JP2013102180A - Thermal diffusion sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal diffusion sheet having good thermal conductivity in a thickness direction, small reduction of adhesive strength, and high reliability and low cost obtained by sealing edge surfaces of a graphite sheet.SOLUTION: A thermal diffusion sheet (21) is laminated with a graphite sheet (11) and thermally conductive adhesive layers (12, 14). The thermally conductive adhesive layers (14) are directly adhered on both main surfaces of the graphite sheet (11). Hardness of the thermally conductive adhesive layers (14) on both surfaces of the graphite sheet is 60 or less in the measurement of ASTM D2240 type C, and a tack force reduction rate is 20% or less even after the thermally conductive adhesive layers are exposed at 40°C for 168 hours or more. Edge surfaces of the graphite sheet are sealed. Thereby, the thermal diffusion sheet having good thermal conductivity in a thickness direction, small reduction of adhesive strength, and high reliability and low cost can be provided.

Description

  The present invention relates to a heat diffusion sheet for diffusing heat from heat generating parts of semiconductor components such as light emitting diodes (LEDs), image display devices such as plasma displays (PDP) and liquid crystal display devices (LCDs).

  Computers (CPUs), transistors, semiconductors such as light emitting diodes (LEDs), plasma displays (PDPs), liquid crystal display devices (LCDs), etc. generate heat during use, and the performance of electronic components may deteriorate due to the heat. . Therefore, a heat radiator is attached to an electronic component that generates heat. Graphite sheets are known to have very good lateral thermal conductivity. Utilizing this thermal conductivity as a heat dissipating material has been conventionally known. The graphite sheet alone is fragile and difficult to handle, so it is reinforced with a film and at the same time has an electrical insulation. In order to actually mount the heat-dissipating sheet, it is necessary to temporarily fix the heat-dissipating sheet to the heat generating element or the heat dissipating element, and it has been proposed to provide an adhesive layer by directly mounting an adhesive on a double-sided tape or a graphite sheet. Patent Document 1). Examples in which the graphite sheet is applied to a light emitting diode or a liquid crystal display (LCD) are proposed in Patent Documents 2 to 3.

  On the other hand, graphite sheets are conductive and fragile, and when semiconductors are mounted on an electric circuit, the graphite powder peeled off from the conductive graphite sheet may fall on the electric circuit and cause a short circuit. is there. In order to solve such a problem, Patent Document 4 proposes that a support film is disposed on both surfaces of a graphite sheet and a spacer is inserted on the end surface to integrate them.

However, in Patent Document 4, since the adhesive layer itself is thermally insulating, further improvement with respect to heat conduction is necessary. In general, a double-sided tape is often used in which a thin film is the core and an adhesive layer is provided on both sides. The significance of reinforcing the graphite sheet is great, but unless the film is inserted as a core, the graphite sheet absorbs the substance constituting the adhesive layer, and thus there is a problem that the adhesive force decreases with time. In particular, when the adhesive layer is directly provided on the graphite sheet, the decrease in the adhesive strength with time is conspicuous. In addition, many double-sided tapes and adhesives have low thermal conductivity. Even if a graphite sheet with a large lateral thermal conductivity is used, if the thermal conductivity of the material to reach the graphite sheet is low, it will be `` conducting heat. "Is not preferable in terms of efficiency."
JP-A-11-317480 JP 2007-108547 A JP 2008-028352 A JP 2007-044994 A

  In order to solve the above-mentioned conventional problems, the present invention has a good thermal conductivity in the thickness direction, a small decrease in adhesive force, and a highly reliable and inexpensive thermal diffusion sheet by sealing the end face of the graphite sheet. I will provide a.

  The thermal diffusion sheet of the present invention is a thermal diffusion sheet in which a graphite sheet and a thermal conductive adhesive layer are laminated, and the thermal conductive adhesive layer is directly bonded to both surfaces of the main surface of the graphite sheet, The hardness of the heat conductive adhesive layer on both sides is 60 or less as measured by ASTM D2240 Type C, and the tack reduction rate is 20% even after the heat conductive adhesive layer is exposed at 40 ° C. for 168 hours or more. It is the following, The end surface of the said graphite sheet is sealed, It is characterized by the above-mentioned.

