KR20110094574A - Graphene dispersed polymer matrix and thermal pad and manufacturing method of thermal pad - Google Patents

Abstract

PURPOSE: A method for manufacturing a thermoconductive pad is provided to uniformly disperse graphene to a polymer matrix by directly dispersing graphene and to prepare the thermoconductive pad with heat conductivity. CONSTITUTION: A method for manufacturing a thermoconductive pad comprises the steps of: (i) mixing graphene with surfactants into a dispersing medium and dispersing the graphene using a roll mill; (ii) mixing a silicon- or acryl-based polymer solution with colorants at high speed and mixing with the graphene dispersion to prepare first slurry; (iii) mixing a platinum catalyst, the first slurry and thermoconductive powder into the silicon- or acryl-based polymer solution; and (iv) defoaming and molding second slurry to prepare the thermoconductive pad.

Description

Graphene dispersed polymer matrix and thermal pad and manufacturing method of thermal pad

The present invention relates to a method for producing a thermally conductive pad by directly dispersing the graphene and mixing it with the thermally conductive powder having a variety of shapes and sizes.

As the performance of electronic devices is developed due to the development of electronic and semiconductor technologies, miniaturization and high performance of electronic products have been progressed dramatically. Accordingly, it is becoming an important issue to secure the performance and life of the electronic device through the release of heat generated from the electronic device to the outside.

The heat generated from the electronic device is ideally discharged to the outside through the case. However, there is a space between the electronic device and the case, so heat transfer through radiation occurs. Since heat transfer through radiation is less efficient than heat conduction through conduction, a medium having high thermal conductivity is required.

Conventional thermal conductive pads have been used to improve conductivity by filling alumina in a polymer matrix. This is applicable to low heat generation device, but there is a limit to apply to the high heat generation device has a problem that the specific gravity is increased according to the filling rate of alumina. Therefore, it is necessary to apply a new material having better thermal conductivity and lower specific gravity than alumina.

Meanwhile, graphene is a material excellent in physical, chemical, mechanical, and thermal properties, and research is being conducted in various fields. Graphene is the thinnest structure ever known, forming a two-dimensional, planar, thin film structure of 0.35 nm thick, consisting of numerous layers of carbon atoms stacked in a hexagonal honeycomb with numerous carbon atoms. Graphene not only can deliver about 1,000 times more current than copper per unit area at room temperature, but also has twice the thermal conductivity of diamond, the best thermal conductor, and more than 200 times stronger than steel. In addition, its good elasticity does not lose its electrical conductivity when stretched or folded.

Graphene is superior to carbon nanotubes (CNTs), which are considered to be the next generation of electronic materials. Since the structure is made of carbon nanotubes (CNTs) by rolling graphene, the chemical properties of the two materials are very similar, Therefore, unlike CNTs, which have different characteristics as conductors and semiconductors, graphene has a uniform metallic property, which is easy to apply industrially.

In the case of graphene, since the diameter is only 1 nm level, the graphene does not exist alone, and aggregation occurs due to the attraction of Vander Waals, and thus exists in a bundle shape of several tens to several hundred nm. In order to apply such graphene as a material of the thermal conductive pad, it is necessary to overcome the aggregation phenomenon such as bundle phenomenon and entanglement phenomenon. In the case of agglomerated graphene, the coagulation phenomenon must be overcome because the same effect as using particles of several μm prevents the formation of the three-dimensional network structure and reduces the thermal conductivity relative to the particle.

In other words, graphene has excellent thermal conductivity and low specific gravity, so it is a good material that can reduce the specific gravity of the thermal conductive pad in the final stage by using it alone or in combination with alumina. However, dispersion of graphene in the polymer is the biggest problem.

Graphene dispersion method can be divided into chemical dispersion method using a solvent, surfactant, acid treatment and the like and mechanical dispersion method using ultrasonic wave, ball milling, polishing / friction, shear force and the like. However, there is also a need for a technique capable of preventing reagglomeration after dispersion, regardless of which method the dispersion of graphene is applied.

