COMPOSITION [Technical Field] The present invention relates to an electrically insulating thermally conductive resin composition. More particularly, the present invention relates to an electrically insulating thermally conductive resin composition having excellent electrical insulating properties and thermal conductivity. [Background Art] Thermal conductive materials tend to be widely used due to an increase of power consumption of electronic parts/devices. The conventional thermally conductive material is mainly composed of a metal that has low formality and productivity, and that has limits in design of parts. Therefore, endeavors have been undertaken to substitute the metal with a material having excellent formability and productivity. There have been many efforts to overcome the demerits of metal for developing thermally conductive materials by using polymers, and some metals have been successfully substituted.

The biggest merit of using thermally conductive polymer materials is to enable achievement of high productivity and the fine design by using the injection molding method. Since a thermally conductive polymer material that can be substituted for metal has limits in that the thermal conductivity reaches about 10 [WVmK] at most, metal should still be used for parts requiring high thermal conductivity. The thermally conductive polymer material is developed mainly through combining a polymer/thermally conductive filler, but other methods of remarkably increasing the thermal conductivity of polymer materials have rarely been found and developed. A general polymer material has thermal conductivity of 0.1 to 0.4 [VWmK], which is a thermal insulator value. When thermally conductive fillers are combined therewith, it is possible to provide thermal conductivity of 10 [VWmK] at most, but the viscosity is remarkably increased and the mechanical properties are highly decreased, so that it is hard to obtain merits of a real thermally conductive polymer material. Recently, in order to secure fluidity that is suitable for injection-molding and an appropriate level of physical properties, the development of a thermally conductive polymer material has progressed to provide optimal thermal conductivity by adding a minimum amount of thermally conductive fillers thereto.

Since the theoretical thermal conductivity of a polymer composite that is calculated by the application of Fourier's Law is significantly different from the real thermal conductivity of a polymer composite, a difficulty in developing a thermally conductive polymer material exists. Particularly, an upper boundary value of thermal conductivity of a polymer composite that is calculated by the application of Fourier's Law is significantly higher than the real thermal conductivity of a polymer composite. The real physical properties of the composite generally exist between the lower boundary and the upper boundary, which are theoretically calculated values. In other words, the real thermal conductivity of a polymer composite is remarkably lower than the theoretically calculated values. One reason for this is that thermal conduction is defined by the propagation phenomenon of a quantized acoustic wave, which is referred to as a phonon, and the phonon characteristic of being scattered by phonon-phonon collisions as well as being scattered at all kinds of interfaces. In the thermally conductive polymer composite material, particularly at the interface between the thermally conductive filler and the polymer, a significant amount of phonons are scattered to generate a thermal barrier. This is hypothesized to cause remarkable damage to the functions of the thermally conductive fillers in the real composite material. It is hypothesized that the main factor for determining the thermal conductivity of a composite material with a low amount of a polymer material - wherein the filler amount area does not generate filler/filler contact - is the phonon scattering at the thermally conductive filler/polymer interface, while the main factor for determining the thermal conductivity of a composite material with a high amount of a polymer material - wherein the filler amount area generates filler/filler contact - is not the phonon scattering at the thermally conductive filler/polymer interface, but the phonon scattering at the thermally conductive filler/thermally conductive filler contact interface. That is, the real composite has decreased thermal conductivity since when it is combined it has considerably lower thermal conductivity than that of the thermally conductive filler alone due to the phonon scattering at the thermally conductive filler/thermally conductive filler contact interface that separately exists in the composite.

