WO2018021623A1

WO2018021623A1 - Complex sheet for wireless charging and method for fabricating the same

Info

Publication number: WO2018021623A1
Application number: PCT/KR2016/013187
Authority: WO
Inventors: Sang Seok Park; Doo Hyeon Kim; Jung Il Park; Eun Kwang Hur
Original assignee: Innox Advanced Materials Co Ltd
Current assignee: Innox Advanced Materials Co Ltd
Priority date: 2016-07-27
Filing date: 2016-11-16
Publication date: 2018-02-01
Anticipated expiration: 2019-01-27
Also published as: KR101727159B1

Abstract

A complex sheet for wireless charging and a method of preparing the same are disclosed. The complex sheet for wireless charging according to an exemplary embodiment includes an electromagnetic wave shielding layer configured to shield electromagnetic wave generated in a wireless charging coil; and a graphite layer which is adhered to the electromagnetic wave shielding layer by the electromagnetic wave shielding layer, and includes a plurality of through holes formed therein, wherein at least a portion inside of the through hole is filled with an adhesive component derived from the electromagnetic wave shielding layer.

Description

COMPLEX SHEET FOR WIRELESS CHARGING AND METHOD FOR FABRICATING THE SAME

Embodiments of the present invention relate to a wireless charging technique.

Recently, a variety of mobile terminals satisfying mobility and portability requirements of users such as a smart phone, mobile phone, portable multimedia player (PMP), MP3 player, digital camera, laptop computer, tablet PC, or the like have been widely used. In general, such mobile terminals have a built-in battery, and if the battery is discharged, it should be re-charged and used. In this regard, in order to maximize convenience in charging the battery, techniques of wireless charging the battery have been developed.

However, in the wireless charging techniques, the battery is charged using transmission of electromagnetic wave over air, such that the electromagnetic wave is principally harmful to a human body and affects other electronic parts, which in turn, needs to be shielded. Further, heat is generated in a wireless charging module during wireless charging, and therefore, it is necessary to rapidly transmit the generated heat to an outside to protect damage of the electronic parts caused by the heat. As an electromagnetic wave shielding sheet, some commercially available products made of diverse materials have been widely used. However, such conventional electromagnetic wave shielding sheets have low thermal conductivity and could not obtain sufficient heat radiation effect. Accordingly, it is required that heat radiation effect and electromagnetic wave shielding effect are preferably and simultaneously achieved.

[Prior Art Document]

[Patent Document]

[Patent Document 1] Korean Patent Laid-Open Publication No. 10-2016-0043294 (2016. 04. 21)

Embodiments of the present invention provide a complex sheet for wireless charging able to achieve electromagnetic wave shielding effect and heat radiation effect, simultaneously, and a method for fabricating the same.

According to an exemplary embodiment of the present invention, there is provided a complex sheet for wireless charging, including: an electromagnetic wave shielding layer configured to shield electromagnetic wave generated in a wireless charging coil; and a graphite layer which is adhered to the electromagnetic wave shielding layer by the electromagnetic wave shielding layer, and includes a plurality of through holes formed therein, wherein at least a portion inside of the through hole is filled with an adhesive component derived from the electromagnetic wave shielding layer.

The electromagnetic wave shielding layer may be made of a cured product of a resin mixture including a thermosetting epoxy resin, a rubber binder, a silane coupling agent, a fluorine surfactant, soft magnetic powders, a hardener and a moisture-proof agent.

The resin mixture may include 160 to 350 parts by weight of the rubber binder, 4 to 25 parts by weight of the silane coupling agent, 0.5 to 5 parts by weight of the fluorine surfactant, 700 to 1,500 parts by weight of the soft magnetic powders, 2 to 30 parts by weight of the hardener and 1 to 25 parts by weight of the moisture-proof agent to 100 parts by weight of the thermosetting epoxy resin.

The soft magnetic powder may include at least one selected from an Fe-Si-Al alloy, Fe-Si-Cr alloy, Fe-Si-B alloy, highflux, permalloy alloy, Ni-Zn ferrite alloy and Mn-Zn ferrite alloy.

The soft magnetic powder may have a mean particle diameter of 20 ㎛ to 100 ㎛,

The electromagnetic wave shielding layer may be laminated on the graphite layer, and the through hole may be formed to perforate from one surface of the graphite layer facing the electromagnetic wave shielding layer to the other surface of the graphite layer.

The through hole may have a degree of transformation satisfying Equation 1 below:

[Equation 1]

0.500 ≤ Degree of transformation ≤ 1.300

wherein the degree of transformation is represented by (Internal area of through hole shape/Circumferential length of through hole shape)^1/2.

The through hole may have a cross-section formed in a circular shape, and has a mean diameter of 0.5 mm to 8 mm.

An entire area of the through holes may range from 2% to 30% to an entire area of one surface or the other surface of the graphite layer.

According to another exemplary embodiment of the present invention, there is provided a complex sheet for wireless charging, including: an electromagnetic wave shielding layer configured to shield electromagnetic wave generated in a wireless charging coil; a graphite layer including a plurality of through holes formed therein; and an adhesive layer disposed between the electromagnetic wave shielding layer and the graphite layer to adhere the electromagnetic wave shielding layer and the graphite layer together with each other, wherein at least a portion inside of the through hole is filled with an adhesive component derived from the adhesive layer.

The electromagnetic wave shielding layer, the adhesive layer and the graphite layer may be laminated in this order from one surface to the other surface of the complex sheet for wireless charging, and the through hole may be formed to perforate from one surface of the graphite layer facing the adhesive layer to the other surface of the graphite layer.

The adhesive layer may include a thermosetting resin, a rubber binder, a silane coupling agent, a fluorine surfactant, a hardener, a curing enhancer, a flame retardant and a moisture-proof agent, in a range of: 25 to 100 parts by weight of the rubber binder, 1 to 10 parts by weight of the silane coupling agent, 0.01 to 2 parts by weight of the fluorine surfactant, 5 to 20 parts by weight of the hardener, 1 to 5 parts by weight of the curing enhancer, 30 to 60 parts by weight of the flame retardant, and 0.5 to 10 parts by weight of the moisture-proof agent to 100 parts by weight of the thermosetting epoxy resin.

The adhesive layer may further include thermoconductive filler containing at least one selected from graphite powders, carbon nanotube (CNT), carbon black powders, carbon fiber, ceramic powders and metal powders.

[Equation 1]

0.500 ≤ Degree of transformation ≤ 1.300

According to an exemplary embodiment of the present invention, there is provided a method of preparing a complex sheet for wireless charging, including: introducing a laminate, in which an electromagnetic wave shielding layer and a graphite layer including a plurality of through holes are laminated, into a hot press machine; heating and pressing the laminate at 145℃ to 160℃ and under a pressure of 45 to 60 kgf/cm² to conduct a hot-pressing process; and cooling the hot press and separating the laminate from the hot press.

According to another exemplary embodiment of the present invention, there is provided a method of preparing a complex sheet for wireless charging, including: introducing a laminate in which an electromagnetic wave shielding layer, an adhesive layer and a graphite layer including a plurality of through holes are laminated, into a hot press machine; heating and pressing the laminate at 145℃ to 160℃ and under a pressure of 45 to 60 kgf/cm² to conduct a hot-pressing process; and cooling the hot press and separating the laminate from the hot press.

According to the embodiments of the present invention, the electromagnetic wave shielding layer may be combined with the graphite layer by an adhesive component derived from the electromagnetic wave shielding layer, so as to reduce a thickness of a complex sheet for wireless charging 100 and thus form a thin film type complex sheet for wireless charging. In this case, since the electromagnetic wave shielding layer and the graphite layer are directly adhered to each other, heat transfer performance from the electromagnetic wave shielding layer to the graphite layer may be improved.

