JP2008207967A - Method for producing graphite sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve yield of a graphite sheet that is produced by pyrolysis of an organic film. <P>SOLUTION: In a method for producing a graphite sheet, the method which can improve the yield of the graphite sheet comprises obtaining a flat and uniform graphite sheet by reducing the undulation of the sheet near both ends in its widthwise direction, because the reduction of the undulation is ascribable to the mitigation of the distortion caused by contraction and expansion of an organic film 12, in a process for pyrolyzing the organic film 12 wherein the wound body 17 obtained by winding the organic film 12 around the surface of a first cylinder 11 of a carbonaceous material is housed within a second cylinder 13 of a carbonaceous material, firstly the first cylinder 11 is heated to pyrolyze the organic film, and then the second cylinder 13 is heated to pyrolyze the organic film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a graphite sheet, and more particularly to firing for graphitization.

  2. Description of the Related Art Various electronic parts are used to efficiently diffuse and dissipate heat generated from LSIs, power amplifiers, and the like in electronic devices that are smaller and have higher performance.

  Especially for thin electronic devices such as mobile phones, the main thermal conductivity is 100 to 1000 W / (m · K) in the surface direction even when the thickness is small, and graphite is the most suitable for heat diffusion and heat dissipation. A graphite sheet as a component is used.

  As such a graphite sheet, a pyrolytic graphite sheet obtained by thermally decomposing an organic film such as a polyimide film in a high-temperature neutral or reducing atmosphere, and natural graphite are acid-treated and then heated and expanded. There is a so-called expanded graphite sheet in which a graphite powder is pressed into a sheet shape.

  Among these, a pyrolytic graphite sheet obtained by pyrolyzing an organic film has a higher thermal conductivity than an expanded graphite sheet and is a flexible sheet, and thus is widely used as a heat dissipation component.

For example, Patent Document 1 is known as prior art document information relating to the invention of the present application.
JP 63-256508 A

  However, when a graphite sheet is obtained by thermally decomposing an organic film by the method described in Patent Document 1, it is possible to prevent generation of soot throughout the graphite sheet, but the obtained graphite sheet is planar. 2, as shown in the perspective view of FIG. 2, the vicinity of both ends in the width direction of the graphite sheet 21 undulates like kelp and deforms to form the undulating portion 22.

  When the wavy portions 22 are formed in the vicinity of both ends of the graphite sheet 21, the graphite sheet 21 after pyrolysis is subjected to a softening process by passing between a pair of rotating rollers having a predetermined interval. In the chemical conversion process, the graphite sheet is torn or the wrinkles shift and the yield decreases.

  In addition, a relatively flat sheet can be obtained by removing the wavy portions 22 near both ends. However, in this case as well, the dimensions of the obtained graphite sheet 21 are not flat because a considerably wide area near both ends is not discarded. As the value decreases, the yield decreases.

  Then, an object of this invention is to provide the manufacturing method of the graphite sheet which can improve a yield.

  And in order to achieve this object, in the method for producing a graphite sheet of the present invention, in the step of thermally decomposing the organic film, the wound body in which the organic film is wound around the first cylindrical surface, The organic film is housed inside a cylinder, and the first cylinder is first heated to thermally decompose the organic film, and then the second cylinder is heated to perform thermal decomposition.

  In the step of thermally decomposing the organic film, a wound body in which the organic film is wound around the surface of the first cylinder is accommodated in the second cylinder, and the first cylinder is initially heated to produce the organic film. By performing thermal decomposition of the film and then performing thermal decomposition by heating the second cylinder, distortion due to shrinkage and expansion of the organic film can be reduced, thus reducing the waviness near both ends in the width direction of the sheet. As a result, a flat and uniform graphite sheet is obtained, and the yield is improved.

  The manufacturing method of the graphite sheet of this invention is demonstrated using one Embodiment and drawing.

  FIG. 1 is a cross-sectional view schematically showing a method for producing a graphite sheet in one embodiment of the present invention, in which a wound body 17 in which a plurality of organic films 12 are wound around the surface of a carbonaceous first cylinder 11. Is placed inside a second cylinder 13 having a carbonaceous bottom surface.

  Electrode plates 14 and 15 and a common electrode plate 16 are attached to both ends of the first cylinder 11 and the second cylinder 13, and current is supplied from power sources 19 and 20 through the electrode plates 14 and 15. As a result, the first cylinder 11 and the second cylinder 13 generate heat.

  First, as the organic film 12, a carbonaceous first cylinder 11 having both ends having an outer diameter of 150 mm, an inner diameter of 140 mm, and a height of 550 mm is formed of 50 to 100 polyimide films having a length of 600 mm, a width of 250 mm, and a thickness of 75 μm. The wound body 17 is produced by winding around the outer peripheral surface.