  INDUSTRIAL APPLICABILITY The present invention can provide an inexpensive thermal diffusion sheet that has good thermal conductivity in the thickness direction, little reduction in adhesive strength, and high reliability.

FIG. 1 is a cross-sectional view showing a manufacturing process of a thermal diffusion sheet in Examples 1 to 4 of the present invention. FIG. 2 is a plan view showing a punching die used in the manufacturing process of the thermal diffusion sheet in the same example. FIG. 3A is a plan view showing a manufacturing process of the thermal diffusion sheet in the same example, and FIG. 3B is a sectional view of the same. FIG. 4 is a cross-sectional view showing the manufacturing process of the thermal diffusion sheet in the same example. FIG. 5 is a cross-sectional view showing a manufacturing process of the thermal diffusion sheet in the same example. FIG. 6A is a plan view showing the manufacturing process of the thermal diffusion sheet in the example, and FIG. 6B is a sectional view of the same. FIG. 7 is a plan view showing a manufacturing process of the thermal diffusion sheet in the same example. FIG. 8A is a plan view showing a manufacturing process of the thermal diffusion sheet in the same example, and FIG. 8B is a sectional view of the same. FIG. 9 is a cross-sectional view showing a manufacturing process of the thermal diffusion sheet in Comparative Examples 1 to 4. FIG. 10A is a plan view showing a manufacturing process of a thermal diffusion sheet in Examples 5 to 6 of the present invention, and FIG. 10B is a sectional view thereof. FIG. 11 is a plan view showing a manufacturing process of the thermal diffusion sheet in the same example. FIG. 12A is a plan view showing a manufacturing process of the thermal diffusion sheet in the example, and FIG. 12B is a sectional view of the same. FIG. 13A is a plan view showing a heat dissipation device in one application example of the present invention, and FIG. 13B is a sectional view of the same.

  The graphite sheet is produced by a method of graphitizing a polymer film, a method of forming natural graphite or expanded graphite into a powder, and forming the sheet by rolling. The method of graphitizing a polymer film is characterized by high lateral thermal conductivity. The method of making natural graphite and expanded graphite into powder and rolling them into a sheet is characterized by being inexpensive. In the case of thermal diffusion, it is sufficient to have a certain degree of thermal conductivity. Therefore, it is preferable to use a graphite sheet by a method in which natural graphite and expanded graphite are powdered and formed into a sheet by rolling. A preferable thickness of the graphite sheet is 60 to 500 μm. Further, the thermal conductivity in the lateral direction of the graphite sheet is 120 W / m · K or more and 1200 W / m · K or less.

  The polymer content of the heat conductive adhesive layer is preferably polysiloxane, polyacryl, or polyolefin. Among these, polysiloxane is preferable from the viewpoint of heat resistance and ease of filling with a filler. However, depending on the application, polyacryl or polyolefin may be selected. The polymer preferably has rubber elasticity after curing, but may be a pressure-sensitive adhesive. In particular, the silicone pressure-sensitive adhesive is preferable because it is composed of a resin called a resin and gum, which is a kind of polysiloxane, and has higher heat resistance than polyacryl and polyolefin.

  Fillers added to the polymer include metal oxides and ceramic powders, and the fillers themselves are preferably electrically insulating. There are various types and shapes of metal oxides and ceramic powders, and known ones can be used. Furthermore, these may be subjected to a surface treatment. Further, an insulating film can be formed on a filler having no electrical insulating property to provide an electrical insulating property. The amount of filler added to the polymer is preferably 100 to 3000 parts by weight of filler with respect to 100 parts by weight of polymer. When the filler is added too much, the adhesiveness of the heat conductive adhesive layer is lowered, so the balance with the thermal conductivity is important.

  You may add a plasticizer to a polymer as needed. However, since the graphite sheet easily absorbs oil, the composition of the heat conductive adhesive layer bonded to the graphite sheet is changed and the adhesiveness is likely to be lowered. In addition to the filler, a flame retardant, a heat-resistant agent, a pigment, a vulcanizing agent, and a curing agent can be added to the polymer.

  The thickness of the heat conductive adhesive layer is preferably 20 to 300 μm. The thickness of the single-sided adhesive film or double-sided tape that seals one side of the graphite sheet is preferably 8 to 110 μm. Colored ones may be used for the single-sided adhesive film or double-sided tape. In addition, another heat conductive adhesive layer may be placed instead of the double-sided tape. The thickness is preferably 20 to 300 μm. Therefore, the total thickness of the product is in the range of 90 to 1100 μm, but a more preferable thickness is 90 to 250 μm.

