JP2007173617A - Heat dissipating sheet and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat dissipating sheet (for electronic unit/electronic component) superior in heat dissipation, electric insulation, mechanical strength and flame retardancy, and to provide a method of manufacturing the same. <P>SOLUTION: In the heat dissipation sheet, magnesium hydroxide particles are bound with binder resin having a glass transfer temperature of -50 to 50°C. A volume ratio of magnesium hydroxide particles/binder resin is 50/50 to 70/30, and sheet thickness is 10 to 150μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electronic component such as a large scale integrated circuit (LSI), a plasma display panel (PDP), an organic EL or an inorganic EL, a light emitting diode (LED), a fluorescent display tube (VFD) in an electronic device such as a personal computer or a cellular phone. ), Heat generated from a display device such as a cathode ray tube (CRT) or a lighting device using an incandescent bulb, a fluorescent lamp, an EL (organic or inorganic), LED, etc. is efficiently dissipated outward. It is related with the heat-radiation sheet used for.

In recent years, electronic devices have been remarkably improved in performance and functionality, and the performance of LSIs such as microprocessors (MPUs), image processing chips, and memories that are used has been increasing. Since the amount of heat generated by the LSI has been increasing, heat countermeasures have been a problem.
Conventionally, it is common to use a heatsink such as a small fan motor when proper arrangement in the LSI device is sufficient, otherwise. However, thermal design is becoming difficult for electronic devices such as notebook personal computers and mobile phones that are particularly thin and light (small). And even for MPUs that previously did not require a heatsink, due to an increase in the amount of heat generation, it has become impossible to radiate heat without using a heatsink.
When providing a radiator in an electronic component such as an MPU, a heat radiating sheet made of a material having a high thermal conductivity is usually disposed between the electronic component and the radiator. This is because, when the electronic component and the radiator are directly joined, a gap is generated between the electronic component and the radiator due to a minute warp of the joining surface of the radiator, and this gap becomes a resistance with large heat conduction. In addition, some users are concerned about the noise of fan motors, and notebook PCs that are fan-less by using only heat-dissipating sheets are now on the market.
In addition, in display devices such as PDPs, as the display brightness is increased, more heat is generated, and the temperature of the display panel becomes higher, resulting in deterioration of display quality characteristics of the display panel. It has been proposed to provide a heat conductive sheet so as to be in close contact with the plate (see Patent Document 1), and has been put into practical use.
As described above, the heat dissipation sheet has become extremely important for heat countermeasures of electronic devices, electronic components, display devices, and the like.

Since the heat-dissipating sheet requires flexibility, a rubber-like one has been used. However, as a heat-dissipating sheet with increased thermal conductivity, a heat-dissipating sheet in which boron nitride is dispersed in a polyolefin-based rubber in recent years (Patent Document 2) And a heat-dissipating sheet (see Patent Document 3) in which graphitic carbon fibers having an average aspect ratio of less than 3 are dispersed in a matrix resin have been proposed.
If an electrically insulating material such as boron nitride or alumina is selected as the highly thermally conductive particles (inorganic filler) to be dispersed, an electrically insulating heat dissipation sheet can be obtained, and if an electrically conductive material such as graphite is selected. Electrically conductive heat-dissipating sheets can be obtained and used depending on the application.
These inorganic fillers, especially the latter graphitic carbon fiber, have a fairly high thermal conductivity, but in order to emphasize physical properties such as flexibility and mechanical strength of the heat dissipation sheet, the content of the inorganic filler in the heat dissipation sheet is The film thickness was not so high, and the film thickness was comparatively thick, on the order of several hundred μm. That is, all of these heat radiating sheets inevitably have a low thermal resistance (high heat transmissivity) by increasing the thermal conductivity of the sheet to about 5 to 10 W / mK, thereby radiating heat. A design philosophy that enhances performance was adopted.