Further, since a plurality of through holes are formed in the graphite layer in a thickness direction thereof, a vertical thermal conductivity of the graphite layer may be minimized while maximizing a horizontal thermal conductivity, thereby enhancing heat radiation performance of the graphite layer. Further, a peel-off strength between the electromagnetic wave shielding layer and the graphite layer and an interlayer peel-off strength in the graphite layer may be increased, so that impact resistance and durability of the complex sheet for wireless charging may be improved.

FIG. 1 is a cross-sectional view illustrating a configuration of a complex sheet for wireless charging according to an exemplary embodiment.

FIG. 2 is views illustrating a cross-section of through holes in a graphite layer of the complex sheet for wireless charging according to the exemplary embodiment.

FIG. 3 is a flow chart illustrating a method of preparing a complex sheet for wireless charging according to the exemplary embodiment.

FIG. 4 is a cross-sectional view illustrating a configuration of a complex sheet for wireless charging according to another exemplary embodiment.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. However, the following detailed description is provided to help a comprehensive understanding for the method, apparatus, and/or system described in the present disclosure. However, these are merely illustrative examples and the present invention is not limited thereto.

In descriptions of the embodiments of the present invention, publicly known techniques that are judged to be able to make the purport of the present invention unnecessarily obscure will not be described in detail. Referring to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views. In addition, the terms as used herein are defined by taking functions of the present disclosure into account and can be changed according to the custom or intention of users or operators. Therefore, definition of the terms should be made according to the overall disclosure set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention thereto. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Meanwhile, some terms indicating a direction such as top, bottom, one surface, the other surface, etc. may be used in relation to an orientation of the accompanying drawings. Configurative components in the embodiments of the present invention may be positioned in different orientations, and therefore, such terms indicating the direction are proposed for illustrative purpose only, but not being particularly limited thereto.

FIG. 1 is a cross-sectional view illustrating a configuration of a complex sheet for wireless charging according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a complex sheet for wireless charging 100 may include an electromagnetic wave shielding layer 102 and a graphite layer 104. A coil 50 may be formed on the electromagnetic wave shielding layer 102. The coil 50 may sever to transmit a wireless power, and may serve to receive the wireless power. That is, the complex sheet for wireless charging 100 may be used in a device for wireless power transmission or in another device for wireless power reception. Further, the graphite layer 104 may include a plurality of through holes 104a formed therein. The through holes 104a may be filled with an adhesive component derived from the electromagnetic wave shielding layer 102, which will be described in detail below.

The electromagnetic wave shielding layer 102 may shield electromagnetic wave generated in the coil 50. The coil 50 may be formed on one surface of the electromagnetic wave shielding layer 102. Further, the electromagnetic wave shielding layer 102 may serve to shield the electromagnetic wave, as well as, absorb the electromagnetic wave. According to an exemplary embodiment, the electromagnetic wave shielding layer 102 may be made of a cured product of a resin mixture including, for example, a thermosetting epoxy resin, a rubber binder, a silane coupling agent, a fluorine surfactant, soft magnetic powders, a hardener (curing agent) and a curing enhancer. For instance, the electromagnetic wave shielding layer 102 may be a metal sheet.

When performing a hot-press process for preparing the complex sheet for wireless charging 100, the adhesive component in the electromagnetic wave shielding layer 102 may be partially molten and filled in the through holes 104a of the graphite layer 106. For this, the electromagnetic wave shielding layer 102 and the resin mixture forming the same may have the same as or lower melting point than a hot-press processing temperature (145℃-160℃), and preferably, it is advantageous to more or less lower melting point.

Among the components of the resin mixture used for forming the electromagnetic wave shielding layer 102, the thermosetting epoxy resin may include at least one selected from a bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, Br containing epoxy resin, etc., which may be used alone or in combination with two or more thereof.

Among the components of the resin mixture, the rubber binder may include at least one selected from acryl rubber, silicone rubber, carboxylated nitrile elastomer and phenoxy, and preferably, at least one alone or two or more of acryl rubber and silicone rubber. According to an exemplary embodiment, the rubber binder used therein may be carboxylic elastomer, and preferably, carboxylated nitrile elastomer. Further, it is advantageous that the carboxylic elastomer used herein has a weight average molecular weight of 180,000 to 350,000, preferably, 210,000 to 280,000, and more preferably, 215,000 to 255,000, in terms of securing bending resistance and heat resistance of the complex sheet for wireless charging 100.

An amount of the rubber binder used in the resin mixture may range from 160 to 360 parts by weight ('wt. parts') to 100 wt. parts of thermosetting epoxy resin. The reason is that: if the used amount of the rubber binder is less than 160 wt. parts to 100 wt. parts of thermosetting epoxy resin, the electromagnetic wave shielding layer 102 has reduced flexibility, and thus, when the complex sheet for wireless charging 100 is bent, a bonded portion between the electromagnetic wave shielding layer 102 and the graphite layer 104 may be partially peeled-off; and, if the used amount of the rubber binder exceeds 350 wt. parts to 100 wt. parts of thermosetting epoxy resin, it is economically disadvantageous and amounts of other components may be relatively reduced, hence deteriorating electromagnetic wave shielding performance of the electromagnetic wave shielding layer 102 and adhesiveness to the graphite layer 104. In the above resin mixture, the used amount of the rubber binder preferably ranges from 180 to 300 wt. parts, and more preferably, ranges from 200 to 280 wt. parts to 100 wt. parts of thermosetting epoxy resin.

The silane coupling agent among the components of the resin mixture plays a role of dispersing particles, which may include any typical silane coupling agent used in the related art. Preferably, at least one selected from glycidoxy(C2-C5 alkyl)trialkoxysilane, vinyltri(C2-C5 alkoxy)silane and aminoethyl aminopropyl silanetriol is used. More preferably, one selected from glycidoxyethyl trimethoxysilane, glycidoxypropyl trimethoxysilane, glycidoxypropyl ethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and aminoethyl aminopropyl silanetriol may be used alone or in combination with two or more thereof. Further, an amount of the silane coupling agent used may range from 4 to 25 wt. parts to 100 wt. parts of thermosetting epoxy resin. The reason is that: if the used amount of the silane coupling agent is less than 4 wt. parts to 100 wt. parts of thermosetting epoxy resin, the used amount is too small to obtain effects of dispersing particles of the component in the resin mixture; and, if the used amount of the coupling agent exceeds 25 wt. parts to 100 wt. parts of thermosetting epoxy resin, particle agglomeration due to a reaction between the coupling agents may cause a problem. An amount of the silane coupling agent used preferably ranges from 4 to 18 wt. parts, and more preferably, ranges from 4 to 12 wt. parts to 100 wt. parts of thermosetting epoxy resin.

The fluorine surfactant among the components of the resin mixture plays a role of reducing surface tension thus to improve coating properties, and may include any one used in the related art, preferably, fluoroaliphatic polymeric ester. Particular examples may include FC4430 manufactured by 3M Co., 4300 manufactured by Novec Co., Capstone manufactured by DuPont Co., or the like. Further, an amount of the fluorine surfactant used herein may range from 0.5 to 5 wt. parts to 100 wt. parts of the thermosetting resin. If the fluorine surfactant is used in an amount of less than 0.5 wt. part to 100 wt. parts of the thermosetting resin, the used amount is too small to provide excellent coating properties. If the used amount of the fluorine surfactant exceeds 5 wt. parts to 100 wt. parts of the thermosetting resin, adhesiveness to the graphite layer 104 may be reduced. Preferably, the used amount of the fluorine surfactant ranges from 0.5 to 3 wt. parts to 100 wt. parts of the thermosetting resin.

