WO2004108802A1

WO2004108802A1 - Cellular phone case and method of manufacturing the same

Info

Publication number: WO2004108802A1
Application number: PCT/KR2004/000983
Authority: WO
Inventors: Jong-Hee Kim; Myung-Jin Park
Original assignee: Semtech Corporated
Priority date: 2003-06-11
Filing date: 2004-04-29
Publication date: 2004-12-16
Also published as: KR20040106641A; KR100529590B1

Abstract

The present invention relates to a method of manufacturing a cellular phone case, and more particularly, to a cellular phone case and a method of manufacturing the same, wherein a boron carbide (B4C) coating layer with superior mechanical properties (wear resistance, lubricity, etc.) is deposited on a spay-coated glossy or flat surface of a base material of the cellular phone case by means of a sputtering method, thereby preventing a scratch on the surface of the cellular phone case to improve durability of the cellular phone case. To this end, a boron carbide coating layer with very low friction coefficient and thermal conductivity and high hardness is deposited by means of a sputtering method in which methane (CH4) gas is added as a reactive gas in order to improve crystallinity and adhesiveness of the boron carbide coating layer on the spray-coated glossy or flat surface of the base material of the cellular phone case.

Description

CELLULAR PHONE CASE AND METHOD OF MANUFACTURING THE SAME

Technical Field The present invention relates to a method of manufacturing a cellular phone case of which a surface is coated with boron carbide, and more particularly, to a scratch- . resistant cellular phone case coated with boron carbide, wherein the boron carbide is coated using a sputtering method on a glossy or flat surface thereof formed by spraying powder of metal such as aluminum (Al) onto a surface of a base material of a mixture of PC and ABS resins, thereby improving scratch resistance and prolonging the life of the cellular phone case due to the high hardness of the boron carbide thin film and a semipermanent adhesion property of the boron carbide thin film to the base material, and a method of manufacturing the same.

Background Art Generally, a cellar phone case is molded by pouring a predetermined amount of a mixed slurry of PC (polycarbonate) resin and ABS (acrylonitrile-butadiene-styrene hybrid polymer or alkyl benzene sulfate) resin into an injection mold and then dried on a drying stand. Thereafter, glossy or flat coatings are formed on inner and outer surfaces of the molded cellular phone case through a spraying process. The coated cellular phone case is dried, packaged and shipped.

To shield and protect electromagnetic waves radiating from the interior of a cellular phone case to the outside, silver, copper, aluminum or the like is applied by means of spraying to the inner surface of a cellular phone case with a thickness of several dozen to hundreds of μm. Electromagnetic waves of up to 1,600 MHz radiate from the interior of a cellular phone while in use. The silver, copper, aluminum or the like spray-coated on the inner surface of the cellular phone case serves as a conductor for allowing the electromagnetic waves radiating from the interior thereof to flow to the outside so that the electromagnetic waves can be rapidly collected at a ground terminal mounted in the cellular phone, thereby functioning as a shield against electromagnetic waves. Further, the outer surface of the cellular phone case is generally spray-coated with aluminum or the like in a glossy or flat manner so as to adjust the durability, fanciness, color or the like.

When the outer surface of a cellular phone case is spray-coated in a glossy or flat manner, the surface of the cellular phone case has gloss, fingerprint resistance and some degree of scratch resistance. However, if the cellular phone case is continuously exposed to an external environment, particularly, comes into contact with floors, edges or the like, friction occurs therebetween and the coating layer at the contact portion of the cellular phone case is still peeled off or has many scratches created thereon. To solve these problems, covers for cellular phone cases are recently used. However, most cellular phone cases are used without such covers.

Recently, as cellular phones are used as a means for performing various entertainment functions and exhibiting the individual personalities of cellular phone users in addition to typical communication functions, visual aspects such as design or fanciness becomes more important. Therefore, there is an urgent need for studies on coating layers capable of preventing the occurrence of scratches on cellular phone cases and prolonging the use life of cellular phone cases.