If graphene is mixed directly with the polymeric material, this aggregation cannot be controlled and graphene is not evenly distributed. This is a reason for not implementing a uniform thermal conductivity inside the thermal conductive pad, it is a problem that can not express the function as a product.

The present invention has been made to solve the above problems, it is an object to provide a method for uniformly dispersing the graphene excellent in the thermal conductivity properties in the matrix, thereby producing a thermal conductive pad having a high thermal conductivity. .

Therefore, in the present invention, the graphene is dispersed in the form of a paste, and this is intended to realize high thermal conductivity by preventing reaggregation by homogeneous mixing or uniform mixing with various thermally conductive powders in the polymer matrix.

As an example for achieving the above object, the present invention provides 1) 79 wt% to 93 wt% of a dispersion medium selected from a liquid silicone binder or a liquid acrylic binder, and from 1 wt% to 15 wt% of graphene and 3 to 6 wt% of a surfactant. 2) preparing a graphene dispersion by mixing and dispersing using a roll mill, 2) adding 45 to 90 wt% of a silicone or acrylic polymer solution and 1 to 5 wt% of a dye, and then stirring the graphene dispersion to 5 to 50 wt%. 1) preparing a first slurry for mixing; 3) a second slurry for mixing 1 to 5 wt% of a platinum (Pt) catalyst, 5 to 30 wt% of the first slurry, and 60 to 80 wt% of the thermally conductive powder in a silicone-based or acrylic polymer solution Manufacturing step, and 4) characterized in that the method for producing a thermal conductive pad comprising the step of defoaming and molding the second slurry to prepare a thermal conductive pad.

As another example for achieving the above object, the present invention is characterized by another thermally conductive pad prepared by the above-described method, the graphene is uniformly dispersed.

Hereinafter, the method of manufacturing the thermal conductive pad of the present invention will be described in detail step by step.

1) Preparation of Graphene Dispersion

Graphene is mixed with a surfactant in a dispersion medium to prepare a graphene dispersion.

As the dispersion medium, a liquid polymer binder such as a silicone-based or acrylic polymer may be used, and a nonionic surfactant may be selected as the surfactant. Graphene in the dispersion medium is mixed at a ratio of 1 to 5 wt%, and when the graphene content is more than the above range, the graphene dispersion tends to be insufficient. In the dispersion medium, the surfactant is mixed at a ratio of 3 to 6 wt%, and when the amount of the surfactant exceeds the above range, the dispersion effect of graphene is not sufficient.

When the silicone liquid polymer is used as the dispersion medium, the insulation, cold resistance, heat resistance, and durability are excellent, and when the acrylic liquid polymer is used, the adhesive strength is excellent. In this way, the dispersion medium can be selected in various ways, thereby making it easier to adjust the physical properties of the thermal conductive pad.

Specific examples of the nonionic surfactant include, but are not limited to, those selected from polysorbate, polyethylene oxide, polyglycerol monoalkyl ether, lauryldimethylamine oxide, and the like.

The dispersion medium, the surfactant, and the graphene are dispersed using a roll mill. When stirring using a general stirrer or planetary mixer, etc., the dispersibility of graphene is not good and agglomeration phenomenon occurs [see FIG. 1]. This is not solved even when adjusting the stirring speed or the stirring time, that is, graphene is not uniformly dispersed into the silicone-based polymer or the acrylic polymer even when dispersed for 2 hours at 2000 rpm in a conventional stirrer or planetary mixer. It is impossible to prepare a slurry using this, because the dispersibility is poor, such as agglomeration phenomenon occurs.

1 is an image showing the results of dispersing silicon and graphene using a planetary stirrer and using a 3-roll mill (3-ROLL MILL).

By the above method it is possible to obtain a uniformly dispersed graphene dispersion of the graphene, which is introduced in the manufacture of the thermal conductive pad.

