Abstract:
An exemplary multi-layer film includes a light absorbing layer, a number of metallic layers formed on the light absorbing layer, and a number of transparent medium layers each sandwiched between two respective adjacent of the metallic layers. Each of the metallic layers is configured for reflecting part of light incident thereon to be a reflected light and transmitting another part of the incident light therethrough. The light absorbing layer is capable of absorbing light incident thereon. The medium layers are configured for controlling light path differences between the reflected lights thereby allowing the reflected lights to interfere with each other and provide the multi-layer film with a desired color appearance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to commonly-assigned co-pending applications entitled, “MULTI-LAYER FILM STRUCTURE WITH MEDIUM LAYER,” (Atty. Docket No. US24328), and “MULTI-LAYER FILM AND ELECTRONIC DEVICE SHELL WITH SAME,” (Atty. Docket No. US24274). The above-identified applications are filed simultaneously with the present application. The disclosures of the above-identified applications are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to multi-layer films, and particularly, to a colored multi-layer film, and an electronic device shell coated with the multi-layer film. 
         [0004]    2. Description of Related Art 
         [0005]    Colored shells are widely used in electronic devices, such as mobile phones. Currently, the coloration of such shells is usually produced by painting. However, many paints are not environmentally friendly. For example, some paints or by-products thereof can be harmful to humans. Furthermore, many painted surfaces are not wear-resistant and are easily scratched. 
         [0006]    What is needed, therefore, is a film and an electronic device shell coated with the film, which can overcome the above-described shortcomings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of the present multi-layer film and electronic device shell can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present multi-layer film and electronic device shell. Moreover, in the drawings, all the views are schematic, and like reference numerals designate corresponding parts throughout the views. 
           [0008]      FIG. 1  is a cross-sectional view of a multi-layer film formed on a substrate in accordance with a first embodiment. 
           [0009]      FIG. 2  is a cross-sectional view of a multi-layer film formed on a substrate in accordance with a second embodiment. 
           [0010]      FIG. 3  is a cross-sectional view of an electronic device shell in accordance with a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0011]    Various embodiments of the present multi-layer film and electronic device shell will now be described in detail below and with reference to the drawings. In this description, unless the context indicates otherwise, a reference to “light” includes a reference to a light beam or light beams. 
         [0012]    Referring to  FIG. 1 , an exemplary multi-layer film  100  in accordance with a first embodiment is shown. The multi-layer film  100  includes in sequence a first metallic layer  120 , a first medium layer  130 , a second metallic layer  140 , a second medium layer  150 , a third metallic layer  160 , and a light absorbing layer  170 . The first metallic layer  120 , first medium layer  130 , second metallic layer  140 , second medium layer  150 , third metallic layer  160  and the light absorbing layer  170  have top surfaces and bottom surfaces parallel to each other. The light absorbing layer  170  is configured to cling (adhere) to a surface  11  of a substrate  10 . In this description, the combination of the multi-layer film  100  and the substrate  10  is referred to as a “multi-layer film structure.” 
         [0013]    The first metallic layer  120 , the second metallic layer  140 , and the third metallic layer  160  each contain a material selected from a group consisting of aluminum, nickel, chromium, and alloy of nickel and chromium. Preferably, the first metallic layer  120 , the second metallic layer  140 , and the third metallic layer  160  are made of the same material, and thus have the same reflection capability and refraction capability. A thickness of each of the first metallic layer  120 , the second metallic layer  140  and the third metallic layer  160  is in a range from 0.3 nanometers (nm) to 200 nm. The first metallic layer  120  is capable of reflecting part of incident light (e.g., visible light which includes red, orange, yellow, green, blue, indigo and violet lightwaves) to be a first reflected light L 1 , and allowing another part of the incident light to transmit therethrough. The second metallic layer  140  is capable of reflecting part of the transmitted light to be a second reflected light L 2 , and allowing another part of the transmitted light to transmit therethrough. The third metallic layer  160  is capable of reflecting at least part of the transmitted light to be a third reflected light L 3 . The light absorbing layer  170  is capable of absorbing any light that is transmitted from the third metallic layer  160 . The first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3  are fundamentally derived from a same incident light on the multi-layer film  100 , and thus have the possibility of interfering with each other. Due to the material of the first metallic layer  120 , the second metallic layer  140  and the third metallic layer  160  being the same, the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3  have almost the same vibration direction, thus facilitating any such interference. The higher the reflection capability of the material of the first, second and third metallic layers  120 ,  140 ,  160 , the higher the intensity of the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3 . 
