PATENT DOCUMENT

Publication Number: US-9725819-B2
Application Number: US-201414161482-A
Country: US
Kind Code: B2

Title: Methods for incorporating ultraviolet light absorbing compounds into anodic oxides

Abstract:
The embodiments described herein relate to anodic oxides and methods for forming anodic oxides. The methods involve incorporating an ultraviolet (UV) light absorbing compounds into anodic oxides to prevent color fading of the anodic oxides caused by exposure to UV light. In some embodiments, the UV light absorbing compound includes para-aminobenzoic acid (PABA). The UV light absorbing compound can be incorporated within the anodic oxide during a sealing process. The UV light absorbing compound becomes infused within a seal layer, which is formed during the sealing process. The resultant anodic oxide has a UV light absorbing seal layer that can block UV light from reaching any underlying colorant existing within the anodic oxide.

Claims:
What is claimed is: 
     
       1. A method of forming a part having a color fade resistant anodic oxide disposed over a substrate, the method comprising:
 depositing a colorant within pores of the color fade resistant anodic oxide; 
 forming a first seal layer having an ultraviolet (UV) light absorbing compound incorporated within a metal oxide hydrate of the first seal layer, wherein the UV light absorbing compound comprises at least one of a para-aminobenzoic acid (PABA), a benzophenone, a benzotriazole, or a hindered amine compound; and 
 forming a second seal layer positioned on the first seal layer, wherein the second seal layer is free of the UV light absorbing compound. 
 
     
     
       2. The method as recited in  claim 1 , wherein the second seal layer has an external surface corresponding to an external surface of the color fade resistant anodic oxide. 
     
     
       3. The method as recited in  claim 1 , wherein the metal oxide hydrate has a nickel hydroxide precipitate incorporated therein. 
     
     
       4. The method as recited in  claim 1 , wherein forming the second seal layer comprises exposing the anodic oxide to a solution comprising a metal salt. 
     
     
       5. The method as recited in  claim 4 , wherein a metal hydroxide precipitate of the metal salt becomes infused within the second seal layer. 
     
     
       6. The method as recited in  claim 1 , wherein the UV light absorbing compound is substantially transparent to visible wavelengths of light. 
     
     
       7. The method as recited in  claim 1 , wherein the UV light absorbing compound does not substantially chemically react with the colorant. 
     
     
       8. The method as recited in  claim 1 , wherein the UV light absorbing compound modifies light absorbing properties of the colorant. 
     
     
       9. The method as recited in  claim 1 , wherein the UV light absorbing compound comprises para-aminobenzoic acid (PABA). 
     
     
       10. A part having a color fade resistant anodic oxide disposed over a substrate, the color fade resistant anodic oxide comprising:
 a colorant deposited within pores of the color fade resistant anodic oxide; 
 a first seal layer having an ultraviolet (UV) light absorbing compound incorporated within a metal oxide hydrate of the first seal layer, wherein the UV light absorbing compound comprises at least one of a para-aminobenzoic acid (PABA), a benzophenone, a benzotriazole, or a hindered amine compound; and 
 a second seal layer positioned on the first seal layer, wherein the second seal layer is free of the UV light absorbing compound. 
 
     
     
       11. The part as recited in  claim 10 , wherein the second seal layer has an exterior surface corresponding to an exterior surface of the part, wherein the at least a portion of the UV light absorbing compound is positioned more proximate to the exterior surface than the colorant, thereby blocking at least a portion of UV wavelengths of light incident the exterior surface from reaching the colorant. 
     
     
       12. The part as recited in  claim 10 , wherein the UV light absorbing compound modifies light absorbing properties of the colorant. 
     