The soft magnetic powder among the components of the resin mixture may include at least one or two or more selected from an Fe-Si-Al alloy, Fe-Si-Cr alloy, Fe-Si-B alloy, highflux, permalloy alloy, Ni-Zn ferrite, Mn-Zn ferrite, and preferably, at least one or two or more selected from the Fe-Si-Al alloy, Fe-Si-Cr alloy and Fe-Si-B alloy. The soft magnetic powder may be used in an amount of 700 to 1,500 wt. parts to 100 wt. parts of the thermosetting epoxy resin. If the soft magnetic powder is included in an amount of less than 700 wt. parts to 100 wt. parts of the thermosetting epoxy resin, electromagnetic wave shielding or absorption performance may be deteriorated due to a reduction in magnetic permeability. If the soft magnetic powder is used in an amount of exceeding 1,500 wt. parts to 100 wt. parts of the thermosetting epoxy resin, mechanical properties such as flexibility may be deteriorated although electromagnetic wave shielding effect is excellent. The used amount of the soft magnetic powder preferably ranges from 850 to 1,350 wt. parts, and more preferably, ranges from 900 to 1,300 wt. parts to 100 wt. parts of the thermosetting epoxy resin.

Further, the soft magnetic powder used herein may have an average diameter of 20 ㎛ to 100 ㎛. If the average diameter of the soft magnetic powder is less than 20 ㎛, electromagnetic wave shielding or absorption performance may be deteriorated. If the average diameter of the soft magnetic powder exceeds 100 ㎛, coating properties may be reduced. Herein, soft magnetic powders having an average diameter of 30 ㎛ to 70 ㎛ are preferably used.

The hardener among the components of the resin mixture may include at least one selected from an amine type hardener, anhydride type hardener and phenol type hardener, and preferably, at least one or more selected from the amine type hardener and anhydride type hardener. A particular example of the hardener may be 4,4'-diaminodiphenylsulfone. Further, an amount of the hardener used herein may range from 2 to 30 wt. parts to 100 wt. parts of the thermosetting epoxy resin. If the hardener is used in an amount of less than 2 wt. parts to 100 wt. parts of the thermosetting epoxy resin, a hardening time may be excessively increased to reduce workability. If the hardener is used in an amount of exceeding 30 wt. parts to 100 wt. parts of the thermosetting epoxy resin, an amount of an adhesive component filled in the through holes 104a of the graphite layer 104 during the hot-pressing process may be decreased to cause a problem of reducing adhesiveness to the graphite layer 104. The used amount of the hardener preferably ranges from 3 to 20 wt. parts, and more preferably, ranges from 4 to 15 wt. parts to 100 wt. parts of the thermosetting epoxy resin.

The moisture-proof agent among the components of the resin mixture is used for controlling a water content in the electromagnetic wave shielding layer 102 and a viscosity of the adhesive component, and may include, for example, at least one selected from aluminum sulfate, latex, silicon emulsion, poly(organosiloxane), hydrophobic polymer emulsion and silicon moisture-proof agent, or in combination of two or more thereof. Further, an amount of the moisture-proof agent may range from 1 to 25 wt. parts to 100 wt. parts of the thermosetting resin. If the used amount of the moisture-proof agent is less than 1 wt. part to 100 wt. parts of the thermosetting resin, the amount is too small to provide effects obtained by introducing the moisture-proof agent. If the moisture-proof agent is used in an amount of exceeding 25 wt. parts to 100 wt. parts of the thermosetting resin, there is a difficulty in controlling a proper water content of the electromagnetic wave shielding layer 102 due to excessive use thereof. Preferably, the used amount of the moisture-proof agent ranges from 5 to 20 wt. parts to 100 wt. parts of the thermosetting resin.

The resin mixture may be prepared by introducing a mixture of the above-described thermosetting epoxy resin, rubber binder, silane coupling agent, fluorine surfactant, soft magnetic powders, hardener and moisture-proof agent into an organic solvent, thereby adjusting a viscosity and solid content of a composition for forming an electromagnetic wave shielding layer 102. The organic solvent may include at least one selected from methylethylketone, toluene, tetrahydrofuran (THF) and cyclohexanone. The resin mixture may adjust the viscosity in a range of 800 to 1,200 cps (25℃) and the solid content in a range of 40 to 60 percent by weight ('wt.%'), and preferably, the viscosity in a range of 950 to 1,200 cps (25℃) and the solid content in a range of 48 to 56 wt.%. After applying (or coating) the resin mixture having the above-described constitutional compositions and a compositional ratio to the graphite layer 104, the coated layer may be subjected to drying to semi-harden the same, thereby forming an electromagnetic wave shielding layer 102 on the graphite layer 104.

The electromagnetic wave shielding layer 102 may have a mean thickness of 30 ㎛ to 300 ㎛ in the complex sheet for wireless charging 100. The reason is that: if the mean thickness of the electromagnetic wave shielding layer 102 is less than 30 ㎛, electromagnetic wave shielding effects may be insignificant; and if the mean thickness of the electromagnetic wave shielding layer 102 exceeds 300 ㎛, the prepared layer is very unfavorable in an aspect of a decrease in thickness and has an economic disadvantage. In the complex sheet for wireless charging 100, the mean thickness of the electromagnetic wave shielding layer 102 preferably ranges from 30 ㎛ to 200 ㎛, and more preferably, ranges from 35 ㎛ to 100 ㎛.

The graphite layer 104 may be combined with the electromagnetic wave shielding layer 102 at a bottom of the electromagnetic wave shielding layer 102. The graphite layer 104 may be adhered to the electromagnetic wave shielding layer 102 by an adhesive component included in the electromagnetic wave shielding layer 102. That is, the graphite layer 104 may be adhered to the electromagnetic wave shielding layer 102 by the adhesive component derived from the electromagnetic wave shielding layer 102 without any alternative adhesive layer. As a result, an entire thickness of the complex sheet for wireless charging 100 may be reduced to become a thin film sheet. Further, since the electromagnetic wave shielding layer 102 and the graphite layer 104 are directly combined without any alternative adhesive layer, thermal conductivity from the electromagnetic wave shielding layer 102 to the graphite layer 104 may be improved.

The graphite layer 104 may play a role of discharging a heat generated from the coil 50. The graphite layer 104 may be formed in a sheet or film shape. The graphite layer 104 may have a plurality of through holes 104a formed therein. The through hole 104a may be formed by perforating from one surface of the graphite layer 104 (that is, a surface facing the electromagnetic wave shielding layer 102) to the other surface of the graphite layer 104. The inside of the through hole 104a may fill with the adhesive component 120 derived from the electromagnetic wave shielding layer 102. Adhesion may be performed at an interface between the electromagnetic wave shielding layer 102 and the graphite layer 104 by the adhesive component contained in the electromagnetic wave shielding layer 102, and the adhesive component derived from the electromagnetic wave shielding layer 102 is filled in the through holes 104a to increase adhesiveness between the electromagnetic wave shielding layer 102 and the graphite layer 104.

The graphite layer 104 is formed in a plate-shaped structure, hence causing peel-off in a direction perpendicular to a thickness direction of the graphite layer 104 (that is, a direction parallel to the surface of the graphite layer 104) within the graphite layer 104, when a physical impact occurs (for example, when stripping a protective film or the like). Accordingly, forming the through holes 104a in the thickness direction of the graphite layer 104 (that is, a direction perpendicular to the surface of the graphite layer 104) may prevent the peel-off of the graphite layer 104 from further proceeding, thereby increasing the peel-off strength of the graphite layer 104. Further, forming the through hole 104a in the graphite layer 104 may improve a horizontal thermal conductivity. In this regard, the through hole 104a may be prepared to have a degree of transformation satisfying Equation 1 below, so as to achieve excellent horizontal thermal conductivity and high peel-off strength.

[Equation 1]

0.500 ≤ Degree of transformation ≤ 1.300, preferably, 0.520 ≤ Degree of transformation ≤ 1.200

In Equation 1 above, the degree of transformation may be represented by (internal area of corresponding through hole shape/circumferential length of corresponding through hole shape)^1/2.