  Thereafter, the wound body 17 in which the organic film 12 is wound around the first cylinder 11 is placed inside the bottomed second cylinder 13 whose one end has an outer diameter of 200 mm, an inner diameter of 190 mm, and a height of 520 mm. Place it vertically.

  Then, the second cylinder 13 on which the wound body 17 is placed is housed in the sealed chamber 18 and the inside of the sealed chamber 18 is decompressed.

  Thereafter, an electric current is passed from the power source 20 between the electrode plate 15 attached to both ends of the first cylinder 11 and the common electrode plate 16 to heat the first cylinder 11 to 1200 ° C. and hold it for 2 hours. 12 pyrolysis.

  At this time, the organic film 12 of the wound body 17 starts to shrink with thermal decomposition from the inner side near the surface of the first cylinder 11, and the shrinkage starts from the inner side near the surface of the first cylinder 11 to the outer side. Shrink sequentially.

  Thus, the shrinkage of the organic film 12 proceeds sequentially from the organic film 12 close to the first cylinder 11 toward the organic film 12 close to the surface of the wound body 17, so that the strain applied to the organic film 12 due to the shrinkage stress is reduced. Can be reduced.

  If the second cylinder 13 rather than the first cylinder 11 is heated at this stage, the organic film 12 near the surface of the wound body 17 is heated from the surface side of the wound body 17. First contracts.

  As a result of the shrinkage of the organic film 12 near the surface of the wound body 17, the portion of the organic film 12 that is closer to the inside than the vicinity of the surface receives a large strain due to the shrinkage stress of the organic film 12 near the surface. As indicated, the wavy portions 22 are caused at both ends of the graphite sheet 21 obtained by thermally decomposing the organic film 12.

Next, the atmosphere in the sealed chamber 18 is changed to a neutral atmosphere or a reducing atmosphere using Ar gas or N ₂ gas, and then the current flowing through the first cylinder 11 is increased to raise the first cylinder 11 to 2500 ° C. Warm up.

  After the temperature of the first cylinder 11 reaches 2500 ° C., the temperature of the first cylinder 11 is reduced to 2000 ° C. to 2300 ° C., and then the power supply 19 is connected between the electrode plate 14 and the common electrode plate 16. Similarly, current is passed through the second cylinder 13 and heated to 2500 ° C.

  In this state, the pyrolyzed organic film 12 is further pyrolyzed and converted into graphite.

  Here, when the conversion to graphite occurs, the organic film 12 expands. However, since the temperature of the first cylinder 11 is kept lower than the temperature of the second cylinder 13, the expansion of the organic film 12 is wound. The expansion starts from the vicinity of the outermost surface of the body 17 and then proceeds closer to the surface of the first cylinder 11, that is, toward the inside. As a result, the strain associated with the expansion at the time of conversion to graphite can be alleviated. it can.

  When the current is supplied to the second cylinder 13 for heating, the first cylinder 11 does not necessarily have to be energized for heating. However, if the first cylinder 11 does not generate heat at all, the overall heating efficiency decreases. Therefore, it is preferable to heat the first cylinder 11 to a temperature lower by about 200 to 500 ° C. than the temperature of the second cylinder 13 as described above.

  As a method of heating the first cylinder 11 and the second cylinder 13, resistance heating is performed by using the resistance of a carbonaceous cylinder and flowing current from the electrode plates 14 and 16 or 15 and 16 connected to both ends of the cylinder. It is preferable to carry out.

  This is because in the heating by resistance heating, the resistance value of the cylinder can be changed relatively easily depending on the thickness and material of the cylinder, and precise temperature control is possible by the flowing current.

  As a heating method other than resistance heating, a heating method such as high-frequency induction heating may be used.

  The graphite sheet produced in this manner was taken out from the second cylinder 13 together with the first cylinder 11, and removed from the first cylinder 11 and spread in a flat shape to perform an appearance inspection. The graphite sheet shown in FIG. The wavy portions 22 at both ends were hardly seen, and a graphite sheet that was flat and free from cracks was obtained.

  Next, after softening the graphite sheet, the thermal conductivity was measured by an optical alternating current method using an optical alternating current method thermal constant measuring apparatus (Lacer Pit manufactured by ULVAC-RIKO).

  As a measurement result of thermal conductivity, 800 to 1000 W / (m · K), a satisfactory result as a pyrolytic graphite sheet was obtained.

  The softening process was performed by passing a graphite sheet between a pair of rollers that rotate in reverse directions with a predetermined interval.

