PATENT DOCUMENT

Publication Number: US-9808829-B2
Application Number: US-201514846269-A
Country: US
Kind Code: B2

Title: Methods for applying a coating over laser marking

Abstract:
Coatings for filling cracks within anodic films formed from, for example, a laser marking process are described. The cracks generally have widths of nanometers in scale and can extend from an external surface of an anodic film to an underlying metal substrate. The coatings fill the cracks to prevent liquid and contaminants from entering the cracks and reaching the metal substrate, thereby preventing corrosion of the underlying metal substrate. The coatings can be hydrophobic such that water is wicked away from the cracks. In some cases, the coatings are fluoropolymer coatings. Methods include spray-on techniques that provide a thin and uniform layer of the coating. The spray-on technique can be configured to spray on a fluoropolymer precursor onto the anodic film such that the fluoropolymer precursor diffuses into and polymerizes into the fluoropolymer coating within the cracks.

Claims:
What is claimed is: 
     
       1. An enclosure for an electronic device, the enclosure comprising:
 a metal substrate; 
 an anodic film disposed upon the metal substrate, the anodic film having a channel that extends from an external surface of the anodic film to a transition region of the anodic film and the metal substrate; and 
 a polymerized hydrophobic material that coats the channel providing a moisture resistant barrier that prevents moisture ingress into the metal substrate, wherein the polymerized hydrophobic material includes a fluoropolymer. 
 
     
     
       2. The enclosure of  claim 1 , wherein the external surface of the anodic film includes the polymerized hydrophobic material. 
     
     
       3. The enclosure of  claim 1 , wherein the polymerized hydrophobic material that coats the channel has a generally uniform thickness. 
     
     
       4. The enclosure of  claim 1 , wherein the polymerized hydrophobic material has a thickness ranging from about 5 nanometers to about 20 nanometers. 
     
     
       5. The enclosure of  claim 1 , wherein the channel is positioned within the anodic film proximate to a laser marked region of the enclosure. 
     
     
       6. The enclosure of  claim 1 , wherein the anodic film includes first and second anodic film portions that are separated from each other by an opening that is positioned disposed at an edge of the metal substrate. 
     
     
       7. The enclosure of  claim 1 , wherein the enclosure further comprises:
 a non-metal portion adjacent to the metal substrate, wherein the polymerized hydrophobic material covers the external surface of the anodic film and the non-metal portion. 
 
     
     
       8. The enclosure of  claim 1 , wherein the metal substrate includes an aluminum alloy. 
     
     
       9. The enclosure of  claim 1 , wherein the anodic film is colorized with dye particles. 
     
     
       10. A method of coating an anodized metal part including an anodic film disposed on a metal substrate, the method comprising:
 forming a hydrophobic fluoropolymer material that coats a channel included within the anodic film by spraying the anodic film with a fluoropolymer precursor material, wherein the fluoropolymer precursor material polymerizes within the channel such as to form a hydrophobic barrier that prevents moisture from reaching the metal substrate. 
 
     
     
       11. The method of  claim 10 , further comprising:
 forming the hydrophobic fluoropolymer material along a portion of an external surface of the anodic film that surrounds the channel. 
 
     
     
       12. The method of  claim 10 , wherein the hydrophobic fluoropolymer material that coats the channel has a generally uniform thickness. 
     
     
       13. The method of  claim 10 , wherein the hydrophobic fluoropolymer material that coats the channel has a shape that corresponds to a volume defined by the channel. 
     
     
       14. The method of  claim 10 , wherein the channel extends to the metal substrate. 
     
     
       15. The method of  claim 10 , wherein the channel is a crack. 
     
     
       16. An enclosure for an electronic device, comprising:
 a metal oxide layer disposed on a metal substrate; and 
 a channel that extends from an external surface of the metal oxide layer to a transition layer that separates the metal substrate from the metal oxide layer, wherein a hydrophobic material is disposed (i) within the channel, and (ii) on a portion of the external surface of the metal oxide layer that surrounds the channel such as to prevent moisture ingress into the metal substrate. 
 
     
     
