COMPOSITION OF CELLULAR PHONE CASE FOR SHIELDING ELECTROMAGNETIC WAVE AND METHOD OF MANUFACTURING CELLULAR PHONE CASE USING THE SAME TECHNICAL FIELD The present invention relates to a cellular phone composition and method for manufacturing a case of the cellular phone using the composition which prevents malfunction of the cellular phone due to an electromagnetic wave thereof and minimizes penetration of the electromagnetic wave from the cellular phone into the body.

BACKGROUND ART Typically, cellular phone cases for shielding an electromagnetic wave generating therein were developed by a method in which a case was made by projecting PC/ABS blending and ABS material in thermoplastic resin and metal of high-conductivity was coated inside the case to shield the electromagnetic wave. In this method, materials with high conductivity should be developed to fully shield the electromagnetic wave for preventing malfunction of the cellular phone.

Also, as the cellular phone is getting smaller and driving voltages applied to devices in the cellular phone are getting lower, the more shielding materials should be coated to obtain shielding effect.

Moreover, the method generates manufacturing errors in the process of coating the conductive materials on the cellular phone, which makes the price of product relatively high.

Also, since secondary electromagnetic wave interference occurs between adjacent devices due to electromagnetic wave shield, a shielding means may be additionally installed therebetween with additional work and time. Also, an element in a type of a metal can is inserted in the projectile as the additional shielding means, which increases the manufacturing cost and errors.

Almost, conductive material such as silver (Ag) is used as the electromagnetic wave shielding materials. As the cellular phone is getting smaller and driving voltages applied to devices in the cellular phone are getting lower, the shielding means should have higher conductivity, which makes the price of product high and improvement of quality of devices difficult.

Also, typical cellular phones focus prevention of malfunction of the devices while disregarding the shield of electromagnetic wave that may be harmful to a user with long-term use thereof.

Conventionally, products made by adding inorganic or organic antibacterial agent to plastic such as polyethylene, polypropylene and polyvinyl chloride, epoxy or tiles are applied to various goods such as water containers, sheets, fiber and paint. However, since the

antibacterial agent is relatively expensive, the price of products is high, and color may fade with long-term use.

DISCLOSURE OF INVENTION The present invention is designed to overcome the problems of the prior art. An object of the invention is to provide a composition of cellular phone case made by adding electromagnetic wave absorbents into a resin of case to thereby increase the shielding effect of electromagnetic wave and prevent malfunction of the device together with the simplification of manufacturing process and lower-cost of products, and a manufacturing method of the cellular phone using the composition.

To achieve the above object, there is provided a composition of a cellular phone case comprising: synthetic resin of 90-70wt% selected from the group consisting of polycarbonate, polymer blend of polycarbonate and acrylonitrile-butadiene-styrene and ABS resin; and an electromagnetic wave absorbent of 10-30wt% having the particle size of 0.1 30, um.

Preferably, the electromagnetic wave absorbent is one or more selected from the group onsisting of Mn-Zn-, Ni-Zn-, Mg-Zn-, and Mg-Zn-Cu-ferrite.

According to another aspect of the present invention, there is

provided a cellular phone case which is made by ejaculation using the above composition.

Preferably, the cellular phone case may be coated with a conductive material on over inner and outer surfaces thereof.

Alternatively, the conductive material is coated only on separation walls which are formed inside the case.

According to another aspect of the present invention, there is provided a method for manufacturing a cellular phone case comprising the following steps of: extruding synthetic resin of 90-70wt% selected from the group consisting of polycarbonate, polymer blend of polycarbonate and acrylonitrile-butadiene-styrene and ABS resin, and one or more electromagnetic wave absorbents of 10-30wt% having the particle size of 0.1 ~ 30unl selected from the group consisting of Mn-Zn-, Ni-Zn-, Mg-Zn-, and Mg-Zn-Cu-ferrite at the temperature of 180~315 C to manufacture pallet resin; and ejaculating the pellet resin into a mold at the temperature of 180-315 °C to form the case.

Preferably, the method further comprises the step of coating a conductive material on at least a portion of the surface of the case.

Also, the conductive material is coated by spray coating, sputtering or non-electrolytic plating.