Meanwhile, the present applicant filed a Korean patent application entitled "Computer hard disk and method of forming protection film on hard disk," which discloses the formation of a boron carbide protection film on a coated surface of a hard disk so that the magnetic surface of the hard disk can be semi-permanently used (see Korean Patent No. 10-0368615). Moreover, the present applicant filed another Korean patent application entitled "Wear-resistant parts coated with boron carbide and method of manufacturing the same through sputtering," which discloses the formation of a boron carbide (B₄C) coating film on a surface of a base material of a wear-resistant mechanical part formed with a transition metal adhesive layer so as to ensure the use thereof even in severe environments and improvement of durability due to high hardness and semi-permanent adhesiveness (see Korean Patent Laid-Open Publication No. 2003-0074223). Thus, to solve the problems and meet the requirements in cellular phone cases, the present applicant proposed the application of a boron carbide (B₄C) coating, which is used to improve scratch resistance and prolong the use life by imparting a high hardness property to a base material with poor scratch resistance such as various kinds of plastics, glasses, high strength resins and optical lenses, on the surfaces of conventional cellular phone cases by means of a sputtering method in which a reactive gas is added.

There has not yet been a case where a boron carbide coating is applied to the surface of a cellular phone case. Since boron carbide generally has the following properties: superior thermal and mechanical properties due to its high melting point and hardness, chemical resistance against acids and bases, corrosion resistance and excellent absorbtance of neutrons for molten metal, relatively large thermoelectromotive force, low density and the like, it is suitable for coating the outer surfaces of cellular phone cases. However, boron carbide has a disadvantage in that it is difficult to sinter the boron carbide due to its high degree of covalent bonding greater than 90% as in other carbides or nitrides. Therefore, there is a need for a method of producing a dense sintered material by solving the problem of difficult sintering in the prior art.

As for methods of coating a boron carbide film on a surface of an object to be processed, there are sputtering methods that are vacuum evaporation deposition methods using a sintered material of boron carbide as a target.

The sputtering methods are basically classified into RF sputtering and DC sputtering according to the kind of energy source used. They have been developed into magnetron sputtering mounted with a magnetron to improve ionization of the deposition material.

However, as for a source gas for use in RF or DC magnetron sputtering, only argon (Ar) gas or Ar gas with a reactive gas added thereto is used in a case where a deposition material is an oxide or nitride.

Even though only Ar gas is employed upon use of a boron carbide (B₄C) target, there is difference in sputtering rates due to effects of the atom sizes of boron (B) and carbon (C). Therefore, it is difficult to control the amount of carbon (C) for obtaining an ideal ratio of B/C=4 by atomic percentage and to simultaneously obtain a dense microstructure coating. Further, if the temperature of a substrate is raised upon deposition of a coating, crystallization is exhibited at a temperature equal to or greater than a certain temperature (e.g., 300 °C). However, there is a problem in that a variety of phases such as B₄C, B₈C and B₂₅C shown in Table 1 below rather than a single phase of boron carbide are mixed and increased, resulting in deterioration of wear resistance.

Although boron carbide expressed as B₄C is a unique compound that stably exists in a binary system of boron (B) and carbon (C), carbon content has a wide range of solid solutions of 8 to 21 at%. Therefore, boron carbide is expressed as various formulas in addition to B C according to the carbon content. When a boron carbide coating was formed by means of chemical vapor deposition as shown in Fig. 1 to examine properties of boron carbide, the coating had maximum hardness at a stoichiometric composition ratio of B/C=4. If this ratio is either increased or decreased, hardness decreased. The cause of degradation of the hardness in a range where carbon exists over the solid solution limit (B/C < 4) is the presence of free carbon. Fig. 2 is a graph showing the cause of transition of a crystalline structure according to carbon content in boron carbide.

