HK1192575B

HK1192575B - Method for producing thermally conductive sheet

Info

Publication number: HK1192575B
Application number: HK14105718.4A
Authority: HK
Inventors: 荒卷庆辅
Original assignee: Dexerials Corporation
Priority date: 2012-07-07
Filing date: 2013-07-08
Publication date: 2016-07-08

Description

Method for producing thermal conductive sheet

Technical Field

The present invention relates to a method for producing a thermal conductive sheet.

Background

In order to prevent a failure of a heat generating element such as an IC chip which generates heat during driving, the heat generating element is adhered to a heat radiating body such as a heat sink via a heat conductive sheet. In recent years, as an effort to improve the thermal conductivity of such a thermal conductive sheet, the following have been proposed: in a layered thermosetting resin composition in which a fibrous filler is dispersed in a thermosetting resin using a magnetic field generating device, the fibrous filler is oriented in the thickness direction of the layer, and then the thermosetting resin is cured to prepare a thermal conductive sheet (patent document 1). The thermal conductive sheet has a structure in which an end portion of the fibrous filler is exposed on the surface of the sheet, and the exposed end portion of the fibrous filler is inserted into the thermal conductive sheet when the thermal conductive sheet is applied between the heating element and the radiator.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4814550.

Disclosure of Invention

Problems to be solved by the invention

However, the technique of patent document 1 has a problem that a high-cost magnetic generator must be used to orient the fibrous filler as desired. Further, since it is necessary to reduce the viscosity of the thermosetting resin composition in order to orient the fibrous filler by the magnetic generator, the content of the fibrous filler cannot be increased greatly, and the thermal conductive sheet has a problem of insufficient thermal conductivity. Further, there is also a problem that the end of the exposed fibrous filler does not sink into the thermal conductive sheet due to the application conditions of the thermal conductive sheet between the heating element and the heat radiator. Conversely, the following problems also exist: since the exposed end portion of the fibrous filler is completely immersed in the thermal conductive sheet, a load that hinders normal operation of the heating element and the heat radiator may be applied to the heating element and the heat radiator when the fibrous filler is disposed between the heating element and the heat radiator.

The present invention has been made to solve the above problems of the prior art, and an object of the present invention is to provide a heat conductive sheet which can be prepared by blending a large amount of a fibrous filler into a thermosetting resin composition without using a high-cost magnetic generator when preparing the heat conductive sheet, and which can exhibit good heat conductivity without applying a load that hinders normal operation of a heat generating body and a heat radiating body when the heat conductive sheet is arranged between the heat generating body and the heat radiating body.

Means for solving the problems

The present inventors have studied the orientation state of a fibrous filler under the assumption that orienting the fibrous filler in the thickness direction of a thermal conductive sheet is not a main cause of the problems of the prior art, and have found that a thermal conductive sheet capable of achieving the above object can be produced by preparing a thermal conductive sheet forming composition by containing a relatively large amount of the fibrous filler in a binder resin, forming a molded body block from only the thermal conductive sheet forming composition by a known molding method (preferably, an extrusion molding method or a die molding method) without using a magnetic generator to intentionally orient the fibrous filler, cutting the molded body block, and further subjecting the formed sheet to a pressing treatment, and have completed the present invention.

That is, the present invention provides a method for producing a thermal conductive sheet, the method comprising the following steps (a) to (D):

process (A)

A step of preparing a composition for forming a thermal conductive sheet by dispersing a fibrous filler and a spherical filler in a binder resin,

process (B)

A step of forming a molded block from the prepared composition for forming a thermal conductive sheet,

process (C)

A step of cutting the formed molded block into a sheet having a desired thickness, and

process (D)

A step of pressing the cut surface of the formed sheet, wherein the pressing is performed so that the thermal resistance value of the sheet after the pressing is lower than the thermal resistance value of the sheet before the pressing,

the fibrous filler in the step (A) is a carbon fiber having an average diameter of 8 to 12 μm and an aspect ratio of 2 to 50,

the fibrous filler and the spherical filler are blended in amounts of 16 to 40vol% and 30 to 60 vol%, respectively, in the composition for forming a thermal conductive sheet,

the sheet formed in the step (C) has a thermal resistance value (K · cm) before extrusion²/W) is adjusted to 0.31 to 1.00.

