KR101003840B1 - Multi-functional heat spreading sheet with improved thermal conductivity, electromagentic wave shielding and electiomagnetic wave absorption - Google Patents

Abstract

PURPOSE: A multi-functional heat diffusion sheet is provided to prevent the deterioration of an electronic device by effectively diffusing heat which is generated in an electronic device. CONSTITUTION: A multi-functional heat diffusion sheet(100) comprises a spheroidal graphite heat conduction sheet and a flake graphite heat conduction sheet. The spheroidal graphite heat conduction sheet(10) is made of a spheroidal graphite mixture including a base resin and a spheroidal graphite particle. The flake graphite heat conduction sheet is laminated on the upper or lower part of the spheroidal graphite heat conduction sheet. The flake graphite heat conduction sheet is made of a flake graphite mixture including the base resin and a flake graphite particle.

Description

Multi-functional heat spreading sheet with improved thermal conductivity, electromagentic wave shielding and electiomagnetic wave absorption}

The present invention relates to a composite functional thermal diffusion sheet having improved vertical thermal conductivity, horizontal thermal conductivity, electromagnetic shielding ability, and electromagnetic wave absorbing ability, and more particularly, a composite having a spherical graphite thermal conductive sheet composed of spherical graphite particles dispersed on a base resin. As a functional thermal diffusion sheet, the present invention relates to a composite functional thermal diffusion sheet having excellent horizontal thermal conductivity and vertical thermal conductivity at the same time, and further having electromagnetic wave shielding ability and electromagnetic wave absorbing ability.

In recent years, electronic devices require a large number of electronic components to be installed in a narrow space according to the trend of light and small size, and the amount of heat generated per unit volume is greatly increased. Therefore, the need for heat dissipation means for effectively dissipating the heat generated from the heat source in order to prevent the deterioration of the electronic device is emerging.

Accordingly, heat sinks and heat radiating fans are used as means for effectively dissipating heat generated from electronic devices. Although these heat dissipation means have a large heat dissipation effect, they are difficult to be employed in the field of flat panel displays having a thin thickness due to their large volume. Therefore, the heat dissipation means employable in the field of flat panel display should be provided in the form of a sheet in order to reduce its volume. The heat dissipation means provided in the form of a sheet is mainly used an expanded graphite sheet rolled after expanding a thin metal of copper or aluminum or natural graphite, or a sheet filled with thermal conductive powder on a resin such as silicone or acrylic. However, in the case of a sheet made of metal, the specific gravity is large, which limits the weight of the product, and there is no difference in thermal conductivity in each direction. Therefore, the heat transfer path can absorb heat quickly in the thickness direction (vertical direction). However, there is a problem in that a hot spot is partially generated because heat cannot be diffused quickly in a plane direction (horizontal direction) of which the length of the heat transfer path is long. In addition, the metal has a problem that the manufacturing cost is increased because of the high price. Sheets made of expanded graphite are useful in terms of being able to compensate for the shortcomings of sheets made of metal, but there is a problem in that a top surface coating is required to prevent surface peeling and dust generation. In addition, the sheet made of resin has a low heat conductivity in the horizontal direction due to the characteristics of the material, so the heat dissipation effect is small, and there is a problem that the handling is difficult due to excessive flexibility.

On the other hand, in the electronic device, not only heat but also electromagnetic waves are generated, and these electromagnetic waves cause problems of electronic devices, and adversely affect the human body. In order to block electromagnetic waves, electromagnetic shielding sheets or electromagnetic wave absorbers are used to shield or absorb electromagnetic waves. In recent years, electronic devices require a large number of electronic components to be installed in a narrow space according to the trend of light and small size. There is an increasing demand for hybrid sheets having both thermal diffusion and electromagnetic shielding or absorption characteristics.

The present invention has been made to solve the problem that the vertical thermal conductivity is significantly low in the thermal diffusion sheet containing a conventional graphite particles, the present invention has an excellent horizontal thermal conductivity and vertical thermal conductivity at the same time additionally the electromagnetic wave shielding ability and the electromagnetic wave absorption ability. It is an object of the present invention to provide a composite functional thermal diffusion sheet having the same.

In order to solve the above object, the present invention is composed of a spheroidal graphite thermally conductive sheet molded from a spherical graphite kneaded material comprising a base resin and spheroidal graphite particles kneaded and dispersed in the base resin, and vertical A multi-function thermal diffusion sheet having thermal conductivity, horizontal thermal conductivity, electromagnetic shielding ability, and electromagnetic wave absorbing property, for example, a spherical graphite including 100 parts by weight of a base resin and 300 to 900 parts by weight of spheroidal graphite particles kneaded and dispersed in the base resin. A composite function thermal diffusion sheet composed of a spherical graphite thermally conductive sheet molded from graphite kneaded material is provided.

In addition, the present invention is a spherical graphite heat conductive sheet molded from a spherical graphite kneaded material comprising a base resin and spherodial graphite particles kneaded and dispersed in the base resin; And a flaky graphite heat conductive sheet laminated on or under the spherical graphite thermal conductive sheet and formed of flaky graphite kneaded material comprising flaky graphite particles which are kneaded and dispersed in a base resin and the base resin. , A multi-functional thermal diffusion sheet having vertical thermal conductivity, horizontal thermal conductivity, electromagnetic wave shielding ability, and electromagnetic wave absorbing property, for example, 100 parts by weight of the base resin and 300 to 900 weights of spheroidal graphite particles dispersed and kneaded in the base resin A spherical graphite thermally conductive sheet molded into a spherical graphite kneaded material including a part; And a flaky graphite kneaded product which is stacked on or under the spherical graphite heat conductive sheet and includes 100 parts by weight of the base resin and 300 to 600 parts by weight of flaky graphite particles kneaded and dispersed in the base resin. It provides a composite function thermal diffusion sheet consisting of a graphite thermal conductive sheet.

The composite function thermal diffusion sheet according to the present invention may further include a thermally conductive adhesive layer laminated on one or both sides of the thermal diffusion sheet. In addition, the composite function heat diffusion sheet according to the present invention may further include an electrical insulation layer laminated on one surface of the heat diffusion sheet.

