KR20230085746A - Electromagnetic wave absorber having electromagnetic wave absorption properties in high frequency band and method for preparing the same - Google Patents

Abstract

An electromagnetic wave absorber containing 77 to 83% by weight of barium ferrite as a metal filler and 17 to 23% by weight of acrylic rubber as a curable binder polymer and having a thickness of 0.7 to 0.9mm, a manufacturing method thereof, and the electromagnetic wave absorber Disclosed is an electromagnetic wave absorbing film or electronic device. The electromagnetic wave absorber has excellent return loss characteristics in the high frequency region of the Ka band of 20 to 30 GHz, and in particular, the return loss characteristics may be maximized at a specific frequency of about 28 GHz. Accordingly, it can exhibit excellent absorption characteristics and has excellent reliability, so it can be used as a material for 5G. In addition, it has excellent coating properties and is easy to manufacture.

Description

Electromagnetic wave absorber having electromagnetic wave absorption properties in high frequency band and method for preparing the same}

The present specification discloses an electromagnetic wave absorber having electromagnetic wave absorption characteristics in a high frequency band, a manufacturing method thereof, an electromagnetic wave absorber film including the electromagnetic wave absorber, and an electronic device.

High-speed communication technology/parts are applied in various fields, and since autonomous driving is only possible when 5G or higher communication technology is applied, the importance of high-speed communication technology/parts is even greater. 5G-compatible electric components for self-driving cars tend to use electromagnetic waves in frequencies above 20 GHz and broadband bands at the level of 1 GHz.

Accordingly, self-driving cars that require high-speed communication must have no interference or delay in communication due to electromagnetic noise in their own system, communication between vehicles, and between base stations for real-time control and malfunction prevention. Therefore, it is essential to develop an electromagnetic wave absorber.

Existing electromagnetic wave absorbers use a carbon-based material such as sendusst or graphite as a filler and use a silicon-based polymer resin as a binder.

However, it is difficult to exhibit absorption characteristics in a high frequency band with such a filler. In addition, silicon-based binders have a problem in that they are difficult to use for communication parts or electrical parts for which reliability must be secured because there is a risk of siloxane discharge.

International Patent Application Publication No. 2019-176612

In exemplary implementations of the present invention, on one side, return loss characteristics are excellent in the high frequency region of the Ka band of 20 to 30 GHz, and in particular, return loss characteristics are maximized at a specific frequency of 28 GHZ, and concerns about siloxane discharge, etc. To provide an electromagnetic wave absorber having electromagnetic wave absorption characteristics in a high frequency band, having excellent reliability and excellent coating properties, a method for manufacturing the same, an electromagnetic wave absorbing film including the electromagnetic wave absorber, and an electronic device.

In exemplary embodiments of the present invention, the electromagnetic wave absorber includes 77 to 83% by weight of barium ferrite as a metal filler and 17 to 23% by weight of acrylic rubber as a curable binder polymer, and the thickness of the electromagnetic wave absorber is 0.7 to 0.9%. An electromagnetic wave absorber having a thickness of mm is provided.

In exemplary embodiments of the present invention, the above-described electromagnetic wave absorber manufacturing method includes preparing a slurry by mixing 77 to 83 wt% of barium ferrite as a metal filler and 17 to 23 wt% of acrylic rubber as a curable polymer binder; and coating the slurry on a substrate and curing it.

Exemplary embodiments of the present invention also provide an electromagnetic wave absorbing film or electronic device including the above-described electromagnetic wave absorber.

The electromagnetic wave absorber of exemplary embodiments of the present invention has excellent return loss characteristics in a high frequency region of the Ka band of 20 to 30 GHz, and in particular, the return loss characteristics may be maximized at a specific frequency of about 28 GHz. Accordingly, it can exhibit excellent absorption characteristics and has excellent reliability, so it can be used as a material for 5G. In addition, it has excellent coating properties and is easy to manufacture.

