BACKGROUND

[0001 Electronic devices are getting smaller and lighter. Most electronic devices have a case that protects the internal electrical components. Portable electronic devices are more sensitive to the weight of the case compared to desktop devices. Many portable eiecironic devices use metal for the case to take advantage of the higher strength to weight ratio compared to plastic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a cutaway side view of an example coating.

[0003] FIG. 2 is an isometric to view of an example electronic device 200.

[0004] FIG. 3 is a flow chart for an example method of coating a metal substrate.

DETAILED DESCRIPTION

[0005] Fabricating the case for an electronic device fiom metal may decrease the weight of the case and increase its durability. Many metal cases are painted to prevent the metal from oxidizing. Unfortunately the paint covers the natural luster of the metallic finish. Even when the paint is transparent, the luster of the underlying metal surface may be dimmed. In addition, the paint may not cover defects in the sur face of the case.

[0006] In one example a two layer coating will be applied to a metai case. The bottom layer of the coating adjacent to the metal substrate will be a transparent passivation layer. Tlie top layer will be a semi-transparent metallic coating. A semi- transparent metallic coating may comprise a transparent material with metallic particles suspended within the transparent material. Some of the light striking the top semi- transparent metallic layer will reflect off the metallic particles suspended within the top layer. Some of the light striking the top semi-transparent metallic layer will penetrate through to the bottom layer. The light reaching the bottom layer will be reflected off the top surface of the metal substrate. The light reflected off the top surface of the metal substrate will exit the top semi-transparent metallic layer. Both, the light reflecting from the metallic particles in the top layer and the ligh reflecting from the top surface of the metal substrate will contribute to the appearance of the case.

[0007J Figure 1 is a cutaway side view of a example two layer coating on a metal substrate 102. The two layer coating has a top layer 106 and a bottom layer 104. The bottom layer 104 is formed on the top surface 1 14 of the metal substrate 102. The bottom layer may he a transparent passivation layer. The top layer 106 is formed on the to surface of the bottom layer 104. The top layer 106 may be a semi-transparent metallic coating. A semi-transparent metallic coating comprises a transparent material 1 16 with metallic particles 108 suspended within the transparent material. The drawings are not to scale but are drawn to show the features of the two layer coating.

[0008] The metal substrate 102 can be made from any type of metal, for example magnesium, aluminum, stee , titanium, lithium, zinc, niobium, copper, platinum, gold and the like or alloys thereof. I one example the metal substrate forms a case for an electronic device, for example a phone, a tablet, a notebook or the like. I one example, the metal case may be formed by die casting or thixomoldmg. In some examples the metal case is cleaned before the bottom layer is applied. The cleaning may be done mechanically or chemically.

[0009] The bottom layer 104 is a transparent passivation layer. The transparent passivation layer may be fabricated using transparent polymers, inorganics or hybrids. In one example the transparent passivation layer is fabricated using phosphates, manganese salts, manganese phosphate, calcium phosphate, zinc phosphate, vanadium, stannates and zirconates in combination with sol- gel precursor such as silicon efhoxide (TEOS) and other metal aikoxides. hi one example the bottom layer is fabricated using a dip coating process or a spray coating process, hi this example the thickness T2 of the bottom layer 104 is in a range between 2 and 7 micro-meters (μηι), for example 4 urn. In other examples the bottom layer may be thicker or thinner, hi one example the bottom layer is highly transparent. A highly transparent layer is a layer that is 70% or more transparent. In another example the bottom layer is transparent. A transparent layer is a layer that is at least 50% transparent. [0010] The top layer 106 is a seim-transparent metallic coating. A semi- transparent metallic coating ma coinpri.se a transparent material, for example a resin, with metallic particles suspended within the transparent material. In one example the transparent material may be a po!yaerylate resin including celluloid, polyethylene, polypropylene, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polystyrene, acrylonitrile butadiene, styrene (ABS), polycarbonate, porybutylene (PB), poly vinylidene fluoride (PVDF), fluoro-polymers, epoxies and the mixtures of the above. In one example the top layer is fabricated using a dip coating process or a spray coating process. In this example the thickness T l of the top layer 106 is less than 50 μιη. in another example thickness Tl is less than 25 μπι. In other examples the top layer may be thicker or thinner.

[0011] In this example the metallic particles may be silver, aluminum, nickel, chromium, zinc, tin or the like. In some examples the metalhc particles will all be fabricated from the same metal. In other examples the metallic particles may be fabricated from a mix of different metals. In this example the size or diameter of the metallic particles is between 2 to 3 nanometers (nm). In other examples the metallic particles may be larger or smaller, in this example the metallic particles are all

substantially the same size. In other examples the metallic particles may vary in size between a larger range of values, for example between 0.5 nm to 1 urn in size.