The present invention also provides a thermal conductive sheet obtained by the above production method and an overheat protection device (サーマルデバイス thermal device) in which the thermal conductive sheet is arranged between a heat generating body and a heat radiating body.

The present invention also provides a thermal conductive sheet obtained by pressing a sheet formed from a molded block containing the composition for forming a thermal conductive sheet,

the composition for forming a thermal conductive sheet is obtained by dispersing a fibrous filler and a spherical filler in a binder resin, wherein the fibrous filler is carbon fibers having an average diameter of 8 to 12 [ mu ] m and an aspect ratio of 2 to 50, the fibrous filler and the spherical filler are respectively blended in an amount of 16 to 40% by volume and 30 to 60% by volume,

adjusting the random orientation ratio of the fibrous filler in the molded block material to a range of 55 to 95% to thereby adjust the pre-extrusion thermal resistance value (K-cm) of the sheet formed from the molded block material²/W) is in the range of 0.31 to 1.00.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the production method of the present invention, a composition for forming a thermal conductive sheet is produced by including both carbon fibers as a fibrous filler and a spherical filler in a binder resin in a relatively large amount, and on the other hand, it is preferable that a molded block is formed so that the orientation of the fibrous filler is irregular, and a sheet thermal resistance value (K · cm) obtained by cutting the molded block is obtained²The range of/W) is intentionally set to a high range such as a range of 0.31 to 1.00 before the extrusion treatment of the sheet.

In such a molded block or a sheet obtained by cutting it, since the fibrous filler is not oriented in a specific direction (in other words, randomly oriented), the fibrous filler can be promoted to be in contact with each other by pressing in the step (D) of the following steps. This is because, if the fibrous filler is oriented in a specific direction, particularly horizontally or vertically to the direction of extrusion, it cannot be expected that the fibrous filler will come into contact with each other by extrusion, but as shown in the present invention, if the fibrous filler is intentionally randomly oriented, the fibrous filler will come into contact with each other inside the sheet along with the flow or deformation of the binder resin, and therefore a thermal conductive sheet that improves the thermal conductivity inside the sheet afterwards can be produced. Further, since the surface of the sheet can be made smooth, the sheet has good adhesion to the heating element or the heat radiating body, and a heat conductive sheet having good heat conductivity can be prepared without applying a load to the heating element and the heat radiating body, which would prevent the heating element and the heat radiating body from operating normally.

Best Mode for Carrying Out The Invention

The method for producing a thermal conductive sheet of the present invention includes the following steps (a) to (D). Each step will be described in detail.

< Process (A) >

First, a fibrous filler is dispersed in a binder resin to prepare a composition for forming a thermal conductive sheet.

The fibrous filler constituting the composition for forming a thermal conductive sheet is used for efficiently conducting heat from a heat generating body to a heat radiating body. The fibrous filler is preferably 8 to 12 μm in that when the average diameter is too small, the specific surface area is too large, which may cause an excessive increase in the viscosity of the composition for forming a thermal conductive sheet, and when it is too large, the surface irregularities of the thermal conductive sheet may increase, which may cause a decrease in adhesion to a heating element or a heat radiator. The aspect ratio (length/diameter) is preferably 2 to 50, more preferably 3 to 30, because when too small, the viscosity of the composition for forming a thermal conductive sheet tends to be too high, and when too large, the compression of the thermal conductive sheet tends to be suppressed.

Specific examples of the fibrous filler include, for example, carbon fibers, metal fibers (e.g., nickel, iron, etc.), glass fibers, and ceramic fibers (e.g., non-metallic inorganic fibers such as oxides (e.g., alumina, silica, etc.), nitrides (e.g., boron nitride, aluminum nitride, etc.), borides (e.g., aluminum boride, etc.), and carbides (e.g., silicon carbide, etc.)).

The fibrous filler is selected according to the mechanical properties, thermal properties, electrical properties, and the like required for the thermal conductive sheet, and carbon fibers are particularly preferably used. Among them, pitch-based carbon fibers are preferably used in view of exhibiting a high elastic modulus, good thermal conductivity, high electrical conductivity, electromagnetic wave shielding properties, low thermal expansion properties, and the like. In the following paragraphs, unless otherwise specified, the term "fibrous filler" refers to carbon fibers.

