JP2005303240A - Heat transmission sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a heat transmission sheet excellent in radiation by fitting closely the heat transmission sheet between an electronic component and a radiator plate to make the heat transmission between both good. <P>SOLUTION: In the method for manufacturing a radiator sheet, a binder, such as a synthetic resin or rubber, and a heat transmission filler are incorporated, and its mixed compound is deaerated, then, the mixed compound is introduced into an extruding container and is pressed, thereby, the compound is extruded from a body portion of a wide sectional area through an outlet of a narrow sectional area out, and the filler is oriented in the extrusion direction by shear-deforming the fluid of mixed compound, and after the compound extruded is hardened, the hardened block is sliced in a predetermined thickness to be formed as a radiator sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat conductive sheet for mounting between an electronic component and a heat radiating plate to improve heat transfer between them and to increase a heat radiating effect.

  Heat is generated from various electronic components such as CPUs mounted on electronic devices, and leaving them at a high temperature may deteriorate or damage the characteristics, and in some cases may damage surrounding electronic components. This will shorten the life of the device itself. Recently, electronic components tend to be arranged with high density due to miniaturization of equipment, and exhaust heat has become a very important issue.

  Conventionally, when heat is exhausted from such an electronic component, heat is transferred to an aluminum plate closely attached to the electronic component or a heat sink provided via a heat pipe, and the heat sink is forcibly cooled by a fan. It has been taken. In order to transfer heat well between the electronic parts and the aluminum plate, a filler with high thermal conductivity is mixed in the binder and applied in the form of a cream, or the contact surface gap is changed by phase change due to temperature. A device has been devised to improve heat transfer by interposing a liquid filling the portion without gaps or a sheet-like material having good thermal conductivity.

  Among these, as a manufacturing method of the heat conductive sheet, a filler such as metal or metal oxide is mixed in a binder mainly composed of rubber such as silicone rubber or various synthetic resins, and is stirred in a vacuum and left standing. Alternatively, a method of heating as necessary to form a block of a cured product by a crosslinking reaction, and slicing the cured product block to an appropriate thickness to form a sheet is performed. Further, as a simple method, there is a method of slicing the cured product after kneading the material in the air and leaving it to stand for defoaming.

  In order to increase the thermal conductivity of this thermal conductive sheet, the filler mixing ratio should be increased as much as possible in view of the physical properties of the sheet, and these fillers have thermal conductivity anisotropy and heat in the length direction of the filler. When the conductivity is large, it is desirable that the orientation be perpendicular to the thickness direction of the sheet. Various methods for orienting the filler in this way have been devised, such as an electrostatic flocking method, a magnetic orientation method, and an orientation method using a mesh, but all of these methods have the following problems. It was.

Among the fillers having thermal conductivity anisotropy, there is a method of electrostatic flocking on a plate as a first method for orienting a filler having an aspect ratio and good thermal conductivity in the longitudinal direction of the fiber. In this method, an electric field is formed between the filler outlet and the flocked plate coated with an adhesive, so that the polarization-charged filler is spread on the flocked plate from the outlet and the filler chip is placed on the adhesive surface on the flocked plate. After standing up and flocking, a binder is filled between the flocked fillers, and this is removed from the plate to form a sheet. However, this electrostatic flocking method has the following problems.
(1) The filler chip is a dielectric.
(2) It is difficult to fill a binder between hairs after planting.
(3) It is difficult to plant hair at high density.
(4) Special equipment for electrostatic flocking is required.

Further, as a second method of orienting the filler chip in the thickness direction, there is a method using a magnetic force as described in JP-A-11-283718. In this method, a filler chip having thermal conductivity and magnetism is mixed in a sol-like binder to form a plate, and then a strong magnetic field is applied from the out-of-plane direction of the plate to orient the filler along the magnetic field lines. . However, the method using magnetic force has the following problems.
(1) If the filler is a non-magnetic material, it is necessary to plate the magnetic metal in advance.
{Circle around (2)} A space where the filler rolls is necessary and cannot be arranged at high density.
{Circle around (3)} Since the fillers are magnetically aggregated, it is difficult to distribute them uniformly.
(4) An expensive magnetic field generator is required as equipment.
{Circle around (5)} As another method, the method of filling the binder after arranging with a magnetic field has the same difficulty as described in [0009] above.