In the composite functional thermal diffusion sheet according to the present invention, the base resin is one selected from the group consisting of acrylic resins, urethane resins, silicone resins, ethylene vinyl acetate (EVA) resins, polyvinyl chloride (PVC) resins, and polyester resins. It may be a resin, preferably an acrylate rubber (Acrylate Rubber), NB rubber (Acrylonitrile Butadiene Rubber, NBR), urethane rubber, ethylene-octene rubber (Ethylene-Octene Rubber, EOR), ethylene-propylene rubber (Ethylene- Propylene Rubber), ethylene-propylene-diene rubber (EPDM Rubber) and polyethylene rubber, characterized in that composed of one or more non-halogen-based elastomer resin selected from the group consisting of.

In the composite functional thermal diffusion sheet according to the present invention, the spherical graphite kneaded material and the flake graphite kneaded material may preferably further include 1 to 3 parts by weight of a lubricant, for example, 100 parts by weight of the base resin, kneaded and dispersed in the base resin. . In addition, the spherical graphite kneaded material may preferably further comprise a flame retardant which is kneaded and dispersed in the base resin, wherein the flame retardant is preferably ammonium phosphate, ammonium polyphosphate, melamine cyanurate, melamine phosphate, melamine pyrophosphate, At least one non-halogen flame retardant selected from the group consisting of melamine polyphosphate, red, and oxide or resin coated red. In addition, the spherical graphite kneaded material may preferably further comprise a thermally conductive filler kneaded and dispersed in the base resin, wherein the thermally conductive filler is alumina powder, boron nitride powder, silicon nitride powder, titanium nitride powder, Iron oxide powder, magnesium oxide powder, beryllium oxide powder, nickel powder, copper powder, gold powder, silver powder, tin powder, cobalt powder, aluminum powder, silver coated copper powder, silver coated nickel powder, silver coated aluminum powder, And it may be one or more selected from the group consisting of tin-coated copper powder.

The composite function heat diffusion sheet according to the present invention has excellent thermal conductivity not only in the horizontal direction but also in the vertical direction, and further has electromagnetic wave shielding ability and electromagnetic wave absorbing ability, so that when applied to a flat panel display field such as PDP, LCD, LED lighting field, etc. It is possible to effectively diffuse heat generated in the electronic device (thermal conduction in the vertical direction and thermal conduction in the horizontal direction), to prevent deterioration of the electronic device, and to prevent the failure of the electronic device by electromagnetic waves. In addition, the composite functional thermal diffusion sheet according to the present invention is made of a non-halogen-based elastomer having a certain hardness of the base resin, environmentally friendly, excellent durability, and excellent flexibility (or flexibility) with the outer panel when applied to electronic devices It has excellent adhesion, effectively dissipates and removes heat generated in electronic devices, and provides excellent adhesion to thermally conductive tapes to provide reliability in solving thermal management of electronic devices. In addition, the spheroidal graphite particles have a lower density than the conventional ceramic material thermally conductive fillers, and thus, even when the same weight is used, the spherical graphite particles may realize a high thermal conductivity performance even if a small amount is used.

1 illustrates a laminated structure of a composite functional thermal diffusion sheet according to an embodiment of the present invention, and FIG. 2 illustrates a manufacturing process of the composite functional thermal diffusion sheet illustrated in FIG. 1.
Figure 3 shows a laminated structure of a multi-functional multilayer thermal diffusion sheet according to another embodiment of the present invention, Figure 4 shows a manufacturing process of the multi-functional multilayer thermal diffusion sheet shown in FIG.
5 is a graph showing the electromagnetic shielding rate of the composite functional thermal diffusion sheet according to Example 1, Figure 6 is a graph showing the power loss of the composite functional thermal diffusion sheet according to Example 1.
7 is a graph showing the electromagnetic shielding rate of the thermal diffusion sheet according to Comparative Example 1, Figure 8 is a graph showing the power loss of the thermal diffusion sheet according to Comparative Example 1.
9 is a graph showing the electromagnetic shielding rate of the composite functional multilayer thermal diffusion sheet according to Example 4, Figure 10 is a graph showing the power loss of the composite functional multilayer thermal diffusion sheet according to Example 4.
FIG. 11 schematically illustrates a method for measuring shielding effectiveness, and FIG. 12 schematically illustrates a method for measuring electromagnetic wave absorption (or power loss).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

1 shows a laminated structure of a composite functional thermal diffusion sheet according to an embodiment of the present invention.

As shown in FIG. 1, the composite functional thermal diffusion sheet 100 according to the present invention is a spherical graphite thermally conductive sheet formed of a spherical graphite kneaded material including a spheroidal graphite particle dispersed by being kneaded and dispersed in a base resin ( 10). In addition, the composite functional thermal diffusion sheet according to the present invention may further include a thermally conductive adhesive layer 30 laminated on one surface of the thermal diffusion sheet. Although not shown in FIG. 1, the thermally conductive adhesive layer may be laminated on both sides of the thermal diffusion sheet. In addition, the composite function heat diffusion sheet according to the present invention may further include an electrical insulation layer 40 laminated on one surface of the heat diffusion sheet.

(1) Composite function thermal diffusion sheet composed of spherical graphite thermal conductive sheet

Spherical Graphite Thermal Conductive Sheet

The spherical graphite heat conductive sheet 10 is formed in the form of a sheet formed by kneading a kneaded material including spherodial graphite particles kneaded and dispersed in a base resin using a calendering method.

