JP6860287B2 - Thermally conductive filler and transparent thermally conductive resin composition - Google Patents

Description

The present invention relates to a thermally conductive filler that provides a resin composition having both transparency and thermal conductivity, and a transparent thermally conductive resin composition comprising the same.

In recent years, heat generated from electronic circuits and the like has become a problem in LED lighting and power electronics devices, and aluminum heat sinks and the like have been used. Recently, thermal conductive resins have been actively developed from the viewpoint of weight reduction and the like. It is important to ensure transparency in LED lighting and members around displays, and in addition, it is also required to improve thermal conductivity. Conventionally, as a heat conductive resin, a resin to which a carbon-based filler or boron nitride is added has been disclosed, but if a filler is added at a high concentration in order to improve the heat conductivity, the transparency of the resin is impaired. It ends up. A resin composition having both transparency and thermal conductivity by adding a filler having a refractive index close to the resin is disclosed. For example, a resin obtained by adding silica to a silicone resin is disclosed (Patent Document 1), but when trying to maintain transparency, the type and amount of filler added are limited, and the thermal conductivity is insufficient. there were. Further, this method has a problem that the types of resins are limited and cannot be developed into a wide variety of resins. On the other hand, those in which nanofillers such as CNTs and cellulose nanofibers are added to resins are disclosed (Patent Documents 2 and 3), and both transparency and thermal conductivity are mentioned by nano-dispersion of the fillers. It is difficult to add the nanofiller to the resin at a high concentration, and the transparency is lowered when the nanofiller is added at a high concentration, and this method has a limit in achieving both transparency and thermal conductivity.

Japanese Unexamined Patent Publication No. 2012-82314 Japanese Unexamined Patent Publication No. 2006-241248 JP-A-2007-146143

An object of the present invention is to develop a heat conductive filler that provides a resin material having both high transparency and heat conductivity. Another object of the present invention is to develop a transparent heat conductive resin composition using the heat conductive filler.

As a result of diligent studies aimed at solving the above problems, the present inventor has made a resin material having both transparency and thermal conductivity by using a material provided with a refractive index control layer on the surface of the thermally conductive particles. We have found that we can obtain it, and have completed the present invention.
That is, the present invention is characterized by the matters described in the following [1] to [7].
[1] A thermally conductive filler, characterized in that a refractive index control layer is provided on the surface of the thermally conductive particles.
[2] The thermally conductive filler according to the above [1], wherein the refractive index control layer contains at least one element of Si and Al.
[3] The thermally conductive filler according to the above [1] or [2], wherein the thickness of the refractive index control layer is in the range of 0.05 to 1 μm.
[4] The heat conductive filler according to any one of the above [1] to [3], wherein the heat conductive particles have an average particle size in the range of 0.5 to 100 μm.
[5] The heat conductive filler according to any one of the above [1] to [4], wherein the heat conductive particles have a thermal conductivity of 3 W / mK or more.
[6] A resin composition containing the thermally conductive filler according to any one of the above [1] to [5].
[7] The resin composition according to the above [6], wherein the content of the thermally conductive filler is in the range of 5 to 95 wt% of the resin composition.

Since the resin composition composed of the heat conductive filler of the present invention has both transparency and heat conductivity, it leads to solving the heat problem of transparent members such as around LED lighting and around displays.

The thermally conductive filler of the present invention is characterized in that a refractive index control layer is provided on the surface of the thermally conductive particles. The thermally conductive filler refers to particles that are added to a matrix such as a resin to enhance the thermal conductivity. The thermal conductivity of the thermally conductive particles constituting the thermally conductive filler of the present invention is preferably 3 W / mK or more. When the thermal conductivity of the particles is smaller than 3 W / mK, the effect of increasing the thermal conductivity when the thermally conductive filler of the present invention is added to a matrix such as a resin is small. The thermal conductivity of the thermally conductive particles is preferably 5 W / mK or more, and more preferably 7 W / mK or more.

The thermally conductive particles constituting the thermally conductive filler of the present invention can be used regardless of whether they are organic or inorganic, but inorganic particles have high thermal conductivity and are preferable. Examples of the inorganic filler include metal oxides, hydroxides, carbonates, nitrides, and carbides. Of these, oxides, hydroxides and carbonates are preferable.

Examples of the oxide include silicon oxide, aluminum oxide, magnesium oxide and the like.

Examples of the hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide and the like.

Examples of the carbonate include magnesium carbonate and calcium carbonate.

Of these, hydroxides are preferred. Among the hydroxides, aluminum hydroxide and magnesium hydroxide are preferable, and magnesium hydroxide is particularly preferable.