Since the thermal conductivity decreases when the content of the fibrous filler in the composition for forming a thermal conductive sheet is too small and the viscosity tends to increase when the content is too large, the content of the fibrous filler in the thermal conductive sheet is preferably 16 to 40vol% by adjusting the addition amounts of the respective materials, and is preferably 120 to 300 parts by mass, and more preferably 130 to 250 parts by mass, based on 100 parts by mass of the following binder resin constituting the composition for forming a thermal conductive sheet.

In addition to the fibrous filler, a plate-like filler, a flake-like filler, a spherical filler, or the like may be used as long as the effects of the present invention are not impaired. In particular, from the viewpoint of suppressing secondary aggregation of the fibrous filler in the composition for forming a thermal conductive sheet, the preferable range of the spherical filler (preferably spherical alumina or spherical aluminum nitride) having a diameter of 0.1 to 5 μm is 30 to 60% by volume, more preferably 35 to 50% by volume, and the preferable range is 100 to 900 parts by mass in total relative to 100 parts by mass of the fibrous filler.

The binder resin holds the fibrous filler in the thermal conductive sheet, and is selected according to the properties required for the thermal conductive sheet, such as mechanical strength, heat resistance, and electrical properties. The binder resin may be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins.

Examples of the thermoplastic resin include polyethylene, polypropylene, ethylene-alpha olefin copolymers such as ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, fluorine-containing polymers such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene-ether copolymer (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, polymethacrylic acid, polymethacrylates such as polymethyl methacrylate, and the like, Polyacrylic acid, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, liquid crystal polymer, silicone resin, ionomer, and the like.

Examples of the thermoplastic elastomer include styrene-butadiene block copolymers and hydrogenated products thereof, styrene-isoprene block copolymers and hydrogenated products thereof, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, and diallyl phthalate resin. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluorine rubber, urethane rubber, and silicone rubber.

The composition for forming a thermal conductive sheet can be prepared by uniformly mixing a fibrous filler, a binder resin, and, if necessary, various additives or volatile solvents by a known technique.

< Process (B) >

Next, a molded block is formed from the prepared composition for forming a thermal conductive sheet by a known molding method. In this case, it is preferable to use a molding method in which the fibrous filler is not oriented in a specific direction. In particular, it is preferable to form the molded block by extrusion molding or die molding.

The extrusion molding method and the die molding method are not particularly limited, and various known extrusion molding methods and die molding methods can be suitably used depending on the viscosity of the composition for forming a thermal conductive sheet, the properties required for a thermal conductive sheet, and the like.

In the extrusion molding method, when the composition for forming a thermal conductive sheet is extruded from a die, or in the die molding method, when the composition for forming a thermal conductive sheet is pressed into a die, the binder resin flows, and a part of the fibrous filler is oriented in the flow direction thereof, but most of the fibrous filler is randomly oriented. In this case, the proportion of the fibrous filler that is randomly oriented (the random rate of orientation of the fibrous filler) in the entire fibrous filler is preferably 55 to 95%, more preferably 60 to 90%, because if it is too low, the proportion of the fibrous filler that comes into contact with each other after the extrusion in the following step (D) is low, and the thermal conductivity of the thermal conductive sheet tends to be insufficient, and if it is too high, the thermal conductivity in the thickness direction of the sheet tends to be insufficient. The random rate of orientation of the fibrous filler can be calculated by observation with an electron microscope.

The state where the orientation irregularity rate is 0% means a state where all the fibrous fillers contained in the unit cube (for example, a 0.5mm square) are oriented in a certain specific direction (for example, the sheet thickness direction). The state where the irregularity ratio is 100% refers to a state where a set oriented in a certain specific direction (for example, the sheet thickness direction) does not exist in the fibrous filler contained in the unit cube (for example, 0.5mm quadrangle). The state in which the orientation irregularity rate is 50% refers to a state in which the proportion of fibrous filler belonging to a set oriented in a certain specific direction (for example, the sheet thickness direction) among the fibrous fillers contained in the unit cube (for example, a 0.5mm quadrangle) is 50%. Therefore, a state in which the orientation irregularity ratio is 55% refers to a state in which the proportion of the fibrous filler belonging to a set oriented in a certain specific direction (for example, the sheet thickness direction) among the fibrous fillers contained in the unit cube (for example, 0.5mm quadrangle) is 45%, and a state in which the orientation irregularity ratio is 95% refers to a state in which the proportion of the fibrous filler belonging to a set oriented in a certain specific direction (for example, the sheet thickness direction) among the fibrous fillers contained in the unit cube (for example, 0.5mm quadrangle) is 5%.