1 is a graph in which reflection loss according to frequency according to Example 1 of the present invention is measured according to the thickness of an electromagnetic wave absorbing sheet.
2 is a graph of reflection loss according to frequency according to the thickness of the electromagnetic wave absorbing sheet according to Example 2 of the present invention.
3 is a graph in which reflection loss according to frequency of Comparative Example 1 of the present invention is measured according to the thickness of the electromagnetic wave absorbing sheet.
4A and 4B are graphs obtained by measuring the reflection loss according to the frequency of Comparative Example 3 according to the thickness of the electromagnetic wave absorbing sheet.
5 is a schematic diagram showing a network analyzer for measuring return loss of embodiments and comparative examples of the present invention.
6 is a reference diagram showing a surface roughness Ra calculation process.

Hereinafter, exemplary implementations of the present invention will be described in more detail.

The embodiments of the present invention disclosed in the text are illustrated for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. . The present invention can have various changes and can have various forms, the embodiments are not intended to limit the present invention to a specific form disclosed, and all changes, equivalents or substitutes included in the spirit and technical scope of the present invention It will be understood to include.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "comprise" or "having" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features The possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not excluded.

In the present specification, reliability refers to a characteristic capable of maintaining an appearance or product characteristics even when an electromagnetic wave absorber is exposed to an external environment. In detail, when the electromagnetic wave absorber is mounted on a component and exposed to the external environment for a long time, it can be said that reliability is secured only when there is no change in the appearance or product characteristics due to conditions such as temperature, humidity, and light. In the case of a silicon binder, when exposed to an external environment for a long time, siloxane is discharged and reacts with other functional groups to contaminate the surface of the absorber or affect the driving of other parts, and thus reliability is poor.

In this specification, the reflection loss is related to the absorption performance of the incident electromagnetic wave, and the unit uses dB (decibels). A generated electromagnetic wave signal, that is, an incident wave, and an electromagnetic wave that is partially reflected after being absorbed by the electromagnetic wave absorber, that is, a reflected wave, are measured, and the degree of absorption of the electromagnetic wave is expressed as a reflection loss.

In this specification, coatability can be evaluated by the surface roughness of the coating film after coating. The lower the surface roughness, the better the coating property. When the finely dispersed filler is large, the surface roughness increases, and the finely dispersed filler may cause poor appearance due to surface roughness of the absorber.

Description of Exemplary Embodiments

In exemplary embodiments of the present invention, among various ferrite materials, barium ferrite (BaFe ₁₂ O ₁₉ ), which has excellent properties at high frequencies, is used in a specific content, and acrylic rubber is used as a curable polymer binder to secure long-term stability and reliability. An electromagnetic wave absorber having a specific thickness using a specific content is provided. The electromagnetic wave absorber has excellent return loss characteristics in the high frequency region of the Ka band, and in particular, the return loss characteristics may be maximized at a specific frequency of about 28GHz (28±0.2GHz).

Since 28 GHz is a frequency for high-speed communication such as 5G, and its utilization is high, the absorber of exemplary embodiments of the present invention in which the return loss characteristic is maximized at about 28 GHz as described above can be used as a material for 5G.

In detail, 28 GHz is a frequency used for 5G communication, and the maximum reflection loss at this frequency means that the electromagnetic wave absorption performance of the electromagnetic wave absorber is maximized. That is, from the standpoint of a product that selectively uses the 28 GHz frequency, since the absorption capacity is maximized at this frequency, the generated electromagnetic noise can be removed to a high level, which has the advantage of preventing electromagnetic delay caused by electromagnetic waves. Therefore, the higher the return loss is, the more advantageous it is because there are fewer elements that interfere with signal delay. The absorbers of exemplary implementations of the present invention have the maximum return loss at about 28 GHz, so they are useful as materials for 5G.

Specifically, exemplary embodiments of the present invention provide an electromagnetic wave absorber including 77 to 83 wt% of barium ferrite as a metal filler and 17 to 23 wt% of acrylic rubber as a curable polymer binder.

Here, it is preferable that the electromagnetic wave absorber has a thickness of 0.7 to 0.9 mm.

The reflection loss of the electromagnetic wave absorber varies depending on the thickness as well as the powder content. That is, even if the powder content is the same, the frequency region in which the reflection loss is maximized is different depending on the thickness. As can be seen in the embodiments described later, in the exemplary implementations of the present invention, the return loss is maximized at 28 GHz only in the thickness range of 0.7 to 0.9 mm. Referring to FIGS. 1 to 3, reflection loss is low at other thicknesses outside the corresponding thickness range, resulting in degraded performance of the absorber. That is, it can be said to be frequency selective according to the thickness and composition.

