JP2019171657A - Heat conductive sheet and process for producing same - Google Patents

Abstract

To provide a heat conductive sheet that has a low heat resistivity in the thickness direction.SOLUTION: Provided are: a heat conductive sheet having a plurality of carbon material-containing layers laminated and integrated via a glass layer and the thickness of the glass layer is from 0.5 μm or more and 50 μm or less; and further, a process for producing heat conductive sheet comprising a step (A) in which carbon material-containing layers are overlapped by applying a liquid composition containing a glass precursor on at least one overlapping surface to yield an overlapped body, and a step (B) in which, after step (A), the liquid composition is solidified to form a glass layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat conductive sheet and a method for producing the heat conductive sheet.

  In recent years, as electronic devices have become smaller and higher in performance, the importance of measures to dissipate heat generated from CPUs and the like that are densely integrated has increased.

  In addition, as a heat conductive material that can be used for heat dissipation of electronic devices and the like, carbon material sheets such as graphite sheets that are excellent in heat conductivity and flexibility have attracted attention. However, it is difficult to increase the thickness of a carbon material sheet such as a graphite sheet.

  Therefore, with an increase in the heat generation amount of the heat source, for example, as a heat conductive material using a graphite sheet, a heat conductive sheet obtained by bonding a plurality of graphite sheets with a double-sided adhesive tape or a liquid resin is used (for example, , See Patent Document 1).

JP 2002-160970 A

  However, the heat conductive sheet obtained by laminating a graphite sheet using a double-sided adhesive tape or liquid resin has a high thermal resistance in the thickness direction because the double-sided adhesive tape or liquid resin is interposed between the graphite sheets, It was difficult to convey heat in the thickness direction.

  Then, an object of this invention is to provide the heat conductive sheet with low heat resistance of the thickness direction.

  The present inventor has intensively studied for the purpose of solving the above problems. And this inventor is the heat conductive sheet which laminates | stacks and integrates the layer containing a carbon material through the glass layer of predetermined thickness, and the heat resistance of a thickness direction is low, and it is easy to convey heat to a thickness direction ( In other words, the present invention was completed.

That is, the present invention aims to advantageously solve the above problems, and the heat conductive sheet of the present invention has a plurality of carbon material-containing layers laminated and integrated via glass layers, The glass layer has a thickness of 0.5 to 50 μm. Thus, if a plurality of carbon material-containing layers are laminated and integrated via a glass layer having a thickness of 0.5 μm or more and 50 μm or less, heat resistance in the thickness direction is low and heat is easily transferred in the thickness direction. A conductive sheet is obtained.
In the present invention, the “thickness of the glass layer” can be measured using the method described in the examples of the present specification.

Here, as for the heat conductive sheet of this invention, it is preferable that the ratio of the area which the said glass layer occupies on the said carbon material containing layer is 20% or more and 100% or less. If the ratio of the area which a glass layer occupies is in the said range, the thermal resistivity of the thickness direction of a heat conductive sheet can fully be reduced, integrating carbon material content layers well.
In addition, in this invention, "the ratio of the area which a glass layer occupies on a carbon material containing layer" can be measured using the method as described in the Example of this specification.

  And as for the heat conductive sheet of this invention, it is preferable that the said carbon material content layer consists of a graphite sheet. If a graphite sheet is used, a heat conductive sheet having a sufficiently low thermal resistance in the thickness direction and easily conducting heat in the thickness direction can be easily obtained.

  Moreover, this invention aims at solving the said subject advantageously, The manufacturing method of the heat conductive sheet of this invention is a manufacturing method of any of the heat conductive sheets mentioned above, Comprising: Carbon material A step (A) of obtaining a superposed body by applying a liquid composition containing a glass precursor on at least one superposed surface of the containing layers, and after the step (A), the liquid composition (B) which solidifies and forms a glass layer. Thus, if the liquid composition containing a glass precursor is used, the heat conductive sheet having a low thermal resistivity in the thickness direction and easy to conduct heat in the thickness direction can be easily obtained.

  Here, in the manufacturing method of the heat conductive sheet of this invention, it is preferable to press the said laminated body at a pressure (gauge pressure) 0.1 MPa or more and 30 MPa or less during the said process (B). In the step (B), if the stacked body is pressed at a pressure (gauge pressure) of 0.1 MPa or more and 30 MPa or less, the carbon material-containing layers are well integrated with each other, and the thickness direction of the obtained heat conductive sheet is obtained. The thermal resistivity can be further reduced.

