KR20210103884A - Composite material with enhanced electromagnetic wave shielding and heat dissipation characteristic including controlled agglomeration hexaferrite particle cluster - Google Patents

Abstract

Provided is a composite material with an improved electromagnetic wave shielding and heat dissipation property comprising a hexaferrite particle cluster with a controlled agglomeration. The composite material having the electromagnetic wave shielding and heat dissipation property comprises: a hexaferrite particle cluster wherein a plate-shaped hexaferrite particle is aggregated; and a polymer wherein the cluster is dispersed. Therefore, the present invention is capable of improving thermal conductivity.

Description

COMPOSITE MATERIAL WITH ENHANCED ELECTROMAGNETIC WAVE SHIELDING AND HEAT DISSIPATION CHARACTERISTIC INCLUDING CONTROLLED AGGLOMERATION HEXAFERRITE PARTICLE CLUSTER}

The present invention relates to a composite material with improved electromagnetic wave shielding and heat dissipation properties, including a hexaferrite particle cluster with controlled agglomeration. Specifically, the present invention relates to a method for manufacturing a hexaferrite particle cluster by controlling the degree of aggregation of hexaferrite particles, a method for manufacturing a composite material with improved electromagnetic wave shielding and heat dissipation properties using the same, and electromagnetic wave shielding and heat dissipation manufactured through the method It relates to a composite material with improved properties.

Ferrite refers to a type of iron having a body centered cubic (bcc) structure. In general, it is used to mean an iron oxide-based ceramic material containing alloying elements or impurities.

Ferrite has magnetism and is used in magnetic tapes, memory devices, magnets, and permanent magnets. In addition, ferrite has transmission loss characteristics with respect to electromagnetic waves. Accordingly, research on electromagnetic wave shielding articles using ferrite materials is being conducted.

On the other hand, as electronic devices such as sensor devices, display devices, portable terminal devices, and information processing devices have recently been improved in performance and miniaturization, electronic components therein are also being highly integrated. Accordingly, there is a need to develop a heat dissipation material or component capable of effectively removing heat generated from electronic components.

However, even if the ferrite material has electromagnetic wave shielding properties for a specific frequency, there is a problem in that it is difficult to be used as a heat dissipation material because the thermal conductivity and the like are not high.

Korean Patent Application Laid-Open No. 10-2019-0005585 (2019.01.16.), "Method for manufacturing composite heat dissipation sheet"

As described above, while ferrite material has electromagnetic wave shielding properties for a specific frequency, there is a limit to improving thermal conductivity. In particular, when ferrite particles are used and dispersed in a polymer to constitute an electromagnetic wave shielding and/or heat dissipation coating material, thermal barrier resistance (thermal barrier resistance, TBR) is present. Accordingly, there is a problem in that the heat transfer properties of the ferrite-polymer composite material are further deteriorated.

Patent Document 1 discloses an invention related to a composite heat dissipation sheet having an electromagnetic wave blocking function and a method for manufacturing the same. Patent Document 1 is an invention for the purpose of providing a composite heat dissipation sheet that effectively blocks electromagnetic waves, suppresses noise generation, and has high thermal conductivity.

Patent Document 1 discloses a configuration in which a graphite sheet is used as a heat dissipation sheet for this purpose, and a ferrite material is integrated with the sheet or coated on one or more surfaces of the graphite sheet. That is, it is based on a graphite material used as a conventional heat dissipation material, and it is a gist to add a ferrite material having electromagnetic wave shielding properties.

However, Patent Document 1 has a difference in that it only uses a graphite material and a ferrite material having separate characteristics, and does not relate to increasing the thermal conductivity of the ferrite material. In addition, according to Patent Document 1, inevitably, there are limitations such as a complicated configuration and a thick sheet.

As a result of continuous research and development on hexaferrite, the inventors of the present invention have completed the present invention by focusing on improving the heat dissipation characteristics while maintaining the electromagnetic wave shielding characteristics by controlling the degree of aggregation of the hexaferrite particles.

That is, an object of the embodiments of the present invention is to provide a method for controlling the degree of aggregation of hexaferrite particles.

In addition, an object of the embodiments of the present invention is to provide a method of manufacturing a composite material having improved electromagnetic wave shielding and heat dissipation properties by controlling the degree of aggregation of hexaferrite particles.