When carbon content decreased from 20 at% to 17.5 at% in Zone I, the lattice constant increased. This is because the amount of carbon among C-B-C bonds in the rhombohedral structure of B₄C decreased and C atoms having an atom radius of 0.77Awere replaced with B atoms having an atom radius of 0.82A, resulting in the enlargement of the crystal lattice.

Zone II is a region where carbon content deceased from 17.7 at% to 13.5 at% and the lattice constant of the crystal lattice of the boron carbide did not vary according to changes in the carbon content. Zone III is a region where the carbon content was below 13.5 at% and the lattice constant along the c-axis of a lattice point of boron carbide decreased and a lattice constant a_h along the a-axis increased peculiarly according to decreases in the carbon content.

Therefore, it is most important to construct a coating at a deposition condition where adhesiveness, hardness, friction coefficient and scratch resistance are maximized, by controlling the carbon content. Accordingly, it is possible to form the strongest coating at a carbon content of 20 at% in which the value of the lattice constant is smallest.

Although the conventional method of depositing the boron carbide coating on a base material with poor scratch resistance and the properties of the boron carbide coating have been described, there is a need for methods of forming a coating with superior reactivity and cohesion to a base material of a cellular phone case in order to apply such a boron carbide coating on the outer surface of the cellular phone case.

Further, to meet requirements for reliability of a cellular phone case, it is necessary to consider conditions of a coating with superior scratch resistance, change in the color of the cellular phone case after the formation of the boron carbide coating, and the like.

Moreover, it should be noted that when boron carbide is deposited on a glossy or flat material coated on a mixed PC and ABS resin of a substrate material for a cellular phone case, a uniform coating should be formed at a temperature condition where the resin does not deform.

In connection with these considerations, it can be understood that since a glossy or flat material composed of boron carbide and a metal component with superior adhesiveness has already been coated on the base material (mixed PC and ABS resin) of the cellular phone case by means of spraying, there is no problem with adhesiveness of boron carbide to the base material upon deposition of the boron carbide thereon (see U.S. Patent No. 5,750,231, 5,897,931, and 6,010,601, which disclose methods of improving adhesiveness using an intermediate layer of various metal elements).

However, as described above, since there has not yet been a case where a boron carbide coating is applied to the outer surface of a cellular phone case, there is a need for a method of producing a dense sintered material with superior reactivity and cohesion to a base material of a cellular phone case by solving the problem of difficult sintering in the prior art. Further, to meet reliability of a cellular phone case, there are needs for deposition conditions and coating methods capable of meeting reliability requirements such as conditions of creating a coating with superior scratch resistance, managing changes in color of the cellular phone case after boron carbide is coated, and the like.

Description of Drawings Fig. 1 is a graph showing variation of hardness value according to a stoichiometric composition ratio of B/C. Fig. 2 is a graph showing variation of a lattice constant according to carbon content in a crystal structure of boron carbide.

Fig. 3 is an enlarged sectional view showing a structure in which a glossy or flat spray-coating layer and a boron carbide coating layer are deposited on a surface of a cellular phone case in accordance with the present invention. Fig. 4 is a sectional view of a sputtering apparatus for forming the boron carbide coating layer on the surface of the cellular phone case in accordance with the present invention.

Fig. 5 is a graph showing results of scratch tests according to an introduction ratio of methane gas. Fig. 6 is a diagrammatic view of a pencil hardness (ASTM D3363) tester for measuring the hardness of the boron carbide coating layer.

1 : Base material 2: Spray-coating layer 3: Boron carbide coating layer 10: Sputtering apparatus 11 : DC or RF power source 12: Boron carbide target 13: Argon gas inlet

14: Methane gas inlet 15: Plasma 16: Substrate holder 17: Vacuum pump 18 : Deposition sample

19: RF bias

Disclosure of Invention

Technical Problem The present invention is conceived to solve the problems in the prior art. An object of the present invention is to provide a wear-resistant cellular phone case coated with boron carbide, wherein a boron carbide coating layer is formed by means of a sputtering method adding methane as a reactive gas on a surface of a base material (glossy or flat substrate obtained through spray coating on a mixed PC and ABS resin) of the cellular phone case, thereby improving durability due to high scratch resistance and a semipermanent adhesion property of the boron carbide coating layer.