Japanese Patent No. 3503625 Japanese Patent Laid-Open No. 7-246628 JP-A-9-283955

  Under such circumstances, the present invention provides a heat-dissipating sheet that is excellent in heat dissipation and excellent in electrical insulation, mechanical strength and flame retardancy (for electronic equipment / electronic parts), and for the same. The object is to provide a manufacturing method.

  As a result of investigations for achieving the above object, the present inventors have dispersed a specific amount of specific particles in a thermoplastic resin having a glass transition temperature (Tg) in a certain range, and the sheet thickness of the heat radiating sheet. It has been found that the above problem can be solved by controlling the thickness. The present invention has been completed based on such findings.

That is, the present invention
(1) A heat dissipation sheet formed by binding magnesium hydroxide particles with a binder resin having a glass transition temperature of −50 to 50 ° C., and the volume ratio of magnesium hydroxide particles / binder resin is 50/50 to 70 / 30, and the sheet thickness is 10 to 150 μm,
(2) The heat dissipation sheet according to the above (1), wherein the magnesium hydroxide particles have an average particle size of 0.1 to 10 μm,
(3) The above (1) or (2), wherein the binder resin is at least one selected from a polyester resin and an ethylene-vinyl acetate copolymer resin having a vinyl acetate unit ratio of 40 to 80 mol%. Heat dissipation sheet as described in
(4) A heat-dissipating sheet with a releasable protective film in which the heat-dissipating sheet according to any one of the above (1) to (3) is stuck on a releasable protective film,
(5) The heat dissipation sheet with the adhesive layer which provided the adhesion layer in the upper surface and / or lower surface of the heat dissipation sheet in any one of said (1)-(3), and (6) Magnesium hydroxide particle and glass transition temperature. A method for producing a heat-dissipating sheet in which an ink composition comprising a binder resin and a solvent at −50 to 50 ° C. is applied by a coating machine, and the solvent is dried and solidified. In the solvent, A method for producing a heat-dissipating sheet comprising a component having a relative evaporation rate of 190 or more, a boiling point of 60 to 130 ° C., and a solubility parameter of 8 to 12% by mass,
Is to provide.

The heat-dissipating sheet of the present invention binds magnesium hydroxide, which is a material having good thermal conductivity, thermal radiation, electrical insulation and flame retardancy, with as little binder resin as possible, and the sheet thickness can be as small as possible. Since it is thinned, it has good heat conduction, heat radiation by heat radiation, electrical insulation and flame retardancy.
In addition, such a heat radiating sheet is obtained by dispersing magnesium hydroxide particles in a resin solution in which a binder resin having a specific glass transition temperature is dissolved in a solvent, coating it, and drying to form a thin heat radiating sheet. Thus, a heat radiating sheet excellent in practical electrical insulation and flame retardance can be obtained not only in heat dissipation but also in mechanical strength and flexibility.

The magnesium hydroxide particles used in the present invention can be a general grade for plastics or rubber, and are not particularly limited. Magnesium hydroxide has a relatively low hardness, and therefore has an advantage that the coating roll is not damaged during coating in the method of coating using the ink composition which is a preferred production method of the present invention. Moreover, since it is also a non-halogen and non-phosphorus flame retardant, there is an advantage that the burden on the environment during combustion or disposal is small.
In order to obtain a uniform dispersion state of magnesium hydroxide particles in the ink composition used in the preferred production method of the present invention and to obtain a sufficient thin film formability, the average particle size (measured by laser diffraction method) is 0. It is preferable to use one having a thickness of about 1 to 10 μm, more preferably about 0.2 to 3 μm. That is, when the average particle size is 0.1 μm or more, uniform dispersion in the resin solution is facilitated, and an increase in the viscosity of the resin solution is prevented to improve fluidity, thereby improving coating suitability. And uniform film formation becomes easy. On the other hand, when the average particle size is 10 μm or less, it is easy to reduce the thickness of the heat-dissipating sheet having a thickness of 150 μm or less, and the contact area between the magnesium hydroxide particles is increased, so that high thermal conductivity is easily obtained. Furthermore, a reduction in mechanical strength of the heat dissipation sheet can be prevented, and sufficient flame retardancy can be imparted.
As the magnesium hydroxide particles, for example, general flame retardant grades such as “Kisuma 5A” manufactured by Kyowa Chemical Industry Co., Ltd. and “Maxies N-4” manufactured by Kamishima Chemical Industry Co., Ltd. can be preferably used.