An object of the embodiments of the present invention is to provide a composite material with improved electromagnetic wave shielding and heat dissipation properties by controlling the degree of aggregation of hexaferrite particles.

Objects of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A composite material having electromagnetic wave shielding and heat dissipation characteristics according to an embodiment of the present invention includes a hexaferrite particle cluster in which plate-shaped hexaferrite particles are aggregated; and a polymer in which the clusters are dispersed.

The average particle size of the cluster may be 1 μm or more and 500 μm or less.

The thermal conductivity of the composite material may be 1.0 W/mK or more.

The dielectric constant (@1.0 GHz) of the composite material may be 4.0 or more, and the magnetic permeability (@1.0 GHz) of the composite material may be 1.6 or more.

The hexaferrite may include at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), and radium (Ra). However, other elements may be included alone or together, and are not limited to the aforementioned Group 2 elements.

The hexaferrite may further include one or more of cobalt (Co), zinc (Zn), and manganese (Mn). However, it is not limited to the mentioned metal elements.

According to an embodiment of the present invention, a method for manufacturing a composite material including a hexaferrite particle cluster in which agglomeration is controlled through calcination temperature control includes calcining ferrite particles; and molten-salt sintering the calcined ferrite particles. However, the calcination temperature and the sintering temperature may be determined according to the particle composition, and the temperature is not limited to the above.

The ferrite particles may include a single hexaferrite of any one of Z-type, M-type, and W-type or a combination thereof.

The ferrite particles may be Z-type, and the calcination temperature may be 1,000° C. or higher.

The hexaferrite may include at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), and radium (Ra). However, other elements may be included alone or together, and are not limited to the aforementioned Group 2 elements.

In the molten salt sintering step, the salt may include sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium sulfate (Na ₂ SO ₄ ), or a combination thereof. However, the type of salt used in the sintering step is not limited to the above-mentioned type.

The sintering may be performed at a temperature of 1,100° C. or more for 6 hours or more, and the cooling rate may be 5 K/min or less. However, the calcination process and the sintering process may be controlled according to the type of ferrite to be synthesized.

Mixing and curing the sintered ferrite particles with a polymer may further include mixing and curing the sintered ferrite particles to 1 wt% or more of the total mixture. However, it is not limited to the above weight ratio.

The average particle size of the ferrite particle cluster may be 1 μm or more and 500 μm or less, and the ferrite particles of the ferrite particle cluster may be in direct contact with each other to form a bond.

The thermal conductivity of the composite material may be 1.0 W/mK or more.

The method may further include mixing the sintered ferrite particles with at least one of metal particles, carbon particles, ceramic particles, and magnetic particles.

The method for controlling the agglomeration size of ferrite particles according to an embodiment of the present invention includes a calcination step performed at a predetermined temperature and a molten salt sintering step performed at a predetermined temperature to control the agglomeration of ferrite particles. .

The details of other embodiments are included in the detailed description.

According to embodiments of the present invention, it is possible to control the degree of aggregation of ferrite particles by controlling the temperature of the calcination process and the temperature of the sintering process, thereby improving the thermal conductivity of the composite material including the ferrite particles. can do it

In addition, according to embodiments of the present invention, it is possible to provide a composite material excellent in both electromagnetic wave shielding properties and heat dissipation properties.

Effects according to the embodiments of the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.

1 is a microscope image of a composite material according to Example 1 of the present invention.
2 is a microscope image of a composite material according to Example 2 of the present invention.
3 is a microscope image of a composite material according to Example 3 of the present invention.
4 is a microscope image of a composite material according to Comparative Example 1 of the present invention.
5 is a microscope image of a composite material according to Comparative Example 2 of the present invention.
6 is a microscope image of a composite material according to Comparative Example 3 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings and the contents described in the accompanying drawings, but the present invention is not limited or limited by the embodiments.

The terminology used herein is for the purpose of describing the embodiments and is not intended to limit the present invention. As used herein, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, "comprises" and/or "comprising" refers to the presence of one or more other components, steps, operations and/or elements mentioned. or addition is not excluded.

As used herein, “embodiment”, “example”, “aspect”, “exemplary”, etc. are to be construed as advantageous in which any aspect or design described is preferred or advantageous over other aspects or designs. it is not doing

Also, the term 'or' means 'inclusive or' rather than 'exclusive or'. That is, unless stated otherwise or clear from context, the expression 'x employs a or b' means any one of natural inclusive permutations.

