JP7410171B2 - heat dissipation sheet - Google Patents

Description

The present invention relates to a heat dissipation sheet.

In recent years, with the advancement of electronics, many components that generate heat have been used in electronic equipment such as power devices. When controlling an electronic circuit, it is important to dissipate heat from these heat generating components and cool the entire system. For example, a heat dissipation sheet is installed between a heat generating component and a heat dissipating fin or a metal plate, and is tightly attached to the heat generating component without any gaps by crimping, exhibiting thermal conductivity and transferring the heat generated from the heat generating component to the heat dissipating fin. etc., to remove heat from the entire system.

The heat dissipation sheet is made of, for example, a thermally conductive inorganic filler and a resin. Examples of inorganic fillers used include inexpensive aluminum hydroxide and aluminum oxide (alumina), as well as silicon carbide, boron nitride, and aluminum nitride, which are expected to have higher thermal conductivity. Further, as the resin, for example, acrylic resin or urethane resin is used.

As the heat dissipation sheet, those disclosed in Patent Documents 1 to 3 are known, for example.

Japanese Patent Application Publication No. 2007-277405 JP2007-277406A Japanese Patent Application Publication No. 2009-274929

In recent years, small portable electronic devices such as smartphones have become more sophisticated, and the amount of heat generated by components within the portable electronic devices has also increased accordingly. Therefore, there is a need for a heat dissipation sheet that can be used in small electronic devices such as portable electronic devices.

Furthermore, the portable electronic devices are required to be made thinner, and accordingly, heat dissipation sheets are also required to be made thinner. However, when attempting to reduce the thickness of the heat dissipation sheets disclosed in Patent Documents 1 to 3, there was a problem in that the film forming properties were poor and it could not be obtained in the form of a sheet, or even if it could be obtained, it would be brittle and easily break.

The present invention has been made in view of the above, and an object of the present invention is to provide a heat dissipation sheet that can be obtained with good film formability even if it is thin.

As a result of intensive studies to achieve the above object, the present inventors used resin and alumina as the components constituting the heat dissipation sheet, and found that the particle size distribution of the alumina has a peak within three specific particle size ranges. It has been found that a thin heat dissipating sheet can be obtained with good film formability by setting specific proportions of alumina having the above-mentioned three types and within specific particle size ranges. The present invention was completed based on these findings.

That is, the present invention is a heat dissipation sheet containing alumina particles and a resin,
The content of the alumina particles in the heat dissipation sheet is 70% by volume or more,
The alumina particles have peaks in the particle size distribution of 30 to 60 μm, 2 to 12 μm, and 0.1 to 1 μm, respectively,
In the above particle size distribution, the proportion of alumina particles with a particle size of 30 to 60 μm in the above alumina particles is 9 to 60 volume %, the proportion of alumina particles with a particle size of 2 to 12 μm is 30 to 90 volume %, and the particle size is 0.1 Provided is a heat dissipation sheet in which the proportion of alumina particles of ~1 μm is 1 to 20% by volume.

In the above particle size distribution, the alumina particles having a peak at 30 to 60 μm, the alumina particles having a peak at 2 to 12 μm, and the alumina particles having a peak at 0.1 to 1 μm are preferably spherical particles.

The heat dissipation sheet preferably has a thermal conductivity of 3.5 W/mK or more and less than 5.0 W/mK.

The heat dissipation sheet preferably has a thermal diffusivity of more than 1.6×10 ⁻⁶ m ² /s.

The heat dissipation sheet preferably has a thickness of 2.3 mm or less.

The heat dissipation sheet of the present invention can be obtained not only as a thick sheet but also as a thin sheet with good film forming properties. Therefore, the heat dissipation sheet of the present invention can be preferably applied to small portable electronic devices such as smartphones.

