KR101911331B1 - Manufacturing method of injection-molded heat-radiating material with improved emissivity - Google Patents

Abstract

The present invention relates to a method for manufacturing an injection molded heat radiating material having improved emissivity. More specifically, the present invention relates to a method for manufacturing an injection molded heat radiating material having improved emissivity, simply and easily injection molding a heat radiating material such as a heat radiating board, used in various industrial fields, by mixing polymer resins, carbon nanotubes (CNT), and aluminum powder to enable the heatradiating material to have emissivity higher than aluminum even without performing aluminum die casting with respect to the heat radiating material. Accordingly, functional characteristics can be increased in all the aspects such as molding capacity, manufacturing costs, heat radiating characteristics, and weight reduction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing an injection-molded heat-

The present invention relates to a method of manufacturing an injection molded heat-radiating material with improved emissivity, and more particularly, to a method of manufacturing an injection-molded heat-radiating material having improved emissivity and, more particularly, A carbon nanotube, and an aluminum powder. The present invention also relates to a method of manufacturing an injection-molded heat-radiating material having improved emissivity in all aspects, such as moldability, manufacturing cost, heat dissipation characteristics, .

Heat dissipation materials with heat dissipation properties are used in various industries including heat sinks used in LED lighting fixtures.

These heat-dissipating materials are traditionally manufactured by die-casting aluminum, which limits the manufacturing cost as well as the formability.

In particular, electric vehicles, autonomous vehicles, electronic devices, wearable devices, robotic devices, and the like, which are rapidly advancing in the world, require high performance, light weight, and high integration.

However, the heat-dissipating material manufactured by the conventional aluminum die-casting method does not meet this global change trend, and it is difficult to further improve the heat dissipation performance above all, and the performance degradation of the heat dissipation material due to high heat and radio wave interference The life span is deteriorated, and further, the human body is also adversely affected, and there is also a limit in weight reduction.

As a part of this, efforts have been made to improve this, and there have been examples of using a CNT master batch by dispersing a certain amount of CNTs based on various polymer resins, but this is an intermediate material rather than a raw material as a final material, It is impossible to completely replace aluminum die-casted heat dissipation material because it can not be formed at a level that can be molded by a method other than die casting while using them as basic raw materials.

Korean Patent Registration No. 10-1240662 (Feb. 28, 2013) 'Heat Sink Using Carbon Nanotubes and Its Manufacturing Method' Korea Patent Registration No. 10-1483758 (Feb. 12, 2015) 'LED light fixture with excellent heat dissipation characteristics including carbon nanotubes'

The present invention has been made in view of the above-mentioned problems in the prior art, and it is an object of the present invention to provide a heat dissipating material such as a heat sink, which is used in various industrial fields, The present invention provides a method of manufacturing an injection-molded heat-radiating material with improved emissivity in all aspects, such as moldability, manufacturing cost, heat dissipation characteristics, and light weight, by simple and easy injection molding using a mixture of Carbon NanoTube and aluminum powder. There is a main purpose in.

The present invention provides a method of manufacturing a heat-radiating material capable of performing injection molding with improved emissivity, comprising the steps of: A first step of uniformly dispersing MWCNT (Multi Walled CNT) in a polymer resin; A second step of extruding the polymer resin in which the MWCNT is dispersed into resin pellets; A third step in which the resin pellets are placed in a freeze-crusher, filled with nitrogen gas, rapidly cooled, and then pulverized; A fourth step of drying the pulverized resin pellet powder to control the water content; A fifth step of mixing graphite and metal or nonmetal powder into the dried resin pellet powder, mixing the mixture with an electromagnetic mixer, and extruding the pellet into a material pellet as a pellet for heat radiation material; And a sixth step of dehydrating and drying the material pellets, placing the material pellets in a wrapping paper made of an aluminum foil, and vacuum-packing the pellets. The method of manufacturing an injection molded heat radiating material with improved emissivity.

