JP2022130051A - thermally conductive sheet - Google Patents

Abstract

To provide a thermally conductive sheet excellent in handleability and heat dissipation characteristics.SOLUTION: The thermally conductive sheet of the present invention is a thermally conductive resin sheet in which an adhesive thermally conductive layer and a non-adhesive resin layer are laminated. The adhesive thermally conductive layer contains an acrylic resin obtained by curing an acrylic compound, and a thermally conductive filler. The non-adhesive resin layer contains a thermoplastic resin, a curing agent, and a filler. The tackiness of the adhesive thermally conductive layer is higher than that of the non-adhesive resin layer. The non-adhesive resin layer contains a substance which softens at 30-90°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to thermally conductive sheets.

Thermally conductive sheets are used to improve heat dissipation of electronic components by filling gaps between electronic components and the like that generate heat and heat sinks such as radiator plates and housings. The thermally conductive sheet preferably has adhesiveness in order to be attached to a predetermined location, and various thermally conductive sheets have been proposed from the viewpoint of correcting misalignment during assembly of electronic components and heat sinks. It is

For example, in a thermally conductive sheet containing an acrylic polyurethane resin, a non-functional acrylic polymer, and a thermally conductive filler, by changing the compounding ratio of the acrylic polyurethane resin and the non-functional acrylic polymer in the front layer and the back layer, , a thermally conductive sheet with different adhesiveness (see, for example, Patent Document 1), an adhesive thermally conductive layer containing an acrylic resin and a thermally conductive filler, and a glass transition temperature of 10 ° C. having a functional group such as a hydroxyl group. A thermally conductive sheet laminated with a non-adhesive resin layer containing the above resin, a curing agent and a flame-retardant filler (see, for example, Patent Document 2), the thermally conductive layer has a glass transition temperature of 60 ° C. or higher. A thermally conductive sheet in which a tack-free layer containing a plastic resin and an inorganic filler is laminated (see, for example, Patent Document 3), and a tack-free layer in which wax fine particles are dispersed in an acrylic rubber-based resin is laminated on the thermally conductive flexible layer. A thermally conductive sheet (see, for example, Patent Document 4) has been proposed.

JP 2010-93077 A JP 2015-79948 A JP 2015-170606 A Japanese Patent Application Laid-Open No. 2018-113403

In the techniques of Patent Documents 1 to 4, by making the adhesiveness of the back layer lower than that of the surface layer, it is possible to improve the handling properties such as workability and reworkability of the thermally conductive sheet. The adhesiveness and followability of the sheet were not sufficient, the surface contact resistance increased, and as a result, the thermal properties of the thermally conductive sheet were inferior.

The present invention has been made in view of the above, and an object of the present invention is to provide a heat conductive sheet that is excellent in handleability and heat dissipation properties.

In order to solve the above-described problems and achieve the object, a thermally conductive sheet according to the present invention is a thermally conductive resin sheet in which an adhesive thermally conductive layer and a non-adhesive resin layer are laminated, The adhesive thermally conductive layer contains an acrylic resin obtained by curing an acrylic compound and a thermally conductive filler; the non-adhesive resin layer contains a thermoplastic resin, a curing agent and a filler; The tackiness of the conductive layer is higher than the tackiness of the non-adhesive resin layer, and the non-adhesive resin layer contains a substance that softens at 30°C to 90°C.

ADVANTAGE OF THE INVENTION According to this invention, the heat conductive sheet which is excellent in handleability and can improve a heat dissipation characteristic can be obtained.

1 is a perspective view showing an example of a thermally conductive sheet according to an embodiment of the present technology; FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment described below. Moreover, in the description of the drawings, the same or corresponding elements are given the same reference numerals as appropriate. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationship of each element may differ from the actual one. Even between the drawings, there are cases where portions with different dimensional relationships and ratios are included.

(Thermal conductive sheet)
1 is a perspective view showing an example of a thermally conductive sheet according to an embodiment of the present technology; FIG. In the thermally conductive sheet shown in FIG. 1, an adhesive thermally conductive layer 10 and a non-adhesive resin layer 20 are laminated. A release film 30 is attached to the side surface. The release film 30 is to be released during use.

The thermally conductive sheet according to the present invention has excellent heat dissipation properties, and the surface contact resistance of the thermally conductive sheet is preferably 1.5°C·cm ² /W or less, and preferably 1.4°C·cm 2 /W or less. cm ² /W or less is more preferable.