The heat dissipation sheet of the present invention contains at least alumina particles and a resin. The alumina particles have peaks in the particle size distribution of 30 to 60 μm, 2 to 12 μm, and 0.1 to 1 μm, respectively. In this specification, in the particle size distribution, alumina particles with a particle size of 30 to 60 μm are referred to as "first alumina particles," alumina particles with a particle size of 2 to 12 μm are referred to as "second alumina particles," and particles with a particle size of 0.1 to 1 μm. The alumina particles may be referred to as "tertiary alumina particles".

The first alumina particles are the largest large-diameter particles among the first to third alumina particles, and mainly exhibit thermal conductivity. The peak particle size of the first alumina particles is in the range of 30 to 60 μm, preferably in the range of 40 to 50 μm, and more preferably in the range of 42 to 48 μm. By using alumina particles having the above particle size as the large-diameter particles, when a thin heat dissipation sheet is produced, the alumina particles are less likely to fall off and the heat dissipation sheet is less likely to crack.

Preferably, the first alumina particles are spherical particles. When the first alumina particles are spherical particles, the first alumina particles have good dispersibility in the resin (especially silicone resin) that is the matrix of the heat dissipation sheet, and can be used even when producing a thin heat dissipation sheet. Excellent film properties. In this specification, spherical particles refer to particles whose average value of circularity (perimeter of equivalent circle/perimeter of projected image of particle) is 0.8 or more.

The first alumina particles are preferably surface-treated with a silane coupling agent. When the surface is treated with a silane coupling agent, the first alumina particles have good dispersibility in the resin (especially silicone resin) that is the matrix of the heat dissipation sheet, even when producing a thin heat dissipation sheet. Excellent film formability. The above-mentioned silane coupling agents may be used alone or in combination of two or more.

Examples of the silane coupling agent include non-alkoxy groups such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane. A silane coupling agent having a functional group (functional group-containing silane coupling agent); a silane coupling agent having no functional group other than an alkoxy group such as n-decyltrimethoxysilane (non-functional group-containing silane coupling agent) Examples include. Among these, a silane coupling agent that does not contain a functional group is preferable, and more preferably a silane coupling agent that does not contain a functional group, from the viewpoint that it has good wettability with alumina particles and is expected to improve the bulk strength and flexibility of the heat dissipation sheet. is an alkyl group (silane coupling agent containing a terminal alkyl group), particularly preferably n-decyltrimethoxysilane.

The content ratio of the first alumina particles contained in the heat dissipation sheet of the present invention is 9 to 60 volume %, preferably 25 to 55 volume %, more preferably 35 to 55 volume %, based on the total amount of alumina particles of 100 volume %. It is 55% by volume, more preferably 45-55% by volume. When the content ratio is 9% by volume or more, thermal conductivity is excellent. When the above-mentioned content ratio is 60 volume % or less, when a thin heat dissipation sheet is produced, falling off of the alumina particles and cracking of the heat dissipation sheet are less likely to occur.

The second alumina particles are the second largest medium-sized particles among the first to third alumina particles, and fill the space between the first alumina particles in the heat dissipation sheet, increasing the thermal conductivity between the first alumina particles. Improve. The peak particle size of the second alumina particles is in the range of 2 to 12 μm, preferably in the range of 3 to 8 μm. By using alumina particles having the above-mentioned particle size as the medium-sized particles, the filling rate of the gaps between the large-sized particles is high, and the thermal conductivity is excellent.

The second alumina particles are preferably spherical particles. When the second alumina particles are spherical particles, the second alumina particles have good dispersibility in the resin (especially silicone resin) that is the matrix of the heat dissipation sheet, and can be used even when producing a thin heat dissipation sheet. Excellent film properties.

The second alumina particles are preferably surface-treated with a silane coupling agent. When the surface is treated with a silane coupling agent, the second alumina particles have good dispersibility in the resin (especially silicone resin) that is the matrix of the heat dissipation sheet, even when producing a thin heat dissipation sheet. Excellent film formability. The above-mentioned silane coupling agents may be used alone or in combination of two or more.