According to the present invention, a heat dissipation material such as a heat sink used in various industrial fields can be easily and easily injected through a mixture of a polymer resin, carbon nanotube (CNT) and aluminum powder so as to have a higher emissivity than aluminum tie casting It is possible to obtain an effect of improving the functional characteristics in all respects such as moldability, manufacturing cost, heat dissipation characteristics, and light weight.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a method of manufacturing an injection molded heat radiating material with improved emissivity according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Before describing the present invention, the following specific structural or functional descriptions are merely illustrative for the purpose of describing an embodiment according to the concept of the present invention, and embodiments according to the concept of the present invention may be embodied in various forms, And should not be construed as limited to the embodiments described herein.

In addition, since the embodiments according to the concept of the present invention can make various changes and have various forms, specific embodiments are illustrated in the drawings and described in detail herein. It should be understood, however, that it is not intended to limit the embodiments according to the concepts of the present invention to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.

The present invention can never be expected to remarkably improve the emissivity characteristic as well as the interfacial delamination of the heat-radiating coating layer at the level of a simple heat-radiating coating layer as disclosed in the prior art. In addition, the heat-radiating coating layer is coated on the outer surface The molding composition itself is manufactured, but it is constituted so as to be injection-molded so that the heat-radiating property is remarkably improved as compared with the existing aluminum die casting product even though it is an injection molded product .

That is, the present invention can easily mold the molding composition by pelletizing and molding the molding composition so as to maximize the mechanical properties of the polymer resin and the high thermal conductivity and electrical conductivity of CNT and aluminum, Provides a heat-dissipating material that improves productivity, has excellent price competitiveness, significantly improves heat dissipation characteristics, and is lightweight.

In particular, currently, the conversion rate of LED lighting equipment, which converts incandescent and fluorescent lamps into LED lighting, remains at 22%, but the explosive demand for heat dissipation materials is expected to be 60% until 2022, Development of a composite material with high heat dissipation is urgently required.

Such heat dissipation materials are not limited to light fixtures, but as described above, they are required in the industry as a whole, such as electric automobiles, autonomous vehicles, electronic devices, wearable devices, robotic devices, computer ECUs, electric vehicle inverters, Repeater inverters, and so on.

To this end, a method for manufacturing an injection molded heat-radiating material with improved emissivity according to the present invention includes a first step of uniformly dispersing MWCNT (Multi Walled CNT) in a polymer resin, as shown in FIG. A second step of extruding the polymer resin in which the MWCNT is dispersed into resin pellets; A third step in which the resin pellets are placed in a freeze-crusher, filled with nitrogen gas, rapidly cooled, and then pulverized; A fourth step of drying the pulverized resin pellet powder to control the water content; A fifth step of mixing graphite and metal or nonmetal powder into the dried resin pellet powder, mixing the mixture with an electromagnetic mixer, and extruding the pellet into a material pellet as a pellet for heat radiation material; And a sixth step of dehydrating and drying the material pellets, placing the material pellets in a wrapping paper made of aluminum and then vacuum-packing the pellets.

That is, the present invention provides a heat dissipation material, more precisely a pellet type heat dissipation material, which is a raw material capable of injection molding a product having a heat dissipation property such as a heat dissipation plate.

At this time, in the present invention, CNTs having high thermal conductivity and electrical conductivity are utilized, among which MWCNT is used.

The CNT has a hexagonal honeycomb-shaped graphene sheet with a diameter of several nanometers and is formed into a tubular shape by rounding and has different properties depending on the dried direction and shape.

These CNTs are divided into Sing Walled CNT (SWCNT), Double Walled CNT (DWCNT), Multi Walled CNT (MWCNT) and Nanotube Rope according to the number of outer walls.

Among them, the present invention utilizes MWCNT, which can improve dispersion and cohesion, but is relatively inexpensive.

However, since the CNTs are easily aggregated due to their very low dispersion characteristics, desired characteristics can be obtained by simple addition. Therefore, in order to uniformly disperse the CNTs in a stable state without agglomeration or precipitation when adding CNT, it is necessary to provide simultaneous affinity between the CNTs and the matrix of the composite material.

Examples of the CNT dispersion method include an ultrasonic method, a chemical treatment method, a surfactant treatment method, and a polymer wrapping method.

Here, the ultrasonic method is convenient as a method of uniformly spraying and dispersing the CNT diluting solution with the ultrasonic device, but there are problems such as damage of the nanotube and re-coagulation.

