WO2015157941A1

WO2015157941A1 - Composition for high thermal conductive materials

Info

Publication number: WO2015157941A1
Application number: PCT/CN2014/075493
Authority: WO
Inventors: Hongyu Chen
Original assignee: Dow Global Technologies Llc; Yang, Yunfeng
Priority date: 2014-04-16
Filing date: 2014-04-16
Publication date: 2015-10-22
Also published as: TWI667338B; TW201604272A

Abstract

A composition containing (A) resin, (B) a filler with thermally conductive, electrically insulative and (C) a filler with thermally conductive, electrically conductive, wherein the content of (C) is 0.2 to 2.0 volume% is disclosed. A molded article formed from the composition has unexpected high thermal conductivity with good electrical insulation as well as easy processability suitable for a thermal management component.

Description

COMPOSITION FOR HIGH THERMAL CONDUCTIVE MATERIALS

Field of the invention

[0001] The present invention relates to a composition for an insulating polymer material with high thermal conductivity suitable for a thermal management element of electronic devices, to a molded article and to a device containing such article.

Background of the invention

[0002] Thermal management is critical in every aspect of the microelectronics space, such as integrated circuits (IC), light-emitting diode (LED), power electronics, displays and photovoltaics. The performance of those devices can be directly affected by operating temperature. Lowering the operating temperature of these devices increases lifetime and improves performance, as compared to operation at higher temperatures.

[0003] In solid state lighting business, there is strong need to improve heat management. Proper dissipation of heat in LED devices is critical to their reliable long-term operation. Failure to adequately manage the heat can have an undesirable impact on the performance of LEDs. Prolonged exposure to excessive operating temperatures can lead to irreversible damage to the semiconductor components within the LED die, resulting in lowered light outputs, changes to the color rendering index, and significantly reduced LED lifetimes. Therefore, a material with higher heat conductive property is desired for heat management of LED devices.

[0004] A heat sink in an electronic system is a passive component that cools a device by dissipating heat into the surrounding air. Heat sinks are used to cool electronic components or semiconductor components such as high-power semiconductor devices, and optoelectronic devices such as higher-power lasers and light emitting diodes (LEDs). Traditional heat sink uses aluminum fins and several copper heat pipes for cooling of high-heat-dissipation processors. A heat sink is designed to increase the surface area in contact with the cooling medium surrounding it, such as the air. However, the metals are heavy and difficult to process a complex form. Therefore, it has been required to develop a material with higher thermal conductive as well as less weight and lower processing cost as alternative to metal.

[0005] Although polymer materials are light and easy to processing, their low thermal conductive property is a barrier of application to a heat sink. To increase thermal conductivity of polymer materials, high amounts of thermal conductive fillers such as boron nitride are added in polymer materials, see e.g.

EP2094772B, WO2013012685A, US20090069483A, WO2012114309A, WO2009043850A, WO2011106252 A, WO2012114310A, US20080265202A and US20120229981A. However, since quite a high amount of filler is needed for thermal conductive polymer materials, it causes a difficulty for process because the high pressure is needed to mold such polymer.

[0006] Carbon based fillers such as graphite have much higher thermal conductivity than boron nitride. Some of the above references disclose the use of graphite in the amount of 5 volume % or more. However, the electrical conductivity of those fillers is high, so the electrical insulation of polymer materials comprising such filler is poor.

[0007] Accordingly, an electrical insulative polymer material with easy processability and high thermal conductivity suitable for a thermal management element of electronic devices is desired.

Summary of the invention

[0008] Inventors of this invention have now found that a molded article formed from a composition comprising at least two kind of fillers; thermally conducte, electrically insulative filler (Filler- 1) and thermally conductive, electrically conductive filler (Filler-2), and when the amount of the Filler-2 is small, the molded article achieved unexpected high thermal conductivity with good electrical insulation suitable for a thermal management component.

[0009] Therefore, one aspect of the invention relates to a composition comprising (a) resin, (b) thermally conductive, electrically insulative filler and (c) thermally conductive, electrically conductive filler, and the content of (c) is 0.2 to 2.0 volume % based on the total volume of the composition.

[0010] Another aspect of the invention relates to a molded article formed from the above composition.

[0011] Further aspect of the invention relates to a device comprising the molded article.

Detailed description of the invention

[0012] As used throughout this specification, the abbreviations given below have the following meanings, unless the context clearly indicates otherwise: g = gram; mg = milligram; m=meter; mm = millimeter; cm=centimeter; min.= minute(s); s = second(s); hr.= hour(s); °C = degree(s) C = degree(s) Centigrade; K=kelvin; W=watt; Q=ohm; wt%=weight percent(s); vol%=volume percent(s). Throughout this specification, the word 'resin' and 'polymer' is used

interchangeably.