2) Preparation of slurry in which graphene is dispersed

The slurry is prepared in two stages, and the slurry prepared in each stage is called a first slurry and a second slurry, respectively, and a slurry means said second slurry.

First, the first slurry is dispersed by adding a pigment (pigment) to the silicone polymer solution or acrylic polymer solution to adjust the color of the thermal conductive pad. This is done by adjusting the color of the final product to gray so that it is not sensitive to dust and other contamination. Although it does not restrict | limit as a pigment | dye, For example, using a carbon type pigment, an inorganic type pigment | dye, etc. is suitable for a thermal conductive pad.

The silicone polymer solution or the acrylic polymer solution and the dye are stirred at a speed of 1,500 rpm to 3,000 rpm for 30 minutes to 2 hours, preferably 1 hour, so that the pigment is uniformly dispersed in the polymer solution. Here, the graphene dispersion prepared above was added and stirred at a speed of 1,500 rpm to 3,000 rpm for 1 hour to 3 hours, preferably for 2 hours, using a planetary mixer so that the graphene was uniformly dispersed in the polymer solution. The pigment is added in the range of 1 to 5 wt% in the silicone polymer solution or acrylic polymer solution.

The second slurry is prepared by mixing the first slurry and the thermally conductive powder in a polymer solution.

5 to 15 wt% of a silicone polymer solution or an acrylic polymer solution and 1 to 5 wt% of a metal (Pt) catalyst are mixed, the first slurry is added, stirred and mixed at room temperature, and a thermally conductive powder is added to the second slurry. Manufacture. For the agitation, it is preferable to use a mixer, in particular a planetary mixer. In the second slurry, the first slurry is suitably added in a range of 5 to 30 wt% in terms of expression of high thermal conductivity.

The thermally conductive powder is preferably in terms of ensuring stable dispersibility using a thermal conductivity of 20 to 40W / mK. As the thermally conductive powder, it is preferable to use silica or ceramic powder, and spherical or amorphous powder may be used. The size of the thermally conductive powder may be used to 4 to 40 ㎛, preferably in the case of spherical thermally conductive powder of 5 to 40 ㎛ in diameter, in the case of amorphous thermally conductive powder of 4 to 20 ㎛ size It is preferable to use one in view of good dispersion compatibility with a silicone polymer solution or an acrylic polymer solution. When the size of the thermally conductive powder is larger than the above range, dispersion compatibility with the silicone polymer solution or the acrylic polymer solution tends to be difficult, which is not preferable.

Such thermally conductive powder is added in the range of 60 to 80 wt%, preferably 70 to 80 wt%. If the amount of the thermally conductive powder is less than the above range, the thermal conductivity does not come out. If the thermally conductive powder is used more than the above range, dispersion with the silicone-based polymer solution or the acrylic polymer solution tends to be difficult.

 When there are a lot of spherical thermoelectric powders among the thermally conductive powders, dispersion with silicone polymer solution or acrylic polymer solution tends to be difficult, and when there are many amorphous thermal conductive powders, dispersion with silicone polymer solution or acrylic polymer solution is difficult, and it is advantageous in price. This is less. Therefore, in the present invention, it is preferable to use a combination of spherical thermally conductive powder and amorphous thermally conductive powder in a ratio of 1: 0.5 to 1.5 by weight in order to maintain proper dispersibility with silicone-based polymer solution or acrylic polymer solution and price competitive property in the market. Do.

In the present invention, the thermally conductive powder is added in a split method, and the split criterion is the size of the thermally conductive powder. The thermally conductive powder is preferably injected from small particles sequentially in view of easy dispersion and stable thermal conductivity. The number of divided doses is adjusted to a level of 2 to 5 times, preferably divided into three times. After the divided feeding, each stirring is done in a vacuum state and the vacuum is turned off to allow the stirring for the remaining stirring time so that the graphene can be uniformly mixed with the thermally conductive powder.

