KR102575427B1 - Electromagnetic wave absorber and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an electromagnetic wave absorber and a method for manufacturing the same, and more particularly, by forming a composite fiber sheet including conductive carbon fibers and bio nanofibers and impregnating a binder resin therein to improve electromagnetic wave absorption in a high frequency range. It relates to an electromagnetic wave absorber with excellent flexibility and formability at the same time and a manufacturing method thereof.

Description

Electromagnetic wave absorber and its manufacturing method {ELECTROMAGNETIC WAVE ABSORBER AND MANUFACTURING METHOD THEREOF}

The present invention relates to an electromagnetic wave absorber that efficiently absorbs electromagnetic waves in a high frequency band and at the same time is thin and has excellent flexibility and formability, and a manufacturing method thereof.

In consideration of convenience and stability, recently released vehicles are equipped with long- and short-range radar equipment that detects nearby objects through oscillation and reception of electromagnetic waves having a frequency of GHz. These automotive radars have forward collision warning (FCW), lane departure warning (LDW), emergency braking system (AEBS), and adaptive cruise control (ACC) functions. It plays a key role in vehicle safety and driving assistance systems.

However, conventional automotive radars are sensitive to interference from minute electromagnetic waves and easily cause malfunctions. For example, there is a possibility that a malfunction may be caused by a reflected wave caused by an obstacle such as a floor or a manhole cover. In addition, there is a problem in that the radar efficiency is lowered and the life span is shortened due to the reflected wave. In addition, there is a problem in that signal quality is degraded by generating mutual disturbance with other electronic equipment.

In order to solve the electromagnetic wave interference problem, a technique for absorbing electromagnetic waves by an electromagnetic wave absorber has been developed. In the conventional Korean Patent Publication No. 2008-0114148, magnetic powder is coated with a liquid mixed resin containing a binder resin and a solvent, the mixed resin coated magnetic powder is dried, and then an electromagnetic wave absorber is formed using the dried magnetic powder. A method for manufacturing an electromagnetic wave absorber including a forming step is disclosed. However, when the electromagnetic wave absorber is manufactured using magnetic powder in the form of particles as described above, there is a problem in that flexibility is poor and the ability to efficiently absorb electromagnetic waves in a wide frequency range is poor.

Therefore, it is necessary to develop a thin and flexible material that efficiently absorbs electromagnetic waves so as not to interfere with radar signal transmission.

Korean Patent Publication No. 2008-0114148

In order to solve the above problems, an object of the present invention is to provide an electromagnetic wave absorber having improved electromagnetic wave absorptivity by impregnating a binder resin into a composite fiber sheet including conductive carbon fibers and bio nanofibers and then curing the composite fiber sheet.

Another object of the present invention is to provide a method for manufacturing an electromagnetic wave absorber with improved flexibility and moldability due to the composite fiber sheet.

Another object of the present invention is to provide a vehicle including an electromagnetic wave absorber.

The object of the present invention is not limited to the object mentioned above. The objects of the present invention will become more apparent from the following description, and will be realized by the means and combinations described in the claims.

The present invention may include the following configuration in order to achieve the above object.

The electromagnetic wave absorber of the present invention comprises 25 to 35% by weight of conductive carbon fibers; 30 to 35% by weight of bio nanofibers; and 30 to 45% by weight of a binder resin; however, the binder resin may be impregnated into the composite fiber sheet including the conductive carbon fibers and bio nanofibers.

The conductive carbon fibers may be carbon nanotubes, carbon fibers, or mixtures thereof.

The carbon nanotubes may have a three-dimensional spiral shape with a diameter of 5 to 20 nm and a length of 1 to 30 μm.

The carbon nanotube is one type selected from the group consisting of single-walled, double-walled, thin multi-walled, multi-walled, and roped. It may be one or more carbon nanotubes.

The carbon fibers may have an average fiber diameter of 30 to 100 nm and an average fiber length of 30 to 60 μm.

The bio nanofibers may be cellulose, cellulose ether, or a mixture thereof.

The bio nanofibers may have an average fiber diameter of 30 to 100 nm and an average fiber length of 30 to 60 μm.

The binder resin may be an epoxy resin.

On the other hand, the manufacturing method of the electromagnetic wave absorber of the present invention comprises the steps of preparing a composite fiber sheet by mixing conductive carbon fibers and an alcohol-based solvent with an aqueous solution of bio nanofibers; removing water and alcohol-based solvent contained in the composite fiber sheet; impregnating the composite fiber sheet from which the water and the alcohol-based solvent are removed with the binder resin composition; and preparing an electromagnetic wave absorber by curing the impregnated composite fiber sheet.