The chemical treatment method is an acid solution treatment method in which surface functional groups are introduced onto the surface by sulfuric acid or nitric acid, but it is not widely used because of cutting of CNT particles and low dispersion stability.

The surfactant treatment method is a method of inducing and dispersing electrostatic repulsion force or Steric repulsion force after CNT surface coating, which can maintain CNT intrinsic characteristics and is good in dispersion stability. However, it has a disadvantage of removing surface surfactant in a subsequent process .

In contrast, the polymer lapping method is suitable for the present invention because CNTs are mixed at the monomer level to produce a composite, and thus the dispersion efficiency is very high and the uniformity can be maintained.

Examples of the polymer resin that can be used in the polymer lapping method include polypropylene (PP), polyamide 6 (PA6), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) PA can also be applied.

At this time, how much MWCNT is dispersed for polymer lapping is very important factor.

This is because the degree of dispersion of the MWCNT changes the thermal conductivity, emissivity and weight.

Accordingly, in order to confirm the most efficient MWCNT dispersion effect of the first step, graphite and metal or non-metal powder, preferably aluminum powder are mixed and made into test pellets as described later, (W / mK), emissivity (%), and weight loss (%) were tested for MWCNT.

That is, the basic composition of the heat-radiating material according to the present invention is composed of 30 wt% of MWCNT-dispersed polymer resin, 10 wt% of graphite, and 60 wt% of metal or nonmetal powder. In this case, This is because it is necessary to clearly distinguish the product from the product by aluminum die casting.

Here, as described in the preferred embodiments of the present invention, there are various kinds of polymer resins. However, nylon 6 is exemplified by polymer resin, and in the case of metal or non-metal, aluminum, copper, nickel, silver, gold, ceramics , Magnesium, tungsten and the like can be exemplified, but aluminum powder will be described as the most preferable example.

In addition, the graphite should have a 200 mesh particle size in order to obtain a light weight and a high emissivity while improving the dispersion effect. In the case of metal or non-metal powder, a 210 mesh particle size should be used. Particularly, So that the heat conduction characteristics and the smooth dispersion effect are obtained.

In the present invention, at least a thermal conductivity of 3 W / mK or more and an emissivity of 0.5% is required in order to have characteristics as a heat-dissipating material. In addition, the object of the present invention is to reduce the weight by 30%.

For this purpose, the most desirable dispersing amount of MWCNT was tested. Nylon 6 was used as the polymer resin, aluminum powder (210 mesh) was used as the metal or nonmetal powder, and the dispersion amount of MWCNT was 3%, 5% %, And the results are shown in Table 1. In this case, the content is a weight ratio, and the final blending ratio of the heat-radiating material according to the present invention, which will be described in the fifth step, will be described first.

division Nylon 6 Aluminum Powder 210 # Graphite Thermal conductivity
(W / mK) Emissivity
(%) Lightweight
(%) Remarks MWCNT3% 30 60 10 2 0.5 30.6 Default MWCNT5% 30 60 10 3.2 0.5 30.6 Goal Value MWCNT10% 30 60 10 8 0.5 30.6 Above target value

(Where "# " means a mesh having particle size)

As shown in Table 1, when 3% dispersion of MWCNT was dispersed in nylon 6, which is a polymer resin, and aluminum powder and graphite were mixed and pelletized with heat-resistant pellets (hereinafter referred to as "material pellets"), the thermal conductivity and emissivity The basic characteristics were shown, and the light weight achieved the target value of 30%.

However, the thermal conduction rate and the emissivity of the present invention are not achieved.

On the other hand, when 5% dispersion of MWCNT in nylon 6, a polymer resin, was mixed with aluminum powder and graphite, the thermal conductivity, emissivity value and light weight were both achieved.

In addition, when 10% dispersion of MWCNT is dispersed in nylon 6, a polymer resin, it is possible to secure a superior thermal conductivity. However, it is practically possible to disperse MWCNT in an amount of 10% or more, It is difficult to commercialize.

