JP2021054968A - Thermally conductive resin sheet - Google Patents

Abstract

To provide a thermally conductive resin sheet that has superior thermal conductivity, flexibility, and long-term stability in physical properties, such as not hardening over time, is good in gloss retention rate, and is capable of preventing haze in a camera lens or the like.SOLUTION: A thermally conductive resin sheet has a thermal conductivity of 5 W/m K or higher and has a 30% compressive strength of 2,000 kPa or less. In a fogging test, it has a gloss retention rate of 70% or more. After a heat-resistance test, it has a change in 30% compressive strength of 30% or less.SELECTED DRAWING: None

Description

The present invention relates to a thermally conductive resin sheet.

The heat conductive resin sheet is mainly arranged between a heating element such as a semiconductor package and a heat radiating element such as aluminum or copper, and has a function of quickly transferring the heat generated by the heating element to the heating element. Have. In recent years, the amount of heat generated per unit area of a semiconductor package has increased due to the high integration of semiconductor elements and the high density of wiring in the semiconductor package. There is an increasing demand for thermally conductive resin sheets that have an improved rate and can promote faster heat dissipation.
As such a heat conductive resin sheet, a heat conductive resin sheet containing a heat conductive filler is known. For example, Patent Document 1 describes an invention relating to a heat conductive resin sheet containing a liquid polybutene and a heat conductive filler, and Patent Document 2 describes an epoxy resin and hexagonal boron nitride as a heat conductive filler. An invention relating to a thermosetting resin sheet containing the above is described.

Japanese Unexamined Patent Publication No. 2012-38763 Japanese Unexamined Patent Publication No. 2013-254880

In general, when the content of the heat conductive filler is increased in order to improve the heat conductivity of the heat conductive resin sheet, the sheet becomes hard, and solder cracks and substrates are formed inside the electronic device using the sheet. There is a concern that warpage may occur and damage electronic components. That is, it is difficult to maintain good flexibility while increasing the thermal conductivity of the thermally conductive resin sheet, and a technique for achieving both of these is desired.
In addition to this, in recent years, it has been regarded as a problem that the physical properties change over time and damage electronic parts, such as the heat conductive resin sheet becoming hard when used for a long time, and the physical properties are stable for a long period of time. Is required to maintain. Further, the heat conductive resin sheet is often used for electronic devices having a camera lens, and the fog of the lens due to the outgas generated from the sheet and the malfunction caused by the fog are regarded as problems. Therefore, the outgas There is a demand for a small amount of heat conductive resin sheet.
The present invention has been made in view of the above-mentioned conventional problems, and is an electronic device provided with a camera lens, which is excellent in thermal conductivity, flexibility, and long-term stability of physical properties such as not becoming hard with time. It is an object of the present invention to provide a heat conductive resin sheet capable of suppressing fogging of a lens even when it is used for such purposes.

As a result of diligent research to achieve the above object, the present inventors have a thermal conductivity of 5 W / m · K or more, a 30% compression strength of 2000 kPa or less, and a gloss retention rate in a fogging test. The present invention has been completed by finding that a thermally conductive resin sheet having 70% or more and a change rate of 30% compressive strength after a heat resistance test of 30% or less solves the above-mentioned problems.

That is, the present invention relates to the following [1] to [9].
[1] Thermal conductivity is 5 W / m · K or more, 30% compression strength is 2000 kPa or less, gloss retention in fogging test is 70% or more, and rate of change in 30% compression strength after heat resistance test. A heat conductive resin sheet having a value of 30% or less.
[2] The thermally conductive resin sheet according to the above [1], wherein the content of the compound having an ester bond is 1000 ppm or less.
[3] The thermally conductive resin sheet according to the above [1] or [2], which contains an antioxidant.
[4] The heat conductive resin sheet according to the above [3], wherein the antioxidant is an antioxidant having no ester bond.
[5] The heat conductive resin sheet according to any one of the above [1] to [4], which contains an elastomer resin.
[6] The thermosetting resin sheet according to the above [5], wherein the elastomer resin contains a liquid elastomer resin.
[7] The heat conductive resin sheet according to any one of the above [1] to [6], which contains a heat conductive filler.
[8] The heat conductive resin sheet according to the above [7], wherein the heat conductive filler contains a non-spherical filler.
[9] The thermally conductive resin sheet according to any one of the above [1] to [8], which is crosslinked.

According to the present invention, there is provided a heat conductive resin sheet which is excellent in heat conductivity, flexibility, and long-term stability of physical properties such as not becoming hard with time, and can prevent fogging of a lens provided in an electronic device or the like. can do.

It is a schematic cross-sectional view of the heat conductive resin sheet composed of a laminated body. It is a schematic cross-sectional view in the use state of the heat conductive resin sheet made of a laminated body.