     
       13. The part as recited in  claim 10 , wherein the metal oxide hydrate has a nickel hydroxide precipitate incorporated therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/884,911 filed Sep. 30, 2013 entitled “METHODS FOR INCORPORATING ULTRAVIOLET LIGHT ABSORBING COMPOUNDS INTO ANODIC OXIDES,” which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to anodic oxides. More specifically, methods for incorporating ultraviolet light (UV) light absorbing compounds into anodic oxides are disclosed. 
     BACKGROUND 
     Anodizing is an electrolytic oxidative process used to increase the thickness of a natural passive layer on a surface of a metal part, where the part to be treated forms the anode electrode of an electrical circuit. The resultant metal oxide film, referred to as an anodic oxide, increases the corrosion resistance and wear resistance of the surface of the metal part. Anodic oxides can also be used for a number of cosmetic effects. For example, techniques for colorizing anodic oxides have been developed that can provide an anodic oxide with a perceived color. In many cases, colorants such as dyes are added within pores of the anodic oxide to give the anodic oxide particular colors. However, with exposure to ultraviolet (UV) light, the color of the anodic oxides can fade from their original color. 
     SUMMARY 
     According to one embodiment, a method for preparing a color fade resistant anodic oxide is described. The anodic oxide has a colorant deposited within pores of the anodic oxide. The method includes incorporating an ultraviolet (UV) light absorbing compound into the anodic oxide by exposing the anodic oxide to a solution containing the UV light absorbing compound. The UV light absorbing compound is configured to absorb at least a portion of UV wavelengths of light. The incorporated UV light absorbing compound blocks at least a portion of UV tight incident a top surface of the anodic oxide from reaching the colorant. 
     According to another embodiment, a part is described. The part includes a substrate. The part also includes a color fade resistant anodic oxide layer disposed over the substrate. The color fade resistant oxide layer has a number of pores. The color fade resistant oxide layer includes an ultraviolet (UV) light absorbing layer having a UV light absorbing compound infused therein. The UV light absorbing compound is configured to absorb at least a portion of UV wavelengths of light. The color fade resistant oxide layer also includes a colorant deposited with the pores of the anodic oxide. The infused UV light absorbing compound blocks at least a portion of UV light incident a top surface of the anodic oxide from reaching the colorant. 
     According to a further embodiment, a method for preparing a color fade resistant anodic oxide is described. The anodic oxide has a colorant deposited within pores of the anodic oxide. The method includes adding an ultraviolet (UV) light absorbing compound to a sealing solution. The sealing solution suitable for sealing the pores of an anodic oxide. The UV light absorbing compound is configured to absorb at least a portion of UV wavelengths of light. The method also includes incorporating the UV light absorbing compound into the anodic oxide by exposing the anodic oxide to the sealing solution. During the exposing, the UV light absorbing compound becomes infused within a UV light absorbing seal layer. The UV light absorbing seal layer blocks UV light incident a top surface of the anodic oxide from reaching the colorant within the pores. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIG. 1  shows a cross-section view of a part after undergoing an anodizing process showing an anodic oxide having anodic pores. 
         FIG. 2  shows an anodic oxide after a colorant is absorbed within anodic pores of the anodic oxide. 
         FIGS. 3A and 3B  show a part after undergoing two different types of sealing processes, respectively. 
         FIG. 4A  shows an apparatus used to introduce UV light absorbing compounds into an anodic oxide during a sealing process. 
         FIGS. 4B and 4C  show close-up cross-section views of a part undergoing a. sealing process including a UV light absorbing compound. 
         FIG. 5A  shows an apparatus used to introduce UV light absorbing compounds into an anodic oxide during a sealing process that includes a sealant compound. 
         FIGS. 5B-5D  show close-up cross-section views of a part undergoing a sealing process including a sealant compound and a UV light absorbing compound. 
         FIG. 6  shows a flowchart indicating a process for incorporating UV absorbing compound into anodic oxide. 
     
    
    
