KR101568687B1 - Heat-radiating sheet and method for manufacturing the same - Google Patents

Abstract

(a) cleaning the surface of the thermally-conductive substrate with an alkaline solution, (b) pretreating the surface of the thermally-conductive substrate, (c) oxidizing the surface of the pretreated thermally-conductive substrate to form an organic coating, and (d) coating the surface of the thermally-conductive substrate subjected to the oxidation treatment with a solution containing a heat-dissipating powder, and a heat-radiating sheet produced thereby. Such a heat-radiating sheet can meet the light-weight shortening tendency of the electronic device and the flexible function that can bend while performing the heat-dissipating function in the heat-generating small electronic device parts.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a heat-radiating sheet,

The present invention relates to a heat-radiating sheet and a method of manufacturing the heat-radiating sheet, and more particularly, to a heat-radiating sheet that is flexible using a thermally conductive substrate having flexibility and has an excellent thermal conductivity and a method of manufacturing the same.

In recent electronic devices, a large number of electronic components are installed in a narrow space in accordance with the trend of short and light shortening, so that the amount of heat generated per unit volume is greatly increased. Therefore, in order to prevent the deterioration of the electronic equipment, there is a need for a heat dissipating means for effectively dissipating the heat generated from the heat source.

Heat sinks, heat-dissipating fans, and the like are used as means for effectively releasing heat generated in electronic devices according to the necessity. Such a heat dissipating means has good heat dissipation effect, but it is difficult to adopt it in a flat panel display field requiring a thin thickness because of its large volume. Especially, in order to be applied to a flexible display field which is currently in the limelight, there is a limit to adopt existing heat dissipation means because sheets used have flexibility.

For this reason, the heat dissipating means usable in the field of flat panel displays should be provided in a sheet form in order to reduce their volume. As such a sheet-shaped heat dissipating means, a graphite sheet rolled after a thin metal or natural graphite (hereinafter referred to as graphite) of copper or aluminum is rolled or a sheet filled with a thermally conductive powder on a resin such as silicone or acrylic is mainly used have.

Korean Patent Registration No. 10-0721462 discloses a tacky heat-radiating sheet comprising a thermally conductive metal sheet and a tacky foam sheet formed on at least one surface of the metal sheet and having cells formed therein as a foam structure, Discloses an adhesive heat-release sheet in which the sheet is formed of an adhesive mixture containing an adhesive and a cell forming agent, and the adhesive is an acrylic resin, a silicone resin, or a polyurethane resin, and the cell forming agent is composed of a microsampler. However, such a heat-radiating sheet has a problem that it is difficult to use the heat-radiating sheet for electronic appliances having a small thickness such as a portable electronic device because the sheet is used by attaching a sticky foam sheet to the surface of the metal plate. In addition, since the metal sheet has a large specific gravity, there is a limit to lighten the product and there is no large difference in thermal conductivity in each direction. Therefore, it is possible to quickly absorb heat in the thickness direction (vertical direction) in which the length of the heat conduction path is short However, since the heat can not be rapidly diffused in the plane direction (horizontal direction) in which the length of the heat conduction path is long, hot spot is partially generated.

The graphite sheet is useful in that it can compensate for the disadvantages of the sheet made of metal, but it requires a surface coating to prevent the occurrence of surface peeling and dust, and has a problem of low flexibility. Further, the sheet made of a resin has a low thermal conductivity in the horizontal direction due to the characteristics of the material, so that the heat radiation effect is small, and the flexibility is too much to handle.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a hybrid type heat dissipation sheet capable of meeting the trend of thinning and bending of an electronic device while flexibly functioning while performing a heat dissipation function in heat dissipating small electronic device parts.

Another object of the present invention is to provide a heat-radiating sheet produced by the method for producing a heat-radiating sheet, which is flexible by using a thermally conductive substrate having flexibility and has an excellent thermal conductivity.