The alcohol-based solvent may be isopropyl alcohol, ethanol, or a mixture thereof.

The step of preparing the composite fiber sheet may include passing it through a homogenizer rotating at 5000 to 5500 rpm.

In the step of removing the water and the alcohol-based solvent, the composite fiber sheet may be dried at a temperature of 35 to 55 ° C. for 9 to 23 hours.

The binder resin composition may include 35 to 45 wt% of an epoxy resin, 50 to 64.9 wt% of a curing agent, and 0.1 to 5 wt% of an amine-based catalyst.

In the step of manufacturing the electromagnetic wave absorber, it may be cured by heat treatment at a temperature of 110 to 130 °C for 2 to 6 hours.

The electromagnetic wave absorber includes 25 to 35% by weight of conductive carbon fiber; 30 to 35% by weight of bio nanofibers; And 30 to 45% by weight of the binder resin; may include.

In addition, the vehicle of the present invention may include the electromagnetic wave absorber.

The electromagnetic wave absorber according to the present invention forms a composite fiber sheet including conductive carbon fibers and bio nanofibers and impregnates the binder resin therein, thereby improving electromagnetic wave absorption in a high frequency range and having excellent flexibility and formability. there is.

The effects of the present invention are not limited to the effects mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 is a cross-sectional view showing an electromagnetic wave absorber according to the present invention.
2 is a flowchart of a method for manufacturing an electromagnetic wave absorber according to the present invention.

The above objects, other objects, features and advantages of the present invention will be easily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content will be thorough and complete and the spirit of the present invention will be sufficiently conveyed to those skilled in the art.

Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where another part is present in the middle. Conversely, when a part such as a layer, film, region, plate, etc. is said to be "under" another part, this includes not only the case where it is "directly below" the other part, but also the case where another part is in the middle.

Unless otherwise specified, all numbers, values and/or expressions expressing quantities of components, reaction conditions, polymer compositions and formulations used herein refer to the number of factors that such numbers arise, among other things, to obtain such values. Since these are approximations that reflect the various uncertainties of the measurement, they should be understood to be qualified by the term "about" in all cases. Also, when numerical ranges are disclosed herein, such ranges are contiguous and include all values from the minimum value of such range to the maximum value inclusive, unless otherwise indicated. Furthermore, where such ranges refer to integers, all integers from the minimum value to the maximum value inclusive are included unless otherwise indicated.

In this specification, where ranges are stated for a variable, it will be understood that the variable includes all values within the stated range inclusive of the stated endpoints of the range. For example, a range of "5 to 10" includes values of 5, 6, 7, 8, 9, and 10, as well as any subrange of 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like. inclusive, as well as any value between integers that fall within the scope of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5 and 6.5 to 9, and the like. Also, for example, the range of "10% to 30%" includes values such as 10%, 11%, 12%, 13%, etc., and all integers up to and including 30%, as well as values from 10% to 15%, 12% to 12%, etc. It will be understood to include any sub-range, such as 18%, 20% to 30%, and the like, as well as any value between reasonable integers within the scope of the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

In general, electromagnetic wave absorbing materials can effectively attenuate the intensity of electromagnetic waves by absorbing and shielding incident electromagnetic wave energy using conduction, dielectric and magnetic losses and converting it into other energy. In addition, the electromagnetic wave absorbing material may have a different absorption method depending on the frequency band, and an absorber using a conventional magnetic powder has a problem of poor flexibility. In the present invention, in order to solve the problems of existing automotive radars, conductive carbon fiber with excellent electromagnetic wave absorption performance is applied even in the high frequency range of GHz, resulting in malfunction due to reflected waves, radar efficiency and life shortening, and signal quality degradation. Solved. In addition, a composite fiber sheet was formed by mixing bio nanofibers with conductive carbon fibers, and flexibility and moldability were improved by impregnating the binder resin therein.

Hereinafter, the electromagnetic wave absorber and the manufacturing method of the present invention as described above will be described in detail together with FIGS. 1 and 2 .

1 is a cross-sectional view showing an electromagnetic wave absorber according to the present invention. Referring to FIG. 1, an electromagnetic wave absorber 10 having a structure in which conductive carbon fibers 20 and bio nanofibers 30 form a composite fiber sheet and a binder resin 40 is impregnated into the composite fiber sheet is shown.