     DETAILED DESCRIPTION 
     Representative applications of methods according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     The present application describes various methods of treating anodic oxides. In particular, various methods for improving the color retention of anodic oxides are described. In particular, reducing or eliminating color fading due to exposure to light is described. In a specific embodiment, methods include incorporating ultraviolet (UV) light absorbing compounds within anodic oxides to prevent color fading caused by exposure to UV light. The UV protected anodic oxides are well suited for providing protective and attractive surfaces to visible portions of consumer products. For example, methods described herein can be used for providing protective and cosmetically appealing exterior portions of metal enclosures and casings for electronic devices, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     Anodizing is an electrolytic chemical process whereby at least a portion of a metal substrate is converted to a metal oxide finish, also referred to as an anodic oxide. During an anodizing process, nanometer scale voids, referred to as anodic pores, form within the anodic oxide.  FIG. 1  shows a cross-section view of part  100  after undergoing an anodizing process. During the anodizing process, a portion of substrate  102  is converted to anodic oxide  104 . As described herein, substrate  102  can be made of any suitable anodizable material. At least a portion of substrate  102  can be made of a metal material, including, but not limited to, aluminum, titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum. The metal material can include a substantially pure metal material or be made of a metal alloy. 
     Anodic oxide  104  includes a matrix of metal oxide  105  that has a number of pores  106  formed therein. Each of pores  106  has a bottom portion positioned at the surface of the un-converted substrate  102  and a top portion positioned proximate to and open at top surface  107  of anodic oxide  104 . In many cases, anodic oxide  104  can be substantially translucent in appearance in that most of the visible light incident top surface  107  of anodic oxide  104  is transmitted through anodic oxide  104  and reflect off of underlying un-converted substrate  102 . Some visible light may reflect off of surfaces of anodic oxide  104 , such as the pore walls of pores  106  or off of top surface  107 , adding an opaque quality to anodic oxide  104 . The amount of transparency of anodic oxide  104  can depend, in part, on the thickness of anodic oxide  104 , with thicker anodic oxides being less transparent. In some cases, anodic oxide  104  can have an off-white or yellowish hue. 
     At  FIG. 2 , colorant  208  is absorbed within pores  106 . Colorant  208  can include any suitable coloring agent such as one or more metallic materials, inorganic dyes, and organic dyes. In some embodiments, colorant  208  is situated at the bottom portions of pores  106 , as shown in  FIG. 2 . In some embodiments, colorant  208  is situated at the top portion of pores  106 , or substantially fills the entire volume of pores  106 . When colorant  208  is inserted within pores  106 , visible light entering top surface  107  of anodic oxide  104  can transmit through anodic oxide  104  and reach colorant  208  positioned within pores  106 . Some of the visible wavelengths of light can be absorbed by colorant  208 . The wavelengths of visible light that do not get absorbed by colorant  208  can reflect back through and exit anodic oxide  104  and will correspond to the color of anodic oxide  104 . Thus, for example, if wavelengths corresponding to the color blue are reflected, anodic oxide  104  will take on a blue appearance. In some embodiments, colorant  208  absorbs substantially all wavelengths of visible light, imparting a black appearance to anodic oxide  104 . In some cases, over time and exposure to ITV light, colorant  208  can degrade and lose its ability to absorb visible wavelengths of light. This is because UV light can break down chemical bonds within colorant  208 . In effect, UV light bleaches and fades the color imparted to anodic oxide  104 . 
     Methods described herein can be used to prevent or reduce the occurrence of color fading of anodic oxide  104  caused by exposure to UV light. The methods involve introducing UV light absorbing compounds within anodic oxide  104  such that the energy of incident UV light will be absorbed by the UV light absorbing compounds and not by colorant  208 . That is, the UV light absorbing compounds can protect or block colorant  208  from exposure to at least a portion of incident UV light. The UV light absorbing compounds can be deposited within anodic oxide  104  by exposing anodic oxide  104  to a UV light absorbing compound mixed within a liquid or within a gas. For example, anodic oxide  104  can be exposed to a solution containing a UV light absorbing compound. The solution can be any type of solution, including aqueous or non-aqueous solutions. In some embodiments, the solution is also a sealing solution used for sealing the pores of anodic oxide  104  during a sealing process. In a sealing process, pores  106  are sealed in order to retain colorant  208  within pores  106  and also to increase the corrosion resistance of anodic oxide  104 . 
       FIGS. 3A and 3B  show part  100  after undergoing two different types of sealing processes, respectively.  FIG. 3A  shows part  100  after being exposed to a hot aqueous sealing process. A hot aqueous sealing process involves exposing anodic oxide  104  to an aqueous solution that dissolves exposed portions of metal oxide  105  to its metal oxide hydrate  310  form. The hydrating process dissolves and collapses the top portions of pores  106 , forming a seal layer  313  at top surface  312 . Seal layer  313  is denser than and enhances the corrosion resistance of the underlying portion of anodic oxide  104 , providing anodic oxide a protective top surface  318 . Seal layer  313  can also protect pores  106  from contaminants such as dirt, grease, and oil. In addition, colorant  208  becomes sealed within anodic oxide  104 , preventing colorant  208  from leaching out of pores  106 . Conversion of the metal oxide  105  to metal oxide hydrate  310  generally requires the sealing solution to be hot, e.g., 80 degrees C. or above. Other factors such as the pH of the sealing solution can also determine the degree to which the sealing process occurs. Exposing part  100  to a hot aqueous solution can include any suitable method, including immersing part  100  into a boiling-hot solution of aqueous solution or by exposing part  100  to steam. 
       FIG. 3B  shows part  100  after being exposed to a variation of the hot water sealing process described above with reference to  FIG. 3A . At  FIG. 313 , the sealing solution includes a sealant compound. As with the hot aqueous solution sealing process described above, exposed portions of metal oxide  105  are converted to its metal oxide hydrate  314 , forming seal layer  317 . The sealant compound is mixed into the aqueous sealing solution and generally contains a hydrolysable metal salt, such as a nickel salt (e.g., nickel acetate). The metal salt hydrolyzes and precipitates in the sealing solution as metal hydroxide  316 . For example, a nickel salt will form a nickel hydroxide precipitate. During the sealing process, metal hydroxide  316  becomes absorbed and infused within metal oxide hydrate  314  within anodic oxide  104 . The presence of metal hydroxide  316  within anodic oxide  104  can enhance the sealing ability of the seal layer  317  and better prevent leaching out of colorant  208  from pores  106 . The presence of metal hydroxide  316  within seal layer  317  can also make top surface  318  more chemically inert. 
     In order to deposit a UV light absorbing compound within pores  106 , the light absorbing compound can be introduced during a sealing process, such as described above with reference to  FIGS. 3A and 3B .  FIG. 4A  shows apparatus  400  used to introduce UV light absorbing compounds during a sealing process, in accordance with described embodiments. Apparatus  400  includes tank  402 , which is configured to hold sealing solution  404  and part  401 . Sealing solution  404  is an aqueous solution that has UV light absorbing compound  406  mixed therein. Sealing solution  404  can be heated so as to promote the pore sealing process described above with reference to  FIGS. 3A and 3B . Light absorbing compound  406  can be any compound or mix of compounds capable of absorbing at least a portion of UV wavelengths of light. In some embodiments, UV light absorbing compound  406  includes para-aminobenzoic acid, also known as PABA. Provided below is a chemical structure of PABA. 
     