Also, as used herein and in the claims, the singular expression "a" or "an" generally means "one or more" unless stated otherwise or clear from the context that it relates to the singular form. should be interpreted as

The terms used in the description below are selected as general and universal in the related technical field, but there may be other terms depending on the development and/or change of technology, customs, preferences of technicians, and the like. Therefore, the terms used in the description below should not be understood as limiting the technical idea, but should be understood as exemplary terms for describing the embodiments.

In addition, in a specific case, there is a term arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the corresponding description. Therefore, the terms used in the description below should be understood based on the meaning of the term and the content throughout the specification, not the simple name of the term.

Meanwhile, terms such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly defined in particular.

In this specification, the term 'electromagnetic wave shielding' is used to include reflection, absorption, and internal multiple reflection of electromagnetic waves.

Meanwhile, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. And, the terms (terminology) used in this specification are terms used to properly express the embodiment of the present invention, which may vary according to the intention of the user or operator, or customs in the field to which the present invention belongs. Accordingly, definitions of these terms should be made based on the content throughout this specification.

Hereinafter, the present invention will be described in detail.

A method of manufacturing a composite material according to an embodiment of the present invention includes preparing ferrite particles, calcining the ferrite particles at a predetermined temperature, and sintering the calcined ferrite particles with molten salt. In addition, the method for producing a composite material according to the present invention may further include mixing the ferrite particle cluster with the polymer and/or mixing the ferrite particle cluster with at least one of metal particles, carbon particles, ceramic particles and magnetic particles. can

Hereinafter, each step will be described.

[Step to prepare ferrite particles]

As used herein, ferrite means iron oxide having a body-centered cubic structure. Among them, hexaferrite may mean ferrite containing barium (Ba) or strontium (Sr) as a main raw material. Ferrite can be prepared through a known method.

In an exemplary embodiment, the ferrite is one, or two selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr) and radium (Ra), or It may contain more elements. That is, the ferrite may include at least one element selected from the group consisting of beryllium, magnesium, calcium, barium, strontium, and radium. Preferably, the ferrite according to an embodiment may include barium and strontium. In this case, the ferrite may not include beryllium, magnesium, calcium, and radium, but the present invention is not limited thereto.

In addition, the ferrite may further include one or more elements of cobalt (Co), zinc (Zn), and manganese (Mn). Preferably, the ferrite according to an embodiment may further include a cobalt element. In this case, the stoichiometric ratio of barium and cobalt or strontium and cobalt may be about 1.5:2.0, respectively, but the present invention is not limited thereto.

In some embodiments, the ferrite according to the present invention is a single hexaferrite of any one of Z-type, M-type, and W-type, or a combination of hexaferrite. may include. In addition, the ferrite particles may have a plate-like structure.

After preparing the ferrite particles, milling, pulverizing, and sieving may be further performed.

[Step of calcining ferrite particles]

This step may be a step of controlling the degree of aggregation of the ferrite particles. That is, the inventors of the present invention have completed the present invention by confirming that the aggregation of ferrite particles can be controlled by changing the calcination heating conditions performed before molten salt sintering, which will be described later.

As used herein, calcination refers to a heat treatment in which a target material is dehydrated, decomposed, separated, or volatilized by applying heat.

In an exemplary embodiment, the calcination temperature is at least about 1,000°C, or at least about 1010°C, or at least about 1,020°C, or at least about 1,030°C, or at least about 1,040°C, or at least about 1,050°C, or at least about 1,060°C, or at least about 1,080°C, or at least about 1,100°C, or at least about 1,120°C, or at least about 1,140°C, or at least about 1,160°C, or at least about 1,180°C. When the calcination temperature is lower than the above range, aggregation of the ferrite particles may not be sufficiently performed. That is, the calcination temperature may affect the size of the hexaferrite particles to be produced or the size of the hexaferrite particle cluster.

The upper limit of the calcination temperature is not particularly limited, as long as the reaction does not occur in the composition of the hexaferrite particles. For example, the upper limit of the calcination temperature may be about 2,000°C, or about 1,900°C, or about 1,800°C, or about 1,700°C, or about 1,600°C, or about 1,500°C, or about 1,400°C, or about 1,300°C. .

