Patent Abstract:
A method of evaluating a coating applied to a surface comprises the step of applying the coating to the surface. The coating including a conversion gel to chemically bind the surface and an indicator substantially uniformly distributed throughout the coating wherein the indicator modifies an appearance of the coating. The method further comprising the step of determining whether the indicator is present on the surface at a substantially uniform concentration.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of and claims priority to pending application Ser. No. 11/213,707 entitled COLORED COATING AND FORMULATION filed on Aug. 30, 2005, the entire contents of which is incorporated by reference herein. 
     
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    (Not Applicable) 
       FIELD 
       [0003]    The present invention generally relates to a surface coating and formulation. More particularly, the present invention pertains to a colored solution for coating a surface and formulation thereof. 
       BACKGROUND 
       [0004]    In various manufacturing and construction industries, items are produced that benefit from a surface coating or primer. Typically, these coatings provide some protection for the underlying surface or facilitate the adhesion of subsequent coatings such as paint. Metal or reactive surfaces, are typically coated or chemically altered to reduce reactivity and thereby reduce corrosion or oxidation. For example, parts containing aluminum or titanium often undergo a chromate conversion coating process such as Alodine™ treatment to reduce corrosion. Unfortunately, these treatments tend to generate waste that is expensive to process. Thus, for relatively large metal items, such as airplanes, conversion coatings may add considerable cost to the item. 
         [0005]    Accordingly, it is desirable to provide a coating capable of overcoming the disadvantages described herein at least to some extent. 
       BRIEF SUMMARY 
       [0006]    The foregoing needs are met, to a great extent, by the present invention wherein a method of evaluating a coating is provided. In an embodiment, the method may comprise the steps of applying the coating to the surface. The coating may include a conversion gel to chemically bind to the surface and an indicator substantially uniformly distributed throughout the coating. The indicator may modify an appearance of the coating. The method may further comprise the step of determining whether the indicator is present on the surface at a substantially uniform concentration. 
         [0007]    In a further embodiment, provided is a method of determining a thickness of a substantially clear coating on a surface. The method may comprise the steps of applying the coating to the surface. The coating may include an indicator that may be substantially uniformly distributed throughout the coating. The indicator may color the coating. The method may further comprise the steps of determining a color of the coating on the surface and determining a thickness of the coating on the surface based on the determined color. The method may further include removing the color from the coating. 
         [0008]    The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numerals refer to like parts throughout and wherein: 
           [0010]      FIG. 1  is a block diagram of a coated surface in accordance with an embodiment of the invention; 
           [0011]      FIG. 2  is a flow diagram illustrating steps that are followed in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The present invention provides a surface coating and formulation thereof that includes an indicator or colorant. In an example of a preferred embodiment, the coating chemically bonds to a surface and provides a protective layer and/or an adhesive layer upon which subsequent coatings adhere. A description of such coatings are to be found in U.S. Pat. Nos. 5,849,110; 5,869,141; 5,958,578; and 6,605,365, respectively titled: SOL-COATING OF METALS; SURFACE PRETREATMENT FOR COATING OF METALS; HYBRID LAMINATE HAVING IMPROVED METAL-TO-RESIN ADHESION; and PIGMENTED ALKOXYZIRCONIUM SOL, the disclosures of each of which is incorporated herein by reference in their entirety. 
         [0013]    Preferred embodiments of the invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. As shown in  FIG. 1 , a coated surface  10  includes a surface  12  and a coating  14 . The surface  12  includes any suitable material and item. General examples of suitable materials include, at least, those materials classified as electron acceptors and/or electron donors. More particularly, suitable materials include metals, plastics, resins, and the like. Specifically, aluminum and aluminum alloys, titanium and titanium alloys, and the like are suitable for use in various embodiments of the invention. Examples of suitable items generally include manufactured parts and goods. More particularly, airplanes, spacecraft, cars, boats, golf clubs, parts for these and other items, and the like are suitable for use in various embodiments of the invention. 