       17. The enclosure of  claim 16 , wherein the hydrophobic material includes a fluoropolymer material. 
     
     
       18. The enclosure of  claim 16 , wherein the hydrophobic material has a generally uniform thickness. 
     
     
       19. The enclosure of  claim 16 , wherein the metal oxide layer includes colored dye particles. 
     
     
       20. The enclosure of  claim 16 , wherein the channel is a crack.

Description:
FIELD 
     This disclosure relates to coatings for substrates, especially anodized substrates with laser markings. The coatings can be applied over anodic films such that the coatings enter small cracks within the anodic films, thereby preventing entry of moisture and other contaminants within the cracks that can corrode an underlying metal substrate. 
     BACKGROUND 
     Anodic films are metal oxide layers that are integrally formed on anodizable metals such as aluminum and aluminum alloys. The anodic films are formed by exposing a metal substrate to anodizing process, whereby a portion of the substrate is converted to its corresponding metal oxide. Anodic films are generally hard and resistant to corrosion, and are therefore widely used in industry to provide durable thin coatings to outer surfaces of parts. 
     One of the challenges associated with anodic films relates to the differences in thermal expansion of the anodic film, which is generally amorphous similar to glass, and the underlying metal substrate. In particular, the metal substrate will expand more than the anodic film when exposed to heat. As a consequence, when the metal substrate and anodic film cool down, the metal substrate will shrink more than the anodic film, causing micro-cracks to form within the anodic film. This can happen, for example, when a laser marking process locally heats the metal substrate, forming micro-cracks in the anodic film above the laser marked area of the substrate. In some applications, these micro-cracks are not large enough to cause cosmetic or functional problems. However, in other applications, these micro-cracks act as entry points for moisture and other contaminants that can reach the underlying metal substrate and cause corrosion products to form. 
     SUMMARY 
     This paper describes various embodiments that relate to coatings that are used to fill cracks and spaces within anodic films, such as formed by laser marking procedures. In particular embodiments, the methods involve applying certain types of fluoropolymer materials on surfaces of the anodic films. 
     According to one embodiment, an enclosure for an electronic device that includes a metal substrate is described. The enclosure includes an anodized metal portion having an anodic film formed from the metal substrate. The anodic film has a crack that defines a channel that extends from an external surface of the anodic film to a transition region of the anodic film proximate to the metal substrate. The enclosure further includes a polymerized hydrophobic material infused within the channel so as to prevent ingress to the metal substrate. 
     According to a further embodiment, a method of coating an anodized metal part including an anodic film formed on a metal substrate is described. The method includes positioning the anodized metal part with respect to a spray nozzle. The spray nozzle is configured to create a stream of atomized precursor material of a fluoropolymer material. The anodic film has a crack that extends from an external surface of the anodic film to a transition region of the anodic film proximate to the metal substrate. The method also includes exposing a surface of the anodic film to the stream such that the precursor material is infused into and polymerizes within the crack as the fluoropolymer material. The fluoropolymer material prevents liquid from entering the crack and reaching the metal substrate. 
     According to another embodiment, a spray-on apparatus configured to apply a fluoropolymer coating an anodized part having an anodic film on a metal substrate is described. The spray-on apparatus includes a spray nozzle configured to create a stream of atomized precursor material on a surface of the anodic film. The precursor material corresponds to a monomer precursor of the fluoropolymer coating. The anodic film includes a crack that extends from an external surface of the anodic film to the metal substrate. The spray-on apparatus also include a support configured to position the anodized part with respect to the spray nozzle such that a surface of the anodic film is exposed to the stream of atomized precursor material. The precursor material enters into and polymerizes within the crack. 
     These and other embodiments will be described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIGS. 1A and 1B  show a front view and a back view, respectively, of a housing for an electronic device. 
         FIG. 2  shows a cross section view of a laser marked portion of the housing of  FIG. 1 . 
         FIG. 3  shows a cross section view of the laser marked portion of  FIG. 2  treated with a hydrophobic coating. 
         FIG. 4  shows a spray-on apparatus configured to spray on a coating precursor material onto the housing of  FIG. 1 . 
         FIG. 5  shows a cross section view of a portion of a junction region between a metal portion and a non-metal portion of the housing of  FIG. 1 . 
         FIG. 6  shows a cross section view of the junction region of  FIG. 5  treated with a hydrophobic coating. 
         FIG. 7  shows a cross section view of the junction region of  FIG. 5  treated with a hydrophobic coating in an alternative embodiment. 
         FIG. 8  shows a flowchart indicating a process for coating an anodized metal substrate in accordance with some embodiments. 
         FIGS. 9A-9C  show image data indicating evidence of a fluoropolymer coating deposited within cracks of an anodized film after using the coating methods described herein. 
         FIG. 10  shows a scanning electron microscope image of a cross-section of an anodic film treated with a hydrophobic coating. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, they are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments. 