For the stirring of the second slurry, it is preferable to use a mixer, in particular, a planetary mixer, and to adjust the inside of the mixer to a vacuum state of 76 cmHg and to stir. Applying a vacuum inside the mixer can remove bubbles in the polymer generated during the dispersion process. When the split conduction of the thermally conductive powder in the second slurry, the stirring speed of the prenary mixer is 10 to 20 rpm, and the stirring time is 10 to 20 minutes for each divided injection, and 5 to 10 minutes of each stirring time is used to adjust the inside of the mixer. 76cmHg in a vacuum to adjust the condition is good to stir. The temperature of the slurry during the stirring was maintained to 20 to 30 ℃. If the temperature of the slurry is less than the above range, the agitation tends not to be performed smoothly, and if the temperature is higher than the above range, the slurry tends to react with the Pt catalyst. It is preferable.

As described above, each particle of graphene and thermally conductive powders such as silica or ceramics are uniformly filled in the polymer matrix by the divided injection and vacuum stirring of the thermally conductive powder, thereby providing uniform and optimal thermal conductivity (thermal conductivity of 3 to 10 W / mk). It is possible to manufacture a thermally conductive pad having

After the slurry is prepared by the above process, the slurry is defoamed. For this purpose, the stirring speed of the planetarium mixer is set to 10 to 20 rpm, and the high speed defoaming is performed under vacuum for 40 to 60 minutes, and the stirring speed of the planetarium mixer is 1 to 1. Adjust to 5rpm and proceed to low speed defoaming under vacuum for 10 to 20 minutes. When bubbles are present in the polymer matrix, the thermal conductivity is reduced by bubbles, which can be prevented by the defoaming.

3) Forming of thermal conductive pad

The thermally conductive pads are molded into the slurry in which the graphene is dispersed, and methods for molding may include extrusion molding, press molding, and comma coating molding, and other methods. It is made by the choice of those skilled in the art within the range that does not lower the physical properties of the polymer used for the production and the properties of the thermal conductive pad, and thus the scope of the present invention is not limited.

As the molding method, a case in which the coater method is applied will be described in detail. For example, a heat conductive pad may be manufactured by attaching a press to the planetary mixer, discharging the slurry, casting the slurry, and curing the slurry. After forming the thermal conductive pad, the embossed release film may be further laminated to prevent contamination of the pad and damage to the pad.

According to the present invention, since the graphene can be directly dispersed, it is possible to uniformly disperse the graphene in the polymer matrix, thereby introducing a thermally conductive pad having improved thermal conductivity.

In addition, according to the present invention can be expected to effect the workability and physical properties of the product in the manufacture of the thermal conductive pad by the selection of the polymer solution used in the production of the graphene dispersion medium and slurry.

In addition, according to the present invention can be expected to further improve the thermal conductivity of the thermal conductive pad by the mixed use and dispersion of the thermal conductive powder.

1 is a photograph showing the state of the graphene dispersed in the silicon solution by Example 1 (a) and Comparative Example 1 (b).
FIG. 2 is an electron micrograph of the slurry prepared in Example 3, wherein graphene, a large thermal conductive powder, and a small thermal conductive powder are dispersed in a polymer matrix (silicon).

Hereinafter, the present invention will be described in detail with reference to examples and drawings, but the present invention is not limited to the following examples and drawings.

Example  1 and 2. Graphene  Preparation of Dispersion

As a binder, the polymer was mixed at a ratio of 87 wt% of silicon polymer (TS-5100A, Tong Yang Silicon, Korea), 10 wt% of graphene, and 3 wt% of Tween-80 to a thickness of 2 U using a 3-roll mill. After setting and repeatedly stirring for 1 hour to prepare a graphene dispersion [Example 1]. The graphene dispersion degree of the graphene dispersion was shown in FIG. 1, and it can be seen that the graphene was uniformly dispersed as shown in FIG.