         [0014]    The coating  14  includes any suitable formulation, solution, or composition operable to form a coating on a surface. More particularly, the coating  14  includes clear, transparent, or translucent coatings. For example, Boegel EPII produces a high performance conversion coating that is a viable replacement for chromate conversion coatings and that lessen the environmental impact of painting operations. However, the Boegel EPII and other such coatings are difficult to detect visually because they are essentially clear and do not substantially alter the appearance of the surface. As such, generating consistent applications and processing quality assurance inspections are difficult. By including an indicator  16 , the conversion coating is visually detectable during and/or after application. 
         [0015]    In various embodiments, the indicator  16  is: 1) visible essentially always; 2) visible for a predetermined time period; 3) substantially transparent until induced to become visible; 4) visible until induced to become essentially transparent; and/or  4 ) controlled to become visible and essentially transparent. 
         [0016]    In an embodiment, any suitable dye is included as indicator  16  in a formulation for the conversion coating. In general, suitable dyes include those that remain suspended in solution. Particular examples of suitable dyes that are visible under white light include: Basic Blue 41, Direct Red 81, Fluorescent Yellow AA225, Methylene Blue, and the like. Particular examples of suitable dyes visible under ultraviolet (UV) light include: Pyranine dye; Basic Red 1 (rhodamine 6G); L-142; L-174; L-182; L-187; L-212; and the like. These and other suitable dyes that are visible under white light and/or UV light are available at: Sigma-Aldrich, Milwaukee, Wis., USA; VWR Scientific Products, West Chester, Pa., USA; Keystone Aniline Corporation, Chicago, Ill., USA; and Beaver Luminescers, Newton, Mass., USA. 
         [0017]    In another embodiment, the indicator  16  includes a colorant chemically tethered or bound via hydrogen bonds, covalent bonds and the like, to a constituent of the coating  14 . For example, by reacting hydroxyl or amine terminated colorant compounds with an isocyanate terminated alkoxysilane, the colorant may be substantially immobilized within the coating  14 . It is an advantage of this embodiment that the tendency of the colorant to migrate out of the coating  14  is reduced. It is another advantage of this embodiment that relatively large and/or insoluble molecules may be tethered and substantially prevented from precipitating or otherwise coming out of solution. In particular, Lenhart, et al., (J. L. Lenhart, J. H. van Zanten, J. P. Dunkers, C. G. Zimba, C. A. James, S. K. Pollack, R. S. Pamas; “Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface,” J. Colloid Interface Science, 221 (2000): 75) have synthesized a material that features a fluorescent moiety attached to a silicon alkoxide group. In the following example, hydroxy-methylaminonitrostilbene (HMANS) reacts with isocyanatopropyltriethoxysilane (IPS) to produce the DMANS/silane coupling agent (DMSCA). 
         [0000]    
       
                 
         
             
             
         
       
     
         [0018]    In a similar example, Dispersion Red 19 is reacted with 3-isocyanatopropyl-triethoxysilane over a range of times and temperatures and with a variety of solvents (chloroform, dioxane, tetrahydrofuran (THF)). In one such reaction method, dibutyl tin dilaurate is added to THF solvent and results in complete reaction of the isocyanate reactant overnight as monitored by the disappearance of the isocyanate peak (2230 cm −1 ). The reaction product is isolated by evaporation. The product is dissolved in ethanol and filtered to remove some darker insoluble material. The ethanol is evaporated and the resulting product is a dark red pasty solid. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0019]    The adduct is then dissolved in 6 ml of ethanol and diluted with 6 ml of deionized (DI) water prior to adding drop wise to 100 ml of Boegel EPII with stirring. Aluminum substrates are coated with the colored coating by drench coating the panels with a spray application, for example. The dried coating exhibits a pale red hue. Doubling the concentration of the dye adduct to 0.06 wt % does not appreciably increase the intensity of the red color on coated panels. Following room temperature curing for 72 hours, the coated panels are partially immersed in 120° F. (48.89° C.) DI water for 24 hours. A very slight loss of color is noted in the coatings. 