(A) cleaning the surface of the thermally conductive substrate with an alkaline solution, (b) pretreating the surface of the thermally-conductive substrate, (c) removing the surface of the pre-treated thermally- And (d) coating the surface of the thermally-conductive substrate with the heat-dissipating powder-containing solution.

The heat-radiating sheet according to an embodiment of the present invention comprises a heat-radiating substrate and a heat-radiating layer including heat-radiating powder coated on one surface of the thermally-conductive substrate, wherein the heat- do.

Since the heat-radiating structure for an electronic module manufactured according to an embodiment of the present invention can be formed of a heat-releasing sheet composed of a plurality of thermally-conductive sheets, when such a heat-radiating structure for an electronic module is used, It is possible to meet the trend of light and small size of electronic devices.

Further, since the heat radiating structure for an electronic module according to the present invention is constituted without a conventional heat conduction blocking member, the local temperature difference due to the conventional heat conduction blocking member and various problems caused thereby can be prevented in advance.

In addition, the present invention can be applied to a flexible electronic device material that has been emphasized to solve the problem of flexibility of a graphite sheet used in existing expensive electronic equipment.

1 is a schematic diagram illustrating a step of oxidizing a copper sheet surface according to an embodiment of the present invention.
2 is a photograph showing the state of the surface of the copper sheet before the oxidation treatment of the surface of the copper sheet according to one embodiment of the present invention.
3 is a photograph showing the state of the surface of the copper sheet after the surface of the copper sheet is oxidized according to an embodiment of the present invention.
4 is a photograph showing a cross section of the surface of a copper sheet after oxidation treatment of the surface of the copper sheet according to an embodiment of the present invention.
5 is a schematic diagram of heat radiation measurement of a copper / graphite coated sheet according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. It should be understood, however, that the invention is not limited thereto and that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. .

(A) cleaning the surface of the thermally conductive substrate with an alkaline solution, (b) pretreating the surface of the thermally-conductive substrate, (c) removing the surface of the pre-treated thermally- And (d) coating the surface of the oxidized thermally-conductive substrate with a solution containing a heat-dissipating powder.

Each step will be described in detail below.

The thermally conductive substrate may be a copper sheet or an aluminum sheet.

In the step (a), the surface of the thermally-conductive substrate is cleaned with an alkaline solution, preferably lithium hydroxide, sodium hydroxide or potassium hydroxide solution, in order to remove the organic coating and contaminants. In this case, the temperature at which the cleaning is carried out is preferably 40 ° C to 60 ° C, more preferably 48 ° C to 52 ° C.

After the step (a), a step of cleaning the thermally-conductive substrate surface with deionized water at 50 ° C and deionized water at 25 ° C may be further included. This is to remove the cleaning liquid on the surface of the thermally conductive substrate.

In the step (b), the pretreatment step for activating the surface is carried out with a mixed solution of methanol and 1,2,3-benzotriazole (BTA) in order to increase the oxidation treatment effect of the subsequent thermally conductive substrate surface .

In the step (c), an anchor shape is introduced on the surface of the thermally conductive substrate, and the surface of the pre-treated thermally conductive substrate is oxidized to increase the chemical affinity with the coating material by increasing the surface energy. This is a step of forming an organic film on the surface of the thermally conductive substrate. In this case, it is preferable to carry out oxidation treatment with a solution in which hydrogen peroxide, sodium hydroxide, sulfuric acid, 1,2,3-benzotriazole and polyethylene glycol are uniformly mixed. The surface states of the thermally conductive substrate surface before and after the oxidation treatment are shown in Figs. 2 and 3, respectively.

After the step (c), a step of removing moisture on the surface of the substrate using hot air may be further included. This is to prevent excessive oxidation and contamination of the thermally conductive substrate surface.