Even though the phonon scattering occurs at the thermally conductive filler/thermally conductive filler contact interface, in order to develop the thermally conductive polymer composite material, the most important factor is to increase the possibility to contact between thermally conductive fillers since the thermal conductivity is higher than that of isolated fillers do not contact in the composite. Needless to say, when the phonon scattering is minimized at the thermally conductive filler/polymer interface, the thermal conductivity may be optimized under the same condition. However, since the thermal conductivity of the polymer itself is remarkably lower than that of thermally conductive filler, it is considered that the thermal conductivity of the entire composite material is not affected by controlling the phonon scattering at the thermally conductive filler/polymer interface. This has been proven through thermal conductivity tests of composite materials with respect to the degree of scattering at the thermally conductive filler/polymer interface phonon. Therefore, it is important to develop a thermally conductive polymer composite material such that the phonon scattering is minimized at the filler/filler contact interface, and simultaneously to maximize the possibility of contact between fillers. However, because the filler/filler contact interface is a material characteristic rather than a controllable factor, maximizing the possibility of filler/filler contact is considered to be a core factor in the development of a thermally conductive polymer composite.

Properties of such a thermally conductive resin composite material may be roughly divided into electrically conductive and electrically insulative properties. The electrical conductivity characteristic should be suitably determined by the application field to be used. For example, the semi-conductor or electrical/electronic parts that heat up in which the electrical interference should be prohibited should include the thermally conductive resin having an electrical insulating characteristic. Generally, as metals or graphite fillers that are materials used for the conductive fillers in the thermally conductive resin composite materials are electrical conductors, the composite material also has electrical conductivity. The electrically insulating thermally conductive resin composite materials include ceramic fillers, and the ceramic fillers, such as BN, AIN, SiC and the like, have thermal conductivity that is not superior to metals or graphite, and have drawbacks of considerably high costs and poor physical properties when combined in a resin. However, since there are no alternatives for the ceramic filler so far, the polymer/ceramic filler composite is being used to develop the electrically insulating thermally conductive resin in spite of the drawbacks.

Japanese Patent Laid-Open Publication No. 2006-22130, which is one study on the conventional thermally conductive polymer composite, discloses a composite material including a low-melting point metal and metal or alloy powders for increasing the dispersing property of the metal in the crystalline polymer, and including an inorganic powder having incompatibility with the metal powder and an enforcing material of a glass fiber. However, in this case, since the main thermal conductor is composed of a low-melting point metal and an inorganic powder having incompatibility with the metal powder, contact efficiency between thermally conductive fillers is decreased, and a matrix of the crystalline polymer includes a high amount of materials having incompatibility with each other so as to deteriorate the physical properties.

Japanese Patent Laid-Open Publication No. 2005-074116 discloses a thermally conductive polymer composite prepared by using expansion graphite and general graphite in a sequential ratio of 1/9 to 5/5. However, this technique relates to a composite material that increases thermal conductivity by adjusting the ratio of the expansion graphite to the general graphite and increases the contact possibility, but it has drawbacks of high viscosity of the material and fragility, and drawbacks of slurping in which the graphite is smeared on the material surface.

In addition, U.S. Patent No. 6,048,919 discloses a technique of combining a thermally conductive filler having an aspect ratio of at least 10:1 and a thermally conductive filler having an aspect ratio of 5:1 or less in a volume ratio ranging from 30 to 60% and from 25 to 60%, respectively. However, this invention also has problems of a low possibility of contact between thermally conductive fillers.

Further, U.S. Patent No. 5,011 ,872 discloses a technology of combining a 130 to 260 μ m-sized ceramic filler material such as BN, SiC, and AIN with a polymer, and U.S. Patent No. 5232970 discloses a technology of adding at least 35 volume% of a ceramic filler that is capable of including silica in a polyamide and polybenzocyclobutene. As another invention of an electrically insulating thermally conductive resin composite material, U.S. Patent No. 6,822,018 discloses an electrically insulating material-coated metal filler and a ceramic filler that are combined with epoxy silicon or a polyurethane binder. The electrically insulating thermally conductive resin composite material is developed by using ceramic fillers. However, the electrically insulating highly thermally conductive resin composition using the conventional ceramic filler has problems in that the physical properties and the thermal conductivity deteriorate. [DETAILED DESCRIPTION] [Technical Problem]

An exemplary embodiment of the present invention provides an electrically insulating thermally conductive resin composition. In order to solve the problems of the deteriorated physical properties and the decreased thermal conductivity of the electrically insulating thermally conductive resin composition including conventional ceramic fillers, another embodiment of the present invention provides an electrically insulating highly thermally conductive resin composition in which the contact between thermally conductive fillers is maximized by using different kinds of metal fillers having different shapes to increase the thermal conductivity, and to accomplish the instinct characteristics along with the thermally conductive filler, so as to improve the electrical insulating property and the physical properties. Yet another embodiment of the present invention provides a molded product fabricated using the electrically insulating highly thermally conductive resin composition.