In some embodiments, it is desirable to perform the calcination process for a sufficient time to allow the desired operation to be sufficiently achieved. For example, the calcination time may be performed for a period of about 3 hours or more and 10 hours or less, or about 4 hours or more and 9 hours or less, or about 5 hours or more and 8 hours or less.

[Step of molten-salt sintering of ferrite particles]

This step may be a step in which the slenderness ratio of the ferrite particles is controlled and the aggregation of the ferrite particles is performed in earnest. That is, the inventors of the present invention have completed the present invention by confirming that a difference occurs in the result of the molten salt sintering process depending on the calcination heating temperature, etc. performed before the molten salt sintering process.

The step of performing molten salt sintering may include mixing and sintering the calcined ferrite particles with salt. The sintering may be performed in air.

In the step of mixing the calcined ferrite particles with the salt, the salt used for sintering the molten salt may include a sodium salt. For example, the salt may include sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium sulfate (Na ₂ SO ₄ ), or a combination thereof.

In addition, the ferrite particles and the salt may be mixed in a weight ratio of about 0.8:1.2 to 1.2:0.8, or about 0.9:1.1 to 1.1:0.9, or about 1.0:1.0.

In addition, in the sintering step, the sintering temperature may be about 1,000° C. or more, or about 1,050° C. or more, or about 1,100° C. or more, or about 1,150° C. or more. If the sintering temperature is lower than the above range, complete sintering may not be achieved. The upper limit of the sintering temperature is not particularly limited as long as it is equal to or lower than the melting point of the ferrite particles, and may be appropriately adjusted according to the composition of the ferrite particles. For example, the upper limit of the sintering temperature may be about 1,350°C, or about 1,300°C, or about 1,250°C, or about 1,200°C.

In some embodiments, the heating rate (heating rate) and cooling rate of the furnace in the sintering process is about 5K/min or less, or about 4K/min or less, or about 3K/min or less. min or less. In particular, if the cooling rate is too fast, complete sintering may not be achieved and the growth of particles or particle clusters may be inhibited, so that the cleaning ratio may not be good.

[Step of mixing ferrite particle cluster and polymer]

According to the present invention, the hexaferrite particle cluster with controlled agglomeration degree can be dispersed in a polymer matrix to form a hexaferrite-polymer composite material. The polymer is not particularly limited as long as it is a material in which hexaferrite is easily dispersed and easily applied, but may be, for example, a siloxane-based polymer. Specific examples of the siloxane-based polymer include polydimethylsiloxane (PDMS), but the present invention is not limited thereto.

The mixing weight ratio between the sintered ferrite particles (or clusters thereof) and the polymer is about 0.7:1.3 to 1.3:0.7, or about 0.8:1.2 to 1.2:0.8, or about 0.9:1.1 to 1.1:0.9, or about 1.0:1.0 days. can However, the present invention is not limited thereto, and the mixing ratio between the sintered ferrite particles and the polymer may be changed in consideration of intended thermal conductivity. For example, the ferrite particles may be mixed to contain about 1 wt% or more, or about 3 wt% or more, or about 5 wt% or more, based on the total mixture of the ferrite particles and the polymer.

The hexaferrite-polymer mixture prepared according to this embodiment may be applied and cured to form a film or sheet-shaped hexaferrite-polymer composite material. However, it goes without saying that the present invention is not limited thereto.

[Step of adding functional particles]

Examples of the functional particles include metal particles, carbon particles, ceramic particles and magnetic particles. The mixing of the functional particles and the ferrite particles may be performed before the polymer solution mixing step, simultaneously with the polymer solution mixing step, or after the polymer solution mixing step.

The functional particles may further improve the electromagnetic wave shielding rate and/or heat dissipation characteristics of the hexaferrite-polymer composite material, or may reinforce strength and rigidity. As the functional particles for this purpose, a known material may be used, and a detailed description thereof will be omitted.

[Hexaferrite-Polymer Composite Material]

The hexaferrite-polymer composite material prepared through the above-described process may include agglomerated hexaferrite particle clusters. The average particle size of the particle clusters may be about 1 μm or more, or about 5 μm or more, or about 10 μm or more, or about 50 μm or more, or about 100 μm or more, or about 150 μm or more, or about 200 μm or more. As the average particle size of the particle clusters increases, the heat transfer efficiency may increase and the function as a parallel material may be improved. That is, as plate-shaped hexaferrite particles having a size of 1 μm to 20 μm are aggregated to form clusters having a particle size of at least 10 μm, a significant level of thermal conductivity improvement can be achieved.