         [0020]    The concentration of the Dispersion Red 19 dye adduct is then increased to 0.15% and 0.3 wt % of the dyed Boegel EPII mixture. The resulting coating mixture is an intense red-orange suspension. The resulting dyed Boegel EPII mixture sprayed uniformly on the aluminum panels with flood coating and after room temperature drying produces a coating with a reddish color. The coating from the 0.3 wt % mixture is visually only slightly more intense than the 0.15 wt % mix. Subsequent evaluation of different dye adducts is carried out at the 0.15 wt % level for comparison. 
         [0021]    In addition, other suitable compounds for use as covalently linked indicators  16  include at least those with —OH or —NH 2  groups. Particular examples of dye compounds suitable for use as covalently linked indicators  16  due to the —OH or —NH 2  groups on the indicator  16  molecules include: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0022]    As a general procedure, each dye is dissolved in THF at ˜10 wt % concentration and reacts with the isocyanate terminated alkoxysilane at a 1:1 molar ratio. Dibutyl tin dilaurate, is added as a catalyst and the reaction is heated at 60° C. overnight. Disappearance of the isocyanate absorption in the infra red (IR) is interpreted as complete reaction. The dye adduct is isolated by removing the THF under vacuum, dissolving the residue in ethanol, filtering and removing the ethanol under vacuum. The solid product is considered to be the dye adduct and is used to color the coating  14 . 
         [0023]    In a specific example, Acid Blue 25 dye is incorporated into the coating  14 . Acid Blue 25 has a—NH 2  functionality as well as containing the sodium salt of a sulfonic acid group. The dye is soluble in THF and water. The dye comes from the supplier as only 45% dye so filtration of THF solutions is carried out to remove the non-dye components. The dye adduct is soluble in ethanol and produces a nice uniform intense blue coating  14 . The coated aluminum panel is significantly blue. 
         [0024]      FIG. 2  is a flow diagram of a method  20  according to an embodiment of the invention. In general, the method  20  includes an optional surface preparation step  22 , coating application step  24 , curing step  26 , evaluation step  28 , and an optional color removal step  30 . 
         [0025]    At step  22 , the surface  12  is optionally prepared for coating. If performed, the surfacing preparation may include one or more of cleaning, degreasing, abrading, acid etching, and the like. Depending upon the various manufacturing procedures performed to generate the surface, preparation of the surface  12  may not be required. If the surface  12  includes oils or other such contaminants, sufficient surface preparation is performed to remove the contaminants. For example, the surface  12  may be washed with a detergent to remove any oils present. The surface  12  may further be evaluated prior to coating. For example, a layer of water may be applied to the surface. If the surface  12  is determined to be “water break free,” it may be determined that the surface  12  is ready for application of the coating  14 . If the surface  12  includes coatings such as paint and the like, the coatings may be chemically and/or mechanically abraded until the surface  12  is exposed. It is an advantage of various embodiments of the invention that some oxidation may be present on the surface. Conventional coatings such as Alodine™, for example, require oxidation-free surfaces and thus require acid etching or other such treatments to remove all oxidation. It is another advantage of various embodiments that the surface  12  may be oxidized or anodized prior to application and this oxidation or anodized coating will not adversely affect subsequent application steps of the present invention. 
         [0026]    At step  24 , the coating  14  is applied to the surface  12 . In an embodiment, the coating  14  with the included indicator  16  is applied to the surface  12 . For example, the surface  12  is dipped in, drenched, or sprayed with the coating  14 . More generally, any suitable coating  14  that includes the indicator  16  may benefit from various embodiments of the invention. More particularly, any clear, transparent, or translucent coating  14  may be formulated to include the indicator  16 . Particular examples of steps performed during the application step  24  are provided herein with respect to steps  32  to  38 . 