The embodiments of the present invention are not limited to the above technical purposes, and a person of ordinary skill in the art can understand other technical purposes. [Technical Solution] According to one embodiment of the present invention, an electrically insulating thermally conductive resin composition is provided that includes (A) 30 to 85 volume% of a polyamide-based resin, (B) 5 to 69 volume% of metal fillers having different shapes from each other, and (C) 1 to 10 volume% of a low melting point metal.

According to another embodiment of the present invention, a molded product fabricated using the electrically insulating highly thermally conductive resin composition is provided. Hereinafter, further embodiments of the present invention will be described in detail. [Advantageous Effects]

The electrically insulating highly thermally conductive resin composition maximizes contact between the thermally conductive fillers, so as to exhibit excellent thermal conductivity along with an excellent electrical insulating property. As the result, it is applicable to various molded products requiring excellent thermal conductivity and an electrical insulating property. [Best Mode]

Exemplary embodiments of the present invention will hereinafter be described in detail. However, these embodiments are only exemplary, and the present invention is not limited thereto.

In this specification, "fiber-shaped" indicates having a thin and long shape and having a length/diameter ratio of 10 or more, wherein the length is the longitudinal distance and the diameter is the width of the cross-section thereof when it is cut across the longitudinal direction. "Plate-shaped" indicates having a thin and flat shape and having a diameter/thickness ratio of 10 or more wherein the thickness is the height of a crystal structure and the diameter is the diameter of the plate. The electrically insulating highly thermally conductive resin composition according to one embodiment includes (A) 30 to 85 volume% of a polyamide-based resin, (B) 5 to 69 volume% of metal fillers having different shapes from each other, and (C) 1 to 10 volume% of a low-melting point metal. Exemplary components included in the electrically insulating highly thermally conductive resin composition according to embodiments of the present invention will hereinafter be described in detail. (A) Polvamide-based resin The polyamide-based resin is one in which an amide (-NHCO-) group is bound to a polymer main chain. Specific examples may be selected from the group consisting of polycaproamide (nylon 6), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), poly(hexamethylene nonanediamide) (nylon 69), poly(hexamethylene sebacamide) (nylon 610), poly(hexamethylenedodecanediamide), polyhexamethylene dodecanamide (nylon 612), nylon 611 , nylon 1212, nylon 1012, polyundecanoamide (nylon 11), polydodecanamide (nylon 12), polyhexamethylene terephthalamide (nylon 6T), polyhexamethylene isophthalamide (nylon 6I), nylon 9T, nylon 10T, polyundecamethylene terephthalamide (nylon 11T), nylon 12T, nylon 121, polyphthalamide (PPA), polycaproamide/polyhexamethylene adipamide copolymer (nylon 6/66), polyhexamethylene terephthalamide/polyhexamethylene isophthalamide copolymer (nylon 6T/6I), polyhexamethylene adipamide/polyhexamethylene terephthalamide copolymer (nylon 66/6T), poly-bis-(4-aminocyclohexyl)methanedodecamide (nylon PACM12), poly-bis-(3-methyl-4-aminocyclohexyl)methanedodecamide (nylon dimethyl PACM 12), polymetaxylene adipamide (MXD 6), polyundecamethylene hexahydroterephthalamide (nylon 11T(H)), and combinations thereof.