In Equation 1 above, if the degree of transformation is less than 0.500, overall heat diffusion of the graphite layer 104 may be improved. However, the peel-off strength of each through hole 104a, and the peel-off strength between the electromagnetic wave shielding layer 102 and the graphite layer 104 may be decreased. On the other hand, if the degree of transformation exceeds 1,300, there may be a problem of increasing a vertical thermal conductivity although the peel-off strengths described above are improved.

A cross-sectional shape of the through hole 104a may include different cross-sectional shapes satisfying the above degree of transformation, as illustrated in FIG. 2. As shown in FIG. 2A, the cross-section of the through hole 104a may be formed in a circular shape. When the through hole 104a has a circular cross-sectional shape, a mean diameter of the through hole may range from 0.5 mm to 8mm. If the mean diameter of the through hole 104a is less than 0.5 mm, there may be a problem of deteriorating durability to thermal impact due to an increase in the number of through holes 104a provided in the graphite layer 104, and a reduction in a filling rate of the adhesive component filled in the through holes 104a. Further, if the mean diameter of the through hole 104a exceeds 8 mm, heat diffusion performance of the graphite layer 104 in a horizontal direction is deteriorated and, when manufacturing a complex sheet, shape maintaining ability of the graphite 104 may be reduced to increase a failure rate. Further, there may be a problem of reducing an interlayer peel-off strength between the graphite layers themselves 104. The mean diameter of the through holes 104a preferably ranges from 0.5 to 5 mm, and more preferably, from 1 to 4 mm.

Further, the cross-section of the through hole 104a may be formed in a circular shape. In this case, a diameter ratio of an inscribed circle to a circumscribed circle of an oval shape may range from 1: 2 to 10.

Herein, a distance between the through holes 104a may defer to a size of the through hole 104, however, since the through holes are formed with a separation distance of, for example, 4 mm to 16 mm in a major axis direction of the graphite layer 104 (a transversal direction in FIG. 2) and 6 mm to 18 mm in a minor axis direction of the graphite layer 104 (a longitudinal direction in FIG. 2) based on a central part of each through hole 104, it is possible to secure a desired horizontal thermal conductivity of the graphite layer 104 and desired adhesiveness between the electromagnetic wave shielding layer 102 and the graphite layer 104, while preventing delamination between the graphite layers 104. Preferably, a distance between the through holes 104a may be a separation distance ranging from 6 mm to 14 mm in the major axis direction and ranging from 8 to 14 mm in the minor axis direction, respectively.

Further, as shown in FIG. 2B, the cross-sectional shape of the through hole 104a may be at least one selected from circle, oval, + shape, x shape, ┣ shape, L shape, I shape and linear shape, and such through holes 104a having various cross-sectional shapes may be formed in the graphite layer 104. In other words, the through hole 104a may be formed to have such a cross-sectional shape that two through holes having a linear cross-section are perpendicularly crossed (for example, + shape or x shape). Further, the through hole 104a may be formed to have such a cross-sectional shape that a through hole having a linear cross-section is perpendicularly extending from one surface or an end of another through hole having a linear cross-section (for example, ┣ shape or L shape).

Further, an entire area of the through holes 104a may be set to have 2% to 30% of an entire area of upper or lower surface of the graphite layer 104. If the area of the through hole 104a is less than 2%, a peel-off strength between the electromagnetic wave shielding layer 102 and the graphite layer 104 may be reduced. If the area of the through hole 104a exceeds 30%, there are problems of increasing a vertical thermal conductivity while deteriorating heat diffusion performance although the above peel-off strength is excellent. The entire area of the through holes 104a preferably ranges from 3.5 to 15%, and more preferably, from 3.5 to 10% to an entire area of the upper or lower surface of the graphite layer 104.

A graphite sheet (or film) forming the graphite layer 104 may include any typical graphite sheet used in the related art. Preferably, a graphite sheet including at least one selected from pyrolytic graphite and graphitized polyimide may be used. The pyrolytic graphite refers to high purity graphite having high thermal conductivity and electric conductivity, is used at a high temperature, prepared by a vapor immersion method and may have a greatly developed microfine structure.

The graphitized polyimide may be prepared by following graphitization processes. First, an advance preparation step of the graphitization may include laminating polyimide on a natural graphite sheet, then introducing the laminate into a calcination furnace. In such the preparation step, polyimide may have a film form, this step may be conducted to prevent fusion between the films.

Next, a first step of the graphitization may include a carbonization of polyimide at a temperature of 600 to 1,800℃ for 2 to 7 hours. According to such carbonization as described above, nitrogen and hydrogen or other components in the polyimide as well as carbon may be removed.

Lastly, as a second step of the graphitization, heat treatment may be performed thereon at a temperature of 2,000℃ to 3,200℃. According to such heat treatment as described above, carbon atoms may be aligned in different forms. More particularly, pores may be present between carbon stacks in the polyimide after the first step. By passing these stacks through a mill roll at a temperature of 2,000 to 3,200℃, such pores may be eliminated while increasing a density of the stacks, thereby preparing graphitized polyimide having maximum heat radiation performance.

According to the embodiment of the present invention, since the electromagnetic wave shielding layer 102 and the graphite layer 104 are combined by the adhesive component derived from the electromagnetic wave shielding layer 102. Therefore, a thickness of the complex sheet for wireless charging 100 may be decreased thus to produce a thin film type complex sheet for wireless charging 100. In this regard, since the electromagnetic wave shielding layer 102 and the graphite layer 104 are directly adhered to each other, heat transfer performance from the electromagnetic wave shielding layer 102 to the graphite layer 104 may be improved.

Further, forming a plurality of through holes 104a in a thickness direction of the graphite layer 104 may minimize a vertical thermal conductivity of the graphite layer 104 while maximizing a horizontal thermal conductivity thereof, so as to improve heat radiation performance of the graphite layer 104. In addition, the peel-off strength between the electromagnetic wave shielding layer 102 and the graphite layer 104 and the interlayer peel-off strength in the graphite layer 104 may be increased thus to improve impact resistance and durability of the complex sheet for wireless charging 100.

FIG. 3 is a flow chart illustrating a method for preparing the complex sheet for wireless charging according to the exemplary embodiment.

Referring to FIG. 3, the electromagnetic wave shielding layer 102 is laminated on the graphite layer 104 (S101). That is, the electromagnetic wave shielding layer 102 may be formed and laminated on the graphite layer 104 having a plurality of through holes 104a formed therein.

Next, a laminate in which the electromagnetic wave shielding layer 102 is laminated on the graphite layer 104 is introduced into a hot press machine, followed by conducting a hot-pressing process (S103) by heating and pressing the same at 145℃ to 160℃ under a pressure of 45 to 60 kgf/cm².

More particularly, if the hot-pressing process temperature is less than 145℃, the adhesive component in the electromagnetic wave shielding layer 102 is not sufficiently molten and may reduce the filling rate of the graphite layer 104 in the through holes 104. If the hot-pressing process temperature exceeds 160℃, the adhesive component in the electromagnetic wave shielding layer 102 is molten too much and may cause a deterioration in mechanical properties while having a difficulty in maintaining a shape of the electromagnetic wave shielding layer 102.

Further, a pressure during hot pressing is less than 45 kgf/cm², an amount of the adhesive component in the electromagnetic wave shielding layer 102 flowing into the through holes 104a may become small. Further, the pressure exceeding 60 kgf/cm² is economically disadvantageous.

Further, the hot-pressing process may be executed by heating and pressing the laminate under the above pressure and temperature for 40 minutes to 80 minutes, and preferably, 50 minutes to 70 minutes. If the hot-pressing process is conducted for less than 50 minutes, the adhesive component is not sufficiently outflowed from the electromagnetic wave shielding layer 102 and an amount filled in the through holes 104a is small, hence causing a problem of reducing the peel-off strength. Further, a time for the hot-pressing process exceeding 70 minutes is economically disadvantageous.

