WO2020219061A1

WO2020219061A1 - Electronic device housings with chamfered edges

Info

Publication number: WO2020219061A1
Application number: PCT/US2019/029252
Authority: WO
Inventors: Kuan-Ting Wu; Cheng-Feng Liao; Chi-Hao Chang
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2019-04-26
Filing date: 2019-04-26
Publication date: 2020-10-29
Anticipated expiration: 2021-10-26
Also published as: TW202041123A; TWI718869B

Abstract

In one example, an electronic device housing may include a metal substrate having a peripheral edge and a non-metal layer formed on a first side of the metal substrate. The first side of the metal substrate facing an interior of the electronic device housing. Further, the electronic device housing may further include a paint coating formed on the non-metal layer. Furthermore, the electronic device housing may include an oxide layer formed on a second side of the metal substrate. The second side of the metal substrate facing an exterior of the electronic device housing. Also, the electronic device housing may include a chamfer formed on the peripheral edge of the metal substrate and a transparent protective passivation layer formed on the chamfer.

Description

ELECTRONIC DEVICE HOUSINGS WITH CHAMFERED EDGES

BACKGROUND

[0001] In recent years, metal housings with lightweight and high rigidity properties have become popular since the portable electronic products are developed to be lighter arid smaller. In such requirements, the technology of composite material that combines metal housings with plastic members or carbon liber members has become a focus in the industry. Composite materials may refer to materials made from two or more constituent materials with different physical properties. The resultant housings with tee composite materials may have high strength and low density.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Examples are described in tee following detailed description and in reference to the drawings, in which:

[0003] FIG, 1A illustrates a cross-sectional side view of an example electronic device housing, depicting a transparent protective passivation layer on a chamfer,

[0004] FIG. 1B illustrates the cross-sectional side view of the example electronic device housing of FIG. 1 A, depicting additional features;

[0005] FIG. 1C illustrates a top view of the example electronic device housing of FIG. 1 A, depicting the chamfer;

[0006] FIG. 2 illustrates an example flowchart for making a cover for an electronic device;

[0007] FIG. 3 illustrates another example flowchart for manufacturing an electronic device housing; [0008] RGs. 4 and 5 illustrate example processes for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-plastic composite frame; and

[0009] FIGs. 6 and 7 illustrate example processes for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-carbon fiber composite frame.

DETAILED DESCRIPTION

[0010] Housings for electronic devices such as mobile phones, laptop computers, music players, personal digital assistants, global positioning system devices, and the like can be made by plastic or metal. Metal housings have a better mechanical strength, but are electrically conductive, which may weaken the communication signals. Plastic housings are non-conductive, but lack mechanical strength. Some housings may have composite materials such as a combination of plastic material and metal. For example, a housing may include a plastic layer and a metal layer assembled together as a whole to achieve both good communication and mechanical strength. For instance, an outer layer of a housing portion may be formed by a metal layer, which may be supported by an inner plastic layer. The outer metal layer may provide a wear resistant, robust, and aesthetic appearance to the housing.

[0011] Example metal layer may be a magnesium or magnesium alloy layer.

Because of the light weight and high mechanical strength, magnesium alloys are suitably used in housings for electronic devices. However, the magnesium alloy layer may have poor color stability, hardness, and chemical resistance. Therefore, it may be difficult to fabricate metallic luster feeling at peripheral edge surfaces of the magnesium alloy housings as the magnesium alloys can be oxidized on the surface.

[0012] Examples described herein may provide an electronic device housing including a composite material such as a combination of a metal substrate and a non-metal layer (e.g., a plastic layer or a carbon fiber composite layer). The metal substrate may have a peripheral edge. Further, the electronic device housing may include a paint coating formed on the non-metal layer and an oxide layer formed on the metal substrate. The electronic device housing may include a chamfer formed on the peripheral edge of the metal substrate. The electronic device housing may further include a transparent protective passivation layer formed on the chamfer. Also, the electronic device housing may indude an electrophoretic deposition layer formed on the transparent protective passivation layer and the oxide layer. The transparent protective passivation layer and the electrophoretic deposition layer thus formed on the chamfer can pass 96 hours salt fog test.