  When the heat conductive adhesive layer is bonded to both sides of the graphite sheet, the same material may be bonded, or another material may be bonded. In the case of bonding another material, it is preferable that at least one surface needs adhesiveness, but the other surface has no adhesiveness. When a heat-conductive adhesive layer having a strong adhesive force is defined as a tack (adhesive) surface, it is preferable that there is a difference of 15% or more between the tack surface and the non-tack surface.

  It is preferable that the heat conductive adhesive layer material which is not a tack surface has lower thermal conductivity than the heat conductive adhesive layer material which is a tack surface. A preferable difference in thermal conductivity is 1 W / m · K or more. Moreover, it is preferable that the heat conductive adhesive layer material which is not a tack surface has higher hardness than the heat conductive adhesive layer material which is a tack surface. In some cases, the end face of the graphite sheet is sealed with a heat conductive adhesive layer material that is not a tack surface. The greater the rubber component, the lower the rubber hardness, the greater the adhesion to the graphite sheet. This is because the layer material is difficult to peel off. It is preferable that the hardness of the heat conductive adhesive layer material which is not the tack surface and the tack surface is different by 10 or more. That is, the hardness of the heat conductive adhesive layer material that is not the tack surface is preferably 10 or more higher than the hardness of the heat conductive adhesive layer material that is the tack surface. The hardness is defined as measured by ASTM D2240 type C. For the above reasons, the same can be said for the end face of the graphite sheet.

  The thermal emissivity of a graphite sheet varies depending on the method for producing the graphite sheet. In the method such as rolling, the surface becomes a mirror surface and the emissivity is lowered. Polymer products such as tape have an emissivity of 0.5 or more. In recent years, thermographs are often used for heat countermeasures. If the emissivity is not set when using the thermograph, accurate thermal analysis cannot be performed. Therefore, specifying the emissivity helps thermal analysis.

  The method of applying a single-sided adhesive film or double-sided tape to the graphite sheet is preferably a laminate. This is because, if a rolled product of graphite sheet is prepared, a film with a single-sided adhesive or a double-sided tape and a graphite sheet can be bonded continuously. Moreover, since the integrated product which stuck the film with a single-sided adhesive or the double-sided tape on the graphite sheet is marketed, you may use these.

  There are a knife coater, rolling, pressing, laminating, screen printing, and the like as methods for placing the heat conductive adhesive layer on the graphite sheet, and any of them may be used. In some cases, the heat conductive adhesive layer material may be diluted with a solvent or the like, converted into ink or paste, and placed on the graphite sheet.

  In order to strengthen the adhesion by placing a heat conductive adhesive layer, a single-sided adhesive film or a double-sided tape on the graphite sheet, a primer treatment may be performed as necessary. The primer treatment agent can be selected depending on the type of polymer to be selected.

  The end surface of the graphite sheet is sealed. A preferable example of sealing is that a single-sided adhesive film or double-sided tape is bonded to one side of the graphite sheet to be slightly larger than the graphite sheet, and the opposite side of the thermally conductive adhesive layer is the same size as the graphite sheet. The single-sided adhesive film or the double-sided adhesive film is attached to the size of the single-sided adhesive film or double-sided tape so as to overlap a part of the thermally conductive adhesive layer. In addition, it is preferable that the single-sided adhesive film or double-sided tape to be attached to one side of the graphite sheet is 2 to 5 mm larger than one side of the graphite sheet. Furthermore, the single-sided adhesive film that is pasted so as to overlap a part of the thermally conductive adhesive layer is pasted so as to overlap 1 to 5 mm with respect to one side of the thermally conductive adhesive layer, but the single-sided adhesive film or double-sided tape that is pasted on one side of the graphite sheet The size of the outer periphery is preferably the same. When viewed from above, it is preferably a frame shape. This does not apply when attaching a screw hole or an outlet.