[0013] <Composition>

The composition of the invention comprises (a) a resin, (b) a thermally conductive, electrically insulative filler and (c) a thermally conductive, electrically conductive filler, and the content of (c) is 0.2 to 2 volume percent based on the total volume of the composition.

[0014] (a) Resin

Resin used in the invention may be selected from a wide variety of

thermoplastic resins, thermosetting resins, or mixture thereof. The resin may also be a blend of polymers, copolymers, terpolymers, or combinations comprising at least one of the foregoing organic polymers. The resin can also be an oligomer, a homopolymer, a copolymer, a block copolymer, an alternating block copolymer, a random polymer, a random copolymer, a random block copolymer, a graft copolymer, a star block copolymer, a dendrimer, or the like, or a combination comprising at least one of the foregoing polymers.

[0015] Examples of the thermoplastic resin include polyamide,

polyphenylene sulfide (PPS), polyolefin, polyacetal, polycarbonate (PC), polyoxymethylene (POM), polystyrene (PS), polyesters such as polyethylene telephthalate (PET) and polybutylene terephthalate (PBT), liquid crystal polyester (LCP), ethylene-vinyl acetate copolymer,

acrylonitrile-butadiene-stylene (ABS), acrylic resin such as polymethyl methacrylate, polyvinyl chloride, polyacrylonitrile, polyphenylene oxide, polysulfone, polyether sulfone, polyether ether ketone, polyimide, fluorine resin.

[0016] Examples of the thermosetting resin include epoxy resin,

thermosetting polyimide, phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, silicone resin and thermosetting urethane resin.

[0017] Preferably, resin is selected from thermoplastic resins because of their easy processability, such as injection moldability into heat dissipating element with various shape in electronic devices.

[0018] The content of the resin is 15 volume % or more, preferably 20 volume % or more, more preferably 30 volume % or more based on the total volume of the composition. The content of the resin is 55 volume % or less, preferably 45 volume % or less, more preferably 40volume % based on the total volume of the composition.

[0019] (b) Thermally conductive, electrically insulative filler (Filler- 1) The composition used in the invention comprises a thermally conductive, electrically insulative filler (Filler-1). The filler has 20 W/mK or more of intrinsic thermal conductivity. More preferably, the intrinsic thermal

conductivity of the filler is 30 W/mK or more. The volume resistivity of the filler is 10¹² Ω .cm or more, preferably 10¹³ Ω .cm or more. The volume resistivity of a filler can be measured by a method according to ASTM D257-07.

[0020] Examples of Filler-1 include boron nitride (BN), aluminum nitride (A1N), magnesium oxide (MgO), silicon nitride (Si₃N₄) and alumina (AI₂O₃). Preferably, Filler-1 is selected from boron nitride, aluminum nitride, magnesium oxide and silicon nitride. Filler-1 may be used as a mixture.

[0021] The particle size of Filler-1 is 0.1 micro meter or more, preferably 5 micro meter or more. The particle size of Filler-1 is 400 micro meter or less, preferably 100 micro meter or less, more preferably 50 micro meter or less for good processability and mechanical properties. Particle size means median size (D50) and can be measured by laser diffraction particle sizing technique.

[0022] The content of Filler-1 is 45 volume % or more, preferably

55 volume % or more, more preferably 60 volume % or more based on the total volume of the composition. At the same time, the content of Filler-1 is 84.8 volume % or less, preferably 80 volume % or less, more preferably 75 volume % or less based on the total volume of the composition.

[0023] (c) Thermally conductive, electrically insulative filler (Filler-2)

The composition used in the invention also comprises a thermally conductive, electrically conductive filler (Filler-2). Intrinsic thermal conductivity of the filler is 20W/m-K or more, preferably 30W/mK or more. At the same time, the electric volume resistivity of the filler is 10 ² Q.cm or less, preferably 10^~4 Q.cm or less. The volume resistivity of a filler can be measured same as the above.

[0024] Examples of Filler-2 include graphite, carbon nanotube, carbon fiber, carbon black and metal particle. Filler-2 may be used as a mixture. Preferably, Filler-2 is graphite. The graphite can be synthetically produced or naturally produced, or can be expanded graphite. Naturally produced graphite includes three types of graphite, i.e. crystalline flake graphite, amorphous graphite and crystal vein graphite. Expanded graphite is made by immersing natural flake graphite in a bath of chromic acid, then concentrated sulfuric acid, which forces the crystal lattice planes apart, thus expanding the graphite. After expanding, functional acids and OH groups are introduced and thus promote affinity of expanded graphite to organic compounds and polymers. Besides, expanded graphite is thermally more conductive when compared to conventional carbon materials such as standard graphite. Expanded graphite is the most preferred Filler-2.