[0013] Examples described herein may provide metallic fostering chamfer cosmetic surface at the peripheral edge of plastic-metal alloy housings and carbon- fiber composite-metal alloy housings. Examples described herein may enhance the mechanical strength (i.e., stiffness) of the plastic or carbon-fiber composite enclosures through combining with magnesium alloy layers. Examples described herein may provide a lighter and stronger metal-plastic composite structures or metal-carbon fiber composite structures.

[0014] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present techniques. It will be apparent, however, to one skilled in the art that the present apparatus, devices and systems may be practiced without these specific details. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described is included in at least that one example, but not necessarily in other examples.

[0015] Turning now to the figures, FIG. 1 A illustrates a cross-sectional side view of an example electronic device housing, depicting a transparent protective passivation layer 112 on a chamfer 110. Example electronic device housing 100 may indude a smart phone housing, tablet or notebook personal computer housing, digital camera housing, or the like.

[0016] Example electronic device housing 100 may include a metal substrate 102 having a peripheral edge 114. Example metal substrate 102 may include aluminium, magnesium, aluminium alloy, magnesium alloy, or any combination thereof. Electronic device housing 100 may include a non-metal layer 104 formed on a first side of metal substrate 102. The first side of metal substrate 102 may face an interior ofelectronic device housing 100. Example non-metal layer may include plastic, carbon fiber composite, or a combination thereof.

[0017] Further, electronic device housing 100 may include a paint coating

106 formed on non-metal layer 104. Example paint coating 106 is explained with respect to FIG. 1B. Furthermore, electronic device housing 100 may indude an oxide layer 108 formed on a second side of metal substrate 102. The second side

Of metal substrate 102 may face an exterior of electronic device housing 100. For example, oxide layer 108 may be a micro-arc oxidized layer or a passivation layer.

[0018] Furthermore, electronic device housing 100 may include chamfer

110 formed on peripheral edge 114 of metal substrate 102. In one example, chamfer 110 may be formed on side walls of metal substrate 102. Further, chamfer 110 can have any suitable shape (e.g., chamfer, round, ogee, or the like), thus giving peripheral edge 114 (i.e., an outer periphery) of metal substrate 102 any suitable cross-sectional shape. Chamfer 110 may be aesthetically and tactilely pleasing feature for electronic device housing 100.

[0019] Further, electronic device housing 100 may include transparent protective passivation layer 112 formed on chamfer 110. Example transparent protective passivation layer 112 may include a complex of a metal ion and a chelatin Example chelating agent may indude ethylenediaminetetraacetic add (EDTA), ethylenediamine, nitrilotriacetic acid (NTA), diethylenetriaminepenta(methyienephosphonic acid) (DTPPH), nitrilotris(methylenephosphonic add) (NTMP), 1 -hydroxyethane-1 ,1 -diphosphonic acid (HEDP), sulfuric add, phosphoric add, or any combination thereof. Example metal ion may be aluminum ion, nickel ion, tin ion, indium ion, chromium ion, zinc ion, or any combination. In one example, transparent protective passivation layer 112 may have a thickness in a range of 30 nm to 3 mm.

[0020] FIG. 1 B illustrates the cross-sectional side view of example electronic device housing 100 of FIG. 1A, depicting additional features. FIG. 10 illustrates a top view of example electronic device housing 100 of FIG. 1A, depicting chamfer 110 (i.e., a chamfered edge). For example, similarly named elements of FIGs. 1B and 1C may be similar in structure and/or function to elements described With respect to FIG. 1A. Chamfer 100 may be formed in an outwardly curved shape or in an inwardly curved shape at a boundary portion of metal substrate 102. As shown in FIG. 1B, electronic device housing 100 may include an electrophoretic deposition layer 152 formed on transparent protective passivation layer 112 and Oxide layer 108. Example electrophoretic deposition layer 152 may include polymer, such as polyacrylic polymer or epoxy polymer, in combination with inorganic and/or metallic particles. In one example, electrophoretic deposition layer 152 may have a thickness in a range of 5 - 40 mm.