The adhesive thermally conductive layer 10 contains an acrylic resin obtained by curing an acrylic compound and a thermally conductive filler. The adhesive thermally conductive layer 10 has higher tackiness than the non-adhesive resin layer 20 for the purpose of attaching the thermally conductive sheet 10 to a predetermined place of an adherend such as an electronic component.

The acrylic resin is obtained by curing an acrylic compound, and those having a glass transition temperature of -80°C to 15°C can be preferably used. Acrylic compounds to be used include 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, isononyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate. , 4-hydroxybutyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, isobornyl (meth)acrylate, ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate ) acrylate, phenyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl acrylate, and the like (meth)acrylates can be exemplified. Among them, 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate can be preferably used.

Also, the above compounds can be used in combination as the acrylic compound. In addition, other compounds that can be copolymerized with the above acrylic compounds can also be used as long as they do not impair the tackiness of the adhesive thermally conductive layer. Examples of copolymerizable compounds include (meth)acrylic acid, N-vinylpyrrolidone, and itaconic acid.

As a method for curing the acrylic compound, for example, a photopolymerization initiator, a photocrosslinking agent, or the like is used, and the acrylic compound can be cured by irradiating the compound with ultraviolet rays. In this case, the deterioration of the adhesive thermally conductive layer 10 can be suppressed by irradiating with long-wavelength ultraviolet rays (wavelength 320 nm to 400 nm) for the amount of energy necessary for disassembling the photopolymerization initiator.

The thermally conductive filler contained in the adhesive thermally conductive layer 10 includes metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metals such as aluminum, copper, and silver, metal oxides such as aluminum oxide and magnesium oxide, Nitrides such as aluminum nitride, boron nitride, and silicon nitride, carbon nanotubes, and the like are exemplified, and one or more of these can be used in combination. Among these, from the viewpoint of flame retardancy and insulation, it is preferable to use one or more selected from aluminum hydroxide, alumina, aluminum nitride, and magnesium oxide. For the purpose of strengthening the interface and improving the dispersibility in the resin, those treated with a silane coupling agent, a titanate-based coupling agent, stearic acid, or the like may be used.

The average particle size of the thermally conductive filler is preferably 0.5 μm or more and 100 μm or less. It is preferable to use a large-diameter thermally conductive filler together.

The mixing ratio of the acrylic resin and the thermally conductive filler in the adhesive thermally conductive layer 10 is preferably 100 parts by mass or more and 2000 parts by mass or less of the thermally conductive filler with respect to 100 parts by mass of the acrylic compound. More preferably, the thermally conductive filler is 300 parts by mass or more and 1000 parts by mass or less. When the blending ratio of the thermally conductive filler is less than 100 parts by mass, it becomes difficult to sufficiently increase the thermal conductivity of the thermally conductive sheet. The flexibility of the elastic sheet tends to decrease. When two types of thermally conductive fillers having different average particle diameters are used, the ratio of small-diameter to large-diameter thermally conductive fillers is preferably 15:85 to 90:10.

The adhesive thermally conductive layer 10 may contain a plasticizer in addition to the acrylic resin and the thermally conductive filler. Plasticizers include adipic acid compounds such as dioctyl adipate and diisononyl adipate; sebacic acid compounds such as octyl sebacate and diisodecyl sebacate; phosphoric acid compounds such as tricresyl phosphate; castor oil and other derivatives; Examples include acids, higher fatty acids such as oleic acid and derivatives thereof, phthalic acid compounds such as dibutyl phthalate and dioctyl phthalate, low molecular weight acrylic polymers, waxes, tackifiers and the like. The proportion of the plasticizer in the adhesive thermally conductive layer 10 is preferably 20 parts by mass or more and 80 parts by mass or less, more preferably 30 parts by mass or more and 70 parts by mass or less, relative to 100 parts by mass of the acrylic compound. . The adhesive thermally conductive layer 10 may contain an antioxidant, a heat deterioration inhibitor, a flame retardant, a coloring agent, etc., if necessary.

The layer thickness of the adhesive thermally conductive layer 10 is preferably 150 μm or more and 3000 μm or less. If the layer thickness is less than 150 μm, sufficient conformability to irregularities on the adherend cannot be obtained, and if it exceeds 3000 μm, curing takes a long time, resulting in a decrease in productivity.

