JP5735874B2 - Thermally conductive sheet - Google Patents

Description

  The present invention relates to a thermally conductive sheet excellent in thermal conductivity, heat dissipation, heat distortion resistance, workability, surface smoothness, and flexibility.

  With high performance and long life of LSI semiconductor elements and LED lighting, the semiconductor elements and LED light emitting sections are likely to generate heat. In order to maintain the characteristics of these members over a long period of time, it is necessary to provide a heat conductive sheet on the back surface of the heat generation source and to release heat to the external environment through a member such as a heat sink. Also, with the miniaturization of LSI semiconductor elements and LED lighting, it has been studied to use only a heat conductive sheet instead of a heat sink having a large use volume.

As the heat conductive sheet, a sheet made of silicone resin or acrylic resin is generally used. A heat conductive sheet made of a silicone resin or an acrylic resin is very useful because it is flexible and easy to mold.
However, a thermally conductive sheet made of a silicone resin generates a small amount of siloxane gas, which may adhere to electrode contacts and the like and cause contact failure. Moreover, the heat conductive sheet which consists of acrylic resin may become inadequate in heat resistance.

Therefore, the present inventor forms a heat conductive sheet using polybutylene terephthalate (hereinafter also referred to as “PBT”) having heat resistance without generating a gas that causes poor adhesion of electrode contacts. It was investigated.
Polybutylene terephthalate is widely used in fields such as electric and electronic equipment and automobiles because it has excellent heat resistance and mechanical strength over a long period of time and is easily flame retardant. It is also used for food and pharmaceutical applications because of its heat resistance, heat absorption, low water absorption, excellent wear resistance, chemical resistance, oxygen / water vapor barrier properties, and the like. On the other hand, since it is very strong, it is often used as a molded product and is rarely used as a sheet.
Patent Document 1 discloses a heat-dissipating resin composition using polybutylene terephthalate and a molded product including the same, but it is not applicable to materials that require flexibility or LED-related members.

JP 2008-239898 A

  This inventor makes it a subject to provide the heat conductive sheet which was excellent in workability and a softness | flexibility using polybutylene terephthalate.

The present invention has been made under such knowledge, and the gist thereof is as follows.
30 to 70 parts by weight of boron nitride having a particle size of 3 to 15 μm (D50) is contained with respect to 100 parts by weight of polybutylene terephthalate having a flexural modulus of 500 MPa or less and a thickness of 0.05 to 3.0 mm. to become thermally conductive sheet.

  In the heat conductive sheet of the present invention, 30 to 70 parts by weight of boron nitride having a particle size of 3 to 15 μm (D50) as a heat conductive agent is added to 100 parts by weight of polybutylene terephthalate having a bending elastic modulus of 500 MPa or less. Thus, even when polybutylene terephthalate is used, a flexible sheet can be provided. The heat conductive sheet having excellent flexibility is sufficiently adhered to the heat generating body and the heat radiating body, so that there is little loss of heat conduction and maximum heat conductivity can be exhibited.

  Hereinafter, the present invention will be described in detail.

  The polybutylene terephthalate used in the present invention is obtained by continuous polymerization using terephthalic acid and 1,4-butanediol as main raw materials. The main raw material means that terephthalic acid accounts for 50 mol% or more of the total dicarboxylic acid component, and 1,4-butanediol accounts for 50 mol% or more of the total diol component. The terephthalic acid preferably accounts for 80 mol% or more of the total dicarboxylic acid component, and more preferably 95 mol% or more. 1,4-butanediol preferably accounts for 80 mol% or more of the total diol component, and more preferably 95 mol% or more.

  The dicarboxylic acid component other than terephthalic acid is not particularly limited. For example, phthalic acid, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenylether dicarboxylic acid, 4,4′-benzophenone dicarboxylic acid, 4 , 4′-diphenoxyethanedicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, aromatic dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, It is possible to use alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, etc. I can do it.

  The diol component other than 1,4-butanediol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, polytetramethylene ether glycol, and 1,5-pentane. Diol, neopentyl glycol, 1,6-hexanediol, aliphatic diol such as 1,8-octanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, 1,4 -Arocyclic diols such as cyclohexane dimethylol, aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. use To it can be.

  In the present invention, further, as a copolymerization component, hydroxycarboxylic acid such as glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, p-β-hydroxyethoxybenzoic acid, etc. Monofunctional components such as alkoxycarboxylic acid, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, benzoylbenzoic acid, tricarbaric acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, Trifunctional or higher polyfunctional components such as trimethylolethane, trimethylolpropane, glycerol, pentaerythritol and the like can be used.