[0021] In the example shown in FIG. 1B, paint coating 106 may include a primer coat 154 formed on a surface of non-metal layer 104. Example primer coat 154 may include polyurethane. In one example, primer coat 154 may have a thickness in a range of 5-20 mm. Further, paint coating 106 may indude a base coat 156 formed on primer coat 154. Example base coat 156 may indude polyurethane in combination with at least one pigment selected from a group consisting of carbon black, titanium dioxide, day, mica, talc, barium sulfate, calcium carbonate, synthetic pigment, metallic powder, aluminum oxide, an organic powder, an inorganic powder, plastic bead, color pigments, and dyes. In one example, base coat 156 may have a thickness in a range of 10-20 mm. [0022] Furthermore, paint coating 108 may indude an ultraviolet top coat

158 formed on base coat 156. Example ultraviolet top coat 158 may include polyacrylic, polyurethane, urethane acrylates, acrylic acrylates, epoxy acrylates, or any combination thereof. In one example, ultraviolet top coat 158 may have a thickness in a range of 10-25 mm. For example, ultraviolet top coat 158 may be a clear polyurethane top coat and can be formed by thermal curing at 60-80°C.

[0023] In the example shown in FIG. 1B, oxide layer 108 may be formed on the second side of metal substrate 102, transparent protective passivation layer 112 may be formed on chamfer 110 along peripheral edge 114, and electrophoretic deposition layer 152 may be formed on transparent protective passivation layer 112 and oxide layer 108. Transparent protective passivation layer 112 and electrophoretic deposition layer 152 thus formed on chamfer 110 can pass 96 hours salt fog test. Further, transparent protective passivation layer 112 and electrophoretic deposition layer 152 on chamfer 110 may provide a shiny, flat, and smooth metallic appearance for peripheral edge 114. Thus, peripheral edge 114 induding chamfer 110 may provide an aesthetically appealing appearance for electronic device housing 100.

[0024] FIG. 2 illustrates an example flowchart 200 for malting a cover for an electronic device. Example cover may be a part of a display housing that houses a display, a keyboard housing that houses a keyboard, or a combination thereof. At 202, a paint coating may be applied on a surface of a composite metal substrate. Example composite metal substrate may be a metal-plastic composite substrate or a metal-carbon fiber composite substrate. Example metal may include aluminum, magnesium, aluminum alloy, magnesium alloy, or any combination thereof. An example for applying the paint coating is explained in FIG. 3.

[0025] At 204, a peripheral edge of the composite metal substrate may be chamfered to form an exposed surface portion of the composite metal substrate. After the chamfer is formed on the peripheral edge, the metal substrate may be exposed to one or more additional finishing processes such as transparent passivation treatment and electrophoretic deposition. At 206, a transparent passivation treatment may be applied on the exposed surface portion of tee peripheral edge to form a transparent protective passivation layer. In one example, tee transparent passivation treatment may be applied by applying a passivation solution comprising a complex of a metal ion and a chelating agent on the exposed surface portion. Further, ah electrophoretic deposition may be applied on the composite metal substrate induding the transparent protective passivation layer.

[0026] FIG. 3 illustrates another example flowchart 300 for manufacturing an electronic device housing. Example electronic device housing may tie a display housing, a keyboard housing, or any combination thereof. At 302, a non-metal layer may be formed on a first side of a metal substrate. The first side of the metal substrate may face an interior of the electronic device housing, in one example, the non-metal layer may include plastic. In this example, a plastic layer may be formed on the first side of the metal substrate using an insert molding process. Example plastic layer may include at least one material selected from a group consisting of polyacrylonitrile, polyethylene, polypropylene, polystyrene, polyvinylacetate, poly(meth)acrylate, polyvinylchloride, fluoropolymer, chlorinated polyether, polyurethane, polyamide, polycarbonate, polyester, polyimide, polyphthalamide, polyphenylene sulfide, and poiysulphone. In another example, tee non-metal layer may include carbon fiber composite. In this example, a carbon fiber composite layer may be formed on the surface of the metal substrate using a compression molding process.

[0027] At 304, an oxide layer may be formed on a second side of the metal substrate. The second side of the metal substrate may face an exterior of tee electronic device housing. Example metal substrate may include aluminum, magnesium, aluminum alloy, magnesium alloy, or any combination thereof. In other examples, the metal substrate can indude lithium, zinc, titanium, lithium alloy, zinc alloy, titanium alloy, or combinations thereof. In one example, tee oxide layer is farmed on the second side of the metal substrate by applying one of a micro-arc oxidation process and a passivation treatment, which can be electrochemical surface treatment processes for generating oxide coatings on metals.