     Described herein are coatings applied to anodized substrates, especially those anodized substrates with laser markings. In general, anodic films have different coefficients of thermal expansion than their underlying metal substrates. Thus, when a substrate is heated using, for example, a laser marking process, the anodic film tends to crack. Although these cracks can be very small, for example in the scale of nanometers in width, these crack can be entry points for liquid and other types of contaminants during service use of a part, which can reach the underlying metal substrate and ultimately corrode the metal substrate. 
     The methods described herein involve sealing the anodic film by depositing a hydrophobic coating on a surface of the anodic film and within the cracks of the anodic film. The hydrophobic nature of the hydrophobic coating deters entry of water and other contaminates from entering the cracks, thereby preventing such water and contaminants from reaching the underlying metal substrate and preventing the metal substrate from corroding. In some embodiments, the coating is made of a hydrophobic and oleophobic material. In some embodiments, the hydrophobic coating is a polymer material, such as a fluoropolymer material. 
     In specific embodiments, the coating is applied using a spray-on technique. If a fluoropolymer material is used, the fluoropolymer material can be in its monomer liquid form and sprayed under pressure using a spray nozzle onto a surface of the anodic film. Once on the anodic film, the monomer precursor can seep into the cracks and polymerizes within the cracks. This creates a hydrophobic seal within and around the cracks, which has shown to remain within the cracks even after portions of the fluoropolymer material is worn off of external surfaces of the part. 
     As used herein, the terms anodic film, anodic oxide, anodic oxide coating, anodic layer, anodic coating, oxide film, oxide layer, oxide coating, etc. can be used interchangeably and can refer to suitable metal oxide materials, unless otherwise specified. 
     Methods described herein are well suited for providing cosmetically appealing surface finishes to consumer products. For example, the methods described herein can be used to form durable and cosmetically appealing anodized finishes for housing for computers, portable electronic devices, wearable electronic devices, and electronic device accessories, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-10 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIGS. 1A and 1B  show a front view and a back view, respectively, of housing  100 , which can correspond to a housing for an electronic device such as a mobile phone or tablet computer. Housing  100  includes display cover  101 , which covers a display assembly for the electronic device. Housing  100  also includes metal portions  102   a ,  102   b , and  102   c , and non-metal portions  104   a  and  104   b . Metal portions  102   a ,  102   b , and  102   c  can be made of an anodizable metal such as aluminum or aluminum alloy. In some embodiments, metal portions  102   a ,  102   b , and  102   c  are made of a 6000 or 7000 series aluminum alloy, as designated by the International Alloy Designation System. In some embodiments, metal portions  102   a ,  102   b , and  102   c  are made of custom aluminum alloys that have custom alloying element compositions. Non-metal portions  104   a  and  104   b  can be made of a moldable material, such as plastic or ceramic, which are molded onto adjacent metal portions  102   a ,  102   b , and  102   c . In some embodiments, non-metal portions  104   a  and  104   b  correspond to radio frequency (RF) antenna windows that allow transmission of RF waves to and/or from one or more RF antennas within housing  100 . 
     Metal portions  102   a ,  102   b , and  102   c  can be anodized such that a thin protective anodic film  106  is formed on exposed surfaces of metal portions  102   a ,  102   b , and  102   c . In some cases anodic film  106  is colorized using dyes or pigments to give housing  100  a particular color. Text  108  and symbol  110  can be formed on housing  100  for aesthetic, informative or identifying purposes. In some cases, text  108  and symbol  110  are formed using a laser marking procedure, whereby a laser is used to engrave or etch a pattern beneath anodic film  106 . 
     Portions of anodic film  106  can have tiny cracks and crevices that, by themselves, are often not observable. For example, portions of anodic film  106  over text  108  and symbol  110  can have tiny nanometer-scaled cracks as a consequence of the laser marking procedure. Although some of these cracks are not readily visible, they can act as entry points for water and other contaminants that housing  100  can be expected to encounter during normal use. For example, housing  100  will likely be exposed to moisture and sweat from a user&#39;s hands and be subjected to spills or drops within liquids. Additionally, anodic film  106  near junction regions  112  between adjacent metal portions  102   a ,  102   b , and  102   c  and non-metal portions  104   a  and  104   b  can have cracks or thinned areas, which can also act as entry points for water and other contaminants. 
       FIG. 2  shows a cross section view A-A of housing  100  at laser marked text  108 , showing anodic film  106  positioned over metal substrate  202 . Note that  FIG. 2  shows a close-up cross section view of housing  100 , and only shows portions of metal substrate  202  and anodic film  106 . Therefore, features are not necessarily to scale. Metal substrate  202  corresponds to the base metal material of metal portion  102   b , such as aluminum or aluminum alloy (e.g., 6000 or 7000 series aluminum alloy), but can be of any suitable anodizable material. Anodic film  106  corresponds to a metal oxide of metal substrate  202 , which is integrally formed on metal substrate  202  using, for example, an anodizing process. Thus, metal substrate  202  made of aluminum alloy will result in an aluminum oxide anodic film  106 . 