Although the present invention is not limited to any theory, the hexaferrite particles may be in direct contact or in direct contact with each other to increase heat transfer efficiency between particles and improve heat dissipation properties as a whole of the composite material. For example, the inventors of the present invention have confirmed that the thermal conductivity of the composite material according to an embodiment is about 1.0 W/mK or more.

In addition, the average particle size of the particle clusters may be about 1,000 μm or less, or about 900 μm or less, or about 800 μm or less, or about 500 μm or less, or about 100 μm or less, or about 50 μm or less. If the average particle size of the particle clusters is too large, dispersibility with the polymer matrix may be deteriorated, which may be undesirable.

In addition, since ferrite, especially hexaferrite, can exhibit the unique electromagnetic wave shielding properties, it can function as a composite material with excellent heat dissipation properties and electromagnetic wave shielding properties at the same time.

The composite material according to an embodiment has a dielectric constant of about 2.5 or more, or about 3.0 or more, or about 3.5 or more, or about 3.6 or more, or about 3.7 or more, or about 3.8 or more, or about 3.9 or more, or about 4.0 under 1.0 GHz. or greater, or about 4.1 or greater, or about 4.2 or greater, or about 4.3 or greater, or about 4.4 or greater, or about 4.5 or greater.

In addition, the composite material according to an embodiment may have excellent magnetic permeability characteristics of about 1.2 or more, or about 1.4 or more, or about 1.6 or more, or about 1.8 or more, or about 2.0 or more under 1.0 GHz.

Hereinafter, the present invention will be described in more detail with reference to Examples and Preparation Examples of the present invention.

[Example 1: Preparation of agglomerated ferrite cluster 1]

Example 1-1: Preparation of ferrite particles (powder)

Barium carbonate (BaCO ₃ ) (99.98%), strontium carbonate (SrCO ₃ ) (99.9%), calcium carbonate (CaCO ₃ ) (99% up), cobalt oxide (Co ₃ O ₄ ) (99.7%), and iron oxide ( Fe ₂ O ₃ ) (99.9%) powder was prepared. And from these solid state reaction (solid state reaction) to prepare a particulate hexaferrite. The composition of ferrite may be expressed as _{Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _{1.5 Z).}

Example 1-2: Preparation of calcined ferrite particles

And the stoichiometric mixture of these powders was ball-milled. Specifically, the prepared hexaferrite particles were placed in a polypropylene container and milled for 24 hours using a zirconia ball together with ethanol to prepare a slurry.

The dried slurry was then crushed and sieved, and then calcined at 1,180°C.

Example 1-3: Preparation of Molten Salt Sintered Ferrite Particles

The calcined powder was mixed with sodium chloride (NaCl) in a weight ratio of 1:1 and compressed into a disk. Then, the compressed disk sample was sintered in air at 1,100° C. for 6 hours.

In the sintering process, the heating rate and cooling rate were maintained at 4K/min. And the temperature of the furnace (furnace) was measured and calibrated using a processing temperature control ring (PTCR).

Then, the sintered disk sample was pulverized, and the mixture was washed with distilled water to obtain hexaferrite powder from which salts were removed.

Example 1-4: Preparation of Polymer Composite Composite Material

A hexaferrite powder obtained through molten salt sintering was prepared, and this powder was dispersed in a polymer matrix. Polydimethylsiloxane (PDMS) was used as the polymer. As the polydimethylsiloxane, Sylgard 184 manufactured by DOW Corning was used.

Specifically, hexaferrite powder and polydimethylsiloxane were mixed and mixed for 3 minutes using a defoaming mixer (planetary mixer). The stirring speed was 1,300 rpm. In addition, the mixing weight ratio of the hexaferrite powder and the polydimethylsiloxane polymer was 1:1.

Then, a mixture of hexaferrite powder and polydimethylsiloxane was poured onto a Teflon film and cured by hot pressing at 130° C. for 30 minutes to prepare a hexaferrite-polymer composite material.

[Example 2: Preparation of agglomerated ferrite clusters 2]

A hexaferrite-polymer composite material was prepared in the same manner as in Example 1, except that the sintering temperature of ferrite was changed to 1,150° C. in Example 1-3.

