Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2002-03-07
2003-05-20
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S475000, C427S482000, C427S486000, C427S195000, C427S424000
Reexamination Certificate
active
06565926
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to coated high speed flat stock material. More particularly, the invention pertains to metal strapping material having a powder coating thereon and a method for making same.
BACKGROUND OF THE INVENTION
Strapping material is well known in the art. Such material is used for packaging, i.e. strapping goods, for example, to a pallet for transportation, storage and the like. Strapping materials, because they are used in such large quantities and are discarded after a single use, must be manufactured from relatively common materials in efficient, low-cost processes.
As will be recognized by those skilled in the art, often goods that are stored and or transported strapped to a base, such as a pallet, may be subjected to relatively severe environmental conditions. This is particularly true when the goods are transported overseas, such as by cargo ship. To this end, the severe environmental conditions may include exposure to saltwater and saltwater-laden air.
In addition, goods may be stored, in albeit less severe conditions, for prolonged periods of time. To this end, while the strapping may not be subjected to the severe conditions of saltwater-laden air, they may nevertheless be subjected to relatively high humidity environments.
It has been found that common steel strapping can corrode rapidly. That is, oxidation has been observed to begin almost immediately when the strapping is subjected to relatively high humidity conditions. Oxidation, i.e., rust can also compromise the integrity of the strap. In addition, it has been found that rust can stain or mar the appearance of the “strapped” goods. This is particularly problematic with appearance sensitive products. Coatings have been used to prevent or retard corrosion of the strapping. One type of corrosion inhibiting coating is a water based coating much like a paint. Although these coatings work to an extent, it has been found that the process of coating the strapping material results in inconsistent coating or coverage and as such localized areas of corrosion can be readily observed. In addition, it has been found that with painted strapping, regardless of the coating thickness, corrosion of the strapping may nevertheless occur under prolonged or lengthy exposure conditions. It will be recognized by those skilled in the at that various qualities of liquid coatings are available, and that their corrosion resistance characteristics will vary. Nevertheless, there are drawbacks and limits to their performance characteristics.
Conventional wisdom provides that powder coatings be cured at temperatures of about 350° F. to about 450° F. for about 5 minutes to about 10 minutes. This precludes powder coatings for strap in that typical manufacturing lines speeds (about 180 to about 220 feet per minute) would require a curing oven hundreds of feet in length.
In addition, in the manufacture of steel strapping, the side edges of the strap are sharp and can create a personal hazard. Typically, the strap is conveyed around or over V-type pulleys which can abrasively remove the strap material at the edges resulting in sharp edges. Moreover, the protective function of a coating can be compromised by abrasive removal of the coating at the edges.
It has also been found that strap often requires an additional or subsequent application of an agent, such as wax, to increase the “slip” value of the finished material. A slip value is the force necessary to tension the strap when used in a strapping machine, when the strap is secured at one end and pulled or tensioned at an opposing end around a load. Slip values of less than about 15 Newton-meters are required for reliable tensioning of the strap. The use and operation of such a strapping machine is more fully disclosed in Bobren, U.S. Pat. No. 5,097,874, which patent is incorporated herein by reference.
Accordingly, there exists a need for a coating for strapping material that provides an effective barrier against corrosion. Desirably, such a coating is applied in a cost effective and efficient process that is compatible with existing metal strap manufacturing processes which require high manufacturing speeds (i.e., line speeds). Most desirably, such coating is applied resulting in a substantially uniform thickness of coating on the strapping material and, if desired, an over-coating of the strapping edges.
SUMMARY OF THE INVENTION
A corrosion-resistant strap is formed from an elongated steel bare strap material having width and a thickness and defining first and second sides and a pair of edge regions. A coating is applied and cured onto the bare strap material. The cured coating has a substantially consistent thickness at the first and second sides and at the edges. Optionally, the coating has a greater thickness at about the edge regions and on the first and second sides adjacent to the edge regions, defining a dog-bone profile.
For purposes of the present description and the claims that follow, reference will be made to bare strap, coated strap and cured strap. Bare strap is the base material prior to the application of the coating material. It is essentially the uncoated material that results from the “traditional” strap manufacturing process. Coated strap is the bare strap having the coating applied thereto, prior to curing or hardening. Last, cured strap refers to the strap having the coating applied thereto and cured or hardened.
As provided herein, a strap in accordance with the present invention has been shown to exhibit corrosion resistance characteristics in various simulated environments that are far superior to commercially available liquid coated strap. In some cases, these characteristics are more than ten-fold, and even twenty-fold increases over the known products.
Preferably, the coating is applied as a powder that is melted and cured onto the strap base material. A current powder is an epoxy material. Other contemplated powder materials include polyesters, urethanes, hybrids and the like.
A method for making the cured strap includes the steps of providing a bare strap having first and second sides and opposing edges. The strap is provided from a source, and is conveyed from the source to a coating apparatus. In that the coating operation or process can be fully integrated with the traditional strap manufacturing process, the “source” can be the output of the strap making operation.
The bare strap or base material is directed through the coating apparatus. In a present method, the apparatus is oriented vertically so that the bare strap, coated strap and cured strap traverse upwardly through the apparatus. The apparatus can, however, be oriented horizontally or at any incline as well.
A powder is applied on the first side of the strap, which covers the first side and the opposing edges. The powder is likewise applied on the second side of the strap, covering the second side and the opposing edges. The method can include, when applying the powder to the first side, covering that portion of the second side immediately adjacent to the opposing edges, and when applying the powder to the second side, covering that portion of the first side immediately adjacent to the opposing edges. In this manner, there is a framing effect on the opposing side to that being covered. This results in a “dog-bone” profile of the coating on the bare strap.
The powder is melted to form a flowable material that coats the bare strap. The flowable material is cured on the strap, and the cured strap is cooled. The cured strap is then wound onto a storage member. When the vertical coating method is employed, the strap is preferably supported from only an uppermost point as it moves in the vertically upward direction. This prevents marring or damage to the newly applied coating.
The powder is applied using an electrostatic application process. Preferably, the powder is first applied to the first side of the strap and subsequently is applied to the second side of the strap. The coated strap is heated with the powder thereon as it moves through the apparatus.
In one meth
Fredericksen Dave
Merritt Christopher
Nelson Jim
Rocheleau Dennis
Suopys Al
Breh Donald J.
Croll Mark W.
Illinois Tool Works
Parker Fred J.
Welsh & Katz Ltd.
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