     In a laser marking procedure, a laser beam selectively heats portions of anodic film  106  and/or metal substrate  202 , such that the laser-affected areas appear a different color than surrounding non-laser marked areas. For example, a laser can be tuned to burn portions of anodic film  106  at transition region  204 , which corresponds to the region of anodic film  106  between metal substrate  202  and anodic film  106 . The laser marking process makes transition region  204  appear darker than surrounding areas, thereby giving text  108  a dark appearance. In other embodiments (not shown), the laser is tuned to affect portions of anodic film  106  above transition region  204 , which can create cracks within those portions of anodic film  106 , making these affected regions appear white in color. 
     One of the consequences of the laser marking procedure is that cracks  206  form within anodic film  106 . This occurs because the laser beam locally heats metal substrate  202  and/or anodic film  106 . Since metal substrate  202  has a higher coefficient of thermal expansion than anodic film  106 , those portions of metal substrate  202  locally heated by the laser beam expand more relative to anodic film  106 . When metal substrate  202  cools back down, metal substrate  202  contracts relative to anodic film  106 , which creates stress within anodic film  106 , and causes anodic film  106  to crack. 
     Cracks  206  are generally very small. For example, cracks  206  typically have an averages on the scale of nanometers. In some embodiments, width w is less than about 100 nanometers. In some embodiments, width w is less than about 50 nanometers. In some embodiments, width w is about 10 nanometers or less. Thus, cracks  206 , by themselves, may not be readily visible when viewing housing  100  from external surface  208  of anodic film  106 , especially if underlying metal substrate  202  has a textured surface (e.g., blasted or etched). However, cracks  206  can span the thickness of anodic film  106 . In particular, cracks  206  can extend from external surface  208  to transition region  204 , and even down to metal substrate  202 . Thus, cracks  206  can act as channels for liquid, such as water (e.g., moisture) and/or oils, and other contaminants (e.g., dirt) to travel form external surface to underlying metal substrate  202 . When exposed to water or other contaminate, metal substrate  202  can corrode and form corrosion products  210  within or near transition region  204 . Corrosion products  210  are formed when water or other contaminants chemically react with metal substrate  202 , i.e., either the base metal itself or alloying elements within the base metal. The prevalence of corrosion products  210  will depend, in part, on the type of metal substrate  202 . For example, some alloys are more prone to producing corrosion products  210  than others. 
     Corrosion products  210  are can have a different color than metal substrate  202 , such as a dark color, and can therefore be visible when viewing housing  100  from external surface  208 . This can negatively affect the aesthetic clean lines of text  108 . In some cases, corrosion products  210  spread laterally across transition region  204  and reduce the adhesion of anodic film  106  to metal substrate  202  and possibly cause formation of more cracks within anodic film  106 , further exacerbating the problem. In some cases, corrosion products  210  exit the openings of cracks  206  at external surface  208 , further negatively affecting the cosmetic quality of housing  100 . 
     Methods described herein address the above-described problems associated with cracks and spaces within anodic films using a hydrophobic coating, such as a fluoropolymer coating.  FIG. 3  shows a cross section view A-A of housing  100  at laser marked text  108  after treatment with a hydrophobic coating  300 , in accordance with some embodiments. Hydrophobic coating  300  is applied onto external surface  208  of anodic film  106  such that at least some of hydrophobic coating  300  enters into cracks  206 . Hydrophobic coating  300  is applied onto external surface  208  of anodic film  106  using any of a number of suitable techniques, such dipping, paint-on, wipe-on, spin-on, or spray-on techniques. A spray-on technique, in accordance with some embodiments, is described in detail below with reference to  FIG. 4 . 
     Hydrophobic coating  300  can be made of any suitable hydrophobic material capable of being deposited within cracks  206 . In some embodiments, hydrophobic coating extends all the way down to terminal ends  302  of cracks  206 . Since hydrophobic coating  300  is positioned within cracks  206 , this provides a physical barrier that prevents moisture and/or other contaminants from entering cracks  206 . Furthermore, the hydrophobic nature of hydrophobic coating  300  wicks away and repels water away from external surface  208  and cracks  206 . In some embodiments, hydrophobic coating  300  is also oleophobic such that hydrophobic coating  300  can also repel and keep out grease and oils (e.g., from user&#39;s hands) from entering cracks  206 . Such hydrophobic and oleophobic coatings include fluoropolymer materials. In this way, metal substrate  202  is protected from exposure to moisture and/or other contaminants and, as a result, transition region  204  is free from corrosion products. Even if, during normal use of housing  100 , portions of hydrophobic coating  300  at external surface  208  are rubbed or scratched off, it will be difficult to remove hydrophobic coating  300  from within cracks  206  due to their size. Therefore, hydrophobic coating  300  can prevent entry of water and contaminants within cracks  206  long after application of hydrophobic coating  300  and throughout the service lifetime of housing  100 . 
     In some embodiments, hydrophobic coating  300  is preferably substantially transparent such that anodic film  106  is visible through hydrophobic coating  300 . In some embodiments, hydrophobic coating  300  is a polymer material, such as a fluoropolymer material, which is generally a fluorocarbon-based polymer that is resistant to solvents, acids and bases. Fluoropolymers may be preferable in some embodiments due to their hydrophobic/oleophobic qualities, chemical stability, transparency and ease of application. In particular embodiments, one or more types of fluoropolymer materials provided by Daikin Industries, Ltd., headquartered in Osaka, Japan are used. The fluoropolymer material can be applied in its monomer precursor form onto external surface  208  of anodic film  106 , where it can seep into cracks  206  by diffusion. Once within cracks  206 , the precursor material polymerizes into its long-chain polymeric form. Since the precursor material molecules polymerizes with cracks  206 , a final shape of the polymer material conforms to the volume defined by the cracks  206 . This creates a seal that deters entry of foreign materials. 