  The end face of the graphite sheet can be sealed with a heat conductive adhesive material. In this case, a heat conductive adhesive material having the same size as that of the graphite sheet is bonded to one side of the graphite sheet, and the heat conductive adhesive layer on the opposite side is bonded larger than the graphite sheet. In order to seal the end face of the graphite sheet, the size of the thermally conductive adhesive layer to be sealed is preferably 2 to 5 mm larger than one side of the graphite sheet.

  The thermal conductivity of the heat conductive adhesive layer is preferably 0.7 W / m · K or more and 20 W / m · K or less. Within this range, heat transfer and diffusion from the heat generating part is practically sufficient. Moreover, it is preferable that the thermal emissivity of the said graphite sheet is 0.3-0.95, and the thermal emissivity of parts other than the said graphite sheet is 0.50 or more. If it is in this range, the movement and diffusion of heat from the heat generating part is also practically sufficient.

  The heat diffusion sheet may be wound on a reel. The reel winding specification is a specification in which heat diffusion sheets are neatly arranged on a long film. Although there are various specification forms, the heat diffusion sheet is held on the long film with self-adhesiveness, the heat diffusion sheet is regularly cut or punched out, etc., and finally the roll form Is preferred. As a result, the work of applying the heat diffusion sheet can be automated.

  The heat diffusion sheet of the present invention is provided with a heat conductive adhesive layer directly on the graphite sheet, and is less expensive with less decrease in tack force. Further, since the end face of the graphite sheet is sealed, the graphite powder does not peel from the graphite sheet, and there is no fear of short circuit even in mounting on an electric circuit, and a reliable thermal diffusion sheet can be provided.

Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to the following examples.
The heat conductive adhesive layer was prepared as follows.

(Thermal conductive adhesive material 1)
200 parts by weight of alumina (AS20: Showa Denko) and 5 parts by weight of iron oxide are added to 100 parts by weight of silicone polymer (XE14-C2068: Momentive Performance Materials), and defoamed for 10 minutes with a planetary mixer. The mixture was stirred to obtain a compound (mixture).

(Thermal conductive adhesive material 2)
200 parts by weight of alumina (AS20: Showa Denko), 1.2 parts by weight of cross-linking agent (CR300: Kaneka) and 100 parts by weight of polyisobutylene polymer (EP200A: Kaneka), platinum catalyst: PT-VTSC -3.0 IPA (Humicore Precious Metals Japan) 0.3 parts by weight, retarder: Surfinol 61 (Nissin Chemical Industry) 0.1 parts by weight, iron oxide 5 parts by weight, planetary The mixture was stirred while defoaming for 10 minutes to obtain a compound.

(Thermal conductive adhesive material 3)
Planetary by adding 100 parts by weight of alumina (AS20: Showa Denko), 5 parts by weight of iron oxide and 80 parts by weight of xylene to 110 parts by weight of silicone adhesive (TSR1510: manufactured by Momentive Performance Materials) The mixture was stirred for 10 minutes with a mixer to obtain a coating solution.

(Thermal conductive adhesive material 4)
100 parts by weight of alumina (AS20: Showa Denko KK) and 100 parts by weight of cross-linking agent (TSF484: Momentive Performance Materials) with respect to 100 parts by weight of silicone polymer (XE14-C2068: Momentive Performance Materials) Part by weight and 5 parts by weight of iron oxide were added, and the mixture was stirred for 10 minutes while defoaming with a planetary mixer to obtain a compound.

(Adhesive material)
50 parts by weight of xylene was added to 110 parts by weight of a silicone adhesive (TSR1510: manufactured by Momentive Performance Materials) to obtain a coating solution.

  The physical properties of the adhesive material and the heat conductive adhesive materials 1 to 4 are summarized in Table 1.

Hardness: Measured with ASTM D2240 type C.
Thermal conductivity: ASTM D5470
Adhesive strength: JIS Z0237 (aluminum plate to be bonded)
A test sample for measuring the adhesive strength was prepared as follows.
(Materials A and B)
A heat conductive adhesive material was sandwiched between a polyester film subjected to a fluorine release treatment and an untreated polyester film having a thickness of 100 μm, and the untreated polyester film surface was heated by a press at 120 ° C. for 60 minutes. After cooling, the polyester film that had been subjected to the fluorine release treatment was peeled off to bond the heat conductive adhesive layer to a thickness of 0.1 mm.
(Materials C and D)
The coating solution was applied to an untreated polyester film having a thickness of 100 μm by knife coating. This was air-dried for 30 minutes and further cured at 120 ° C. for 10 minutes. The adhesive thickness was 50 μm.