Alternatively, the polyamide-based resin may be a blend including a polyamide-based polymer resin. Examples of the blend include polyphthalamide (PPA)/polyphenylene ether (PPE), polyamide

(PA)/polyphenylene sulfide (PPS), polyamide

(PA)/acrylonitrile-butadiene-styrene (ABS), and the like.

The conventional polymer/metal composite material has electrical conductivity, but the polyamide-based resin exhibits an electrical insulating property when it is used with a metal component of less than a certain level by including a polar amide (-NHCO-) group due to the phenomenon of trapping electrons. Accordingly, the polyamide-based resin is very suitable for a resin composition requiring both an electrical insulating property and high thermal conductivity together with excellent formability. According to one embodiment, it includes nylon 66 or PPA. The PPA is advantageously applicable to a material requiring high thermal resistance used for electrical insulation/thermal conductivity since it has high thermal resistance. The material uses may include as a connector, a lamp socket, a lamp reflector, and the like, which are applied in a lead-free soldering process. According to one embodiment, the polyamide-based resin is included at

30 to 85 volume% based on the total volume of the resin composition. When the polyamide-based resin is included at 30 to 85 volume%, it can obtain both excellent processability and excellent thermal conductivity since it secures thermal conductivity of more than a certain level, thereby satisfying the real use environment.

(B) Metal filler

The electrically insulating highly thermally conductive resin composition according to one embodiment of the present invention includes different kinds of metal fillers having different shapes from each other in order to maximize contact between the thermally conductive fillers.

The specific shapes are not limited, but the metal filler may include a first fiber-shaped metal filler and a second plate-shaped metal filler considering the contact possibility between fillers. In one embodiment, the first fiber-shaped metal filler and the second plate-shaped metal filler may be mixed in a volume ratio ranging from 9:1 to 1 :9, but in another embodiment, they may mixed in a volume ratio ranging from 4:6 to 6:4. When the first metal filler and the second plate-shaped metal filler are mixed in a volume ratio ranging from 9:1 to 1 :9, the contact efficiency between thermally conductive fillers is improved.

These fiber-shaped or plate-shaped first and second metal fillers may include metals having thermal conductivity of 50[VWmK] or more. Greater thermal conductivity is better.

Particularly, it may include a metal having excellent thermal conductivity such as aluminum, copper, zinc, silver, nickel, stainless steel, titanium, and the like, and the mixture thereof is prepared in accordance with any method such as cutting, milling, fusion spraying, electrolysis, grinding, and chemical reducing.

In one embodiment, the first fiber-shaped metal filler has a length/diameter ratio (aspect ratio) in a range of 10 to 10,000, and in another embodiment, it is in a range of 50 to 300. When the fiber-shaped length/diameter ratio is between 10 and 10,000, it improves the contact efficiency between fillers and the physical property, and it facilitates preparation of a resin composition. In one embodiment, the second plate-shaped metal filler has a diameter/thickness ratio in a range of 10 to 100,000, but in another embodiment, it is in a range of 50 to 500. When the diameter/thickness ratio is in a range of 10 to 100,000, the contact between fillers is more effective, and the packing factor in the resin is increased to improve intercalation into the resin. According to one embodiment, the different kinds of metal fillers having different shapes from each other are included at 5 to 69 volume% based on the total volume of the resin composition. When the metal filler is included at 5 to 69 volume%, it can secure thermal conductivity of more than an appropriate level for applying to the application field requiring the thermal conductivity, facilitate the process of fabricating the composite material, and provide the physical property balance between the excellent processability and the thermal conductivity.

(C) Low-melting point metal

The low-melting point metal plays a role of maximizing the contact between thermally conductive fillers, and may be one kind of metal or a solid solution consisting of two or more kinds of metal elements. In one embodiment, it is a solid solution.

According to one embodiment, the low-melting point metal of the solid solution is a metal solid solution having a solidus temperature that is lower than the melting point of the crystal polymer of the (A) polyamide-based resin. Particularly, when the solidus temperature is lower than the melting point of the polyamide-based resin as 20 ^° C or more, it improves the stability during preparation of the electrically insulating highly thermally conductive resin composition. The solidus temperature is beneficial when it is at least 100 ° C higher than the environment of use of the composition.