[0028] For example, the micro-arc oxidation process may refer to a process for generating oxide coatings on the metal substrate. During the microarc oxidation process, the metal substrate may be placed in an electrolytic solution including electrolytes selected from a group consisting of sodium silicate, sodium phosphate, potassium fluoride, potassium hydroxide, sodium hydroxide, fluorozirconate, sodium hexametaphosphate, sodium fluoride, aluminum oxide, silicon dioxide, ferric ammonium oxalate, phosphoric add salt₎ and polyethylene oxide alkylphenolic ether. The electrolyte may be present in a concentration of 0.05 to 15% by weight based on the total weight of the electrolytic solution and a voltage in the range of 200-600 V may be passed across the electrolytic solution with the metal substrate (e.g., magnesium alloy substrate) placed in the electrolytic solution to form a micro-arc oxidized layer (i.e., the oxide layer). In one example, the voltage may be applied for about 3 to 20 minutes and the micro-arc oxidation process can be carried out at a temperature between room temperature and 45° C. The thickness of the micro-arc oxide layer can be in the range of 3-15 pm. The micro- arc oxidation properties may indude wearing resistance, corrosion resistance, high hardness, arid electrical insulation.

[0029] Similarly, passivation treatment may refer to the process of treating or coating the metal substrate to reduce the chemical reactivity of a surface of the metal substrate. For example, the passivation treatment may involve creation of an outer layer of shield material around the metal substrate to make the metal substrate "passive", i.e., less affected or corroded by the environment. The non- metal layer may cover substantially the entire first side of the metal substrate so that after performing micro-arc oxidation or passivation treatment, the first side may not be covered with the oxide layer.

[0030] At 306, a paint coating may be applied on the non-metal layer. In one example, applying the paint coating on the non-metal layer may indude applying a primer coat on a surface of the non-metal layer, applying a base coat on the prirher coat, and applying an ultraviolet top coat on the base coat.

[0031] For example, applying the primer coat on the surface of the non- metal layer may include applying polyurethane mixture on the surface of the nonmetal layer, and subsequently drying the polyurethane mixture at a temperature of 60-80° C for about 15-40 minutes. The primer coat may have a thickness in a range of 5-20 mm.

[0032] Further, applying the base coat on the primer coat may include applying a mixture of polyurethane in combination with at feast one pigment selected from a group consisting of carbon black, titanium dioxide, day, mica, talc, barium sulfate, calcium carbonate, synthetic pigment, metallic powder, aluminum oxide, an organic powder, an inorganic powder, plastic bead, color pigments, and dyes, and subsequently drying the mixture at a temperature of 60-80° C for about 15-40 minutes. The base coat may have a thickness in a range of 10-20 mm.

[0033] Furthermore, applying the ultraviolet top coat on the base coat may include applying a mixture selected from the group consisting of polyacrylic, polyurethane, urethane acrylates, acrylic acrylates, and epoxy acrylates, and subsequently drying the mixture at a temperature of 50-60° C for about 10-15 minutes followed by ultraviolet exposure in a range between 700-1,200 mJ/cm2 for 10-30 seconds. The ultraviolet top coat may have a thickness in a range of 10-25 mm.

[0034] At 308, a peripheral edge of the metal substrate may be chamfered to form an exposed surface portion of the metal substrate. In one example, the peripheral edge may be chamfered using a computer numerical control (CNG) machining, a laser engraving process, or the like. At 310, a transparent protective passivation layer may be formed on fee exposed surface portion of the peripheral edge. In one example, the transparent protective passivation layer may be formed on the exposed surface portion by applying a passivation solution comprising a complex of a metal ion and a chelating agent. Example metal ion and chelating agent is explained in FIG. 1A. The transparent protective passivation layer may prevent corrosion of the metal substrate exposed through the exposed surface portion.

[0035] Further, an electrophoretic deposition layer may be formed on the transparent protective passivation layer and the oxide layer by applying electrophoretic deposition. Electrophoretic deposition may be a process in which the metai substrate is placed in a fluid and a potential difference is applied to cause charged particles in the fluid to be deposited on the metal substrate. Electrophoretic deposition may be used to impart certain desired properties, such as hardness or toughness, or a certain desired appearance to the substrate. The paint coating may cover substantially a first surface of the non-metal layer so that after performing transparent passivation treatment or electrophoretic deposition, tine first surface may not be covered with the transparent protective passivation layer or the electrophoretic deposition layer.

