JP4978284B2 - Method for producing graphite sheet - Google Patents

Description

  The present invention relates to a method for producing a flexible graphite sheet used for a heat dissipation component or the like.

  In electronic devices that are becoming smaller and have higher performance, various heat dissipating parts have been proposed and used for efficiently diffusing and dissipating heat generated from LSIs and power amplifiers.

  Especially in small and thin electronic devices such as cellular phones, the thermal conductivity in the surface direction is as large as 100 to 1000 W / (m · K), and it is mainly composed of graphite, which is optimal for heat diffusion and heat dissipation. A graphite sheet is used.

  Among graphite sheets, pyrolytic graphite sheets obtained by thermally decomposing organic films at high temperatures have high thermal conductivity and have been widely used.

  In this pyrolytic graphite sheet, it is suggested that a graphite sheet that has been heat-treated at 2500 ° C. or higher at a high temperature is somewhat hard and lacks flexibility. Yes.

For example, Patent Document 1 is known as prior art document information relating to the invention of the present application.
JP 2000-16808 A

  In the above pyrolytic graphite sheet, the organic film shrinks when thermally decomposing, but since this shrinkage is slightly different in the width direction and the length direction of the organic film, shrinkage strain is generated at both ends of the pyrolytic graphite sheet. It may occur, and the both end portions of the sheet may be wavy.

  For this reason, when the rolling process is performed by sandwiching between the rolling rollers using the method described in Patent Document 1, a relatively flat portion and a wavy portion simultaneously force a narrow gap between the rolling rollers. Because it is allowed to pass through, a part of the graphite sheet is torn at the boundary between the flat part and the undulated part, or the undulated both ends cannot follow the rotation of the rolling roller and are crushed by the rolling roller to cause wrinkles. Or a problem that the yield decreases.

  Accordingly, the method for producing a graphite sheet of the present invention aims to improve the yield by reducing the tearing of the graphite sheet and the generation of wrinkles in the step of softening the graphite sheet after pyrolysis.

  In order to achieve this object, the method for producing a graphite sheet of the present invention comprises a step of thermally decomposing an organic film to produce a graphite sheet, and a softening step of softening the graphite sheet after the pyrolysis. In this softening step, the pyrolytic graphite sheet is sandwiched between a pair of parallel flat plates, and at least one of the pair of flat plates is slid in a direction substantially parallel to the graphite sheet. A graphite sheet manufacturing method characterized by softening a graphite sheet.

  According to the present invention, since the graphite sheet is sandwiched between flat plates and at least one of the flat plates is slid, the softening can be performed while extending the strain at both ends of the pyrolytic graphite sheet. It is possible to suppress the breakage of the graphite sheet and the generation of wrinkles and improve the yield.

  Hereinafter, a method for producing a graphite sheet of the present invention will be described with reference to an embodiment and drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view schematically showing a process of softening a graphite sheet according to the first embodiment, in which a graphite sheet 1 after pyrolysis is sandwiched between a pair of mutually parallel stainless steel plates 2 and 3. Cover layers 4 and 5 made of polypropylene (hereinafter referred to as PP) are provided on the surfaces where the pair of flat plates 2 and 3 are in contact with the graphite sheet 1.

  The cover layers 4 and 5 have a role of preventing the graphite sheet from being damaged or defective due to the influence of the state of the flat plate when the hard flat plate and the graphite sheet are in direct contact.

  In the figure, the portions denoted by reference numerals 6 and 7 are drive shafts for sliding the flat plates 2 and 3, and the arrows in the figure indicate the rotation directions of the drive shafts 6 and 7.

  Of the method for producing a graphite sheet according to the first embodiment, first, the production of the graphite sheet will be described below.

  The graphite sheet of the first embodiment is obtained by thermally decomposing an organic film at a high temperature. As the organic film used for the pyrolysis, a condensed aromatic polymer film capable of performing a graphitization reaction, for example, aromatic A group polyimide film is used.