Specifically, _{ferrite represented by Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _1.5 Z) was prepared. The stoichiometric mixture of this powder was then ball milled, the slurry was ground and sieved, and then calcined at 1,180°C.

Then, the calcined powder was mixed with sodium chloride in a weight ratio of 1:1, compressed into a disk, and the disk sample was sintered at 1,150° C. in air for 6 hours. The sintering conditions were the same as in Example 1-3. Thereafter, the sintered disk sample was pulverized and the mixture was washed with distilled water to obtain hexaferrite powder from which the salt was removed.

Then, the hexaferrite powder was mixed and stirred with polydimethylsiloxane in a weight ratio of 1:1, and cured on a Teflon film to prepare a hexaferrite-polymer composite material. Curing conditions were the same as in Examples 1-4.

[Example 3: Preparation of agglomerated ferrite clusters 3]

A hexaferrite-polymer composite material was prepared in the same manner as in Example 1, except that the sintering temperature of ferrite in Example 1-3 was changed to 1,200°C.

Specifically, _{ferrite represented by Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _1.5 Z) was prepared. The stoichiometric mixture of this powder was then ball milled, the slurry was ground and sieved, and then calcined at 1,180°C.

Then, the calcined powder was mixed with sodium chloride in a weight ratio of 1:1, compressed into a disk, and the disk sample was sintered at 1,200° C. in air for 6 hours. Thereafter, the sintered disk sample was pulverized and the mixture was washed with distilled water to obtain hexaferrite powder from which the salt was removed.

Then, the hexaferrite powder was mixed and stirred with polydimethylsiloxane in a weight ratio of 1:1, and cured on a Teflon film to prepare a hexaferrite-polymer composite material. Curing conditions were the same as in Examples 1-4.

[Comparative Example 1]

A hexaferrite-polymer composite material was prepared in the same manner as in Example 1, except that the calcination temperature of the ferrite particles was changed to 1,040° C. in Example 1-2.

Specifically, _{ferrite represented by Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _1.5 Z) was prepared. The stoichiometric mixture of this powder was then ball milled, the slurry was ground and sieved, and then calcined at 1,040°C.

Then, the calcined powder was mixed with sodium chloride in a weight ratio of 1:1, compressed into a disk, and the disk sample was sintered at 1,100° C. in air for 6 hours. The sintering conditions were the same as in Example 1-3. Thereafter, the sintered disk sample was pulverized and the mixture was washed with distilled water to obtain hexaferrite powder from which the salt was removed.

Then, the hexaferrite powder was mixed and stirred with polydimethylsiloxane in a weight ratio of 1:1, and cured on a Teflon film to prepare a hexaferrite-polymer composite material. Curing conditions were the same as in Examples 1-4.

[Comparative Example 2]

A hexaferrite-polymer composite material was prepared in the same manner as in Comparative Example 1, except that the sintering temperature of the ferrite in Comparative Example 1 was changed to 1,150°C.

Specifically, _{ferrite represented by Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _1.5 Z) was prepared. The stoichiometric mixture of this powder was then ball milled, the slurry was ground and sieved, and then calcined at 1,040°C.

Then, the calcined powder was mixed with sodium chloride in a weight ratio of 1:1, and after compression into a disk, the disk sample was sintered at 1,150° C. in air for 6 hours. The sintering conditions were the same as those of Comparative Example 1. Thereafter, the sintered disk sample was pulverized and the mixture was washed with distilled water to obtain hexaferrite powder from which the salt was removed.

Then, the hexaferrite powder was mixed and stirred with polydimethylsiloxane in a weight ratio of 1:1, and cured on a Teflon film to prepare a hexaferrite-polymer composite material. Curing conditions were the same as in Comparative Example 1.

[Comparative Example 3]

A hexaferrite-polymer composite material was prepared in the same manner as in Comparative Example 1, except that the sintering temperature of the ferrite in Comparative Example 1 was changed to 1,200°C.

Specifically, _{ferrite represented by Ba 1.5} Sr _1.5 Co ₂ Fe ₂₄ O ₄₁ (Ba _1.5 Sr _1.5 Z) was prepared. The stoichiometric mixture of this powder was then ball milled, the slurry was ground and sieved, and then calcined at 1,040°C.