     If cracks  206  within anodic film  106  are very small, i.e., average width w is in the order of nanometers, the material of hydrophobic coating  300  should be chosen accordingly. For example, for hydrophobic coating  300  made of a fluoropolymer material, the fluoropolymer material should be deposited while in its precursor form. This is because fluoropolymer material in its polymer form will generally consist of long molecular chains that are too large to fit within cracks  206  having an average width w in the order of nanometers. Thus, fluoropolymers should be deposited while in their monomer form, where an average molecular length of the monomer material is about equal to or less than average width w of cracks  206 . It should be noted however, that if average width w is much larger than the average molecular length of the monomer material, the fluoropolymer coating might not be capable of adequately filling cracks  206 . Thus, in some embodiments, the average molecular length of the monomer material is on the scale of average width w of cracks  206 . In a particular embodiment, the average molecular length of the monomer material is about half of average width w of cracks  206 . 
     It should be noted that, hydrophobic coating  300  could also be used to fill other types of cracks and crevices within anodic film  106 . For example, in some applications, cracks (not shown) are formed in intermediate locations above transition region  204  within anodic film  106 . In some cases, these cracks are intentionally formed by tuning a focal point of the laser beam to within anodic film  106  instead of at metal substrate  202 . This can create a white color, rather than a dark color associated with traditional laser marking procedures. Since these intermediately located cracks do not generally extend down to metal substrate  202 , they generally do not cause the above-described substrate corrosion problems. However, it is possible that these intermediately located cracks can propagate through to metal substrate  202  during normal use of a consumer product, thereby eventually providing a pathway for water and/or other contaminants. Thus, hydrophobic coating  300  can also be used to fill these intermediately located cracks in case they do propagate through to metal substrate  202 . In fact, hydrophobic coating  300  can be used to fill substantially any suitable type of cracks, spaces or crevices, formed intentionally or unintentionally, within anodic film  106 . Some more examples will be described later below. 
     In some embodiments, good coverage within cracks  206  is accomplished using a spray-on technique using spray-on apparatus  400  shown in  FIG. 4 . Spray-on apparatus  400  is configured to spray precursor material  401  onto housing  100 , which includes anodic film  106  formed on substrate  202 . In some embodiments, housing  100  is positioned on and secured by support  412 . Spray-on apparatus  400  includes reservoir  402  that contains precursor material  401  in liquid form. Precursor material  401  corresponds to a precursor material for forming coating  300 . As described above, for polymer coatings, precursor material  401  can correspond to a monomer form of the polymer coating. For example, precursor material  401  can correspond to a monomer precursor to a fluoropolymer coating. 
     Spray-on apparatus  400  also includes nozzle  404 , which is configured to dispense precursor material  401  onto surface  208  of anodic film  106 . In some embodiments, nozzle is configured to atomize precursor material  401  in mist form, i.e., in small droplets. Reservoir  402  can provide nozzle  404  with a continuous supply of precursor material  401  via tubing  408 . Nozzle  404  can be pressurized so as to produce stream  406  of atomized precursor material  401 . In the embodiment shown, nozzle  404  is configured to spray a full cone-shaped stream  406  that dispenses precursor material  401  in a circular pattern. In particular embodiments, diameter D of cone-shaped stream  406  ranges between about 2 and 10 millimeters—in one particular embodiment about 6 millimeters. However, other types of spray configurations other than cone-shaped stream  406  can be used. For example, precursor material  401  can be applied using a nozzle configured to spray a flat sheet stream of coating precursor  401 , or multiple nozzles configured to spray multiple plumes of coating precursor  401 . 
     Nozzle  404  can be passed over surface  208  of anodic film  106  to cover all of surface  208 . That is, nozzle  404  is translated laterally until stream  406  reaches all of surface  208  of anodic film  106 . In some embodiments, nozzle  404  is translated using a translation mechanism, such as a robotic arm. Alternatively or additionally, support  412  can be configured to move housing  100  with respect to nozzle  404 . In some embodiments, nozzle  404  and/or support  412  are configured to move in three-dimensional space with respect to each other such that edges and corners of housing can be reached with a uniform stream  406  of coating precursor  401 . 