         [0027]    At step  26 , the coating  14  is cured. Curing of the coating  14  may be performed in any suitable manner. In various embodiments, curing is accomplished by allowing the coating  14  to air dry for a predetermined amount of time and/or until a predetermined surface characteristic is achieved such as, the coated surface  10  is dry to the touch, or the like. 
         [0028]    At step  28 , the coating  14  is optionally evaluated. In various embodiments, the coating  14  is not evaluated following curing, but rather, at the time of application. Alternatively, a post-application inspection is performed to verify appropriate application of the coating  14 . Particular examples of steps performed during the optional evaluation step  28  are provided herein with respect to steps  42  to  48 . 
         [0029]    At step  30 , the coating  14  is optionally “demodified” or returned to an essentially clear state. In general, if performed, the color is removed from the coating  14  by chemically altering the indicator  16  to reduce its visibility or by diffusing the indicator  16  from the coating  14 . Particular examples of steps performed during the color removal step  30  are provided herein with respect to steps  50  to  54 . 
         [0030]    At step  32 , the coating  14  is applied to the surface  12 . In an embodiment, the coating  14  with the included indicator  16  is applied to the surface  12 . For example, the surface  12  is dipped in, drenched, brushed, rolled, or sprayed with the coating  14 . In a particular example, a user or operator sprays the coating  14  on the surface  12  with a suitable spray gun. Suitable examples of spray guns include high volume low pressure (HVLP) systems, high pressure low volume (HPLV) systems, electrostatic systems, and the like. In another example, a robotically controlled applicator nozzle is controlled to apply the coating  14  to the surface  12 . 
         [0031]    At step  34  the indicator  16  is inspected. For example, the user observes the color of the surface  12 . In an embodiment, the indicator  16  is controlled to generate the visible color. For example, a dye configured to fluoresce in response to exposure to UV light may be utilized as the indicator  16  is included in the coating  14  and is exposed to a suitable wavelength of electromagnetic radiation to fluoresce at a visible wavelength. In other embodiments, the indicator  16  is visible in other wavelengths of light such as white light. 
         [0032]    At step  36 , it is determined if a sufficient amount of the indicator  16  is present. In an embodiment, the color or intensity of color is dependent upon a thickness of the applied coating  14 . Thus, based on the color or intensity of color, the thickness of the coating  14  may be determined. It is an advantage of various embodiments that the thickness of any suitable coating  14  may be determined. Examples of suitable coatings include any otherwise transparent or translucent coating such as polyurethane, varnish, shellac, and the like. In response to one or more area being essentially devoid of the indicator  16  or below a predetermined color or color intensity, it may be determined that an insufficient amount of the indicator  16  is present and, therefore, more of the coating  14  is applied at step  32 . In response to the color or intensity of color being at a predetermined sufficient color level on the surface  12  and/or the sufficient color being substantially uniformly distributed upon the surface  12 , it is determined if an excess of the indicator  16  is present at step  38 . 
         [0033]    At step  38 , it is determined if an excess of the indicator  16  is present upon the surface  12 . For example, the coated surface  10  is inspected for runs and/or pooling of the indicator  16 . Specifically, relatively low points, creases, or other such surface characteristics are inspected. In response to an excess of the indicator  16  being present upon the surface  12 , the excess is removed at step  40 . In response to determining that an excess of the indicator  16  is not present upon the surface  12 , the coating  14  is cured at step  26 . 
         [0034]    At step  40 , excess coating  14  is removed. For example, a squeegee or absorbent cloth is utilized to remove any excess coating  14 . In another example, a stream of air from an air gun or air knife is utilized to remove any excess coating  14 . 
         [0035]    At step  42 , the indicator  16  is inspected. For example, the user observes the color of the surface  12 . In an embodiment, the indicator  16  is controlled to generate the visible color. For example, a dye configured to fluoresce in response to exposure to UV light may be utilized as the indicator  16  is included in the coating  14  and is exposed to a suitable wavelength of electromagnetic radiation to fluoresce at a visible wavelength. In other embodiments, the indicator  16  is visible in other wavelengths of light such as white light. 
