JP2013131563A - Thermally conductive sheet and method for manufacturing thermally conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive sheet good in thermal conductivity in the thickness direction thereof.SOLUTION: A thermally conductive sheet includes a thermally conductive composition containing: a silicone resin; thermally conductive fillers; and a filling material for aligning the thermally conductive fillers in a predetermined direction. The thermally conductive fillers are oriented along the thickness direction of the thermally conductive sheet, and at least aluminum nitride is contained as the filling material. Further, the lightness (L*) represented by the "L*" value in the L*a*b color system described in "JIS Z 8729" and "JIS Z 8730" when the surface of the thermally conductive sheet is measured is 32.5 or more.

Description

  The present invention relates to a heat conductive sheet that promotes heat dissipation from a heat-generating electronic component and the like, and a method for manufacturing the heat conductive sheet.

  As electronic devices are further enhanced in performance, the density and mounting of semiconductor elements are increasing. Along with this, it is important to more efficiently dissipate the heat generated from the electronic components constituting the electronic device. In order to efficiently dissipate heat, the semiconductor is attached to a heat sink such as a heat dissipating fan or a heat dissipating plate via a heat conductive sheet. As the heat conductive sheet, a sheet in which a filler such as an inorganic filler is dispersed and contained in silicone is widely used. In such a heat radiating member, further improvement in thermal conductivity is required, and in general, for the purpose of high thermal conductivity, it is possible to respond by increasing the filling rate of the inorganic filler mixed in the matrix. Yes. However, when the filling rate of the inorganic filler is increased, flexibility is impaired, or powder falling occurs because the filling rate of the inorganic filler is high, so there is a limit to increasing the filling rate of the inorganic filler.

  Examples of the inorganic filler include alumina, aluminum nitride, and aluminum hydroxide. Further, for the purpose of high thermal conductivity, scale-like particles such as boron nitride and graphite, carbon fibers, and the like may be filled in the matrix. This is due to the anisotropy of the thermal conductivity of the scaly particles. For example, in the case of carbon fiber, it has a thermal conductivity of about 600 to 1200 W / mK in the fiber direction. Boron nitride has a thermal conductivity of about 110 W / mK in the plane direction and about 2 W / mK in a direction perpendicular to the plane direction, and is known to have anisotropy. .

  In general, it is known that the thermal conductivity of a thermal conductive sheet is improved when the filling amount of the thermal conductive filler is increased. However, the fibrous heat conductive filler cannot increase the filling amount as compared with the spherical filler. Therefore, high thermal conductivity cannot be obtained with the fibrous thermal conductive filler alone. Here, the surface direction of the fibrous heat conductive filler is made the same as the thickness direction of the heat conductive sheet, which is the heat transfer direction, that is, the fibrous heat conductive filler is arranged in the thickness direction of the heat conductive sheet. By orienting, the thermal conductivity can be dramatically improved.

  Patent Document 1 describes a method of applying a heat conductive composition containing carbon fiber and orienting the carbon fiber by applying a magnetic field. However, since fluidity is required for the orientation of the carbon fibers, the method described in Patent Document 1 cannot increase the filling amount of the heat conductive filler. Therefore, a heat conductive sheet is desired in which the heat conductive filler is oriented along the thickness direction of the heat conductive sheet and the heat conductivity in the thickness direction is good.

JP 2006-335957 A

  This invention is proposed in view of such a situation, and it aims at providing the manufacturing method of the heat conductive sheet with favorable heat conductivity of the thickness direction, and a heat conductive sheet.

  As a result of diligent study, the present inventor has expressed the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet is measured. It was found that there is a high correlation between the brightness L * and the thermal conductivity, and the present invention has been completed.

  The present invention relates to a thermally conductive sheet comprising a thermally conductive composition containing a curable resin composition and a filler that aligns the thermally conductive filler in a predetermined direction, wherein the thermally conductive filler is thermally conductive. L * a * described in “JIS Z 8729” and “JIS Z 8730” when the surface of the thermally conductive sheet is measured, which is oriented along the thickness direction of the sheet and contains at least aluminum nitride as a filler. The lightness L * represented by the “L *” value in the b color system is 32.5 or more.

  The manufacturing method of the heat conductive sheet which concerns on this invention produces the heat conductive composition containing the curable resin composition, the heat conductive filler, and the filler which aligns a heat conductive filler in a predetermined direction. A thermal conductive composition creation process, an orientation process in which the thermal conductive composition created in the thermal conductive composition creation process is formed into a columnar shape, and the thermal conductive filler is oriented in the longitudinal direction of the columnar shape, and the columnar heat Cutting the conductive composition into a predetermined dimension by an ultrasonic cutter in a direction perpendicular to the longitudinal direction to obtain a heat conductive sheet, and the heat conductive sheet is made of a heat conductive filler. , Orientated along the thickness direction of the heat conductive sheet, and contains at least aluminum nitride as a filler, and described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet is measured. * Lightness represented by "L *" value in the a * b colorimetric system L * is 32.5 or more.

  The thermal conductivity evaluation method according to the present invention includes a thermally conductive composition containing a curable resin composition, a thermally conductive filler, and a filler that aligns the thermally conductive filler in a predetermined direction. The lightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the adhesive sheet was measured, The thermal conductivity of the sheet is evaluated. In the thermally conductive sheet, the thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet, and includes at least aluminum nitride as a filler.

  According to the present invention, the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the thermally conductive sheet is measured by including at least aluminum nitride in the thermally conductive sheet. By setting the lightness L * represented by the “L *” value at 32.5 or more, the heat conductive filler is oriented along the thickness direction of the heat conductive sheet, and the heat in the thickness direction of the heat conductive sheet is The conductivity can be improved.