In this case, methyl ethyl ketone (MEK) and ethyl acetate (EA) are mixed at a ratio of 1: 1 to 1: 1 in order to coat the surface of the thermally conductive substrate with the heat dissipating powder in the step (d) To prepare a mixed solution. 1 to 10% by weight of the heat radiation powder is mixed into the mixed solution thus prepared. The heat radiation powder preferably has a particle size of 0.5 to 3 microns, and preferably has a thermal conductivity of 100 W / m · K or more.

In the step (d), when the thermally conductive substrate is coated with the heat dissipation powder, a spray method, a bar coater method, or a slit die coating method may be used. However, the coating method is not particularly limited as long as it is known in the art.

The heat-radiating sheet according to one embodiment of the present invention is a heat-radiating sheet manufactured by the above manufacturing method, and is a heat-radiating sheet composed of a heat-radiating sheet having flexibility and a heat-radiating layer coated on one surface of the heat- . In this case, a heat dissipation adhesive layer is provided so as to be adhered to a heat generating portion of a small electronic device as a heat dissipation target, and the heat dissipation adhesive layer is closed with a release film so that the heat dissipation adhesive layer can remain in an adhered state until substantially adhered to the electronic device. The heat-dissipating adhesive layer is formed on the other surface of the substrate coated with the heat-dissipating layer so as to be attached to the electronic device.

The heat-radiating sheet may further include a heat sink for rapidly transferring heat generated by attaching the heat-radiating sheet to the heat-generating portion of the electronic device. The heat sink absorbs heat from the heat generating portion and emits heat. The heat sink is installed in direct contact with the heat generating portion, or indirectly in thermal contact with the heat generating portion by conduction, convection, radiation, or the like.

The heat-radiating sheet comprises a heat-dissipating adhesive layer adhered to a heat-generating portion of an electronic device on one side or both sides of the substrate, a heat-radiating substrate having one side coated with a solution containing a heat-dissipating powder, and a heat- . In this case, the thermally conductive substrate coated with the solution containing the exoergic powder serves as a conduction layer that receives heat.

And a conductive layer for quickly transferring heat generated in the electronic device to the outside of the heat-dissipative adhesive layer (opposite to the electronic device), wherein the conductive layer is arranged outside the conductive layer, And a heat dissipation layer for emitting electrons in a vertical direction and a horizontal direction of the electronic apparatus.

 The heat-radiating adhesive layer may be made of an acrylic adhesive commonly used in the industry. The adhesive may include a heat-dissipating powder so that heat generated in an electronic device may be conducted to the conductive layer to provide conductivity and heat resistance. Specifically, the heat-radiating adhesive layer is composed of a heat-dissipating resin including epoxy, acrylic, silicone, or the like. The heat radiation adhesive layer may include a curable material including a thermosetting resin, a room temperature curing resin, or a UV curable resin.

 The conductive layer allows the heat of the electronic device to be quickly transferred using aluminum or copper, preferably copper, which has a low emissivity but has good thermal conductivity.

 The heat dissipation layer uniformly disperses the heat dissipation powder, especially the graphite powder, in a mixed solution of methyl ethyl ketone (MEK) and ethyl acetate (EA), and uses the dispersion to coat the surface of the conductive layer to have a uniform thickness. In this case, the heat dissipation layer allows the conductive layer to rapidly discharge the heat conducted to the outside. The heat dissipation layer may include at least one selected from the group consisting of boron nitride, graphite, carbon nanotube (CNT), and graphene.

The thickness of the heat dissipation / adhesive layer, the conductive layer, and the heat dissipation layer is preferably about 20 to 30 microns. The thickness of the heat dissipation / adhesion layer, the conductive layer, and the heat dissipation layer may be changed to secure thermal conductivity depending on the use and size of the electronic device.

The heat radiation powder preferably has a thermal conductivity of 100 W / m · K or more, and the thermally conductive substrate is preferably an aluminum sheet or a copper sheet.

In another embodiment of the present invention, the heat-radiating sheet may be formed on the other surface of the conductive layer having the heat-radiating adhesive layer and the heat-radiating layer, that is, the heat-

Hereinafter, the heat radiating action of the heat radiating sheet according to an embodiment of the present invention will be described in detail.