The non-adhesive resin layer 20 contains thermoplastic resin, curing agent and filler. The tackiness of the non-adhesive resin layer 20 is lower than that of the adhesive resin layer 10 . The tackiness is measured, for example, at a temperature of 40°C, an aluminum cylindrical probe, a pressing speed of 30 mm/min, a peeling speed of 120 mm/min, a load of 196 g, a pressing time of 5.0 seconds, a pulling distance of 5 mm, a probe heating of 40 ° C, a sheet It can be evaluated by probe tack measured by pressing against the surface of the non-adhesive resin layer 10 and peeling it off under a stage heating condition of 40 ° C. The probe tack of the non-adhesive resin layer 20 is 6 kN / m ² More than 30 kN/m ² or less is preferable. More preferably, it is 7 kN/m ² or more and 28 kN/m ² or less.

From the viewpoint of the tackiness of the non-adhesive resin layer 20 and the adhesion and conformability to the adherend, the thermoplastic resin has at least one functional group selected from a hydroxyl group, an acyl group and a glycidyl group, Those having a glass transition temperature of 10° C. or higher are more preferable. Thermoplastic resins to be used include modified polyolefins such as polyethylene and polypropylene having functional groups such as hydroxyl groups, glycidyl groups, acid anhydride groups, and ionomers, polyesters such as polyethylene terephthalate and polybutylene terephthalate, nylons, ionomers, polyvinyl alcohol, 2-ethylhexyl acrylate-glycidyl methacrylate copolymer, polyparahydroxystyrene, modified polyacrylonitrile, ethylene-maleic anhydride-methyl (meth)acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer Examples include polymers, ethylene-methacrylic acid copolymers, and the like. The thermoplastic resin preferably has a number average molecular weight of 100,000 to 500,000. The curing agent is appropriately selected according to the functional groups of the thermoplastic resin used. As the binder resin, a thermoplastic resin having a glass transition temperature of 10° C. or higher having functional groups such as hydroxyl groups, acyl groups, and glycidyl groups is used to improve the tackiness of the non-adhesive resin layer 20 at room temperature. It can be kept below 10. As the thermoplastic resin, an ethylene-vinyl acetate copolymer is preferable because it can be easily formed into a film, and the solvent solubility and melting point can be easily adjusted. In addition, the glass transition temperature of the thermoplastic resin to be used is preferably 110° C. or less from the viewpoint of adhesive strength with the adhesive heat conductive layer.

The non-adhesive resin layer 20 contains a substance that softens at 30.degree. C. to 90.degree. Since the non-adhesive resin layer 20 contains a substance that softens at 30° C. to 90° C., the non-adhesive resin layer 20 is softened by the heat generated by the adherend during use, Adhesion and conformability to adherends can be exhibited.

Preferably, the substance that softens between 30°C and 90°C is wax. Since the non-adhesive resin layer 20 contains a wax, which is an organic component, as a substance that softens at 30° C. to 90° C., the fluidity of the non-adhesive resin layer 20 can be increased during heating, and the non-adhesive Thinning of the resin layer 20 is facilitated, and the surface contact resistance value of the thermally conductive sheet can be reduced.

Any wax can be used as long as it softens at 30° C. to 90° C. Examples include microcrystalline wax, montanic acid wax, montanic acid ester wax, paraffin wax, polyethylene wax, polypropylene wax, etc., which are solid at room temperature. can do. These waxes may be used singly or in combination of two or more.

The blending ratio of the substance that softens at 30 to 90°C in the non-adhesive resin layer 20 is 30 to 200 parts by mass of the substance that softens at 30 to 90°C per 100 parts by mass of the thermoplastic resin. It is preferable to make it below a part. If the amount of the substance that softens at 30° C. or higher and 90° C. or lower is less than 30 parts by mass, the adhesion and conformability to the adherend will be low, and if it is more than 200 parts by mass, the handleability may be reduced. More preferably, the blending ratio in the non-adhesive resin layer 20 is 75 parts by mass or more and 150 parts by mass or less of the substance that softens at 30° C. or more and 90° C. or less with respect to 100 parts by mass of the thermoplastic resin.

The non-adhesive resin layer 20 contains filler. The filler to be used is appropriately selected according to the required function, but from the viewpoint of thermal conductivity, inorganic oxides and inorganic nitrides are preferable. Examples of inorganic oxides include silica and alumina. Examples of inorganic nitrides include aluminum nitride and boron nitride. In addition, from the viewpoint of emphasizing handling during production and flame retardancy, organic fillers are preferable because they are less likely to settle in the non-adhesive resin layer 20 and are more likely to be uniformly dispersed. Examples of fillers to be used include cyanuric acid compounds such as melamine cyanurate and organic phosphates such as melamine polyphosphate and ammonium polyphosphate. These fillers may be used alone or in combination of two or more.

