomes large and the particles cannot be filled with high density, and as a result, high thermal conductivity cannot be realized. Conversely, the length of the BN particles is 100 μm
When the ratio exceeds the limit, it becomes impossible to avoid the increase in the thickness of the heat conductive sheet in spite of the demand to make the sheet as thin as possible, and there arises a problem that large particles easily fall off the sheet. When using such BN particles, if appropriate, the BN particles may be used in different lengths.

The amount of the thermally conductive filler (typically, BN particles) in the binder resin can be widely varied depending on the effect of the addition required for the filler. Usually, the volume fraction is preferably in the range of about 30 to 70 parts with respect to 100 parts of the binder resin. If the amount of the filler is less than 30 parts, the thermal conductivity does not reach the high level intended in the present invention, and if it exceeds 70 parts, the uncured heat conductive compound May decrease, and it may be difficult to form a sheet. However, in practicing the present invention, thermally conductive fillers may be incorporated in amounts outside the above ranges if acceptable results are obtained.

The thermally conductive sheet of the present invention can preferably be provided in the form of a relatively thin sheet.
The thickness of the heat conductive sheet is usually about 50 to 1,000 μm.
m, more preferably about 100-500.
μm range. If the thickness of the heat conductive sheet is less than 50 μm, it is too thin to make it difficult to handle, and there is a possibility that tearing or wrinkling may occur during the sticking operation. Conversely, if the thickness of the heat conductive sheet exceeds 1,000 μm, it will not be possible to cope with downsizing of the heat-generating parts.

Since the heat conductive sheet of the present invention has a slight tackiness on the surface of the sheet, it is exposed in order to prevent the surface from being contaminated before it is actually attached to an electronic component or the like. It is preferable that the surface of the sheet is covered with a release sheet or another protective sheet. The release sheet, the protection sheet, and the like may be conventional ones. The heat conductive sheet of the present invention is a self-supporting sheet, and therefore can be advantageously used as it is as a heat transfer means. However, if desired, the sheet may be used in combination with a suitable substrate, especially supported on such a substrate. Suitable substrates include:
For example, a plastic film, a woven fabric, a nonwoven fabric, a metal foil and the like can be mentioned.

For example, a plastic film useful as a substrate is a polyolefin film having a thermal conductivity,
A film having good weather resistance and relatively high substrate strength can be advantageously used. Suitable polyolefin films are not limited to those listed below, but may include polyethylene films, polypropylene films, EVA films, EAA films, ionomer films and the like. Among such polyolefin films, highly crystalline high-density polyethylene, ultra-high molecular weight polyethylene, and the like can be most preferably used because they are excellent in strength even when they are thin and have relatively high thermal conductivity. Although the thickness of such a polyolefin film can be widely changed according to various factors, it is preferably as thin as possible, and usually, it is preferably in the range of about 1 to 25 μm.

The metal foil useful as the substrate is a foil of various metal materials such as aluminum, copper, gold, silver, lead, and stainless steel. Here, the term “foil” generally refers to a material having a small thickness, and thus includes a material called a metal sheet, a metal foil, or the like. Although the thickness of such a metal foil can be widely changed according to various factors, it is preferable that the thickness be as thin as possible similarly to the above-mentioned plastic film.
Preferably, it is in the range of 1 to 20 μm.