[Thermal conductive resin sheet]
The thermally conductive resin sheet of the present invention has a thermal conductivity of 5 W / m · K or more and a 30% compressive strength of 2000 kPa or less. In general, the heat conductive resin sheet tends to decrease in flexibility as the heat conductivity is increased, but the heat conductive resin sheet of the present invention has a high thermal conductivity of 5 W / m · K or more. Nevertheless, the 30% compression strength is 2000 kPa or less, and the flexibility is also excellent.
Further, the thermally conductive resin sheet of the present invention has a 30% change rate of compressive strength after a heat resistance test of 30% or less, and is excellent in stability of physical properties for a long period of time.
Further, the heat conductive resin sheet of the present invention has a gloss retention rate of 70% or more in a fogging test, and can suppress fogging of lenses and the like of electronic devices.

(Thermal conductivity)
The thermal conductivity of the thermally conductive resin sheet of the present invention is 5 W / m · K or more. If the thermal conductivity is less than 5 W / m · K, the heat generated from the heating element cannot be sufficiently dissipated. From the viewpoint of improving the heat dissipation of the heat conductive resin sheet, the heat conductivity of the heat conductive resin sheet is preferably 7 W / m · K or more, and more preferably 10 W / m · K or more. Further, the thermal conductivity of the thermally conductive resin sheet should be as high as possible, but is usually 100 W / m · K or less. The thermal conductivity can be easily adjusted to a desired value by adjusting, for example, the content and orientation of the thermally conductive filler described later.

(30% compression strength)
The 30% compressive strength of the heat conductive resin sheet of the present invention is 2000 kPa or less. When the 30% compression strength exceeds 2000 kPa, the flexibility of the sheet is lowered, and it becomes easy to damage the electronic parts inside the electronic device using the sheet. From the viewpoint of increasing the flexibility of the heat conductive resin sheet, the 30% compressive strength of the heat conductive resin sheet is preferably 1500 kPa or less, more preferably 1000 kPa or less, still more preferably 800 kPa or less. The 30% compressive strength of the heat conductive resin sheet is usually 50 kPa or more, preferably 200 kPa or more.
The 30% compressive strength of the heat conductive resin sheet can be adjusted by the type of resin constituting the heat conductive resin sheet described later, the presence or absence of cross-linking, the amount of the heat conductive filler, and the like.
The 30% compressive strength can be determined by the method described in Examples.

The heat conductive resin sheet of the present invention has a 30% change rate of compression strength after a heat resistance test of 30% or less. If the rate of change in 30% compression strength after the heat resistance test exceeds 30%, the heat conductive resin sheet will become hard when used for a long period of time, causing damage to electronic components inside electronic devices that use the sheet. It will be easier to give. From the viewpoint of maintaining the appropriate flexibility of the heat conductive resin sheet and using it stably for a long period of time, the rate of change in the 30% compression strength of the heat conductive resin sheet after the heat resistance test is 0 to 20%. It is preferably 0 to 15%, more preferably 0 to 10%.
The rate of change in the 30% compression strength after the heat resistance test can be adjusted by the presence or absence of the antioxidant to be used, which will be described later, the type of resin, the amount of the heat conductive filler, the gel fraction, and the like.
In the present specification, the heat resistance test means a test in which a sample (thermally conductive resin sheet) is heated at 150 ° C. for 1000 hours. Further, the rate of change (%) of the 30% compression strength after the heat resistance test is calculated by the following formula (1).
｜ (1-30% compression strength before heat resistance test / 30% compression strength after heat resistance test) × 100 ｜ Equation (1)
The formula (1) represents an absolute value of (1-30% compression strength before heat resistance test / 30% compression strength after heat resistance test) × 100.

(Gloss retention rate)
The gloss retention rate in the fogging test of the heat conductive resin sheet of the present invention is 70% or more. If the gloss retention rate is less than 70%, lenses and the like provided in electronic devices and the like are likely to become cloudy, and malfunctions are likely to occur. The gloss retention of the heat conductive resin sheet in the fogging test is preferably 75% or more, more preferably 80% or more. The upper limit of the gloss retention rate is 100%.
The fogging test is carried out in accordance with the German industrial standard DIN75201-A. Specifically, a disk-shaped heat conductive resin sheet having a thickness of 2 mm and a diameter of 80 mm is placed in a beaker with a height of 1000 mL, a glass plate is placed so as to cover the upper part of the beaker, and the temperature is further placed on the glass plate. A cooling plate kept at 21 ° C. is placed. Next, the beaker containing the heat conductive resin sheet is heated to 100 ° C. by an oil bath. Then, after holding in this state for 16 hours, the glossiness of the surface of the glass plate is measured. From the gloss value of the glass plate after the test (gloss value after the test) and the gloss value of the glass plate before the test (gloss value before the test) obtained in this way, the gloss retention rate is calculated by the following formula. be able to.
Gloss retention rate (%) = 100 x (gloss value after test) / (gloss value before test)
The gloss value is a gloss value of 60 °, which is a value measured by a gloss meter (“Precision gloss meter GM-26PRO” manufactured by Murakami Color Technology Research Institute).
The gloss retention rate can be adjusted by adjusting the content of the compound having an ester bond, which will be described later, the type of the antioxidant, the amount of the resin, the amount of the thermally conductive filler, and the like.