Spherical graphite particles are graphite particles having a spherical shape or an elliptic shape close to a spherical shape, preferably having a density of about 0.5 to 2.0 g / cm 3 and an average particle diameter of about 1 to 200 μm. The content of the spherical graphite particles in the spherical graphite thermally conductive sheet is not particularly limited, but is preferably about 300 to 900 parts by weight, more preferably 500 to 700 parts by weight based on 100 parts by weight of the base resin described later. If the content of the spherical graphite particles is less than 300 parts by weight, the vertical thermal conductivity of the spherical graphite thermal conductive sheet is not high, there is a fear that the vertical thermal conductivity effect is insufficient when applied to electronic devices. In addition, when the content of the spherical graphite particles exceeds 900 parts by weight, it is difficult to uniformly disperse the spherical graphite particles by mixing with the base resin, the bonding strength with the base resin is difficult to be formed into a sheet form by calendering, The amount of base resin is so small that the flexibility (or flexibility) of the finally formed spherical graphite thermally conductive sheet is inferior, which may make it difficult to manufacture the spherical graphite thermally conductive sheet in roll type, and the adhesion force in the application of electronic devices Apart from this, its scope of application is narrow. When the content of the spherical graphite particles is about 500 to 700 parts by weight with respect to 100 parts by weight of the base resin, the vertical thermal conductivity of the spherical graphite heat conductive sheet is high and at the same time excellent in formability.

The base resin is not particularly limited as long as it can uniformly disperse spherical graphite particles by kneading, and specifically, acrylic resin, urethane resin, silicone resin, ethylene vinyl acetate (EVA) resin, polyvinyl chloride (PVC). ) Resins, and polyester resins. In addition, the base resin is preferably an acrylate rubber (Ncrylate rubber), NB rubber (Acrylonitrile Butadiene Rubber, NBR), urethane rubber, ethylene-octene rubber (Ethylene-Octene Rubber, EOR), ethylene-propylene rubber (Ethylene-Propylene Rubber), ethylene-propylene-diene rubber (EPDM Rubber) and polyethylene rubber, and at least one non-halogen-based elastomer resin selected from the group consisting of. The non-halogen-based elastomer resin is more environmentally friendly because it has excellent heat resistance, impact resistance, adhesion, etc., and does not emit halogen substances causing environmental problems, and the base resin has a hardness of 50 to 50 according to ASTM D-2240. It is more preferable that it is 95 Shore A. The spherical graphite heat conductive sheet having a hardness of 50 to 95 Shore A of the base resin has commercially satisfactory wear resistance.

The spherical graphite kneaded material preferably further comprises a lubricant. Lubricants aid in flow by lubricating metal surfaces in contact with plastics during calendering, forming and extrusion, making the surfaces even. That is, it prevents the adhesion between the mold surface or the extruder surface and the resin and is kneaded with the resin as an additive for improving the slip property, thereby lowering the melt viscosity to improve molding processability. The lubricant is not limited as long as it can reduce the friction between the surface of the roller and the spherical graphite mixture and promote the sliding in the calendering, which will be described later. Specifically, stearic acid and metal salts of fatty acids (usually, the metal components are calcium and zinc). Synthetic waxes in the form of esters and amides, paraffin waxes, mineral oils, low molecular weight polyethylene, and the like. Although the content of the lubricant is not particularly limited, it is preferably about 1 to 3 parts by weight with respect to 100 parts by weight of the base resin, but if the content of the lubricant is less than 1 part by weight, the inherent functions exerted by the lubricant may be insufficient. This is because if the weight part is exceeded, the function increase effect of the lubricant according to the excess is not large.

In addition, the spherical graphite kneaded material preferably further includes a flame retardant to impart flame retardancy to the spherical graphite heat conductive sheet. The type of flame retardant is not particularly limited, but is preferably characterized by being a more environmentally friendly non-halogen flame retardant. The non-halogen flame retardant may be one or more selected from the group consisting of ammonium phosphate, ammonium polyphosphate, melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, red, and oxide or resin coated red. The content of the flame retardant is not particularly limited, for example, about 10 to 100 parts by weight based on 100 parts by weight of the base resin.

In addition, the spherical graphite kneaded material preferably further includes a thermally conductive filler other than graphite particles in order to further improve the vertical thermal conductivity of the spherical graphite thermally conductive sheet. Thermally conductive fillers include alumina powder, boron nitride powder, silicon nitride powder, titanium nitride powder, iron oxide powder, magnesium oxide powder, beryllium oxide powder, nickel powder, copper powder, gold powder, silver powder, tin powder, cobalt powder It may be at least one selected from the group consisting of aluminum powder, silver coated copper powder, silver coated nickel powder, silver coated aluminum powder, and tin coated copper powder. The content of the thermally conductive filler is not particularly limited, for example, about 10 to 100 parts by weight based on 100 parts by weight of the base resin.

Thermal conductivity Adhesive layer  Or electrical Insulation layer

The composite function heat diffusion sheet according to the present invention may optionally further include a thermally conductive adhesive layer 30. The thermally conductive adhesive layer is for adhering the heat diffusion sheet to the heat generating portion of the electronic device to increase the heat conduction efficiency between the heat generating portion and the heat diffusion sheet, and is formed by being laminated on one surface of the heat diffusion sheet as shown in FIG. 1. In addition, although not shown in FIG. 1, it may be formed by being stacked on both sides of the thermal diffusion sheet. When the thermally conductive adhesive layer is formed on both sides of the thermal diffusion sheet, the thermally conductive adhesive layer on one surface closely adheres to the heat generating portion of the electronic device, and the thermally conductive adhesive layer on the other surface is closely connected to an active heat spreader such as a thin film heat pipe. Can be glued.

The thermally conductive adhesive layer may be formed by, for example, attaching a thermally conductive double-sided tape to one or both sides of the thermal diffusion sheet, wherein the thermally conductive double-sided tape is a film-shaped thermal conductive adhesive, a silicone-based adhesive or an acrylic adhesive on both sides of a metal substrate. And an adhesive selected from the group consisting of an epoxy-based adhesive, or a thermally conductive adhesive applied to both surfaces of a metal substrate. The thermally conductive adhesive includes alumina powder, boron nitride powder, silicon nitride powder, titanium nitride powder, iron oxide powder, magnesium oxide powder, beryllium in any one selected from the group consisting of silicone pressure sensitive adhesives, acrylic pressure sensitive adhesives, and epoxy pressure sensitive adhesives. With oxide powder, nickel powder, copper powder, gold powder, silver powder, tin powder, cobalt powder, aluminum powder, silver coated copper powder, silver coated nickel powder, silver coated aluminum powder, and tin coated copper powder It is formed by charging at least one thermally conductive filler selected from the group consisting of: In addition, the metal substrate is preferably characterized in that made of a thermally conductive foil (Foil) made of aluminum, copper, nickel or a combination thereof.