       
         
         
             
             
         
       
     
     As shown above, PABA has resonance bonds within its benzene ring and its carboxyl group. These resonance bonds can capture energy corresponding to UV wavelengths of light and dissipate the energy as heat. Because of its UV light absorbing ability, PABA has widely been used as an agent in sunscreen. Alternative UV light absorbing compounds, such as other compounds having resonance structures, can also be used. Examples of other suitable UV light absorbing compounds can include, but are not limited to, benzophenone, benzotriazole, and hindered amine compounds. In some embodiments, more than one type of UV light absorbing compound is used. The choice of UV light absorbing compound  406  can depend on a number of factors, such as how miscible the compound is in aqueous sealing solution  404 . In some embodiments, another agent can be included within sealing solution  404  to make UV light absorbing compound  406  more miscible. For example, a surfactant or a dispersant agent can be used. In some embodiments, UV light absorbing compound  406  is completely dissolved in sealing solution  404 . In other embodiments, UV light absorbing compound  406  is only partially dissolved in sealing solution  404  and allowed to exist in colloidal form. In some embodiments, sealing solution  404  is continually agitated in order to keep UV light absorbing compound  406  suspended with sealing solution  404 . PABA, particular, is slightly soluble in aqueous solution and can therefore be at least partially dissolved within sealing solution  404 . Another consideration for choosing an appropriate type of UV light absorbing compound can be its transparency to visible wavelengths of light. This consideration will be described in detail below. 
     During the pore seating process, UV light absorbing compound  406  will become deposited within the seal of anodic oxide  410  on part  401 .  FIGS. 4B and 4C  show close-up cross-section views of a portion of part  401 , which has anodic oxide  410  disposed over substrate  402 , during a sealing process.  FIG. 4B  shows anodic oxide  410  being exposed to sealing solution  404  having UV light absorbing compound  406  mixed therein. Pores  405  of anodic oxide  410  have colorant  408  deposited therein. As shown, UV light absorbing compound  406  is allowed to at least partially diffuse within pores  405  during the sealing process. In some embodiments, UV tight absorbing compound  406  and colorant  408  are chosen such that they do not chemically react during the sealing process. In other embodiments, UV light absorbing compound  406  is chosen such that it can chemically react with colorant  408  and modify or enhance the light absorbing properties of colorant  408 . 
       FIG. 4C  shows part  401  after the sealing process is complete. As shown, exposed portions of the metal oxide of anodic oxide  410  are converted to metal oxide hydrate  414 , forming seal layer  407 . Seal layer  407  seals in colorant  208  within pores  405 . UV light absorbing compound  406  can be incorporated within the metal oxide material of seal layer  407 , which substantially entirely covers top surface  412  of anodic oxide  410 . Note that in some embodiments a portion of UV light absorbing compound  406  can remain within pores  405 . Since UV light absorbing compound  406  absorbs UV light incident top surface  412 , underlying colorant  408  is protected from exposure to UV light. That is, seal layer  407  acts as a UV blocking layer that absorbs incident UV light. As described above, one factor that can be taken into consideration regarding choosing a type of UV light absorbing compound  406  is its transparency to visible light. In some embodiments, UV light absorbing compound  406  is substantially transparent or translucent to visible wavelengths of light entering top surface  412  so that the visible light can reach and be absorbed by colorant  408  giving anodic oxide  410  a corresponding color. In other embodiments, UV light absorbing compound  406  absorbs at least a portion of visible wavelengths of light and contributes to the final color of anodic oxide  410 . In some embodiments, it can be desirable to perform a second sealing process, whereby part  401  is exposed to a second sealing solution. In some embodiments, the second sealing solution does not include UV light absorbing compound  406 , thereby forming a second sealing layer on the top of anodic oxide  410  that does not include UV light absorbing compound  406 . 