The shape of the thermally conductive particles is not particularly limited, and spherical, rod-shaped, plate-shaped, scaly, needle-shaped, fibrous, hollow, square, and lump-shaped particles can be used.

The thermally conductive particles preferably have an average particle size in the range of 0.5 to 100 μm measured by a laser diffraction method. If the average particle size of the thermally conductive particles is less than 0.5 μm, it becomes difficult to achieve both transparency and thermal conductivity, and if it exceeds 100 μm, the mechanical properties such as the strength of the resin composition are impaired. The average particle size of the thermally conductive particles is preferably in the range of 1 to 50 μm, more preferably in the range of 5 to 30 μm.

The average particle size of the thermally conductive particles is measured by laser diffraction.

The refractive index control layer constituting the heat conductive filler of the present invention is characterized by being composed of a component having a refractive index different from that of the heat conductive particles. The component of the refractive index control layer may be an organic system, an inorganic system, or an organic / inorganic composite, but is preferably an inorganic system or an organic / inorganic composite, and is an inorganic system. More preferably. The refractive index control layer preferably contains at least one element selected from the group consisting of Si, Al and Ti, and more preferably contains at least one element among Si and Al. Furthermore, the refractive index control layer is preferably selected from silicon oxide, aluminum oxide and composite oxides thereof. Further, the refractive index control layer may be composed of a single component or a plurality of components. When it is composed of a plurality of components, it may have a multi-layer structure or an inclined structure in which the components are slightly different from the innermost surface to the outermost surface.

The thickness of the refractive index control layer is preferably in the range of 0.05 to 1 μm. When the thickness of the refractive index control layer is less than 0.05 μm, the effect of increasing the transparency when the heat conductive filler of the present invention is added to a matrix such as a resin becomes small, and when it exceeds 1 μm, the effect of increasing the thermal conductivity May be smaller. The thickness of the refractive index control layer is more preferably in the range of 0.1 to 0.5 μm. Further, the refractive index control layer preferably completely covers the heat conductive particles, but may not completely cover the heat conductive particles. The shape of the refractive index control layer does not necessarily have to be layered, and it may be in the form of particles and adhere to the thermally conductive particles. In the case of the particle shape, the particle size is preferably in the range of 0.05 to 1 μm, more preferably in the range of 0.1 to 0.5 μm.

The difference in refractive index between the thermally conductive particles and the refractive index control layer is preferably 0.15 or less in absolute value. If the difference in refractive index exceeds 0.15, the effect of the refractive index control layer is extremely reduced, and the effect of increasing transparency when the thermally conductive filler of the present invention is added to a matrix such as a resin is reduced. When the refractive index control layer is composed of a plurality of layers, the difference between the refractive index of the innermost surface of the refractive index control layer and the heat conductive particles is used. The difference in refractive index is more preferably 0.10 or less, further preferably 0.05 or less, and even more preferably less than 0.01.

In the heat conductive filler of the present invention, it is preferable that both the heat conductive particles and the refractive index control layer are selected from metal compounds. In this case, the ratio of the content of the metal component (M1) constituting the thermally conductive particles to the content (M2) of the metal component constituting the refractive index control layer, M2 / M1 is 0 in the atomic number concentration ratio of each metal. It is preferably 1 or more. If each consists of a plurality of metal components, the total value is used. When the atomic number concentration ratio is smaller than 0.1, the effect of providing the refractive index control layer is small. The atomic number concentration ratio is preferably 0.5 to 5.0, more preferably 1.0 to 2.5. The atomic number concentration ratio is measured by energy dispersive X-ray analysis (EDS).

The method for producing the thermally conductive filler of the present invention includes a method of mixing the thermally conductive particles and the components of the refractive index control layer in a solvent, and a sol-gel method using a metal alkoxide, which is a refractive index control layer in a solvent. The method of forming the heat conductive particles, the method of coating the heat conductive particles with the components of the refractive index control layer by spraying, or the method of mechanically mixing the heat conductive particles and the components of the refractive index control layer with a ball mill, a mixer, etc. Can be mentioned. Of these, the sol-gel method is preferable because uniform particles can be obtained with high accuracy.

The thermally conductive filler of the present invention may be surface-treated with a silane coupling agent or the like.

The resin composition of the present invention comprises the resin and the thermally conductive filler of the present invention. The refractive index of the refractive index control layer of the heat conductive filler of the present invention is preferably a value between the refractive indexes of the resin and the heat conductive particles. The refractive index control layer may be a single layer, but it is preferable that the layer is composed of a plurality of layers and the refractive index is gradually changed between the heat conductive particles and the resin because the transparency of the resin is excellent. Further, it is more preferable to have an inclined structure in which the components are slightly different from the innermost surface to the outermost surface.