As a third method for orienting the filler, there is a method using a mesh. In this method, a plurality of layers of mensh are arranged in the vicinity of the outlet of an extrusion apparatus containing a binder mixed with a thermally conductive filler, and mechanically and forcedly orientate when a long thin filler passes. . However, the method using a mesh has the following problems.
(1) It is necessary to select a mesh that allows the filler to pass through without clogging the mesh and that can adjust the direction.
{Circle around (2)} When orienting the filler, the mesh is forced to pass through the mesh in a viscous fluid, so that the rigidity and strength that the filler itself does not break are required.
(3) A space where the filler rolls is necessary and cannot be arranged at high density.
(4) A sol-like binder mixed with a mesh generates a Karman vortex immediately after passing through the mesh, resulting in turbulent flow, making it difficult to align the fillers in a certain direction.

  Therefore, as a method for avoiding these problems, Japanese Patent Application Laid-Open No. 11-302545 discloses that a kneaded mixture of a binder and a filler is introduced into a large number of pipes arranged in parallel, and extruded by a differential pressure to cause Newtonian fluid to flow through the tube wall. A method is described in which the filler is oriented in the direction of flow by applying a shearing force generated by friction between the filler and shear deformation. However, this method requires a large number of pipes, and requires a length sufficient for the orientation to be completed. Further, the pipe friction resistance between the inner wall of the pipe and the kneaded material is increased by this number. Therefore, there is a problem that it is necessary to give a differential pressure to overcome this, and thereby the equipment becomes excessive.

Japanese Patent Laid-Open No. 11-302545

Problems to be solved by the invention

  The present invention has been made in order to eliminate the problems of the prior art in the method for producing a heat-dissipating sheet in which fillers are oriented and filled as described above, and is a thin heat-conducting sheet that has high thermal conductivity and is flexible and elastic. It provides the method of manufacturing efficiently.

Means to solve the problem

  The present invention provides a method for producing an anisotropic heat-radiating sheet having good thermal conductivity in the thickness direction by kneading a binder mainly composed of rubber or synthetic resin having elasticity after being cured and a thermal conductive filler, A heat-dissipating sheet produced by extruding the kneaded product and orienting the filler in the extrusion direction and then curing to produce a cured product block, and slicing the cured product block to a predetermined thickness perpendicular to the orientation direction of the filler. In the production method, the filler is oriented in the extrusion direction by extruding from a wide cross-sectional area storage area through a narrow cross-sectional area discharge port during extrusion (Claim 1).

  In the present invention, when extruding the kneaded material from the wide cross-sectional area storage area through the narrow cross-sectional area discharge port, the ratio of the dimension D of the body section of the extruding container to the cross-sectional dimension d of the discharge port is d <D. (Claim 2).

  Further, in the present invention, when the kneaded product is extruded from the wide cross-sectional area storage area through the narrow cross-sectional area discharge port, the discharge port has an orifice shape or a tapered nozzle shape, and the body section of the extrusion container The ratio of the dimension D to the dimension d of the discharge port cross section is d / D <0.7 (claim 3).

The invention's effect

  In the present invention, when extruding the kneaded product, the kneaded product is extruded through a narrow cross-sectional area discharge port through a narrow cross-sectional area discharge port, so that the kneaded product is shear-deformed to ensure the high-density thermally conductive filler in the kneaded product in the extrusion direction. Therefore, it is possible to provide a method for manufacturing a heat-dissipating sheet that is remarkably excellent in thermal conductivity without requiring an expensive device.

  The most preferred embodiment of the present invention will be described in more detail with reference to FIGS.

  The heat radiating sheet of the present invention is a sheet-like thin heat radiating sheet made of a binder material and a heat conductive filler material. The present invention basically includes the steps shown in FIG. 1, and includes a kneading step of kneading the binder 1 and the heat conductive filler 2 to obtain a kneaded product 3, which is contained in the kneaded product 3 and inhibits thermal conductivity. A defoaming process for removing gas such as air, an extrusion process for orienting the filler 2 in the binder 1 in the extrusion direction by extruding the kneaded product 3 after defoaming from the container for extrusion, and curing the extruded kneaded product 3 It consists of a curing step for making a cured product block, and a slicing step for slicing this cured product block to form the heat radiation sheet 4.

  The material for the binder 1 can be selected from cross-linked rubber materials or synthetic resin materials from materials having elasticity after being cured. Specifically, silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene copolymer, acrylic rubber, polyolefin elastomer, and polyethylene resin as synthetic resin materials are used as rubber materials. Polypropylene resin, polyester resin, etc. can be used. Among these, silicone rubber is most preferable because it is highly flexible and has excellent adhesion and heat resistance.