Further, heating during the hot-pressing process may be executed by heating a hot press from 10℃-35℃ to 145℃-160℃ at a heating rate of 3℃/min to 5℃/min.

Next, after cooling the hot press, the laminate is separated from the hot press (S105). The cooling of the hot press may be executed by cooling the hot press from 145℃-160℃ to 10℃-35℃ at a cooling rate of 3℃/min to 5℃/min.

The complex sheet for wireless charging 100 according to an exemplary embodiment of the present invention may have a horizontal thermal conductivity ranging from 100 to 1,000 W/m·k, and a vertical thermal conductivity of 1 to 15 W/m·k or less. Preferably, the horizontal thermal conductivity ranges from 200 to 1,000 W/m·k and the vertical thermal conductivity ranges from 1 to 10 W/m·k or less.

Further, the complex sheet for wireless charging 100 may have a peel-off strength of the graphite layer 104 in a range of 390 gf/cm² to 770 gf/cm², preferably, 450 gf/cm² to 750 gf/cm², and more preferably, 500 gf/cm² to 740 gf/cm², when the above peel-off strength is measured by 90° Peel Test according to JIS C 6741 standard.

Further, the complex sheet for wireless charging 100 may have a peel-off strength of each through hole 104a in a range of 50 to 1,500 gf/hole, preferably, 250 to 1,000 gf/hole, and more preferably, 350 to 950 gf/hole.

Referring to FIG. 4, a complex sheet for wireless charging 200 may include an electromagnetic wave shielding layer 202, a graphite layer 204 and an adhesive layer 206. Herein, the graphite layer 204 is substantially the same as the graphite layer 104 illustrated in FIG. 1, and therefore will not be described in detail.

The electromagnetic wave shielding layer 202 is made of a material having heat radiation and electromagnetic wave shielding functions, which may be any typical metal foil used in the related art. Preferable examples thereof may include copper foil or aluminum foil. Further, the electromagnetic wave shielding layer 202 may have a mean thickness of 5 ㎛ to 70 ㎛. The reason is that: if the mean thickness of the electromagnetic wave shielding layer 202 is less than 5 ㎛, there may be problems of poor appearance and an occurrence of tearing.; and if the mean thickness of the electromagnetic wave shielding layer 202 exceeds 70 ㎛, there are a difficulty in forming a thin film and a problem of reducing product flexibility. The mean thickness of the electromagnetic wave shielding layer 202 preferably ranges from 8 to 40 ㎛, and more preferably, from 8 to 35 ㎛.

The adhesive layer 206 may be formed between the electromagnetic wave shielding layer 202 and the graphite layer 204. The adhesive layer 206 may adhere the electromagnetic wave shielding layer 202 and the graphite layer 204 to each other. The adhesive layer 206 may include a high heat-resistant and heat radiation adhesive in order to effectively transfer heat from the electromagnetic wave shielding layer 202 to the graphite layer 204. Herein, the adhesive layer 206 may contain a thermosetting resin, a rubber binder, a silane coupling agent, a fluorine surfactant, a hardener, a curing enhancer, a flame retardant and a moisture-proof agent.

Among components of the adhesive layer 206, the thermosetting resin may include at least one selected from a thermosetting epoxy resin, thermosetting phenoxy resin, thermosetting amino resin, thermosetting polyester resin and thermosetting polyurethane resin. Preferably, the thermosetting epoxy resin is used. More preferably, at least one or two or more selected from a bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, halogen-containing epoxy resin may be included. Further, when two or more of thermosetting epoxy resins are mixed and used, it is advantageous that the bisphenol A epoxy resin and novolac epoxy resin is mixed in a weight ratio of 1 : 0.15-0.4, and preferably, 1 : 0.18-0.35, in terms of improving a melting point of the heat radiation adhesive and enhancing adhesiveness thereof.

Among the components of the adhesive layer 206, the rubber binder may play a role of endowing bending resistance, and may include at least one selected from acryl rubber, silicone rubber, carboxylated nitrile elastomer and phenoxy, and preferably, one or two or more among the acryl rubber and silicon rubber may be included. The above rubber binder used herein may be carboxyl elastomer, and preferably, carboxyl nitrile elastomer. Further, it is advantageous that the carboxyl elastomer has weight average molecular weight of 180,000 to 350,000, preferably, 210,000 to 280,000, and more preferably, 215,000 to 255,000, in terms of securing desired bending-resistance of the complex sheet and desired heat-resistance of the heat radiation adhesive layer. Further, a used amount of the rubber binder may range from 25 to 100 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the rubber binder is used in an amount of less than 25 wt. parts to 100 wt. parts of the thermosetting resin, the hardened adhesive layer has deteriorated flexibility to cause a problem of partially stripping the bonded portion between the electromagnetic wave shielding layer 202 and the graphite layer 204 when the complex sheet is bent; and if the rubber binder is used in an amount of exceeding 100 wt. parts to 100 wt. parts of the thermosetting resin, an amount of other components in the adhesive layer 206 is relatively decreased to hence reduce adhesiveness of the adhesive layer 206. Preferably, the used amount of the rubber binder ranges from 35 to 80 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the silane coupling agent may play a role of dispersing particles, which may include any typical silane coupling agent used in the related art. Preferably, at least one selected from glycidoxy(C2-C5 alkyl) trialkoxysilane, vinyl tri(C2-C5 alkoxy)silane and aminoethyl aminopropylsilane triol is used. More preferably, one selected from glycidoxyethyl trimethoxysilane, glycidoxypropyl trimethoxysilane, glycidoxypropyl ethoxysilane, vinyl trimethoxysilane, vinyl triethoxysilane, aminoethyl aminopropylsilane triol, or a mixture of two or more thereof is used. Further, a used amount of the silane coupling agent may range from 1 to 10 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the silane coupling agent is used in an amount of less than 1 wt. part to 100 wt. parts of the thermosetting resin, the used amount is too small to achieve particle dispersion effects; and if the silane coupling agent is used in an amount of exceeding 10 wt. parts to 100 wt. parts of the thermosetting resin, particle agglomeration may occur due to a reaction between the coupling agents. The used amount of the silane coupling agent preferably ranges from 1 to 5 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the fluorine surfactant plays a role of reducing surface tension to improve coating properties, and may include any one typically used in the related art. Preferably, fluoroaliphatic polymeric ester is used. Particular examples thereof may include FC4430 manufactured by 3M Co., 4300 manufactured by Novec Co., Capstone manufactured by DuPont Co., or the like. Further, an amount of the fluorine surfactant used herein may range from 0.01 to 2 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the fluorine surfactant is used in an amount of less than 0.01 wt. part to 100 wt. parts of the thermosetting resin, this amount is too small to improve coating properties; and if the fluorine surfactant is used in an amount of exceeding 2 wt. parts to 100 wt. parts of the thermosetting resin, adhesiveness may be reduced. The used amount of the fluorine surfactant preferably ranges from 0.02 to 1.2 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the hardener may include at least one selected from an amine type hardener, anhydride type hardener and phenol type hardener, and preferably, at least one or more selected from the amine type hardener and anhydride type hardener. A particular example of the hardener may be 4,4'-diaminodiphenylsulfone. Further, an amount of the hardener used herein may range from 5 to 20 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the hardener is used in an amount of less than 5 wt. parts to 100 wt. parts of the thermosetting resin, durability may be deteriorated; and if the hardener is used in an amount of exceeding 20 wt. parts to 100 wt. parts of the thermosetting resin, adhesiveness may be reduced. The used amount of the hardener preferably ranges from 8 to 17 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the curing enhancer may include at least one of aromatic amine, aliphatic amine and aromatic tertiary amine, and preferably, at least one selected from the aromatic amine and aromatic tertiary amine. An amount of the curing agent used herein may range from 1 to 5 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the curing enhancer is used in an amount of less than 1 wt. part to 100 wt. parts of the thermosetting resin, a curing rate of a heat radiation adhesive is too low, hence deteriorating workability; and if the curing enhancer is used in an amount of exceeding 5 wt. parts to 100 wt. parts of the thermosetting resin, curing proceeds too rapidly, hence causing a problem of completely curing a heat radiation cure layer before hot pressing. The used amount of the curing enhancer preferably ranges from 1.5 to 4.5 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the flame retardant is used for providing flame retardant effect to a product, and may include any one typically used in the related art, and preferably, one selected from phosphorous flame retardant, inorganic flame retardant and chloride flame retardant, or a combination of two or more thereof. Particular examples thereof may include Clariant EXOLIT OP 935, H42M and/or H43M manufactured by Showa Denko Co. Further, an amount of the flame retardant used herein may range from 30 to 60 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the flame retardant is used in an amount of less than 30 wt. parts to 100 wt. parts of the thermosetting resin, it is difficult to achieve perfect flame-retardant effect; and if the flame retardant is used in an amount of exceeding 60 wt. parts to 100 wt. parts of the thermosetting resin, there may be a problem of reducing adhesiveness to the product by excessively using a flame retardant component. The used amount of the flame retardant preferably ranges from 35 to 55 wt. parts to 100 wt. parts of the thermosetting resin.