  And in the manufacturing method of the heat conductive sheet of this invention, it is preferable that the said liquid composition is liquid glass. If liquid glass is used, the glass layer mentioned above can be formed easily.

  According to the present invention, a heat conductive sheet having a low thermal resistivity in the thickness direction can be obtained.

It is a perspective view which shows schematic structure of an example of the heat conductive sheet according to this invention.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the heat conductive sheet of this invention is not specifically limited, For example, it can be used for heat dissipation, such as an electronic device. And the heat conductive sheet of this invention can be manufactured, for example using the manufacturing method of the heat conductive sheet of this invention.

(Heat conduction sheet)
The heat conductive sheet of the present invention is obtained by laminating and integrating a plurality of carbon material-containing layers via a glass layer. Specifically, as shown in FIG. 1 of a schematic configuration of an example of the heat conductive sheet of the present invention, the heat conductive sheet 10 is adjacent to a plurality (four in the illustrated example) of carbon material-containing layers 1 in the stacking direction. And a total of three glass layers 2 positioned between the carbon material-containing layers 1, and the carbon material-containing layers 1 adjacent to each other in the stacking direction are integrated via the glass layer 2.
In addition, although the case where the lamination direction both ends consist of a carbon material containing layer was shown in the example shown in FIG. 1, as for the heat conductive sheet of this invention, the lamination direction one end or both ends may be comprised with the glass layer.

<Carbon material containing layer>
Here, the carbon material-containing layer is not particularly limited, and includes, for example, carbon materials such as graphite, carbon nanotubes, carbon nanohorns, fullerenes, and carbon fibers, and arbitrarily binds carbon materials together. Examples thereof include a layer further containing a material. The carbon material contained in the carbon material-containing layer is preferably graphite, carbon nanotube, or a mixture thereof, more preferably graphite, from the viewpoint of thermal conductivity.
In addition, the several carbon material content layer which a heat conductive sheet has may be mutually the same, or may differ.

Especially, it is preferable that a carbon material content layer is a layer which consists only of carbon materials from a viewpoint of fully reducing the thermal resistivity of the thickness direction of a heat conductive sheet. And, from the viewpoint of easily obtaining a heat conductive sheet that has a sufficiently low thermal resistance in the thickness direction and easily conducts heat in the thickness direction, the carbon material-containing layer is a carbon nanotube sheet that may be referred to as a bucky paper, Alternatively, it is preferably made of a graphite sheet, and more preferably made of a graphite sheet.
The graphite sheet is not particularly limited. For example, a graphite sheet obtained by heating and baking a polymer film such as polyimide in an inert gas (for example, PGS (registered trademark) manufactured by Panasonic Corporation). A graphite sheet or the like can be used.

The thickness of the carbon material-containing layer is preferably 1 μm or more, more preferably 10 μm or more, further preferably 20 μm or more, preferably 150 μm or less, and preferably 100 μm or less. More preferably, it is 80 μm or less. If the thickness of the carbon material-containing layer is not less than the above lower limit, a heat conductive sheet that can easily transfer heat in the thickness direction can be obtained. Moreover, if the thickness of a carbon material content layer is below the said upper limit, the heat resistivity of the thickness direction of a heat conductive sheet can fully be reduced.
The carbon material-containing layer is usually thicker than the glass layer. And in this invention, "the thickness of a carbon material content layer" can be measured using the method as described in the Example of this specification.

<Glass layer>
The glass layer is a layer capable of integrating the carbon material-containing layers adjacent to each other in the lamination direction, and is usually made of non-porous glass. If a glass layer made of non-porous glass is used, heat can be transmitted well in the thickness direction of the heat conductive sheet.

  In addition, it is preferable that a glass layer consists of glass obtained by solidifying liquid glass. Further, the glass layer may contain components other than glass such as a heat conductive filler (except for those corresponding to the above-mentioned carbon material).

  The glass layer needs to have a thickness of 0.5 μm or more and 50 μm or less, and the thickness of the glass layer is preferably 1 μm or more, more preferably 3 μm or more, and more preferably 5 μm or more. More preferably, it is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. When the thickness of the glass layer is less than 0.5 μm, the carbon material-containing layers adjacent to each other in the stacking direction cannot be well integrated, and the thermal resistivity in the thickness direction of the heat conductive sheet increases. Moreover, when the thickness of a glass layer exceeds 50 micrometers, the thermal resistivity of the thickness direction of a heat conductive sheet rises, and it becomes difficult to convey heat to the thickness direction of a heat conductive sheet. And if the thickness of a glass layer is more than the said lower limit, the carbon material containing layer adjacent to a lamination direction can be favorably integrated, and the thermal resistivity of the thickness direction of a heat conductive sheet can be reduced. Moreover, if the thickness of the glass layer is not more than the above upper limit value, it is possible to suppress an increase in thermal resistivity in the thickness direction of the heat conductive sheet due to the glass layer while suppressing a decrease in productivity of the heat conductive sheet. can do.