(Content of compound having ester bond)
The heat conductive resin sheet of the present invention preferably has a content (weight) of a compound having an ester bond of 1000 ppm or less. This makes it easier to adjust the gloss retention rate within the above range. A compound having an ester bond is easily decomposed when it is heated when producing a heat conductive resin sheet or when the heat conductive resin sheet is crosslinked by organic peroxide or ionizing radiation, and the decomposed product causes the decomposition product. It is presumed that the gloss retention rate is reduced.
The content of the compound having an ester bond in the thermally conductive resin sheet is preferably 500 ppm or less, more preferably 100 ppm or less, still more preferably 0 ppm.
Examples of the compound having an ester bond include a resin having an ester bond, various additives having an ester bond, and the like.
Examples of the resin having an ester bond include an acrylic resin, a polyester resin such as polyethylene terephthalate and polybutylene terephthalate, and the like.
Examples of various additives having an ester bond include antioxidants having an ester bond, heat stabilizers, colorants, flame retardants, antistatic agents and the like.
From the viewpoint of adjusting the gloss retention of the heat conductive resin sheet of the present invention to the above-mentioned desired range, it is particularly preferable to adjust the content of the antioxidant having an ester bond to the above-mentioned constant value or less.

(resin)
The heat conductive resin sheet of the present invention contains a resin, and the type of the resin is not particularly limited, but an elastomer resin is preferable from the viewpoint of improving flexibility.
Examples of the elastomer resin include acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, natural rubber, polyisoprene rubber, polybutadiene rubber, hydrogenated polybutadiene rubber, styrene-butadiene block copolymer, and hydrogenated styrene. Examples thereof include a-butadiene block copolymer, a hydrogenated styrene-butadiene-styrene block copolymer, a hydrogenated styrene-isoprene block copolymer, and a hydrogenated styrene-isoprene-styrene block copolymer.
The above-mentioned elastomer resin may be a solid elastomer at normal temperature (23 ° C.) and normal pressure (1 atm), or may be a liquid elastomer.

Based on the total amount of resin in the heat conductive resin sheet of the present invention, the content of the elastomer resin is preferably 60% by mass or more, more preferably 80% by mass or more, and further preferably 100% by mass.

From the viewpoint of improving the flexibility of the heat conductive resin sheet of the present invention, the elastomer resin in the heat conductive resin sheet preferably contains a liquid elastomer resin. The liquid elastomer resin is not particularly limited, and for example, liquid ones among the above-mentioned elastomer resins can be used. Among them, liquid acrylonitrile butadiene rubber, liquid ethylene-propylene-diene rubber, liquid polyisoprene rubber, and liquid polybutadiene can be used. Rubber is preferred.
Only one type of elastomer resin may be used, or a plurality of types may be used in combination.

The viscosity of the liquid elastomer resin at 25 ° C. is preferably 1 to 150 Pa · s, more preferably 10 to 100 Pa · s. When two or more kinds of liquid elastomer resins are mixed and used, it is preferable that the viscosity after mixing is as described above. Within the above range, it becomes easy to prevent contamination of electronic parts.

The content of the liquid elastomer is preferably 60% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass with respect to the total amount of elastomer resin.

(Thermal conductive filler)
The thermally conductive resin sheet of the present invention preferably contains a thermally conductive filler. The thermally conductive filler is preferably dispersed in the resin in the thermally conductive resin sheet. The thermal conductivity of the thermally conductive filler is not particularly limited, but is preferably 12 W / m · K or more, more preferably 12 to 300 W / m · K, still more preferably 15 to 70 W / m · K, still more preferably. It is 25 to 70 W / m · K.
Examples of the material of the thermally conductive filler include carbides, nitrides, oxides, hydroxides, metals, carbon-based materials and the like.
Examples of the carbide include silicon carbide, boron carbide, aluminum carbide, titanium carbide, and tungsten carbide.
Examples of the nitride include silicon nitride, boron nitride, boron nitride nanotubes, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, magnesium nitride, molybdenum nitride, and lithium nitride.
Examples of oxides include iron oxide, silicon oxide (silica), aluminum oxide (alumina) (including aluminum oxide hydrate (bemite, etc.)), magnesium oxide, titanium oxide, cerium oxide, zirconium oxide and the like. Can be mentioned. Further, examples of the oxide include transition metal oxides such as barium titanate, and further examples of which metal ions are doped, such as indium tin oxide and antimonthine oxide.

Examples of the hydroxide include aluminum hydroxide, calcium hydroxide, magnesium hydroxide and the like.
Examples of the metal include copper, gold, nickel, tin, iron, or alloys thereof.
Examples of carbon-based materials include carbon black, graphite, diamond, graphene, fullerenes, carbon nanotubes, carbon nanofibers, nanohorns, carbon microcoils, nanocoils and the like.