Also, the method further comprises the step of attaching a conductive sheet inside the case.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: FIG. 1 shows a cellular phone case provided with electromagnetic shield composition according to the present invention; FIGs. 2 and 3 show a cellular phone case on which conductive coating layer is formed according to the present invention; and FIG. 4 is a diagram for illustrating a cellular phone case whose separating walls are coated with coating layer.

BEST MODES FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 exemplarily shows a cellular phone adopting a composition of the present invention. Generally, the cellular phone comprises a case 12 and separating walls 14 to separate a plurality elements each

other in the case 12. The case 12 and separating walls 14 are made of an electromagnetic wave shield composition of the invention as described below.

In order to manufacture the electromagnetic wave shield composition, an electromagnetic wave absorbent 10-30wt%, one or more selected from the group consisting of Mn-Zn-, Ni-Zn-, Mg-Zn-, and Mg-Zn-Cu-ferrite, having the particle size of 0.1-30fLni is mixed with polycarbonate (hereinafter'PC), polymer blend of polycarbonate and acrylonitrile-butadiene-styrene (hereinafter'ABS'), or ABS resin 90-70wt%, and then extruded by an extruder at the temperature of 180 315 C. Here, the extrudate is manufactured as electromagnetic wave shield pellet resin suitable for mass production using a pelletizer.

After that, the cellular phone case 12 is manufactured by injecting the electromagnetic wave shield resin containing the electromagnetic absorbent of 10wt% or 20wt% into a mold utilizing a catapult. Here, the resin is ejaculated to the cellular phone case under the condition of the temperature of 180-315 °C in the catapult, the mold temperature of 60-125°C, the screw speed of 30~110rpm, the ejaculating pressure of 400-1200kg/m.

A cellular phone case by the above method turned out to have an absorption capacity over the broad band enough to fully shield electromagnetic wave generating from the local oscillation frequency of

19.6MHz, the RX intermediate frequency of 85.38MHz, the TX intermediate frequency of 130.38MHz and the communication frequency of 800-900MHz for CDMA, and the RX intermediate frequency of 130.38MHz, the TX intermediate frequency of 260.76MHz and the communication frequency of 1500-2000MHz for PCS The inner sides of the cellular phone case 12 may be coated with a conductive material in order to increase an electromagnetic wave shielding ratio thereof. FIG. 2 shows a cellular phone case 12 whose inner surfaces are formed with a coating layer 20 by coating a conductive material thereon. Such a coating layer 20 increases the electromagnetic wave shielding ratio to thereby efficiently prevent the emission of electromagnetic wave.

The conductive materials used in the conductive coating layer 20 may be one of a copper (Cu) ion, a nickel (Ni) ion, an iron (Fe) ion, a silver (Ag) ion, or a mixture thereof, or conductive polyethylene.

For example, the coating layer 20 may be formed by manufacturing two cellular phone cases with two resin containing the electromagnetic wave absorbent of 10wt% and 20wt% respectively under the same ejaculating condition as the above and coating conductive materials on the inner sides of the cellular phone cases.

In the above embodiment, a cellular phone case made of the resin containing the electromagnetic wave absorbent of 10wt% had the

electromagnetic wave shielding ratio of 90%, while the electromagnetic wave shielding ratio of a cellular phone case whose inner surfaces are formed with the conductive coating layer 20 amount to more than 95%.

In case that the conductive coating layer 20 was formed on the inner surfaces of a cellular phone case containing the electromagnetic wave absorbent of 20wt% having a superior shielding ratio, malfunction of the cellular phone due to the electromagnetic wave absolutely did not occur and attenuated the electromagnetic wave to thereby minimize the penetration of electromagnetic wave into body without any interferences to telephone conversation.

In a cellular phone case made of pellet resin containing the electromagnetic wave absorbent of more than 20wt%, additional effect by the conductive layer was not so much. Accordingly, in the manufacture of cellular phone case made of pellet resin containing the electromagnetic wave absorbent of 20-30wt%, the coating process can be omitted to reduce the manufacture cost.

Also, when a cellular phone case ejaculated from a pellet resin containing the electromagnetic wave absorbent of more than 10wt% is coated with the conductive materials, a manufacturing error, if it occurs, in the coating process never influence the quality of products, which reduce inferior products and manufacturing cost.