  As the polybutylene terephthalate, one having a flexural modulus (ISO 178) of 500 MPa or less is used. If the flexural modulus exceeds 500 MPa, the flexibility of the resulting sheet is impaired. When the flexibility is impaired, the adhesion with the heating element and the heat radiating element is also impaired, so that the thermal conductivity imparted to the sheet is hardly exhibited.

In the present invention, boron nitride is used as a thermal conductive agent for imparting thermal conductivity to polybutylene terephthalate.
In general, the heat conductive agent is a metal heat conductive agent such as silver, copper, or aluminum, a carbon heat conductive agent such as graphite, carbon fiber, carbon nanotube, or silicon carbide, or a metal oxide heat conductive such as alumina or magnesia. Agents, metal hydroxide heat conductive agents such as aluminum hydroxide and magnesium hydroxide, and nitride heat conductive agents such as aluminum nitride are widely used.
However, in the present invention, when a metal or carbon-based thermal conductive agent is used, it cannot be used for a member that requires insulation because it has electrical conductivity. When a metal hydroxide is used as the thermal conductive agent, the matrix is polybutylene terephthalate with a high softening point, so the water in the metal hydroxide evaporates and foams at the sheet molding temperature, or on the sheet surface. Since unevenness may occur, it is not preferable. When aluminum nitride, alumina, or magnesia is used, the hardness of the particles is high. For example, when sheet forming is performed with a T-die extruder, the screw may be worn during kneading. Furthermore, aluminum nitride and silicon nitride have a problem that they are easily hydrolyzed and decomposed under wet heat to generate ammonia.
From the above, in the present invention, boron nitride is used as the thermal conductive agent.

  In the present invention, boron nitride is blended in an amount of 30 to 70 parts by weight with respect to 100 parts by weight of the polybutylene terephthalate. If it is less than 30 parts by weight, the thermal conductivity is difficult to develop. On the contrary, when it exceeds 70 parts by weight, not only the thermal conductivity imparting effect is saturated, but also the sheet formability, the sheet surface smoothness and the flexibility are deteriorated.

  The average particle diameter (D50) of boron nitride is 3 to 15 μm. When it is less than 3 μm, boron nitride is difficult to disperse in polybutylene terephthalate, and sheet workability is impaired. Moreover, when it exceeds 15 micrometers, it exists in the tendency for the surface of a sheet to become rough, and surface smoothness is impaired.

  The heat conductive sheet of the present invention maintains flexibility by adding 30 to 70 parts by weight of boron nitride having a particle size of 3 to 15 μm (D50) as a heat conductive agent to 100 parts by weight of polybutylene terephthalate. It is possible to provide a sheet having thermal conductivity. The heat conductive sheet having excellent flexibility is sufficiently adhered to the heat generating body and the heat radiating body, so that there is little loss of heat conduction and maximum heat conductivity can be exhibited.

  In the present invention, it is possible to use two or more types of boron nitrides having different particle diameters in combination or to use a thermal conductive agent other than boron nitride in combination in order to increase the filling amount of particles as required. The amount of the sheet of the present invention is required to be an amount that does not impair the formability, mechanical properties, and physical properties.

In the present invention, various additives such as a flame retardant, a light stabilizer, an antioxidant, a stabilizer, an antistatic agent, a lubricant, a colorant, and an adhesive can be used.
Flame retardants include melamine cyanurate, ammonium polyphosphate, phosphate ester compounds, ammonium phosphate, ammonium carbonate, zinc stannate, triazine compound, melanin compound, guanidine compound, boric acid, zinc borate, zinc carbonate, hydrotalcite, expansion Examples thereof include graphite. Among these, melamine cyanurate is preferably used in terms of weather resistance and environmental aspects. The blending amount of the flame retardant is about 10 to 30 parts by weight with respect to 100 parts by weight of polybutylene terephthalate. These flame retardants may be used alone or in combination of two or more.

The heat conductive sheet of the present invention is formed by a calendar forming method, an extrusion forming method, an inflation forming method, or the like. The thickness of the heat conductive sheet is preferably 0.05 to 3.0 mm. If the thickness is less than 0.05 mm, the strength of the film tends to decrease. If the thickness exceeds 3.0 mm, the flexibility is impaired, and the heat conductivity may not be sufficiently exhibited due to difficulty in close contact with the heat generator or the heat radiator. There is.

  In forming the heat conductive sheet of the present invention, it is preferable to disperse boron nitride in a small amount of polybutylene phthalate in advance (form a master batch). If boron nitride is dispersed in a small amount of polybutylene terephthalate in advance, it is easily dispersed uniformly in the sheet composition. Also, by making a masterbatch, aggregation of boron nitride can be suppressed and the flowability of the composition at the time of sheet molding is improved, so that a film having excellent surface properties without aggregated grains of boron nitride is obtained. be able to.