Examples of the thermally conductive filler other than the above include talc, which is a silicate mineral.
These thermally conductive fillers can be used alone or in combination of two or more. The thermally conductive filler is at least one selected from the group consisting of aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, graphene, boron nitride nanotubes, carbon nanotubes, and diamond from the viewpoint of thermal conductivity. Is preferable. Further, in the case of a non-spherical filler described later, the heat conductive filler is preferably at least one of boron nitride and graphene, while in the case of a spherical filler, aluminum oxide is preferable. Boron nitride is more preferred for applications that require more electrical insulation.

The average particle size of the thermally conductive filler is preferably 0.1 to 300 μm, more preferably 0.5 to 100 μm, and even more preferably 5 to 50 μm. The average particle size can be obtained by measuring the particle size distribution with a laser diffraction type particle size distribution measuring device.

The content of the heat conductive filler in the heat conductive resin sheet is preferably 180 to 3000 parts by mass, more preferably 200 to 2500 parts by mass, and further preferably 250 to 1000 parts by mass with respect to 100 parts by mass of the resin. It is a department.
The content of the thermally conductive filler is preferably adjusted as appropriate according to the shape of the filler.

The shape of the thermally conductive filler is not particularly limited and may be a spherical filler or a non-spherical filler, but a non-spherical filler is preferable.
The thermally conductive filler preferably contains a non-spherical filler. By using the non-spherical filler, it is easy to improve the thermal conductivity with a relatively small amount, so that it is easy to obtain a thermally conductive resin sheet having both good flexibility and high thermal conductivity.
Here, "spherical" means that the shape has an aspect ratio of 1.0 to 2.0, preferably 1.0 to 1.5, and does not necessarily mean that it is a true sphere. The aspect ratio in the case of a spherical filler means a major axis / minor axis ratio. Further, the “non-spherical” means a shape other than the spherical shape, that is, a shape having an aspect ratio of more than 2.

Examples of the non-spherical filler include plate-like fillers such as scaly and flaky fillers, needle-like fillers, fibrous fillers, dendritic fillers, and amorphous fillers. Above all, a plate-shaped filler is preferable from the viewpoint of improving the thermal conductivity of the thermally conductive resin sheet.
The aspect ratio of the heat conductive filler is preferably 5 or more, more preferably 10 or more, and even more preferably 15 or more, from the viewpoint of improving the heat conductivity.
The heat conductive resin sheet can further improve the heat conductivity in the thickness direction by orienting the heat conductive filler having a high aspect ratio at a high orientation angle as described later.
In the non-spherical filler, the aspect ratio is the ratio of the maximum length of the filler to the minimum length (maximum length / minimum length). For example, when the shape is plate-shaped, the maximum length of the filler is The ratio of the thickness to the thickness (maximum length / thickness). The aspect ratio may be determined as an average value by observing a sufficient number (for example, 250) of thermally conductive fillers with a scanning electron microscope.

The minimum length of the thermally conductive filler (corresponding to the thickness in the case of the plate-shaped filler) is preferably 0.05 to 500 μm, more preferably 0.25 to 250 μm from the viewpoint of improving the thermal conductivity.

When the thermally conductive filler contains a non-spherical filler, the content of the non-spherical filler is preferably 180 to 700 parts by mass, and more preferably 200 to 600 parts by mass with respect to 100 parts by mass of the resin. , More preferably 300 to 500 parts by mass. When it is 180 parts by mass or more, the thermal conductivity becomes high, and it becomes easy to achieve the thermal conductivity specified in the present invention. Further, when it is 700 parts by mass or less, the flexibility tends to be good.
The content of the non-spherical filler in the thermally conductive filler is preferably 60% by mass or more, more preferably 90% by mass or more, and preferably 100% by mass based on the total amount of the thermally conductive filler. More preferred.

(Antioxidant)
The thermally conductive resin sheet of the present invention preferably contains an antioxidant. By containing an antioxidant, the rate of change in the 30% compressive strength of the thermally conductive resin sheet after the heat resistance test is reduced, and the long-term physical property stability is improved.
The antioxidant is not particularly limited, and examples thereof include a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-based antioxidant.
Here, the phenolic antioxidant is a compound having a phenolic hydroxyl group. Amine-based antioxidants are compounds having an amino group. A sulfur-based antioxidant is a compound having a sulfur atom. If it has two of these groups, it corresponds to two types of antioxidants. For example, a compound having a phenolic hydroxyl group and an amino group shall correspond to both a phenolic antioxidant and an amine-based antioxidant.