Further, a single-sided adhesive film may be used as a substrate. Since this film has an adhesive layer on one side, the operation of attaching the substrate to the support can be performed efficiently. The pressure-sensitive adhesive layer is preferably covered with a release sheet or another conventional surface protection sheet. Although the heat conductive sheet according to the present invention can be manufactured according to various methods, it is preferable that the kneaded material contains the following steps: a thermoplastic resin as a binder resin and particles of a heat conductive filler. To form a primary sheet in which the particles of the thermally conductive filler are oriented in a direction substantially parallel to the main surface, a plurality of primary sheets are laminated to a predetermined thickness, and the obtained laminate is formed. Slicing in a direction perpendicular to the lamination plane, comprising particles of a thermally conductive filler oriented in a direction substantially perpendicular to the plane of the thermally conductive sheet and having a high thermal conductivity in that direction. It can be manufactured by manufacturing a heat conductive sheet. That is, the heat conductive sheet of the present invention,
Although it may be changed as needed, it can be advantageously implemented in the steps shown in FIG. (1) Kneading step Particles of thermoplastic resin and heat conductive filler (preferably,
(BN particles) and optional additives. (2) Sheeting Step A kneaded material such as a thermoplastic resin is preferably formed by extrusion molding to produce a primary sheet having a predetermined thickness. In this primary sheet, a state is obtained in which the particles of the thermally conductive filler are oriented in a direction substantially parallel to the main surface. (3) Lamination Step A plurality of primary sheets are laminated to a predetermined thickness and integrated. This step can be preferably performed by thermocompression bonding. (4) Slicing Step The laminate of the primary sheet is sliced in a direction perpendicular to the lamination surface to obtain a heat conductive sheet having a predetermined thickness. The slicing step is a so-called second sheet forming step. Here, the term “slicing” is used in a broad sense, and includes various thinning methods that can be made into sheets.

Hereinafter, each manufacturing process will be described. In the kneading step, which is the first step, for example, filler particles are prepared in a predetermined amount and mixed with a binder component containing a separately prepared binder resin, additive, and the like. During the mixing, the filler particles are sufficiently kneaded until the filler particles are uniformly dispersed in the binder resin and kneaded. For the kneading device, for example, a kneader or the like can be used. Further, at the stage of preparing the binder component, the filler particles may be added and dispersed in several times.

The sheet formation as the second step can be performed according to various methods. For example, the kneaded product obtained in the previous step is sandwiched between two release-treated liners (for example, a silicone-treated polyester film),
The sheet may be formed by pressing with a press machine in which the gap is adjusted to have a predetermined thickness. Also, according to another law,
It is also possible to continuously form a sheet by passing the kneaded material between the two rolling rolls whose gap has been adjusted. In particular, in the present invention, it is advantageous to produce a primary sheet having a predetermined thickness by extrusion. In this case, the first kneading step is performed by a single-screw or twin-screw extruder, and usually, subsequently, the sheet is continuously formed. The T-die method can be suitably used for sheet formation. In any primary sheet, the filler particles dispersed in the binder resin are in a state parallel to the sheet surface, that is,
Each is oriented in a state of lying on the sheet surface.

After the completion of sheeting, as a third step, the obtained primary sheets are laminated and integrated. For example, a rectangular parallelepiped laminate (block) can be obtained by laminating rectangular primary sheets and fusing and integrating a binder resin by heating and pressing. That is, in the practice of the present invention, the shape of the laminate is not particularly limited as long as a desired heat conductive sheet can be cut out from the laminate.

The slicing step (sheeting step), which is the fourth step, is performed in the laminate (block) prepared in the previous step.
Can be carried out by adopting an appropriate method according to the shape of. The slicing direction must be perpendicular or nearly perpendicular to the lamination direction of the primary sheet in the laminate in order to make the orientation of the filler particles in the thermally conductive sheet substantially perpendicular to the sheet surface. In the slicing of a rectangular parallelepiped laminate, the laminate repeatedly reciprocates with respect to the fixed slicing knife, and each time the sheet is cut out from one end face. Of course, the slicing of the laminate may be performed by a method other than such a method.

Through a series of steps as described above, the filler particles are oriented in a direction substantially perpendicular to the surface of the heat conductive sheet, and a heat conductive sheet having high heat conductivity in that direction is obtained. be able to. The heat conductive sheet according to the present invention may be impregnated with a plasticizer, if necessary. Usually, it is preferable to impregnate the heat conductive sheet with the plasticizer after slicing as described above. Impregnation with a plasticizer is effective for controlling the strength, hardness or tackiness of the heat conductive sheet. The reason why the plasticizer impregnation is effective will be described below.