In non-limiting examples, the thickness is 0.7 mm or more, 0.71 mm or more, 0.72 mm or more, 0.73 mm or more, 0.74 mm or more, 0.75 mm or more, 0.76 mm or more, 0.77 mm or more, 0.78 mm or more, 0.79 mm or more, 0.8 mm or more, 0.81 mm or more, 0.82 mm or more, 0.83 mm or more, 0.84 mm or more, 0.85 mm or more, 0.86 mm or more, 0.87 mm or more, 0.88 mm or more, or 0.89 mm or more; 0.88mm or less, 0.87mm or less, 0.86mm or less, 0.85mm or less, 0.84mm or less, 0.83mm or less, 0.82mm or less, 0.81mm or less, 0.80mm or less, 0.79mm or less, 0.78mm or less, 0.77mm or less, 0.76mm or less, 0.75 mm or less, 0.74 mm or less, 0.73 mm or less, 0.72 mm or less, 0.71 mm or less, preferably 0.75 mm to 0.85 mm, more preferably 0.8 mm.

In an exemplary embodiment, the barium ferrite may have an average particle diameter D50 of 5 to 40 μm or 15 to 25 μm. Here D50 can be measured using a laser particle size analyzer. If the D50 is out of 5 to 40㎛, it affects the coatability and may cause coating defects such as no coating. That is, as shown in Examples and Comparative Examples to be described later, reflection loss varies depending on the thickness and filler filling amount, and does not have a significant effect on the powder size, but the powder size affects the coating thickness, and when considering the coating thickness, the above-mentioned D50 Range is preferred.

In non-limiting examples, the D50 may be greater than or equal to 5 μm, greater than or equal to 10 μm, greater than or equal to 15 μm, greater than or equal to 20 μm, greater than or equal to 25 μm, greater than or equal to 30 μm, or greater than or equal to 35 μm, or less than or equal to 40 μm, less than or equal to 35 μm, or less than or equal to 30 μm. , 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

In one exemplary embodiment, acrylic rubber, which is the curable binder polymer, is used.

In the electromagnetic wave absorber, since the binder does not affect the reflection loss, there is no difference in the reflection loss value depending on the binder, but the binder is a factor that affects the mixing amount of the filler and workability.

In an exemplary embodiment of the present invention, by using acrylic rubber, there is an advantage of easy handling of the product due to excellent flexibility during sheet manufacturing, and, as described above, there is no problem of siloxane discharge and reliability is excellent. In addition, in the case of silicone rubber, due to the self-release characteristics of silicone, the coating film is easily peeled off when additional coating or application is applied to the surface, making it impossible to perform a post-process. The acrylic rubber binder may be cured using isocyanate.

In an exemplary embodiment, the return loss of the electromagnetic wave absorber may exhibit a value of 20 db or more in a frequency bandwidth of about 2.5 GHz from 27 to 29.5 GHz.

In an exemplary embodiment, the reflection loss of the electromagnetic wave absorber may be a maximum value, for example, 40 db at about 28 GHz (28±0.2 GHz).

On the other hand, in exemplary embodiments of the present invention, as a method for manufacturing an electromagnetic wave absorber, as described above, preparing a slurry by mixing barium ferrite as a metal filler and acrylic rubber as a curable binder polymer; It provides a method for manufacturing an electromagnetic wave absorber comprising curing the curable polymer resin of the slurry.

In an exemplary embodiment, the slurry may be prepared by mixing an isocyanate-based curing agent resin for curing acrylic rubber.

In addition, in one exemplary embodiment, the prepared slurry may form a coating film on a substrate by a coating method (comma coating, slot die, etc. as described later). The coated film is cured by thermal compression to become an electromagnetic wave absorber.

In an exemplary embodiment, the viscosity of the slurry in which the barium ferrite and acrylic rubber are mixed may be 1,000 cp.s to 10,000 cp.s. If the viscosity is lower than the above range, the flowability is good and the thickness of the coating film is not formed during high-thickness coating, so there may be a problem in adjusting the coating thickness. In addition, when the viscosity is higher than the above viscosity range, productivity may be lowered because it is difficult to coat the coating film in a roll-to-roll coating method and the work must be performed in units of sheets.