As the antioxidant, an antioxidant having no ester bond is preferable. By using an antioxidant that does not have an ester bond, the gloss retention rate of the fogging test is increased, fogging of lenses and the like provided in electronic devices and the like is prevented, and malfunctions are less likely to occur.
Antioxidants that do not have an ester bond include, for example, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6. -(1H, 3H, 5H) -trione, 4,4', 4'-(1-methylpropanol-3-iriden) tris (6-tert-butyl-m-cresol), 6,6'-di- tert-Butyl-4,4'-butylidene-di-m-cresol, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxyphenylmethyl) -2,4,6-trimethylbenzene Phenolic antioxidants such as 2-mercaptobenzothiazole, 2-mercaptobenzoimidazole, sulfur-based antioxidants such as tetramethylthium monosulfide, phenylnaphthylamine, 4,4'-dimethoxydiphenylamine, 4,4'-bis Amines such as (α, α-dimethylbenzyl) diphenylamine, 4-isopropoxydiphenylamine, 3- (N-salicyloyl) amino-1,2,4 triazole, N, N'-di-2-naphthyl-p-phenylenediamine Examples include system antioxidants.
Among these, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxyphenylmethyl) -2,4,6-trimethylbenzene, 3- (N-salicyloyl) amino-1,2 , 4-Triazole, N, N'-di-2-naphthyl-p-phenylenediamine and the like are preferred.

As the antioxidant, an antioxidant having no ester bond and having no tertiary or quaternary carbon is preferable. By using such an antioxidant, the gloss retention rate in the fogging test of the heat conductive resin sheet is more effectively improved, and the physical property stability for a long period of time is also improved. Here, the tertiary carbon is a carbon bonded to three carbon atoms, and the quaternary carbon is a carbon bonded to four carbon atoms. The carbon atoms constituting the aromatic ring such as the benzene ring and the naphthalene ring do not correspond to the tertiary carbon and the quaternary carbon.

Among the antioxidants having no ester bond and having no tertiary or quaternary carbon, preferred antioxidants are 3- (N-salicyloyl) amino-1,2,4 triazole, N, N'. -Di-2-naphthyl-p-phenylenediamine and the like can be mentioned.

The content of the antioxidant in the thermally conductive resin sheet is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and further preferably 1 with respect to 100 parts by mass of the resin. ~ 5 parts by mass. When the content of the antioxidant is at least these lower limit values, the rate of change in the 30% compression strength after the heat resistance test becomes small, and the long-term physical property stability is improved. When the content of the antioxidant is not more than these upper limit values, the gloss retention rate in the fogging test becomes high.

(Other additives)
Additives other than the antioxidant may be added to the heat conductive resin sheet of the present invention as needed. Other additives include heat stabilizers, colorants, flame retardants, antistatic agents, fillers other than the heat conductive fillers, decomposition temperature adjusters, and other additives generally used for heat conductive resin sheets. May be blended.

(Orientation)
In the heat conductive resin sheet, the long axis of the heat conductive filler is preferably oriented at an angle larger than 45 ° with respect to the sheet surface which is the surface of the heat conductive resin sheet, and more preferably 50 ° or more. It is more preferably oriented at an angle of 60 ° or more, more preferably 70 ° or more, still more preferably 80 ° or more. When the heat conductive filler has such an orientation, the heat conductivity in the thickness direction of the heat conductive resin sheet is improved. The long axis of the heat conductive filler coincides with the maximum length of the above-mentioned heat conductive filler.

The above angle can be measured by observing the cross section of the heat conductive resin sheet in the thickness direction with a scanning electron microscope. For example, first, a thin film section of the central portion in the thickness direction of the heat conductive resin sheet is prepared. Then, the thermally conductive filler in the thin film section is observed with a scanning electron microscope (SEM) at a magnification of 3000 times, and the angle formed by the long axis of the observed filler and the surface constituting the sheet surface is measured. Can be obtained by In the present specification, an angle of 45 °, 50 °, 60 °, 70 °, 80 ° or more means that the average value of the values measured as described above is the angle or more. For example, "aligned at an angle of 70 ° or more" does not deny the existence of a thermally conductive filler having an orientation angle of less than 70 ° because 70 ° is an average value. If the angle formed exceeds 90 °, the complementary angle is used as the measured value.

(Gel fraction)
The thermally conductive resin sheet of the present invention is preferably crosslinked, and preferably has a constant gel fraction (crosslinking degree), from the viewpoint of excellent long-term physical stability.
The overall gel fraction of the thermally conductive resin sheet is preferably 50% by mass or less, more preferably 40% by mass or less, and 30% compression after the heat resistance test from the viewpoint of improving flexibility. From the viewpoint of reducing the rate of change in strength, the gel fraction is preferably 5% by mass or more, and preferably 10% by mass or more.

(Laminated body)
The heat conductive resin sheet of the present invention may be a single layer or a laminated body. From the viewpoint of improving thermal conductivity, a laminate in which a resin layer containing a resin and a non-spherical filler is laminated is preferable. Hereinafter, an example of an embodiment in which a resin layer containing a resin and a non-spherical filler is laminated will be described with reference to FIG.
In each figure, each filler overlaps with the fillers adjacent to the top and bottom, but in the present invention, the fillers do not necessarily overlap with each other.
As shown in FIG. 1, the heat conductive resin sheet 1 has a structure in which a plurality of resin layers 2 are laminated. The surface perpendicular to the laminated surface of the plurality of resin layers 2 is the sheet surface 5 which is the surface of the resin sheet 1.