In addition, the composite function heat diffusion sheet according to the present invention may optionally further include an electrical insulation layer (40). The electrical insulation layer is formed by laminating on one surface of the thermal diffusion sheet as shown in FIG. The electrical insulation layer is formed by bonding an insulating tape such as a polyester film (PET film) or polyimide film (PI film) to one surface of the thermal diffusion sheet. The electrical insulation layer is an electrical short circuit between the surface of the thermal diffusion sheet and the electronic component. (short circuit) and vertically transferred heat is prevented from being transferred directly to the part opposite the heat source, thereby protecting the part from heat.

(2) Manufacturing method of composite functional thermal diffusion sheet composed of spherical graphite thermal conductive sheet

Figure 2 shows the manufacturing process of the composite functional thermal diffusion sheet shown in Figure 1 of the present invention.

In the method of manufacturing a composite functional thermal diffusion sheet of a preferred embodiment according to the present invention, (a) 100 parts by weight of the base resin and 300 to 900 parts by weight of spherical graphite particles are added to a pressure-dispersion kneader and kneaded at 100 to 140 ° C to form spherical graphite. Forming a kneaded material; And (b) forming the spherical graphite kneaded material with a calender having a roller surface temperature of 50 to 80 ° C. to form a spherical graphite heat conductive sheet. In addition, the method for producing a composite function thermal diffusion sheet according to the present invention may preferably further comprise (c) attaching a thermally conductive double-sided tape to one or both sides of the thermal diffusion sheet to form a thermally conductive adhesive layer. . In addition, the method of manufacturing a composite function thermal diffusion sheet according to the present invention may further comprise the step of (d) adhering an electrical insulating tape to one surface of the thermal diffusion sheet to form an electrical insulating layer.

Spheroidal Graphite Containing Base Resin And Spheroidal Graphite Particles Kneading  Forming step ( S1 )

The forming step of the spherical graphite kneaded material including the base resin and the spherical graphite particles consists of weighing 100 parts by weight of the base resin, and measuring 300 to 900 parts by weight of the spherical graphite particles and then kneading them. Kneading (or kneading) is an operation of mixing a highly viscous material or semi-plastic material. Evenly, spherical graphite particles are beaten in a base resin made by applying mechanical shear force to have a constant acceleration. It is the work of mixing. In this case, the mixing means not only having spherical graphite particles fed into the base resin, but also sufficiently dispersing the spherical graphite particles in the base resin. Kneading takes place at a temperature of about 100 to 140 ° C, preferably at about 130 ° C.

In addition, the forming step of the spherical graphite kneaded product is preferably characterized in that 1 to 3 parts by weight of the lubricant is further added to the pressure dispersion kneader and kneaded in the base resin to form a kneaded product.

In addition, the forming step of the constituent graphite kneaded material is preferably characterized by further adding a thermally conductive filler other than a flame retardant or graphite particles to the pressure dispersion kneader and kneading the base resin to form a kneaded material.

Spheroidal graphite Kneading  Forming into a calender to form a spherical graphite thermally conductive sheet ( S2 )

The method for producing a composite functional thermal diffusion sheet according to the present invention is characterized by using a calendering method in the step of forming a spherical graphite kneaded material to form a spherical graphite heat conductive sheet. The calendering method is a method in which a hollow roller made of two to four cast irons is stacked and rolled while passing a kneaded material therebetween to make a sheet. When kneaded material passes between rollers, The pressurization between the rollers and the heat of the steam sent from them is applied. When using a calendering process, the highly viscous kneaded material can be easily formed into a sheet, and the kneaded material may contain a much higher content of spheroidal graphite particles than the base resin, and the final molded sheet is smooth and uniform. It has a surface. At this time, it is preferable that the roller surface temperature of the calender is 50-80 ° C, but if the roller surface temperature of the calender is less than 50 ° C, the base resin does not soften, making the surface of the sheet uneven and making it difficult to manufacture a sheet having a thickness of 2 mm or less, The mechanical properties of the sheet are also poor. In addition, when the roller surface temperature of the calender exceeds 80 ℃, the softening of the base resin is active and the sheet sticks to the roll surface, the tension is weakened when the sheet is manufactured in the roll type, the sheet is cut and thus the winding ( Winding) becomes difficult and ultimately makes it difficult to manufacture the sheet into a roll type. On the other hand, the spherical graphite heat conductive sheet according to the present invention preferably has a thickness of 0.02 to 2.0 mm, the thickness of the spherical graphite heat conductive sheet can be controlled by appropriately adjusting the interval between the rollers of the calendar.

Thermal diffusion  On one or both sides of the sheet Thermal conductivity Adhesive layer  Forming step ( S3 )

The composite functional thermal diffusion sheet according to the present invention may be made of only a spherical graphite thermal conductive sheet, but preferably further includes a thermally conductive adhesive layer formed on one or both surfaces of the thermal diffusion sheet. The method of forming a thermally conductive adhesive layer includes a method of directly applying a thermally conductive adhesive to one or both sides of a thermal diffusion sheet made of only a spherical graphite thermally conductive sheet. Preferably, a thermally conductive double-coated tape is applied to one or both sides of the horizontal thermal conductive layer. There is a way to attach.

Thermal diffusion  Electrical on one side of the sheet Insulation layer  Forming step ( S4 )

The composite function heat diffusion sheet provided with a spherical graphite heat conductive sheet and a heat conductive adhesive layer preferably further includes an electrical insulating layer formed on one surface of the heat diffusion sheet. The method of forming the electrical insulation layer is a method of bonding an insulating tape such as a polyester film (PET film) or a polyimide film (PI film) to one surface of the thermal diffusion sheet.

The composite function heat diffusion sheet manufactured by the above manufacturing method is then cut to an appropriate size and can be used to solve thermal management problems of various electronic devices.

Figure 3 shows a laminated structure of a multi-functional multi-layer thermal diffusion sheet according to another embodiment of the present invention.