Examples of the silane coupling agent include those exemplified and explained as the silane coupling agent that can be used for the surface treatment of the first alumina resin described above. Among these, a silane coupling agent that does not contain a functional group is preferable, and a silane coupling agent that does not contain a functional group is more preferable because it has good wettability with alumina particles and is expected to improve the bulk strength and flexibility of the heat dissipation sheet. is an alkyl group (silane coupling agent containing a terminal alkyl group), particularly preferably n-decyltrimethoxysilane. Preferred is n-decyltrimethoxysilane.

The content ratio of the second alumina particles contained in the heat dissipation sheet of the present invention is 30 to 90% by volume, preferably 35 to 75% by volume, more preferably 40 to 75% by volume, based on the total amount of alumina particles of 100% by volume. The amount is 60% by volume, more preferably 40 to 55% by volume. By having the above content ratio, the filling rate of the gaps between the large-diameter particles is high, and the thermal conductivity is excellent.

The third alumina particles are small-diameter particles that are the smallest among the first to third alumina particles, and fill the space between the first and second alumina particles in the heat dissipation sheet, and the filling rate of the alumina particles in the heat dissipation sheet is and improve thermal conductivity. The peak particle size of the tertiary alumina particles is in the range of 0.1 to 1 μm, preferably in the range of 0.1 to 0.5 μm, and more preferably in the range of 0.1 to 0.4 μm. It's within. By using alumina particles having the above-described particle size as the small-diameter particles, the filling rate of the gaps between the large-diameter and medium-diameter particles is high, and the thermal conductivity is excellent.

The third alumina particles are preferably spherical particles. When the third alumina particles are spherical particles, the dispersibility of the third alumina particles into the resin (especially silicone resin) that is the matrix of the heat dissipation sheet is good, and even when producing a thin heat dissipation sheet, the dispersibility of the third alumina particles is good. Excellent film properties.

The third alumina particles are preferably surface-treated with a silane coupling agent. When the surface is treated with a silane coupling agent, the tertiary alumina particles have good dispersibility in the resin (especially silicone resin) that is the matrix of the heat dissipation sheet, even when producing a thin heat dissipation sheet. Excellent film formability. The above-mentioned silane coupling agents may be used alone or in combination of two or more.

Examples of the silane coupling agent include those exemplified and explained as the silane coupling agent that can be used for the surface treatment of the first alumina resin described above. Among these, a silane coupling agent that does not contain a functional group is preferable, and a silane coupling agent that does not contain a functional group is more preferable because it has good wettability with alumina particles and is expected to improve the bulk strength and flexibility of the heat dissipation sheet. is an alkyl group (silane coupling agent containing a terminal alkyl group), particularly preferably n-decyltrimethoxysilane.

The content ratio of the third alumina particles contained in the heat dissipation sheet of the present invention is based on 100% by volume of the total amount of alumina particles. The amount is 1 to 20% by volume, preferably 2 to 10% by volume, more preferably 3 to 8% by volume, and even more preferably 4 to 6% by volume. When the above-mentioned content ratio is 1% by volume or more, the filling rate of alumina particles in the heat dissipation sheet becomes high, resulting in excellent thermal conductivity. If the above content exceeds 20% by volume, the surface of the heat dissipation sheet may become powdery, or the heat dissipation sheet may crack when the release sheet is removed after being sandwiched between two release sheets. be.

The content ratio (total amount) of alumina particles in the heat dissipation sheet of the present invention is 70 volume% or more, preferably 75 volume% or more, based on 100 volume% of the heat dissipation sheet of the present invention. When the content ratio is 70% by volume or more, the filling rate of alumina particles in the heat dissipation sheet is high and the thermal conductivity is excellent. The content ratio is preferably 90% by volume or less, more preferably 85% by volume or less, still more preferably 80% by volume or less. When the content ratio is 90% by volume or less, the heat dissipation sheet is less likely to become brittle and has excellent film formability when producing a thin heat dissipation sheet.