The thickness of the heat conductive resin sheet 1 (that is, the distance between the sheet surface 5 and the sheet surface 5) is not particularly limited, but can be, for example, in the range of 0.1 to 30 mm.
The thickness of one layer of the resin layer 2 (resin layer width) is not particularly limited, but is preferably 1000 μm or less, more preferably 500 μm or less, and preferably 0.1 μm or more, more preferably 0.5 μm or more, and further. It can be preferably 1 μm or more. By adjusting the thickness in this way, the thermal conductivity can be increased.
The resin layer 2 is a heat conductive resin layer 7 containing a heat conductive filler 6. The heat conductive resin layer 7 has a structure in which the heat conductive filler 6 is dispersed in the resin 8.
In each resin layer 2, the thermally conductive filler has an angle larger than 45 ° with respect to the sheet surface, more preferably 50 ° or more, still more preferably 60 ° C or more, still more preferably 70 ° or more, and further. It is preferably oriented at an angle of 80 ° or more.

The thickness of the heat conductive resin layer 7 is preferably 1 to 1000 times, more preferably 1 to 500 times, the thickness of the heat conductive filler 6 contained in the heat conductive resin layer 7.
By setting the width (thickness) of the heat conductive resin layer 7 in the above range, the long axis of the heat conductive filler 6 can be easily oriented at an angle close to 90 ° with respect to the sheet surface. The width of the heat conductive resin layer 7 does not have to be uniform as long as it is within the above range.

[Manufacturing method of thermally conductive resin sheet]
The method for producing the thermally conductive resin sheet of the present invention is not particularly limited, but when producing a single-layer thermally conductive resin sheet, for example, a non-spherical thermally conductive filler, a resin, and if necessary, are added. A heat conductive resin sheet may be formed by supplying the agent to an extruder and extruding the mixture obtained by melt-kneading into a sheet from the extruder.

(Manufacturing method of laminated body)
The method for producing the thermally conductive resin sheet composed of the laminate of the present invention is not particularly limited, but as described below, it can be produced by a method including a kneading step, a lamination step, and if necessary, a slicing step. it can.

<Kneading process>
The heat conductive filler and the resin are kneaded to prepare a heat conductive resin composition.
In the above-mentioned kneading, for example, it is preferable to knead the thermally conductive filler and the resin under heating using a twin-screw kneader such as a plast mill, a twin-screw extruder, or the like, whereby the thermally conductive filler is preferably kneaded. Can be obtained as a heat conductive resin composition uniformly dispersed in the resin.
Next, by pressing the heat conductive resin composition, a sheet-shaped resin layer (heat conductive resin layer) can be obtained.

<Laminating process>
In the laminating step, the resin layers obtained in the kneading step are laminated to prepare a laminated body having an n-layer structure. A lamination method, for example, a resin layer was prepared in the kneading step is laminated with x _i split, after making a stack of x _i layer structure, if necessary, subjected to hot pressing, then, further, needs Correspondingly, a method of producing a laminated body having an n-layer structure with a width of D μm can be used by repeating the division, the lamination, and the above-mentioned heat press.
When the heat conductive filler is plate-shaped, the width (D μm) of the laminated body and the thickness (d μm) of the heat conductive filler after the laminating step satisfy 0.0005 ≦ d / (D / n) ≦ 1. It is more preferable to satisfy 0.001 ≦ d / (D / n) ≦ 1, and further preferably 0.02 ≦ d / (D / n) ≦ 1.
In this way, when molding is performed a plurality of times, the molding pressure at each time can be reduced as compared with the case where the molding is performed once, so that a phenomenon such as destruction of the laminated structure due to molding can be caused. It can be avoided.
As another laminating method, for example, a method of preparing the multi-layer forming block using an extruder equipped with the multi-layer forming block and coextruding to obtain the n-layer structure and the laminated body having the thickness of D μm. Can also be used.
Specifically, the heat conductive resin composition obtained in the kneading step is introduced into both the first extruder and the second extruder, and the heat conductivity is transmitted from the first extruder and the second extruder. Extrude the resin composition at the same time. The thermally conductive resin composition extruded from the first extruder and the second extruder is sent to the feed block. In the feed block, the heat conductive resin composition extruded from the first extruder and the second extruder merges. Thereby, a two-layer body in which the heat conductive resin composition is laminated can be obtained. Next, the two-layer body is transferred to the multi-layer forming block, and the two-layer body is divided into a plurality of layers along a plurality of surfaces parallel to the extrusion direction and perpendicular to the laminated surface, and then laminated. , An n-layer structure and a laminated body having a thickness of D μm can be produced. At this time, the thickness (D / n) per layer can be set to a desired value by adjusting the multilayer forming block.