It is a flowchart for demonstrating an example of the manufacturing method of the heat conductive sheet which concerns on this invention. It is an external view which shows an example of the ultrasonic cutting machine used in the cutting process in the manufacturing method of the heat conductive sheet which concerns on this invention. It is an external view which shows an example of a slicing apparatus. It is a flowchart for demonstrating an example of the arrangement | sequence process in the manufacturing method of the other heat conductive sheet which concerns on this invention. It is a schematic diagram for demonstrating an example of the temporary shaping | molding process, the alignment process, and this shaping | molding process in the manufacturing method of the heat conductive sheet which concerns on this invention. It is a perspective view which shows an example of the laminated body obtained at the alignment process in the manufacturing method of the heat conductive sheet which concerns on this invention. (A) is a perspective view which shows an example of this molded object which has not performed the press, (B) is a perspective view which shows an example of this molded object which performed the press.

Hereinafter, embodiments of the present invention (hereinafter referred to as the present embodiment) will be described in detail in the following order with reference to the drawings.
1. 1. Thermally conductive sheet 2. Manufacturing method of heat conductive sheet 3. Manufacturing method of other heat conductive sheet Thermal conductivity evaluation method

<1. Thermal conductive sheet>
The thermally conductive sheet 1 according to the present embodiment includes a thermally conductive composition containing a curable resin composition, a thermally conductive filler, and a filler that aligns the thermally conductive filler in a predetermined direction. The heat conductive filler is oriented along the thickness direction of the heat conductive sheet. In addition, the thermally conductive sheet according to the present embodiment includes at least aluminum nitride in the thermally conductive sheet, and described in “JIS Z 8729” and “JIS Z 8730” when the surface of the thermally conductive sheet is measured. The lightness L * represented by the “L *” value in the L * a * b color system is 32.5 or more. By setting the lightness L * when the surface of the thermally conductive sheet is measured to be 32.5 or more, the thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet, and the thickness direction of the thermally conductive sheet is Thermal conductivity can be improved.

(Correlation between lightness L * and thermal conductivity in L * a * b color system)
The color of an object generally consists of three elements: lightness (brightness), hue (hue), and saturation (brightness). In order to accurately measure and express these, a color system that expresses these numerically objectively is necessary. An example of such a color system is the L * a * b color system. The L * a * b color system can be easily measured by a measuring instrument such as a commercially available spectrophotometer.

  The L * a * b color system is a color system described in “JIS Z 8729” and “JIS Z 8730”, for example, and is shown by arranging each color in a spherical color space. In the L * a * b color system, lightness is indicated by a position in the vertical axis (z-axis) direction, hue is indicated by a position in the outer peripheral direction, and saturation is indicated by a distance from the central axis.

  The position in the vertical axis (z-axis) direction indicating the brightness is indicated by L *. The value of the lightness L * is a positive number. The smaller the number, the lower the lightness and the darker the tendency. Specifically, the value of L * varies from 0 corresponding to black to 100 corresponding to white.

  Further, in a cross-sectional view obtained by horizontally cutting a spherical color space at a position of L * = 50, the positive direction of the x axis is the red direction, the positive direction of the y axis is the yellow direction, the negative direction of the x axis is the green direction, y The negative direction of the axis is the blue direction. The position in the x-axis direction is represented by a * taking a value of −60 to +60. The position in the y-axis direction is represented by b * taking a value of −60 to +60. Thus, a * and b * are positive and negative numbers representing chromaticity, and the closer to 0, the blacker the color becomes. Hue and saturation are represented by these a * and b * values.

  In the L * a * b color system, when the lightness L * is 32 or more, it becomes whitish, and when the lightness L * is less than 32, it becomes blackish. In the L * a * b color system, when a * is less than -1, the color becomes green, and when a * is -1 or more, the color becomes red. When b * is less than -1, the color becomes bluish, and when b * exceeds +1, the color becomes yellow.

  For example, when the blackness of a cross section of a heat conductive sheet containing carbon fiber as a heat conductive filler and containing aluminum nitride and alumina as a filler is measured using the L * a * b color system, the lightness L * When it becomes 32.5 or more, it becomes whitish. This is because when the lightness L * is 32.5 or more, when the heat conductive sheet is observed from the direction perpendicular to the cut surface, the area of the heat conductive filler in the heat conductive sheet decreases, This is because white alumina and aluminum nitride are exposed on the surface of the heat conductive sheet. That is, when the lightness L * is 32.5 or more, it means that the thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet.

  On the other hand, when the blackness was measured using a L * a * b color system, the lightness L was obtained when the cross section of the heat conductive sheet containing carbon fiber as the heat conductive filler and aluminum nitride and alumina as the filler was used. When it becomes less than 32.5, it becomes dark. This is because when the lightness L * is less than 32.5, when the thermally conductive sheet is observed from a direction perpendicular to the cut surface, the area of the thermally conductive filler in the thermally conductive sheet increases, This is because white alumina and aluminum nitride are not easily exposed from the surface of the heat conductive sheet. That is, when the lightness L * is less than 32.5, it means that the heat conductive filler is not oriented along the thickness direction of the heat conductive sheet, compared to when the lightness L * is 32.5 or more. .

  In general, when a thermally conductive sheet having a high thermal conductivity is filled in a thermally conductive sheet, the thermal conductivity of the thermally conductive sheet is improved. Originally, it is considered that the thermal conductivity is improved when a large amount of pitch-based carbon fibers, for example, is filled as the thermally conductive filler. That is, it is considered that the thermal conductivity is improved when the lightness L * on the surface of the thermal conductive sheet is reduced. However, in order to obtain high thermal conductivity, the viscosity of the thermally conductive composition at the time of extrusion is not only increased by adding the content of the thermally conductive filler, but also by maintaining the shape by adding a filler. It is important to orient the heat conductive filler along the thickness direction of the heat conductive sheet.