By attaching the heat radiation sheet to the electronic device as a heat dissipation target, the heat generated in the display is rapidly discharged to the outside in the vertical direction and the horizontal direction of the display. First, after the release film of the heat-radiating adhesive layer is separated, the heat-release adhesive layer is adhered closely to the electronic device as a target. In this state, the heat generated in the electronic device is quickly conducted to the conductive layer through the heat-dissipative adhesive layer, and the heat conducted by the conductive layer is transmitted to the outside in the vertical direction and the horizontal direction through the heat- .

Specifically, the heat transferred to the conductive layer in a state in which the entire electronic device and the heat-radiating adhesive layer are in close contact with each other can not be heat-dissipated because the copper sheet of the thin plate constituting the conductive layer has a low emissivity do. However, by oxidizing the surface of the copper sheet of the conductive layer to improve the bonding force between the conductive layer and the graphite coating layer on the outside and lowering the contact resistance, the coating layer is formed on the oxidized surface, The widening effect is produced. In addition, the heat that has been conducted thereby can be quickly discharged through the heat dissipation layer.

In this case, if the coating speed is too high, the surface may become coarse and hard to be hardened, and if it is too slow, the production speed will be slow. Therefore, the coating speed should be appropriately adjusted according to the viscosity of the mixed solution of the graphite powder and the coating operation temperature. Curing and drying conditions are not particularly limited as long as they are well known in the art.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples.

Example  1: Manufacture of heat-radiating sheet

The copper sheet surface was cleaned at 50 ° C for 180 seconds using sodium hydroxide (NaOH) to remove the organic coating and contaminants, and the first wash with deionized water at 50 ° C for 60 seconds , Followed by secondary and tertiary washing with deionized water at 25 DEG C for 60 seconds each. After washing, pretreatment was carried out at 25 ° C for 60 seconds with a mixture of methanol and 1,2,3-benzotriazole (BTA) in order to increase the activation and oxidation effect of the copper sheet surface.

An anchor shape was introduced on the surface of the copper sheet and the surface of the copper sheet was oxidized at 38 DEG C to increase the surface energy and increase the chemical affinity with the coating material. This is a process for forming an organic film on a copper sheet. When oxidizing the copper sheet surface, sodium hydroxide, sulfuric acid, 1,2,3-benzotriazole and polyethylene glycol were uniformly mixed and used. This oxidation process is shown in Fig.

Thereafter, primary, secondary and tertiary rinses were performed with deionized water at 25 DEG C to remove the cleaning liquid on the surface.

In order to prevent excessive oxidation and contamination of the copper sheet surface, hot water was used to remove water from the surface. Thereafter, a mixed solution of methyl ethyl ketone (MEK) and ethyl acetate (EA) in a ratio of 1: 1 was prepared in order to coat the oxidized copper sheet with graphite. To this mixed solution, 5% by weight of graphite The powders were mixed. In this case, the crystal size of the graphite powder is preferably 0.5 탆 to 3 탆, and preferably 1% to 10% by weight.

The dispersed mixed solution was coated on the surface using a spraying method and dried and surface polished at room temperature to produce a composite sheet.

Comparative Example  One

A copper sheet whose surface was not coated with graphite was used.

Experimental Example  1: Heat dissipation evaluation

The specimens of Example 1 and Comparative Example 1 were used to confirm the heat dissipation characteristics of the heat dissipating structure in which the surface of the copper sheet was coated with graphite.

In order to evaluate the heat dissipation characteristics of the composite thermally conductive substrate, the specimen used was an electrodeposited sheet having a thickness of 15 microns and a sheet coated with a 5 micron thick graphite sheet. An untreated specimen for the comparison of heat dissipation characteristics was an electrolytic sheet with a thickness of 20 microns. Each of the prepared specimens was processed into a rectangular sheet having a length of 80 mm and a width of 50 mm, and then a heating element having a length of 30 mm, a width of 30 mm and a height of 30 mm was attached to the upper left edge.