In addition to the above heat conductive adhesive materials A to D and the adhesive material E, the following were prepared to prepare a heat diffusion sheet.
(1) Graphite sheet (TYK graphite sheet: Akechi Ceramics) Thickness 80 μm, 250 μm, thermal conductivity 400 W / m · K, emissivity 0.40
(2) Double-sided tape (thickness 30 μm: Nitto Denko Corporation)
(3) Single-sided adhesive film (thickness 30 μm: Nitto Denko Corporation)
(Examples 1-4)
Using the polyester film (3a, 3b) that has been subjected to the fluorine release treatment, the graphite sheet (1) of each thickness and the heat conductive adhesive layer A or B (2) are sandwiched from above and below, and the graphite sheet (1) The heat conductive adhesive layer (2) was integrated with a thickness of 0.1 mm by heating at 120 ° C. for 60 minutes only on one side (FIG. 1). Next, the polyester film (3a) on the graphite sheet (1) surface side was removed, and the polyester film on the heat conductive adhesive material side was punched with a punching die (9) shown in FIG. Subsequently, the burr portion was removed (FIG. 3).

  After removing the burrs, the double-sided tape or single-sided adhesive film (4) was laminated from above so that air would not enter. Next, the polyester film (3b) on the heat conductive adhesive layer (2) side was peeled off (FIG. 5). Next, a single-sided adhesive film (5) slit to several millimeters in width is used to fill the end surface of the graphite sheet (1) and to overlap a part of the heat conductive adhesive layer (2). (FIG. 6A). 6B is a cross-sectional view taken along the line II of FIG. 6A.

  Next, the intermediate part of the single-sided adhesive film (5) attached so as to fill the end face part of the graphite sheet (1) was fully cut as indicated by a cut line (8) (FIG. 7). Finally, a protective cover (6) was placed on the heat conductive adhesive layer (2) to obtain a heat diffusion sheet product (10) in which the end face of the graphite sheet (1) was sealed (FIG. 8A). 8B is a cross-sectional view taken along the line II-II in FIG. 8A.

  The above is a method for creating a full cut product, but it is also possible to create a specification in which heat diffusion sheets are arranged on a mount.

(Comparative Examples 1-4)
An adhesive material or a heat conductive adhesive material C was applied to the same graphite sheet used in Example 1 with a knife coat. This was air-dried for 30 minutes and further cured at 120 ° C. for 10 minutes. The adhesive thickness is 50 μm. A fluorine release film was pasted on the adhesive surface (FIG. 9). Except this, the thermal diffusion sheet was created similarly to Examples 1-4. Table 2 shows the experimental results of the thermal diffusion sheet obtained by these methods.

The measurement method is as follows.
(Thermal resistance value)
According to ASTM D5470.
(LED temperature)
A circuit was made with an LED with 5 W output and a power source (0.6 A current, 10 V voltage). A thermal diffusion sheet was cut out to a width of 25 mm and a length of 100 mm on a stainless steel plate having a thickness of 5 mm. One LED was fixed using the adhesion of the heat diffusion sheet. The fixing place was a tip having a width of 25 mm and a length of 100 mm. Two hours after turning on the power, the heat generation temperature of the LED was measured with a thermograph (Apiste).
(Insulation)
A terminal was applied to the end face of the heat diffusion sheet with an ohmmeter, and the electrical resistance value at that time was measured.
(Adhesive force)
The measurement method conformed to JIS Z0237. The adherend was an aluminum plate. For the exposure, the thermal diffusion sheet was cut out to a width of 25 mm and a length of 100 mm, the adhesive surface was exposed, and the upper surface was exposed in a hot air circulation oven at 100 ° C. for 168 hours.

  From the above results, Examples 1 to 4 of the present invention had a low thermal resistance value and good thermal conductivity, and there was little decrease in adhesive strength when exposed to hot air. On the other hand, Comparative Examples 1 and 2 were not preferable because the thermal resistance value was high and the LED temperature was high because there was no filler of the thermally conductive adhesive material. Moreover, the fall of the adhesive force when it exposed to hot air was not preferable for Comparative Examples 3-4.