  As a result of diligent study, the present inventor has expressed the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet is measured. It was found that there is a high correlation between the brightness L * and the thermal conductivity. Moreover, in order to orient the heat conductive filler along the thickness direction of the heat conductive sheet, the amount of aluminum nitride having a lower thermal conductivity than the heat conductive filler is less than the amount of heat conductive filler. I found that it has a big influence. That is, at least aluminum nitride is contained in the heat conductive sheet, and the lightness L * when the surface of the heat conductive sheet is measured is set to 32.5 or more, whereby the heat conductive filler is in the thickness direction of the heat conductive sheet. The thermal conductivity in the thickness direction of the thermal conductive sheet can be improved.

(Curable resin composition)
The curable resin composition contained in the heat conductive sheet is not particularly limited, and for example, a silicone-based adhesive, an acrylic resin-based adhesive, or the like is used. As the silicone-based adhesive, a condensation curable type or an addition curable type can be used. Although content of curable resin composition is not specifically limited, For example, it can be 25-45 volume%.

(Thermal conductive filler)
As the thermally conductive filler, for example, carbon fibers can be used, and it is particularly preferable to use pitch-based carbon fibers. Pitch-based carbon fibers are made from pitch as a main raw material and graphitized by heat treatment at a high temperature exceeding 2000 to 3000 ° C. or 3000 ° C. after each processing step such as melt spinning, infusibilization, and carbonization. The raw material pitch is divided into an isotropic pitch that is optically disordered and does not exhibit deflection, and an anisotropic pitch (mesophase pitch) in which constituent molecules are arranged in a liquid crystal form and exhibit optical anisotropy. Carbon fibers manufactured from anisotropic pitch have better mechanical properties than carbon fibers manufactured from isotropic pitch, and electrical and thermal conductivity is increased. Therefore, it is preferable to use a mesophase pitch graphitized carbon fiber.

  The average fiber length of the heat conductive filler is preferably 100 μm or more. By setting the average fiber length of the heat conductive filler to 100 μm or more, the heat conductive filler can be easily aligned in the same direction, so that the heat conductivity in the thickness direction of the heat conductive sheet can be improved.

  It is preferable that content of the heat conductive filler in a heat conductive sheet shall be 15-25 volume%. By setting the content of the heat conductive filler to 15% by volume or more, the thermal resistance value can be more effectively lowered, so that the heat conductivity in the thickness direction of the heat conductive sheet can be improved. . Moreover, when content of a heat conductive filler shall be 25 volume% or less, when extruding a heat conductive composition with an extruder, it can prevent that extrusion becomes difficult, for example.

(Filler)
The filler makes it easy to align the thermally conductive filler in a predetermined direction due to the difference in flow rate from the thermally conductive filler in the thermally conductive composition, that is, the thermally conductive filler is thermally conductive along the extrusion direction. It is used to facilitate the orientation of the filler. The filler is also used to function as a heat conductive material.

  As the filler, for example, alumina, aluminum nitride, boron nitride, zinc oxide, silicon powder, and metal powder can be used, and at least aluminum nitride is used. Aluminum nitride has nitrogen in the molecule, and this nitrogen inhibits the reaction of the curable resin composition and suppresses the increase in the viscosity of the thermally conductive composition. Therefore, by using at least aluminum nitride as the filler, the heat conductive filler is more effectively placed in a predetermined direction, that is, the thickness of the heat conductive sheet, compared to when only alumina particles are used as the filler. It can be oriented along the direction. Therefore, since at least aluminum nitride is used as the filler, the thermally conductive filler can be more effectively oriented along the thickness direction of the thermally conductive sheet. Property can be improved.

  Moreover, as a filler, it can make it easier to orient a heat conductive filler along the thickness direction of a heat conductive sheet by using 2 or more types of spherical particles from which a particle size differs. As a result, the brightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet was measured It can be surely 32.5 or more. Thus, since the thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet by using two or more kinds of spherical particles having different particle diameters as the filler, the thickness direction of the thermally conductive sheet The thermal conductivity of can be made better.

  The content of the filler in the heat conductive sheet is preferably 40 to 50% by volume. Moreover, it is preferable to contain 5.1 volume% or more of aluminum nitride in a heat conductive sheet. By making the content of aluminum nitride in the thermally conductive sheet 5.1 volume% or more, the increase in the viscosity of the thermally conductive composition is effectively suppressed, and the thermally conductive filler is more effectively thermally conducted. Can be oriented along the thickness direction of the adhesive sheet. As a result, the brightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet was measured, It can be more effectively 32.5 or more. Thus, the heat conductivity of the thickness direction of a conductive sheet can be made more favorable by content of aluminum nitride in a heat conductive sheet being 5.1 volume% or more.

  The average particle diameter of the filler is preferably 0.5 to 5 μm. By setting the average particle size of the filler to 0.5 μm or more and 5 μm or less, it functions sufficiently as a thermally conductive material, and the orientation of the thermally conductive filler is less likely to be disturbed in the thermally conductive composition. The thermal conductivity in the thickness direction of the thermal conductive sheet 1 can be made better.

  Further, as described above, when two or more kinds of spherical particles having different particle diameters are used as the filler, the large spherical particles may be 2 to 5 μm and the small spherical particles may be 0.3 to 2 μm. preferable. Thereby, it can be made easier to orient the thermal conductive filler along the thickness direction of the thermal conductive sheet more effectively. As a result, the brightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet was measured It can be surely 32.5 or more.

  In the above description, the L * a * b color system is taken as an example, but the method of selecting the color system is not particularly limited, and a table that can be converted into the L * a * b color system. Any color system may be used. For example, an XYZ color system or an L * C * h color system may be used.

<2. Manufacturing method of heat conductive sheet>
The heat conductive sheet 1 mentioned above can be produced by the following manufacturing method, for example. The manufacturing method of the heat conductive sheet which concerns on this Embodiment has heat conductive composition preparation process S1, orientation process S2, and cutting process S3, as shown in FIG.