  This organic film is first preliminarily heat-treated from a maximum temperature of 1000 ° C. to 1200 ° C. in an inert gas atmosphere such as nitrogen or argon.

  Thereafter, similarly, a high-temperature heat treatment is performed at a maximum temperature of 2500 ° C. or higher in an inert gas atmosphere to produce a pyrolytic graphite sheet.

  The pyrolytic graphite sheet produced in this way is hard and brittle, and is not flexible enough to be broken several times to several tens of times when subjected to repeated bending tests.

  In this case, as a repeated bending test, using a repeated bending tester (for example, an MIT fatigue resistance tester manufactured by Toyo Seiki Co., Ltd.), the bending radius R is 5 mm, and the left and right are 90 degrees (total) The test was conducted at a bending angle of 180 degrees.

  Therefore, a softening step is performed in order to give sufficient flexibility to the graphite sheet after the heat treatment.

As shown in FIG. 1, the softening process is performed by sandwiching the above-mentioned heat-treated graphite sheet 1 between the flat plates 2 and 3 provided with the cover layers 4 and 5 made of PP, and between the flat plates 2 and 3 at 2 kg / cm. ^The drive shafts 6 and 7 are rotated at a speed of 5 to 20 revolutions per minute while a pressure of about ^{2 to 20} kg / cm ² is applied.

  Then, the rotation of the drive shafts 6 and 7 causes the flat plates 2 and 3 to be in parallel with each other, and the sliding movement is performed in which the rotation directions of the flat plates are opposite to each other, thereby performing the softening process.

  For example, when the flat plate 2 slides clockwise in the in-plane direction of the flat plate as viewed from the top of the drive shaft 6, the flat plate 3 slides counterclockwise. means. The flat plates 2 and 3 are sufficiently wide so that the graphite sheet 1 to be softened does not protrude.

  Thus, the graphite sheet 1 after the softening treatment did not have a torn part or wrinkles, and a uniform graphite sheet was obtained.

  The graphite sheet 1 was repeatedly subjected to a bending test under the conditions described above. As a result, it was confirmed that the flexibility was remarkably improved without being broken even in the bending test of 50000 times.

  In the first embodiment, both the flat plate 2 and the flat plate 3 are rotated and slid in opposite directions with both the flat plate 2 and the flat plate 3 facing each other in parallel. However, it is not always necessary to slide both the flat plates 2 and 3. Even if one of the plate 2 and the flat plate 3 is fixed and the other is slid, the uniform softening treatment can be performed.

  In the first embodiment, the positions of the drive shafts 6 and 7 are fixed and rotated around the drive shaft to rotate. However, the positions of the drive shafts 6 and 7 draw a circle or an ellipse. The revolving sliding which moves to (3) may be performed, and the softening treatment may be performed by combining this rotational sliding and the revolving sliding.

(Embodiment 2)
FIG. 2 is a cross-sectional view of the softening process in the second embodiment. In FIG. 2, the same components as those in FIG.

  The difference between the second embodiment and the first embodiment is that the pair of flat plates 2 and 3 sandwiching the graphite sheet 1 slides linearly in the plane direction of the flat plates 2 and 3 to be flexible. It is a point to process.

As shown in FIG. 2, the graphite sheet 1 after the same heat treatment as that obtained in the first embodiment is sandwiched between flat plates 2 and 3 whose surfaces are covered with cover layers 4 and 5, and 2 kg / cm ^{2 to} 20 kg. while applying a pressure of / cm ^2, while little by little slide at a speed of 10 to 30 cm / sec in the reverse direction to drive shaft 6, 7 linearly as the relative speed, the flat plate 2 and the flat plate 3 in the opposite direction It was slid back and forth several times in a straight line.

  For example, when the flat plate 2 moves to the right in the direction parallel to the graphite sheet 1 in FIG. 2, the flat plate 3 moves to the left, and conversely when the flat plate 2 moves to the left, the flat plate 3 moves to the right. The flat plate 2 and the flat plate 3 repeat reciprocating sliding in opposite sliding directions.