(Slicing process)
A heat conductive resin sheet can be produced by slicing the laminated body obtained in the laminating step in a direction parallel to the laminating direction.

(Other processes)
In the method for producing a thermally conductive resin sheet, it is preferable to provide a step of cross-linking the resin. By cross-linking, it becomes easy to reduce the rate of change in the 30% compressive strength of the thermosetting resin sheet after the heat resistance test. Crosslinking may be performed by, for example, a method of irradiating ionizing radiation such as electron beam, α ray, β ray, γ ray, or a method using an organic peroxide. From the viewpoint of reducing the rate of change in the 30% compression intensity, the acceleration voltage when performing electron beam irradiation is preferably 50 to 800 kV, more preferably 200 to 700 kV, and even more preferably 400 to 600 kV. From the same viewpoint, the irradiation amount of electron beam irradiation is preferably 200 to 1200 kGy, more preferably 300 to 1000 kGy, and even more preferably 400 to 800 kGy.

The thermally conductive resin sheet of the present invention has a low rate of change in thermal conductivity, flexibility, and 30% compression strength after a heat resistance test, and is excellent in long-term physical property stability. Utilizing such characteristics, the heat conductive resin sheet of the present invention promotes heat dissipation from the heating element to the heat radiating element by, for example, arranging it between the heating element and the heat radiating element inside the electronic device. be able to. This will be described with reference to the thermally conductive resin sheet 1 described with reference to FIG.
As shown in FIG. 2, the heat conductive resin sheet 1 is arranged so that the sheet surface 5 is in contact with the heating element 3 and the heat radiating element 4. Further, the heat conductive resin sheet 1 is arranged in a compressed state between two members such as the heating element 3 and the heat radiating element 4. The heating element 3 is, for example, a semiconductor package or the like, and the heat radiating element 4 is, for example, a metal such as aluminum or copper. By using the heat conductive resin sheet 1 in such a state, the heat generated by the heating element 3 is easily diffused to the heat radiating body 4, and efficient heat dissipation is possible.

Further, the thermally conductive resin sheet of the present invention has a high gloss retention rate in the fogging test. Therefore, it is particularly preferable to use it for an electronic device having a camera lens such as an in-vehicle camera, a drive recorder, a digital camera, a smartphone, and a mobile phone. As a result, fogging of the camera lens can be suppressed, and malfunction of the electronic device can be prevented.

The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

The materials used in the following examples and comparative examples are as follows.
Resin / Liquid Elastomer 1: Liquid polybutadiene rubber, manufactured by Kuraray Co., Ltd., trade name "L-1203"

(2) Thermally conductive filler (i) Boron nitride Denka Co., Ltd., trade name "SGP"
Shape; non-spherical (plate-shaped)
Aspect ratio; 20
Thermal conductivity in the long side direction; 250 W / m · K
Thickness: 1 μm

(3) Antioxidant (i) Antioxidant 1 (with ester group, with quaternary carbon)
Pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], manufactured by ADEKA Corporation, trade name "ADEKA STAB AO-60"
(Ii) Antioxidant 2 (no ester group, no tertiary and quaternary carbon)
3- (N-salicyloyl) amino-1,2,4 triazole, manufactured by ADEKA Corporation, trade name "ADEKA STAB CDA-1"
(Iii) Antioxidant 3 (with ester, without tertiary and quaternary carbon)
Distearyl thiodipropionate, "Nocrack 400S" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
(Iv) Antioxidant 4 (without ester group, with quaternary carbon)
1,3,5-Tris (3,5-di-tert-butyl-4-hydroxyphenylmethyl) -2,4,6-trimethylbenzene, manufactured by ADEKA Corporation, trade name "ADEKA STAB AO-330"
(V) Antioxidant 5 (no ester group, no tertiary and quaternary carbon)
N, N'-di-2-naphthyl-p-phenylenediamine, "Nocrack White" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

Various physical properties and evaluation methods are as follows.
<Viscosity>
50 g of the resin was measured at 25 ° C. with a B-type viscometer (manufactured by Toyo Sangyo Co., Ltd.).
<Thermal conductivity>
The thermal conductivity in the thickness direction of the obtained thermally conductive resin sheet was measured using a laser flash method thermal constant measuring device (“LFA447” manufactured by NETZSCH).
<30% compression strength>
The 30% compressive strength of the obtained thermally conductive resin sheet was measured using "RTG-1250" manufactured by A & D Co., Ltd. The sample dimensions were 2 mm × 15 mm × 15 mm, the measurement temperature was 23 ° C., and the compression rate was 1 mm / min.