       FIG. 5A  shows apparatus  500  of another embodiment used to introduce UV light absorbing compounds during a sealing process, in accordance with described embodiments. Apparatus  500  includes tank  514 , which is configured to hold sealing solution  504  and part  500 . Sealing solution  504  has UV light absorbing compound  506  and metal hydroxide  503  mixed therein. Metal hydroxide  503  is formed by the exposure of the anodic finish (oxide) and reaction with a metal salt in the aqueous sealing solution  504 . The metal salt precipitates in solution  504  as metal hydroxide  503 , as described above with reference to  FIG. 3B . Light absorbing compound  506  can be any compound or mix of compounds capable of absorbing at least a portion of UV wavelengths of light, such as PABA. In some embodiments, UV light absorbing compound  506  is chosen such that it does not react with metal hydroxide  503  or its metal salt.  FIG. 5B  shows a close-up cross-section view of part  501  showing anodic oxide  504 , which is positioned on substrate  502 , exposed to sealing solution  504  during a sealing process. Sealing solution has UV light absorbing compound  506  and metal hydroxide  503  mixed therein. During the sealing process, UV light absorbing compound  506  and metal hydroxide  503  are allowed to diffuse within pores  505 . 
       FIG. 5C  shows part  501  after the sealing process is complete. As shown, the exposed portions of the metal oxide of anodic oxide  504  are converted to metal oxide hydrate, forming seal layer  507 . Seal layer  507  seals colorant  508  within pores  505 . UV light absorbing compound  506  and metal hydroxide  503  are incorporated within seal layer  507 . Metal hydroxide  503  can enhance the quality of the seal and prevent or reduce leaching out of colorant  508  from pores  505 . UV light absorbing compound  506  can absorb UV light incident top surface  512  of anodic oxide  504  and prevent or reduce UV light from reaching colorant  508 . 
     As described above, in some embodiments, a second sealing process is performed.  FIG. 5D  shows part  501  after an optional second sealing process, whereby part  501  is exposed to a second sealing solution that does not include UV light absorbing compound  506 . The second sealing process forms second seal layer  509  over seal layer  507 . In some embodiments, second seal layer  509  can prevent UV light absorbing compound  506  from leaching out of seal layer  507 , which can reduce the UV blocking ability of seal layer  507 . In some embodiments, second seal layer  509  includes metal hydroxide  503 . In some embodiments, second seal layer  509  does not include metal hydroxide  503 . 
       FIG. 6  shows flowchart  600  indicating a process for incorporating UV absorbing compound into anodic oxide. At  602 , a sealing solution for sealing pores of an anodic oxide is provided. in some embodiments, the sealing solution includes a sealant compound, such as a metal hydroxide, that improves the quality of the sealing. At  604 , a UV light absorbing compound is added to the sealing solution. The UV light absorbing compound can be any suitable compound capable of absorbing at least a portion of UV light wavelengths. In some embodiments, more than one type of UV light absorbing compound is used. At  606 , a UV light absorbing seal layer is formed by incorporating the UV light absorbing compound into the anodic oxide during a sealing process. In some embodiments, this involves immersing the anodic oxide into a sealing solution bath that has the UV light absorbing compound mixed therein. The UV light absorbing compound can become incorporated with the metal oxide hydrate formed during the sealing process. The UV light absorbing seal layer can block UV light from reaching any underlying colorant existing within the pores of the anodic oxide and decrease the occurrence of color fading. At  608 , an optional second seal layer is formed over the UV light absorbing seal layer. The second seal layer can be formed by exposing the anodic oxide to a second sealing solution that does not include a UV light absorbing compound. The second seal layer can prevent leaching out of the UV light absorbing compound from the UV light absorbing seal layer. 
     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 specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described 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: 20140122
Publication Date: 20170808
Grant Date: 20170808
Priority Date: 20130930
Inventors: RUNGE JUDE MARY
WIELER PATRICK S.
THORNTON, III JOHN MURRAY
MALONEY MAX A.
Assignee: APPLE INC
CPC Classifications: [{"code": "C25D11/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D11/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/246", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24997", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/246", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24997", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/243", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D11/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/30", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 52740436