The random orientation ratio can be calculated by removing the fibrous filler which is arranged in the thickness direction and has a predetermined length when one cross section of the sheet is observed. Further, the numerical accuracy can be improved by increasing the number of cross sections to be observed and averaging the obtained random ratios of the orientations.

The size and shape of the shaped block can be determined according to the size of the thermal conductive sheet required. For example, the cross section of the rectangular solid is 0.5 to 15cm in the longitudinal direction and 0.5 to 15cm in the lateral direction. The length of the rectangular parallelepiped can be determined as needed.

< Process (C) >

Next, the formed molded block is cut to form a sheet. The degree of orientation of the fibrous filler in the molded block and the sheet obtained by cutting the molded block can be considered to be substantially the same. The fibrous filler is exposed on the surface (cut surface) of the sheet obtained by cutting. The method of cutting is not particularly limited, and can be appropriately selected from known cutting devices (preferably ultrasonic cutters) according to the size and mechanical strength of the molded block. When the molding method is an extrusion molding method, the cutting direction of the molded block is 60 to 120 degrees, and more preferably 70 to 100 degrees with respect to the extrusion direction, in order to allow the fibrous filler oriented in the extrusion direction. A 90 degree (vertical) orientation is particularly preferred.

As described above, in the sheet obtained by cutting the molded block material, when the irregular rate of the orientation of the molded block material is maintained, the fibrous filler used is designated as carbon fiber, and the shape and blending amount thereof are also specified, the thermal resistance value of the sheet before pressing can be limited to a predetermined range. Specifically, the thermal resistance value before extrusion (before extrusion) in the following step (D) can be made to be more than 0.31 and less than 1.00 by using carbon fibers having an average diameter of 8 to 12 μm and a planar shape of 2 to 50 as fibrous fillers and by using 16 to 40% by volume and 30 to 60% by volume as the fibrous fillers and the spherical fillers, respectively. In the measurement of the thermal resistance value, 1kg/cm was applied to the sheet²The load of (2).

The width of the cut shaped block (thickness of the formed sheet) is not particularly limited, and may be appropriately selected depending on the purpose of use of the thermal conductive sheet, and the like. Here, regarding the relationship with the thermal resistance value, when the molded body block is cut so that the cutting width of the molded body block (the sheet thickness of the formed sheet) in the step (C) is less than 0.65mm, the thermal resistance value (K · cm) of the sheet is²/W) is preferably in a range of more than 0.31 and less than 0.47. When the molded block is cut so as to be 0.65mm or more and 3mm or less, the sheet has a thermal resistance value (K · cm)²/W) is preferably in a range of more than 0.47 and less than 1.00.

< Process (D) >

Next, the cut surface of the obtained sheet was pressed. Thereby obtaining a thermal conductive sheet. As a method of pressing, a pair of pressing devices composed of a flat plate and a flat-surface pressing head may be used. Alternatively, the extrusion may be performed by a pinch roll.

As the pressure at the time of pressing, in general, when it is too low, pressing is not performed and the heat resistance tends to be constant, and when it is too high, the sheet tends to be elongated. In addition, when the gasket (スペーサー spacer) is inserted to prevent extension during pressing, a high pressing pressure can be set. Usually, applied to a sheetThe pressure is 1 to 100kgf/cm²However, when no spacer is used, it is preferably 2 to 8kgf/cm²More preferably 3 to 7kgf/cm²When a gasket is used, the set pressure at the time of extrusion is 0.1 to 30MPa, preferably 0.5 to 20 MPa.

In the present invention, as the spacer, a frame or a flat plate made of a hard material having the same thickness as the thickness of the sheet desired to be produced can be used. For example, a gasket having a frame shaped like a chinese character "tian" formed by providing 4 square (e.g., 10cm square) holes in a square (e.g., 25cm square) stainless steel plate having the same thickness as the sheet desired to be produced, may be exemplified as the gasket, but not limited thereto.

In order to further improve the effect of extrusion and shorten the extrusion time, such extrusion is preferably performed at a temperature equal to or higher than the glass transition temperature of the binder resin. The extrusion is generally carried out at a temperature in the range of 0 to 180 ℃, preferably at room temperature (about 25 ℃) to 100 ℃, more preferably at 30 to 100 ℃.