Technical Solution The object of the present invention is achieved by a method of manufacturing a cellular phone case, comprising the steps of forming a base material composed of a mixture of PC and ABS resins; applying a spray-coating layer to a surface of the base material; and depositing a boron carbide coating layer by means of a sputtering method on the surface of the base material with the spray-coating layer applied thereto.

Preferably, the step of depositing the boron carbide coating layer comprises the steps of placing a boron carbide target within a sputtering apparatus; maintaining the interior of the sputtering apparatus in a vacuum state; introducing argon gas and a reactive gas into the sputtering apparatus; placing the base material with the spray-coating layer applied thereto within the sputtering apparatus; cleaning the base material with an RF bias; and depositing the boron carbide coating layer by means of the sputtering method on the surface of the base material with the spray-coating layer applied thereto, wherein the reactive gas is methane gas, and the methane gas is introduced into the sputtering apparatus in a range of 0.4 to 1.6% by volume.

More preferably, the inner temperature of the sputtering apparatus upon deposition of the boron carbide coating layer is not grater than 80 ^°C . Further, the spray-coating layer is formed by applying a material containing an aluminum (Al) component to the surface of the base material.

The object of the present invention is also achieved by a cellular phone case comprising a base material composed of a mixture of PC and ABS resins; a spray-coating layer applied to a surface of the base material; and a boron carbide coating layer formed on the spray-coating layer.

Preferably, the spray-coating layer contains an aluminum (Al) component. More preferably, the boron carbide coating layer is deposited by means of a sputtering method using methane gas as a reactive gas.

Further, the boron carbide coating layer has a thickness of 0.02 to 0.1 μm. Moreover, the methane gas is used in a range of 0.4 to 1.6% by volume. Advantageous Effects The present invention provides a thin film coating technique using a sputtering method in which methane (CH₄) gas is added as a reactive gas. Since the coating of the present invention has superior hardness and surface lubricity to those of the existing ceramic coating, it is applicable to various kinds of touch screens, bio fingerprint sensor devices, optical lenses and various kinds of protection coatings through the improvement of scratch resistance and durability of a cellular phone case.

Mode for Invention Hereinafter, a preferred embodiment of the present invention will be described in detail in view of its constitution with reference to the accompanying drawings.

Fig. 4 is a sectional view of a sputtering apparatus for forming a boron carbide coating layer on a surface of a cellular phone case in accordance with the present invention. A method of manufacturing a cellular phone case will be described in detail below with reference to constitutional elements of a sputtering apparatus 10.

In the method of manufacturing a cellular phone case according to the present invention, it is assumed that a boron carbide coating layer 3 is deposited by means of a sputtering method that is one of the physical vacuum deposition (PND) methods suitable for deposition of a base material 1 of the cellular phone case having a planar shape rather than a complex shape since the method has properties such as deposition at low temperature (deposition at room temperature), a coating process without discharge of pollutants, coating on a base material having a simple shape, deposition only in a region of plasma 15, a planar surface configuration, generation of various composition phases including an amorphous phase, and adaptation to a thin coating not greater than the order of μ . First, the cellular phone case of the present invention is prepared through a step of spray-coating a glossy or flat coating layer 2 on a surface of the base material 1 molded by a manufacturing apparatus.

More specifically, the base material 1 of the cellular phone case is molded by means of injection molding by pouring a slurry obtained through proper combination of PC and ABS resins into a mold for the cellular phone case and is then dried.

Then, an inner surface of the base material 1 is spray-coated with a conductive material such as aluminum (Al), silver or copper with a predetermined thickness (several dozen μm so as to shield electromagnetic waves. An outer surface of the base material 1 is spray-coated in a glossy or flat manner with metal powder containing aluminum so as to provide functions of decoration and a protection film against external environments.