The difference in refractive index between the resin and the refractive index control layer is preferably 0.15 or less in absolute value. If the difference in refractive index exceeds 0.15, the transparency of the resin composition is extremely lowered. When the refractive index control layer is composed of a plurality of layers, the difference between the refractive index of the outermost surface of the refractive index control layer and the resin is used. The difference in refractive index is more preferably 0.10 or less, further preferably 0.05 or less, and even more preferably less than 0.01. Further, the difference in refractive index between the resin and the thermally conductive particles is preferably 0.35 or less in absolute value. When the difference in refractive index exceeds 0.35, the effect of the refractive index control layer becomes extremely small. The difference in refractive index is more preferably 0.25 or less, further preferably 0.15 or less, and even more preferably 0.05 or less.

As the heat conductive filler constituting the resin composition of the present invention, one kind may be used alone, or two or more kinds may be used in coexistence. It is preferable to use two or more types in coexistence from the viewpoint of achieving both thermal conductivity and transparency. Here, as the two or more types of fillers, two or more types of fillers of different types may be used, or fillers of the same type having different average particle sizes may be used in coexistence. In particular, from the viewpoint of transparency, the latter is more preferable.

Further, in addition to the heat conductive filler of the present invention, it is possible to use a small amount of other heat conductive fillers in coexistence as long as the object of the present invention is not impaired. Examples of the thermally conductive filler in this case include CNTs, cellulose nanofibers and inorganic nanoparticles such as titanium oxide, zinc oxide, zirconium oxide and indium tin oxide.

Further, the resin composition of the present invention may contain a filler other than the thermally conductive filler as long as the object of the present invention is not impaired. As such a filler, a flame retardant, an impact resistance improving agent, a reinforcing agent, a weather resistance improving agent, an antioxidant, an antistatic agent, a pigment, a dye and the like can be used.

The resin of the present invention is not particularly limited, but various thermoplastic resins, thermosetting resins such as epoxy resins, rubber-based resins such as silicone resins, and the like can be used. Of these, silicone resin is preferable from the viewpoint of transparency and heat resistance. Further, it is preferable to use a thermoplastic resin that can be melt-molded because the process is simplified. Examples of the thermoplastic resin include polyethylene, polypropylene, polyvinyl alcohol, EVA resin, EVOH resin, polystyrene, AS resin, ABS resin, ASA resin, AES resin, acrylic resin such as PMMA, MS resin, MBS resin, SBC resin, and cycloolefin. Examples thereof include resins, polyacetal resins, polyamide resins, polyester resins, polycarbonate resins, polyurethane resins, liquid crystal polymers, PPS, PEEK, PPE, polysulfone resins, polyimide resins, fluororesins, and thermoplastic elastomers. As the resin, a resin alone having high transparency is preferable, and an amorphous resin is more preferable. The copolymerized polymer is preferable because the refractive index of the resin can be adjusted by changing the copolymerization ratio, and examples of such a resin include MS resin, MBS resin, and transparent ABS resin.

One type of resin may be used alone, or two or more types of resins may be used in coexistence. The refractive index of the resin can be adjusted by using two or more kinds of resins in coexistence. In this case, it is preferable that two or more kinds of resins are compatible with each other at the molecular level from the viewpoint of transparency, and examples of such a combination include PMMA / AS resin, PMMA / PVDF, PVC / AS resin and the like.

The refractive index of the resin is preferably in the range of 1.4 to 1.7, and more preferably in the range of 1.4 to 1.6.

In the resin composition of the present invention, the amount of the filler added is preferably in the range of 5 to 95 wt%. If the amount of the filler added is less than 5 wt%, the thermal conductivity of the resin composition becomes low, and if it exceeds 95 wt%, it becomes difficult to obtain a uniform resin composition and the transparency is lowered. The addition amount is more preferably in the range of 10 to 90 wt%, further preferably in the range of 30 to 90 wt%, and particularly preferably in the range of 50 to 80 wt%.

The method for producing the resin composition of the present invention is not particularly limited, but the resin and filler are predetermined by a uniaxial or multiaxial kneader, a lab plast mill, a batch mixer such as a kneader or a dynamic mixer, a roll kneader or the like. A method of kneading by blending, a method of mixing in a dissolved or suspended state using a solvent, and the like are used, and among these, a method of mixing with a kneader or a mixer without using a solvent is preferable.

The resin composition of the present invention can be molded by a molding method such as injection molding, extrusion molding, compression molding, blow molding, etc., and is a molded product having various three-dimensional shapes other than plate-shaped, film-shaped, and sheet-shaped. Can be. It can also be used in the form of sealants, paints and adhesives.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

In the examples and comparative examples, the evaluation was performed as follows.
(1) Thermal conductivity The thermal conductivity was measured by Kyoto Denshi Kogyo Co., Ltd. QTM-500 using thin film measurement software.
(2) Total light transmittance The measurement was performed using a haze meter HZ-2 manufactured by Suga Test Instruments Co., Ltd.