Therefore, it was an important experiment to confirm that the target characteristics can be obtained in the 5% dispersion treatment of MWCNT that can be practically realized through the experiment of Table 1 above.

Therefore, in the present invention, MWCNT is dispersed in 5% of the polymer resin, which is the first step of the manufacturing method according to the present invention.

Meanwhile, in the present invention, it was necessary to confirm the results of how the thermal conductivity and emissivity characteristics of the MWCNT are affected by the change of the polymer content and the content of the metal or non-metal powder.

Since the graphite is usually fixed at 10% by weight, the content of the metal or non-metallic powder is changed by changing the content within the range of the minimum value of 30% by weight and the maximum value of 50% by weight which can change the content of the polymer resin The results are shown in Table 2. For reference, the MWCNT dispersion was performed for 5% and 10% of the two. At this time, 3% dispersion was excluded because it did not reach the target value.

division Nylon 6 Aluminum powder
210 # Graphite Thermal conductivity
(W / mK) Emissivity
(%) Remarks MWCNT5% 30 60 10 3.2 0.5 Goal Value MWCNT5% 50 40 10 2.5 0.25 Default MWCNT10% 30 60 10 8 0.5 Above target value MWCNT10% 50 40 10 5 0.25 Above target value

As a result of the experiment, it was confirmed that when the polymer resin, the metal or the non-metal powder and the graphite were mixed at 30 wt%, 60 wt% and 10 wt%, respectively, as shown in Table 2, The ground thermal conductivity and emissivity were all found to be low.

In the present invention, the ratio is determined as a basic mixing ratio.

In addition, in the present invention, a pre-treatment step of further increasing the dispersing power of the MWCNT before the first step and treating the surface for stable occlusion of the MWCNT may be further performed.

The pretreatment step may include a first step of desmearing the surface of the MWCNT with a plasma processor, a second step of preparing a surface modification by spraying a silane mixture on the surface of the plasma-treated MWCNT, And modifying the surface of the MWCNT by irradiating ultraviolet rays onto the MWCNT surface.

In this case, the first step is a process of irradiating the plasma generated in the plasma processor installed on the chamber with the MWCNT by rotating the chamber, rotating the chamber, and irradiating the plasma on the MWCNT surface to proceed the desmear by the radical reaction. This is also one of the reasons for improving the affinity and adhesiveness of the MWCNT with other materials as a surface modification work, thereby facilitating dispersion.

In addition, the second step is a process of applying a silane component before irradiating ultraviolet rays because the silane component reacts with ultraviolet rays and efficiently modifies the surface of MWCNT.

The silane mixture used in this process is a mixture of octadecyltrichlorosilane and aminosilane in a weight ratio of 1: 1.

The third step is to improve the environment friendliness and the adhesion improvement by modifying the surface by using the vacuum ultraviolet ray having a wavelength band of 10-200 nm in order to increase the reactivity with the silane and to increase the modifying effect.

In addition, a fourth process of spraying SnO ₂ on the surface of the MWCNT may be further performed to enhance the wettability of the MWCNT after the third process.

Thus, when the first step is completed, a second step of extruding the polymer resin in which the MWCNT is dispersed into resin pellets is carried out.

The reason for making resin pellets through the second step is to facilitate redissolving power while facilitating frozen pulverization in a subsequent step.

In the present invention, it is most preferable to adopt nylon 6 as a polymer resin. In the case of a nylon single, the abrasion resistance, the heat resistance, the strength and the resin flowability are excellent, so that when the MWCNT is dispersed, the mechanical properties of the polymer are well expressed Because.

In addition, as described later, the extrudability is good, the water content is easily controlled, and the surface state after extrusion is smooth, thereby maintaining the conductivity constant.

In the third step, the resin pellets are placed in a freeze grinder, filled with nitrogen gas, cooled rapidly at -40 to -60 ° C, pulverized at a rate of 25 Hz, and powdered to have a particle size of 200-300 mesh.

The reason why the resin pellets are re-pulverized is that it is possible to formulate the resin pellets in a quantitative manner in the following step 5, but when dispersed MWCNTs are made into resin pellets by re-pulverizing them into fine powders, A completely uniform dispersion effect can be obtained.

