JP2008291220A - Thermally conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive film having low heat resistance as well as tackiness. <P>SOLUTION: The thermally conductive film is constructed by applying a thermally conductive composition comprising a binder resin and a thermally conductive filler dispersed in the binder resin to both main surfaces of a metal foil to form a thermally conductive layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat conductive film. More specifically, the present invention relates to a heat conductive film that is applied to a heat dissipation system of an electronic device such as a personal computer (PC) and can efficiently conduct heat generated from a heat source to a heat radiator.

  Currently, in the field of electronic devices, cooling (heat radiation) technology that suppresses temperature rise when operating them is becoming important. In particular, while the volume of a PC is decreasing, the operating frequency of a CPU (central processing unit) mounted on the PC is increasing, and the power consumption of components other than the CPU is also increasing. The calorific value is rising rapidly. Therefore, efficient heat dissipation technology is required. In particular, a heat dissipation system that does not rely on air cooling by a fan is required in order to meet demands for quieting electronic devices and reducing power consumption.

As a typical heat dissipation technique in this technical field, a heat dissipation system is known in which an electronic device is provided with a heat sink made of aluminum or copper having high thermal conductivity. In this heat dissipation system, a technique for reducing a contact thermal resistance by interposing a heat conductive adhesive member made of a silicone gel sheet, silicone grease, or other various materials between an electronic device and a heat sink has been studied. As an example of the heat conductive adhesive member, a heat conductive adhesive tape containing an ethylene propylene elastic body, an isobutylene elastic body, and a heat conductive filler has been proposed (Patent Documents 1 and 2). As another example, a thermally conductive electrical insulating tape containing 20 to 400 parts by weight of thermally conductive particles with respect to 100 parts by weight of an acrylic adhesive has been proposed (Patent Document 3).
JP 52-118300 A U.S. Pat. No. 4,071,652 JP-A-6-88061

  In order to efficiently transfer heat generated from electronic equipment as a heat source to a heat sink, such as a heat sink, by applying a heat conductive adhesive member to the heat dissipation system, the adhesion of the member is increased and the adhesiveness to the heat source and heat sink is increased. It is desirable to improve the thermal resistance. However, any of the conventional heat conductive adhesive members has high heat resistance, and it is difficult to obtain good heat conductivity using them. Generally, it is possible to reduce the thermal resistance by reducing the thickness of the member. However, such a method has a limit because the strength decreases as the member is thinned, and not only the handleability is deteriorated, but also safety such as flame retardancy tends to be difficult. . Therefore, there is a need for a thermally conductive adhesive member that has both sufficient strength that facilitates handling and low thermal resistance that realizes efficient thermal conduction. In view of such a situation, an object of the present invention is to provide a heat conductive film having sufficient strength and low thermal resistance in addition to excellent adhesiveness.

  As a result of studies, the present inventors have found that a film-like structure using a metal foil having a high thermal conductivity as a support and having layers having adhesiveness and thermal conductivity on both main surfaces has good heat resistance. The present inventors have found that it can be a conductive member and have completed the present invention. That is, the present invention relates to the following.

  The heat conductive film of the present invention has a metal foil and a heat conductive resin layer provided on both main surfaces of the metal foil, and the heat conductive resin layer is included in the binder resin and the binder resin. And a dispersed heat conductive filler.

Here, the heat conductive filter preferably has a thermal resistance of 1.0 ° C. · cm ² / W or less and a peel adhesive strength of 0.1 N / 10 mm or more. The total thickness of the heat conductive film is preferably in the range of 50 to 200 μm, and the thickness of the metal foil is preferably 10 to 40 μm.

  Moreover, it is preferable that binder resin contained in a heat conductive resin layer is a thermoplastic resin, and the heat conductivity of a heat conductive filler is 10 W / mK or more. The thermally conductive filler preferably contains graphite.

  Moreover, it is preferable that a heat conductive film has the flame retardance of V-0 by UL-94 specification.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the heat conductive film excellent in the adhesiveness with respect to a heat source and a heat radiator, low thermal resistance, and excellent in the handleability. The heat conductive film according to the present invention is suitable for a heat dissipation system in an electric device, and the heat generated from the heat source is efficiently conducted to the heat radiating body to dissipate the heat, thereby suppressing the rapid temperature rise of the electric device and their reliability. It becomes possible to improve the nature.