(Thermal conductive composition creation step S1)
In heat conductive composition creation process S1, the heat conductive composition mentioned above is created. As for the compounding quantity in a heat conductive composition, it is preferable that a heat conductive filler shall be 15-25 volume% and a filler shall be 40-50 volume%, for example. In the thermally conductive composition, it is preferable to contain 5.1% by volume or more of aluminum nitride as a filler.

(Orientation step S2)
In the alignment step S2, the thermally conductive composition created in the thermally conductive composition creating step S1 is formed in a columnar shape, and the thermally conductive filler is oriented in the columnar longitudinal direction. In the alignment step S2, for example, a columnar heat conductive composition in which the heat conductive filler is aligned in the columnar longitudinal direction L as shown in FIG. Article 2 can be formed. In the alignment step S2, for example, the heat conductive composition prepared in the heat conductive composition preparation step S1 is applied onto a polyester film coated with a release material, and the columnar heat conduction as shown in FIG. The composition 2 may be formed.

(Cutting step S3)
In the cutting step S3, the columnar heat conductive composition 2 formed in the alignment step S2 is cut into a predetermined dimension by an ultrasonic cutting machine in a direction orthogonal to the longitudinal direction to obtain the heat conductive sheet 1.

  In the cutting step S3, for example, as shown in FIG. 2 and FIG. 3, the columnar thermal conductivity in the direction V perpendicular to the longitudinal direction L of the columnar thermal conductive composition 2 using an ultrasonic cutter 3 is used. By slicing the composition 2 with the ultrasonic cutter 4, the thermally conductive sheet 1 can be formed while maintaining the orientation of the thermally conductive filler. Therefore, the orientation of the heat conductive filler is maintained in the thickness direction, and the heat conductive sheet 1 having good heat conduction characteristics can be obtained.

  As shown in FIG. 3, the ultrasonic cutting machine 3 includes a work table 5 on which the columnar heat conductive composition 2 is placed, and a columnar heat conductive composition on the work table 5 while applying ultrasonic vibration. And an ultrasonic cutter 4 for slicing 2.

  The work table 5 is provided with a silicone rubber 7 on a metal moving table 6. The moving table 6 can be moved in a predetermined direction by the moving mechanism 8, and sequentially feeds the columnar heat conductive composition 2 to the lower part of the ultrasonic cutter 4. The silicone rubber 7 has a thickness sufficient to receive the cutting edge of the ultrasonic cutter 4. When the columnar thermal conductive composition 2 is placed on the silicone rubber 7, the work table 5 is moved in a predetermined direction according to the slicing operation of the ultrasonic cutter 4, and the columnar thermal conductivity. The composition 2 is sequentially sent to the lower part of the ultrasonic cutter 4.

  The ultrasonic cutter 4 includes a knife 9 for slicing the columnar thermally conductive composition 2, an ultrasonic oscillation mechanism 10 that applies ultrasonic vibration to the knife 9, and an elevating mechanism 11 that moves the knife 9 up and down.

  The knife 9 has its cutting edge directed toward the work table 5 and is lifted and lowered by the lifting mechanism 11 to slice the columnar thermal conductive composition 2 placed on the work table 5. The dimensions and material of the knife 9 are determined according to the size and composition of the columnar heat conductive composition 2. For example, the knife 9 is made of steel having a width of 40 mm, a thickness of 1.5 mm, and a cutting edge angle of 10 °.

  The ultrasonic oscillation mechanism 10 applies ultrasonic vibration to the knife 9 in the slicing direction of the columnar thermal conductive composition 2. For example, the transmission frequency is 20.5 kHz, the amplitude is 50 μm, 60 μm, Adjustment is possible in three stages of 70 μm.

  Such an ultrasonic cutting machine 3 slices the columnar thermal conductive composition 2 while applying ultrasonic vibration to the ultrasonic cutter 4, thereby aligning the thermal conductive filler of the thermal conductive sheet 1. Can be maintained in the thickness direction of the heat conductive sheet 1.

  The heat conductive sheet 1 sliced while applying ultrasonic vibration by the ultrasonic cutting machine 3 has a lower thermal resistance than the heat conductive sheet sliced without applying ultrasonic vibration. Since the ultrasonic cutter 3 imparts ultrasonic vibration in the slicing direction to the ultrasonic cutter 4, the thermal conductive filler has a low interface thermal resistance and is oriented in the thickness direction of the thermal conductive sheet 1. This is because it is difficult to be laid down by the knife 9. On the other hand, in a thermally conductive sheet sliced without applying ultrasonic vibration, the orientation of the thermally conductive filler is disturbed due to the frictional resistance of the knife, and the exposure to the cut surface is reduced, which increases the thermal resistance. End up. Therefore, by using the ultrasonic cutting machine 3, the heat conductive sheet 1 having excellent heat conduction characteristics can be obtained.

  According to the manufacturing method of the heat conductive sheet as described above, the heat conductive filler is oriented along the thickness direction of the heat conductive sheet 1 and the surface of the heat conductive sheet 1 is measured. A heat conductive sheet 1 having a lightness L * of 32.5 or more represented by an “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” can be obtained. .

<3. Manufacturing method of other heat conductive sheet>
You may produce the heat conductive sheet 1 with the following manufacturing methods. That is, as shown in FIG. 4, the alignment step S <b> 2 of the above-described method for manufacturing a heat conductive sheet may include a temporary molding step S <b> 21, an alignment step S <b> 22, and a main molding step S <b> 23. According to such a method for producing a heat conductive sheet, “L” in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” when the surface of the heat conductive sheet 1 is measured. The heat conductive sheet 1 having a lightness L * represented by a value of “*” of 32.5 or more can be obtained more reliably. That is, the heat conductive fillers in the heat conductive sheet 1 can be more reliably aligned in the same direction, and the heat conductivity in the thickness direction of the heat conductive sheet 1 can be further improved. In addition, in the following description, the detailed description is abbreviate | omitted about heat conductive composition preparation process S1 mentioned above.