<30% change rate of compression strength after heat resistance test>
The obtained thermally conductive resin sheet was heated in an oven at 150 ° C. for 1000 hours, 30% compression strength was measured, and the rate of change in physical properties after the heat resistance test was determined by the following formula.
The rate of change in 30% compression strength after the heat resistance test was calculated by the following formula (1).
｜ (1-30% compression strength before heat resistance test / 30% compression strength after heat resistance test) × 100 ｜ Equation (1)

<Assembly test>
An assembly test was conducted on the test substrate on which BGA (Ball Grid Array) was mounted so that the obtained heat conductive resin sheets before and after the heat resistance test were compressed by 30%, and solder cracks, short circuits, etc. after assembly were performed. The presence or absence of defects such as discoloration was observed using an X-ray apparatus. It was evaluated according to the following evaluation criteria.
A: No defects B: With cracks
C: With discoloration D: With cracks and discoloration

<Gloss retention in fogging test>
According to the German industrial standard DIN75201-A, the gloss retention rate was measured as follows, and the degree of glass fogging was evaluated.
A disk-shaped heat conductive resin sheet having a thickness of 2 mm and a diameter of 80 mm is placed in a beaker with a height of 1000 mL, a glass plate is placed so as to cover the upper part of the beaker, and the glass plate is further maintained at a temperature of 21 ° C. A cooling plate was placed. Next, the beaker containing the heat conductive resin sheet was heated to 100 ° C. by an oil bath. Then, after holding in this state for 16 hours, the glossiness of the surface of the glass plate was measured. From the gloss value of the glass plate after the test (gloss value after the test) and the gloss value of the glass plate before the test (gloss value before the test) obtained in this way, the gloss retention rate is calculated by the following formula. , The degree of glass frostiness was evaluated according to the following criteria.
Gloss retention rate (%) = 100 x (gloss value after test) / (gloss value before test)
The gloss value is a gloss value of 60 °, which is a value measured by a gloss meter (“Precision gloss meter GM-26PRO” manufactured by Murakami Color Technology Research Institute).
A: Gloss retention rate is 80% or more B: Gloss retention rate is 60% or more and less than 80% C: Gloss retention rate is 40% or more and less than 60% D: Gloss retention rate is less than 40%

(Example 1)
A mixture consisting of 100 parts by mass of liquid elastomer 1 (manufactured by Kuraray Co., Ltd., trade name "L-1203") and 330 parts by mass of boron nitride (manufactured by Denka Co., Ltd., trade name "SGP") is melt-kneaded and then pressed. As a result, a sheet-like resin layer having a thickness of 0.5 mm, a width of 80 mm, and a depth of 80 mm was obtained. Next, as a laminating step, the obtained resin layer was divided into 16 equal parts and laminated to obtain a laminated body consisting of 16 layers having a total thickness of 8 mm, a width of 20 mm, and a depth of 20 mm. Next, slices were sliced parallel to the stacking direction to obtain a heat conductive resin sheet having a thickness of 2 mm, a width of 8 mm, and a depth of 20 mm. The thickness of one layer of the resin layer constituting the laminated body of the heat conductive resin sheet was 0.5 mm. Next, both sides of the thermosetting resin sheet were irradiated with electron beams having an acceleration voltage of 525 kV and a dose of 600 kGy to crosslink the sheets. Each item in Table 1 was evaluated for this thermally conductive resin sheet.

(Examples 2 and 3, Comparative Examples 1 and 2)
A thermally conductive resin sheet was obtained in the same manner as in Example 1 except that the composition was changed as shown in Table 1. Each item in Table 1 was evaluated for this thermally conductive resin sheet.

The thermally conductive resin sheet of the present invention shown in Examples 1 to 3 had high thermal conductivity and flexibility, had good assembly test results, and had stable physical properties for a long period of time without becoming hard over time. .. In addition to this, it was found that the gloss retention rate was high and it was easy to prevent fogging of the glass. On the other hand, it was found that the heat conductive resin sheets shown in Comparative Examples 1 and 2 had a low gloss retention rate and it was difficult to prevent fogging of the glass.

1 Thermal conductive resin sheet 2 Resin layer 3 Heating element 4 Heat radiator 5 Sheet surface 6 Thermal conductive filler 7 Thermal conductive resin layer 8 Resin

Claims (9)

Thermal conductivity is 5 W / m · K or more, 30% compression strength is 2000 kPa or less, gloss retention in fogging test is 70% or more, and change rate of 30% compression strength after heat resistance test is 30%. The following is a heat conductive resin sheet. The heat conductive resin sheet according to claim 1, wherein the content of the compound having an ester bond is 1000 ppm or less. The heat conductive resin sheet according to claim 1 or 2, which contains an antioxidant. The heat conductive resin sheet according to claim 3, wherein the antioxidant is an antioxidant that does not have an ester bond. The heat conductive resin sheet according to any one of claims 1 to 4, which contains an elastomer resin. The thermosetting resin sheet according to claim 5, wherein the elastomer resin contains a liquid elastomer resin. The heat conductive resin sheet according to any one of claims 1 to 6, which contains a heat conductive filler. The heat conductive resin sheet according to claim 7, wherein the heat conductive filler contains a non-spherical filler. The heat conductive resin sheet according to any one of claims 1 to 8, which is crosslinked.

Images