Then, the calcined powder was mixed with sodium chloride in a weight ratio of 1:1, compressed into a disk, and the disk sample was sintered at 1,200° C. in air for 6 hours. The sintering conditions were the same as those of Comparative Example 1. Thereafter, the sintered disk sample was pulverized and the mixture was washed with distilled water to obtain hexaferrite powder from which the salt was removed.

Then, the hexaferrite powder was mixed and stirred with polydimethylsiloxane in a weight ratio of 1:1, and cured on a Teflon film to prepare a hexaferrite-polymer composite material. Curing conditions were the same as in Comparative Example 1.

The calcination temperature and the sintering temperature used in Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1 below.

calcination temperature (℃) Sintering temperature (℃) Example 1 1,180 1,100 Example 2 1,180 1,150 Example 3 1,180 1,200 Comparative Example 1 1,040 1,100 Comparative Example 2 1,040 1,150 Comparative Example 3 1,040 1,200

[Experimental Example 1: Observation of agglomeration of particles]

The hexaferrite-polymer composite materials prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were photographed under a microscope, and the results are shown in FIGS. 1 to 6 , respectively.

1 to 6 , it was confirmed that the hexaferrite particles were aggregated in the hexaferrite-polymer composite material according to Examples 1 to 3, whereas the hexaferrite-polymer composite according to Comparative Examples 1 to 3 It can be seen that the hexaferrite particles are not substantially aggregated in the material. That is, the hexaferrite calcined at a relatively high temperature as in the Examples forms clusters by controlling agglomeration between particles, whereas in the hexaferrite calcined at a relatively low temperature as in Comparative Examples, it can be seen that agglomeration is hardly achieved. have.

The average particle size of the hexaferrite particle cluster according to Example 1 was about 100 μm, and the average particle size of the hexaferrite particle according to Comparative Example 1 was about 20 μm. In addition, it can be seen that the Examples exhibit an excellent slenderness ratio compared to Comparative Examples.

That is, it can be seen that the aggregation of hexaferrite particles can be controlled and clusters can be formed by changing the calcination temperature condition.

[Experimental Example 2: Measurement of Thermal Conductivity]

The thermal conductivity of the hexaferrite-polymer composite material prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 was measured. And the results are shown in Table 2 below.

The thermal conductivity (λ) of the composite material was calculated using the following equation after measuring the thermal diffusivity (α) at room temperature (25°C) using the Laser-Flash method (LFA-447, Netzch, Germany).

λ = α × Cp × ρ

where, α (mm ² /s), Cp (J/gK) and ρ (g/cm ³ ) mean thermal diffusivity, specific heat capacity, and density, respectively. The specific heat of the sample was measured at room temperature (25° C.) using DSC (DSC-200F3, Netzch, Germany). The shape of the specimen was realized through cutting/processing with a diameter of 25.4 mm and a thickness of 1 mm. The density was calculated from the volume obtained in the above shape and the measured mass.

[Experimental Example 3: Measurement of dielectric constant]

The dielectric constants of the hexaferrite-polymer composite materials prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 were measured. And the results are shown in Table 2 below.

The dielectric constant of the composite material was measured at 1.0 GHz using an impedance analyzer E4991A (Keysight) and a dielectric material test fixture 16453A (Keysight). The composite geometry was machined to 17.5 mm and 1.0 mm in diameter and thickness, respectively.

[Experimental Example 4: Measurement of Permeability]

The permeability of the hexaferrite-polymer composite material prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 was measured. And the results are shown in Table 2 below.

The permeability of the composite material was measured at 1 GHz using an impedance analyzer E4991A (Keysight) and a magnetic material test fixture 16454A (Keysight). The composite geometry was machined to 10.0 and 17.5 mm in inner and outer diameters and 1 mm in thickness, respectively.

Thermal Conductivity (W/mK) permittivity (@1.0GHz) Permeability (@1.0GHz) Example 1 1.0 4.6 1.8 Example 2 1.1 4.0 1.6 Example 3 1.2 4.2 1.7 Comparative Example 1 0.6 4.8 1.9 Comparative Example 2 0.5 4.1 1.6 Comparative Example 3 0.7 4.5 1.5

Referring to Table 2, it can be seen that the hexaferrite-polymer composite material according to the Examples exhibits a dielectric constant at the same level as that of the hexaferrite-polymer composite material according to the Comparative Examples.