  The material for the binder 1 may be a one-component curable material or a two-component curable material. The viscosity of the binder itself before vulcanization is selected to be about 1 to 5000 cP, preferably about 300 to 500 cP in consideration of workability and the like. If the binder has a high viscosity, it may be diluted with an organic solvent. However, if the organic solvent does not evaporate sufficiently, it may affect the physical properties of the heat dissipation sheet. It is preferable to consider.

  As the material for filler 2, carbon graphite (graphite), mica, alumina, zinc oxide, boron nitride, molybdenum disulfide, and other metal materials such as copper and aluminum can be considered. The rate is as high as 50 to 1500 w / m · K, which is most suitable. Here, the size of the filler is as follows: diameter (φ) = 0.05 to 1000 μm, length (l) = 0.05 to 50 mm, preferably diameter (φ) = 1 to 50 μm, length (l) = 0. A thing of about 1-5 mm is suitable.

  The blending ratio of the binder 1 and the filler 2 is preferably 10 to 400 parts by weight, particularly 50 to 300 parts by weight with respect to 100 parts by weight of the binder. When the filler 2 is 10 parts by weight or less, the thermal conductivity is lowered, and when it is 400 parts by weight or more, kneading becomes difficult. Then, the binder 1 and the filler 2 are put into a kneading container and kneaded to obtain a viscous and uniform kneaded product 3.

  The kneaded product 3 is introduced into a defoaming container. The defoaming container is hermetically sealed, and the degree of vacuum for defoaming in a depressurized or vacuumed container is preferably about 500 Pa in absolute pressure. At that time, a centrifugal defoaming device or the like may be used instead of the device.

  Subsequently, the kneaded material 3 after defoaming is introduced into the extrusion tank 11 shown in FIG. The extrusion tank 11 has a compressed gas supply port 11a at the top, and pushes down the piston 11b in the body 11c having a wide cross-sectional area by a gas pressure such as air. Further, it is pushed out through a tapered nozzle constriction portion 11d communicating with the body portion 11c and a discharge port 11e having a narrow sectional area at the lower portion. At this time, the kneaded product 3 introduced into the extrusion tank 11 has an irregular orientation of the filler 2 in the binder 1 as shown in FIG.

  Therefore, the kneaded product 3 is extruded from the lower discharge port 11e by supplying the gas 5 such as air to the compressed gas supply port 11a of the extrusion tank 11 and pushing it down through the piston 11b. At that time, the gas pressure in the extrusion tank 11 is appropriately changed depending on the viscosity of the kneaded material 3, but the gauge pressure is 100 kPa. The above is preferable. Thus, when the kneaded material 3 passes through the discharge port 11e through the lower restricting portion 11d, the filler 2 in the binder 1 is oriented in substantially the same direction as shown in FIG. According to the verification result, the ratio of the cross-sectional dimension D of the body 11c of the extrusion tank 11 and the cross-sectional dimension d of the discharge port 11e may be d <D, but preferably d / D <0.5 to 0.7. . More preferably, it became 0.3. The planar shape of the discharge port 11e is preferably circular. The portion of the throttle portion 11d reaching the discharge port 11e may be an orifice shape, but a nozzle shape is desirable. For example, when the nozzle shape is as shown in the figure, the ratio of the cross-sectional dimension D of the body 11c of the extrusion tank 11 to the nozzle dimension L is preferably L / D> 2, more preferably L / D> 3. It was. The longer the tapered nozzle is, the easier it is to discharge into the block-shaped object forming container. However, if the cross-sectional size d of the discharge port 11e is too small and the nozzle is too long, the extrusion resistance increases, and it is necessary to increase the applied pressure or to make a strong container that can withstand the pressure.

  At this time, when the kneaded material 3 is extruded through the narrow cross-sectional area outlet of the discharge port 11e from the wide cross-sectional area storage area of the body 11c, the filler in the mixture 3 is shown in FIG. In the direction of extrusion (longitudinal direction in the figure). That is, when the behavior of the kneaded material 3 is schematically shown in FIG. 3, a fixed capacity of the kneaded material 3 in the body portion 11c of the extrusion tank 11 (area of dimension D in the figure) is indicated by an imaginary line in FIG. From the state indicated by the circle as described above, it passes through the discharge port 11e of the extrusion tank 11 (area of the dimension d in the figure) and is extruded into a substantially elliptical state as indicated by the phantom line in FIG. The

If the discharge speed is changed to increase the production efficiency or the size of the discharge port 11e is changed, the flow at the discharge port 11e may be disturbed. However, the Reynolds number (Re) expressed by the following equation is kept constant. By maintaining, the flow line of the viscous fluid discharged from the inside of the extrusion tank 11 becomes similar to the stream line before the change, and therefore, the discharge fluid of the same quality with the filler oriented in a predetermined direction can be obtained.