     One of the advantages of using spray-on apparatus  400  compared to other application techniques is that nozzle  404  allows for accurate control of thickness t of hydrophobic coating  300 . This may be an important consideration in embodiments where it is desirable for hydrophobic coating  300  to be substantially transparent. For example, some types of hydrophobic coating  300  materials may become less transparent as the material thickens. Nozzle  404  can deposit thin layers in a controlled manner, thereby making it easier to control a thickness t of hydrophobic coating  300 . In some embodiments, thickness t of hydrophobic coating  300  is in the scale of nanometers. In some embodiments, thickness t is between about 5 nanometers and 20 nanometers, although a thinner or thicker hydrophobic coating  300  can be used. In a particular embodiment, thickness t is about 10 nanometers. Nozzle  404  can be passed over surface  208  of anodic film  106  one or multiple times until a desired thickness is achieved. In some embodiments, nozzle  404  is passed over surface  208  only one time, while in other embodiments nozzle  404  is passed over surface  208  multiple times (e.g., three times) such that hydrophobic coating  300  consists of multiple layers. In addition to good thickness t control, spray-on apparatus  400  can provide a uniform layer hydrophobic coating  300 —that is having little thickness variation. 
     The size of nozzle  404 , the pressure at which nozzle  404  dispenses coating precursor  401 , and distance between nozzle  404  and surface  208  of anodic film  106  can vary depending on a number of factors, such as the geometry of housing  100  (e.g., corners, curved or irregular surfaces) and the type of hydrophobic coating  300  used. In some embodiments, the pressure of nozzle  404  forces precursor material  401  within the cracks of anodic film  106 , and does not solely relying on diffusive action. However, the spray pressure should not be so high as to cause conglomeration of precursor material  401  on surface  208  of anodic film  106 . Spray-on apparatus  400  can be configured to apply hydrophobic coating  300  in a short amount of time, which can be important in manufacturing settings. 
     As described above, if hydrophobic coating  300  is a polymer material, it may be important to assure that precursor material  401  be deposited onto anodic film  106  prior to polymerization into large, long chains. This is to assure that hydrophobic coating  300  gets sufficiently deposited within cracks  206  that are very small. Some fluoropolymer materials ready polymerize when exposed to moisture, such as in the air, and/or heat. Thus, distance x between nozzle  404  and surface  208  of anodic film  106  can be minimized to reduce exposure of precursor material  401  to moisture in ambient conditions. The pressure at which nozzle  404  expels precursor material  401  can also be adjusted to minimize polymerization prior to reaching external surface  208 . It may also be necessary to take precautions to assure that tubing  408  is flushed out of any polymerized material between applications, such as when reservoir  402  is replaced or refilled with a new batch of coating precursor  401 . 
     In some embodiments, the coating operation is performed within chamber  410  such that the temperature and humidity of precursor material  401  during the spraying can be controlled. High temperatures can cause anodic film  106  to temporarily swell and close up the cracks therein, thereby making it more difficult to deposit precursor material  401  within the cracks. Therefore, it may be beneficial to keep the temperature within chamber  410  below temperatures at which anodic film  106  would swell. In some embodiments, the temperature within chamber  410  is maintained around room temperature, which can make integration into manufacturing lines simpler. Chamber  410  can also keep dust out of stream  406  so that the dust does not become deposited with hydrophobic film  300 , or otherwise interfere with the depositing process. One other function of chamber  410  can be for safety and/or cleanliness. Even though the material of precursor material  401  and hydrophobic coating  300  can be safe to humans, it may be beneficial to contain any possible odors from stream  406  within chamber  410  and to keep hydrophobic coating  300  from coating other surfaces of the manufacturing floor. 
     Returning back to  FIGS. 1A and 1B , hydrophobic coating  300  can be applied to other areas of anodic film  106  other than laser marked regions of text  108  and symbol  110 . For example, hydrophobic coating  300  can be applied to junction regions  112  positioned between metal portions  102   a ,  102   b , and  102   c  and non-metal portions  104   a  and  104   b.    
       FIG. 5  shows a cross section view B-B of housing  100  at junction region  112  between metal portion  102   a  and non-metal portion  104   a . Non-metal portion  104   a  can correspond, for example, to a plastic or ceramic material that is RF transparent, as described above. Metal portion  102   a  includes metal substrate  202  with anodic film  106  positioned thereon. The geometry of metal portion  102   a  includes edge  502  to accommodate the interface with adjacent non-metal portion  104   a . The sharp geometry of edge  502  makes it difficult to form a continuous anodic film  106  at edge  502 . As a consequence, anodic film  106  can be separated into two anodic film portions  106   a  and  106   b  that are adjacent to each other and separated by crack  504 . That is, external surface  508  of anodic film  106  can be discontinuous at edge  502 . Note that space  510  between metal portion  102   a  and non-metal portion  104   a  can also exist due to manufacturing tolerances. 
     The size of crack  504  can vary depending on the sharpness of edge  502 , the thickness of anodic film  106 , and other factors. In some embodiments, crack  504  is on the scale of micrometers or nanometers. In some embodiments, anodic film portions  106   a  and  106   b  physically touch at some level, but the oxide material connecting anodic film portions  106   a  and  106   b  is very thin and/or contains small cracks. As with the cracks associate with laser marking described above, crack  504  formed between anodic film portions  106   a  and  106   b  can also act as entry points and channels for moisture and other contaminants to reach underlying metal substrate  202  and cause creation of corrosion products  506 . As described above, corrosion products  506  can cause cosmetic defects and/or undermine adhesion strength of anodic film  106  to metal substrate  202 . 