Subsequently, the boron carbide coating layer 3 is deposited on the surface of the base material 1 or the spray-coating layer 2 of the cellular phone case, in order to improve the durability of the cellular phone case due to scratch resistance even through the cellular phone case is exposed to external environments by complementing a disadvantage in which a portion or corner portion of the cellular phone case exposed to the outside is partially worn and thus the spray-coating layer 2 is peeled off.

To perform deposition, a boron carbide target 12 that is a sputtering material for improving scratch resistance and adhesiveness of the cellular phone case is placed within the sputtering apparatus 10, and the interior of the sputtering apparatus is maintained in a vacuum state. At this time, the boron carbide coating layer 3 is deposited by controlling deposition time in a range of 1 hour or less at a process pressure of 1 to lOmtorr without heating the substrate.

As specific deposition conditions, a substrate holder 16 of the sputtering apparatus 10 is maintained under ultra high vacuum (10^"7torr or higher) using a vacuum pump 17, argon gas is introduced at a flow rate of 5 to 80sccm through an argon gas inlet 13 into the sputtering apparatus 10, methane gas as a reactive gas is introduced in a range of 0.4 to 1.6% by volume through a methane gas inlet 14 thereinto, and DC power 11 of 0.5 to 5.5W/cm² is then applied. Then, the base material 1 with the spray-coating layer 2 applied thereto is placed within the apparatus 10 under these conditions, and the surface of the base material 1 is cleaned using an RF bias 19.

That is, when the boron carbide coating layer 3 is deposited on the surface of the base material 1 with the spray-coating layer 2 formed thereon, the interior of the sputtering apparatus 10 is in a state where there exists the plasma 15 under an argon gas atmosphere or a hydrocarbon atmosphere having methane (CH₄) gas as a reactive gas added thereto.

Here, it is preferred that methane gas in a range of 0.4 to 1.6% by volume be used as a reactive gas (in a case where the thickness of a coating layer is 0.1 μm). This reason can be seen from results of scratch tests shown in Fig. 5. Fig. 5 shows the results of scratch tests in which cellular phone cases coated with a boron carbide coating layer having a thickness of 0.1 μm at a deposition temperature for cellular phone cases according to the present invention, i.e. room temperature, while controlling the introduction ratio of methane gas were tested using test instruments of Fig. 6. Generally, it shows that if a critical load was 3 ON or greater, superior scratch resistance was obtained. From the test results shown in Fig. 5, it can be seen that if the introduction ratio of methane gas is in the range of 0.4 to 1.6% by volume, the critical load is 30N or greater and thus superior scratch resistance is obtained. More particularly, it can be seen that at the introduction ratio of methane gas of about 0.8% by volume, the critical load is about 40N and thus scratch resistance is maximized (this means that even though the coating is subjected to a scratch force of 40N, the coating withstands the force without any damage thereto). The influence of deposition temperature on the deposition of a general boron carbide coating layer rather than the coating layer of the cellular phone case according to the present invention will be discussed with reference to Fig. 5. Even when deposition is performed at 100^°C, it can be seen that the critical load is maximized at the introduction ratio of methane gas of about 0.8% by volume. Moreover, it can be seen that if the introduction ratio of methane gas further increases to 1.2% by volume at a deposition temperature below 100^°C, the critical load decreases. On the contrary, it can be seen that at a deposition temperature of 200 °C, the critical load continuously increases along with the introduction ratio of methane gas so that the critical load can reach 32N at 1.6% by volume, thereby obtaining superior scratch resistance. After cleaning of the base material, boron carbide atoms of the target 12 are vacuum deposited on the glossy or flat coated surface under the plasma 15 that is a group of cations and electrons charged due to electrical discharge of the introduced gases, thereby forming the scratch-resistant protection coating layer.