The solid solution of a low-melting point metal includes a first metal element selected from the group consisting of tin, bismuth, lead, and combinations thereof; and a second metal element selected from the group consisting of copper, aluminum, nickel, silver, germanium, indium, zinc, and combinations thereof. For example, when the aluminum is a thermally conductive filler, the aluminum is included to a component of a solid solution; while when copper is the thermally conductive filler, the copper is included to a component of a solid solution. In addition, it is advantageous to use tin for the first metal element considering the environmental view.

In addition, it is possible to control a physical property such as solidus temperature, liquidus temperature, mechanical strength, and the like of the low-melting point metal by adjusting the amount ratio of the first metal element and the second metal element. According to one embodiment, the first metal element and the second metal element are included in a weight ratio of 99.5:0.5 to 89:11. When they are included in the weight ratio range, it is possible to provide a low-melting point metal with the optimal solidus temperature.

In one embodiment, the low-melting point metal is added at 1 to 10 volume% based on the total amount of resin composition. When the amount of the low-melting point metal is between 1 and 10 volume%, the function to apply networking between filters is sufficient to increase the possibility of contact between filters and improve the thermal conductivity and the physical property balance.

(D) Fiber-shaped filling material

The electrically insulating highly thermally conductive resin composition according to one embodiment may selectively further include a fiber-shaped filling material in order to enforce the physical property of the composition. The fiber-shaped filling material may include a fiber-shaped glass fiber, a carbon fiber, an aramid fiber, a potassium titanate fiber such as potassium titanate, wallostonite, mica, aluminum borate, whisker, and the like. According to one embodiment, it includes a glass fiber considering the view of enforcing the mechanical strength and the impact strength. According to one embodiment, the fiber-shaped filling material has a diameter in a range of 8 to 13 μ m and a length in a range of 2 to 5mm. When it has the diameter and length in the above ranges, the enforcing effects and processability are improved.

The surface of the fiber-shaped filling material is treated to improve the adhesive strength to the polyamide resin and the mechanical physical property of the resin composition. The surface treating agent may include a titanate-based agent, an epoxy-based agent, an amino silane-based agent, and the like.

According to one embodiment, the fiber-shaped filling material is included at 50 parts by weight based on 100 parts by weight of the polyamide-based resin (A), the different kinds of metal filler (B), and the low-melting point metal (C), and in another embodiment, it is in a range of 10 to 50 parts by weight. When the fiber-shaped filling material is included at less than 50 parts by weight, it secures the excellent physical property balance of mechanical strength and impact strength by improving the mechanical strength of the resin composition.

(E) Other additives

The electrically insulating highly thermally conductive resin composition having the composition may further include an antioxidant, a release agent, a flame retardant, a lubricant, a colorant such as a pigment, a dye, and the like in order to maximize the contact between thermally conductive fillers or improve the mechanical properties of the resin composition.

The antioxidant may include a phenol, a phosphite, a thioether, or an amine antioxidant, and the weather-resistance agent may include a benzophenone or amine weather-resistance agent.

The release agent may include a fluorine-included polymer, silicone oil, a metal salt of stearylic acid, a metal salt of montanic acid, a montanic acid ester wax, or a polyethylene wax, and the colorant may include a dye or pigment. The flame retardant is not specifically limited, but it may include a halogen-based, a phosphorous-based, a metal salt-based, or a silicone-based flame retardant.

The electrically insulating highly thermally conductive resin composition having the composition may be prepared in accordance with a general method. For example, it may be prepared by simultaneously mixing the constituent components and other additives, and fusion-extruding in an extruder to provide a pellet shape.