An acrylic polymer (JK-320, Jinkwang Chemical, Korea) was used as a binder instead of the silicone polymer, and a graphene dispersion was prepared under the same conditions [Example 2].

Comparative example  One.

A graphene dispersion was prepared in the same manner as in Example 1, but was stirred at 200 rpm for 2 hours using a planetary mixer as a dispersion means. The graphene dispersion degree of the graphene dispersion was confirmed in FIG. 1, and it can be seen that the dispersion of graphene was not uniformly performed as shown in FIG. 1B.

Example  3. Graphene  Distributed Slurry  Manufacturing_Silicone Polymer

1 wt% of pigment was added to 79 wt% of the silicone polymer solution (TS-5100A, Tong Yang Silicon, Korea), and the pigment was dispersed for 60 minutes at a speed of 2,000 rpm using a high speed stirrer to change the color of the thermal pad to gray. 20 wt% of the graphene dispersion prepared in Example 1 was added thereto, followed by stirring for 10 minutes at 2,000 rpm at room temperature using a planetary mixer [first slurry].

5 wt% of a Pt catalyst was added to 10 wt% of a silicon-based polymer solution (TS-5100B, Tong Yang Silicon, Korea), 5 wt% of the first slurry was added, and then 2,000 rpm at room temperature using a planetary mixer. It stirred for 10 minutes.

Spherical silica having an average diameter of 10 μm and amorphous silica having an average diameter of 20 μm were mixed with a thermally conductive powder in a 1: 1 weight ratio to prepare 80 wt%.

Into the planetarium mixer, one-third of the thermally conductive powder having a diameter of 10 to 20 μm of the thermally conductive powder was added to the total weight of the thermally conductive powder, and stirred at 2,000 rpm for 30 minutes at 2,000 rpm, and 2,000 rpm with the vacuum turned off. It stirred for 10 minutes. Among the thermally conductive powders, a thermally conductive powder having a diameter of 20 to 30 μm was added to the next 1/3 based on the total weight of the thermally conductive powder, and stirred at 2,000 rpm for 30 minutes at 76 cmHg vacuum atmosphere, and stirred at 2,000 rpm for 10 minutes while the vacuum was turned off. In addition, 1/3 of the remaining thermal conductive powder was added, and again, the mixture was stirred in a 76 cmHg vacuum atmosphere for 30 minutes at 2,000 rpm, and stirred at 2,000 rpm for 10 minutes while the vacuum was turned off to prepare a second slurry.

In the slurry obtained by stirring as described above, graphene and thermally conductive powder particles are uniformly filled in a polymer matrix (silicone-based polymer), which can be confirmed by FIG. 2.

Example  4. Graphene  Distributed Slurry  _ Acrylic Polymer

A slurry was prepared in the same manner as in Example 3, except that an acrylic polymer (JK-320, Jinkwang Chemical, Korea) was used as a polymer.

Example  5. Defoaming  And Of thermal pad  Molding

The slurries prepared in Examples 3 and 4 were subjected to a high speed defoaming in a vacuum state for 15 minutes at a stirring speed of the planetary mixer at 50 rpm, and low speed defoaming in a vacuum state at a stirring speed of 3 rpm for 15 minutes.

The slurry prepared in Example 3 (using a silicone-based polymer) was degassed and the thermal conductive pad was molded in the following manner.

That is, the reactor of the planetarium mixer was mounted on a ram press, and the slurry prepared inside the mixer was discharged by hydraulic pressure of 20 psi on average, and loaded on a comma coater head.

The thickness of the molded body was adjusted through a gap control device of the comma coater, and the slurry was cast on a PET release film fluorinated to the comma coater. The slurry cast on the PET release film is thermally cured by passing through an air dry chamber, wherein the dry chamber includes five drying sections, four heating sections, and a heating section (130 to 175 ° C.). It consists of one cooling section, and the cast slurry passes through this chamber, and the heating and drying process is repeated, followed by final cooling and molding.