  The graphite sheet 1 after the softening treatment thus obtained was repeatedly subjected to a bending test in the same direction as in the first embodiment.

  As a result, as in the first embodiment, the graphite sheet 1 was not broken even in a bending test of 50000 times, and it was confirmed that the graphite sheet 1 was sufficiently softened.

  In the second embodiment, both the flat plate 2 and the flat plate 3 are slid back and forth. However, either the flat plate 2 or the flat plate 3 is slid, and the other flat plate is slid by the flat plate while being fixed. May be added.

  In addition to the sliding in the left-right direction parallel to the flat plates 2 and 3 in FIG. 2, the sliding in the front-rear direction parallel to the flat plate in the direction perpendicular to the paper surface may be performed. However, in this case, first, when the flat plate 2 moves in the left-right direction, the flat plate 3 moves in the opposite left-right direction to perform the softening process, and then when the flat plate 2 moves in the front-back direction, the flat plate 3 moves in the reverse front-back direction. Thus, it is preferable to slide the flat plates 2 and 3 so that the sliding directions are not orthogonal.

  In the first and second embodiments, the cover layers 4 and 5 made of PP are provided on the flat plates 2 and 3 opposed to the graphite sheet 1 to perform the softening treatment. In such a case, a cover layer such as PP is not always necessary.

  The material of the cover layers 4 and 5 is not limited to PP (polypropylene), and organic films such as polyimide, polyethylene terephthalate, and PPS (polyphenylene sulfide) can also be used.

  In addition, since the graphite sheet 1 is slippery, it is also effective to perform a softening treatment by generating appropriate friction between the graphite sheet 1 and the flat plates 2 and 3. In this case, the flat plates 2 and 3 face the graphite sheet. The surface roughness of the surface to be processed may be set to an appropriate value, or fine groove-shaped irregularities may be formed on this surface.

  Moreover, it is also preferable to perform the softening process by sandwiching a flexible buffer between the flat plate and the cover layer provided on the surface facing the graphite sheet of the pair of flat plates 2 and 3.

  By softening with a buffer, even if the graphite sheet to be softened has uneven thickness or uneven parts, local stress on the graphite sheet is relieved by the action of the buffer. Therefore, it is possible to produce a more uniform graphite sheet with no defects.

  The buffer is not particularly limited. For example, a cushioning material such as urethane foam or a sponge such as cellulose sponge may be used, for example, a nonwoven fabric, or a combination thereof. May be used.

  By softening the graphite sheet between flat plates, it is possible to soften the graphite sheet while reducing the occurrence of tears and wrinkles at both ends, and to improve the yield of the graphite sheet. It is useful in a method for producing a pyrolytic graphite sheet.

Sectional drawing which shows typically the softening process in Embodiment 1 of this invention. Sectional drawing which shows typically the softening process in Embodiment 2 of this invention

Explanation of symbols

1 Graphite sheet 2, 3 Flat plate 4, 5 Cover layer 6, 7 Drive shaft

Claims (5)

A method for producing a graphite sheet, comprising: pyrolyzing an organic film to produce a graphite sheet; and a softening step for softening the graphite sheet, wherein the softening step is performed after the pyrolysis. A method for producing a graphite sheet, comprising: sandwiching a pair of flat plates between each other and sliding at least one of the pair of flat plates in a direction substantially parallel to the graphite sheet. The method for producing a graphite sheet according to claim 1, wherein the flat plate is rotated and slid in a plane direction. The method for producing a graphite sheet according to claim 1, wherein the flat plate is slid back and forth linearly in a plane direction. The method for producing a graphite sheet according to any one of claims 1 to 3, wherein a cover layer is provided on a surface of the pair of flat plates facing the graphite sheet. The method for producing a graphite sheet according to claim 4, wherein a buffer is provided between the flat plate and the cover layer.

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