The electrically insulating highly thermally conductive resin composition may be used for forming various articles, particularly, a main body, a chassis, or a heat dissipating plate and the like of an electro-electronic product such as a TV, a computer, a mobile phone, and an office automating device requiring the excellent electric insulating property and the thermal conductivity. According to another embodiment of the present invention, provided is a molded product fabricated by the electrically insulating highly thermally conductive resin composition. [Mode for Invention]

The following examples illustrate the present invention in more detail. However, they are exemplary embodiments of the present invention and are not limiting.

[Examples]

The (A) polyamide-based resin, (B) metal filler, (C) low-melting point metal, and (D) fiber-shaped filling material used in examples and comparative examples are as follows. (A-1) Polyamide-based resin

PPA (polyphthalic amide) (HTN-501 manufactured by Dupont) having Tm of 300 ^° C and Tg of 125 ^° C was used. (A-2) Polyamide-based resin PA66/PPE (polyamide 66/polyphenylene ether) were alloyed at a weight ratio of 55:45 to provide a PA66 blend.

(A-3) Polyphenylene sulfide resin

A polyphenylene sulfide resin having a melting point of 280 ^° C was used.

(B-1) Metal Filler b1 : a first fiber-shaped metal filler included aluminum having an average diameter of 40 μ m and an average length of 2.5mm (length/diameter ratio=62.5). b2: a second plate-shaped metal filler included aluminum having an average thickness 350nm and an average length 40 μ m (length/thickness ratio=114).

(B-2) Ceramic-based Filler

Boron nitride having an average particle diameter of 45 μ m was used. (B-3) Ceramic-based Filler

Ammonium nitride having an average particle diameter of 2.5 μ m was used.

(C) Low-melting point metal

Tin/aluminum low-melting point metal having a main component of tin was used. It used a tin/aluminum solid solution having 99.7 wt% of tin and 0.3 wt% of aluminum based on the weight ratio, and a solidus temperature of 228 ⁰ C .

(D) Fiber-shaped Filling Material

It used glass fiber (ECS 03 T-717PL, manufactured by Nippon Electric Glass) having a diameter of 10 μ m and a length of 3mm.

Examples 1-6 and Comparative Examples 1-4

Each of composition components were mixed in a mixer in the compositions shown in the following Table 1 and extruded by a twin screw extruder of L/D=35, Φ =45mm under the conditions of a process temperature (310 ^° C in the case of PPA; 290° C in the case of PA66/PPE; and 300° C in the case of PPS), a screw rotation speed of 150rpm, a first vent pressure of about -600mmHg, and a self-supply speed of 60 kg/h. The extruded strand was cooled with water and cut by a rotary cutter into a pellet. Table 1

The pellets obtained from Examples 1-6 and Comparative Examples 1-4 were dried with hot air at 80° C for about 5 hours and extruded in a 10 oz extruder to provide a specimen for determining physical properties.

The specimen was measured to determine the physical properties in the following method, and the results are shown in the following Table 2.

(1) Thermal Conductivity: measured in accordance with the guarded heat flow method.

(2) Electrical characteristic: measured to determine the surface resistance in accordance with ASTM D257.

Table 2

As shown in Table 2, the resin compositions obtained from Examples 1 to 6 showed a superior electrical insulating property to those of Comparative Examples 1 and 2 including the main resin of polyphenylene sulfide, and higher thermal conductivity than those of Comparative Examples 3 and 4 including ceramic filler. From the results, it is confirmed that the resin compositions obtained from Examples 1 to 6 had an excellent electrical insulating property and thermal conductivity. The resin compositions of Examples 2, 3, 5, and 6 further including a fiber-shaped filling material of glass fiber had higher thermal conductivity than those of Examples 1 and 4. The polyamide-based resin of which the viscosity was increased by adding the glass fiber more easily fused/dispersed the low-melting point metal to further enforce the interface between metal fillers. The present invention is not limited to the embodiments illustrated with the drawings and table, but can be fabricated into various modifications and equivalent arrangements included within the spirit and scope of the appended claims by a person who is ordinarily skilled in this field. Therefore, the aforementioned embodiments should be understood to be exemplary but not limiting the present invention in any way.