  Furthermore, one side of the graphite sheet is bonded with a heat conductive adhesive material, and the other side is bonded with another heat conductive adhesive material, and the end surface of the graphite sheet is sealed with the heat conductive adhesive material itself. A thermal diffusion sheet was created.

(Examples 5-6)
A polyester sheet (13) subjected to a fluorine release treatment is sandwiched between a graphite sheet (11) having a predetermined thickness and a heat conductive adhesive layer (12) up and down, and only one side of the graphite sheet (11) surface is pressed at 120 ° C., The heat conductive adhesive layer (12) was provided with a thickness of 0.1 mm by heating for 60 minutes. The polyester film on the graphite sheet (11) surface side was removed, and the polyester film 13 on the heat conductive adhesive material side was punched out with a punching die (9) shown in FIG. Subsequently, the burr portion was removed. Next, a heat conductive adhesive material is poured onto the graphite sheet surface, covered with a polyester film that has been subjected to a fluorine release treatment, and heated by a press at 120 ° C. for 60 minutes, so that the heat conductive material D has a thickness of 0.1 mm. A heat conductive adhesive layer (14) was provided. At this time, the end surface of the graphite sheet (11) was sealed with the heat conductive adhesive layer (14). Next, the polyester film subjected to the fluorine release treatment on the heat conductive adhesive layer (14) side was peeled off (FIG. 10A). 10B is a cross-sectional view taken along line III-III in FIG. 10A.

  Next, a blade was inserted into the groove and cut (FIG. 11). Reference numeral 15 denotes a cut line.

  Finally, a protective cover (16) was placed on the heat conductive adhesive layer (14) to obtain a thermal diffusion sheet product (20) in which the end face of the graphite sheet (11) was sealed (FIG. 12A). 12B is a cross-sectional view taken along line IV-IV in FIG. 12A. In FIG. 12B, 21 is a thermal diffusion sheet portion when actually used.

(Comparative Examples 7-8)
Comparative Examples 7 to 8 are examples of thermal diffusion sheets in which only one side of the graphite sheet is pasted with a double-sided tape. A polyester film with a predetermined thickness of graphite sheet applied to a polyester film that has been subjected to fluorine release treatment, a double-sided tape with a thickness of 30 μm is applied, the release paper of the other double-sided tape is peeled off, and the surface is subjected to fluorine release treatment Was pasted and cut into a release mount.

  The above Examples 1-2, 5-6, and Comparative Examples 5-8 are summarized in Table 3.

From Tables 2-3, the following was found.
(1) In Comparative Examples 1 and 2, since a commercially available silicone adhesive material was directly bonded to a graphite sheet, the graphite sheet absorbs the plasticizer contained in the silicone adhesive material, so that the adhesive strength decreases with time. Recognize.
(2) When a filler is added to the silicone adhesive material as in Comparative Examples 3 and 4, the adhesive strength is significantly reduced with time.
(3) The thermal resistance values of Comparative Examples 1 and 2 were high because there was an adhesive layer with low thermal conductivity. Accordingly, the temperature of the LED was higher than that of Examples 1 to 6, which was not preferable.
(4) Since Comparative Examples 3 and 4 are adhesive materials having thermal conductivity and the thickness is small, the thermal resistance value is the same as in Examples 1 and 2, and the LED temperature is the same as in Examples 1 and 2. It became about.
(5) In Comparative Examples 5 and 6, the heat conductive adhesive material 1 is placed on one side of the graphite sheet, and the graphite sheet surface is exposed on the opposite side. The end face of the graphite sheet is not sealed. The difference from Examples 1 and 2 is that the end face of the graphite sheet is not sealed and there is no 30 μm single-sided adhesive film on one side. For this reason, the absence of a 30 μm single-sided adhesive film that obstructs heat transfer negates the increase in thermal resistance even though the contact thermal resistance with the graphite sheet has increased. Therefore, the temperature of the LED is lower than that of Examples 1 and 2. However, there is a problem that electricity flows because the end face is not sealed, and there is a problem that graphite powder is generated from the graphite sheet cut surface and falls when touched.
(6) In Comparative Examples 7 and 8, a double-sided tape of 30 μm is pasted on one side of the graphite sheet, and the graphite sheet side is exposed on the opposite side. The end face of the graphite sheet is not sealed. The difference from Examples 1 and 2 is that the end face of the graphite sheet is not sealed and there is no 30 μm single-sided adhesive film on one side. A simple double-sided tape is attached instead of the heat conductive adhesive material. For this reason, the absence of a 30 μm single-sided adhesive film that obstructs heat transfer negates the increase in the thermal resistance value despite the increase in the contact thermal resistance value with the graphite sheet. Therefore, it is lower than Examples 1 and 2. However, electricity flows because the end face is not sealed. Graphite powder is generated from the graphite sheet cut surface and falls when touched. This is the same as Comparative Examples 3 and 4.
(7) In contrast, Examples 1 to 6 were end-face sealed and no electricity flowed. Moreover, no graphite powder was generated. In addition, the heat generation temperature of the target LED tended to be low.