More specifically, the electromagnetic wave absorber 10 of the present invention includes 25 to 35% by weight of the conductive carbon fiber 20; 30 to 35% by weight of bio nanofibers (30); and 30 to 45% by weight of the binder resin 40; however, the binder resin 40 may be impregnated into the composite fiber sheet including the conductive carbon fibers 20 and the bio nanofibers 30.

The conductive carbon fibers 20 may impart conductivity to the electromagnetic wave absorber 10 to absorb electromagnetic waves and improve rigidity at the same time. In addition, the conductive carbon fiber 20 has a high specific surface area in a fibrous form compared to the conductive material in a particulate form, thereby increasing the electromagnetic wave absorption rate, and being in the form of a fiber, it can impart flexibility to the electromagnetic wave absorber 10 .

Specifically, the conductive carbon fibers 20 may include 25 to 35% by weight based on the total weight of the electromagnetic wave absorber 10 . At this time, if the content is less than 25% by weight, the electromagnetic wave absorption rate may be low, and conversely, if it is more than 35% by weight, there is a disadvantage in that the flexibility of the final product is lowered. The conductive carbon fibers 20 may be carbon nanotubes, carbon fibers, or mixtures thereof. The carbon nanotubes may have a three-dimensional spiral shape with a diameter of 5 to 20 nm and a length of 1 to 30 μm. If the diameter and length are out of the above ranges, mixing uniformity may deteriorate, and thus electromagnetic wave shielding performance may be deteriorated. Preferably, the carbon nanotubes may have a diameter of 6 to 17 nm and a length of 2 to 25 μm, more preferably a diameter of 6 to 13 nm and a length of 2.5 to 20 μm.

In addition, the carbon nanotube is 1 selected from the group consisting of single-walled, double-walled, thin multi-walled, multi-walled, and roped. It may be more than one kind of carbon nanotube.

The carbon fibers may have an average fiber diameter of 30 to 100 nm and an average fiber length of 30 to 60 μm. If the diameter and length of the carbon fibers are out of range, mixing uniformity may deteriorate, thereby deteriorating electromagnetic wave shielding performance.

The bio-nanofibers 30 have excellent bonding strength with the conductive carbon fibers 20 and can serve to impart flexibility to the electromagnetic wave absorber 10 . In addition, the bio-nanofibers 30 have very high tissue uniformity and can effectively absorb electromagnetic waves in a wide frequency range. Specifically, the bio nanofibers 30 may include 30 to 35% by weight based on the total weight of the electromagnetic wave absorber 10 . At this time, if the content is less than 30% by weight, the formability and flexibility of the electromagnetic wave absorber 10 may be reduced, and conversely, if the content is greater than 35% by weight, the electromagnetic wave absorption rate may be reduced. The bio nanofiber 30 may be cellulose, cellulose ether, or a mixture thereof. In addition, the bio nanofibers 30 may have an average fiber diameter of 30 to 100 nm and an average fiber length of 30 to 60 μm. If the average fiber diameter is less than 30 nm, the dispersibility may be reduced and shielding performance may be deteriorated, and if the average fiber diameter is greater than 100 nm, dispersion uniformity and super weave density may be deteriorated, thereby deteriorating shielding performance. Preferably, the average fiber diameter may be 40 to 60 nm, and the average fiber length may be 45 to 55 μm.

The binder resin 40 serves to physically hold the composite fiber sheet including the conductive carbon fibers 20 and bio nanofibers 30 and is mixed to impart workability and mechanical properties to the electromagnetic wave absorber 10. It can be. Specifically, the binder resin 40 may include 30 to 45% by weight based on the total weight of the electromagnetic wave absorber 10 . At this time, if the content is less than 30% by weight, the mechanical properties of the electromagnetic wave absorber 10 may deteriorate, and if it exceeds 45% by weight, the electromagnetic wave absorption rate may be reduced due to too much of the binder resin 40. The binder resin 40 may be an epoxy resin.

Meanwhile, FIG. 2 is a flowchart of a method of manufacturing the electromagnetic wave absorber 10 according to the present invention. Referring to this, the manufacturing method of the electromagnetic wave absorber 10 includes manufacturing a composite fiber sheet (S1), removing water and solvent contained in the composite fiber sheet (S2), and adding a composite fiber sheet to a binder resin composition. A step of impregnating (S3) and a step of manufacturing the electromagnetic wave absorber 10 (S4) are included.