[Example 1]
Magnesium hydroxide (average particle size 1 μm, thermal conductivity 8 W / mK refractive index 1.56) and tetraethoxysilane were mixed with a catalyst in ethanol, and then stirred at room temperature for 24 hours to obtain a white slurry. After the solute is collected by filtration, it is vacuum-dried at 80 ° C. for 12 hours and then vacuum-dried at 200 ° C. for 30 hours to obtain particles in which magnesium hydroxide (thermally conductive particles) is coated with Si oxide (refractive index control layer). It was. As a result of SEM observation, the thickness of the refractive index control layer was 0.4 μm. As a result of EDS, the atomic number concentration ratio (Si / Mg ratio) of the metal component Si constituting the refractive index control layer and the metal component Mg constituting the heat conductive particles was 2.2. The refractive index of the refractive index control layer was 1.45.

[Example 2]
Magnesium hydroxide (average particle size 1 μm, thermal conductivity 8 W / mK refractive index 1.56), tetraethoxysilane and aluminum chloride are mixed with a catalyst in ethanol, and then stirred at room temperature for 24 hours to obtain a white slurry. It was. After the solute is collected by filtration, it is vacuum dried at 80 ° C. for 12 hours, then vacuum dried at 200 ° C. for 30 hours, and a composite oxide of Si and Al (refractive index control layer) is added to magnesium hydroxide (thermally conductive particles). Coated particles were obtained. As a result of SEM observation, the thickness of the refractive index control layer was 0.2 μm. As a result of EDS, the sum of the metal components Si and Al constituting the refractive index control layer and the atomic number concentration ratio ((Si + Al) / Mg ratio) of the metal component Mg constituting the heat conductive particles were 1.3. The atomic number concentration ratio (Si / Al ratio) of Si and Al was 3. The refractive index of the refractive index control layer was 1.53.

[Example 3]
After mixing 50 parts by weight of silicone resin (two-component mixed type, refractive index after curing 1.41) and 50 parts by weight of particles obtained in Example 1 with a dynamic mixer, press at 120 ° C. using a press molding machine. After molding, the mixture was subsequently heated in an oven at 150 ° C. for 4 hours to obtain a sheet-shaped molded product having an outer diameter of 100 mm × 50 mm and a thickness of 0.5 mm. The thermal conductivity and the total light transmittance were measured using the molded product. The results are shown in Table 1.

[Example 4]
The same operation as in Example 3 was performed except that the particles obtained in Example 2 were used instead of the particles obtained in Example 1. The results are shown in Table 1.

[Comparative Example 1]
The same operation as in Example 3 was performed except that magnesium hydroxide before the refractive index control layer was provided was used instead of the particles obtained in Example 1. The results are shown in Table 1.
[Comparative Example 2]
The same operation as in Example 3 was carried out without adding the particles obtained in Example 1. The results are shown in Table 1.

Comparing each example and the comparative example, the resin composition using the heat conductive filler of the present invention has a higher thermal conductivity than the one without the filler, and the filler without the refractive index control layer is provided. It was found that the thermal conductivity was the same and the total light transmittance was higher than that used, and that it had both thermal conductivity and transparency.

The transparent heat conductive resin composition composed of the heat conductive filler of the present invention is a transparent member such as around an LED lighting or a display, or a transparent member such as a case or a wall material of an electronic device, where there is a heat problem. Can be applied.

Claims (5)

A thermally conductive filler containing thermally conductive particles, wherein the thermally conductive particles are among silicon oxide, aluminum oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, magnesium carbonate, and calcium carbonate. is either one or more, the particle size is in the range of 0.5~100μm an average particle size measured by a laser diffraction method, the refractive index control layer provided on the surface of the thermally conductive particles, the refractive index control The layer is selected from one or more of silicon oxide (except when the heat conductive particles are silicon oxide), aluminum oxide (except when the heat conductive particles are aluminum oxide) and a composite oxide thereof, and the heat is said. A thermally conductive filler characterized in that the difference in refractive index between the conductive particles and the refractive index control layer is 0.15 or less.
The thermally conductive filler according to claim 1, wherein the thickness of the refractive index control layer is in the range of 0.05 to 1 μm. The heat conductive filler according to claim 1 or 2 , wherein the heat conductive particles have a thermal conductivity of 3 W / mK or more. A resin composition containing the thermally conductive filler according to any one of claims 1 to 3. The resin composition according to claim 4 , wherein the content of the thermally conductive filler is in the range of 5 to 95 wt% of the resin composition.