[0025] The particle size of Filler-2 is preferably 1 micro meter or more, more preferably 5 micro meter or more. The particle size of Filler-2 is preferably 100 micro meter or less, more preferably 50 micro meter or less. Particle size means median size (D50).

[0026] The content of Filler-2 is 2.0 volume % or less based on the total volume of the composition. If the amount of the filler is more than 2.0 volume %, the insulation of the obtained cured polymer material is low. The content of the filler is 0.2 volume % or more, preferably 0.5 volume % or more based on the total volume of the composition.

[0027] If the amounts of (a) resin, (b) Filler- 1 and (c) Filler-2 of the invention are disclosed as weight % based on the total weight of the composition, the preferable amount of (a) is 5 to 45 weight %, (b) is 50 to 95 weight % and (c) is 0. lto 8 weight % based on the weight of the composition. More preferably, the amount of (a) is 15 to 30 weight %, (b) is 65 to 85 weight % and (c) is 0.5 to 4.5 weight %.

[0028] The composition used in the invention can comprise other additives such as flame retardant, antioxidant, plasticizer, coupling agent, mold release agent, pigment and dye.

[0029] Examples of flame retardant used for the composition include antimony oxides, halocarbon, halogenated ester, halogenated ether, brominated flame retardant agent, and halogen free compounds such as organophosphorus compounds, organonitrogen compounds, intumescent flame retardants.

[0030] Examples of antioxidant used for the composition include sodium sulfite, sodium pyrosulfite, sodium hydrogen sulfite, sodium thiosulfate and dibutyl phenol.

[0031] Examples of plasticizer used for the composition include dicarboxylic /tricarboxylic ester-based plasticizers such as phthalates ester; trimellitates;

adipates; sebacates; maleates; organophosphates; benzoates and polymeric plasticizers such as polybutene. [0032] Examples of coupling agent used for the composition include chrome complex, silane coupling agent, titanate coupling agent, zirconium coupling agent, magnesium coupling agent and tin coupling agent.

[0033] Examples of mold release agent used for the composition include inorganic mold release agent such as talcum powder, mica powder, argil and clay; organic mold release agent such as aliphatic acid soap, fatty acid, paraffin, glycerol and vaseline; polymer mold release agent such as silicone oil, polyethylene glycol and polyethylene.

[0034] Examples of pigment or dye used for the composition of the invention include chromate, sulfate, silicate, borate, molybdate, phosphate, vanadate, cyanate, sulfide, azo pigment, phthalocyanine pigment, anthraquinone, indigo, quinacridone and dioxazinedyes.

[0035] <Molded article>

The molded article of the invention can be formed from the composition disclosed above. The method comprises the steps of; mixing (blending) the composition; pouring or injecting the blended composition in a mold and curing the mixture.

[0036] The method to blending of the composition can be used any known method, such as melt blending or solution blending. Melt blending is preferable. The melt blending can be conducted using a melt-mixer such as HAAKE Rheomix mixer, single or twin-screw extruder, kneader, Banbury mixer to until homogeneously. The melt blending is preferably carried out at a temperature at which the composition has a low viscosity, for example, at least 10 °C higher than the melting point of the resin in the composition.

[0037] The blended composition can be formed into articles using methods known to those skilled in the art, such as, for example, injection molding or extrusion at a temperature at which the blended composition has a low viscosity and good flowability.

[0038] The molded article has high thermal conductivity as well as good insulative properties. The thermal conductivity of the molded article is preferably 5 W/m-K or more, more preferably 6 W/m-K or more. Further preferably, the thermal conductivity is 8 W/m-K or more. The volume resistivity of the molded article is preferably 1X10⁸ Q.cm or more, more preferably 1X10¹ Q.cm or more, and further preferably 1X10¹³ Q.cm or more.

[0039] <Device>

[0040] The device of this invention comprises a heat source and a thermal management component located in proximity to the heat source. The thermal management component comprises a molded article formed from the composition described above. Since the molded article used in the invention has high thermal conductivity, the heat generated by the heat source is adequately transferred and removed from the heat source.

[0041] Examples of such heat source comprise integrated circuit (IC) chip, light-emitting diode (LED), power electronics, displays and photovoltaics.

