Colored coating and formulation

A composition for coating a surface includes a carrier and an indicator distributed throughout the carrier. The indicator is configured to modify an appearance of the coating. The indicator facilitates determining a thickness of the coating in response to the appearance of the coating.

FIELD OF THE INVENTION

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 OF THE INVENTION

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.

Accordingly, it is desirable to provide a coating capable of overcoming the disadvantages described herein at least to some extent.

SUMMARY OF THE INVENTION

The foregoing needs are met, to a great extent, by the present invention, wherein in one respect a surface coating and formulation thereof is provided.

An embodiment of the present invention pertains to a composition for coating a surface. The composition includes a carrier and an indicator distributed throughout the carrier. The indicator is configured to modify an appearance of the coating. The indicator facilitates determining a thickness of the coating in response to the appearance of the coating and the indicator is controllable to demodify the appearance of the coating.

Another embodiment of the present invention relates to a composition for coating a surface. The composition includes a carrier and a colorant. The carrier includes an alkoxyzirconium aqueous sol, an organosilane coupling agent, and a catalyst. The alkoxyzirconium aqueous sol includes (R—O)4—Zr, where R is C2-C5aliphatic and the zirconium is configured to chemically bond the surface. The catalyst includes an effective amount of acetic acid. The colorant is distributed throughout the carrier and modifies an appearance of the coating.

Yet another embodiment of the present invention pertains to a method of evaluating a coating applied to a surface. In this method, the coating having an indicator is applied to the surface and it is determined if the indicator is present on the surface at a substantially uniform concentration. The coating includes a conversion gel to chemically bind the surface and the indicator. The indicator modifies an appearance of the coating.

Yet another embodiment of the present invention pertains to a method of determining a thickness of a substantially clear coating on a surface. In this method, a coating is applied to the surface. The coating included an indicator distributed substantially evenly throughout. The indicator colors the coating. The color of the coated surface is determined. The thickness of the coating is determined in response to the color. The color is removed from the coating.

Yet another embodiment of the present invention pertains to an apparatus for evaluating a coating applied to a surface. The apparatus includes a means for applying the coating to the surface, an indicating means, and a means for determining whether the indicating means is present on the surface at a substantially uniform concentration. The coating includes a conversion sol gel to chemically bind the surface and the indicating means substantially evenly distributed throughout the coating. The indicating means modifies an appearance of the coating.

Yet another embodiment of the present invention pertains to an apparatus for determining a thickness of a substantially clear coating on a surface. The apparatus includes a means for applying a coating to the surface, means for determining a color of the coated surface, means for determining the thickness of the coating in response to the color, and means for removing the color from the coating. The coating includes an indicating means substantially evenly distributed throughout the coating. The indicating means colors the coating.

DETAILED DESCRIPTION

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.

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 inFIG. 1, a coated surface10includes a surface12and a coating14. The surface12includes 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. The coating14includes any suitable formulation, solution, or composition operable to form a coating on a surface. More particularly, the coating14includes 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 coating 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 indicator16, the conversion coating is visually detectable during and/or after application.

In various embodiments, the indicator16is: 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.

In an embodiment, any suitable dye is included as indicator16in 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.

In another embodiment, the indicator16includes a colorant chemically tethered or bound via hydrogen bonds, covalent bonds and the like, to a constituent of the coating14. For example, by reacting hydroxyl or amine terminated colorant compounds with an isocyanate terminated alkoxysilane, the colorant may be substantially immobilized within the coating14. It is an advantage of this embodiment that the tendency of the colorant to migrate out of the coating14is 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).

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.

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.

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.

In addition, other suitable compounds for use as covalently linked indicators16include at least those with —OH or —NH2groups. Particular examples of dye compounds suitable for use as covalently linked indicators16due to the —OH or —NH2groups on the indicator16molecules include:

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 coating14.

In a specific example, Acid Blue 25 dye is incorporated into the coating14. Acid Blue 25 has a —NH2functionality 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 coating14. The coated aluminum panel is significantly blue.

FIG. 2is a flow diagram of a method20according to an embodiment of the invention. In general, the method20includes an optional surface preparation step22, coating application step24, curing step26, evaluation step28, and an optional color removal step30.

At step22, the surface12is 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 surface12may not be required. If the surface12includes oils or other such contaminants, sufficient surface preparation is performed to remove the contaminants. For example, the surface12may be washed with a detergent to remove any oils present. The surface12may further be evaluated prior to coating. For example, a layer of water may be applied to the surface. If the surface12is determined to be “water break free,” it may be determined that the surface12is ready for application of the coating14. If the surface12includes coatings such as paint and the like, the coatings may be chemically and/or mechanically abraded until the surface12is 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 surface12may be oxidized or anodized prior to application and this oxidation or anodized coating will not adversely effect subsequent application steps of the present invention.

At step24, the coating14is applied to the surface12. In an embodiment, the coating14with the included indicator16is applied to the surface12. For example, the surface12is dipped in, drenched, or sprayed with the coating14. More generally, any suitable coating14that includes the indicator16may benefit from various embodiments of the invention. More particularly, any clear, transparent, or translucent coating14may be formulated to include the indicator16. Particular examples of steps performed during the application step24are provided herein with respect to steps32to38.