On the other hand, it can be seen that the hexaferrite-polymer composite material according to the Examples has thermal conductivity as high as about 1.6 times higher than that of the hexaferrite-polymer composite material according to Comparative Examples. This may be because, in the case of the embodiment, hexaferrite particle clusters are formed to exhibit a relatively large particle size, and thus heat transfer efficiency between the hexaferrite particles and the hexaferrite particles is increased. However, the present invention is not limited to any theory.

That is, it can be seen that the thermal conductivity can be greatly improved without causing a substantial decrease in the dielectric constant and permeability characteristics according to the particle size of the hexaferrite dispersed in the polymer of the composite material.

On the other hand, the embodiments of the present invention disclosed in the present specification and drawings are merely presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims (19)

a hexaferrite particle cluster in which plate-shaped hexaferrite particles are aggregated; and
A composite material having electromagnetic wave shielding and heat dissipation properties, comprising a polymer in which the clusters are dispersed.
According to claim 1,
The average particle size of the cluster is a composite material of 1 μm or more and 500 μm or less.
According to claim 1,
The composite material has a thermal conductivity of 1.0 W/mK or more.
According to claim 1,
The dielectric constant (@1.0 GHz) of the composite material is 4.0 or more,
The composite material has a magnetic permeability (@1.0GHz) of 1.6 or more.
According to claim 1,
The hexaferrite is a composite material comprising at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), and radium (Ra).
6. The method of claim 5,
The hexaferrite is a composite material further comprising one or more elements of cobalt (Co), zinc (Zn) and manganese (Mn).
According to claim 1,
The ferrite particles are Z-type (Z-type), M-type (M-type) and W-type (W-type) composed of hexaferrite particles of a single composition or two or more compositions, electromagnetic wave shielding and / or heat dissipation Composite materials with properties.
According to claim 1,
The ferrite particles are Z-type (Z-type), manufactured through a calcination process of 1,000 ℃ or more, a composite material having electromagnetic wave shielding and / or heat dissipation properties.
According to claim 1,
The composite material is prepared through molten salt sintering, and the salt is produced through a salt containing sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium sulfate (Na ₂ SO ₄ ) or a combination thereof. Composite material with electromagnetic wave shielding and/or heat dissipation properties.
According to claim 1,
Manufactured through a sintering process carried out at a temperature of 1,100 ° C or higher for 6 hours or more,
In the sintering process, the cooling rate is 5K/min or less, a composite material having electromagnetic wave shielding and/or heat dissipation properties.
According to claim 1,
The composite material is formed by mixing and curing sintered ferrite particles and the polymer, wherein the sintered ferrite particles are mixed so that 1 wt% or more of the total mixture has electromagnetic wave shielding and / or heat dissipation properties.
According to claim 1,
A composite material having electromagnetic wave shielding and/or heat dissipation properties further comprising at least one of metal particles, carbon particles, ceramic particles, and magnetic particles.
calcining the ferrite precursor particles; and
Comprising the step of molten-salt sintering (molten-salt sintering) the calcined ferrite particles,
A method for manufacturing a composite material including a hexaferrite particle cluster whose agglomeration is controlled by controlling the calcination temperature and the sintering temperature.
14. The method of claim 13,
The ferrite particles are Z-type (Z-type), M-type (M-type), and W-type (W-type) of any one single hexaferrite or a method for producing a combination hexaferrite cluster thereof.
14. The method of claim 13,
The ferrite particles are Z-type (Z-type), the calcination temperature is 1,000 ℃ or more hexaferrite cluster manufacturing method.
16. The method of claim 15,
The hexaferrite is a method of manufacturing a composite material including at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), and radium (Ra) .
17. The method of claim 16,
In the molten salt sintering step, the salt is sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium sulfate (Na ₂ SO ₄ ), or a method of manufacturing a composite material comprising a combination thereof.
16. The method of claim 15,
The sintering is performed at a temperature of 1,100° C. or higher for 6 hours or more,
A method for manufacturing a composite material with a cooling rate of 5 K/min or less.
14. The method of claim 13,
The average particle size of the ferrite particle cluster is 1 μm or more and 500 μm or less,
The ferrite particles of the ferrite particle cluster are in direct contact with each other to form a bonding, a method of manufacturing a composite material.

Images