More specifically, the manufacturing method of the electromagnetic wave absorber 10 of the present invention comprises the steps of preparing a composite fiber sheet by mixing the conductive carbon fibers 20 and an alcohol-based solvent in a bio nanofiber aqueous solution; removing water and alcohol-based solvent contained in the composite fiber sheet; impregnating the composite fiber sheet from which the water and the alcohol-based solvent are removed with the binder resin composition; and manufacturing the electromagnetic wave absorber 10 by curing the impregnated composite fiber sheet.

A detailed description of each step of the manufacturing method of the electromagnetic wave absorber 10 of the present invention is as follows.

1) Manufacturing a composite fiber sheet (S1)

The step of preparing the composite fiber sheet (S1) may be a step of preparing a composite fiber sheet by mixing the conductive carbon fibers 20 and an alcohol-based solvent with an aqueous solution of bio nanofibers. Here, the bio nanofiber aqueous solution may be a mixture of 1 to 10 parts by weight of bio nanofibers 30 in 100 parts by weight of water.

In the step (S1), a composite fiber sheet may be prepared by mixing the conductive carbon fibers 20 and an alcohol-based solvent in an aqueous solution of bio-nanofibers and passing the mixture through a homogenizer rotating at 5000 to 5500 rpm. At this time, it is important to mix the alcohol-based solvent in the step (S1), because the reason is to improve the dispersibility of the conductive carbon fibers 20 to increase the binding force with the bio nanofibers 30. Specifically, the alcohol-based solvent may be isopropyl alcohol, ethanol, or a mixture thereof.

2) Removing water and solvent contained in the composite fiber sheet (S2)

The step of removing the water and the solvent contained in the composite fiber sheet (S2) may be a step of removing the water and the alcohol-based solvent contained in the composite fiber sheet. If water and an alcohol-based solvent remain in the composite fiber sheet, physical properties may deteriorate due to an unnecessary reaction with the binder resin composition in the subsequent step (S3). In order to prevent such a problem from occurring, it is preferable to completely remove water and an alcohol-based solvent included in the composite fiber sheet in the step (S2). At this time, in order to efficiently remove the water and the alcohol-based solvent, the composite fiber sheet may be dried at a temperature of 35 to 55 ° C. for 9 to 23 hours.

3) Impregnating the composite fiber sheet into the binder resin composition (S3)

Impregnating the composite fiber sheet into the binder resin composition (S3) may be a step of impregnating the composite fiber sheet from which the water and the alcohol-based solvent are removed into the binder resin composition. In the step (S3), the binder resin composition may be impregnated into the dry composite fiber sheet after the water and the alcohol-based solvent are removed.

The binder resin composition may include 35 to 45 wt% of an epoxy resin, 50 to 64.9 wt% of a curing agent, and 0.1 to 5 wt% of an amine-based catalyst. In particular, if the content of the epoxy resin is less than 35% by weight, mechanical properties may be deteriorated, and conversely, if the content of the epoxy resin is greater than 45% by weight, it is difficult to form a composite fiber sheet due to the excessive content of the epoxy resin. The epoxy resin may be a product name KDS-8128 manufactured by Kukdo Chemical Co., Ltd. The curing agent may be used a product name KFH-271 manufactured by Kukdo Chemical Co., Ltd. In addition, the amine-based catalyst may be 2-ethyl-4-methylimidazole.

4) Manufacturing the electromagnetic wave absorber 10 (S4)

The manufacturing of the electromagnetic wave absorber 10 (S4) may be a step of manufacturing the electromagnetic wave absorber 10 by curing the impregnated composite fiber sheet. In the step (S4), the sheet-shaped electromagnetic wave absorber 10 may be manufactured by heat-treating and curing the composite fiber sheet impregnated with the binder resin composition. At this time, in the step (S4), the heat treatment may be cured by heat treatment at a temperature of 110 to 130 ° C. for 2 to 6 hours. At this time, if the heat treatment temperature is less than 110 °C or heat treatment is performed for less than 2 hours, the shape of the electromagnetic wave absorber 10 may not be uniform. Conversely, if the temperature exceeds 130 °C or heat treatment exceeds 6 hours, the epoxy resin is denatured by high heat, and the electromagnetic wave absorption rate may be reduced. The electromagnetic wave absorber 10 manufactured through the step (S4) includes 25 to 35% by weight of the conductive carbon fiber 20; 30 to 35% by weight of bio nanofibers (30); And a binder resin (40) 30 to 45% by weight; may include.