The thermal conductive pad formed in the final section was further laminated with embossed release film to prevent contamination and damage to the pads on the pads.

Experimental Example  One. Graphene  Dispersibility Check

The degree of dispersion of the graphene can be confirmed by an electron microscope, and the results are shown in FIG. 2.

As shown in Figure 2, it can be seen that the graphene is uniformly dispersed between the polymer matrix and the thermally conductive powder.

Experimental Example  2. Of thermal pad  Check thermal conductivity

Prepared in the same manner as in Example 3, except that the thermal conductive pad prepared in the same manner as in Example 5 with a slurry that does not use graphene, and prepared by Example 5 by defoaming the slurry prepared in Example 3 When the graphene-dispersed thermal conductive pad is measured by a method of ASTM D5470 using a thermal conductivity apparatus (manufacturer: Netzsch, model name: Netzsch COM-88), the conventional thermal conductive pad is 1.5 W / The mk value came out, and the graphene-dispersed thermally conductive pads showed 3.2 W / mk value.

As a result of the above, according to the present invention, it is possible to prepare a slurry in which graphene is uniformly dispersed, and it can be confirmed that the thermally conductive pads of the present invention prepared using the same have excellent remarkable thermal conductivity.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

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Claims (10)

1) preparing a graphene dispersion prepared by mixing 1 to 15 wt% of graphene and 3 to 6 wt% of surfactant with 79 to 93 wt% of a dispersion medium selected from a liquid silicone binder or a liquid acrylic binder and dispersing it using a roll mill. ,
2) a first slurry manufacturing step of mixing 5 to 50 wt% of the graphene dispersion after high-speed stirring by adding 45 to 90 wt% of a silicone or acrylic polymer solution and 1 to 5 wt% of a pigment,
3) preparing a second slurry of mixing 1 to 5 wt% of a platinum (Pt) catalyst, 5 to 30 wt% of the first slurry, and 60 to 80 wt% of the thermally conductive powder in a silicon-based or acrylic polymer solution, and
4) defoaming and molding the second slurry to prepare a thermal conductive pad
Method for producing a thermally conductive pad comprising a.
The method according to claim 1,
The surfactant is a method of producing a thermally conductive pad, characterized in that the nonionic surfactant.
The method according to claim 1,
The thermally conductive powder is a thermal conductive pad manufacturing method, characterized in that the thermal conductivity in the range 20 to 40W / mK.
The method according to claim 1,
The thermally conductive powder is a method for producing a thermal conductive pad, characterized in that the diameter of 4 to 40 ㎛ range.
The method according to claim 1,
The thermally conductive powder is a spherical powder having a diameter of 5 to 40 ㎛ range or amorphous powder having a diameter of 4 to 20 ㎛ range.
The method according to claim 1,
The thermal conductive powder is a method of producing a thermal conductive pad, characterized in that the silica or ceramic.
The method according to claim 1,
The thermally conductive powder is a method for producing a thermally conductive pad, characterized in that the spherical powder and the amorphous powder in a 1: 1 to 0.5 to 1.5 weight ratio range.
The method according to claim 1,
The thermally conductive powder is added from the small size of the particles, the first of the total amount of the thermally conductive powder is added by stirring first, then the third is added by stirring and then the other 1/3 is added to the divided input method of stirring Method of producing a thermal conductive pad, characterized in that administered.
The method according to claim 1,
Stirring of the second slurry is to maintain the temperature of the second slurry at 20 to 30 ℃ and stirring the thermal conductive powder is divided into 10 to 20rpm, stirring time is 10 to 20 minutes for each divided injection, each stirring time 5 to 10 minutes is a method for producing a thermal conductive pad, characterized in that the interior of the mixer is adjusted to a vacuum state of 76cmHg beforehand stirring.
A thermal conductive pad prepared by any one of claims 1 to 9, wherein graphene is uniformly dispersed.

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