(Application examples)
The example which applied the thermal diffusion sheet | seat product (20) obtained in Examples 5-6 to the heat radiating device (30) is demonstrated using FIG. 13A-B. FIG. 13A is a plan view when a heat diffusion sheet portion (21) is interposed between a light bar (31) made of LEDs and a radiator (32), and FIG. 13B is a cross-sectional view thereof. The thermal diffusion sheet portion (21) is obtained by removing the release paper (13) and the protective cover (16) from the thermal diffusion sheet product (20) shown in FIG. 12B. The heat generated from the light bar (31) passed through the heat diffusion sheet portion (21) and efficiently moved to the radiator (32). In particular, the thermal diffusion sheet portion (21) was excellent in soaking.

1,11 Graphite sheets 2,12,14 Thermal conductive adhesive layers 3a, 3b Fluorine release polyester film 4 Double-sided tape or single-sided adhesive film 5 Single-sided adhesive film 6,16 Protective cover 8,15 Cut line 9 Punched Mold 10, 20 Thermal diffusion sheet product 13 Release paper 21 Thermal diffusion sheet portion 30 Heat dissipation device 31 Light bar (LED)
32 Heatsink

Claims (10)

A heat diffusion sheet in which a graphite sheet and a heat conductive adhesive layer are laminated,
The heat conductive adhesive layer is directly bonded to both surfaces of the main surface of the graphite sheet,
The hardness of the heat conductive adhesive layers on both sides is 60 or less as measured by ASTM D2240 Type C,
The tack reduction rate of the heat conductive adhesive layer is 20% or less even after exposure for 168 hours or more at 40 ° C.,
An end face of the graphite sheet is sealed.   The area of one of the heat conductive adhesive layers directly bonded to both surfaces of the main surface of the graphite sheet is wider than the other, and the end surface of the graphite sheet is covered with the heat conductive adhesive layer of the wide area. The thermal diffusion sheet according to claim 1, which is sealed.   There is a difference of 15% or more between the adhesive force of the heat conductive adhesive layer on the one surface and the adhesive force of the heat conductive adhesive layer on the other surface as measured by JIS Z0237 (adhered aluminum plate). Item 3. The thermal diffusion sheet according to Item 1 or 2.   The thermal diffusion sheet according to any one of claims 1 to 3, wherein there is a difference between the hardness of the thermally conductive adhesive layer on the one surface and the hardness of the thermally conductive adhesive layer on the other surface.   The thermal diffusion sheet according to claim 1, wherein an end face of the graphite sheet is sealed by attaching a non-adhesive film or an adhesive film to a surface including at least the end face of the graphite sheet.   The thermal diffusion sheet according to claim 1, wherein the polymer constituting the thermally conductive adhesive layer is polysiloxane, polyacryl, or polyolefin, and a thermally conductive filler is dispersed in the polymer.   The thermal diffusion sheet according to claim 1 or 6, wherein the thermal conductivity of the thermal conductive adhesive layer is 0.7 W / m · K or more and 20 W / m · K or less.   2. The thermal diffusion sheet according to claim 1, wherein the thermal conductivity of the graphite sheet in the lateral direction is 120 W / m · K or more and 1200 W / m · K or less.   The thermal diffusion sheet according to claim 1, wherein the thermal emissivity of the graphite sheet is 0.3 to 0.95, and the thermal emissivity of a portion other than the graphite sheet is 0.50 or more.   The thermal diffusion sheet according to claim 1, wherein the thermal diffusion sheet is wound on a reel.

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