The above resin is a component that forms the matrix of the heat dissipation sheet. Examples of the resin include thermosetting resins, thermoplastic resins, active energy ray-curable resins, and the like. Examples of the thermoplastic resin include, but are not limited to, styrene resins, vinyl acetate resins, polyester resins, polyethylene resins, polypropylene resins, imide resins, acrylic resins, and the like. Examples of the thermosetting resin include, but are not particularly limited to, silicone resins, phenol resins, epoxy resins, urethane resins, melamine resins, alkyd resins, and the like. The active energy ray-curable resin is not particularly limited, but for example, a polymer of a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule can be used. The above resins may be used alone or in combination of two or more. Note that the above-mentioned thermosetting resin is a concept that includes both a resin that can be cured by heating and a resin that is cured by heating.

Among these resins, silicone resins are preferred from the viewpoint of excellent thermal conductivity. Furthermore, when a silicone resin is used as the matrix resin, film forming properties are excellent even when producing a thin heat dissipation sheet. As the silicone resin, silicone resins used in known or conventional heat dissipation sheets can be used. The silicone resin is preferably a two-component curing type silicone resin from the viewpoint of being able to disperse alumina particles well without using a solvent. The above silicone resins may be used alone or in combination of two or more.

The content ratio of the resin is not particularly limited, but is preferably 10% by volume or more, more preferably 15% by volume or more, even more preferably 20% by volume or more, based on 100 volumes of the heat dissipation sheet of the present invention. When the content is 10% by volume or more, the heat dissipation sheet is less likely to become brittle and has excellent film formability when producing a thin heat dissipation sheet. The content ratio is preferably 30% by volume or less, more preferably 25% by volume or less. When the content ratio is 30% by volume or less, the filling rate of alumina particles in the heat dissipation sheet can be increased, resulting in better thermal conductivity. In particular, it is preferable that the content ratio of the silicone resin is within the above range.

The thickness of the heat dissipation sheet of the present invention is, for example, 0.2 to 10 mm, preferably 0.3 to 5 mm. The heat dissipation sheet of the present invention can be produced with good film formability even if it is thin, and is suitable for use in small portable electronic devices, so it is preferably 2.3 mm or less, more preferably 2 mm or less, and even more preferably It is 1.2 mm or less, more preferably 1 mm or less, particularly preferably 0.5 mm or less.

The heat dissipation sheet of the present invention preferably has a thermal conductivity of 3.5 W/mK or more, more preferably 3.6 W/mK or more. When the thermal conductivity is 3.5 W/mK or more, the heat dissipation property is more excellent. The thermal conductivity is, for example, less than 5.0 W/mK.

The heat dissipation sheet of the present invention preferably has a thermal diffusivity of more than 1.6×10 ⁻⁶ m ² /s, more preferably 1.65×10 ⁻⁶ m ² /s or more, still more preferably 1.6×10 −6 m 2 /s or more. It is 7×10 ⁻⁶ m ² /s or more. When the thermal diffusivity is more than 1.6×10 ⁻⁶ m ² /s, the heat dissipation property is more excellent.

The heat dissipation sheet of the present invention may be in a form without a base material (base material layer), so-called "substrate-less", or may be a heat dissipation sheet provided on at least one side of the base material. In particular, since the heat dissipation sheet of the present invention can be manufactured with good film formability, even a thin heat dissipation sheet can be obtained without a base material. Note that the above-mentioned "base material (base material layer)" does not include a release sheet that is peeled off when the heat dissipation sheet is used.

The method for forming the heat dissipating sheet of the present invention is not particularly limited, and any known or commonly used method for forming a film or method for forming a molded body can be employed. Among these, from the viewpoint of continuous film formation and excellent productivity, it is preferable to form a film by roll-to-roll.

The heat dissipation sheet of the present invention can be produced by, for example, coating a resin composition containing the resin and the alumina particles on a base material or a release-treated surface of a release sheet to form a resin composition layer, and then curing it by heating. It can be manufactured by forming a film. Heating may be performed with a release-treated surface of a release sheet further bonded onto the resin composition layer.

The resin composition includes the resin and the alumina particles. The above three types of alumina particles may be mixed in advance and then mixed with the above resin, or the above three types of alumina particles and the above resin may be mixed simultaneously. The resin composition is preferably in the form of a paste that does not contain an organic solvent.