In non-limiting examples, the viscosity is 1,000 cp.s or more, 2,000 cp.s or more, 3,000 cp.s or more, 4,000 cp.s or more, 5,000 cp.s or more, 6,000 cp.s or more, 7,000 cp.s or more , 8,000 cp.s or more, or 9,000 cp.s or more, or 10,000 cp.s or less, 9,000 cp.s or less, 8,000 cp.s or less, 7,000 cp.s or less, 6,000 cp.s or less, 5,000 cp.s or less , 4,000 cp.s or less, 3,000 cp.s or less, or 2,000 cp.s or less.

In an exemplary embodiment, the slurry is coated on a substrate such as a release film and then cured at a temperature of, for example, 130 to 170 ° C, or 140 to 160 ° C, or 150 ° C and 30 minutes or more, or 35 minutes or more, or 40 minutes or more. The curing reaction can be induced by leaving it for more than 45 minutes, or more than 50 minutes, or more than 55 minutes, or more than 60 minutes. For production efficiency and stability, preferably 1 hour is appropriate, and up to 1 hour 30 minutes can be cured up to If the curing time is less than 30 minutes, the uncured ratio of the resin is high, and if it exceeds 1 hour and 30 minutes, damage to the product due to heat in addition to curing may occur.

After such thermal curing, the release film is removed to obtain an electromagnetic wave absorber.

Meanwhile, exemplary embodiments of the present invention also provide an electromagnetic wave absorbing film or electronic device including the above-described electromagnetic wave absorber.

The coating process may be applied by a method commonly used in the technical field of the present invention. For example, the coating is performed by coating the above-described slurry on a substrate using one or more coating processes such as gravure coating, micro gravure coating, spin coating, screen printing, comma coating, and die coating, It may be cured, and preferably comma coating or slot die coating is used.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as being limited by these examples.

[Production and test examples]

Electromagnetic wave absorbers (electromagnetic wave absorbing sheets) of Examples and Comparative Examples were prepared with compositions shown in Table 1 below, and coating properties and reflection loss according to frequency were measured.

manufacturing method

1. After mixing acrylic rubber and barium ferrite, mixed dispersion was performed for 30 minutes using a planetary mixer. After confirming that the barium ferrite was completely mixed, isocyanate curing was added and additional mixed dispersion was performed for 30 minutes to prepare a slurry.

2. The slurry formed a coating film on the release surface of the release film by comma coating method and dried with hot air.

3. The coated product was subjected to thermal compression at 150° C. for 1 hour for curing to form an electromagnetic wave absorber.

Coatability evaluation

Coatability was determined primarily through visual inspection to determine the defect of the coating film, and secondarily, the Ra value was confirmed through surface roughness measurement.

로 정의될 수 있다. 즉, 거칠기 곡선의 함수 y=f(x)에서 평균선 방향으로 기준길이 L을 설정하고, 평균선 방향을 X축으로 하고, 높이 방향을 Y축으로 하였을 때의 적분 값을 L로 나눈 것으로 표현될 수 있다(도 6 참조).For reference, Ra (center line surface roughness)

can be defined as That is, in the function y = f (x) of the roughness curve, when the reference length L is set in the direction of the average line, the direction of the average line is the X axis, and the height direction is the Y axis, the integral value divided by L can be expressed. Yes (see FIG. 6).

Return loss evaluation

To evaluate the return loss, a network analyzer measurement was performed. A reflector was installed on the opposite side of the cable connected to port 1 of the measuring device as shown in FIG. 5 to measure the reflection coefficient (S11) and graph the return loss.

로 정의 한다. Z는 전압 의미하며 Z_L은 Load 전압, Z_O는 초기 전압이다. 즉 분모는 반사전압, 분자는 입력 전압을 나타내며, 임피던스 차에 의해 발행하는 반사량을 입력전압 대 반사 전압의 비로 계산한 지표가 반사계수이다. 장비에서 입력전압과 반사 전압을 측정하여 반사계수 S11으로 표시한다.For reference, RL(Reflection Loss)(dB)=

defined as Z means voltage, Z _L is the load voltage, and Z _O is the initial voltage. That is, the denominator represents the reflected voltage, the numerator represents the input voltage, and the index calculated by calculating the amount of reflection generated by the impedance difference as the ratio of the input voltage to the reflected voltage is the reflection coefficient. The equipment measures the input voltage and the reflected voltage and displays it as the reflection coefficient S11.