The average particle diameter of the filler is preferably 0.1 μm or more and 25 μm or less, more preferably 0.5 μm or more and 20 μm or less, from the viewpoint of dispersion stability and appearance. The blending ratio of the filler in the non-adhesive resin layer 20 is preferably 3 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. If the amount of the filler is less than 3 parts by mass, the surface of the adhesive resin layer may become sticky, resulting in deterioration of workability. The traces of paint are easily noticeable, and the appearance deteriorates. More preferably, the blending ratio in the non-adhesive resin layer 20 is 5 parts by mass or more and 25 parts by mass or less of the filler with respect to 100 parts by mass of the thermoplastic resin.

The layer thickness of the non-adhesive resin layer 20 is preferably 2 μm or more and 15 μm or less. If the thickness of the non-adhesive resin layer 20 is less than 2 μm, the handleability of the thermally conductive sheet is reduced, and if the thickness of the non-adhesive resin layer 20 is greater than 15 μm, the thermal resistance of the thermally conductive sheet increases. As a result, the heat dissipation characteristics become insufficient.

As the release film 30, for example, a film of polyethylene terephthalate, polyethylene naphthalate, oriented polypropylene, poly(4-methyl-1-pentene), polytetrafluoroethylene, or the like coated with a release agent such as silicone may be used. can be done.

The non-adhesive resin layer 20 has low tackiness before mounting, and is excellent in handleability. As a result, the surface contact thermal resistance value becomes low and exhibits excellent heat dissipation characteristics. After mounting, the non-adhesive resin layer 20 is thinned by heating and becomes a single layer.

[Method for producing thermally conductive sheet]
The thermally conductive sheet of the present invention is prepared by mixing each component forming the adhesive thermally conductive layer described above with a solvent for the adhesive thermally conductive layer paint, and mixing the component forming the non-adhesive resin layer with the solvent. A coating for forming a non-adhesive resin layer is prepared, and the coating for forming a non-adhesive resin layer and the coating for forming an adhesive thermally conductive layer are sequentially applied to a predetermined thickness on the cover film, and the adhesive thermally conductive layer is applied. It can be produced by covering the layer-forming paint with a release film and irradiating ultraviolet rays from there to cure the acrylic compound of the adhesive heat-conductive layer-forming paint.

The thermally conductive sheet produced as described above can be stored by being rolled up in a state in which the cover film is peeled off and the release film is adhered. The roll-shaped thermally conductive sheet is cut into a predetermined shape, peeled off the release film, and used by being adhered between an adherend such as an electronic component and a heat sink.

Hereinafter, the thermally conductive sheet of the present invention will be described in detail based on examples and comparative examples.

[Materials used]
(Adhesive heat conductive layer)
・Acrylic compound 2-ethylhexyl acrylate ・Plasticizer castor oil-derived fatty acid ester ・Photopolymerization initiator Darocure 1173, manufactured by BASF ・Hardening agent Polypropylene glycol diacrylate, Aronix M270 (propylene chain length n = 12), manufactured by Toagosei・Thermal conductive filler aluminum hydroxide (average particle size 80 μm)
Aluminum hydroxide (average particle size 8 μm)
(Non-adhesive resin layer)
・Thermoplastic resin ethylene-vinyl acetate copolymer (melting point 63°C, Evaflex V523, manufactured by Mitsui Dow Polychemicals)
・Filler fumed silica (Aerosil RY200, manufactured by Evonik)
・Wax Microcrystalline wax (melting point 64°C, Hi-Mic-2045, manufactured by Nippon Seiro)
Microcrystalline wax (melting point 101°C, Hi-Mic-2095, manufactured by Nippon Seiro)

(Example 1)
[Adhesive Thermal Conductive Layer Adjustment]
100 parts by mass of an acrylic compound, 47 parts by mass of a plasticizer, 1.4 parts by mass of a photopolymerization initiator, 1.5 parts by mass of a curing agent, 400 parts by mass of aluminum hydroxide powder (average particle size 80 μm) as a thermally conductive filler, 400 parts by mass of aluminum hydroxide powder (average particle size: 8 μm) was mixed to prepare a coating material for forming an adhesive heat conductive layer.
[Adjustment of non-adhesive resin layer]
100 parts by weight of a thermoplastic resin as a binder resin, 100 parts by weight of wax (Hi-Mic-2045, melting point 64° C.), and 20 parts by weight of a filler were dissolved in toluene and mixed to prepare a paint for forming a non-adhesive resin layer. .
[Thermal conductive resin sheet]
A coating material for forming a non-adhesive resin layer was applied to a 50 μm-thick transparent PET film that had been subjected to release treatment so that the coil bar thickness was 2 μm, and dried at 75° C. for 5 minutes. An adhesive thermally conductive layer was applied thereon with a bar coater so as to have a thickness of 150 μm. After that, one side was covered with a transparent cover film (release layer) made of PET having a thickness of 12 μm that had been subjected to mold release treatment with silicone, and long-wavelength ultraviolet rays were irradiated from both the PET film side and the cover film side with a chemical lamp for 5 minutes. , the thermally conductive sheet of Example 1 was produced.
(Examples 2 and 3)
A thermally conductive sheet was produced under the same conditions as in Example 1, except that the thickness of the non-adhesive resin layer was changed to 8 μm and 14 μm.