According to the manufacturing method of the present invention described above, the glossy or flat spray-coating layer 2 and the boron carbide coating layer 3 are formed on the surface of the base material 1 of the cellular phone case. The cellular phone case with the spray-coating layer and the boron carbide coating layer and its section are shown in Fig. 3.

Here, it is preferred that the boron carbide coating layer 3 deposited on the base material 1 by means of the sputtering method be formed to have a thickness of 0,02 to 0.1 μm. Accordingly, the coating layer can be semi-permanently used while keeping high hardness without peeling thereof. The reason will be described in detail below based on the test results for the cellular phone case, according to the present invention.

Since the mixed PC and ABS resin of the base material can withstand about 80 °C, it is preferred that the inner temperature of the sputtering apparatus 10 be maintained not greater than 80 °C , more preferably at room temperature without raising the temperature of the base material 1. The reason is because the inner temperature of the sputtering apparatus 10 cannot be raised in view of the property of the base material 1. Therefore, to improve the quality of a coating layer and enhance adhesiveness at an interface, methane gas is added as a reactive gas so that carbon particles can be absorbed between aluminum particles of the spray-coating layer 2 to enhance the adhesive property at the interface. Since a crystalline phase is formed as temperature increases, the surface friction coefficient becomes better when deposition is performed at room temperature at which an amorphous phase is formed. To further enhance the adhesiveness in addition thereto, the reactive gas is controllably mixed.

In the sputtering apparatus 10 shown in Fig. 4, the substrate holder 16 is rotated and carbon particles relatively smaller than boron (B) particles are uniformly distributed in the coating layer by means of addition of the reactive gas and control of supplied power. Thus, it is possible to obtain the boron carbide coating layer 3 having strong cohesion to the base material 1 of the cellular phone case even at low (room) temperature. Further, as the density of the plasma 15 is increased, the deposition rate of the boron carbide for forming the scratch-resistant boron carbide coating layer 3 is increased so that a coating layer with higher crystallinity can be produced more rapidly.

Moreover, the introduction of methane gas as the reactive gas is employed upon control of a chemical composition of boron carbide to improve strength, durability, cohesion and the like according to the glossy or flat spray-coating layer 2. In fact, even though the target 12 of B₄C is used, there are many cases where the composition of deposited boron carbide does not have the same crystalline phase of B₄C as the target but has an amorphous phase (B₈C, B₁₂C, B₂₅C, etc.) according to the kind of a substrate material used. At this time, when a reactive gas including hydrocarbon such as methane (CEU), acetylene (C₂H₂), or ethane (C₂H₆) is introduced while the boron carbide coating layer 3 is deposited on the spray-coating layer 2, it is possible to obtain the stoichiometric crystalline phase of B₄C due to the addition of carbon that is lacking in the deposition. Next, test results for scratch resistance, transparency, color variation and the like of the cellular phone case formed with the boron carbide coating layer 3 will be described in detail.

In the tests listed in Table 2 below, cellular phone cases each of which the surface of a base material 1 of a mixed PC and ABS resin was spray-coated in a glossy or flat manner were cut into 2x2cm²to prepare samples 18. Boron carbide coating layers 3 having different thicknesses were deposited by means of a sputtering method while changing deposition time under conditions of DC power of 0.5 to 5.5W/cm², Ar flow of 5 to 80sccm and CH₄ flow of 0.8% by volume.

<Table 2> Conditions of depositing the boron carbide coating layer on the cellular phone cases for scratch resistance evaluation

The boron carbide coating layers were deposited on glossy spayed-coated surfaces of the base materials of the cellular phone cases under the conditions of Table 2. Then, variations in pencil hardness, corrosion resistance, color and the like according to the thicknesses of the coating layers were evaluated.