Details of the present invention will be described below. FIG. 1 is a schematic cross-sectional view showing an embodiment of a thermally conductive film according to the present invention. As shown in FIG. 1, the heat conductive film 100 by this invention has the metal foil 101 and the heat conductive resin layer 102 provided in both the main surfaces of the metal foil 101, and the heat conductive resin layer 102 is shown. Is characterized by comprising a thermally conductive composition containing at least a binder resin and a thermally conductive filler. Considering application to electronic equipment, the thermal resistance of the thermally conductive film according to the present invention is preferably 1.0 ° C. · cm ² / W or less, and 0.8 ° C. · cm ² / W or less. Is more preferably 0.6 ° C. · cm ² / W or less. When the thermal resistance of the heat conductive film exceeds 1.0 ° C. · cm ² / W, it tends to be difficult to efficiently conduct the heat generated from the heat source to the radiator. The measurement of thermal resistance is not particularly limited, and can be performed according to a known method such as a temperature gradient method or a steady comparison method. The thermal resistance defined in the present invention is a value measured according to a temperature gradient method.

  Further, the peel adhesive strength of the heat conductive film according to the present invention is preferably 0.1 N / 10 mm or more, more preferably 0.15 N / 10 mm or more, and further preferably 0.2 N / 10 mm. . When the peel adhesive strength is less than 0.1 N / 10 mm, the adhesion to the heat source and the heat radiating body tends to decrease, and the contact thermal resistance tends to increase. In addition, the peeling adhesive force prescribed | regulated by this invention is the value of 90 degree peeling adhesive force measured according to JISZ0237.

  Furthermore, the heat conductive film according to the present invention preferably has a total film thickness of 50 to 200 μm, particularly preferably 50 to 150 μm. When the thickness of the heat conductive film is less than 50 μm, it becomes difficult to absorb irregularities on the surfaces of the heat source and the heat radiating body, and the contact thermal resistance tends to increase. Moreover, the malfunction that peeling adhesive force falls arises. On the other hand, if the thickness of the heat conductive film exceeds 200 μm, the thermal resistance of the film increases, and it tends to be difficult to efficiently conduct the heat generated from the heat source to the radiator.

  The heat conductive film of the present invention is typically prepared by applying a heat conductive composition containing at least a resin and a heat conductive filler to both main surfaces of a metal foil serving as a core material. Is possible. The heat resistance and peel adhesive strength of the heat conductive film are set appropriately for the thickness of the metal foil and the heat conductive resin layer provided on both main surfaces thereof, and the heat conductive composition constituting the heat conductive resin layer. It is possible to adjust by.

  More specifically, the metal foil serving as the core material in the thermally conductive film of the present invention is not particularly limited, and it is possible to use a metal, such as gold, copper, or aluminum, processed into a sheet shape. . Although it does not specifically limit, what heat-processed copper, aluminum in the sheet form is preferable at the point which is high in heat conductivity, is industrially mass-produced, and is easy to process. The thickness of such a metal foil is suitably in the range of 10 to 40 μm, preferably 10 to 30 μm, and more preferably 10 to 20 μm. When the thickness of the metal foil is less than 10 μm, the strength of the metal foil is reduced, and when the heat conductive resin layer is formed by coating the heat conductive composition on both main surfaces thereof, the twist, There is a tendency for the coating operation to be difficult due to breakage or tearing. On the other hand, if the thickness of the metal foil exceeds 40 μm, the thermal resistance of the heat conductive film itself increases, and it tends to be difficult to efficiently transfer the heat generated from the heat source to the heat radiating body.

  The heat conductive composition which comprises a heat conductive resin layer contains binder resin and a heat conductive filler at least. Although not particularly limited, it is preferable to use a thermoplastic resin as the binder resin. More specifically, it is preferable to use a rubber having a low glass transition temperature (Tg) excellent in handleability. The Tg of the rubber used is preferably 0 ° C to -50 ° C, more preferably -5 ° C to -45 ° C, and still more preferably -10 ° C to -45 ° C. Specific examples of the rubber are preferably acrylonitrile-butadiene rubber, acrylic rubber, rubber obtained by adding a functional group such as carboxyl group or epoxy group, natural rubber, silicone rubber, and the like. The above-mentioned acrylic rubber is a general term for rubbers mainly composed of acrylic acid esters, and typically includes a copolymer of butyl acrylate and acrylonitrile, a copolymer of ethyl acrylate and acrylonitrile, or the like. Containing rubber is included.