Among the components of the adhesive layer 206, the moisture-proof agent is used for adjusting a water content of the heat radiation adhesive layer and a viscosity of the heat radiation adhesive, and may include any one typically used in the related art. Particular examples thereof may include one selected from aluminum sulfate, latex, silicon emulsion, poly(organosiloxane), hydrophobic polymer emulsion, silicon moisture-proof agent, or the like, or a combination of two or more thereof. An amount of the moisture-proof agent used herein may range from 0.5 to 10 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the moisture-proof agent is used in an amount of less than 0.5 wt. part to 100 wt. parts of the thermosetting resin, it is difficult to achieve effects of introducing the moisture-proof agent; and if the moisture-proof agent is used in an amount of exceeding 10 wt. parts to 100 wt. parts of the thermosetting resin, it is difficult to adjust a proper water content of the heat radiation adhesive layer due to excessive use thereof. The used amount of the moisture-proof agent preferably ranges from 1.5 to 8 wt. parts to 100 wt. parts of the thermosetting resin.

Meanwhile, the adhesive layer 206 of the present invention may further include a thermoconductive filler and/or dispersant. The thermoconductive filler may include one of graphite powder, carbon fiber tube (CNT), carbon black, carbon fiber, ceramic and metal powder, or a combination of two or more thereof, and preferably, one of graphite powders, ceramics and metal powders or a combination of two or more thereof. In a case of using the thermoconductive filler, this filler may be used in an amount of 45 to 1,100 wt. parts to 100 wt. parts of the thermosetting resin. The reason is that: if the thermoconductive filler is used in an amount of less than 45 wt. parts to 100 wt. parts of the thermosetting resin, heat transfer performance from the electromagnetic wave shielding layer 202 to the graphite layer 204 may be reduced; and if the thermoconductive filler is used in an amount of exceeding 1,100 wt. parts to 100 wt. parts of the thermosetting resin, adhesiveness to the graphite layer 204 may be deteriorated while greatly increasing a vertical thermal conductivity of the complex sheet. The used amount of the thermoconductive filler preferably ranges from 75 to 800 wt. parts to 100 wt. parts of the thermosetting resin. The thermoconductive filler used herein may have a mean particle diameter of 3 ㎛ to 25 ㎛. The reason is that: if the mean particle diameter of the thermoconductive filler is less than 3 ㎛, there may be a difficulty in dispersing particles; and if the mean particle diameter of the thermoconductive filler exceeds 25 ㎛, problems of reducing thin film coating properties and adhesiveness may be caused.

Further, the dispersant used herein may include any one typically used in the related art, and preferably, an acryl block amine-based dispersant.

With regard to the adhesive layer 206, a mixture of the curable resin, rubber binder, silane coupling agent, fluorine surfactant, hardener, curing enhancer, flame retardant and moisture-proof agent may be introduced into an organic solvent to adjust a viscosity of the moisture-proof agent and a solid content, a surface condition of the composition for forming a heat radiation adhesive layer may become favorable through the adjustment of viscosity and solid content, and adhesiveness to a material and particle orientation may be controlled. In this regard, the organic solvent used herein may include at least one selected from methylethylketone, toluene, tetrahydrofuran (THF) and cyclohexanone, or a combination of two or more thereof.

After applying (or coating) the heat radiation adhesive prepared with the above constitutional composition and compositional ratio to the other surface of the electromagnetic wave shielding layer 202, the coated layer is subjected to drying to semi-cure the same, thereby forming the heat radiation adhesive layer. In this regard, an applied amount of the heat radiation adhesive may be desirably defined so that a mean thickness of the heat radiation adhesive layer reaches a range of 2 ㎛ to 25 ㎛ based on the complex sheet after the hot-pressing process. The reason is that: if the mean thickness of the heat radiation adhesive layer in the complex sheet is less than 2 ㎛, adhesiveness (cohesion) between the electromagnetic wave shielding layer 202 and the graphite layer 204 may be deteriorated; and if the mean thickness of the heat radiation adhesive layer in the complex sheet exceeds 25 ㎛, it is economically disadvantageous and a thickness of the complex sheet is increased, hence being unfavorable. It is preferable to apply the heat radiation adhesive layer until the mean thickness reaches the range of 4 ㎛ to 15 ㎛.

The adhesive layer 206 may be filled in the through holes 204a formed in the graphite layer 204 in the hot-pressing process of the complex sheet. More particularly, after introducing a laminate in which the electromagnetic wave shielding layer 202, adhesive layer 206 and graphite layer 204 are sequentially laminated into a hot press machine, the laminate may be subjected to a hot-pressing process by heating and pressing the same at 145℃ to 160℃ under a pressure of 45 to 60 kgf/cm². In this regard, a part of the adhesive layer 206 may be filled in the through holes 204a.

Meanwhile, according to the present embodiments, the electromagnetic wave shielding layer 202 has been described as a metal foil, but it is not limited thereto. As illustrated and described in FIG. 1, this layer may also be made of a resin mixture including a thermosetting epoxy resin, rubber binder, silane coupling agent, fluorine surfactant, soft magnetic powder, hardener and curing enhancer.

Hereinafter, the present invention will be described in more detail by means of examples, however, the scope of the present invention to be protected is not particularly limited to the range illustrated by the examples.

[EXAMPLE]

Preparative Example 1-1: Preparation of electromagnetic wave shielding layer 102

To 100 wt. parts of bisphenol A epoxy resin (K Chemical Co., tradename: YD series resin) as the thermosetting epoxy resin, 265.2 wt. parts of carboxyl nitrile elastomer as the polymer binder (weight average molecular weight: 235,500-236,500), 8.5 wt. parts of the silane coupling agent (D Co. in United States, tradename: Z series coupling agent), 2.05 wt. parts of the fluorine surfactant (M Co. in United States, tradename: FC series surfactant), 978 wt. parts of Fe-Si-Al sand dust powders having a mean particle diameter of 42 to 44 ㎛, 9.7 wt. parts of 4,4'-diaminodiphenylsulfone as the hardener and 10.5 wt. parts of the moisture-proof agent (S Co. in Japan, KP 392) were added to form a resin mixture, followed by introducing the resin mixture in methylethylketone as an organic solvent. Then, the mixture was adjusted to have a viscosity of 1,050 to 1,080 cps and a solid content of 53 wt.% and applied to a release substrate, followed by curing the same at 60℃ for 24 hours, thereby preparing an electromagnetic wave shielding sheet in semi-cured status.