(Temporary molding process S21)
In temporary molding process S21, as shown to FIG. 5 (A), the heat conductive composition 12 created by heat conductive composition preparation process S1 is extruded with the extruder 13, and a heat conductive filler is followed along an extrusion direction. A long columnar temporary molded body 14 (hereinafter referred to as a temporary molded body 14) in which is oriented.

  For example, as shown in FIG. 5 (A), the extruder 13 is configured in an elongated cylindrical shape, and the diameter W2 of the opening 12B on the side from which the heat conductive composition 12 is discharged is the main body portion. It is preferable that the diameter is smaller than the inner diameter W1 of 12A. Further, in the extruder 13, the inner diameter W1 of the main body 12A is reduced in a taper shape from a predetermined position in the longitudinal direction toward the extrusion direction, and the aperture W2 of the opening 12B is larger than the inner diameter W1 of the main body 12A. The diameter may be reduced. By extruding the heat conductive composition 12 with such an extruder 13 and passing the heat conductive composition 12 in the extruder 13 toward a portion having a diameter smaller than the inner diameter W1 of the main body 12A. The heat conductive filler is easily along the extrusion direction. Thereby, a heat conductive filler can be more reliably orientated in the longitudinal direction of the temporary molding 14.

  For example, when the content of the heat conductive filler in the heat conductive composition 12 is 15 to 25% by volume, the extruder 13 sets the diameter W2 of the opening 12B to about 1.5 to 9.5 mm. Is preferred. In this case, when the diameter W2 of the opening 12B is set to 1.5 mm or more, it is possible to prevent the extrusion from becoming difficult when the heat conductive composition 12 is extruded by the extruder 13. Moreover, since the orientation of the heat conductive filler is hardly disturbed by setting the diameter W2 of the opening 12B to 9.5 mm or less, the heat conductivity in the thickness direction of the heat conductive sheet 1 can be further improved. it can.

  In the extruder 13, the cross-sectional shape of the opening 12B can be, for example, a circular shape, a triangular shape, a rectangular shape, or a square shape, but is preferably a rectangular shape or a square shape. By making the cross-sectional shape of the opening 12B rectangular or square, the temporary molded body 14 has a prismatic shape. Therefore, in the alignment step S22, the plurality of temporary molded bodies 14 are aligned so as to be adjacent to the direction orthogonal to the longitudinal direction, and the aligned plurality of temporary molded bodies 14 are arranged in a direction substantially orthogonal to the alignment direction. When obtaining the laminated body 14A (hereinafter, referred to as the laminated body 14A), it is difficult to generate a gap between the laminated bodies 14A. Thereby, since it becomes difficult for bubbles to be contained in the laminated body 14A, it is possible to obtain the main molded body 16 having more excellent flame retardancy in the main molding step S23.

  The temporary molded body 14 has heat conductive fillers oriented in the direction of extrusion by the extruder 13 and has an elongated columnar shape, for example, an elongated square columnar shape, an elongated triangular columnar shape, or an elongated columnar shape.

(Alignment step S22)
In the alignment step S22, for example, as shown in FIGS. 5B, 5C, and 6, the plurality of temporary molded bodies 14 formed in the temporary molding step S21 are adjacent to each other in the direction orthogonal to the longitudinal direction. Thus, the laminated body 14A is obtained. For example, in the alignment step S22, the temporary molded bodies 14 are aligned in a predetermined frame 15, and a laminated body 14A in which the temporary molded bodies 14 are arranged in a rectangular parallelepiped shape or a cubic shape is obtained. The frame 15 is used as a fixing means for fixing the laminated body 14A when the main molded body 16 is molded in the main molding step S23, and prevents the laminated body 14A from being greatly deformed. The frame 15 is made of, for example, metal.

(Main molding step S23)
In the main molding step S23, for example, as shown in FIG. 5D, the laminated body 14A obtained in the alignment step S22 is cured, so that FIG. 5E, FIG. 7A, and FIG. As shown in FIG. 3, the molded body 16 in which the temporary molded bodies 14 constituting the laminated body 14A are integrated is molded. Examples of the method of curing the laminate 14A include a method of heating the laminate 14A with a heating device and a method of heating and pressurizing the laminate 14A with a heating and pressurizing device. Moreover, when an acrylic resin is used as the curable resin composition constituting the heat conductive composition 12, for example, the laminate 14A is cured at room temperature by including an isocyanate compound in the heat conductive composition 12. It is possible.

  As a method of curing these laminates 14A, a method of heating and pressurizing the laminate 14A with a heating and pressurizing device, that is, when curing the laminate 14A, a plurality of temporary molded bodies 14 constituting the laminate 14A. It is preferable to press in a direction perpendicular to the longitudinal direction (vertical direction). By pressing the laminated body 14A in this way, air bubbles can be more reliably removed from the laminated body 14A, so that it is possible to obtain the molded body 16 with better flame retardancy in the main molding step S23. It becomes.

  In the cutting step S4, the main molded body 16 molded in the main molding step S23 is cut into a predetermined dimension by the ultrasonic cutting machine 3 in a direction orthogonal to the longitudinal direction of the temporary molded body 14. The ultrasonic cutting machine 3 slices the molded body 16 into individual heat conductive sheets 1 in order to obtain the heat conductive sheet 1. Using the ultrasonic cutting machine 3, the main molded body 16 is sliced by the ultrasonic cutter 4 in the direction of the arrow perpendicular to the longitudinal direction of the temporary molded body 14, so that heat conduction is maintained while maintaining the orientation of the thermally conductive filler. The sheet 1 can be formed. Therefore, it is possible to obtain the heat conductive sheet 1 having good heat conduction characteristics in which the orientation of the heat conductive filler is maintained in the thickness direction.