When the binder resin used is relatively soft, the resulting heat conductive sheet can follow the surface of the heat-generating component or the heat radiator to be adhered to some extent without changing the heat conductive sheet. When heat is applied, the binder resin is thermoplastic, so that the binder resin is softened and the adhesion (conformity of irregularities) is further increased, so that sufficient thermal conductivity can be obtained without adding a plasticizer. is there. However, in such a soft state, the operation of slicing the block-shaped laminate to cut out the thermally conductive sheet cannot be efficiently performed.

According to the present invention, in order to avoid this reduction in workability, it is proposed to provide a block-shaped laminate in a relatively hard state and to carry out slicing work more efficiently. That is, when the binder resin constituting the block-shaped laminate is hard to some extent, the productivity of the heat conductive sheet by the slicing operation can be improved. A hard binder resin can be obtained by using a resin having a relatively high softening temperature. After a successful slicing operation, the last step is to apply a plasticizer to the heat conductive sheet and impregnate it into the binder in order to give the heat conductive sheet good followability. Integrate resin and plasticizer. Here, “impregnation” means impregnating at least the surface portion of the heat conductive sheet with a plasticizer, and therefore, the method of impregnation is not particularly limited.

More specifically, the impregnation of the heat conductive sheet with the plasticizer will be described. In the case where the heat conductive sheet is a single sheet obtained by a slicing method, the sheets are bonded to each other with a weak adhesive tape such as a surface protection tape. And a plasticizer can be continuously applied. As a method for applying the plasticizer, a usual application method, for example, knife coating, roll coating, spray coating, or the like can be used. When a continuous web is directly impregnated with a plasticizer, it is preferable to attach a releasable support base material immediately after the impregnation in order to improve handleability in a post-process such as punching.

It is desirable that the detailed processing conditions in each of the above-described steps be optimized in consideration of the types and characteristics of the raw materials used, the desired effects, and the like. For example, the conditions for extruding the primary sheet in the sheeting step, the heating temperature and time for fusing the primary sheet in the laminating step, the surface temperature of the block when preheating the block of the laminate in the slicing step, or a slicing knife for the block Angle can have a significant effect on the productivity of the heat conductive sheet,
In addition, since the optimal processing conditions can vary depending on the characteristics of the binder resin used, it is recommended to optimize the processing conditions of each step according to the characteristics of the binder resin used and to achieve the highest productivity. .

When the present invention is carried out, some scraps of the primary sheet and scraps of the heat conductive sheet are generated during the production of the heat conductive sheet. Such a scrap can be reused as a raw material because the binder resin used in the present invention is made of a thermoplastic resin. However, in order to minimize the occurrence of sheet deterioration due to resin reuse, it is necessary to adjust the blending amount of the offcuts so that the ratio of offcuts to the raw materials charged as new is constant. desirable. The mixing amount of the offcuts is usually 10% by volume.
It is preferable that the amount is 5 to 30 parts of offcuts based on 0 parts of new raw material. The ability to recycle offcuts means that it is possible to effectively use expensive raw materials such as BN particles and increase the economic efficiency, and this is one of the remarkable effects of the present invention. is there.

By using a thermally conductive resin as the binder resin, the above-mentioned economic advantages can be obtained. In addition, according to the present invention, additional advantages can be obtained by improving the binder resin used. For example, it may be necessary to crosslink the binder resin to some extent from the viewpoint of heat resistance and the like. In such a case, the resin can be crosslinked by irradiating the heat conductive sheet impregnated with the plasticizer in the final step with an electron beam or the like.
In addition to the method of performing crosslinking in this manner, for example, when an acrylic resin is used as a binder resin, by using an ionic crosslinking agent, heat can be maintained while maintaining extrusion characteristics. The cohesive force of the conductive sheet can be improved.