Preparative Examples 1-2 and 1-3, and Comparative Preparative Examples 1-1 and 1-2

Each of electromagnetic wave shielding sheets as the electromagnetic wave shielding layer 102 was prepared by the same procedures as described in Preparative Example 1-1 above, except that the electromagnetic wave shielding sheets had constitutional compositions listed in Table 1 below.

Preparative Example 2-1: Preparation of graphite sheet having through holes

A plurality of through holes 104a were formed in a graphite sheet having a mean thickness of 17 ㎛ (T Co., TGS15). The punched through holes 104a were formed to have a mean particle diameter of 3 mm, an interval in the major axis direction of 10 mm and an interval in the minor axis distance of 12 mm between central parts of the through holes 104a, an entire area of the through holes 104a in a range of 3.9 to 4.1% to an entire area of upper surface of the graphite layer 104. Further, a degree of transformation of the through hole 104a was 0.866 according to Equation 1 below.

[Equation 1]

0.500 ≤ Degree of transformation (= (Internal area of through hole shape/Circumferential length of through hole shape)^1/2) ≤ 1.300

Preparative Examples 2-2 and 2-12, and Comparative Preparative Examples 2-1 and 2-2

Each of graphite sheets having a through hole which was formed in the same graphite sheet as the graphite sheet in Preparative Example 2-1, and had a cross-sectional shape listed in Table 2 below, was prepared. Features of these graphite sheets are listed in Table 2 below.

According to Table 2, the number of through holes and an interval between the same were properly adjusted to satisfy an entire area of the through holes, thereby forming the through holes.

Comparative Preparative Example 2-3

The graphite sheet without any through hole in Preparative Example 2-1 (T Co. in Taiwan, TGS series products) was prepared as Comparative Preparative Example 2-3.

Example 1-1: Preparation of integrated complex sheet

The graphite sheet in Preparative Example 2-1 was temporary bonded and laminated to the electromagnetic wave shielding sheet in Preparative Example 1-1.

Next, such a complex sheet including the laminated electromagnetic wave shielding layer-graphite layer was introduced into a hot press machine.

Then, after raising the temperature of the hot press from 70℃ to 150℃ at a rate of 4℃/min, heat compression was executed at 150℃ and under a pressure of 50 kgf/cm² for 60 minutes.

Following this, after cooling the same to 60℃ at a rate of 4.5℃/min, the heat compressed sheet was taken out of the hot press, thereby providing an integrated complex sheet with electromagnetic wave shielding and heat radiation functions, wherein an adhesive component derived from the electromagnetic wave shielding layer 102 was filled in the through holes 104a of the graphite layer 104 having the shape as shown in FIG. 1.

The prepared integrated complex sheet 100 had an entire thickness of 67 ㎛, while the electromagnetic wave shielding layer 102 had a thickness of 50 ㎛ and the graphite layer 104 had a thickness of 17 ㎛.

Examples 1-2 and 1-17

Integrated complex sheets having combinations listed in Table 3 below were prepared, respectively, by the same procedures as described in Example 1-1, and then, Examples 1-2 and 1-17 were executed, respectively.

Example 2-1

After laminating the electromagnetic wave shielding layer in Preparative Example 1-1 on the graphite sheet in Comparative Preparative Example 2-1, the laminate was introduced into a hot press machine.

Next, after raising a temperature of the hot press from 70℃ to 150℃ at a rate of 4℃/min, heat compression was executed at 150℃ and under a pressure of 50 kgf/ cm² for 60 minutes.

Following this, after cooling the same to 60℃ at a rate of 4.5℃/min, the heat compressed sheet was taken out of the hot press, thereby providing an integrated complex sheet.

Examples 2-2 and 2-4

Each of integrated complex sheets having a combination listed in Table 4 was prepared by the same procedures as described in Example 1-1, and then, Examples 2-2 and 2-4 were executed, respectively.

Example 2-5

An integrated complex sheet was prepared by the same procedures as described in Example 1-1, except that heat compression was executed at 150℃ and under a pressure of 50 kgf/cm² for 30 minutes.

Comparative Example 1

An integrated complex sheet was prepared by the same procedures as described in Example 1-1, except that the graphite layer in Comparative Preparative Example 2-3 was temporary bonded and laminated to the electromagnetic wave shielding sheet in Preparative Example 1-1.

Comparative Example 2

Integrated complex sheets having combinations listed in Table 6 were prepared, respectively, by the same procedures as described in Comparative Example 1.

Comparative Example 3

An integrated complex sheet was prepared by the same procedures as described in Example 1-1, except that heat compression was executed at 130℃ under a pressure of 50 kgf/cm² for 60 minutes.

Comparative Example 4

An integrated complex sheet was prepared by the same procedures as described in Example 1-1, except that heat compression was executed at 150℃ under a pressure of 70 kgf/ cm² for 60 minutes.

Experimental Example: Measurement of peel-off strength and heat diffusion performance

( 1) Entire peel-off strength of graphite layer (gf/cm² ) and peel-off strength per through hole ( gf /Hole)

Using the integrated complex sheet prepared in each of the examples and comparative examples, a specimen was prepared according to JIS C 6741 standard and subjected to measurement of an entire peel-off strength of the graphite layer by means of 180° Peel Test. Results thereof are shown in Table 6 below.

Further, a peel-off strength of each through hole was measured by conducting 90° Peel Test.

(2) Measurement of heat diffusion performance

The integrated complex sheets prepared in the respective examples and comparative examples were cut into a size of 100 mm x 10 mm (width and length).

Next, the prepared sample was attached to a heating block and a temperature of the heating block was raised to 80℃ (evaluation was conducted while raising the temperature to 80 ℃ which is in a temperature level of heat generated on AP chip in a smart phone).

Following this, after sealing the heating block in a box and stabilizing the same for 10 minutes, a temperature of the heating block was measured using IR camera to determine a highest temperature (hot spot) and lowest temperature (cold spot) of the complex sheet. Then, heat diffusion performance of the complex sheet was determined by estimating a difference between the above temperatures. Herein, it could be seen that, as the difference in the above-two temperatures, ΔT, is decreased, heat radiation performance becomes more excellent.

Referring to the measured results of Table 5, it could be seen that the entire peel-off strength was 600 gf/cm² or more and a peel-off strength of each through hole was 400 gf/hole or more in Examples 1-1 to 1-17, thus showing generally high peel-off strengths. Further, a difference between the hot spot and the cold stop was 23.20 or less, thus showing generally excellent heat diffusion performance.

More particularly, as compared to Examples 1-1 to 1-3, it could be seen that: when the amount of the rubber binder in the electromagnetic wave shielding layer is increased, the peel-off strength is slightly reduced but heat diffusion performance tends to be improved; and when the amount of the rubber binder is decreased, the peel-off strength is increased while the heat diffusion performance tends to be deteriorated.

Further, in a case of Examples 1-6 and 1-17, it could be confirmed that a cross-sectional shape of the through holes, an interval between the through holes and an entire area of through holes tend to expert influence on the peel-off strength and the heat diffusion performance.

However, in a case of the integrated complex sheet (Example 2-1) prepared using the graphite sheet in Comparative Preparative Example 2-1, which was provided with the through holes having a degree of transformation of 1.5 and an entire area of through holes of 14.8%, it could be seen that the sheet had excellent peel-off strength compared to other examples. However, this complex sheet showed a little higher hot spot temperature and somewhat deterioration in heat diffusion performance.

Further, in a case of the integrated complex sheet (Example 2-2) prepared by introducing the graphite sheet having a degree of transformation of less than 0.500, which was prepared in Comparative Preparative Example 2-2, it could be seen that the sheet had excellent heat diffusion performance, however, showed a little decreased peel-off strength of each through hole.

Further, in a case of Example 2-3 that included introducing a metal sheet (an electromagnetic wave shielding layer) prepared using the rubber binder in an amount of less than 160 wt. parts, it could be seen that the sheet had excellent peel-off strength and heat diffusion performance. However, when the composite was randomly bent, the bonded portion between the electromagnetic wave shielding layer and the graphite layer was partially peeled-off. The reason of this fact is considered that flexibility of the metal sheet itself was a little reduced.