  The binder resin used in the heat dissipation sheet of the present invention needs to have a glass transition temperature (hereinafter referred to as Tg, measured by DSC method) of −50 to 50 ° C. In particular, Tg is preferably −30 to 10 ° C. When Tg is in this range, even if the content of magnesium hydroxide particles is high, that is, the binder resin amount is low, the film formability, flexibility, and practical mechanical strength of the thin film of the heat dissipation sheet, etc. Can be secured.

The binder resin used in the present invention is not particularly limited as long as it satisfies the above Tg range, but in order to obtain a heat dissipation sheet with excellent electrical insulation, The specific resistance value is preferably 1 × 10 ⁸ Ω · m or more (corresponding to 1 × 10 ⁻⁸ Ω ⁻¹ · m ⁻¹ or less in terms of electrical conductivity), particularly preferably 1 × 10 ¹² Ω · m or more. More preferably, it is 1 × 10 ¹⁴ Ω · m or more.
Examples of such binder resins include polyesters, polyurethanes, polyolefins, acrylic resins, and various synthetic rubbers. In addition to easy solubility in solvents, coating suitability of compositions dissolved in solvents (viscosity, etc.) Polyester resins and ethylene-vinyl acetate copolymer resins are particularly preferred from the viewpoint of the mechanical strength, weather resistance, heat resistance, and the like of the sheet.

In addition to satisfying the above Tg range, the polyester resin is preferably an amorphous polyester resin from the viewpoint of sheet flexibility and easy solubility in a solvent for producing the heat dissipation sheet of the present invention. Moreover, saturated polyester is preferable from the viewpoint of weather resistance.
Examples of the saturated polyester include polyesters of saturated dibasic acids such as succinic acid and adipic acid and saturated dihydric alcohols such as ethylene glycol and 1,6-hexanediol. The number average molecular weight (measured by GPC method) of the saturated polyester is preferably in the range of 5000 to 50000.
From the viewpoint of preventing dioxin generation and preventing contact failure due to low molecular siloxane, a polyester resin that is halogen-free and siloxane-free is preferable.

As the ethylene-vinyl acetate copolymer resin, one satisfying the above Tg range is used. However, from the viewpoints of flexibility and heat resistance of the heat dissipation sheet, those in the range of an elastomer called EVM (ISO 1692 (1995)) in which the ratio of vinyl acetate units is 40 to 80 mol% are particularly preferable. The number average molecular weight (measured by GPC method) of the ethylene-vinyl acetate copolymer resin is preferably in the range of 50,000 to 500,000. Since this EVM elastomer has high heat resistance, the use of this EVM elastomer has the advantage that the thermal stability of the heat dissipation sheet is particularly excellent.
In addition, like a polyester-type resin, it is preferable that it is halogen-free and siloxane-free from a viewpoint of prevention of dioxin generation | occurrence | production and a contact failure by low molecular siloxane.