The reason why nitrogen gas is used is to obtain thermal stabilization. At the same time, when a polymer resin, especially nylon 6, is pulverized by high-speed rotation to generate powder, a nitrogen gas which can be rapidly cooled must be used. It is stable to pulverize and pulverize in a state of rapid cooling.

Such nitrogen gas has a form of vaporizing and supplying liquid nitrogen through a vaporizer.

Then, a fourth step is performed, wherein the fourth step is to dry the pulverized resin pellets to adjust the water content.

The reason for controlling the water content through the fourth step is that the initial water content of the polymer resin dispersed with MWCNT, especially nylon 6, is about 0.2%. If it is not adjusted to 0.04%, when the polymer resin melts together with water during extrusion The hydrolysis phenomenon occurs and the chains of the polymer are destroyed, so that desired physical properties can not be obtained. Therefore, the control of the water content in the fourth step is very important.

In addition, when the powders of the fine powder state are mixed with the graphite and the aluminum powder, it is possible to perform uniform mixing and thus to produce a high quality injection and heat radiation article.

At this time, the water content adjustment to 0.04% is carried out at 80 ° C for 4-6 hours through a dryer.

For example, Table 3 below shows the water content of various polymer resins depending on initial moisture content, drying temperature, and drying time.

Resin type Initial moisture content (%) Drying temperature (° C) Drying time (h) Target water content (%) ABS 0.2 80 2 to 3 0.04 PC 0.2 120 2 to 3 0.004 PA6 0.2 80 4 to 6 0.04 PET 0.1 120 2 to 4 0.004 PBT 0.1 120 2 to 4 0.004

Referring to Table 3, nylon 6, which can easily obtain the target moisture content at a relatively low temperature of 80 ° C, which does not consume a large amount of energy, is most suitable when considering characteristics, price, and the like as a whole.

Then, the fifth step is performed.

In the fifth step, the components are mixed to form a heat-dissipating material, and the material is extruded and made into a material pellet for a heat-radiating material.

In this case, the extrusion conditions are also important in the fifth step.

First, 30% by weight of the dried resin pellet powder, 60% by weight of aluminum powder and 10% by weight of graphite are mixed in an electronic mixer at a speed of 60 rpm for 10 minutes. The reason why the electronic mixer should be used at such a low speed is to ensure uniform and intimate mixing. Unless it is mixed uniformly, when it is extruded through a twin extruder, a certain pressure and temperature are received through the extruding screw in the twin extruder, This is because the surface condition of the back surface is uneven and thermal conductivity and emissivity characteristics may be hindered.

For this reason, the extrusion pressure should be in the range of 2-5 MPa, and the temperature change in extrusion should be in the range of 240-250 ° C.

Otherwise, the surface may become rough as shown in Table 4 below and the conductivity may become irregular.

Nylon 6CNT powder + Aluminum powder + Graphite Screw pressure Temperature change Extruded surface
condition Function Effect MIX OK Stable at 2-5 Mpa 240 ° C to 250 ° C constant lubricity Conductivity schedule MIX NG 2 ~ 10Mpa unstable 220 ℃ ~ 250 Unstable Rough Irregularity of conductivity

Here, aluminum powder is in a fine state, and when it comes into contact with water or flammable substances, there is a risk of explosion due to its strong oxidizing ability.

Therefore, in order to ensure safety, 1.5 parts by weight of sodium pyrosulfite (NaS ₂ O ₅ ) and 1.0 part by weight of DBA (dibytylaurate) are added to 100 parts by weight of the aluminum powder before the aluminum powder is added so as to ensure safety. Add the additive in a mixed state.

At this time, sodium pyrosulfite inhibits oxidation to prevent explosion, and DBA enhances thermal stability and buffering property to prevent explosion.

The twin extruder (L / D 40, 35.6φ) uses a screw having three or more mixing zones. Therefore, the standard temperature of the twin extruder may be different depending on the kind of the polymer resin, and the extrusion conditions may be changed.

In general, a twin extruder is used for the mixing of diatomaceous earth or for mixing fillers and the like, and a twin screw element is provided therein, which is divided into a feeding zone, a reading zone and a mixing zone, and two mixing zones are combined .