As shown in FIG. 3, the multi-functional multilayer thermal diffusion sheet 200 according to the present invention is a spheroidal graphite thermal conductive sheet molded from a spherical graphite mixture including a base resin and spheroidal graphite particles dispersed by being kneaded and dispersed in the base resin. 10; And a flaky graphite thermal conductive sheet 20 laminated on or below the spherical graphite thermal conductive sheet and molded into a flaky graphite kneaded material comprising flaky graphite particles that are kneaded and dispersed in a base resin and a base resin. do. In addition, the multi-functional multilayer thermal diffusion sheet according to the present invention may further include a thermally conductive adhesive layer 30 laminated on one surface of the thermal diffusion sheet. Although not shown in FIG. 1, the thermally conductive adhesive layer may be laminated on both sides of the thermal diffusion sheet. In addition, the multi-functional multi-layer thermal diffusion sheet according to the present invention may preferably further include an electrical insulating layer 40 laminated on one surface of the thermal diffusion sheet.

(3) Multifunctional multi-layered thermal diffusion sheet consisting of spherical graphite thermal conductive sheet and flake graphite thermal conductive sheet

In the multi-functional multilayer thermal diffusion sheet according to another embodiment of the present invention, the spherical graphite thermally conductive sheet, the thermally conductive adhesive layer, and the electrical insulation layer are the same as those of the thermal diffusion sheet composed of the spherical graphite thermally conductive sheet described above, and thus will be omitted. do.

Flotation  Graphite thermal conductive sheet and method for manufacturing same

The flaky graphite heat conductive sheet 20 is formed in the form of a sheet formed by kneading a kneaded material including flaky graphite particles kneaded and dispersed in a base resin using a calendering method.

The flaky graphite particles are graphite particles having a crystalline flake shape. In the present invention, the flaky graphite particles include not only flaky graphite particles of natural form but also expanded graphite particles which have expanded when the final particles are flaky. The flaky graphite particles preferably have a density of about 2.0 to 2.5 g / cm 3 and an average particle diameter of about 1 μm to 1 mm. The content of the spherical graphite particles in the flake graphite thermally conductive sheet is preferably about 300 to 600 parts by weight, more preferably 400 to 500 parts by weight, based on 100 parts by weight of the base resin described later. When the content of the flaky graphite particles is less than 300 parts by weight, the horizontal thermal conductivity of the flaky graphite thermal conductive sheet is not high as less than 20 W / m · K, and thus the horizontal heat conduction synergistic effect due to the addition of the flaky graphite thermal conductive sheet to the electronic device is insufficient. can do. In addition, when the content of the flaky graphite particles exceeds 600 parts by weight, it is difficult to uniformly disperse the flaky graphite particles by mixing them with the base resin, and the bonding force with the base resin is poor, so that it may be difficult to shape the sheet graphite even by calendering. The amount of base resin is too small to reduce the flexibility (or flexibility) of the finally formed flake graphite thermally conductive sheet, which can make it difficult to manufacture the flake graphite thermally conductive sheet in roll type and to improve adhesion in the application of electronic devices. Apart from that its scope of application is narrow. When the content of the flaky graphite particles is about 400 to 500 parts by weight based on 100 parts by weight of the base resin, the horizontal thermal conductivity of the flaky graphite heat conductive sheet is high and at the same time excellent in formability.

The base resin is not particularly limited as long as it can uniformly disperse the flake graphite particles by kneading, and specifically, acrylic resin, urethane resin, silicone resin, ethylene vinyl acetate (EVA) resin, polyvinyl chloride (PVC). ) Resins, and polyester resins. In addition, the base resin is preferably an acrylate rubber (Ncrylate rubber), NB rubber (Acrylonitrile Butadiene Rubber, NBR), urethane rubber, ethylene-octene rubber (Ethylene-Octene Rubber, EOR), ethylene-propylene rubber (Ethylene-Propylene Rubber), ethylene-propylene-diene rubber (EPDM Rubber) and polyethylene rubber, and at least one non-halogen-based elastomer resin selected from the group consisting of. The non-halogen-based elastomer resin is more environmentally friendly because it has excellent heat resistance, impact resistance, adhesion, etc., and does not emit halogen substances causing environmental problems, and the base resin has a hardness of 50 to 50 according to ASTM D-2240. It is more preferable that it is 95 Shore A. The spherical graphite heat conductive sheet having a hardness of 50 to 95 Shore A of the base resin has commercially satisfactory wear resistance.

The flaky graphite kneaded material preferably further contains a lubricant. Lubricants aid in flow by lubricating metal surfaces in contact with plastics during calendering, forming and extrusion, making the surfaces even. That is, it prevents the adhesion between the mold surface or the extruder surface and the resin and is kneaded with the resin as an additive for improving the slip property, thereby lowering the melt viscosity to improve molding processability. The lubricant is not limited as long as it is a material that can reduce the friction between the surface of the roller and the flake graphite mixture and promote the sliding in the calendering described later. Specifically, the metal salts of stearic acid and fatty acids (usually, the metal components are calcium and zinc). Synthetic waxes in the form of esters and amides, paraffin waxes, mineral oils, low molecular weight polyethylene, and the like. The amount of the lubricant is preferably about 1 to 3 parts by weight based on 100 parts by weight of the base resin. If the amount of the lubricant is less than 1 part by weight, the inherent function exerted by the lubricant is insufficient. This is because the function synergistic effect is not large.

In addition, the flaky graphite kneaded material may further include a flame retardant or a thermally conductive filler similar to the above-described spherical graphite kneaded material, and a detailed description thereof will be omitted.

The manufacturing method of the flaky graphite heat conductive sheet includes the steps of forming the flaky graphite kneaded material containing a base resin and flaky graphite particles similarly to the manufacturing method of a spherical graphite heat conductive sheet; And shaping the piece-like kneaded material into a calender to form a piece-shaped graphite heat conductive sheet.

The step of forming the flake graphite kneaded material including the base resin and flake graphite particles is, for example, 100 parts by weight of the base resin, weighing 300 to 600 parts by weight of the flake graphite particles and kneading them. Kneading takes place at a temperature of about 100 to 140 ° C, preferably at about 130 ° C. In addition, the step of forming the flake graphite kneaded is preferably characterized in that 1 to 3 parts by weight of the lubricant is further added to the pressure dispersion kneader and kneaded in the base resin to form a kneaded product.