In the heat dissipation sheet of the present invention, it is essential that the volume ratio of the magnesium hydroxide particles / the binder resin (hereinafter sometimes referred to as PV ratio) is in the range of 50/50 to 70/30. If the PV ratio is lower than 50/50, thermal conductivity and flame retardancy are insufficient, and if it is higher than 70/30, it is difficult to obtain a heat dissipation sheet having sufficient mechanical strength. And when the design is focused on thermal conductivity, specifically, when the thermal conductivity is desired to be 1 W / mK or more, the PV ratio is controlled in the range of 60/40 to 70/30, while the heat dissipation sheet is flexible. If the design is focused on the property, it is preferable to control the PV ratio in the range of 50/50 to 60/40.
Further, in order to obtain a sufficiently low heat resistance of the heat dissipation sheet, the thickness of the heat dissipation sheet needs to be in the range of 10 to 150 μm, and more preferably in the range of 30 to 120 μm. If the thickness of the heat dissipation sheet is less than 10 μm, it is difficult to form a uniform coating film due to the presence of aggregates of magnesium hydroxide particles, and it is difficult to ensure electrical insulation. When the thickness of the heat-dissipating sheet exceeds 150 μm, it is difficult to dry the solvent when forming the coating film, and it becomes difficult to form a smooth coating film, and the heat resistance in the thickness direction of the heat-dissipating sheet is large, and the heat dissipation is It becomes insufficient.
That is, in order to increase the thermal conductivity and thermal radiation in the infrared wavelength region (hereinafter also simply referred to as “thermal radiation”), the filler content is increased and the thickness of the heat dissipation sheet is made as thin as possible. Moreover, the high filler ratio with respect to this binder resin can improve the heat resistance of a thermal radiation sheet.

  The heat radiating sheet of the present invention is obtained by applying a composition in which magnesium hydroxide particles are uniformly dispersed in a solution in which a binder resin is dissolved in a solvent, and drying and solidifying the solvent so that the content of magnesium hydroxide particles is increased. A high heat dissipation sheet with a small sheet thickness can be obtained. That is, in the present invention, by using a solvent, the fluidity of the magnesium hydroxide particles and the binder resin mixture is increased, and the thin film coating suitability is imparted. Furthermore, after coating and film-forming the composition, the film thickness of the solidified heat-dissipating sheet obtained by drying and removing the solvent contained is reduced by the amount of the solvent, thereby further reducing the film thickness.

The solvent used in the production of the heat dissipation sheet of the present invention contains 80% by mass of a component having a relative evaporation rate of 190 or more, a boiling point in the range of 60 to 130 ° C., and a solubility parameter (SP value) of 8 to 12. It is preferable to contain above. By using a solvent that satisfies these conditions, the heat dissipation sheet of the present invention can be produced efficiently. In particular, when the SP value is within this range, the binder resin is dissolved at a high concentration and the dispersibility of the magnesium hydroxide particles is good.
Here, the relative evaporation rate refers to a relative evaporation rate when the evaporation rate of acetic acid-n-butyl is 100, and is preferably in the range of 190 to 600. The boiling point is a boiling point at normal pressure, and the SP value is preferably in the range of 8.5 to 11.
The solvent is not particularly limited as long as the above conditions are satisfied, and solvents such as aromatic hydrocarbons, ketones, and esters can be used. More specifically, toluene (relative evaporation rate: 196, boiling point: 110.8 ° C., SP value: 8.9), methyl ethyl ketone (relative evaporation rate: 465, boiling point: 79.6 ° C., SP value: 9.3) ), Ethyl acetate (relative evaporation rate: 525, boiling point: 76.8 ° C., SP value: 9.1) and the like are preferably used from the viewpoints of drying properties after coating, fluidity of the ink composition, and the like. These solvents may be used alone or in combination of two or more.
Furthermore, as an ink composition for producing the heat-radiating sheet of the present invention, as long as it is necessary, for the purpose of adjusting the fluidity of the ink composition and the drying speed, as long as the solution state of the binder resin is not impaired, 20 An appropriate amount of a slow-drying solvent or the like that is outside the above physical property range can be added up to a mass%.