  The rubber described above is preferably a crosslinked product or has a weight average molecular weight (Mw) of 100,000 or more from the viewpoint of imparting appropriate strength to the heat conductive film. The Mw of the rubber to be used is more preferably 100,000 to 500,000, still more preferably 100,000 to 400,000. When the Mw of the rubber is less than 100,000, it is difficult to impart an appropriate strength to the film, and when the Mw exceeds 500,000, the handleability tends to be inferior.

  Although not particularly limited, acrylic rubber is recommended from the viewpoints of handleability, coatability when forming the resin layer, and flexibility. The above acrylic rubber may be used alone or in combination of two or more. Moreover, you may use combining acrylic rubber and another thermoplastic resin. Examples of resins that can be used in combination include rosin esters.

  Moreover, it is preferable to select the filler of the heat conductive material which has a heat conductivity of 10 W / mK or more as a heat conductive filler. Examples of such heat conductive materials include inorganic fillers such as silica, graphite, alumina, aluminum hydroxide, aluminum nitride, silicon carbide, magnesium hydroxide, metal fillers such as aluminum, copper, silver, and gold. It is done. These thermally conductive fillers may be used alone or in combination of two or more. Although not particularly limited, it is preferable to use graphite as the thermally conductive filler, and the use of graphite is advantageous in terms of thermal conductivity, corrosion resistance, and cost. As the graphite, for example, natural graphite powder, artificial graphite powder, expanded graphite, or expanded graphite powder obtained by pulverizing an expanded graphite sheet can be used. From the viewpoint of cost, it is preferable to use natural or artificial graphite powder.

  The shape of graphite is not particularly limited, and may be spherical, lump, scale, dendritic, etc., but the average particle size is preferably 5 to 100 μm. When the average particle diameter of graphite is smaller than 5 μm, it is difficult for the adherend such as a heat radiating member and the graphite particles to come into contact, and as a result, the thermal resistance tends to increase. On the other hand, when it exceeds 100 micrometers, there exists a tendency for a uniform coating film not to be obtained at the time of film preparation. In addition, the average particle diameter of the graphite prescribed | regulated by this invention is the value measured using the laser diffraction type particle size distribution measuring apparatus.

  The blending ratio of the thermally conductive resin layer with the thermally conductive filler is not particularly limited, but is 30 to 80% by weight, more preferably 40 to 80%, based on the total weight of the components constituting the resin layer. % By weight, more preferably 50 to 80% by weight. When the blending ratio of the heat conductive filler is less than 30% by weight, the heat resistance of the heat conductive film itself increases and it becomes difficult to efficiently transfer the heat generated from the heat source to the heat dissipation material. On the other hand, if it exceeds 80% by weight, the filler is excessively exposed on the surface, so that sufficient tackiness tends not to be obtained.

  In addition to the binder resin and the thermally conductive filler described above, the thermally conductive resin layer includes a toughness improver such as urethane acrylate, a moisture absorbent such as calcium oxide and magnesium oxide, a silane coupling agent, and a titanium coupling as necessary. Flame retardants such as chemicals and phosphorus-containing compounds, tackifiers, wetting improvers such as surfactants and fluorosurfactants, antifoaming agents such as silicone oil, anti-settling agents, surface tension modifiers, viscosity adjustments Various additives such as an agent, an ion trapping agent such as an inorganic ion exchanger, and the like may be included. In consideration of application to electronic equipment, the thermally conductive film according to the present invention preferably has flame retardancy of V-0 according to the UL-94 standard. Therefore, although it does not specifically limit, it is preferable that a heat conductive resin layer contains phosphorus containing compounds, such as phosphate ester, as a flame retardant imparting agent in addition to the above-mentioned binder resin and heat conductive filler. In addition, when using a flame-retarding agent, those compounding ratios are 10 to 50 weight% with respect to the total weight of the component which comprises a resin layer, More preferably, it is the range of 20 to 50 weight%. When the blending ratio of the flame retardant imparting agent is less than 10% by weight, it tends to be difficult to obtain flame retardancy of V-0 according to UL-94 standards. On the other hand, when it exceeds 50% by weight, the film strength of the film tends to decrease.

  The heat conductive composition which comprises a heat conductive resin layer can be prepared by mixing the above-mentioned binder resin, a heat conductive filler, and the various additives selected as needed. The heat conductive composition can be used as a uniform paste in which the filler is sufficiently dispersed in the binder resin by using an appropriate combination of dispersing devices such as lykai machine, planetary mixer, stirrer, homogenizer, and dispersion at the time of preparation. It is preferable to obtain.