[0012] In one example the top layer reflects between 30% and 80% of the light.

The light is reflected by the metallic particles 108 embedded in the top layer 106 (as shown by arrows 110). In this example between 20% and 70% of the light passes through the top layer. The light that passes through the top layer also passes through the bottom layer 104 and is reflected from the to surface of the metal substrate 102 (as shown by arrows 1 12). The ratio of light reflected from the top layer compared to the amount of light reflected from the top surface of the metal substrate can be controlled by varying the concentration of metallic particles in the top layer, hi one example the concentration of metallic particles in the top layer is between 0.1% and 2%.

[0013] Because light is reflected fr om both the metallic particles in the to layer and the top surface of the metal substrate, both contribute to the brightness and luster of the metallic appearance of the finished product. Figure 2 is an isometr ic to view of an example electronic device 200. Electronic device 200 comprises a case 220 and a display

222. In one example, case 220 maybe a two part clam shell design that holds displa 222 in between the two clam shell pails. In another example case 220 may be a one part design that uses a bezel to hold display 222 into case 220. Display may be any type of display , for exampie a touch screen display.

[0014| In some examples case 220 is fabricated from metal, for example magnesium, aluminum, steel, titanium, lithium, zinc, niobium, copper, platinum, gold or the like. In this example a two layer coating is applied to the surface of case 220. The bottom layer of the coating adjacent to the metal case will be a transparent passivation layer. The top layer will be a semi-transparent metallic coating.

[0015] Figure 3 is a flow chart for an example method of coating a metal substrate.

The metal substrate could be a case for an electronic device, for example the case shown in figure 2. At 330 a first layer is applied to a top surface of the metal substrate. In one example the first layer is a transparent passivation layer. In one example the first layer may be applied to the metal substrate using a dip coating process or a spray coating process. At 332 a second layer is applied to a top surface of the first layer. In this example the second layer is a semi-transparent metallic layer. In one example the second layer may be applied using a dip coating process or a spray coating process. In some examples the metal substrate may be cleaned to remove any oxidation before the first layer is applied. The cleaning may be done mechanically or chemically.

[0016] The first layer is a transparent passivation layer. The transparent passivation layer may be fabricated using transparent polymers, inorganics or hybrids. In one example the transparent passivation layer is fabricated using phosphates, manganese salts, manganese phosphate, calcium phosphate, zinc phosphate, vanadium, stannates and zirconates in combination with sol- gel precursor such as silicon et oxide (TEOS) and other metal alkoxides. In one example the first layer is fabricated using a dip coating process or a spray coating process. In this example the thickness T2 of the first layer is in a range between 2 and 7 micro-meters (urn), for example 4 μηι. In other examples the first layer may be thicker or thinner. In one example the first layer is highly transparent. A highly transparent layer is a layer that is 70% or more transparent, in another example the first layer is transparent. A transparent layer is a layer that is at least 50% transparent. [0017] The second layer is a semi-transparent metailic coating. A semi- transparent metallic coating ma comprise a transparent material, for example a resin, with metallic particles suspended within the transparent material. In one example the transparent resin may be polyacrylaie resin including celluloid, polyethylene, polypropylene, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polystyrene, acrvionitrile butadiene styrene (ABS), polycarbonate, porybutylene (PB), poly viny idene fluoride (PVDF), iluoro-polymers, epoxies and the mixtures of the above. In one example the second layer is fabricated using a dip coating process or a spray coating process. In this example the thickness TI of the second layer is less than 50 μηι. hi another example the thickness of the second layer is less than 25 nm. In oilier examples the second layer may be thicker or thinner.

[0018] In this example the metallic particles may be silver, alumiiimn, nickel, chromium, zinc, tin or the like. In some examples the metallic particles will all be fabricated from the same metal. In other examples the metallic particles may be fabricated from a mix of different metals. In this example the size or diameter of the metallic particles is between 2 to 3 nanometers (nm). In other examples the metallic particles may be larger or smaller, in this example the metallic particles are ail

substantially the same size. In other examples the metallic particles may vary in size between a larger range of values, for example between 0.5 ma to 1 um in size.

[0019] In one example the second layer reflects between 30% and 80% of the light. The light is reflected by the metallic particles embedded in the second layer. In this example between 20% and 70% of the light passes through the second layer. The light that passes through the second layer also passes through the first layer and is reflected from the top surface of the metal substrate.