The composition for producing the heat dissipation material layer of the present invention was prepared by adding magnesium hydroxide particles (100 parts by mass of binder resin having a glass transition temperature of −50 to 50 ° C. in a solvent of 75 to 2300 parts by mass in a solvent. Thermally conductive filler) 200 to 480 parts by mass are uniformly and finely dispersed and mixed using a dissolver or the like.
The applicability of the composition depends on the type and amount of each component of the composition, but is greatly affected by the type and amount of the solvent, the shape / particle size of the heat conductive filler, the amount, and the like.
In order to easily obtain the heat dissipation sheet having a thin sheet thickness of 10 to 150 μm according to the present invention by the coating method suitably used in the present invention, the optimum solvent blending amount (the fluidity of the ink composition, the thickness when dried) In order to evaluate the relationship with shrinkage, it is expressed by the ratio of the solvent to the whole composition) as 20 to 80% by mass in the amount of solvent in the composition, and the particle size of the magnesium hydroxide particles is as described above. The viscosity of the ink composition in which the magnesium hydroxide particles are dispersed is preferably about 50 to 10000 mPa · s (B-type viscometer (60 rotations)) at 25 ° C.

  The heat-dissipating sheet of the present invention is non-conductive within a range that does not adversely affect heat-dissipation characteristics and electrical insulation characteristics in order to increase the radiation rate in the infrared wavelength region (hereinafter also simply referred to as “radiation rate”). Black pigments such as carbon black can be added. In addition, as long as the heat dissipation characteristics (thermal conductivity, thermal radiation) are not significantly adversely affected, colorants other than black, silane coupling agents, curing agents such as isocyanate, thermal stabilizers, dispersants, micros An appropriate amount of silica or the like may be appropriately selected and blended.

The ink composition in which the magnesium hydroxide particles, which is a composition for producing the heat-dissipating sheet of the present invention, is dispersed in a normal coating machine (coating machine) such as a comma coater, die head coater, gravure printing machine, etc. It is coated on a film, a resin film with a release layer, and the like, and dried by a far-infrared radiation heater, hot air spraying, etc., thereby forming a sheet with the film thickness reduced by the amount of solvent drying.
As the resin film, a polyester resin such as polyethylene terephthalate (PET), a nylon resin, a polyolefin resin such as polypropylene, or the like is used. Moreover, a silicone resin, a melamine resin, etc. are used as said release layer.

Of course, a higher heat conductivity of the formed heat dissipation sheet is preferable in terms of heat dissipation performance. However, in the present invention, the heat conductivity of the heat dissipation sheet is about 0.8 W / mK or more, more preferably 1.0 W / mK because the heat resistance is reduced by reducing the thickness of the heat dissipation sheet to 150 μm or less. If it is more than it, the heat dissipation performance calculated | required practically will be obtained. Due to this combination of thickness and thermal conductivity and the thermal radiation of magnesium hydroxide, it is possible to obtain the same heat dissipation performance as a conventional heat dissipation sheet having a thickness of 500 μm and a thermal conductivity of about 5 W / mK. If a thin film is formed using the composition having the above composition, this degree of thermal conductivity can be easily obtained.
The thermal conductivity is measured in accordance with a known method such as a method prescribed in ASTM C518, JIS A 1412, or JIS R1611, a laser flash method.
Moreover, the heat-radiation sheet of this invention has a flame retardance equivalent to V-0 in the flame retardance test measured based on UL-94 specification. In addition, since it does not contain halogen, no dioxin or the like is generated at the time of combustion. Further, since it does not contain phosphorus, there is no problem of soil contamination or water pollution during disposal.

The heat dissipating sheet thus obtained is peeled off from the releasable film, or in the form of a product for use as a heat dissipating sheet with the releasable film being laminated as a protective film. Can do.
Moreover, the heat-radiation sheet of this invention is good also as a structure which further provided the adhesive layer in the upper surface or lower surface of the heat-radiation sheet, ie, a heat-radiation sheet with an adhesive layer, and this improves the convenience at the time of product use.