     To address this problem, at  FIG. 6 , hydrophobic coating  602  is applied to external surface  508  of anodic film portions  106   a  and  106   b  and within crack  504 . Similar to as described above with respect to filling cracks at laser marked regions, hydrophobic coating  602  positioned within crack  504  prevents or reduces entry of moisture and/or other contaminants from entering crack  504 . Furthermore, the hydrophobic nature of hydrophobic coating  602  can wick away and repel water from external surface  508  of anodic film  106  and crack  504 . In this way, metal substrate  202  is protected from water and contaminants that can create corrosion products  506 . In addition, hydrophobic coating  602  can also be deposited within space  510  between metal portion  102   a  and non-metal portion  104   a . This can prevent entry of water and other contaminants (e.g., grease, oil and dirt) from entering within space  510  that can darken and aesthetically diminish the appearance of junction region  112 . 
       FIG. 7  shows an alternative embodiment where hydrophobic coating  602  is also applied onto external surface  702  of non-metal portion  104   a . This can assure that hydrophobic coating  602  is deposited within space  510 . In addition, hydrophobic coating  602  can act as a continuous water barrier that protects both anodic film portions  106   a / 106   b  as well as non-metal portion  104   a.    
     Returning to  FIGS. 1A and 1B , hydrophobic coating  300  can be applied to other areas of housing  100 . In some embodiments, hydrophobic coating  300  is applied to all exposed surfaces of anodic film  106 , including along corners  114  and side surfaces  116  of housing  100 . This can be done to assure than any other micro-cracks formed within anodic film  106  due to handling or manufacturing processing are filled and coated. Hydrophobic coating  300  can even be applied onto non-metal surfaces of housing  100 , such as on display cover  101 , and non-metal portions  104   a  and  104   b . In this way, hydrophobic coating  300  can provide a continuous and substantially colorless water-wicking layer to housing  100 . 
     Returning to  FIG. 4 , spray-on apparatus  400  can be adapted to apply hydrophobic coating  300  to all exposed surfaces of housing  100 . For example, support  412  can be configured to move in three-dimensional space so as to rotate and translate housing  100  with respect to nozzle  404  such that stream  406  provides even coverage over the corners, sides, curved and flat surfaces of housing  100  in a single spray-on operation. Alternatively or additionally, nozzle  404  can be configured to move in three-dimensions, using for example a robotic arm, around corners, sides, curved and flat surfaces of housing  100  in a single spray-on operation. 
       FIG. 8  shows flowchart  800  indicating a process for coating an anodized part in accordance with some embodiments. The anodized part includes an anodic film positioned on a metal substrate. The part can correspond to a portion of a consumer part, such as a housing or enclosure for an electronic device. The part can also include non-metal portions, such as plastic or glass sections. The anodic film has cracks formed therein, such as from a laser marking operation. In some embodiments, the cracks are a result of an anodizing process at a sharp edge or corner of the metal substrate. The cracks can be very small in size, sometimes having widths on the scale of micrometers or nanometers. 
     At  802 , the anodized part is positioned with respect to a spray nozzle of a spray-on apparatus. The spray-on apparatus can include a spray nozzle that creates an atomized stream of a precursor form of a polymer coating. The spray-on apparatus can include positioning mechanisms that positions the anodized part with respect to the spray nozzle to expose a surface of the anodic film to a stream of atomized precursor material. In some embodiments, the spray nozzle and anodized part are positioned within a chamber to prevent entry of foreign particles. In some embodiments, a temperature and moisture level within the chamber is controlled. 
     At  804 , the coating precursor is sprayed from the spray nozzle and into at least some of the cracks. In some embodiments, the coating precursor is a monomer precursor to a fluoropolymer coating. The monomer precursor should have an average molecular length that is on the scale of the cracks. This way, the monomer precursor can fit within the cracks, either by diffusion or propelled by pressure from the spray nozzle, prior to polymerizing into larger molecular structures. In addition, a width of the crack is not too large that the resultant fluoropolymer insufficiently fill the cracks. Once within the cracks, the monomer precursor can polymerize into its fluoropolymer form, creating a hydrophobic and physical seal that prevents water and other contaminants from entering the cracks. 
     The spray nozzle and the substrate can be translated with respect to each other such that a desired area of the anodic film is coated. In some embodiments, the spray nozzle and/or the substrate are configured to translate three-dimensional space so that three-dimensional features (e.g., corners and edges) of the anodized part are coated. The translation speed, the distance between the spray nozzle and the anodic film, the pressure at which the coating precursor is sprayed, and the temperature of the coating precursor and substrate can all be chosen to assure that the hydrophobic coating has a substantially uniform thickness. In some embodiments, the distance between the spray nozzle and an external surface of the anodic film is minimized in order to reduce the possibility of polymerization of the coating precursor while in aerosol form prior to reaching the external surface of the anodic film. The translation speed and pressure at which the coating precursor is sprayed onto the anodic film can also be controlled to minimize polymerization prior to reaching the anodic film, as well as to prevent conglomeration of the hydrophobic coating. In some embodiments, non-metal portions, such as plastic or glass sections, of the part are also coated with the hydrophobic coating. This way, a continuous hydrophobic coating can be formed on all external surfaces of the part, creating a uniform protective layer for the part. 