In the present invention, although the sheet thickness after pressing becomes thin by compression, since there is a tendency that the thermal resistance does not decrease if the compression ratio [ { (sheet thickness before pressing-sheet thickness after pressing)/sheet thickness before pressing } × 100] of the sheet is too small, and there is a tendency that the sheet is elongated if it is too large, the pressing is performed so that the compression ratio is 2 to 15%.

In addition, the surface of the sheet can be smoothed by pressing. The degree of smoothness can be evaluated by the surface glossiness (gloss value). Since the thermal conductivity is lowered when the surface gloss is too low, it is preferable to perform the pressing so that the surface gloss (gloss value) measured by a gloss meter at an incident angle of 60 degrees and a reflection angle of 60 degrees becomes 0.2 or more.

The thermal conductive sheet obtained by the above-described method for producing a thermal conductive sheet is also an embodiment of the present invention, and a preferred embodiment is a thermal conductive sheet in which the fibrous filler has an orientation irregularity ratio of 55 to 95%, a thickness of 0.1 to 50mm, and a surface gloss (gloss value) of 0.2 or more by a glossmeter.

Such a thermal conductive sheet can provide an overheat protection device having a structure in which heat generated by the heat generating body is dissipated to the heat dissipating body and arranged therebetween. Examples of the heat generating body include an IC chip and an IC module, and examples of the heat radiating body include a heat radiating sheet made of a metal material such as stainless steel.

As described above, although the thermal properties of the thermal conductive sheet greatly depend on the random orientation rate of the fibrous filler contained therein, the thermal properties can be evaluated by the angle at which the fibrous filler is arranged in the thickness direction of the sheet. Specifically, one cross section of the thermal conductive sheet may be photographed with an optical microscope of 50 to 300 times, and when the surface direction of the sheet is 90 degrees, the photographed image may be acquired, the angular distribution of the fibrous filler may be obtained, and the standard deviation may be obtained. The standard deviation is preferably 10 ° or more.

The thermal conductive sheet obtained by the production method of the present invention is an embodiment of the present invention, and may be referred to as an "article" as follows.

That is, the thermal conductive sheet of the present invention is a "thermal conductive sheet, and in a thermal conductive sheet obtained by pressing a sheet formed from a molded block material containing a composition for forming a thermal conductive sheet,

adjusting the random orientation ratio of the fibrous filler in the molded block material to a range of 55 to 95% to thereby adjust the pre-extrusion thermal resistance value (K-cm) of the sheet formed from the molded block material²/W) is in the range of 0.31 to 1.00. ".

The composition of the invention in this thermal conductive sheet has the same meaning as that described in the production method of the present invention, and the effects of the invention are also the same as those of the thermal conductive sheet produced by the production method of the present invention.

Examples

Example 1

A silicone resin composition for forming a thermal conductive sheet was prepared by uniformly mixing 17 vol% of a silicone A liquid (an organopolysiloxane having a vinyl group), 16 vol% of a silicone B liquid (an organopolysiloxane having a hydrosilyl group), 22 vol% of alumina particles (average particle diameter of 3 μm), 22 vol% of spherical aluminum nitride (average particle diameter of 1 μm), and 23 vol% of pitch-based carbon fibers (average major axis length of 150 μm, average axis diameter of 8 μm). 153 parts by mass of pitch-based carbon fiber was mixed with 100 parts by mass of silicone resin in terms of parts by mass to prepare a silicone resin composition for forming a thermal conductive sheet.

This silicone resin composition for forming a thermal conductive sheet was cast in a mold having a rectangular parallelepiped inner space, and cured by heating in an oven at 100 ℃ for 6 hours to prepare a molded body block. The peeled polyethylene terephthalate film was previously stuck to the back surface of the mold so that the peeled surface was on the inner side.

The obtained molded block was cut into a thickness of 0.2mm with an ultrasonic cutter to obtain a sheet. On the surface of this sheet, a part of the fibrous filler is exposed on the surface by a shearing force at the time of cutting, and minute irregularities are formed on the surface of the sheet. After applying 1kgf/cm to the sheet²While the load was being applied, thermal resistances [ (K/W) and (K. cm) were measured using a thermal resistance measuring apparatus conforming to ASTM-D5470²/W)]. The results obtained are shown in table 1. The thermal resistance value is 0.41K cm²/W。

Will thus obtainThe sheet was placed on a stainless steel flat plate, and 2kgf/cm was applied to the sheet by using a flat stainless steel indenter whose surface was mirror-polished at normal temperature (25 ℃ C.) to form a flat sheet²The sheet was pressed for 30 minutes under the load of (1) to obtain a thermal conductive sheet having a smooth surface. The sheet thickness and compression ratio before and after pressing are shown in table 1.