  The heat-dissipating sheet of the present invention is affixed to the surface, back surface, side surface, etc. of heating elements such as transistors, LSIs, MPUs, and other electronic devices, and display devices such as PDPs, at positions that do not hinder assembly, light emission, and image display . Thereby, the heat-radiation sheet of this invention expresses the heat-radiation mechanism according to the usage form. For example, when used by being stacked or connected to a heat exhaust system such as a heat sink, a water-cooled or air-cooled cooler, the heat-dissipating sheet of the present invention serves as a passage for transferring heat from the heating element to the heat exhaust system. Heat is released from the heat exhaust system exclusively by heat conduction and / or heat radiation. In this case, the heat dissipation sheet of the present invention contributes to a good heat dissipation mechanism by transporting heat from the heating element to the heat exhaust system with high efficiency due to its low thermal resistance. On the other hand, when the heat-dissipating sheet of the present invention is used by sticking to the surface of the heat generating body, the heat transferred from the heat generating element by heat conduction in the thickness direction and in-plane direction of the heat-dissipating sheet exclusively. Due to the heat radiation from (and in addition to this, partly by heat conduction to the surrounding atmosphere). In this case, the heat radiating sheet of the present invention transports heat from the heating element to the heat radiating surface of the heat radiating sheet with high efficiency due to its low thermal resistance, and heat that has reached the heat radiating surface on the surface. By radiating with high efficiency by high heat radiation, it contributes to a good heat dissipation mechanism.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, evaluation of the thermal radiation sheet obtained by each Example and the comparative example was performed with the following method.
(1) Sheet density (g / cm ³ )
The film thickness and weight (mass) (g) of the heat-dissipating sheet cut to a size of 5.0 × 10.0 cm were measured and calculated.
(2) Heat dissipation The heat dissipation was evaluated by the following measurement. The heat-dissipating sheets obtained in each of the examples and comparative examples were attached to the entire side surface of a metal can (stainless steel with a mirror surface) having a diameter of 83 mm and a height of 100 mm. The temperature was adjusted to 89 ° C. This can was placed in a box made of sealed corrugated paper having a length of 290 mm, a width of 380 mm and a height of 360 mm adjusted to 25 ° C., and the change in water temperature after 30 minutes, 60 minutes and 90 minutes was measured. In addition, the same experiment was conducted without attaching the heat-dissipating sheet, and the change in water temperature after 30 minutes, 60 minutes and 90 minutes was measured (displayed in Table 1 as Reference Example 1), and this was used as a reference value. The temperature decrease rate was also displayed.
(3) Thermal conductivity In accordance with ASTM C518, JIS A 1412, and JIS R1611, the thermal diffusivity is obtained by a laser flash method, and the thermal conductivity is calculated as the product of the thermal diffusivity and the heat capacity (density × specific heat). It was done by the method.
(4) Flame retardance Flame retardancy was evaluated according to the UL-94 standard vertical flame retardant test.
(5) Mechanical strength The elongation at break and tensile strength of the heat-dissipating sheet were determined according to JIS K 7113 and evaluated according to the following criteria.
○: Tensile breaking elongation is 5% or more and tensile strength is 0.5 N / 10 mm or more ×: Tensile breaking elongation is less than 5% or tensile strength is less than 0.5 N / 10 mm