Also, the vehicle of the present invention may include the electromagnetic wave absorber 10.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Examples 1-5

Each electromagnetic wave absorber was prepared with each component and mixing ratio shown in Table 1 below. Specifically, after adding carbon nanofibers and isopropyl alcohol to an aqueous solution of cellulose nanofibers in which 5 parts by weight of cellulose nanofibers were mixed with 100 parts by weight of water, a homogenizer equipment rotating at 5000 rpm was used to obtain a composite fiber sheet with a thickness of 1 mm. was manufactured. Then, the composite fiber sheet was dried at a temperature of 45° C. for 9 hours to remove water and isopropyl alcohol contained in the composite fiber sheet. Then, the composite fiber sheet was impregnated with the binder resin composition. The composite fiber sheet impregnated with the binder resin was hardened by heat treatment at 120° C. for 3 hours to prepare an electromagnetic wave absorber.

Comparative Examples 1 to 9

It was carried out in the same manner as in Examples 1 to 5, except that the electromagnetic wave absorber was prepared with each component and mixing ratio shown in Table 1 below.

Experimental Example: Property Evaluation of Electromagnetic Wave Absorber

The electromagnetic wave absorption coefficient and bending bendability of the electromagnetic wave absorbers prepared in Examples 1 to 5 and Comparative Examples 1 to 9 were measured. The measurement results were carried out in the following manner, and the results are shown in Tables 2 and 3.

(1) Electromagnetic wave absorption coefficient: The electromagnetic wave absorption coefficient was measured using an electromagnetic wave transmittance measuring device (Agilent E8364A PNA type vectornetwork analyzer).

(2) Flexural property: Flexural property was measured by utilizing cracks generated when strain was applied to the composite specimen using tensile property evaluation equipment. The result was excellent when no crack was visible under the 45-degree bending condition, good when fine whitening at the bending deformation point was observed, and poor when two or more whitening at the bending deformation point were observed.

(3) Appearance: When looking at the appearance of the planar body after molding, if 2 or less micropores are visible and the flatness is excellent, it is excellent, if 3 or less micropores are visible, it is good, and if 4 or more are visible, it is indicated as poor.

According to the results of Tables 2 and 3, in the case of Examples 1 to 5, it was confirmed that the electromagnetic wave absorption efficiency in the high frequency range of 20 GHz and 40 GHz satisfies all required physical property levels. In addition, it was confirmed that the bending properties and appearance after molding were excellent.

On the other hand, in the case of Comparative Examples 1 to 9, it was confirmed that all of the required physical property levels were not satisfied in the frequency domains of 20 GHz and 40 GHz. In addition, it was found that compatibility was poor due to poor bending properties or poor appearance after molding.

10: electromagnetic wave absorber
20: conductive carbon fiber
30: bio nanofiber
40: binder resin

Claims (16)

delete delete delete delete delete delete delete delete Preparing a composite fiber sheet by mixing conductive carbon fibers and an alcohol-based solvent in an aqueous solution of bio nanofibers;
removing water and alcohol-based solvent contained in the composite fiber sheet;
impregnating the composite fiber sheet from which the water and the alcohol-based solvent are removed with the binder resin composition; and
preparing an electromagnetic wave absorber by curing the impregnated composite fiber sheet;
including,
The alcohol-based solvent is isopropyl alcohol,
The manufacturing method of the electromagnetic wave absorber comprising the step of manufacturing the composite fiber sheet through a homogenizer rotating at 5000 to 5500 rpm.
delete delete According to claim 9,
In the step of removing the water and the alcohol-based solvent, the composite fiber sheet is dried at a temperature of 35 to 55 ° C. for 9 to 23 hours.
According to claim 9,
The method of manufacturing an electromagnetic wave absorber, wherein the binder resin composition includes 35 to 45% by weight of an epoxy resin, 50 to 64.9% by weight of a curing agent, and 0.1 to 5% by weight of an amine-based catalyst.
According to claim 9,
In the step of manufacturing the electromagnetic wave absorber, the method of manufacturing the electromagnetic wave absorber is cured by heat treatment at a temperature of 110 to 130 ° C. for 2 to 6 hours.
According to claim 9,
The electromagnetic wave absorber includes 25 to 35% by weight of conductive carbon fiber; 30 to 35% by weight of bio nanofibers; and 30 to 45% by weight of a binder resin.
An automobile comprising an electromagnetic wave absorber manufactured by the manufacturing method according to any one of claims 9 and 12 to 15.