  In this invention, when forming a heat conductive resin layer, in order to improve the coating property of a heat conductive composition, you may further add a diluent to the above-mentioned heat conductive composition. As the diluent, for example, an organic solvent having a relatively high boiling point such as butyl cellosolve, carbitol, butyl acetate, butyl acetate cellosolve, carbitol acetate, dipropylene glycol monomethyl ether, ethylene glycol diethyl ether, α-terpineol is preferable, and a binder resin. Select in consideration of compatibility. The addition amount is preferably in the range of 10 to 70% by weight with respect to the entire heat conductive composition. In addition, it is preferable that a heat conductive composition has a viscosity of 10-50 Pa.s from a viewpoint of forming a uniform coating film. The term “viscosity” used in the present specification indicates a value measured by a RE80 viscometer (trade name, manufactured by Toki Sangyo Co., Ltd.).

The heat conductive film by this invention is obtained by applying the heat conductive composition comprised as mentioned above to both main surfaces of metal foil, and forming a heat conductive resin layer. The coating method is not particularly limited, and a known method that can form a uniform coating film can be applied. In consideration of productivity, it is preferable to select a binder resin that can form a tough coating film in a short time, or a suitable diluent for such a binder resin. In order to adjust the heat resistance of the heat conductive film to 1.0 ° C. · cm ² / W or less, various components are appropriately blended to prepare a heat conductive composition, and these compositions are used. The coating is preferably performed so that the thickness of the entire film is 200 μm or less.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
(1) Preparation of binder resin As binder resin for forming the thermally conductive resin layer, 30 g of acrylic rubber (referred to as acrylic rubber A) having a Tg of −40 ° C. and an Mw of 250,000 was added to phosphate ester (Daihachi Chemical Industry). 13.5 g, manufactured by Co., Ltd., product name: CR733S) and 150 g of butyl acetate (industrial) were added and mixed uniformly using a raikai machine.

(2) Preparation of heat conductive composition (paste) After adding 92.8 g of natural graphite (made in China) with an average particle size of 20 μm to the binder resin prepared in (1) and mixing them with a lye machine Furthermore, using a homogenizer, the heat conductive composition was prepared by stirring for 5 minutes at 5000 rpm. The weight fraction of the obtained composition was graphite: acrylic rubber A: phosphate ester = 68: 22: 10, and the viscosity was 20 Pa · s.

(3) Application of thermal conductive composition By using a 20 μm thick aluminum foil as a support, by applying the previously prepared thermal conductive composition (paste) to each of its front and back surfaces, A thermally conductive film was produced (see FIG. 1). The coating was carried out on each side at a coating speed of 0.5 m / min and a drying temperature of 120 ° C. The total thickness of the obtained heat conductive film was 100 μm. It measured about the thermal resistance and peeling adhesive force of the obtained heat conductive film. The results are shown in Table 1.

(4) Various tests About the heat resistance of the heat conductive film produced as mentioned above, peeling adhesive force, a heat transfer characteristic, and a flame retardance, it measured according to the following methods. The results are shown in Table 1.

  Measurement of thermal resistance: A thermal conductivity measuring device “ARC-TC-1 type” manufactured by Agne Technology Center Co., Ltd. was used and measured according to a temperature gradient method.

  Peeling adhesive strength: The heat-conductive film produced was cut to a width of 10 mm and attached to an aluminum plate with finger pressure, and a 90 ° tensile load was applied for measurement.

Measurement of heat transfer characteristics: FIG. 2 shows a schematic diagram for explaining a method for measuring the heat transfer characteristics of a heat conductive film. As shown in FIG. 2, the measuring apparatus is a ceramic heater 202 (Sakaguchi Heat Transfer Co., Ltd.) 10 × 10 mm square and 2 mm thick on a heat insulating material 200 (fiber reinforced plastic made of glass cloth and phenol resin). And a copper plate 204 having a thickness of 10 × 10 mm and a thickness of 3 mm are sequentially stacked, and a heat dissipation material 206 having a thickness of 15 × 30 mm and a thickness of 15 mm is provided on the thermal conductive film 100 having a size of 30 × 30 mm. Consists of. In the measurement, a current was passed while controlling the output regulator 208 provided in the ceramic heater 202 to a constant output of 2.0 W / cm ² at 120 ° C. The measurement portion of −8060 K) was placed in the center of the copper plate 204. Since it is difficult to directly measure the temperature drop of the ceramic heater 202 in order to examine the heat transfer characteristics, the temperature was evaluated by measuring the temperature of the center of the copper plate 204 between the ceramic heater 202 and the heat dissipation material 206. . The measurement of the temperature of the copper plate is performed 20 minutes after the start of the test, and in order to avoid the influence of the ambient environmental temperature, the difference between the copper plate temperature T1 and the environmental temperature T2 (T1-T2) is defined as the evaluation temperature. did. The results are shown in Table 1.