As will be understood from the above description, the heat conductive sheet of the present invention is preferably one in which plate-like BN particles are dispersed in a binder resin made of a thermoplastic resin. And a sheet in which a plasticizer is impregnated. With such a configuration, for example, when extruding the kneaded material to form a primary sheet, the BN particles are dispersed along a direction parallel to the die lip of the extruder, that is, the BN particles are ,
The particles are oriented so that the a-axis is parallel to the extruded sheet surface. For this reason, in the heat conductive sheet finally obtained, the a-axis of the BN particles is highly oriented in a direction perpendicular to the sheet surface, and high heat conductivity is obtained. In addition, since a thermoplastic resin that is hard at room temperature is used as the binder resin, even if the sheet cut out in the slicing step is thin, it does not stretch, and a sheet having a uniform thickness can be obtained efficiently. further,
Since the binder resin is thermoplastic, the offcuts generated during the process can be reused as raw materials, which is economical. Furthermore, by impregnating the obtained heat conductive sheet with a plasticizer, the flexibility of the sheet can be increased, the followability to electronic components and the like can be improved, and as a result, the heat radiation effect can be further improved. At this time, the tackiness of the sheet can be adjusted by adjusting the amount of the plasticizer added. In short, the heat conductive sheet of the present invention has high heat conductivity, has excellent followability to the surface of an adherend, and is particularly useful for heat dissipation of electronic components and the like.

[0037]

Next, the present invention will be described with reference to examples. It should be understood that the following embodiments are merely examples, and the present invention is not limited to these embodiments. Example 1 Production of Thermal Conductive Sheet 15 parts by volume (13.7 parts by weight) of hydrogenated synthetic rubber (manufactured by Ciel, trade name "Kraton G1651"), 9 parts by volume (8.4 parts by weight) of aliphatic 9 parts by weight (8.1 parts by weight) of aromatic petroleum resin (manufactured by Hercules, trade name "Crystalex 3085") and 34 parts by volume (76.8 parts by weight) of boron nitride particles (average particle size of 10
μm, manufactured by Mizushima Alloy Iron Co., Ltd., trade name “HP-1”) is 100
After dissolving and mixing in a volume part (87.0 parts by weight) of toluene, the obtained mixture was applied on a polyester film (50 μm thickness) having a siliconized surface,
Dry in oven at 5 ° C. for 5 minutes. 0.22mm thick
Was obtained.

After laminating the primary sheets produced as described above to a total thickness of 12 mm, the laminate was heat-pressed for 1 minute at a heating temperature of 120 ° C. and a pressure of 2 kg / cm ² . A rectangular parallelepiped block in which the respective primary sheets were laminated and integrated was obtained. Next, the block was cut out with a slicing knife in a direction perpendicular to the primary sheet laminating direction. Sheets each having a thickness of 1 mm were obtained.

Subsequently, the sheet prepared as described above was coated with a fluorine-based liner (thickness: 75 μm, manufactured by Fujimori Kogyo Co., Ltd.).
On the surface of the sheet, a plasticizer (manufactured by Ciel, trade name "Shel").
flex371N ") was applied and impregnated. The amount of the plasticizer impregnated was 33 parts by volume (29.7 parts by weight) with respect to 67 parts by volume (107.0 parts by weight) of the sheet. A thermally conductive sheet having a thickness of 1.15 mm was obtained. Evaluation of Characteristics of Thermal Conductive Sheet When the thermal conductive sheet produced as described above was evaluated with respect to the dispersion state and thermal resistance of BN particles, the following results were obtained. (1) Dispersion state of BN particles The central part of the heat conductive sheet was cut with a knife, and the cut surface was observed with a scanning electron microscope at a magnification of 3000 times. Observation of the backscattered electron image revealed that the board surface of the BN particles was oriented perpendicular to the surface direction of the sheet. (2) Thermal resistance After attaching the thermal conductive sheet to the back side of the transistor,
It is fixed on a cooling plate (aluminum plate) maintained at a constant temperature (25 ° C.), and a constant power (12.
2W). After 5 minutes, the thermal resistance was determined from the temperature difference between the transistor temperature and the aluminum plate temperature. The thermal resistance of the heat conductive sheet of this example is 1.3 ° C.
in ² / W (8.4 ° C. · cm ² / W). Comparative Example 1 Preparation of Thermal Conductive Sheet 15 parts by volume (13.7 parts by weight) of hydrogenated synthetic rubber (manufactured by Ciel, trade name “Kraton G1651”), 9 parts by volume (8.4 parts by weight) of aliphatic 9 parts by weight (8.1 parts by weight) of aromatic petroleum resin (manufactured by Hercules, trade name "Crystalex 3085") and 34 parts by volume (76.8 parts by weight) of boron nitride particles (average particle size of 10
μm, manufactured by Mizushima Alloy Iron Co., Ltd., trade name “HP-1”) is 100
After dissolving and mixing in a volume part (87.0 parts by weight) of toluene, the obtained mixture was applied on a polyester film (50 μm thickness) having a siliconized surface,
Dry in oven at 5 ° C. for 5 minutes. 0.22mm thick
Was obtained.