After applying a power of 2.8 W to each specimen with a heating element, the temperature of the heating section was observed at room temperature. The evaluation results of the heat radiation characteristics of the heat radiation sheet according to Example 1 and Comparative Example 1 are shown in the following Table 1. As a result of evaluation, the heat radiation sheet according to Example 1 has a temperature of 3 Lt; 0 > C or more.

Time [min]
Example 1 (A) Comparative Example 1 (B) Primary [℃] Secondary [℃] 3rd order [℃] Primary [℃] Secondary [℃] 3rd order [℃] 0 33.2 39.3 46.8 32.8 39.7 44.0 10 46.4 50.5 51.4 55.1 50.3 54.3 20 50.9 54.4 56.6 58.8 54.3 57.3 30 54.8 56.4 58.5 60.2 58.1 60.6 40 56.6 58.7 59.6 62.0 60.6 62.4 50 57.5 59.8 60.3 62.8 61.3 62.7 60 58.0 60.1 60.5 63.0 62.6 62.7 Average [℃] 59.5 62.8 Delta T [캜]
= (B) - (A) 3.3

Claims (18)

(a) cleaning the surface of the thermally-conductive substrate with an alkaline solution, (b) pretreating the surface of the thermally-conductive substrate, (c) oxidizing the surface of the pretreated thermally-conductive substrate to form an organic coating, and (d) coating a surface of the thermally-conductive substrate subjected to oxidation treatment with a solution containing a heat-dissipating powder, wherein the heat-dissipating powder is 1 wt% to 10 wt% based on the total weight of the solution Wherein the heat-radiating sheet is made of a thermosetting resin. The method of claim 1, wherein the alkaline solution is lithium hydroxide, sodium hydroxide, or potassium hydroxide. The method according to claim 1, wherein the step (a) is performed at a temperature ranging from 40 ° C to 60 ° C. 2. The method of claim 1, wherein the step (b) is pre-treated with a mixture of methanol and 1,2,3-benzotriazole (BTA). The method according to claim 1, wherein the step (c) is oxidation treatment with a solution of hydrogen peroxide, sodium hydroxide, sulfuric acid, 1,2,3-benzotriazole and polyethylene glycol. The method of manufacturing a heat-radiating sheet according to claim 1, wherein the heat-radiating powder is a graphite powder. delete The method of claim 1, wherein the particle size of the heat-dissipating powder in step (d) ranges from 0.5 microns to 3.0 microns. The method of manufacturing a heat dissipation sheet according to claim 1, wherein the coating of step (d) is selected from the group consisting of a spray method, a bar coater method and a slit die coating method. The method according to claim 1, wherein the heat radiation powder has a thermal conductivity of 100 W / m · K or more. A heat-radiating sheet produced by the method of claim 1,
And a heat dissipation layer comprising a thermally conductive substrate and a heat dissipation powder coated on one surface of the thermally conductive substrate. 12. The heat-radiating sheet according to claim 11, wherein the heat-radiating layer includes a heat-dissipating adhesive layer on the other surface of the substrate. 12. The heat-radiating sheet according to claim 11, wherein the heat-radiating powder is a graphite powder. 12. The heat-radiating sheet according to claim 11, wherein the heat-dissipating powder has a particle size of 0.5 to 3.0 microns. The heat-radiating sheet according to claim 11, wherein the heat-radiating powder has a thermal conductivity of 100 W / m · K or more. 12. The heat-radiating sheet according to claim 11, wherein the thermally-conductive substrate is an aluminum sheet or a copper sheet. 12. The heat-radiating sheet according to claim 11, wherein the heat-radiating layer comprises at least one of boron nitride, graphite, carbon nanotubes and graphene. 12. The heat-radiating sheet according to claim 11, further comprising a heat sink.

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