The method for producing the sheet of the resin composition is not particularly limited, and may be any known method such as a sandwich method in which the material is placed between separator films coated with a release agent and laminated with a roll laminator, a hot press molding machine, an extrusion machine, etc. A coating method can be adopted.

The heat dissipation sheet of the present invention comprises first alumina particles having a peak in particle size of 30 to 60 μm, second alumina particles having a peak in particle size of 2 to 12 μm, and third alumina particles having a peak in particle size of 0.1 to 1 μm. By using a combination of three specific types of alumina particles at specific content ratios and blending them into the resin matrix at a ratio of 70% by volume or more, the filling rate of alumina particles is high and excellent thermal conductivity is achieved. However, it can be obtained with excellent film formability, and even with a particularly thin thickness, it can be obtained with excellent film formability.

The present invention will be explained in more detail below based on Examples, but the present invention is not limited only to these Examples.

Example 1
Alumina prepared by mixing 55% by volume of spherical alumina particles with a peak particle size of 45 μm, 40% by volume of spherical alumina particles with a peak particle size of 5 μm, and 5% by volume of spherical alumina particles with a peak particle size of 0.2 μm. Particle composition 1 was produced. The above three types of alumina particles are prepared by adding 1 part of a silane coupling agent (trade name "Z-6210", manufactured by Dow Corning Toray Co., Ltd., n-decyltrimethoxysilane) to 100 parts by mass of alumina particles in advance. The surface treatment was performed using a silane coupling agent by stirring and mixing parts by mass in a solvent. The above alumina particle composition 1 was added to a mixture of one and two parts of silicone resin (trade name "TSE-3062", manufactured by Momentive) so that the amount was 77% by volume (total filling amount of alumina particles 77% by volume). A resin paste was prepared by mixing. Subsequently, the resin paste was placed between the release-treated surfaces of two release sheets and laminated using a roll laminator to produce a laminate of [release sheet/resin paste layer/release sheet]. The resin paste layer was then thermally cured by heating the above laminate at 70° C. for 30 minutes to produce the heat dissipation sheet of Example 1 as a laminate of [release sheet/heat dissipation sheet/release sheet]. In addition, the heat dissipation sheet of Example 1 was produced in three types: a thickness of 0.36 mm (Type 1), a thickness of 0.73 mm (Type 2), and a thickness of 1.99 mm (Type 3).

Example 2
Alumina prepared by mixing 40% by volume of spherical alumina particles with a peak particle size of 45 μm, 50% by volume of spherical alumina particles with a peak particle size of 5 μm, and 10% by volume of spherical alumina particles with a peak particle size of 0.2 μm. Particle composition 2 was produced. Note that the above three types of alumina particles were previously surface-treated with a silane coupling agent in the same manner as in Example 1. Then, a heat dissipation sheet of Example 2 was produced in the same manner as in Example 1 except that alumina particle composition 2 was used instead of alumina particle composition 1. In addition, the heat dissipation sheet of Example 2 was produced in three types: 0.45 mm thick (Type 1), 0.77 mm thick (Type 2), and 1.97 mm thick (Type 3).

Comparative example 1
Alumina prepared by mixing 70% by volume of spherical alumina particles with a peak particle size of 70 μm, 12% by volume of non-spherical alumina particles with a peak particle size of 9 μm, and 18% by volume of non-spherical alumina particles with a peak particle size of 3 μm. Particle composition 3 was produced. Note that the above three types of alumina particles were previously surface-treated with a silane coupling agent in the same manner as in Example 1. Then, a heat dissipation sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that Alumina Particle Composition 3 was used instead of Alumina Particle Composition 1. Note that two types of heat dissipation sheets of Comparative Example 1 were prepared, one having a thickness of 0.99 mm (Type 1) and one having a thickness of 2.32 mm (Type 2).