After laminating the primary sheets produced as described above to a total thickness of 1.2 mm, the laminate was thermocompression-bonded at a heating temperature of 120 ° C. and a pressure of 2 kg / cm ² for 1 minute. . A thermally conductive sheet having a thickness of 1 mm was obtained. Evaluation of Characteristics of Thermal Conductive Sheet When the thermal conductive sheet produced as described above was evaluated in the same manner as in Example 1, the following results were obtained. (1) Dispersion state of BN particles From the observation of the backscattered electron image, it was found that the board surface of the BN particles was oriented parallel to the surface direction of the sheet. (2) Thermal resistance The thermal resistance of the thermally conductive sheet of this example is 1.6 ° C. · in ² / W.
(10.3 ° C. · cm ² / W). Comparative Example 2 Production of Thermal Conductive Sheet 34 parts by volume (76.8 parts by weight) of boron nitride particles (average particle diameter 10 μm, manufactured by Mizushima Alloy Iron Co., Ltd., trade name “HP-1”) and 67 parts by volume (65. 7 parts by weight) silicone gel (manufactured by Dow Corning Toray Silicone Co., Ltd., trade name “SE18”).
86A "and" SE1886B ") were placed in a planetary mixer and kneaded under reduced pressure for 30 minutes. A slurry-like silicone gel compound was obtained.

The obtained silicone gel compound was mixed with 2
The sheets were sandwiched between two fluorine-based liners (thickness: 75 μm, manufactured by Fujimori Kogyo Co., Ltd., trade name: “Film Vina SF-3”) so as to be in contact with the release agent-treated surfaces of the liners, and laminated. The obtained laminate was pressed and heated at 120 ° C. for 1 minute to be cured. A thermally conductive sheet having a thickness of 1.15 mm was obtained. The heat conductive sheet prepared as described above was used in Example 1 described above.
When evaluated according to the same method as in the above, the following results were obtained. (1) Dispersion state of BN particles From observation of the backscattered electron image, it was found that the BN particles were randomly oriented in the sheet. (2) Thermal resistance The thermal resistance of the thermally conductive sheet of this example is 1.6 ° C. · in ² / W.
(10.3 ° C. · cm ² / W).

Table 1 below summarizes the thermal resistance of the heat conductive sheets of Example 1 and Comparative Examples 1 and 2. In Table 1, as a reference example, a commercially available heat conductive sheet (thickness: 1.15 mm, manufactured by Shin-Etsu Chemical Co., Ltd.)
The thermal resistance of the trade name “TC-TKC”) is also described. Number in Table 1 Example Thermal resistance (° C./cm ² / W) Example 1 8.4 Comparative example 1 10.3 Comparative example 2 10.3 Reference example 9.1 As can be understood from the results in Table 1. According to the present invention, the BN particles are efficiently oriented in the direction perpendicular to the sheet surface of the heat conductive sheet, so that a heat conductive sheet having excellent heat dissipation characteristics can be provided.