<4. Thermal conductivity evaluation method>
The thermal conductivity evaluation method according to the present embodiment is the “* in the L * a * b color system described in“ JIS Z 8729 ”and“ JIS Z 8730 ”when the surface of the thermal conductive sheet 1 described above is measured. The thermal conductivity of the thermal conductive sheet 1 is evaluated using the lightness L * represented by the “L *” value. For example, when the lightness L * when the surface of the thermal conductive sheet 1 is measured is 32.5 or more, the thermal conductive filler is oriented along the thickness direction of the thermal conductive sheet 1, and thus the thermal conductivity. It can be evaluated that the thermal conductivity in the thickness direction of the sheet 1 is good. Further, when the lightness L * when the surface of the heat conductive sheet 1 is measured is less than 32.5, the heat conductive filler is not oriented along the thickness direction of the heat conductive sheet 1, and thus the heat conduction. It can be evaluated that the thermal conductivity in the thickness direction of the conductive sheet 1 is not good.

  Examples of the present invention will be described below. The present invention is not limited to these examples. In a present Example, about the heat conductive sheet obtained in Examples 1-6 and Comparative Examples 1-3,

Example 1
In Example 1, 24 parts by volume of alumina particles (filler) (product name: DAW-03, manufactured by Denki Kagaku Kogyo Co., Ltd.) having an average particle diameter of 3 μm and an average particle are added to the two-component addition reaction type liquid silicone resin. Aluminum nitride particles having a diameter of 1 μm (manufactured by Tokuyama Co., Ltd.) 18.3% by volume, pitch-based carbon fiber (thermal conductive filler) having an average major axis length of 150 μm and an average minor axis length of 8 μm (manufactured by Teijin Ltd., Product name: Lahima R-A301) 24.1% by volume was dispersed to prepare a silicone resin composition (thermally conductive composition). The two-component addition reaction type liquid silicone resin is composed of 16.8% by volume of silicone A solution (organopolysiloxane having vinyl group) and 18.8% by volume of silicone B solution (organopolysiloxane having H-Si group). Are mixed. The obtained silicone resin composition was extruded into a mold (20 mm × 20 mm) coated with a release material to mold a silicone molded body. The obtained silicone molding was cured in an oven at 100 ° C. for 1 hour to obtain a silicone cured product. The obtained cured silicone was cut with an ultrasonic cutter so as to have a thickness of 2.0 mm to obtain a thermally conductive sheet having a thickness of 2.0 mm. The slice speed of the ultrasonic cutter was 50 mm per second. The ultrasonic vibration applied to the ultrasonic cutter had an oscillation frequency of 20.5 kHz and an amplitude of 60 μm.

(Example 2)
In Example 2, alumina particles having an average particle diameter of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 16.8 vol% of silicone A liquid and 18.8 vol% of silicone B liquid were mixed. Co., Ltd., product name: DAW-03) 11.7% by volume, aluminum nitride particles having an average particle diameter of 1 μm (manufactured by Tokuyama Co., Ltd.) 31.2% by volume, average major axis length 150 μm, average minor axis The same procedure as in Example 1 was conducted except that 23.5% by volume of pitch-based carbon fiber (trade name: Lahima R-A301, manufactured by Teijin Limited) having a length of 8 μm was dispersed to prepare a silicone resin composition. Thus, a heat conductive sheet was obtained.

(Example 3)
In Example 3, alumina particles having an average particle diameter of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 18.8% by volume of a silicone A liquid and 18.8% by volume of a silicone B liquid were mixed. Co., Ltd., product name: DAW-03) 20.2% by volume, aluminum nitride particles having an average particle diameter of 1 μm (made by Tokuyama Co., Ltd.) 20.1% by volume, average major axis length 150 μm, average minor axis Except that a silicone resin composition was prepared by dispersing 24.1% by volume of pitch-based carbon fiber (trade name: Lahima R-A301, manufactured by Teijin Limited) having a length of 8 μm. Thus, a heat conductive sheet was obtained.

Example 4
In Example 4, alumina particles having an average particle diameter of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 18.8 vol% of silicone A liquid and 18.8 vol% of silicone B liquid were mixed. Product name: DAW-03) 28% by volume, aluminum nitride particles having an average particle diameter of 1 μm (made by Tokuyama Co., Ltd.) 14.3% by volume, average major axis length 150 μm, average minor axis length A silicone resin composition was prepared by dispersing 20.1% by volume of 8 μm pitch-based carbon fiber (trade name: Lahima R-A301, manufactured by Teijin Limited). The obtained silicone resin composition was coated (laminated coating) on a polyester film coated with a release material to prepare a silicone molded body. The obtained silicone molded body was heated in an oven at 100 ° C. for 1 hour to obtain a cured silicone product. The obtained cured silicone was cut with an ultrasonic cutter so as to have a thickness of 2.0 mm to obtain a thermally conductive sheet having a thickness of 2.0 mm. The slice speed of the ultrasonic cutter was 50 mm per second. The ultrasonic vibration applied to the ultrasonic cutter had an oscillation frequency of 20.5 kHz and an amplitude of 60 μm.

(Example 5)
In Example 5, alumina particles having an average particle diameter of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 18.8 vol% of silicone A liquid and 18.8 vol% of silicone B liquid were mixed. Co., Ltd., product name: DAW-03) 37.2% by volume, aluminum nitride particles having an average particle diameter of 1 μm (manufactured by Tokuyama Corporation), 5.1% by volume, average major axis length of 150 μm, average minor axis Except that a silicone resin composition was prepared by dispersing 20.1% by volume of pitch-based carbon fiber (trade name: Lahima R-A301, manufactured by Teijin Limited) having a length of 8 μm. Thus, a heat conductive sheet was obtained.