[0036] FIG. 4 illustrates an example process 400 for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-plastic composite frame. At 402, a metal alloy frame may be pr -formed. For example, preforming the metal alloy frame may include forging, die casting, or CNC machining the metal substrate into a desired shape and then cleaning the forged, die casted, or CNC machined metal alloy frame. The cleaning of the metal substrate includes a pre-cleaning process, such as an alkaline cleaning process, degreasing cleaning process, an acidic cleaning process, or any combination thereof.

[0037] At 404, a plastic layer rhay be formed on one side of the metal substrate using an insert molding process. Insert molding may refer to a process in which plastic is injected into a moid that contains the pre-placed metal substrate. At 406, the plastic layer may be trimmed to remove extra plastic material that extends beyond the metal substrate to obtain a desired shape. At 408, a passivation treatment may be applied on another side of the metal substrate including a peripheral edge. At 410, a paint coating may be formed on the plastic layer. Example paint coating may be explained in FIG. 3.

[0038] At 412, the peripheral edge of the metal substrate may be chamfered to form an exposed surface portion of the metal substrate. At 414, a transparent protective passivation layer may be formed on the exposed surface portion of the peripheral edge, At 416, an electrophoretic deposition layer may be formed on the transparent protective passivation layer and the oxide layer by applying electrophoretic deposition. The electrophoretic deposition may include a polymer in combination with particles selected from the group comprising inorganic and metallic particles.

[0039] FIG. 5 illustrates another example process 500 for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-plastic composite frame. At 502, a metal alloy frame may be pre-formed.

[0040] At 504, a plastic layer may be formed on one side of the metal substrate using an insert molding process. At 506, the plastic layer may be trimmed to remove extra plastic material to obtain a desired shape. At 508, a micro-arc oxidation may be applied on another side of the metal substrate including a peripheral edge. At 510, a paint coating may be formed on the plastic layer.

[0041] At 512, the peripheral edge of the metal substrate may be chamfered to form an exposed surface portion of the metal substrate. At 514, a transparent protective passivation layer may be formed on the exposed surface portion of the peripheral edge. At 516, an electrophoretic deposition layer may be formed on the transparent protective passivation layer and the oxide layer by applying electrophoretic deposition. [0042] FIG. 6 illustrates an example process 600 for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-carbon fiber composite frame.

[0043] At 602, a metal alloy frame may be pr -formed. At 604, a carbon fiber composite layer may be formed on one side of the metal substrate using a compression molding process. The carbon fiber composite layer may be directly adhered to the metal substrate using the compression molding process. Compression molding may refer to a forming process in which carbon fiber composite material can be placed directly into a heated metal mold, softened by the heat, and then forced to conform to the shape of the mold, as the mold closes.

[0044] At 606, the carbon fiber composite layer may be trimmed to remove extra carbon fiber composite material (i.e., unwanted portions) to obtain a desired shape. At 608, a passivation treatment may be applied on another side of the metal substrate including a peripheral edge. At 610, a paint coating may be formed on the carbon fiber composite layer. Example paint coating may be explained in FIG.

3.

[0045] At 612, the peripheral edge of the metal substrate may he chamfered to form an exposed surface portion of the metal substrate. At 614, a transparent protective passivation layer may be formed on the exposed surface portion of the peripheral edge by applying transparent passivation treatment. At 616, an electrophoretic deposition layer may be formed on the transparent protective passivation layer and the oxide layer by applying electrophoretic deposition.

[0046] FIG. 7 illustrates another example process 700 for forming a transparent protective passivation layer and an electrophoretic deposition layer on a chamfered surface of a peripheral edge of a metal-carbon fiber composite frame. At 702, a metal alloy frame may be pr -formed. [0047] At 704, a carbon fiber composite layer may be formed on one side of the metal substrate using a compression molding process. At 706, the carbon fiber composite layer may be trimmed to remove extra carbon fiber composite material (i.e., unwanted portions) to obtain a desired shape. At 708, a micro-arc oxidation may be applied on another side of the metal substrate including a peripheral edge. At 710, a paint coating may be formed on the carbon fiber composite layer.