However, in the present invention, at least three mixing zones are combined to stably mix the polymer resin and the metal powder (aluminum powder) to maintain the extrusion temperature and the extrusion pressure constant.

In this case, in order to stabilize and homogenize the extrusion temperature, it is better to inject the nitrogen gas at the time of extrusion with a certain amount of the raw material.

For reference, the extrusion temperature conditions for each type of polymer resin are shown in Table 5 below.

division Feeding zone (℃) Mixing zone (℃) Leading Zone (℃) Dice (℃) PP 180 210 210 220 PA6 200 230 220 230 PET, PBT 200 230 230 240 PA66 210 250 240 250

After the pellet is formed through the above steps, the sixth step is performed.

The sixth step is a step of dehumidifying and drying the material pellets, placing the material pellets in a wrapping paper made of aluminum and then vacuum-packing the pellets.

In this case, the material pellets must be dehumidified before the packaging in the sixth step, because moisture is absorbed during the pavement after extrusion molding to increase the water content.

That is, since the polymer resin absorbs moisture while the heat is cooled after the extrusion, if the water content is high, the characteristics during injection molding may be deteriorated.

Therefore, in the sixth step, it is necessary to carry out dehumidification after wrapping, and the package should also be vacuum packaged, and the inner surface of the wrapping paper should also be made of aluminum.

The dehumidification drying is performed in a chamber having a honeycomb structure in order to increase the dehumidification efficiency because it maximizes the dehumidification efficiency and enables stable dehumidification drying because the sectional area is 5 times larger than that of the small space. %to be.

In addition, the packaging is weighed and packed in vacuum by automatic meter.

In order to confirm the difference in properties when the heat-radiating material manufactured by the manufacturing method according to the present invention was injection-molded into an actual product, a sample was manufactured with the same specifications as those of heat sinks (aluminum die casting) This is shown in Table 6.

Test Items Reference value unit Test result (heat sink) Existing product test result New product test results (present invention) aluminum Emissivity-enhanced
CNT composite material Module Specifications Adhere to Annex A of the Korea Highway Corporation Standard. - fitness fitness Module waterproof and dustproof grade When tested according to KSCIEC 60529, IP66 ㅇ or higher. - Fit (IP66) Fit (IP66) Temperature Test Case Temperature (200H) Above 85 ℃ ℃ 53 60 Light efficiency Must be more than 95ml / W ml / W 131 128 (98%) weight Different by material g / ea 295 205 (30.6%) Emissivity 0.2 or more % 0.2% 0.5%

As shown in Table 6 above, it was confirmed that the heat radiation effect of the present invention was improved by 50% or more compared to the conventional die casting.

Accordingly, the present invention can be summarized as follows by comparing the differences in characteristics and effects between the conventional aluminum die casting method and the heat dissipation method according to the CNT dispersion injection method according to the present invention.

division Advantages Disadvantages Production method Benefit price competitiveness aluminum Excellent heat conduction, excellent strength Low emissivity
Low profitability
Low durability
Design discomfort Die casting Dependence on imports
Can change according to low price CNT composite material Profitability High
Durable
Lightweight
Eco
Excellent heat dissipation performance High initial production cost
Injection molding Can utilize domestic injection technology
Re-exportable
Metal replacement possible
Quality Competitiveness Inventory Low cost and high price

Claims (1)

A method for producing an injection-moldable heat-radiating material having improved emissivity, the method comprising:
A first step of uniformly dispersing MWCNT (Multi Walled CNT) in a polymer resin;
A second step of extruding the polymer resin in which the MWCNT is dispersed into resin pellets;
A third step in which the resin pellets are placed in a freeze-crusher, filled with nitrogen gas, rapidly cooled, and then pulverized;
A fourth step of drying the pulverized resin pellet powder to control the water content;
A fifth step of mixing graphite and metal or nonmetal powder into the dried resin pellet powder, mixing the mixture with an electromagnetic mixer, and extruding the pellet into a material pellet as a pellet for heat radiation material;
And a sixth step of dehydrating and drying the material pellets, and then vacuum packing the pellets in a wrapping paper made of aluminum.

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