Textile surface coatings of iron oxide and aluminum oxide

Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation functions biologically

Reexamination Certificate

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C442S063000, C442S069000, C442S164000, C442S168000

Reexamination Certificate

active

06764969

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to coatings of iron and aluminum oxides for deposition on textile substrates. This invention also relates to a method for the deposition of iron (III) oxides and aluminum oxides in status nascendi from an aqueous solution of iron (II) or iron (III) and aluminum salts so as to form such a coherent, substantially amorphous textile coating. The present invention further relates to articles produced thereby.
DISCUSSION OF THE PRIOR ART
It has long been known that particulates of iron oxides may be used as pigments to dye substrates. Given the multitude of forms of iron oxides known to exist and the natural abundance of iron, iron oxides can potentially provide an inexpensive, readily available method of coloring certain substrates, such as textiles. However, the use of iron oxide pigments to dye textiles has serious drawbacks. This is largely due to the fact that the pigments comprise a plurality of discrete particles or crystals of various iron oxides which do not bind directly to the fabric. Because of this, a binder must be applied with the pigment to hold the individual pigment particles in place. Furthermore, the particles have a very limited ability to penetrate the interstices of the fabric. Thus, the coloring of textiles with iron oxide pigments is limited to a topical treatment.
In addition to its use as a colorant, particulate iron oxide has been applied to substrates in an attempt to increase their conductivity. For example, U.S. Pat. No. 3,958,066 to Imamura et al. discloses one potential method of binding a metal oxide particle directly to a textile fiber. In this method a fiber, in a heated, softened state, is coated with a metal powder. The fiber is cooled effectively binding the individual metal particles to the fiber and the bound particles are subsequently oxidized to form metal oxides. This method suffers from the requirement of high temperatures in order to soften and necessarily weaken the fiber as well as the inability to form a truly smooth, coherent, uniform coating of metal oxide from the oxidation of individual metal particles.
The prior art suggests iron oxides may be formed in films under certain conditions. For example, an article by Rochelle M. Cornell, “The Film-Forming Abilities of Iron Oxides and Oxyhydroxides,”
Clay Minerals
, vol. 18, pp. 209-213 (1983), suggests that under appropriate conditions dispersed synthetic goethite (an iron oxide hydroxide) may form a self-supporting film upon vacuum-filtration and drying. Ferrite films for textiles or fibers are disclosed in U.S. Pat. No. 4,515,850 to Ishino et al. and U.S. Pat. No. 4,911,957 to Oishi et al. However, these films are not produced within the same required pH, temperature, and concentration parameters of the instant invention. In U.S. Pat. No. 4,435,220 to Watanabe et al. transparent, colored pigments are disclosed which are formed by precipitating a mixture of metal oxides, including alkali earth metal oxides, from an aqueous solution and depositing the precipitate of this mixture onto platelet-shaped, inorganic particles, of from 1 to 100 microns in size, formed from materials such as mica, glass, and talc. The precipitation of goethite in crystalline form has also been discussed in a more recent article by Kulamani Parida and Jasobanta Das, “Studies in Ferric Oxide Hydroxides,”
Journal of Colloid and Interface Science
, vol. 178, pp. 586-593 (1996). U.S. Pat. Nos. 3,657,003 and 3,767,590, both to Kenney, disclose methods of making non-wettable surfaces wettable in applications such as the printing of electrical circuits. Patentee's method entails first providing a salt solution which produces a colloidal mixture of hydrous oxide particles and subsequently immersing the non-wettable surface in this colloidal mixture, ultimately forming a new wettable surface on top of the non-wettable surface.
There is no teaching within this prior art of a textile coating or film comprised of iron oxide and aluminum oxide. Such a film provides an effective and inexpensive method of providing color to surfaces. This is accomplished through the formation of smooth, durable, substantially amorphous, coherent iron (III) oxide/aluminum oxide films on the surfaces of certain fabric substrates utilizing inexpensive, readily available iron and aluminum salts. Such coatings provide other benefits such as improved color fastness and vastly improved bacteriostatic properties.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide a film for fabric surfaces comprising iron oxide and aluminum oxide, as well as a method of producing such smooth, substantially amorphous, coherent coatings. It is another object of the present invention to produce textile composites by this method. Another object of the invention is to color textiles with these coatings. Still another object of the present invention is to provide colored coatings for textiles which are durable, smooth, and coherent. Yet another object of the invention is to apply iron oxide/aluminum oxide coatings to a substrate without subjecting the substrate to damagingly high temperatures and without using binders to adhere the coating to the surface. A further object of this invention is to coat different types of substrates, notably textiles, with such an iron oxide/aluminum oxide film in order to provide vastly improved bacteriostatic properties. Such a coated textile can be utilized in water filtration processes. The utilization of iron (II) and aluminum oxides within such a filtration article provides extremely low toxicity to a consumer since such oxides are already frequently ingested for medicinal purposes (i.e., to increase red blood cell production or as an antacid, respectively).
Accordingly, a method for producing a substrate coating is provided in which a substrate is contacted with a water-based solution containing a dissolved ferrous or ferric salt in addition to an aluminum salt. In order to produce a substantially amorphous coating on the substrate surface an in situ formation of iron and aluminum oxide hydroxide (hydrated forms) articles must first take place. Most important in this in situ formation is that the particles be sub-colloidal in size; they must have a sufficiently small average particle size so as to permit film generation on the surface of the textile. If the average particle size were too large, and if the colloidal particles would pack together, it could effectively prevent the film-forming ability of the metal oxide hydroxides. These necessarily small metal-oxide-hydroxide particles then are adsorbed onto the surface of the substrate. This adsorption is obtained because the rate of reaction of in situ formation of iron oxide and aluminum oxide particles is slower than the rate of adsorption of such particles to the fabric surface. Also, this surface adsorption rate for the oxides is greater than the rate of coagulation between such oxide particles. This can be achieved by maintaining the pH of the water-based solution at about 2.5 or higher, with preferred ranges (up to 8) dependent upon the particular metal oxide films desired, and, at the same time, by heating the solution to a temperature of about 50° C. or higher, again with particular ranges for specific metal oxides. It is believed that the iron (II) salt, when utilized, which dissociates in solution to form the corresponding ion is first hydrolyzed to the soluble iron (II) hydroxide and then oxidized to form iron (III) oxide (actually iron oxide hydroxide). If iron (III) salt is utilized, then the corresponding ion is only hydrolyzed, since it has already been oxidized to the iron (III) state, to form iron (III) oxide (again, actually, iron oxide hydroxide). Although the iron (III) oxide has an extremely slight solubility in water, the conditions of the system such as pH, temperature, and concentrations are controlled such that the iron (III) oxide does not precipitate in solution, but it adsorbs onto the substrate surface, as noted above. In this manner, the iron (III) oxide is not deposited i

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