The heat conductive sheet of the present invention is used by being bonded to a heat source. At this time, you may provide the adhesion layer containing a thermal radiation agent in the adhesive surface with the heat source of a sheet | seat.
Moreover, in order to improve heat dissipation, it is also possible to apply metal plating to the heat conductive sheet or to apply a heat dissipating paint containing silica, metal powder or the like.
Furthermore, it is also possible to apply a conductive wiring print to the heat conductive sheet, use it as a wiring board sheet, and install it between the LED light emitting board and the heat sink and thermocompression-bond it to make a module.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited by these Examples.

<Examples 1-5, Comparative Examples 1-10>
The compounded materials shown in Table 1 were dried in a vacuum oven (80 ° C. × 760 mmHg condition) for 6 hours, and the resin composition consisting of the compounds shown in Table 1 was used in a T-die extruder (processing temperature 220 ° C.). Thus, a sheet having a thickness of 0.08 mm was obtained.

The following measurements and evaluations were performed on the films obtained from the blends of the examples and comparative examples.
In Comparative Example 3, since the boron nitride particles were fine and the aggregation energy was high, the aggregation state was not solved when kneading with the resin, and a thermally conductive sheet could not be obtained stably. For Comparative Example 6, the magnesium hydroxide was dehydrated and decomposed by the heat of resin fusion and foamed the resin during sheet molding, so a heat conductive sheet could not be obtained.

<Thermal conductivity>
Based on the unsteady hot wire comparison method (hot wire method), the thermal conductivity was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Industry Co., Ltd.) and evaluated according to the following criteria.
○ ・ ・ ・ 1W / mK or more × ・ ・ ・ less than 1W / mK

<Flexibility>
In accordance with ISO 17235, the softness (deflection amount) of the sheet was measured with a softness measuring device (manufactured by MSA, ST-300) and evaluated according to the following criteria.
○ ・ ・ ・ 2mm or more × ・ ・ ・ less than 2mm

<Processability>
The film formability of the sheet was evaluated.
○ ・ ・ ・ No problem △ ・ ・ ・ Difficult to knead × ・ ・ ・ Discharge of the extruder is unstable or the screw of the extruder is worn

<Heat resistance>
The properties of the sheet after an electric oven (130 ° C., 1 hr) were evaluated.
○ ・ ・ ・ No deformation × ・ ・ ・ Deformation

<Surface smoothness>
The surface roughness of the sheet was measured with a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd., Handy Gloss Meter PG-1), and the 60 ° gloss rate was measured and evaluated according to the following criteria. In addition, smoothness is excellent when the numerical value of the gloss rate is large.
○ ・ ・ ・ 5 or more × ・ ・ ・ less than 5

<Heat and heat resistance>
Using a softness measuring device (STA-300, manufactured by MSA), the degree of deterioration of the film that was allowed to stand for 4 weeks in an atmosphere of a constant temperature bath 70 ° C. × 95% RH was measured, and before and after the test. The rate of change in deflection was evaluated.
○ ・ ・ ・ less than 7% × ・ ・ ・ 7% or more

In the table;
PBT1: Polybutylene terephthalate (Mitsubishi Engineering Plastics, Novaduran 5510S, flexural modulus 360 MPa)
PBT2: Polybutylene terephthalate (Mitsubishi Engineering Plastics, Novaduran 5505S, flexural modulus 720 MPa)
Olefin resin 1: ethylene-methacrylic acid copolymer (manufactured by Mitsui DuPont Polychemical Co., Ltd., Nuclerel AN49021C)
Olefin resin 2: Low density polyethylene (Tosoh Corporation, Petrocene 180R)
Olefin resin 3: Polypropylene (manufactured by Nippon Polypropylene, RFG4VA)
Thermal conductive agent 1: Boron nitride (particle size 9.5 μm (D50))
Thermal conductive agent 2: Boron nitride (particle size 13 μm (D50))
Thermal conductive agent 3: Boron nitride (particle size: 4.0 μm (D50))
Thermal conductive agent 4: Boron nitride (particle size 2.2 μm (D50))
Thermal conductive agent 5: Boron nitride (particle size 18 μm (D50))
Thermal conductive agent 6: Aluminum nitride (particle size 6.5 μm (D50))
Thermal conductive agent 7: Magnesium hydroxide (particle size 6.8 μm (D50))

  Examples 1-5 were able to obtain the heat conductive sheet excellent in a softness | flexibility, workability, heat resistance, surface smoothness, and moist heat resistance so that Table 1 might show.

Claims (1)

30 to 70 parts by weight of boron nitride having a particle size of 3 to 15 μm (D50) is contained with respect to 100 parts by weight of polybutylene terephthalate having a flexural modulus of 500 MPa or less and a thickness of 0.05 to 3.0 mm. to become thermally conductive sheet.