At step26, the coating14is cured. Curing of the coating14may be performed in any suitable manner. In various embodiments, curing is accomplished by allowing the coating14to air dry for a predetermined amount of time and/or until a predetermined surface characteristic is achieved such as, the coated surface10is dry to the touch, or the like.

At step28, the coating14is optionally evaluated. In various embodiments, the coating14is not evaluated following curing, but rather, at the time of application. Alternatively, a post-application inspection is performed to verify appropriate application of the coating14. Particular examples of steps performed during the optional evaluation step28are provided herein with respect to steps42to48.

At step30, the coating14is optionally “demodified” or returned to an essentially clear state. In general, if performed, the color is removed from the coating14by chemically altering the indicator16to reduce its visibility or by diffusing the indicator16from the coating14. Particular examples of steps performed during the color removal step30are provided herein with respect to steps50to54.

At step32, the coating14is applied to the surface12. In an embodiment, the coating14with the included indicator16is applied to the surface12. For example, the surface12is dipped in, drenched, brushed, rolled, or sprayed with the coating14. In a particular example, a user or operator sprays the coating14on the surface12with 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 coating14to the surface12.

At step34the indicator16is inspected. For example, the user observes the color of the surface12. In an embodiment, the indicator16is 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 indicator16is included in the coating14and is exposed to a suitable wavelength of electromagnetic radiation to fluoresce at a visible wavelength. In other embodiments, the indicator16is visible in other wavelengths of light such as white light.

At step36, it is determined if a sufficient amount of the indicator16is present. In an embodiment, the color or intensity of color is dependent upon a thickness of the applied coating14. Thus, based on the color or intensity of color, the thickness of the coating14may be determined. It is an advantage of various embodiments that the thickness of any suitable coating14may 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 indicator16or below a predetermined color or color intensity, it may be determined that an insufficient amount of the indicator16is present and, therefore, more of the coating14is applied at step32. In response to the color or intensity of color being at a predetermined sufficient color level on the surface12and/or the sufficient color being substantially evenly distributed upon the surface12, it is determined if an excess of the indicator16is present at step38.

At step38, it is determined if an excess of the indicator16is present upon the surface12. For example, the coated surface10is inspected for runs and/or pooling of the indicator16. Specifically, relatively low points, creases, or other such surface characteristics are inspected. In response to an excess of the indicator16being present upon the surface12, the excess is removed at step40. In response to determining that an excess of the indicator16is not present upon the surface12, the coating14is cured at step26.

At step40, excess coating14is removed. For example, a squeegee or absorbent cloth is utilized to remove any excess coating14. In another example, a stream of air from an air gun or air knife is utilized to remove any excess coating14.

At step42, the indicator16is inspected. For example, the user observes the color of the surface12. In an embodiment, the indicator16is 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 indicator16is included in the coating14and is exposed to a suitable wavelength of electromagnetic radiation to fluoresce at a visible wavelength. In other embodiments, the indicator16is visible in other wavelengths of light such as white light.

At step44, it is determined if the indicator16is present on the surface in a substantially even coating14and/or that sufficient amounts of the indicator16is present. In response to one or more area being essentially devoid of the indicator16or 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 evenly distributed upon the surface, it is determined if an excess of the indicator16is present at step46.

At step46, it is determined if an excess of the indicator16is present upon the surface12. For example, the coated surface10is inspected for runs and/or pooling of the indicator16. Specifically, relatively low points, creases, or other such surface characteristics are inspected. In response to an excess of the indicator16being present upon the surface12, it may be determined that an application error has occurred. In response to determining that an excess of the indicator16is not present upon the surface12, it is determined if any color generated by the indicator16is to be removed at step50.

At step48, in response to determining an application error has occurred, the surface12is optionally prepared at step22.

At step50, it is determined if any color generated by the indicator16is to be modified. For example, if the product is intended to have a clear, transparent, or translucent coating, any color generated by the indicator16may be removed. In another example, color generated by the indicator16may 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 step52. In response to a determination that any color present is acceptable, the coated surface10receives 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 indicator16may remain, as is, in the coating14. 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 indicator16may remain, as is, in the coating14.

At step52, any color present is modified from the coated surface10. In various embodiments, the color may be removed, reduced, or otherwise altered, by UV breakdown of the indicator16, heating the indicator16, chemically altering the indicator16, and/or leaching the indicator16from the coating14. That is, in a particular embodiment, the indicator16is controllable to “demodify” or otherwise revert the appearance of the coated surface10to an essentially uncolored state. In a specific example, the colorant AA225 is removed from the coating14by soaking the coated surface10in water for 24 hours. In another example, Methyl Blue is controlled to change to a less visible color by altering the pH of the coating14. It is an advantage of embodiments that coating an aluminum or titanium surface with the coating14containing Methyl Blue, induces such a change in the Methyl Blue colorant. Thus, by utilizing Methyl Blue as the indicator16, a strong blue color is observed during application of the coating14which facilitates determining the thickness of the applied coating14and, thereafter, the indicator16is controlled to fade to a lighter color. By including Methyl Blue in the coating14at a concentration which results in a blue color that is at or near the limit of visibility, upon conversion of the indicator16to a less visible color, the indicator16is 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 indicator16and appropriate conditions to render the indicator16colorless are applied to the coated surface10.

At step54, it is determined if the color has been sufficiently modified. For example, the user or operator may visually inspect the coated surface10to 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 surface10may be further modified at step52.