[0042] The thermal management component of the invention could be a heat sink or connecting material with heat source and heat sink. As disclosed above, heat sink is used to cool electronics components or semiconductor components such as high-power semiconductor devices, and optoelectronic devices such as higher-power lasers and light emitting diodes (LEDs). Since the molder article of our invention has high thermal conductivity, the heat generated by the heat source is effectively transferred and removed from the heat source.

[0043] Other examples of the thermal management components are, electronic packaging agent, sealing agent, adhesive agent, electric switch, printed circuit board and wire coating.

[0044] The device of the invention could be a substrate with electronics element or semiconductor element such as IC chips or power electronics (heat source) and plastic substrate or plastic film contacted to such heat source (a thermal management component). IC chips or other electronics elements are normally mounted on a laminated plastic substrate such as epoxy or polyimide resin. Ceramic substrate such as aluminum or aluminum nitrate is also used as a substrate for power electronics because of the need for heat management generated by the power electronics. Since ceramic substrate is difficult to laminate or process, plastic substrate with high thermal conductivity is desired. The molded article of our invention can be used for the purpose.

[0045] The device of the invention could be a system comprising electronics device (heat source) and a covering thermoset resin of the device (a thermal management component). To protect electronics devices from mechanical damages, electronics devices are covered by a material such as thermoset resin. Since electronics devices generate heat, thermal management of the material is required. The molded article of our invention with high thermal conductivity can be used for the purpose. Example of such device is LED lightning system with LED light encapsulated by the molded article.

[0046] The device of the invention could be a solid state lightening system comprising LED light (heat source) and a base which is mounted the LED light (a thermal management component). In solid state lightning system, LED light is mounted on a base and surrounded by a side-wall. Since the LED light generates heat, thermal management of the solid state lightning system is required. The molded article of our invention with high thermal conductivity can be used for the purpose.

Examples

[0047] Raw material shown in Table 1 is used.

[0048]

Table 1

Specification Supplier

Resin Polyphenylene Product name: Sichuan Deyang sulfide (PPS) PPS-hb, melt index is (China)

752 (5kg, 315°C,

2.095mm)

Polyamide 66 (PA Product name:Zytel DuPont 66) 101F

Filler- 1 Aluminum nitride Product name: Destek Desunmet

(AlN-1) (D50=30 μιη) Ceramic Material

Co. Ltd.

Aluminum nitride Product name: Toyo Aluminum (A1N-2) W15/WJB=8/2 (W15

D50=15 μιη, WJB

ϋ50=2μιη)

Aluminum nitride Product name: WLS Toyo Aluminum (A1N-3) (D50=9.8 μιη)

Aluminum nitride Product name: Toyo Aluminum (A1N-4) WLS-C (D50=10.2

μηι)

Alumina (A1₂0₃) Product name: Denka

ASFP-20 (spherical

Alumina) D50=0.3

μηι

Filler-2 Expand graphite- 1 Product name: SGL Group

THERMOPHIT GFG, GFG5 D50=5-7 μηι

Expand graphite-2 Product name: TIMCAL Ltd.

TIMREX C-therm Ol l

(ash content < 2.5%)

[0049] Process

A laboratory scale HAAKE mixer was used to prepare samples. Filler- 1 and Filler-2 were mixed by dramatic shaking. The mixer was initially set at 280 °C for PA 66, 290 °C for PPS and a rotor speed of 50 revolutions per minute (rpm). Resin was loaded in a mixer and melted completely. Then the already mixed fillers were added slowly and totally mixed for 15 min at 50 rpm. Depending on the filler type and loading content, melt temperatures ranged from 290 to 294 °C at the end of the mixing cycle. The composites thus obtained were compression molded (at 290-294 °C and 16 MPa) into thin film of 1 mm for electrical resistivity measurement, 0.5 mm for dielectric strength measurement and thin plates of 2 mm for thermal conductivity measurement respectively. The thermal conductivity and electrical properties of those samples were analyzed by the following methods.