Example 1
Polyester resin A (amorphous saturated copolyester; manufactured by Toyobo Co., Ltd., trade name: “Byron 300”, Tg: 6 ° C., number in a container equipped with a 300 mL stirring mixer Magnesium hydroxide was added to 100 parts by mass of a solution in which 30% by mass of an average molecular weight of 23,000, a specific gravity of 1.20, and a volume resistivity of 1.3 × 10 ¹⁵ Ω) were dissolved in a methyl ethyl ketone / toluene mixed solvent (mixing ratio 20:80). 60 parts by mass of particles (“Magsees N-4” manufactured by Kamishima Chemical Co., Ltd., average particle size: 1.1 μm) was added, and the mixture was stirred and mixed to obtain an ink composition in which magnesium hydroxide particles were uniformly dispersed. . The obtained ink composition is coated on a release layer of a release agent-coated PET film by a comma coater (manufactured by Inoue Metal Industry Co., Ltd.), dried with hot air, and the solvent contained therein is removed by drying. A heat dissipation sheet was obtained. 4 units of drying zone with a coating speed of 3 m / min and a drying temperature of 50 to 120 ° C. (unit length: 2 m × 4, drying temperature: first unit: 50 ° C., second unit: 80 ° C., third unit : 100 ° C., fourth unit: 120 ° C.) to obtain a heat dissipation sheet having a sheet thickness of 60 μm. Magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 50/50. Table 1 shows the physical properties and heat dissipation of the obtained heat dissipation sheet.

Example 2
A heat radiating sheet was obtained in the same manner as in Example 1 except that EVM elastomer (ISO1692 (1995), vinyl acetate unit ratio was 80 mol%, Tg: 5 ° C., number average molecular weight 91000) was used instead of polyester resin A. And evaluated in the same manner as in Example 1. The magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 50/50. The results are shown in Table 1.

Example 3
A heat radiating sheet was obtained in the same manner as in Example 1 except that the content of the polyester resin A was 20 parts by mass and the content of the magnesium hydroxide particles was 80 parts by mass. Magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 66/34. Table 1 shows the results of evaluating the obtained heat dissipation sheet by the above method.

Comparative Example 1
Instead of the heat-dissipating sheet of the present invention, aluminum having a thickness of 60 μm was attached, and the heat dissipation was evaluated by the above method. The results are shown in Table 1.

Comparative Example 2
A heat radiating sheet was obtained in the same manner as in Example 1 except that the content of the polyester resin A was 40 parts by mass and the content of the magnesium hydroxide particles was 60 parts by mass. Magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 43/57. Table 1 shows the results of evaluating the obtained heat dissipation sheet by the above method.

Comparative Example 3
A heat radiating sheet was obtained in the same manner as in Example 1 except that the content of the polyester resin A was 14 parts by mass and the content of the magnesium hydroxide particles was 86 parts by mass. Magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 75/25. Table 1 shows the results of evaluating the obtained heat dissipation sheet by the above method.

Comparative Example 4
Polyester resin B (amorphous saturated copolyester; manufactured by Toyobo Co., Ltd., trade name: “Byron 200” (Tg: 67 ° C., number average molecular weight 17000, specific gravity 1.26, SP value 11.73) Except that a specific volume resistivity of 7.2 × 10 ¹⁶ Ω) was used, an attempt was made to produce a heat dissipation sheet in the same manner as in Example 1. However, a sheet having practical mechanical strength could be obtained. The volume ratio of magnesium hydroxide particles / binder resin (PV ratio) = 50/50.

Comparative Example 5
A heat radiating sheet was produced in the same manner as in Example 1 except that polyester resin C (manufactured by Toyobo Co., Ltd., prototype urethane-modified polyester, Tg: −54 ° C.) was used as the polyester resin. However, a sheet having practical mechanical strength could not be obtained. The magnesium hydroxide particle / binder resin volume ratio (PV ratio) = 50/50.

* 1 Polyester resin A; amorphous saturated copolyester; manufactured by Toyobo Co., Ltd., trade name: “Byron 300”, Tg: 6 ° C., number average molecular weight 23000, specific gravity 1.20, volume resistivity 1. 3 × 10 ¹⁵ Ω
* 2 Polyester resin B; amorphous saturated copolyester; manufactured by Toyobo Co., Ltd., trade name: “Byron 200”, Tg: 67 ° C., number average molecular weight 17,000, specific gravity 1.26, volume resistivity 7. 2 × 10 ¹⁶ Ω
* 3 Polyester resin C; manufactured by Toyobo Co., Ltd., prototype urethane-modified polyester, Tg: -54 ° C
* 4 EVM: ISO 1692 (1995), vinyl acetate unit ratio of 80 mol%, Tg: 5 ° C., number average molecular weight 91000