In a case where a silicon (Si) wafer is typically used as a substrate material and a ceramic coating layer is deposited, surface hardness may be measured using nano- indentation, and coating cohesion may be evaluated based on critical load through a scratch test. However, in these tests, since the mixed PC and ABS resin of the base material of each cellular phone case has very excellent ductility and the boron carbide coating layers can perform a sufficient protection function even below lOOnm in thickness, the hardness and adhesiveness of the coating layers were simultaneously estimated through the pencil hardness (ASTM D3363) measurement method.

To evaluate the hardness of adhesiveness of the coating layers, the samples 18 were subjected to scratch forces by pushing respective pencils from a 6B pencil with the lowest hardness to an 8H pencil with the highest hardness thereon at an angle of about 45 degrees with a predetermined load of 500g using a pencil hardness tester as shown in Fig. 6. Then, the degree of scratch was measured. According to the degree of scratch, the mechanical properties of the boron carbide coating layers 3 were evaluated qualitatively.

In the evaluation of corrosiveness, the samples 18 were immersed in an aqueous solution of NaOH (20%) and variations of configurations of the coating layers were observed and evaluated. In the measurement of transparency of back surfaces according to the thicknesses of the boron carbide coating layers 3, characters were written on the samples 18 prior to the sputtering and visibility of the characters were observed and evaluated qualitatively.

Table 3 below compares various surface properties according to the thicknesses of the boron carbide coating layers on the spray-coated surfaces of the cellular phone cases. It shows results of a comparison of Comparative example 1 (article on the market), which was a spray-coated mixed PC and ABS resin, with the boron carbide coating layers 3 having different thicknesses formed by depositing boron carbide for 2, 4 and 10 minutes on a glossy spray-coated mixed PC and ABS resin in view of pencil hardness, transparency, color, corrosiveness and the like.

<Table 3> Comparison of various surface properties according to the thicknesses of the boron carbide coating layers on the spray-coated surfaces of the cellular phone cases

In the pencil hardness, it is generally determined that if a product surface is scratched with a B pencil, it has low hardness, whereas if it is scratched with an H pencil, it has a certain degree of hardness. As the results of the measurement of the hardness of the coating layers 3 by means of the pencil hardness (ASTM D3363) measurement method, Comparative example 1 was scratched with an H pencil, Example 1 was scratched with a 4H pencil, and Examples 2 and 3 were scratched with 5H and 2H pencils, respectively. Therefore, it can be seen that the deposition of the boron carbide coating layers 3 considerably improve the hardness over the existing article on the market, and more particularly, the deposition of boron carbide in a thickness of about 60nm maximizes hardness.

From the observation results of transparency, it can be seen that the deposition time of 2 minutes (corresponding to a coating thickness of about 20nm) represented a transparency of 95%, almost similar to that of Comparative example 1, deposition time of 4 minutes (corresponding to a coating thickness of about 60nm) represented a transparency of about 90%, and deposition time of 10 minutes (corresponding to a coating thickness of about lOOnm) represented a very degraded transparency, i.e. about 70%.

In the color variations due to the deposition, both the cellular phone cases of Comparative example 1 in which glossy metal powder was spray-coated and Example 1 in which the boron carbide coating layer 3 was deposited for about 2 minutes represented silver color. Meanwhile, the cellular phone case of Example 2 in which the boron carbide coating layer 3 was deposited for about 4 minutes represented dark silver color. That is, Example 2 maintained silver color of Example 1 to a certain extent. However, the cellular phone case of Example 3 in which the boron carbide coating layer 3 was deposited for about 10 minutes to obtain a coating thickness of about lOOnm represented a brown tone including light brown. Therefore, it can be seen that Example 3 could not maintain the color of the cellular phone case prior to the deposition but was changed.