[0050] Analysis

1. Thermal conductivity

The thermal diffusivity a (mm²/s) of the samples was determined in through-plane direction of plates with Netzsch Nano flash LFA 447 instrument, conforming to ASTM D1461-01. The experimental parameters used to collect the data were: Temperature 25 °C, sample diameter 12.67 mm. A laser light absorbing spray was applied to surfaces of disk-shaped samples, so that the disk-shaped samples ware dried. Four flash shots were conducted and then the a average and Std. Dev. was obtained. The density p (g/cm³) of the samples at room temperature was measured by hydrostatic weighing, which uses the displacement of water due to a submerged object to determine the density of the object. The heat capacity Cp (J/g C) at 25 °C of the samples was determined by

DSC (DSC-Q2000) method (ASTM E1269-11 Standard Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry). The thermal conductivity (W/m-K) was calculated according to the following equation:

TC = a * p * Cp

[0051]

2. Electrical properties Volume / Surface resistivity of the cured sample was measured using 6517B Electrometer / High Resistance Meter, Keithley Instruments, Inc.; Fixture: 8009 Resistivity Test Fixture; according to ASTM D257-07; Sample size: 1mm x 10 cm x 10 cm

Dielectric strength was measured using D149 AC Dielectric Breakdown Test Sets, according to ASTM D149 - 09 (2013). The voltage raising rate is lkV/sec.

[0052] Inventive example 1

35 volume % of PA66 (20.7g), 64.5 volume % of A1N-2 (109.7g) and 0.5 volume % of expanded graphite-2 (0.58g) were used for Inventive example 1. Cured sample was prepared by the process disclosed above. The results are shown in Table 2.

[0053] Inventive examples 2-5 and Comparative examples 1-8

Cured samples were prepared same as inventive example 1 excepting for the components and their amounts were changed as shown in Table 2 to 5.

[0054]

Table 2

[0055] The thermal conductivity of Inventive Examples 1 and 2 were increased around 20 % over the one of Comparative example 1. In addition, the surface resistivity and volume resistivity were maintained 10¹⁴ order or more, so it shows good electrical insulation property. A dielectric strength of 9 or kV/mm was obtained in the Inventive examples 1 and 2, which allows applications requiring relative high breakdown resistance.

[0056]

Table 3 Composition Inventive Comparativ Inventive Comparative (Volume %) example 3 e Example 2 Example 4 Example 3

Resin PA66 32.5 32.5 30 30

Filler- 1 A1N-3 66.5 67.5 - -

A1N-4 - - 67.5 69.0

A1₂0₃ - - 1.0 1.0

Filler-2 Expand

1.0 - - - graphite- 1

Expand

- - 1.5 - graphite -2

Thermal conductivity

7.46 5.71 9.58 7.14 (W/mK)

Surface resistivity (Ω) 2.05 x lO¹⁴ 2.50 xlO¹⁵ 5.40 xlO¹⁵ 4.30 xlO¹⁵

Volume resistivity

4.70 x lO¹⁴ 9.80 xlO¹⁴ 2.30 x lO⁸ 1.50 xlO¹⁵ (Ω-cm)

Dielectric strength

8.20 18.5 2.5 18.4 (kV/mm)

[0057]

Table 4

[0058]

Table 5

Composition Comparative Comparative Comparative Comparative (Volume %) example 5 example 6 example 7 example 8

Resin PA66 99.0 98.5 97.5 95.0

Filler-2 Expand

1.0 1.5 2.5 5.0 graphite-2

[0059] The results of Comparative examples 5 to 8 show that when the volume % of Filler-2 exceeds 2.5, the electrical insulation is poor.

Claims

WHAT IS CLAIMED IS:

1. A composition comprising (A) a resin, (B) a filler which has an intrinsic thermal conductivity more than 20 W/mK, a volume resistivity of at least 10¹² Ω .cm and particle size is 0.1 to 400 micro meter and (C) a filler of which has electric volume resistivity of 10^~2 Ωχηι or less and an intrinsic thermal conductivity more than 20 W/mK, and the content of (C) is 0.2 to 2 volume percent based on the total volume of the composition.

2. The composition of claim 1, wherein (B) is selected from magnesium oxide, boron nitride, aluminum nitride and silicon nitride.

3. The composition of claims 1 or 2, wherein (C) is graphite.

4. The composition of claim 3, wherein (C) is expanded graphite.

5. The composition of any of claims 1 to 4, wherein the volume percent of (A) is 15 or more and 55 or less, the volume percent of (B) is 45 or more and 84.8 or less based on the total volume of the composition.

6. A molded article formed from the composition any of claims 1 to 5.

7. The molded article of claim 6, wherein the electric volume resistivity of the material is 10⁸ Q.cm or more.

8. The molded article of claim 6, wherein the thermal conductivity of the article is 5 W/mK or more.

9. A device comprising a heat source and an electrically insulating thermal management component located in proximity to the heart source, wherein the thermal management component comprises the molded article any of claims 6 to 8.

10. The device of claim 9, wherein the heat source is an electrical element or a semiconductor element.

11. The device of claims 9 or 10, wherein the electrical element or semiconductor element is selected from lighting elements, display elements, power elements and photovoltaic cells.