(Example 6)
In Example 6, aluminum nitride particles having an average particle diameter of 1 μm (inc.) Were added to a two-component addition reaction type liquid silicone resin in which 17.1% by volume of silicone A liquid and 17.1% by volume of silicone B liquid were mixed. 42.6% by volume) and 23.2% by volume of pitch-based carbon fiber having an average major axis length of 150 μm and an average minor axis length of 8 μm (manufactured by Teijin Limited, trade name: Lahima R-A301). A thermally conductive sheet was obtained in the same manner as in Example 1 except that the silicone resin composition was prepared by dispersing.

(Comparative Example 1)
In Comparative Example 1, alumina particles having an average particle size of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 18.8 vol% of silicone A liquid and 18.8 vol% of silicone B liquid were mixed. Co., Ltd., product name: DAW-03) 42.3% by volume, pitch-based carbon fiber having an average major axis length of 150 μm and an average minor axis length of 8 μm (manufactured by Teijin Limited, trade name: Lahima R-A301) A thermally conductive sheet was obtained in the same manner as in Example 1 except that 24.1% by volume was dispersed to prepare a silicone resin composition.

(Comparative Example 2)
In Comparative Example 2, alumina particles having an average particle diameter of 3 μm (electrochemical industry) were added to a two-component addition reaction type liquid silicone resin in which 18.8 vol% of silicone A liquid and 18.8 vol% of silicone B liquid were mixed. Product name: DAW-03) 41.3% by volume, pitch-based carbon fiber with an average major axis length of 150 μm and an average minor axis length of 8 μm (manufactured by Teijin Limited, trade name: Lahima R-A301) A thermally conductive sheet was obtained in the same manner as in Example 4 except that 20.1% by volume was dispersed to prepare a silicone resin composition.

(Comparative Example 3)
In Comparative Example 3, alumina particles having an average particle diameter of 3 μm (manufactured by Denki Kagaku Kogyo Co., Ltd.) were added to a two-component addition reaction type liquid silicone resin in which 18 volume% of silicone A liquid and 18 volume% of silicone B liquid were mixed. Product name: DAW-03) 44.8% by volume, pitch-based carbon fiber having an average major axis length of 150 μm and an average minor axis length of 8 μm (trade name: Lahima R-A301, manufactured by Teijin Limited), 19.2 volumes % Was dispersed in the same manner as in Example 1 except that a silicone resin composition was prepared.

  Table 1 summarizes the conditions of Examples 1 to 6 and Comparative Examples 1 to 3.

(Regarding the orientation of pitch-based carbon fibers)
The orientation of the pitch-based carbon fibers was evaluated by observing the cross section of the thermally conductive sheet with an SEM and measuring the blackness using the L * a * b color system.

  When the cross section of the heat conductive sheet obtained in Examples 1 to 6 was observed with an SEM, the pitch-based carbon fibers were oriented with respect to the thickness direction of the heat conductive sheet. In particular, the heat conductive sheets obtained in Examples 1 to 3, Example 5 and Example 6 are more favorable than the heat conductive sheets obtained in Example 4, and pitch-based carbon fibers are better. Were oriented along the thickness direction of the thermally conductive sheet. This is considered to be because in Examples 1 to 3, Example 5 and Example 6, the silicone molded body was molded by extrusion into a mold coated with a release material.

  On the other hand, when the cross section of the heat conductive sheet obtained in Comparative Examples 1 to 3 was observed with an SEM, the pitch-based carbon fiber was compared with the heat conductive sheets obtained in Example 1 to Example 6. However, it was not oriented with respect to the thickness direction of the heat conductive sheet.

  Moreover, about the cross section of the heat conductive sheet, the blackness was measured using the L * a * b color system. As an index of blackness, a color display method represented by the L * a * b color system defined in “JIS Z 8729” was used. A spectrophotometer (product name: CM-700d, manufactured by Konica Minolta Sensing Co., Ltd.) was used to measure blackness using the L * a * b color system.

  The heat conductive sheets obtained in Examples 1 to 6 are the “L *” values in the L * a * b color system described in “JIS Z 8729” when the surface of the heat conductive sheet is measured. The lightness L * expressed was 32.5 or more. On the other hand, the heat conductive sheets obtained in Comparative Examples 1 to 3 are “L *” in the L * a * b color system described in “JIS Z 8729” when the surface of the heat conductive sheet is measured. The lightness L * represented by the value was less than 32.5. From this result, the heat conductive sheets obtained in Examples 1 to 6 are more effective in pitch-based carbon fibers than the heat conductive sheets obtained in Comparative Examples 1 to 3. It is thought that it is orientated along the thickness direction of a heat conductive sheet.

  From these results, the lightness L * represented by the “L *” value in the L * a * b color system when aluminum nitride is contained in the heat conductive sheet and the surface of the heat conductive sheet is measured is 32. It was found that the pitch-based carbon fiber was oriented along the thickness direction of the heat conductive sheet and the heat conductivity in the thickness direction of the heat conductive sheet could be improved by being 0.5 or more.

(About evaluation of thermal conductivity)
Table 1 shows the measurement results of the thermal conductivity of the thermal conductive sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 3. Evaluation of thermal conductivity was performed by the measuring method based on ASTM-D5470.

  In the heat conductive sheets obtained in Examples 1 to 6, the heat resistance value in the thickness direction of the heat conductive sheet is 22.3 to 33.1 W / mK across the entire cross section of the heat conductive sheet. It was found that the thermal conductivity in the thickness direction was good. This is the brightness represented by the “L *” value in the L * a * b color system when the surface of the heat conductive sheet measured in Examples 1 to 6 is measured. Since L * was 32.5 or more, it is considered that the pitch-based carbon fibers were oriented along the thickness direction of the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet could be improved. .