  Next, the kneaded product 3a after extrusion is cured. The curing method varies depending on the raw materials used, but when a silicone rubber-based two-component curable material is used, for example, it is allowed to stand at room temperature for 24 hours or heated to 100 to 160 ° C, preferably about 150 ° C, It can be cured by causing a crosslinking reaction to obtain a cured product block.

  Examples of the present invention will be described.

  During the process of manufacturing the heat dissipation sheet, the filler in the kneaded product was oriented in the extrusion direction by extruding a material consisting of a binder and a filler, and the effect on the thermal conductivity of the produced thermal conductive sheet was verified and confirmed as feasible. .

  Silicone rubber (made by Die Corning: trade name Sylgard A and B) as the material for the binder, and carbon graphite having a thermal conductivity of 900 W / m · K (made by Nippon Graphite Fiber Co., Ltd .: the trade name XN-100) as the material for the filler -01Z) was kneaded at a weight ratio of 1: 1.75.

  After defoaming this kneaded product, it was introduced into an extrusion tank (body diameter (D) = 50 mm, body length (L) = 200 mm, outlet diameter (d) = 15 mm) and extruded to obtain a block-like product. The block-like product was vulcanized and sliced to produce a heat dissipation sheet having a thickness of 10 mm.

  On the other hand, as a comparative example, the same material as in this example was kneaded, and this kneaded product was defoamed in the same manner as in this example, and vulcanized without passing through the alignment step as in this example. Then, a heat radiating sheet having a thickness of 10 mm was prepared by slicing.

Table 1 shows the result of comparing the heat conduction performance of the heat radiating sheets prepared according to the present example and the comparative example.

  From this, it was confirmed that the heat conduction performance is greatly improved by the orientation effect of this example. Moreover, when the surface cut | disconnected in parallel with the orientation of the manufactured block was expanded with the microscope, it was confirmed that the fiber was orientated in one direction (discharge direction) with high density.

  The heat-dissipating sheet according to the present invention can dissipate heat generated from various electronic components such as a CPU to the outside very efficiently by being mounted on a heat source inside the electronic device. Further, the present invention can be applied not only to the electronic device but also to heat radiation from a wide range of devices that generate medium to high temperature heat.

It is a block diagram showing a basic process in the Example of this invention. It is sectional drawing of the apparatus used for extrusion in the Example of this invention. It is a schematic diagram which shows the behavior of a kneaded material and the filler contained therein when extruding a kneaded material in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Binder 2 Filler 3, 3a Kneaded material 4 Heat radiation sheet 4a Filler 4b Elution part 11 Extrusion tank 11a Extraction port 11b Piston 11c Trunk part 11d Restriction part 11e Discharge port

Claims (3)

  In a method for producing an anisotropic heat-radiating sheet having good thermal conductivity in the thickness direction, a binder mainly composed of rubber or synthetic resin having elasticity after being cured and a thermal conductive filler are kneaded, and this kneaded product is In a method for manufacturing a heat-dissipating sheet, which is extruded and oriented in the extrusion direction, and then cured to produce a cured product block, and the cured product block is sliced into a predetermined thickness perpendicular to the orientation direction of the filler. A method for orienting a thermally conductive filler, wherein the filler is oriented in the extrusion direction by extruding from a wide cross-sectional area storage area through a narrow cross-sectional area discharge port during extrusion.   When extruding the kneaded material from the wide cross-sectional area storage area through the narrow cross-sectional area discharge port, the ratio of the dimension D of the body section of the extruding container to the dimension d of the cross-section of the discharge port is d <D. The manufacturing method of the heat-radiation sheet of Claim 1.   When the kneaded material is extruded from the wide cross-sectional area storage area through the narrow cross-sectional area discharge port, the discharge port has an orifice shape or a tapered nozzle shape, and the size D and the discharge port of the body section of the extrusion container The ratio of the dimension d of a cross section is d / D <0.7, The manufacturing method of the thermal radiation sheet of Claim 1 and Claim 2 characterized by the above-mentioned.

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