         [0014]    The first medium layer  130  is sandwiched between the first metallic layer  120  and the second metallic layer  140 . The second medium layer  150  is sandwiched between the second metallic layer  140  and the third metallic layer  160 . Each of the first medium layer  130  and the second medium layer  150  is transparent, and each contains a material selected from a group consisting of silicon dioxide (SiO 2 ), titanium oxide (TiO 2 ), niobium pentoxide (Nb 2 O 5 ), aluminum oxide (Al 2 O 3 ), and magnesium fluoride (MgF 2 ). In certain embodiments, each of the first medium layer  130  and the second medium layer  150  is made of the material selected from the group consisting of SiO 2 , TiO 2 , Nb 2 O 5 , Al 2 O 3 , and MgF 2 . A thickness of each of the first medium layer  130  and the second medium layer  150  can be in a range from 50 nm to 1000 nm. The thickness of the first medium layer  130  impacts a light path difference between the first reflected light L 1  and the second reflected light L 2 . The thickness of the second medium layer  150  impacts a light path difference between the second reflected light L 2  and the third reflected light L 3 . With this configuration, the first medium layer  130  and the second medium layer  150  control light path differences between the first reflected light L 1 , the second reflected light L 2 , and the third reflected light L 3 , such that the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3  interfere with each other on the multi-layer film  100  to produce a desired color appearance of the multi-layer film  100 . 
         [0015]    When the light path difference between any two of the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3  is an even multiple of half of a central wavelength of a particular color lightwave of the visible light, that color lightwave is enhanced. Under this condition, the multi-layer film  100  (and also the entire multi-layer film structure) appears to have a color substantially that of a mixture of the enhanced color lightwaves produced by the interferences between the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3 . In one example, among the color lightwaves of visible light, i.e., red, orange, yellow, green, blue, indigo and violet, two of these color lightwaves may be enhanced in interferences between each two of the first reflected light L 1 , the second reflected light L 2  and the third reflected light L 3 . For instance, red and green lightwaves may both be enhanced. In such example, the interferences give the multi-layer film  100  a color appearance comprised of a mixture of red and green; i.e., yellow. 
         [0016]    In an alternative embodiment, the third metallic layer  160  can be configured to transmit little or no light therethrough. That is, the third metallic layer  160  can have very high reflectivity or be a total reflection layer. In such case, the light absorbing layer  170  can be omitted. 
         [0017]    Referring to  FIG. 2 , an exemplary multi-layer film  200  in accordance with a second embodiment is shown. The multi-layer film  200  is similar in principle to the multi-layer film  100  described above. However, the multi-layer film  200  includes in sequence a first metallic layer  210 , a first medium layer  220 , a second metallic layer  230 , a second medium layer  240 , a third metallic layer  250 , a third medium layer  270 , a fourth metallic layer  280 , and a light absorbing layer  260 . The first metallic layer  210 , the second metallic layer  230 , the third metallic layer  250  and the fourth metallic layer  280  are capable of reflecting incident light and allowing another part of the incident light to transmit therethrough to produce a first reflected light L 21 , a second reflected light L 22 , a third reflected light L 23 , and a fourth reflected light L 24 , respectively. Interferences occur between the first reflected light L 21 , the second reflected light L 22 , the third reflected light L 23  and the fourth reflected light L 24  to produce a desired color appearance of the multi-layer film  200 . 
         [0018]    Referring to  FIG. 3 , a shell  300  of an electronic device  310  is provided as an exemplary embodiment of an application environment of a multi-layer film  330 . The shell  300  includes an enclosure  320  configured as a substrate, and the multi-layer film  330  formed on the enclosure  320 . In the illustrated embodiment, the multi-layer film  330  includes in sequence from outside to inside a first metallic layer  331 , a first medium layer  332 , a second metallic layer  333 , a second medium layer  334 , a third medium layer  335  and a light absorbing layer  336 . The multi-layer film  330  is configured to give the shell  300  a desired color appearance. 
         [0019]    It is understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.