       FIGS. 9A-9C  show Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) fluorine-map and scanning electron microscope (SEM) images of an anodic film sample, indicating evidence of a fluoropolymer coating being deposited within cracks of the anodic film sample. The sample is an anodized aluminum alloy substrate after a laser marking operation such that cracks having widths on the scale of nanometers are formed within the anodic film. The anodic film sample can correspond, for example, to laser marked regions of text  108  or symbol  110  of housing  100  describe above with respect to  FIG. 1 . 
       FIGS. 9A-9C  show progressive images of an analysis sequence, with  FIG. 9A  showing fluorine-map images of the anodic film sample after the fluoropolymer coating was applied using a spray-on technique as described above,  FIG. 9B  showing fluorine-map images of the anodic film sample after a portion of the anodic film was removed using an ion milling operation, and  FIG. 9C  showing a fluorine-map image and a scanning electron microscope (SEM) image of the anodic film sample after an additional portion of the anodic film was removed using a second ion milling operation. 
       FIG. 9A  shows the anodic film sample after a fluoropolymer coating was applied. Image  902  shows a fluorine-map image of a 1000 micrometer by 1000 micrometer scan area of a surface of the anodic film sample. Image  904  shows a fluorine-map image of a 100 micrometer by 100 micrometer scan area of a surface of the anodic film sample. The light high intensity areas of images  902  and  904  indicate the presence of fluorine, i.e., from the fluoropolymer coating. 
       FIG. 9B  shows the anodic film sample after a 45 minute ion milling operation was performed, where a depth of about 1.5 micrometers the anodic film was sputtered away (as calibrated against a silicon wafer). Image  906  shows a fluorine-map image of a 1000 micrometer by 1000 micrometer scan area of the sputtered surface of the anodic film sample. Image  908  shows a fluorine-map image of a 100 micrometer by 100 micrometer scan area of a surface of the anodic film sample. Both images  906  and  908  show light areas indicating the presence of fluorine from the fluoropolymer coating. This is evidence that the fluoropolymer coating is present within at least about 1.5 micrometers within the anodic film, indicating that the fluoropolymer coating was infused to at least this depth. 
       FIG. 9C  shows the anodic film sample after a subsequent 60 minute ion milling operation was performed, where an additional 2 micrometers of anodic film was sputtered away (as calibrated against a silicon wafer). Thus,  FIG. 9C  shows the anodic film after about a total of 3.5 micrometers of the anodic film was removed after applying the fluoropolymer coating. Image  910  shows a fluorine-map image of a 1000 micrometer by 1000 micrometer scan area of the sputtered surface of the anodic film sample. Image  912  shows an SEM image (500× magnification) of the anodic film sample, with the area defined within box  914  corresponding to the 1000 micrometer by 1000 micrometer scan area of image  910 . The light areas of SEM image  912  correspond to cracks  915  within the anodic film. Cracks  915  match with light areas of fluorine map image  910 , as indicated by circles  916 . This indicates that the fluorine-rich areas of fluorine-map image  910  correspond to cracks  915  of SEM image  912 , showing that the fluoropolymer is infused within cracks  915 . Furthermore, the fluoropolymer coating is present within cracks  915  at least within a depth of about 3.5 micrometers of the anodic film. 
       FIG. 10  shows a scanning electron microscope (SEM) image of a cross-section of an anodized part that has been treated with hydrophobic coating  1006 . The anodized part includes anodic film  1002  and metal substrate  1004 . In this case, metal substrate  1004  is a 7000 series aluminum alloy and hydrophobic coating  1006  is a fluoropolymer coating. Anodic film  1002  has crack  1008  caused, for example, by a laser marking operation. As shown, crack  1008  spans anodic film  1002  from external surface  1003  of anodic film  1002  down to metal substrate  1004 . A layer of hydrophobic coating  1006  is positioned on external surface  1003  of anodic film  1002 , as well as within crack  1008 . Thus, water and other contaminants are prevented from entering crack  1008  via external surface  1003 . This prevents formation of any corrosion products at transition region  1007  between anodic film  1002  and metal substrate  1004 . As such, hydrophobic coating  1006  protects metal substrate  1004  from exposure to water and/or other contaminates that can cause formation of corrosion products. Note that transition region  1007  includes air pockets  1009 —however, these air pockets  1009  are a result of the anodizing process and do not substantially interfere with cosmetic or adhesion characteristics of anodic film  1002 . Also shown is a 10.0 micrometer scale showing the size of crack  1008  being on the scale of nanometers in width. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20150904
Publication Date: 20171107
Grant Date: 20171107
Priority Date: 20150904
Inventors: KOLE JARED M.
SHUKLA ASHUTOSH Y.
ZHANG YI
YAN VINCENT
KWOK WAI MAN RAYMUND
Assignee: APPLE INC
CPC Classifications: [{"code": "B05B7/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D5/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "B05B3/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D7/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "B05D7/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "B05D2202/25", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D2202/25", "inventive": false, "first": false, "tree": "[]"}, {"code": "B05B7/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D5/083", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D5/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D11/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D5/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "B05D5/083", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05B3/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "B05D1/02", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 58189195