[0048] At 712, the peripheral edge of the metal substrate may be chamfered to form an exposed surface portion of the metal substrate. At 714, a transparent protective passivation layer may be formed on the exposed surface portion of the peripheral edge. At 716, an electrophoretic deposition layer may be formed on the transparent protective passivation layer and the oxide layer by applying electrophoretic deposition.

[0049] In this manner, the present application discloses a metal-plastic cdriniposite housing or metal-carbon fiber composite housing, in which metallic luster feeling can be obtained at peripheral edge surfaces of the metal alloy housings.

[0050] The foregoing describes metal-plastic composite housing or metal· carbon fiber composite housing having metallic luster feeling at peripheral edge surfaces. While tire above application has been shown and described with reference to the foregoing examples, it should be understood that other forms, details, and implementations may be made without departing from the spirit and scope of this application.

Claims

WHAT IS CLAIMED IS:

1. An electronic device housing comprising:

a metal substrate having a peripheral edge;

a non-metal layer formed on a first side of the metal substrate, the first side of the metal substrate facing an interior of the electronic device housing; a paint coating formed on the non-metal layer;

an oxide layer formed on a second side of the metal substrate, the second side of the metal substrate facing an exterior of the electronic device housing; a chamfer formed on the peripheral edge of the metal substrate; and a transparent protective passivation layer formed on the chamfer.

2, The electronic device housing of claim 1 , further comprising:

an electrophoretic deposition layer formed on the transparent protective passivation layer and the oxide layer.

3. The electronic device housing of claim 1 , wherein the metal substrate comprises aluminium, magnesium, aluminium alloy, magnesium alloy, or any combination thereof.

4. The electronic device housing of claim 1 , wherein the non-metal layer comprises plastic, carbon fiber composite, or a combination thereof.

5. The electronic device housing of claim 1 , wherein the paint coating comprises:

a primer coat formed on a surface of the non-metal layer;

a base coat formed on the primer coat; and

an ultraviolet top coat formed on the base coat.

6. The electronic device housing of claim 1 , wherein the transparent protective passivation layer comprises a complex of a metal ion and a chelating agent

7. The electronic device housing of claim 6, wherein the chelating agent comprises ethylenediaminetetraacetic add (EDTA), ethylenediamine, nitrilotriacetic acid (NTA), diethylenetriaminepenta(methylenephosphonic add) (DTPPH), nitrilotris(methylenephosphonic add) (NTMP), 1-hydroxyethane-1,1- diphosphonic acid (HEDP), sulfuric add, phosphoric add, or any combination thereof.

8. A method of making a easing for an electronic device, the method comprising:

applying a paint coating on a surface of a composite metal substrate;

chamfering a peripheral edge Of the composite metal substrate to form an exposed surface portion of the composite metal substrate; end

applying a transparent passivation treatment on the exposed surface portion of the peripheral edge to form a transparent protective passivation layer.

9. The method of claim 8, further comprising:

applying an electrophoretic deposition on the composite metal substrate including the transparent protective passivation layer.

10. The method of claim 8, wherein applying the transparent passivation treatment comprises applying a passivation solution comprising a complex of a metal ion and a chelating agent on the exposed surface portion.

11. A method for manufacturing an electronic device housing, comprising: forming a non-metal layer on a first side of a metal substrate, the first side of the metal substrate facing an interior of the electronic device housing;

forming an oxide layer on a second side of the metal substrate, the second side of the metal substrate facing an exterior of the electronic device housing; applying a paint coating on the non-metal layer;

chamfering a peripheral edge of the metal substrate to form an exposed surface portion of the metal substrate; and forming a transparent protective passivation layer on the exposed surface portion of the peripheral edge.

12. The method of claim 11 , wherein applying the paint coating on the non- metal layer comprises:

applying a primer coat oh a surface of the non-metal layer;

applying a base coat on the primer coat; and

applying an ultraviolet top coat on the base coat.

13. The method of claim 11 , further comprising:

forming an electrophoretic deposition layer cm the transparent protective passivation layer and the oxide layer.

14. The method of claim 11 , wherein the oxide layer is formed on the second side of the metal substrate by applying one of a micro-arc oxidation process and a passivation treatment.

15. The method of claim 11 , wherein the transparent protective passivation layer is formed on the exposed surface portion by applying a passivation solution comprising a complex of a metal ion and a chelating agent