  Further, the ratio of the area occupied by the glass layer on the carbon material-containing layer is preferably 20% or more, more preferably 50% or more, still more preferably 70% or more, and usually 100% or less. It is preferable that it is 90% or less. If the area ratio of a glass layer is more than the said lower limit, the carbon material containing layers adjacent to a lamination direction can be favorably integrated, and the thermal resistivity of the thickness direction of a heat conductive sheet can be reduced. Moreover, if the area ratio of a glass layer is below the said upper limit, it can suppress that the thermal resistivity of the thickness direction of a heat conductive sheet rises resulting from a glass layer.

<Thickness of heat conductive sheet>
The thickness of the heat conductive sheet is not particularly limited, but is preferably 60 μm or more, more preferably 100 μm or more, preferably 200 μm or less, and more preferably 180 μm or less. preferable. If the thickness of a heat conductive sheet is more than the said lower limit, heat can be diffused favorably in the thickness direction of a heat conductive sheet. Moreover, if the thickness of a heat conductive sheet is below the said upper limit, the fall of productivity of a heat conductive sheet can be suppressed.
In addition, in this invention, "the thickness of a heat conductive sheet" can be measured using the method as described in the Example of this specification.

(Method for producing heat conductive sheet)
Moreover, the manufacturing method of the heat conductive sheet of this invention is used when manufacturing the heat conductive sheet of this invention mentioned above, The liquid composition which contains a glass precursor in carbon material content layer at least on one overlapping surface. The method includes a step (A) of applying and stacking objects to obtain an overlapped body, and a step (B) of solidifying the liquid composition to form a glass layer.

<Carbon material containing layer>
Here, as a carbon material content layer, the thing similar to what was mentioned above as a carbon material content layer of the heat conductive sheet of this invention is mentioned. Among these, the carbon material-containing layer is preferably made of a carbon nanotube sheet or a graphite sheet, and more preferably made of a graphite sheet.

<Liquid composition>
The liquid composition containing the glass precursor is not particularly limited as long as it is liquid under conditions of a temperature of 25 ° C. and a pressure (absolute pressure) of 1 atm and can be solidified to form a glass layer. A liquid composition containing a glass precursor and optionally further containing a solvent and additives can be used. Among these, from the viewpoint of easy formation of the glass layer, it is preferable to use liquid glass as the liquid composition.
In addition, as a glass precursor contained in a liquid composition, tetraethoxysilane etc. are mentioned, for example.

  Here, the liquid glass is not particularly limited, and examples thereof include liquid glass containing silicon dioxide, alumina and a solvent, and liquid glass containing tetraethoxysilane, a metal catalyst and water. More specifically, as the liquid glass, for example, “Heatless Glass” manufactured by Bokuto Kasei Kogyo Co., Ltd., “Shidakushitar B4373”, “Fine Crystal (Quartz for NOM series)” manufactured by Mokutech Kamemura Co., Ltd., etc. Can be used.

<Process (A)>
In step (A), when a plurality of carbon material-containing layers are overlapped to obtain an overlapped body, the liquid composition is applied to at least one overlapping surface of the carbon material-containing layers that are overlapped with each other. That is, in the step (A), a plurality of carbon material-containing layers are overlapped with a liquid composition interposed therebetween to obtain an overlapped body. When three or more carbon material-containing layers are overlaid, an overlapping body may be obtained by alternately repeating the application of the liquid composition and the carbon material-containing layer, or the liquid composition An overlapped body may be obtained by overlapping a plurality of carbon material-containing layers coated with an object at a time.

  Here, the method for applying the liquid composition to the superposed surface in the step (A) is not particularly limited, and may be any one of dripping, spray coating, roll coating, spin coating, gravure coating, die coating, bar coating, and the like. The coating method can be used.

  In the step (A), since the liquid composition is applied, it is possible to satisfactorily prevent the carbon material from falling off (powder off) from the carbon material-containing layer during superposition.

<Process (B)>
In the step (B), the liquid composition applied in the step (A) is solidified to form a glass layer, and the multiple carbon material-containing layers that are overlaid are integrated via the glass layer. In addition, what is necessary is just to select the method of solidifying a liquid composition according to the kind of liquid composition, for example, the method of drying and hardening a liquid composition is mentioned.