As a result of the corrosiveness evaluation, the surface of the sample 18 of Comparative example 1 was corroded within 1 minute after immersion thereof in a corrosive solution so that aluminum pieces were peeled off over the entire surface. The surfaces of the samples 18 in which the boron carbide coating layers 3 were deposited to have thicknesses of 20nm, 60nm and lOOnm, respectively, were peeled off after 3, 5 and 10 minutes, respectively. Therefore, it can be seen that corrosion resistance was improved. As described above, as a result of the property comparison of the cellular phone cases in which the boron carbide coating layers 3 were deposited under optimal conditions to have thicknesses of about 20nm (Example 1), about 60nm (Example 2) and about 100 nm (Example 3) on the surfaces of the cellular phone cases obtained by spray-coating the surface of the mixed PC and ABS resin in a glossy or flat manner, it can be seen that pencil hardness is maximized with a thickness of 60nm over the existing product, corrosion resistance is greatly improved and the transparency is degraded as the thickness of the boron carbide coating layer 3 increases, and the original color prior to the deposition of the boron carbide coating layer 3 is gradually lost.

From these test results, since any of the coating conditions exhibits superior pencil hardness or adhesiveness, it can be applicable in consideration of only scratch resistance of a cellular phone case. However, when a cellular phone case is manufactured in synthetic consideration of color and transparency in addition thereto, it is preferred that the boron carbide coating layer 3 have a thickness between 20nm and lOOnm. Particularly, it can be seen that the deposition of the boron carbide coating layer 3 controllably deposited to have a coating thickness of about 60nm can most effectively improve surface properties while maintaining the configuration of an existing product.

The boron carbide coating of the present invention obtained through the manufacturing process using the sputtering method with the added reactive gas has a wider range of deposition conditions than diamond or cubic born nitride known for high hardness, and has easy formulation of chemical compositions and superior wear resistance, surface lubricity and thermal stability. Therefore, the boron carbide coating of the present invention can be widely used as a super-hard coating for use in molds, cutting tools, magnetic heads, hard disks, and the like.

Claims

1. A method of manufacturing a cellular phone case, comprising the steps of: forming a base material (1) composed of a mixture of PC and ABS resins; applying a spray-coating layer (2) to a surface of the base material (1); and depositing a boron carbide coating layer (3) by means of a sputtering method on the surface of the base material (1) with the spray-coating layer (2) applied thereto.

2. The method as claimed in claim 1, wherein the step of depositing the boron carbide coating layer (3) comprises the steps of: placing a boron carbide target (12) within a sputtering apparatus (10); maintaining the interior of the sputtering apparatus (10) in a vacuum state; introducing argon gas and a reactive gas into the sputtering apparatus (10); placing the base material (1) with the spray-coating layer (2) applied thereto within the sputtering apparatus (10); cleaning the base material (1) with an RF bias (19); and depositing the boron carbide coating layer (3) by means of the sputtering method on the surface of the base material (1) with the spray-coating layer (2) applied thereto, wherein the reactive gas is methane gas, and the methane gas is introduced into the sputtering apparatus (10) in a range of 0.4 to 1.6% by volume.

3. The method as claimed in claim 1 or 2, wherein the inner temperature of the sputtering apparatus (10) upon deposition of the boron carbide coating layer (3) is not grater than 80 ^°C .

4. The method as claimed in claim 1 or 2, wherein the spray-coating layer (2) is formed by applying a material containing an aluminum (Al) component to the surface of the base material (1).

5. A cellular phone case, comprising: a base material (1) composed of a mixture of PC and ABS resins; a spray-coating layer (2) applied to a surface of the base material (1); and a boron carbide coating layer (3) formed on the spray-coating layer (2).

6. The cellular phone case as claimed in claim 5, wherein the spray-coating layer (2) contains an aluminum (Al) component.

7. The cellular phone case as claimed in claim 5, wherein the boron carbide coating layer (3) is deposited by means of a sputtering method using methane gas as a reactive gas.

8. The cellular phone case as claimed in claim 5 or 7, wherein the boron carbide coating layer (3) has a thickness of 0.02 to 0.1 μm.

9. The cellular phone case as claimed in claim 7, wherein the methane gas is used in a range of 0.4 to 1.6% by volume.