Such a coating layer may be formed on the outer surface of the

cellular phone case 12. As shown in FIG. 3, coating layers 20 and 22 are formed on both inner and outer surfaces of the cellular phone case 12, which enhances the efficiency of the electromagnetic wave shield.

The coating may be accomplished by spay process, sputtering or non-electrolytic plating.

Alternatively, a sheet having conductivity may be inserted into the cellular phone case treated to shield the electromagnetic wave, instead of forming the conductive coating layer as described above. In this case, the conductive sheet provides the same effect for shielding the electromagnetic wave as the coating layer.

Also, the conductive sheets may be additionally attached after the conductive coating layers are formed on inner surface or on both inner and outer surfaces of the cellular phone case. At this time, the conductive sheets are preferably inserted in the cellular phone case 12.

According to another embodiment, two cellular phone cases containing the electromagnetic wave absorbents of 10wt% and 20wt% respectively are manufactured, and then conductive materials may be coated on separating walls 14 which are formed in the manufactured cellular phone case 12. Referring to FIG. 4, even separating walls 14 are formed to separate electric devices in the cellular phone case 12, the electromagnetic wave may interfere the devices to bring malfunction of operation. Accordingly, interference of electromagnetic wave with each

other can be prevented by forming the conductive coating layer 24 on the separating walls 14.

Since such a configuration can relatively reduce area to be coated, cost for coating process may be saved and manufacturing process may be simplified.

As described above, the cellular phone case of the present invention undergoes the electromagnetic interference treatment in order to minimize the exposure of the body to the electromagnetic wave as well as to prevent malfunction of the cellular phone, which enables manufacture of product with complete electromagnetic compatibility effect.

Also, as a result of application of the present invention to the cellular phone, it was found that the electromagnetic wave shield effect is superior on the broad band of electromagnetic wave from low frequency wave of 10MHz through microwave of 20GHz. Particularly, electromagnetic wave shield ratio amounts to from 90% minimum to 99% maximum in the range of 10-300MHz, 800-900MHz and 1500-2600MHz.

Also, antibacterial effect may enhance by increasing the ions of electromagnetic wave absorbents in manufacturing the cellular phone case. Generally, since the cellular phone is used in contact with a user's body, antibacterial activity is important to provide sanitary

conditions to the user.

The antibacterial activity of the cellular phone case varies with the amount and a kind of the electromagnetic wave absorbents. That is, the antibacterial activity is higher as the amount of the electromagnetic wave absorbents increases. For example, the suppression ratio of coliform bacilli is 30% at 10wt% of the electromagnetic wave absorbents, 40% at 20wt%, and 45% at 30wt%, respectively. Also, the antibacterial activity is better with the electromagnetic wave absorbents such as Ni-Zn group, particularly Mg-Zn-Cu group rather than Mn-Zn or Mg-Zn groups.

Such an antibacterial effect was also found with respect to other bacteria such as staphylococcus aureus and fungus as well as coliform bacilli.

An impact resistance is important to the cellular phone case considering careless drop of the cellular phone. The impact resistance of the cellular phone case containing the electromagnetic wave absorbents according to the present invention turned out to be the same as that of conventional case. Also, in case that surfaces of the electromagnetic wave absorbents was treated with silane-based coating agent of 0.5-3wt% and the cellular phone case was made of the same, the impact resistance was improved by 10% compared to the typical case.

As described above, the present invention may be applicable to cases and sheets of cellular phones and electric home appliances to thereby absorb and remove the electromagnetic wave, suitable to electromagnetic compatibility.

The present invention is not intended to be limited to the embodiment herein, but various modifications and changes will be readily apparent to those skilled in the art within the scope of the present invention, which is set forth in the appended claims.

Industrial Applicability The cellular phone case made of electromagnetic shield materials according to the present invention blocks the electromagnetic wave emitted from the cellular phone devices to help a user avoid the interference of the electromagnetic wave.

Further, electromagnetic wave shield ratio can be improved by forming a conductive coating layer on the cellular phone case, and malfunction of devices in the cellular phone case due to electromagnetic wave interference therebetween can be prevented by forming additional coating layers on the separation walls.