         [0036]    At step  44 , it is determined if the indicator  16  is present on the surface in a substantially even coating  14  and/or that sufficient amounts of the indicator  16  are present. In response to one or more areas being essentially devoid of the indicator  16  or below a predetermined color or color intensity, it may be determined that an application error has occurred. In response to the color or intensity of color being at a predetermined sufficient color level on the surface and/or the sufficient color being substantially uniformly distributed upon the surface, it is determined if an excess of the indicator  16  is present at step  46 . 
         [0037]    At step  46 , it is determined if an excess of the indicator  16  is present upon the surface  12 . For example, the coated surface  10  is inspected for runs and/or pooling of the indicator  16 . Specifically, relatively low points, creases, or other such surface characteristics are inspected. In response to an excess of the indicator  16  being present upon the surface  12 , it may be determined that an application error has occurred. In response to determining that an excess of the indicator  16  is not present upon the surface  12 , it is determined if any color generated by the indicator  16  is to be removed at step  50 . 
         [0038]    At step  48 , in response to determining an application error has occurred, the surface  12  is optionally prepared at step  22 . 
         [0039]    At step  50 , it is determined if any color generated by the indicator  16  is to be modified. For example, if the product is intended to have a clear, transparent, or translucent coating, any color generated by the indicator  16  may be removed. In another example, color generated by the indicator  16  may be altered to a different color, such as, for example, a less visible color. In response to a determination that the color is to be modified, the color is modified at step  52 . In response to a determination that any color present is acceptable, the coated surface  10  receives a passing evaluation and may be advanced to any further manufacturing step or the like. For example, if the colorant is made visible in response to UV illumination but is otherwise essentially clear, it may be determined that the indicator  16  may remain, as is, in the coating  14 . In another example, if it is determined that the colorant will be covered by an opaque coating such as paint or that the colorant is aesthetically acceptable, it may be determined that the indicator  16  may remain, as is, in the coating  14 . 
         [0040]    At step  52 , any color present is modified from the coated surface  10 . In various embodiments, the color may be removed, reduced, or otherwise altered, by UV breakdown of the indicator  16 , heating the indicator  16 , chemically altering the indicator  16 , and/or leaching the indicator  16  from the coating  14 . That is, in a particular embodiment, the indicator  16  is controllable to “demodify” or otherwise revert the appearance of the coated surface  10  to an essentially uncolored state. In a specific example, the colorant AA225 is removed from the coating  14  by soaking the coated surface  10  in water for 24 hours. In another example, Methyl Blue is controlled to change to a less visible color by altering the pH of the coating  14 . It is an advantage of embodiments that coating an aluminum or titanium surface with the coating  14  containing Methyl Blue, induces such a change in the Methyl Blue colorant. Thus, by utilizing Methyl Blue as the indicator  16 , a strong blue color is observed during application of the coating  14  which facilitates determining the thickness of the applied coating  14  and, thereafter, the indicator  16  is controlled to fade to a lighter color. By including Methyl Blue in the coating  14  at a concentration which results in a blue color that is at or near the limit of visibility, upon conversion of the indicator  16  to a less visible color, the indicator  16  is controlled to become effectively clear. In yet other examples, colorants that are unstable in light or UV light or are unstable when exposed to heat are utilized as the indicator  16  and appropriate conditions to render the indicator  16  colorless are applied to the coated surface  10 . 
         [0041]    At step  54 , it is determined if the color has been sufficiently modified. For example, the user or operator may visually inspect the coated surface  10  to determine if color remains. In particular, depending upon the method of color modification, areas calling for increased diligence may include those areas susceptible to shadows, crevices, and the like. If it is determined that some color remains essentially unmodified, the coated surface  10  may be further modified at step  52 . 
         [0042]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Technology Classification (CPC): 2