Forming the flake graphite thermal conductive sheet is characterized by using a calendering method. The calendering method is a method in which a hollow roller made of two to four cast irons is stacked and rolled while passing a kneaded material therebetween to make a sheet. When kneaded material passes between rollers, The pressurization between the rollers and the heat of the steam sent from them is applied. When using the calendering method, the highly viscous kneaded material can be easily formed into a sheet, and the kneaded material may contain much higher content of flaky graphite particles than the base resin, and the final molded sheet is smooth and uniform. It has a surface. At this time, it is preferable that the roller surface temperature of the calender is 50-80 ° C, but if the roller surface temperature of the calender is less than 50 ° C, the base resin does not soften, making the surface of the sheet uneven and making it difficult to manufacture a sheet having a thickness of 2 mm or less, The mechanical properties of the sheet are also poor. In addition, when the roller surface temperature of the calender exceeds 80 ℃, the softening of the base resin is active and the sheet sticks to the roll surface, the tension is weakened when the sheet is manufactured in the roll type, the sheet is cut and thus the winding ( Winding) becomes difficult and ultimately makes it difficult to manufacture the sheet into a roll type. On the other hand, the flaky graphite heat conductive sheet according to the present invention preferably has a thickness of 0.02 to 2.0 mm, the thickness of the flaky graphite heat conductive sheet can be controlled by appropriately adjusting the distance between the rollers of the calendar.

(4) A method for producing a composite multi-layer thermal diffusion sheet composed of a spheroidal graphite thermally conductive sheet and a flake graphite thermally conductive sheet

Figure 4 shows the manufacturing process of the composite functional multilayer thermal diffusion sheet shown in Figure 3 of the present invention.

Method for producing a composite functional multi-layer thermal diffusion sheet according to the present invention comprises the steps of (A) forming a spherical graphite kneaded material with a calender (calender) having a roller surface temperature of 50 ~ 80 ℃ (S10); (B) forming the flake graphite thermally conductive sheet by forming the flake graphite kneaded product into a calender having a roller surface temperature of 50 to 80 ° C. (S20); (C) stacking the flaky graphite thermal conductive sheet on the spherical graphite thermal conductive sheet to obtain a multilayer preform (S30); And (d) inserting the multilayer preform into a mold of a hot press, and compressing and curing the mold (S40). In addition, the method for producing a multi-functional multi-layer thermal diffusion sheet according to the present invention is preferably (e) forming a thermally conductive adhesive layer by attaching a thermally conductive double-sided tape on one or both sides of the thermal diffusion sheet (S50); It may include. In addition, the method of manufacturing a multi-functional multi-layer thermal diffusion sheet according to the present invention may further include (B) adhering an electrical insulating tape to one surface of the thermal diffusion sheet to form an electrical insulating layer (S60). Steps (a), (b), (e) and (b) are the same as the contents of the method of manufacturing the composite functional thermal diffusion sheet composed of the spherical graphite thermal conductive sheet and the method of manufacturing the flaky graphite thermal conductive sheet. , Omitted below.

First, a multilayer graphite thermal conductive sheet is laminated on a spherical graphite thermal conductive sheet to obtain a multilayer preform (S30). The multi-functional multi-layer thermal diffusion sheet is manufactured by putting the obtained multi-layer preform into a mold of a hot press, pressing, curing and discharging (S40).

 In addition, the multilayer preform may be formed by repeatedly alternating one spherical graphite thermally conductive sheet and one piece of thermally conductive sheet, or may be deformed by various laminated structures of the spherical graphite thermally conductive sheet and the single-shaped thermally conductive sheet. In addition, the multilayer preform preferably has a ratio of the number of spherical graphite thermally conductive sheets and the number of spherical graphite thermally conductive sheets to the number of spherical graphite thermally conductive sheets and the number of spherical graphite thermally conductive sheets based on the same thickness of the spherical graphite thermally conductive sheet and the spherical graphite thermally conductive sheet. The ratio is 1 or less. When the number of sheet graphite thermal conductive sheets is larger than the number of spherical graphite thermal conductive sheets of the same thickness, that is, the thickness of the sheet graphite thermal conductive sheet is larger than the thickness of the spherical graphite thermal conductive sheet based on the entire multilayer preform, the vertical thermal conductivity of the composite functional multilayer thermal diffusion sheet. The degree may not satisfy a predetermined range.

Looking more specifically at the process of manufacturing a multi-functional multi-layer thermal diffusion sheet from a multi-layer preform, the obtained multi-layer preform is cut to a suitable size for the rubber mold, and the rubber press of the heating press preheated to a temperature of 150 ℃ to 180 ℃ And then compressed and cured after insertion. At this time, the pressure applied to the multilayer preform is 140 kg / cm 2 to 160 kg / cm 2, and the curing time is preferably 1 to 3 minutes. If the pressure applied to the multilayer preform is less than 140 kg / cm 2, the composite multi-layered thermal diffusion sheet cannot have sufficient density, and by applying a pressure exceeding 160 kg / cm 2, it is no longer possible to improve the density of the composite functional multilayered thermal diffusion sheet. Since it does not show an effect, it is pointless to apply a pressure exceeding 160 kg / cm 2. Preferably, a pressure of 150 kg / cm 2 is applied. In addition, it is preferable that the time of the thermosetting process performed in a compressed state in a heating press is 1 minute to 3 minutes for the multilayer preform having a thickness of 1 mm or less, and the curing time can be flexibly applied according to the molding thickness. If the curing time is less than 1 minute, the curing time may not be sufficiently cured and may be exceeded 3 minutes. More preferably, the conditions for compressing and curing the multilayer preform using a heating press are characterized in that the curing is applied for 3 minutes by applying a pressure of 150 kg / cm 2 on the rubber mold heated to a temperature of 170 ° C.

Hereinafter, the present invention will be described more clearly through specific examples. However, the protection scope of the present invention is not limited by the following examples.

1.Composite function consisting of spherical graphite thermal conductive sheet Thermal diffusion  Manufacture of sheets

Example  One.