Comparative example 2
Alumina particles made by mixing 80% by volume of spherical alumina particles with a peak particle size of 90 μm, 10% by volume of spherical alumina particles with a peak particle size of 5 μm, and 10% by volume of non-spherical alumina particles with a peak particle size of 3 μm. Composition 4 was prepared. Note that the above three types of alumina particles were previously surface-treated with a silane coupling agent in the same manner as in Example 1. Then, a heat dissipation sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that alumina particle composition 4 was used in place of alumina particle composition 1. Note that two types of heat dissipation sheets of Comparative Example 2 were prepared, one having a thickness of 1.77 mm (Type 1) and one having a thickness of 2.50 mm (Type 2).

(evaluation)
Each heat dissipation sheet obtained in Examples and Comparative Examples was evaluated as follows. The evaluation results are listed in the table. In addition, in all the examples, the proportion of alumina particles with a particle size of 30 to 60 μm in the total alumina particles is within the range of 9 to 60% by volume, and the proportion of alumina particles with a particle size of 2 to 12 μm is within the range of 9 to 60 volume %. is within the range of 30 to 90% by volume, and the proportion of alumina particles with a particle size of 0.1 to 1 μm is within the range of 1 to 20% by volume.

(1) Appearance The appearance of the heat dissipation sheet when one release sheet was peeled off from the [release sheet/heat dissipation sheet/release sheet] laminate obtained in Examples and Comparative Examples was evaluated using the following criteria. went.
○ (Good): No falling off or cracking of alumina particles, and no sticking to the peeled release sheet.
× (Poor): Alumina particles fell off, cracked, or stuck to the peeled release sheet.

(2) Thermal diffusivity The heat dissipation sheets obtained in Examples and Comparative Examples were laminated to create a bulk body with a thickness of 1 mm or more, and a thermophysical property measuring device (product name "LFA-502", Kyoto Electronics Industry Co., Ltd. Measurements were carried out using a laser flash method using a commercially available commercially available product.

(3) Thermal conductivity The heat dissipation sheets obtained in Examples and Comparative Examples were measured at 25°C by DSC method using a differential scanning calorimeter (product name "X-DSC7000" type, manufactured by Hitachi High-Tech Science Co., Ltd.). Specific heat measurements were carried out. Further, for each heat dissipation sheet, specific gravity was measured by an underwater displacement method using an electronic hydrometer (trade name "EW-300SG", manufactured by Alpha Mirage Co., Ltd.). Then, the thermal conductivity was calculated using the thermal diffusivity, specific heat, and specific gravity obtained above.

The heat dissipation sheet of the present invention (Example) could be manufactured with good film formability even if the thickness was 0.5 mm or less. In addition, the thermal diffusivity and thermal conductivity were high, and the heat dissipation performance was excellent. On the other hand, in the heat dissipation sheets of Comparative Examples 1 and 2, it was not possible to obtain a film having a thickness of 2 mm or less with good film formability.

Claims (4)

A heat dissipation sheet containing alumina particles and silicone resin,
The content of the alumina particles in the heat dissipation sheet is 70% by volume or more,
The alumina particles have peaks in the particle size distribution of 30 to 60 μm, 2 to 12 μm, and 0.1 to 1 μm, respectively,
In the particle size distribution, the proportion of alumina particles with a particle size of 30 to 60 μm in the alumina particles is 9 to 60% by volume, the proportion of alumina particles with a particle size of 2 to 12 μm is 35 to 90% by volume, and the particle size is 0.1 The proportion of ~1 μm alumina particles is 1 to 20% by volume,
A heat dissipation sheet with a thickness of 2.3 mm or less. The heat dissipation according to claim 1, wherein in the particle size distribution, the alumina particles having a peak at 30 to 60 μm, the alumina particles having a peak at 2 to 12 μm, and the alumina particles having a peak at 0.1 to 1 μm are spherical particles. sheet. The heat dissipation sheet according to claim 1 or 2, having a thermal conductivity of 3.5 W/mK or more and less than 5.0 W/mK. The heat dissipation sheet according to any one of claims 1 to 3, having a thermal diffusivity of more than 1.6×10 ^-6 m ² /s.