As shown in Table 1, the heat-dissipating sheet of the present invention is highly heat-dissipating by a mechanism that radiates the heat conducted to the surface with high efficiency to the outside due to the high-radiation property of the surface. The surface of the can has a low thermal conductivity of 8.3 to 10.3% after 30 minutes as compared to the case where a low thermal conductivity and low thermal radiation property) or aluminum foil (high thermal conductivity and low thermal radiation rate) is applied. After 60 minutes, the temperature decreased by 10.2 to 14.5%, and after 90 minutes, the temperature decreased by 12.9 to 19.0%, and had excellent heat dissipation in a windless environment. Recognize. In addition, since the comparative example 1 which stuck the aluminum foil conducted heat to the surface with high thermal conductivity (about 240 W / mK), since the thermal radiation property of the surface is low (total radiation rate 0.04), As a result, it can be seen that almost no heat dissipation is exhibited. Moreover, it is understood that the thermal conductivity is as high as 0.80 to 1.09, and the heat dissipation by thermal conduction is also high. Furthermore, it can be seen that the heat radiating sheet of the present invention has high flame retardancy and high mechanical strength in the flammability test.
Moreover, as shown in FIG. 1, the heat conductivity of the thermal radiation sheet | seat of this invention is proportional to PV ratio. That is, it can be seen that an arbitrary thermal conductivity can be obtained by controlling the PV ratio.

According to the present invention, magnesium hydroxide, which is a material having good thermal conductivity, thermal radiation, electrical insulation and flame retardancy, can be bound with as little binder resin as possible, and the sheet thickness can be reduced. Since it is possible to reduce the thickness, the heat dissipating sheet of the present invention has good heat conduction, heat dissipating property due to heat radiation, electrical insulation and flame retardancy. Moreover, it is excellent in practical electrical insulation not only in heat dissipation but also in mechanical strength and flexibility.
In addition, such a heat dissipation sheet is manufactured with high productivity by dispersing magnesium hydroxide particles in a resin solution in which a binder resin having a specific glass transition temperature is dissolved in a solvent, and applying and drying the particles. can do.

It is a figure which shows the relationship between the filler amount and heat conductivity in the thermal radiation sheet | seat of this invention.

Claims (6)

A heat dissipation sheet formed by binding magnesium hydroxide particles with a binder resin having a glass transition temperature of −50 to 50 ° C., and the volume ratio of magnesium hydroxide particles / binder resin is 50/50 to 70/30 And a sheet thickness is 10 to 150 μm. The heat dissipation sheet according to claim 1, wherein the magnesium hydroxide particles have an average particle size of 0.1 to 10 μm. The heat dissipation sheet according to claim 1 or 2, wherein the binder resin is at least one selected from a polyester-based resin and an ethylene-vinyl acetate copolymer resin having a vinyl acetate unit ratio of 40 to 80 mol%. A heat-dissipating sheet with a releasable protective film, wherein the heat-dissipating sheet according to any one of claims 1 to 3 is stuck on a releasable protective film. The heat-radiation sheet with the adhesion layer which provided the adhesion layer in the upper surface and / or lower surface of the heat-radiation sheet in any one of Claims 1-3. Manufacture of a heat radiation sheet that is formed into a sheet by coating an ink composition comprising magnesium hydroxide particles, a binder resin having a glass transition temperature of −50 to 50 ° C. and a solvent with a coating machine, and drying and solidifying the solvent. A method for producing a heat-dissipating sheet, wherein the solvent contains a component having a relative evaporation rate of 190 or more, a boiling point of 60 to 130 ° C., and a solubility parameter of 8 to 12 in a solvent.

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