100 parts by weight of ethylene-propylene rubber having a density of 0.870 g / cm 3 and a hardness of 85 Shore A according to ASTM D-2240, spherical graphite having a density of 1.0 g / cm 3 and an average particle diameter of 20 μm. 500 parts by weight of particles) and 2 parts by weight of stearic acid (Stearic acid) as a lubricant were added to a pressure dispersion kneader and kneaded at 130 ° C. for 2 hours to prepare a spherical graphite kneaded product. The spherical graphite kneaded material was charged into a calender having a surface temperature of 60 ° C. and rolled to prepare a roll type spherical graphite thermal conductive sheet having a thickness of about 0.5 mm.

Example  2.

It was the same as Example 1 except for using 700 weight part of spherical graphite particles.

Example  3.

100 parts by weight of ethylene-propylene rubber having a density of 0.870 g / cm 3 and a hardness of 85 Shore A according to ASTM D-2240, spherical graphite having a density of 1.0 g / cm 3 and an average particle diameter of 20 μm. 1000 parts by weight of particles) and 2 parts by weight of stearic acid (Stearic acid) as a lubricant were added to a pressure dispersion kneader, and kneaded at 130 ° C. for 2 hours to prepare a spherical graphite kneaded product. In the prepared spheroidal graphite kneaded material, the agglomeration phenomenon between the spherical graphite particles slightly occurred without the spherical graphite particles being uniformly dispersed in the base resin. The spherical graphite kneaded material was charged into a calender having a surface temperature of 60 ° C. and roll formed. Cracking occurred in a part of the sheet during molding by calendering, and the sheet was sometimes cut when winding in a roll type, and a part of the surface of the sheet was not smooth or rough.

Comparative example  One.

100 parts by weight of ethylene-propylene rubber having a density of 0.870 g / cm 3 and a hardness of 85 Shore A according to ASTM D-2240, crystalline flat graphite having a density of 2.2 g / cm 3 and an average particle diameter of 5 μm. (Crystalline flake graphite, Superior Graphite Co., Ltd.) 500 parts by weight of particles, 2 parts by weight of stearic acid (Stearic acid) as a lubricant was added to the pressure dispersion kneader and kneaded at 130 ℃ for 2 hours to prepare a flake graphite kneaded. The flaky graphite kneaded product was charged into a calender having a surface temperature of 60 ° C. and roll molded to prepare a roll type flaky graphite thermal conductive sheet having a thickness of about 0.5 mm.

Comparative example  2.

100 parts by weight of ethylene-propylene rubber having a density of 0.870 g / cm 3 and a hardness of 85 Shore A according to ASTM D-2240, crystalline flat graphite having a density of 2.2 g / cm 3 and an average particle diameter of 5 μm. (Crystalline flake graphite, Superior Graphite, USA) 700 parts by weight of particles, 2 parts by weight of stearic acid (Stearic acid) as a lubricant was added to a pressure dispersion kneader and kneaded at 130 ℃ for 2 hours to prepare a flake graphite kneaded. In the prepared graphite graphite mixture, agglomeration phenomenon between the graphite graphite particles slightly occurred without the graphite graphite particles being uniformly dispersed in the base resin. The flake graphite kneaded product was charged into a calender having a surface temperature of 60 ° C and rolled. Cracking occurred in a part of the sheet during molding by calendering, and the sheet was sometimes cut when winding in a roll type, and a part of the surface of the sheet was not smooth or rough.

2. Spherical Graphite Thermal Conductive Sheet and Flotation  Composite multi-layer consisting of graphite thermally conductive sheet Thermal diffusion  Manufacture of sheets

Example  4.

In Example 1, the spherical graphite heat conductive sheet and the piece-shaped graphite heat conductive sheet obtained by the comparative example 1 were laminated each, and the multilayer preform was produced. The multi-layer preform was cut to fit the rubber mold size of the hot press, drawn in, and cured for 3 minutes by applying a pressure of 150 kg / cm 2 at a temperature of 170 ° C. to prepare a composite functional multilayer heat diffusion sheet.

3. Thermal diffusion  Measurement of Properties of Sheet

(1) thermal conductivity

The horizontal thermal conductivity and the vertical thermal conductivity of the thermal diffusion sheets prepared in Examples 1, 2, 4 and Comparative Example 1 were measured using a thermal conductivity tester (model name: LFA-447, manufacturer: NETZSCH). The results are shown in Table 1.

division Vertical thermal conductivity (W / mK) Horizontal thermal conductivity (W / mK) Example 1 3.8 6.3 Example 2 4.3 8.2 Example 4 1.4 17.8 Comparative Example 1 0.7 24.6

(2) Electromagnetic shielding ability and electromagnetic wave absorbing ability

The electromagnetic wave shielding ability and the electromagnetic wave absorbing ability of the thermal diffusion sheet prepared in Example 1, Example 4, and Comparative Example 1 were measured.

The electromagnetic shielding ability is obtained by cutting a thermal diffusion sheet into a donut shape having an outer diameter of 7 mm and an inner diameter of 3 mm, and then reflecting the electromagnetic wave reflected by the electromagnetic wave signals incident on the respective thermal diffusion sheets using a vector network analyzer (HP Network Analyzer 8753D). Measurements were made by sensing signals and the results were expressed as changes in return loss [in dB] in the frequency band below 1 GHz.

In addition, the electromagnetic wave absorbing capacity was measured by cutting the thermal diffusion sheet into a square shape having a length of 50 mm, and then using a vector network analyzer (HP Network Analyzer 8753D) at one terminal for the electromagnetic wave signal incident on each thermal diffusion sheet. Measurements were made by sensing the attenuation of the signal going to another terminal, the signal being expressed in power, and the electromagnetic wave absorptivity of each sheet is calculated as follows.

In Equation 1, P (in) is supply power and P (loss) means power lost by the sheet of the supply power.