The plane of the thermal conductive sheet was photographed with an optical microscope at a magnification of 100, and when the surface direction of the sheet was measured to 90 degrees, the photographed image was taken, the angular distribution of the fibrous filler was determined, and the standard deviation thereof was determined. The average of the angular distribution was-12.9 ° with a standard deviation of 15.6 °.

Examples 2 to 45 and comparative example 1

A thermal conductive sheet was obtained in the same manner as in example 1, except that the cut thickness and the pressing conditions (pressure and temperature) of the molded block in example were changed as shown in table 1. In addition, the sheet thickness and compression ratio before and after pressing are shown in table 1.

Comparative example 1

A thermal conductive sheet was obtained by the same operation as in example 1, except that no pressing was performed.

Examples 46 to 51

A thermal conductive sheet was obtained in the same manner as in example 1 except that the cut thickness, the extrusion conditions (pressure, temperature), the average long axis length (μm) and the average axial diameter (μm) of the molded block material of example were changed as shown in table 1, and a spacer (a spacer having 4 quadrangular holes of 10cm formed in a 25cm quadrangular stainless steel plate having the same thickness as that of a sheet desired to be produced) was used in extrusion, and in examples 46 and 47, 240 parts by mass of carbon fiber was mixed in 100 parts by mass of silicone resin, and in examples 48 to 51, 150 parts by mass of carbon fiber was mixed in 100 parts by mass of silicone resin. The sheet thickness and compression ratio before and after pressing are shown in table 1.

< evaluation >

The obtained thermal conductive sheet was applied with a force of 1kgf/cm²The respective thermal resistances [ (K/W) and (K cm) were measured using a thermal resistance measuring apparatus conforming to ASTM-D5470, in addition to the load of (1)²/W)]. The results obtained are shown in table 1. In practical use, it is desirable that the heat resistance is 0.4K/W (1.256 (K. cm) when the thickness of the sheet before extrusion is 0.1mm or more and less than 0.2mm²/W)), and preferably 0.130K/W (0.41 (K.cm)) when the sheet thickness is 0.2mm or more and less than 0.6mm²/W)), and preferably 0.140K/W (0.44 (K.cm)) when the sheet thickness is 0.6mm or more and less than 1.0mm²/W)), and preferably 0.5K/W (1.57 (K. cm)) when the sheet thickness is 1.0mm or more and less than 3.0mm²/W)) below.

The upper limit of the thermal resistance desired in actual use when the sheet thickness before pressing is 0.1mm or more and less than 0.2mm is set higher than the upper limit of the thermal resistance desired in actual use when the sheet thickness is 0.2mm or more and less than 0.6 mm. This is because, if the sheet thickness is too thin, the filler present in the sheet greatly affects the sheet surface, and the smoothness of the sheet surface is likely to be impaired.

In examples 6, 10, 21, 25, 46 to 51 and comparative example 1, the surface gloss (gloss value) was measured using a gloss meter (incident angle 60 degrees, reflection angle 60 degrees). The results obtained are shown in table 1.

[ Table 1]

。

The thermal conductive sheets of examples 1 to 45 of table 1 each showed good low thermal resistance at various sheet thicknesses after pressing. The thermal conductive sheets of examples 6, 10, 21 and 25, which were measured for surface glossiness, had a surface glossiness (gloss value) of 0.2 or more.

Further, it is known that the thermal resistance tends to decrease as the pressing pressure increases, to increase as the pressing temperature increases, and to increase as the sheet thickness becomes thicker.

On the other hand, in the case of the thermal conductive sheet of comparative example 1 in which pressing was not performed, the thermal resistance exceeded 0.41K · cm²A low surface gloss, a gloss value of 0.1.

In the case of the thermal conductive sheet of example 46, since a spacer was used in the extrusion, the extrusion temperature was set high to 100 ℃, and since the average major axis length of the carbon fiber was short and 100 μm, the compressibility of the sheet was very high to 67%. Thus, a good low thermal resistance is shown at a sheet thickness of 0.10mm before pressing. The surface gloss (gloss value) is 0.1 or more.