  Measurement of flame retardancy: A flame retardancy test based on UL-94 standard was performed.

(Example 2)
A heat conductive film was prepared in the same manner as in Example 1 except that the heat conductive composition was prepared by replacing the graphite used with artificial graphite having an average particle diameter of 20 μm (product name: KS44, manufactured by Timcal). Similar measurements were performed. The results are shown in Table 1.

(Example 3)
A heat conductive film was produced in the same manner as in Example 1 except that the heat conductive resin layer was formed so that the total thickness of the heat conductive film was 200 μm, and the same measurement was performed. The results are shown in Table 1.

Example 4
Except for using an aluminum foil having a thickness of 30 μm as a support, a heat conductive film was prepared in the same manner as in Example 1, and the same measurement was performed. The results are shown in Table 1.

(Example 5)
A heat conductive film is produced in the same manner as in Example 1 except that a heat conductive composition is prepared by adding rosin ester (product name “Pencel C” manufactured by Arakawa Chemical Industries, Ltd.) as a binder component. Then, the same measurement was performed. The results are shown in Table 1. In addition, the weight fraction of the heat conductive composition was graphite: acrylic rubber A: rosin ester: phosphate ester = 68: 17: 5: 10, and the viscosity was 20 Pa · s.

(Comparative Example 1)
A heat conductive film was produced in the same manner as in Example 1 except that graphite was not blended in the heat conductive composition, and the same measurement was performed. The results are shown in Table 1.

(Comparative Example 2)
A heat conductive film was produced in the same manner as in Example 1 except that the heat conductive resin layer was formed so that the total thickness of the heat conductive film was 400 μm, and the same measurement was performed. The results are shown in Table 1.

(Comparative Example 3)
A heat conductive composition was prepared in the same manner as in Example 1 except that an acrylic rubber (referred to as acrylic rubber B) having a Tg of −4 ° C. and an Mw of 250,000 was used instead of the acrylic rubber A. A thermally conductive film was prepared and the same measurement was performed. The results are shown in Table 1. The viscosity of the heat conductive composition was 25 Pa · s.

(Comparative Example 4)
A heat conductive film was prepared in the same manner as in Example 1 except that a PET film having a thickness of 20 μm was used instead of the aluminum foil, and the same measurement was performed. The results are shown in Table 1.

  As can be seen from the above results, according to the present invention, it is possible to obtain a heat conductive film having excellent adhesion to a heat source and a heat radiating body and low heat resistance. These heat conductive films are excellent in handleability and can be easily applied to a heat dissipation system of various electronic devices such as a PC.

It is typical sectional drawing which shows one Embodiment of the heat conductive film by this invention. It is the schematic for demonstrating the method to measure the heat transfer characteristic of a heat conductive film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Thermal conductive film 101 Metal foil 102 Thermal conductive resin layer 200 Heat insulating material 202 Ceramic heater 204 Copper plate 206 Heat radiation material 208 Output regulator 210 Thermologger

Claims (9)

A heat conductive film having a metal foil and a heat conductive resin layer provided on both main surfaces of the metal foil,
The thermally conductive film, wherein the thermally conductive resin layer includes a binder resin and a thermally conductive filler dispersed in the binder resin. The heat conductive film according to claim 1, which has a heat resistance of 1.0 ° C. · cm ² / W or less.   The heat conductive film according to claim 1, wherein the heat conductive film has a peel adhesive strength of 0.1 N / 10 mm or more.   The heat conductive film according to claim 1, which has a thickness of 50 to 200 μm.   The heat conductive film according to claim 1, wherein the binder resin is a thermoplastic resin.   The heat conductive film according to any one of claims 1 to 5, wherein the heat conductivity of the heat conductive filler is 10 W / mK or more.   The thickness of the said metal foil is 10-40 micrometers, The heat conductive film in any one of Claims 1-6 characterized by the above-mentioned.   The thermally conductive film according to any one of claims 1 to 7, which has flame retardancy of V-0 according to UL-94 standard.   The thermally conductive film according to claim 1, wherein the thermally conductive filler contains graphite.

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