5 is a graph showing the electromagnetic shielding rate of the composite functional thermal diffusion sheet according to Example 1, Figure 6 is a graph showing the power loss of the composite functional thermal diffusion sheet according to Example 1. 7 is a graph showing the electromagnetic shielding rate of the thermal diffusion sheet according to Comparative Example 1, Figure 8 is a graph showing the power loss of the thermal diffusion sheet according to Comparative Example 1. 9 is a graph showing the electromagnetic shielding rate of the composite functional multilayer thermal diffusion sheet according to Example 4, Figure 10 is a graph showing the power loss of the composite functional multilayer thermal diffusion sheet according to Example 4. In addition, FIG. 11 schematically illustrates a method of measuring shielding effectiveness, and FIG. 12 schematically illustrates a method of measuring electromagnetic wave absorption (or power loss).

In the composite function thermal diffusion sheet according to Example 1, the shielding effectiveness rate was 7.5 dB on average, and the electromagnetic wave absorption rate (or power loss) was 32% at 1 ㎓. The average shielding effectiveness of the functional multilayer thermal diffusion sheet was 16.8 dB, and the absorption rate (or power loss) was 82% at 1 dB. Meanwhile, in the thermal diffusion sheet according to Comparative Example 1, the shielding effectiveness rate was 14 dB on average, and the electromagnetic wave absorption rate (or power loss) was 60% at 1 Hz.

10: spherical graphite thermally conductive sheet; 20: flake graphite thermal conductive sheet
30: heat conductive adhesive layer; 40: electrical insulation layer

Claims (18)

delete delete A spherical graphite heat conductive sheet molded from a spherical graphite kneaded material comprising a base resin and spheroidal graphite particles kneaded and dispersed in the base resin; And
And a spheroidal graphite thermally conductive sheet laminated on or under the spherical graphite thermally conductive sheet and molded into a spheroidal graphite kneaded material comprising a base resin and flaky graphite particles that are kneaded and dispersed in the base resin.
Multi-function thermal diffusion sheet with vertical heat conduction, horizontal heat conduction, electromagnetic shielding and electromagnetic wave absorbing properties.
The spherical graphite thermal conductive sheet according to claim 3, further comprising: a spherical graphite thermal conductive sheet formed of a spherical graphite kneaded material including 100 parts by weight of the base resin and 300 to 900 parts by weight of spheroidal graphite particles kneaded and dispersed in the base resin; And
Laminated graphite formed on the upper or lower portion of the spheroidal graphite thermally conductive sheet and formed into a flake graphite kneaded material containing 100 parts by weight of the base resin and 300 to 600 parts by weight of flake graphite particles kneaded and dispersed in the base resin. Composite function thermal diffusion sheet consisting of a thermally conductive sheet.
The resin of claim 3 or 4, wherein the base resin is selected from the group consisting of acrylic resins, urethane resins, silicone resins, ethylene vinyl acetate (EVA) resins, polyvinyl chloride (PVC) resins, and polyester resins. A composite function thermal diffusion sheet characterized by being a species.
According to claim 3 or 4, wherein the base resin is an acrylate rubber (Acrylate Rubber), NB rubber (Acrylonitrile Butadiene Rubber, NBR), urethane rubber, ethylene-octene rubber (Ethylene-Octene Rubber, EOR), ethylene- A composite functional thermal diffusion sheet comprising at least one non-halogen-based elastomer resin selected from the group consisting of ethylene-propylene rubber, ethylene-propylene-diene rubber, and polyethylene rubber.
The composite functional thermal diffusion sheet according to claim 3 or 4, wherein the spherical graphite particles have a density of 0.5 to 2.0 g / cm 3 and an average particle diameter of 1 to 200 µm.
The composite functional thermal diffusion sheet according to claim 3 or 4, wherein the spherical graphite kneaded material or the flake graphite kneaded material further comprises a lubricant kneaded and dispersed in a base resin.
The composite functional thermal diffusion sheet according to claim 8, wherein the amount of the lubricant is 1 to 3 parts by weight per 100 parts by weight of the base resin.
The composite functional thermal diffusion sheet according to claim 3 or 4, wherein the spherical graphite kneaded material further comprises a flame retardant kneaded and dispersed in a base resin.
The flame retardant according to claim 10, wherein the flame retardant is selected from the group consisting of ammonium phosphate, ammonium polyphosphate, melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, red, and oxide or resin coated red It is the above non-halogen flame retardant, The composite function thermal diffusion sheet characterized by the above-mentioned.
The method according to claim 3 or 4, wherein the spherical graphite kneaded material further comprises a thermally conductive filler kneaded and dispersed in a base resin,
The thermally conductive filler is alumina powder, boron nitride powder, silicon nitride powder, titanium nitride powder, iron oxide powder, magnesium oxide powder, beryllium oxide powder, nickel powder, copper powder, gold powder, silver powder, tin powder, cobalt A composite function thermal diffusion sheet, characterized in that at least one selected from the group consisting of powder, aluminum powder, silver coated copper powder, silver coated nickel powder, silver coated aluminum powder, and tin coated copper powder.
delete The composite function thermal diffusion sheet according to claim 3 or 4, further comprising a thermally conductive adhesive layer laminated on one or both surfaces of the thermal diffusion sheet.
The composite functional thermal diffusion sheet of claim 14, wherein the thermally conductive adhesive layer is formed by attaching a thermally conductive tape to one or both surfaces of the thermal diffusion sheet.
The method of claim 15, wherein the thermally conductive tape is a silicone powder, boron nitride powder, silicon nitride powder, titanium nitride powder, iron oxide Powder, magnesium oxide powder, beryllium oxide powder, nickel powder, copper powder, gold powder, silver powder, tin powder, cobalt powder, aluminum powder, silver coated copper powder, silver coated nickel powder, silver coated aluminum powder, and The thermally conductive adhesive formed by filling at least one thermally conductive filler selected from the group consisting of tin-coated copper powder or a composite functional thermal diffusion sheet, characterized in that the thermally conductive adhesive is applied to both sides of the metal substrate.
17. The composite functional thermal diffusion sheet of claim 16, wherein the metal substrate is made of a thermally conductive foil made of aluminum, copper, nickel, or a combination thereof.
The composite function thermal diffusion sheet according to claim 3 or 4, further comprising an electrical insulation layer laminated on one surface of the thermal diffusion sheet.

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