In the case of the thermal conductive sheet of example 47, the same operation as in example 46 was repeated except that the pressing temperature was set to 70 ℃. Therefore, the compression ratio was about 43%, which was lowered as compared with the case of example 46, but showed good low thermal resistance at a sheet thickness of 0.10mm before pressing. The surface gloss (gloss value) is 0.1 or more.

In the case of the thermal conductive sheets of examples 48 to 51, a gasket was used for the pressing. And the sheet thickness is thick, but since a high extrusion pressure is set to 1.2 to 20MPa, a good low thermal resistance is shown at a sheet thickness of 1.55 to 2.54mm before extrusion. The surface gloss (gloss value) is 0.2 or more.

In the thermal conductive sheet showing good thermal conductivity, the thermal resistance value before pressing is 0.1 to 0.32.

Industrial applicability

According to the production method of the present invention, although many fibrous fillers are randomly oriented during molding, a thermal conductive sheet in which the thermal conductivity inside the sheet is improved by contacting the fibrous fillers inside the sheet by compressing the sheet by pressing after cutting can be produced. Further, since the surface of the sheet can be made smooth, the sheet has good adhesion to the heating element or the heat radiating body, and a heat conductive sheet having good heat conductivity can be prepared without applying a load to the heating element and the heat radiating body, which would prevent the heating element and the heat radiating body from operating normally. Therefore, the present invention is useful for preparing a thermal conductive sheet to be disposed between a heat generating body such as an IC chip or an IC module and a heat radiator.

Claims

1. A method for producing a thermal conductive sheet, comprising the following steps (A) to (D):

process (A)

process (B)

process (C)

process (D)

adjusting the thermal resistance value of the sheet formed in the step (C) to 0.31 to 1.00K-cm before extrusion²/W。

2. The production method according to claim 1, wherein in the step (B), the molded block is formed by extrusion molding or die molding.

3. The production method according to claim 1 or 2, wherein the binder resin in the step (a) is a silicone resin.

4. A production method according to any one of claims 1 to 3, wherein, when the thickness of the sheet formed in the step (C) is less than 0.65mm, the thermal resistance value of the sheet before pressing is adjusted to be more than 0.31K-cm²A ratio of W to less than 0.47K cm²The range of/W.

5. A production method according to any one of claims 1 to 3, wherein, when the thickness of the sheet formed in the step (C) is 0.65mm or more and 3mm or less, the thermal resistance value of the sheet before pressing is adjusted to be more than 0.47K-cm²A ratio of W to less than 1.00 K.cm²The range of/W.

6. The production method according to any one of claims 1 to 5, wherein,in the step (D), the pressure applied to the sheet is 1 to 8kgf/cm²Is extruded under pressure.

7. The production method according to any one of claims 1 to 5, wherein in the step (D), when the gasket is used, the extrusion is performed under a set pressure of 0.1 to 30 MPa.

8. The production method according to any one of claims 1 to 7, wherein in the step (D), the extrusion is performed while heating to a temperature of not lower than the glass transition temperature of the binder resin.

9. The production method according to any one of claims 1 to 8, wherein in the step (D), the extrusion is performed so that the sheet has a compressibility of 2 to 15%.

10. The production method according to any one of claims 1 to 9, wherein in the step (D), the extrusion is performed so that the sheet has a surface gloss of 0.1 or more after the extrusion.

11. A thermal conductive sheet obtained by the production method according to any one of claims 1 to 10.

12. The thermal conductive sheet according to claim 11, wherein the irregular orientation ratio of the fibrous filler in the molded block material molded in the step (B) is 55 to 95%, and the irregular orientation ratio is a ratio of the fibrous filler in the irregular orientation in the entire fibrous filler.

13. An overheat protection apparatus comprising a heat generating body and a heat radiating body and the thermal conductive sheet of claim 11 or 12 disposed therebetween.

14. A thermal conductive sheet obtained by pressing a sheet formed from a molded block containing a composition for forming a thermal conductive sheet,

the thermal resistance value of a sheet formed from the molded block material before extrusion is set to 0.31 to 1.00K-cm by adjusting the random orientation ratio of the fibrous filler in the molded block material to 55 to 95%²A range of/W, wherein the orientation irregularity ratio is a ratio of the random fibrous filler to the entire fibrous filler.