barium ferrite
(Ba Ferrite) (wt%) acrylic rubber
(Acrylic rubber) (wt%) isocyanate
(Isocyanates)
(wt%) coating property Example 1 77 20.7 2.3 Good Example 2 83 15.3 1.7 Good Comparative Example 1 76 21.6 2.4 Good Comparative Example 2 84 14.4 1.6 error

Here, the coating property is judged to be defective when external defects such as uncoating and liquid lines are confirmed primarily by visual judgment, and secondarily, when the Ra value is 100 μm or more through surface roughness measurement, the coating is judged to be defective.

1 to 3 are graphs obtained by measuring the return loss according to the frequency of Example 1 (FIG. 1), Example 2 (FIG. 2) and Comparative Example 1 (FIG. 3) of the present invention for each thickness of each electromagnetic wave absorbing sheet.

The composition of Examples 1 and 2 is a condition for ensuring the characteristics of the absorber. When checking the return loss for the thickness of 0.2-2mm, it was confirmed that the return loss value appeared as high as 40db at 28GHz when the thickness was 0.8mm.

In addition, it was confirmed that a return loss of more than 20 dB was measured in a wide band of 2.5 GHz from about 27 to 29.5 GHz. For reference, in FIGS. 1 and 2, the Y-axis is the return loss value (RL), and if you check the X-axis frequency where this value is greater than -20db, you can see that it has a range of 27 to 29.5GHz, that is, a width of 2.5GHz. there is. (-) in the Y-axis value means loss.

Since this means that it can be used in a wide frequency range, it can be determined that the utilization is high.

On the other hand, in the composition of less than 77% of the filler content as in Comparative Example 1, it was measured that the reflection loss was formed low without exceeding 20dB from 0.2 to 2mm.

In addition, Comparative Example 2 was a composition in which the filler content exceeded 83%, and it was impossible to prepare a specimen due to poor coating property due to the high filler content.

Meanwhile, in Comparative Example 3, Carbonyl Iron Powder (CIP), which is widely used as a high-frequency absorber, was additionally used instead of barium ferrite in Example 2. As in Example 2, the powder content was 83wt%, and the binder used was acrylic rubber.

4A and 4B are graphs in which reflection loss according to frequency of Comparative Example 3 is measured for each thickness of the electromagnetic wave absorbing sheet.

As shown in FIGS. 4A and 4B , a return loss value of 20 dB or more was not confirmed in the same frequency domain as the embodiments.

The embodiments of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can improve and change the technical idea of the present invention in various forms. Therefore, these improvements and modifications will fall within the protection scope of the present invention as long as they are obvious to those skilled in the art.

Claims (8)

As an electromagnetic wave absorber,
It contains 77 to 83% by weight of barium ferrite as a metal filler and 17 to 23% by weight of acrylic rubber as a curable binder polymer,
The electromagnetic wave absorber, characterized in that the thickness of the electromagnetic wave absorber is 0.7 ~ 0.9mm.
According to claim 1,
An electromagnetic wave absorber, characterized in that the average particle diameter D50 of the barium ferrite is 5 to 40 μm.
According to claim 1,
The electromagnetic wave absorber, characterized in that the return loss of the electromagnetic wave absorber exhibits a value of 20 db or more at 27 to 29.5 GHz.
According to claim 1,
The electromagnetic wave absorber, characterized in that the reflection loss of the electromagnetic wave absorber exhibits a maximum value at 28 ± 0.2 GHz.
A method for manufacturing the electromagnetic wave absorber according to any one of claims 1 to 4,
preparing a slurry by mixing barium ferrite as a metal filler and acrylic rubber as a curable binder polymer; and
A method of manufacturing an electromagnetic wave absorber comprising the step of curing the curable binder of the slurry.
According to claim 5,
The method of manufacturing an electromagnetic wave absorber, characterized in that the viscosity of the slurry in which the barium ferrite and acrylic rubber are mixed is 1,000 cp.s to 10,000 cp.s.
An electromagnetic wave absorbing film comprising the electromagnetic wave absorber according to any one of claims 1 to 4.
An electronic device comprising the electromagnetic wave absorber according to any one of claims 1 to 4.

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