Further, in a case of Example 2-5 that was subjected to hot pressing for 30 minutes in the preparation of a complex sheet, it could be seen that the peel-off strength of each through hole was slightly decreased and heat diffusion performance was also slightly deteriorated. The reason of this fact is considered that, since the adhesive component was not sufficiently derived from the electromagnetic wave shielding layer and a part of the through holes was not filled with the adhesive component, the peel-off strength was decreased and heat diffusion was inhibited due to a non-filled area.

On the other hand, in a case of the integrated complex sheet in Comparative Example 1, which was prepared by introducing the graphite sheet without any through hole in Comparative Preparative Example 2-3, it could be seen that heat diffusion performance was excellent but the entire peel-off strength was considerably decreased.

Similarly, in a case of the integrated complex sheet in Comparative Example 2, which was prepared by introducing the graphite sheet without any through hole in Comparative Preparative Example 2-3, had a thickness of the graphite sheet of 25 ㎛ and a thickness of the electromagnetic wave shielding layer of 65 ㎛, it could be seen that heat diffusion performance was excellent but the entire peel-off strength was considerably decreased.

Further, in a case of Comparative Example 3 that included hot pressing at a temperature of less than 145℃, that is, at 130℃, since the adhesive component was not sufficiently derived from the electromagnetic wave shielding layer and a part of the through holes was not filled with the adhesive component, it resulted in that the peel-off strength and heat diffusion performance were considerably deteriorated.

Further, in a case of Comparative Example 4 that was subjected to hot pressing under a pressure of 70 kgf/cm², it could be seen that an adhesion intensity was excellent compared to Example 1, however, heat diffusion performance was considerably deteriorated. The reason of this fact is considered that the graphite layer was broken and heat diffusion performance was deteriorated.

Although the representative embodiments of the present invention have been described in detail, it will be understood by persons who have a common knowledge in the technical field to which the present invention pertains that various modifications and variations may be made therein without departing from the scope of the present invention. Accordingly, the scope of the present invention should not be limited to the above-described embodiments, but be defined by the appended claims as well as equivalents thereof.

[Description of Reference Numerals]

100, 200: complex sheet for wireless charging

102, 202: electromagnetic wave shielding layer

104, 204: graphite layer

104a, 204a: through hole

206: adhesive layer

Claims

A complex sheet for wireless charging, comprising:

an electromagnetic wave shielding layer configured to shield electromagnetic wave generated in a wireless charging coil; and

a graphite layer which is adhered to the electromagnetic wave shielding layer by the electromagnetic wave shielding layer, and includes a plurality of through holes formed therein,

wherein at least a portion inside of the through hole is filled with an adhesive component derived from the electromagnetic wave shielding layer.
The complex sheet according to claim 1, wherein the electromagnetic wave shielding layer is made of a cured product of a resin mixture including a thermosetting epoxy resin, a rubber binder, a silane coupling agent, a fluorine surfactant, soft magnetic powders, a hardener and a moisture-proof agent.
The complex sheet according to claim 2, wherein the resin mixture includes 160 to 350 parts by weight of the rubber binder, 4 to 25 parts by weight of the silane coupling agent, 0.5 to 5 parts by weight of the fluorine surfactant, 700 to 1,500 parts by weight of the soft magnetic powders, 2 to 30 parts by weight of the hardener and 1 to 25 parts by weight of the moisture-proof agent to 100 parts by weight of the thermosetting epoxy resin.
The complex sheet according to claim 2, wherein the soft magnetic powder includes at least one selected from an Fe-Si-Al alloy, Fe-Si-Cr alloy, Fe-Si-B alloy, highflux, permalloy alloy, Ni-Zn ferrite alloy and Mn-Zn ferrite alloy.
The complex sheet according to claim 4, wherein the soft magnetic powder has a mean particle diameter of 20 ㎛ to 100 ㎛,
The complex sheet according to claim 1, wherein the electromagnetic wave shielding layer is laminated on the graphite layer, and

the through hole is formed to perforate from one surface of the graphite layer facing the electromagnetic wave shielding layer to the other surface of the graphite layer.
The complex sheet according to claim 1, wherein the through hole has a degree of transformation satisfying Equation 1 below:

[Equation 1]

0.500 ≤ Degree of transformation ≤ 1.300

wherein the degree of transformation is represented by (Internal area of through hole shape/Circumferential length of through hole shape)^1/2.
The complex sheet according to claim 1, wherein the through hole has a cross-section formed in a circular shape, and has a mean diameter of 0.5 mm to 8 mm.
The complex sheet according to claim 1, wherein an entire area of the through holes ranges from 2% to 30% to an entire area of one surface or the other surface of the graphite layer.
A complex sheet for wireless charging, comprising:

an electromagnetic wave shielding layer configured to shield electromagnetic wave generated in a wireless charging coil;

a graphite layer including a plurality of through holes formed therein; and

an adhesive layer disposed between the electromagnetic wave shielding layer and the graphite layer to adhere the electromagnetic wave shielding layer and the graphite layer together with each other,

wherein at least a portion inside of the through hole is filled with an adhesive component derived from the adhesive layer.
The complex sheet according to claim 10, wherein the electromagnetic wave shielding layer, the adhesive layer and the graphite layer are laminated in this order from one surface to the other surface of the complex sheet for wireless charging, and

the through hole is formed to perforate from one surface of the graphite layer facing the adhesive layer to the other surface of the graphite layer.
The complex sheet according to claim 10, wherein the adhesive layer includes a thermosetting resin, a rubber binder, a silane coupling agent, a fluorine surfactant, a hardener, a curing enhancer, a flame retardant and a moisture-proof agent, in a range of: 25 to 100 parts by weight of the rubber binder, 1 to 10 parts by weight of the silane coupling agent, 0.01 to 2 parts by weight of the fluorine surfactant, 5 to 20 parts by weight of the hardener, 1 to 5 parts by weight of the curing enhancer, 30 to 60 parts by weight of the flame retardant, and 0.5 to 10 parts by weight of the moisture-proof agent to 100 parts by weight of the thermosetting epoxy resin.
The complex sheet according to claim 12, wherein the adhesive layer further includes thermoconductive filler containing at least one selected from graphite powders, carbon nanotube (CNT), carbon black powders, carbon fiber, ceramic powders and metal powders.
The complex sheet according to claim 10, wherein the through hole has a degree of transformation satisfying Equation 1 below:

[Equation 1]

0.500 ≤ Degree of transformation ≤ 1.300

wherein the degree of transformation is represented by (Internal area of through hole shape/Circumferential length of through hole shape)^1/2.
The complex sheet according to claim 10, wherein an entire area of the through holes ranges from 2% to 30% to an entire area of one surface or the other surface of the graphite layer.
A method of preparing a complex sheet for wireless charging, comprising:

introducing a laminate, in which an electromagnetic wave shielding layer and a graphite layer including a plurality of through holes are laminated, into a hot press machine;

heating and pressing the laminate at 145℃ to 160℃ and under a pressure of 45 to 60 kgf/cm² to conduct a hot-pressing process; and

cooling the hot press and separating the laminate from the hot press.
A method of preparing a complex sheet for wireless charging, comprising:

introducing a laminate in which an electromagnetic wave shielding layer, an adhesive layer and a graphite layer including a plurality of through holes are laminated, into a hot press machine;

heating and pressing the laminate at 145℃ to 160℃ and under a pressure of 45 to 60 kgf/cm² to conduct a hot-pressing process; and

cooling the hot press and separating the laminate from the hot press.
A wireless power transmission device, comprising the complex sheet for wireless charging according to any one of claims 1 to 15.
A wireless power reception device, comprising the complex sheet for wireless charging according to any one of claims 1 to 15.