  Here, in the step (B), it is preferable to press the laminated body in the stacking direction after the liquid composition is arbitrarily dried and before or during the curing reaction. If the stacked body is pressed in the laminating direction, the carbon material-containing layers can be brought into close contact with each other, and the thermal resistivity in the thickness direction of the obtained heat conductive sheet can be further reduced. And the pressure (gauge pressure) at the time of pressing a laminated body is not specifically limited, It is preferable that it is 0.1 MPa or more, It is more preferable that it is 0.5 MPa or more, It is 50 MPa or less. Is preferable, and it is more preferable that it is 30 MPa or less. If a press pressure is more than the said lower limit, carbon material content layers can be integrated further more favorably and the heat resistance of the thickness direction of the heat conductive sheet obtained can be reduced further. Moreover, if a press pressure is below the said upper limit, the heat conductive sheet with low heat resistance of the thickness direction can be manufactured efficiently.

  In step (B), after pressing the overlapped body, the pressed overlapped body may be allowed to stand to further advance the curing reaction.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
In Examples and Comparative Examples, the carbon material-containing layer, the thickness of the glass layer and the heat conductive sheet, the area ratio of the glass layer, the peel strength of the carbon material-containing layer, and the thermal resistivity in the thickness direction of the heat conductive sheet are as follows: It was measured or evaluated by the method.

<Thickness>
The thickness of the heat conductive sheet and the carbon material-containing layer was measured with an accuracy of 1/1000 mm using a digimatic indicator (ID-C112X, manufactured by Mitutoyo Corporation).
Moreover, the thickness of the glass layer was calculated | required using the sample for a measurement obtained by cut | disconnecting a heat conductive sheet into 1 cm square. Specifically, for each measurement sample, the thickness of the central part was measured with a digimatic indicator (ID-C112X, manufactured by Mitutoyo Corporation), and the total thickness of the carbon material-containing layer was subtracted from the measured value. The thickness of the glass layer of each measurement sample was determined by dividing by the total number of glass layers. And the average value of the thickness of the calculated glass layer of each measurement sample was calculated | required, and it was set as the thickness of the glass layer of a heat conductive sheet.
<Area ratio of glass layer>
The carbon material-containing layer was peeled off, and the area of the glass layer formed on the carbon material-containing layer was determined by observing with a laser microscope (manufactured by Keyence Corporation, VK-X200), and the area ratio of the glass layer was calculated.
<Peel strength>
The prepared measurement sample was cut into a width of 10 mm, and the force required to pull and peel the carbon material-containing layer located on one surface side in the 90 ° direction was measured. The measurement was carried out with a length of 25 mm, and the average value was evaluated as the peel strength based on the following criteria. A universal tensile / compression tester (manufactured by Shinsei Tsushin Kogyo Co., Ltd., TCM-500CR) was used as the measuring device, and the tensile speed during measurement was 20 mm / second.
The larger the peel strength, the better the carbon material-containing layers are closely adhered and integrated.
A: Peel strength is 2.0 N / 25 mm or more B: Peel strength is 1.5 N / 25 mm or more and less than 2.0 N / 25 mm C: Peel strength is 1.0 N / 25 mm or more and less than 1.5 N / 25 mm D: Peel strength is <1.0N / 25mm <Thermal resistivity>
About the measurement sample obtained by cutting the heat conductive sheet into 1 cm square, a pressure of 0.3 MPa was applied at a sample temperature of 50 ° C. using a resin material thermal resistance tester (manufactured by Hitachi Technology & Service Co., Ltd.). The thermal resistance value R (K / W) at the time was measured. Then, the thermal resistance value R was divided by the thickness d of the heat conductive sheet to obtain the thermal resistivity R / d (K / W · μm), and the following criteria were used for evaluation.
A: R / d is less than 0.004 K / W · μm B: R / d is 0.004 K / W · μm or more and less than 0.006 K / W · μm C: R / d is 0.006 K / W · μm or more Less than 0.008 K / W · μm D: R / d is 0.008 K / W · μm or more