(Comparative example 1)
A thermally conductive sheet was produced under the same conditions as in Example 1, except that only the adhesive thermally conductive layer was used as the thermally conductive sheet.

(Comparative example 2)
A thermally conductive sheet was produced under the same conditions as in Example 1 except that the wax in the non-adhesive resin layer was changed to Hi-Mic-1090 (melting point 101° C.) and the thickness of the non-adhesive resin layer was changed to 8 μm. .

(Comparative Examples 3 and 4)
A thermally conductive sheet was produced under the same conditions as in Example 1, except that the thickness of the non-adhesive resin layer was changed to 20 μm and 1 μm.

[evaluation]
The thermally conductive sheets produced in Examples and Comparative Examples were evaluated for surface thermal resistance, handleability, and strength before mounting of the non-adhesive resin layer as follows. Table 1 shows the results.

- Surface resistance value The surface contact thermal resistance value of each sample was measured with a load of 1.0 kgf/cm ² by a method based on ASTM-D5470.
・Handling 〇: No tackiness is felt and the fingers are released smoothly. ×: The tackiness is felt and the fingers are difficult to release.

As shown in Table 1, the thermally conductive sheet of Example 1 is a non-adhesive sheet containing a thermoplastic resin having a specific functional group and a glass transition temperature of 10°C or higher and a substance that softens at 30°C to 90°C. Due to the presence of the resin layer, the non-adhesive resin layer was hard before mounting on the adherend, and the tackiness was low, so the handling property was good. In addition, after mounting, the heat generated by the adherend softens the non-adhesive resin layer, resulting in a structure similar to a single-layer structure consisting of only an adhesive heat-conducting layer, which improves adhesion to the adherend. , the followability was improved, and a surface contact thermal resistance value equivalent to that of the thermally conductive sheet of Comparative Example 1 having no non-adhesive resin layer was obtained.

In the thermally conductive sheets of Examples 2 and 3, although the surface contact thermal resistance value increased as the thickness of the non-adhesive resin layer increased, compared to Comparative Example 2, which does not contain a substance that softens at 30 ° C. to 90 ° C. The surface heat resistance value was sufficiently low, and the handleability was also good.

Comparative Example 1, which does not have a non-adhesive resin layer, has a very low heat resistance value, but is inferior in handleability due to blocking caused by the high tackiness of the adhesive thermally conductive layer.
The thermally conductive sheet of Comparative Example 2 has a hard non-adhesive resin layer and low tackiness, so that it has good handling properties. It has a high surface contact thermal resistance value and poor heat dissipation characteristics.
Comparative Example 3, which has a thick non-adhesive resin layer, is excellent in handleability, but has a high surface contact thermal resistance value.
Comparative Example 4, in which the non-adhesive resin layer was thin, had a low surface contact thermal resistance value, but was fragile and inferior in handleability due to the thin film thickness.

10 adhesive thermally conductive layer, 20 non-adhesive resin layer, 30 release layer

Claims (3)

A thermally conductive resin sheet in which an adhesive thermally conductive layer and a non-adhesive resin layer are laminated,
The adhesive thermally conductive layer contains an acrylic resin obtained by curing an acrylic compound and a thermally conductive filler,
The non-adhesive resin layer contains a thermoplastic resin, a curing agent and a filler,
The tackiness of the adhesive thermally conductive layer is higher than the tackiness of the non-adhesive resin layer,
The non-adhesive resin layer is a thermally conductive sheet containing a substance that softens at 30°C to 90°C. The substance that softens at 30° C. to 90° C. is wax,
The thermally conductive sheet according to claim 1, wherein the non-adhesive resin layer contains the wax in a proportion of 30 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. The thermally conductive sheet according to claim 1 or 2, wherein the non-adhesive resin layer has a thickness of 2 µm or more and 15 µm or less.

Images