  On the other hand, the thermal conductive sheets obtained in Comparative Examples 1 to 3 have a thermal resistance value of 20.2 W / mK or less, compared with the thermal conductive sheets obtained in Examples 1 to 6. Thus, it was found that the thermal conductivity in the thickness direction is not good. This is because the heat conductive sheet obtained in Comparative Examples 1 to 3 does not contain aluminum nitride in the heat conductive sheet, and L * when the surface of the heat conductive sheet is measured. This is presumably because the lightness L * represented by the “L *” value in the a * b color system is not 32.5 or higher.

(About appearance evaluation)
The defect rate was evaluated based on the number of air bubbles entrained on the surface of the thermally conductive sheet or through holes in the thermally conductive sheet when the thermally conductive sheet was sliced from the cured silicone. . The presence or absence of bubbles and whether or not the sheet has a through hole were determined by visually observing the cross section of the thermally conductive sheet.

  In the heat conductive sheets obtained in Examples 1 to 6, no bubbles are involved in the surface of the heat conductive sheet, and there are no through holes in the heat conductive sheet. Was less than 5%.

  On the other hand, the heat conductive sheet obtained in Comparative Example 1 had a high defect rate of 28% because bubbles were entrained on the surface and through holes were present in the sheet. This is presumably because the dispersibility of the silicone resin composition was poor because aluminum nitride was not contained in the heat conductive sheet.

  Since the heat conductive sheet obtained in Comparative Example 2 was produced by laminating, the amount of bubbles was reduced compared to Comparative Example 1, and the defective rate was reduced compared to Comparative Example 1, The orientation of the pitch-based carbon fiber was disturbed, and the variation in thermal conductivity was large. This is presumably because aluminum nitride was not contained in the heat conductive sheet, and a silicone molded body was produced by lamination coating.

  The heat conductive sheet obtained in Comparative Example 3 has no bubbles entrained on the surface of the heat conductive sheet, and since there are no through holes in the heat conductive sheet, the defect rate is less than 5%. It was low. However, compared with Examples 1 to 6, the thermal conductivity was not good. This is presumably because the heat conductive sheet obtained in Comparative Example 3 did not contain aluminum nitride and the amount of alumina was too large.

DESCRIPTION OF SYMBOLS 1 Thermal conductive sheet, 2 columnar thermal conductive composition, 3 Ultrasonic cutting machine, 4 Ultrasonic cutter, 5 Worktable, 6 Moving table, 7 Silicone rubber, 8 Moving mechanism, 9 Knife, 10 Ultrasonic oscillation mechanism , 11 Lifting mechanism, 12 Thermally conductive composition, 13 Extruder, 14 Temporary molded body, 14A Laminated body, 15 Frame, 16 This molded body

Claims (8)

In a thermally conductive sheet comprising a thermally conductive composition containing a curable resin composition, a thermally conductive filler, and a filler that aligns the thermally conductive filler in a predetermined direction,
The thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet,
As the filler, at least aluminum nitride is included,
When the surface of the thermal conductive sheet was measured, the lightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” was 32.5. The heat conductive sheet which is the above.   The heat conductive sheet according to claim 1, comprising 5.1% by volume or more of the aluminum nitride.   The thermally conductive sheet according to claim 2, wherein the filler includes spherical particles having a particle diameter different from that of the aluminum nitride.   The thermally conductive sheet according to claim 3, wherein the spherical particles are alumina particles.   The thermal conductive sheet according to any one of claims 1 to 4, wherein the thermal conductive filler is carbon fiber and has an average fiber length of 100 µm or more. A thermally conductive composition creating step for creating a thermally conductive composition containing a curable resin composition, a thermally conductive filler, and a filler that aligns the thermally conductive filler in a predetermined direction;
While forming the thermal conductive composition created in the thermal conductive composition creation step into a columnar shape, an orientation step of orienting the thermal conductive filler in the columnar longitudinal direction;
Cutting the columnar heat conductive composition in a direction perpendicular to the longitudinal direction to obtain a heat conductive sheet by cutting to a predetermined size with an ultrasonic cutter,
The thermal conductive sheet is
The thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet,
As the filler, at least aluminum nitride is included,
When the surface of the thermal conductive sheet was measured, the lightness L * represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730” was 32.5. The manufacturing method of the heat conductive sheet which is the above. The alignment step is
Extruding the thermal conductive composition created in the thermal conductive composition creating step with an extruder, and molding a long columnar temporary molded body in which the thermal conductive filler is oriented along the extrusion direction; and
An alignment step of aligning a plurality of temporary molded bodies so as to be adjacent to each other in a direction orthogonal to the longitudinal direction, and obtaining a laminate in which the aligned plurality of temporary molded bodies are arranged in a direction substantially orthogonal to the alignment direction;
A main molding step of molding the molded body in which a plurality of temporary molded bodies constituting the laminated body are integrated by curing the laminated body,
The method for producing a thermally conductive sheet according to claim 6, wherein in the cutting step, the thermally conductive sheet is obtained by cutting into a predetermined dimension with an ultrasonic cutter in a direction orthogonal to the longitudinal direction of the molded body. When measuring the surface of a thermally conductive sheet containing a thermally conductive composition containing a curable resin composition, a thermally conductive filler, and a filler that aligns the thermally conductive filler in a predetermined direction, Using the lightness L represented by the “L *” value in the L * a * b color system described in “JIS Z 8729” and “JIS Z 8730”, the thermal conductivity of the thermal conductive sheet was evaluated,
The thermal conductive sheet is
The thermally conductive filler is oriented along the thickness direction of the thermally conductive sheet,
A thermal conductivity evaluation method containing at least aluminum nitride as the filler.

Images