Example 1
As the carbon material-containing layer, a sheet obtained by cutting a 25-μm-thick graphite sheet (PGS (registered trademark) graphite sheet, manufactured by Panasonic Corporation) into a 3 cm square was prepared.
In addition, liquid glass (manufactured by Moctec Kamemura Co., Ltd., fine crystal for NOM) was prepared as a liquid composition.
Then, at a total of five locations including the center of the prepared sheet and the intermediate positions (four points) between the center of the sheet and the four corners, 4 liquid glasses were used with a micropipette (Eppendorf, variable volume micropipette, Research Plus). The operation of dropping 0.0 μL at a time and overlaying the sheets thereon was repeated three times to obtain a superposed body in which four sheets were superposed with liquid glass interposed.
Thereafter, the liquid glass was dried at room temperature (23 ° C.) for 6 hours, and the laminated body was pressed with a press at a pressure of 0.1 MPa for 2 hours. Thereafter, the pressed laminate was taken out and allowed to stand at room temperature for 2 days to cure the liquid glass to obtain a heat conductive sheet.
And the thickness of a carbon material content layer, a glass layer, and a heat conductive sheet, the area ratio of a glass layer, and the thermal resistivity of the thickness direction of a heat conductive sheet were measured and evaluated. The results are shown in Table 1.
In addition, for the measurement of peel strength, a micropipette (Eppendorf, variable volume micropipette, Research Plus) is provided at a total of five locations: the center of the prepared sheet and the middle position (4 points) between the center of the sheet and the four corners. Then, 4.0 μL of liquid glass was dropped at a time, and a sheet was superimposed thereon, and an overlapped body for peel strength measurement was obtained in which two sheets were overlapped with the liquid glass interposed.
Thereafter, the liquid glass was dried at room temperature (23 ° C.) for 6 hours, and the laminate for measuring peel strength was pressed with a press at a pressure of 0.1 MPa for 2 hours. Thereafter, the pressed laminate for measuring peel strength was taken out and allowed to stand at room temperature for 2 days to cure the liquid glass to obtain a sample for measuring peel strength. And peel strength was measured and evaluated. The results are shown in Table 1.

(Example 2)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 1 except that the pressure when pressing the laminated body was changed to 2 MPa. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 2 except that the amount of liquid glass dropped was changed to 1.0 μL. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 2 except that the dropping amount of liquid glass was changed to 2.0 μL. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 1 except that the dripping amount of the liquid glass was changed to 10.0 μL each and the laminated body was not pressed. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 1 except that the sheets were stacked without dropping the liquid glass and the stacked body was not pressed. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
A graphite sheet having a thickness of 100 μm (manufactured by Panasonic Corporation, PGS (registered trademark) graphite sheet) was cut into 3 cm square to obtain a heat conductive sheet. And the thermal resistivity of the thickness direction of a heat conductive sheet was measured and evaluated. The results are shown in Table 1.

(Comparative Example 3)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 1 except that the sheet was overlapped with a double-sided tape having a thickness of 10 μm (NeoFix Corporation, NeoFix 10) instead of liquid glass. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 4)
A heat conductive sheet and a sample for measuring peel strength were prepared in the same manner as in Example 2 except that the amount of liquid glass dropped was changed to 0.5 μL. Measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

  From Table 1, it can be seen that in the heat conductive sheets of Examples 1 to 5, the thermal resistivity in the thickness direction can be sufficiently reduced. On the other hand, in Comparative Examples 1 to 3 in which the glass layer was not used and Comparative Example 4 in which the glass layer was thin, it was found that the thermal resistivity in the thickness direction increased. In particular, in Comparative Examples 1 and 4, it can be seen that the adhesion between the carbon material-containing layers is reduced and the thermal resistivity is remarkably increased.

  According to the present invention, a heat conductive sheet having a low thermal resistivity in the thickness direction can be obtained.

DESCRIPTION OF SYMBOLS 1 Carbon material containing layer 2 Glass layer 10 Thermal conductive sheet

Claims (6)

A plurality of carbon material-containing layers are laminated and integrated via a glass layer,
The heat conductive sheet whose thickness of the said glass layer is 0.5 micrometer or more and 50 micrometers or less.   The heat conductive sheet of Claim 1 whose ratio of the area which the said glass layer occupies on the said carbon material content layer is 20% or more and 100% or less.   The heat conductive sheet according to claim 1, wherein the carbon material-containing layer is made of a graphite sheet. It is a manufacturing method of the heat conductive sheet in any one of Claims 1-3,
The carbon material-containing layers are overlapped by applying a liquid composition containing a glass precursor on at least one overlapping surface to obtain an overlapping body (A);
After the step (A), a step (B) of solidifying the liquid composition to form a glass layer;
The manufacturing method of the heat conductive sheet containing this.   The manufacturing method of the heat conductive sheet of Claim 4 which presses the said laminated body at a pressure (gauge pressure) 0.1 MPa or more and 30 MPa or less during the said process (B).   The manufacturing method of the heat conductive sheet of Claim 4 or 5 whose said liquid composition is liquid glass.

Images