  Also, instead of passing between a pair of rollers, a pyrolytic graphite sheet is placed on a base plate, and a single groove having a spiral groove on the surface is installed on the base plate with a predetermined interval. You may perform a softening process by rotating a roller.

  Here, with the spiral groove provided on the roller surface, an appropriate pressurizing force can be applied while pressing the graphite sheet to efficiently perform the softening.

  The flexibility of the graphite sheet after softening is high. 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 90 degrees from the stationary state to the left and right ( As a result of testing at a bending angle of 180 degrees in total, no defects such as breakage and cracks were found in the graphite sheet even in the repeated bending test of 50000 times.

  As described above in detail, according to the method for producing a graphite sheet of the present embodiment, in the step of pyrolyzing the organic film 12 to produce the graphite sheet, the organic film 12 is made of the carbonaceous first cylinder 11. The wound body 17 wound around the surface is accommodated in the carbonaceous second cylinder 13, and the organic film 12 is initially contracted by heating, so the first cylinder 11 wound with the organic film 12 is heated. Then, the organic film 12 is thermally decomposed while reducing the strain applied to the organic film 12, and then expands when the organic film 12 is converted into graphite by the subsequent thermal decomposition. By performing the decomposition, distortion due to expansion of the organic film 12 can be reduced.

  As a result, the expansion and contraction associated with the thermal decomposition of the organic film 12 are alleviated, and the wavy portions 22 near both ends in the width direction of the graphite sheet when the organic film 12 is thermally decomposed to produce a graphite sheet are reduced and flattened. Thus, a uniform graphite sheet can be obtained, so that the yield is improved.

  Further, in the present embodiment, the organic film 12 cut to a length of 600 mm and a width of 250 mm is used. However, according to the present embodiment, distortion due to shrinkage and expansion generated during the thermal decomposition of the organic film 12 is reduced. Therefore, a flat graphite sheet can be obtained by pyrolyzing the organic film 12 having a longer length, for example, 1000 mm.

  Further, by controlling the heating conditions of the first cylinder 11 and the second cylinder 13 in more detail, it is possible to obtain a continuous long graphite sheet having a length of several meters to several tens of meters.

  Therefore, an unprecedented long continuous pyrolytic graphite sheet can be obtained, which can improve the productivity of the graphite sheet and improve the processing efficiency when punching the graphite sheet into a desired shape. it can.

  In the present embodiment, carbonaceous cylinders are used as the first cylinder 11 and the second cylinder 13, but the present invention is not limited to this, and a graphite cylinder may be used.

  Moreover, after hold | maintaining at 1200 degreeC for 2 hours by thermal decomposition of the organic film 12, temperature was raised further and it heated to 2500 degreeC, but it is limited to 1200 degreeC as temperature to heat-and-hold in the middle stage of temperature rising Instead, it may be any temperature in the temperature range of 600 to 1800 ° C.

  Further, the heating at 1200 ° C. for 2 hours is not necessarily required, and the same effect can be obtained even if the temperature is directly raised to 2500 ° C.

  The wound body in which the organic film is wound around the surface of the first cylinder is accommodated in the second cylinder, and the organic film is first pyrolyzed by heating the first cylinder, and then the second cylinder. By performing thermal decomposition by heating the cylinder, it is possible to reduce distortion due to shrinkage and expansion of the organic film, so that the waviness near both ends in the width direction of the sheet is reduced, and a flat and uniform graphite sheet is formed. It can be obtained and is useful in a method for producing a pyrolytic graphite sheet.

Sectional drawing which shows typically the manufacturing method of the graphite sheet in one embodiment Perspective view of conventional graphite sheet

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st cylinder 12 Organic film 13 2nd cylinder 14,15,16 Electrode plate 17 Winding body 18 Sealed chamber 19,20 Power supply

Claims (4)

A method for producing a graphite sheet, comprising: pyrolyzing an organic film to produce a graphite sheet; and softening the graphite sheet, wherein the step of pyrolyzing the organic film comprises The wound body wound around the surface of the cylinder 1 is accommodated in the second cylinder, the first cylinder is first heated to thermally decompose the organic film, and then the second cylinder is heated. A method for producing a graphite sheet, wherein the thermal decomposition is performed. The method for producing a graphite sheet according to claim 1, wherein the softening step comprises softening the pyrolytic graphite sheet with a rotating roller. The method for producing a graphite sheet according to claim 1, wherein after the first cylinder is heated, the temperature of the first cylinder is lowered, and then the second cylinder is heated. The method for producing a graphite sheet according to claim 1, wherein the first cylinder and the second cylinder are carbonaceous cylinders, and the method of heating the first and second cylinders is resistance heating.

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