[0043]

As described above, according to the present invention, the particles of the thermally conductive filler can be oriented along the direction perpendicular to the sheet surface. A conductive sheet can be provided. Also, the plasticizer can be applied to the heat conductive sheet after the completion of the slicing step and impregnated, so that the productivity in the slicing step is increased, and finally, there is flexibility and unevenness of the adherend. It is possible to provide a heat conductive sheet that can follow a special shape such as a curved surface or a curved surface.

Further, in the present invention, by changing the kind of the thermoplastic resin used as the binder resin, the composition of the binder component, and the addition amount of the plasticizer, the strength, hardness, adhesiveness, and the like of the sheet are appropriately controlled. can do. Furthermore, since a thermoplastic resin is used as a binder resin, scraps generated in the manufacturing process can be recycled by supplying them to the raw materials at an appropriate ratio, and expensive raw materials can be effectively used. There is also an effect.

In addition to such remarkable effects, according to the present invention, there is an effect that such an excellent heat conductive sheet can be efficiently manufactured in a thin film form by a simple method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a heat conductive sheet according to the present invention.

FIG. 2 is a process diagram showing one embodiment for producing the heat conductive sheet of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Binder resin 2 ... Thermal conductive filler 10 ... Thermal conductive sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 3/38 C08L 9/00 C08L 9/00 33/04 33/04 101/00 101/00 H01L 23 / 36 DF term (reference) 4F100 AA01A AA01B AA01C AA01H AA14A AA14B AA14C AA14H AK01A AK01B AK01C AK02 AK17 AK25A AK25B AK25C AL05 AL06 AN02A AN02B AN02C AT00 BA03 BA04C04 BA03 BA04A04 EJ823 EJ851 GB41 JB16A JB16B JB16C JJ01A JJ01B JJ01C JJ01H JK13 JL01 JL02 4J002 AE052 BG041 BP011 DK007 EH146 EW046 FD017 FD022 FD026 GQ00 5F036 AA01 BA23 BB21 BD21

Claims (7)

[Claims] 1. A thermally conductive sheet comprising a binder resin and a thermally conductive filler dispersed in the binder resin, wherein the binder resin is made of a thermoplastic resin, and The filler is an inorganic filler particle oriented in a direction substantially perpendicular to the plane of the thermally conductive sheet and having a high thermal conductivity in that direction, and wherein the thermally conductive sheet is After laminating a plurality of primary sheets molded from a kneaded product of a plastic resin and the particles of the inorganic filler, formed by slicing the obtained laminate in a direction perpendicular to the lamination surface thereof. A thermally conductive sheet, characterized in that: 2. The heat conductive sheet according to claim 1, wherein the thermoplastic resin is a synthetic rubber resin or an acrylic resin. 3. The heat conductive sheet according to claim 1, wherein the inorganic filler is boron nitride. 4. The heat conductive sheet according to claim 1, which is impregnated with a plasticizer. 5. The heat conductive sheet according to claim 1, wherein the heat conductive sheet is supported by a base material. 6. A method for producing a thermally conductive sheet comprising a binder resin and a thermally conductive filler dispersed in the binder resin, comprising: a thermoplastic resin as the binder resin; A kneaded product containing particles of the conductive filler is molded to produce a primary sheet in which the particles of the inorganic filler are oriented in a direction substantially parallel to the main surface, and a plurality of the primary sheets are formed to a predetermined thickness. Laminated, slicing the obtained laminate in a direction perpendicular to the lamination surface, oriented in a direction substantially perpendicular to the surface of the heat conductive sheet, having a high thermal conductivity in that direction A method for producing a thermally conductive sheet comprising particles of an inorganic filler. 7. The method according to claim 6, further comprising a step of impregnating the heat conductive sheet obtained by the slicing step with a plasticizer.