FIELD OF THE INVENTION The present invention relates to closures such as those commonly employed on flexible storage bags, particularly those suitable for use in the containment and protection of various items including perishable materials.

BACKGROUND OF THE INVENTION Flexible storage bags for use in the containment and protection of various items, as well as the preservation of perishable materials such as food items, are well known in the art. Such bags typically comprise a rectangular sheet of polymeric film folded upon itself and sealed along two edges to form a semi-enclosed container having two flexible opposed sidewalls, three sealed or folded edges, and one open edge. A closure integrally formed with the bag such as an interlocking rib-type seal or separately provided such as a plastic or paper-clad-wire tie completes the containment assembly.

As utilized herein, the term"flexible"is utilized to refer to materials which are capable of being flexed or bent, especially repeatedly, such that they are pliant and yieldable in response to externally applied forces. Accordingly,"flexible"is substantially opposite in meaning to the terms inflexible, rigid, or unyielding. Materials and structures which are flexible, therefore, may be altered in shape and structure to accommodate external forces and to conform to the shape of objects brought into contact with them without losing their integrity. Flexible storage bags of the foregoing variety are typically formed from polymeric film, such as polyethylene or other members of the polyolefin family, in thicknesses of between about 0.0002 inches to about 0.002 inches. Such films are frequently transparent but sometimes are opaque and/or colored.

Flexible storage bags of the currently commercially available variety provide a means of conveniently storing a wide range of objects and materials in a generally disposable containment device. Many commercially available flexible storage bags utilize mechanical interlocking seals to achieve closure of the bag opening, and some such bags additionally employ a sliding mechanical closure to improve the ease of opening and closing mechanical interlocking seals.

With either type of mechanical interlocking seal, there remains the issue of determining whether complete closure has in fact been completed across the mouth of the bag to achieve the desired completion of the closing operation.

Currently there are two color change systems on the market for such closures. One system involves the interlocking of blue and yellow elements to produce a green seal, while the other involves the interlocking of red and blue elements to produce a purple seal. These are accomplished by simply dying each side of the translucent zipper closure a different primary color so that when they are pressed together to seal, light passing through the closure produces an apparent color which is the secondary color formed from the original two primary colors. While such systems do provide a color change indication of when sealing has been accomplished, under many lighting conditions it is difficult to discern whether the color seen by the consumer is produced by interlocking of the seals or by light passing through elements which are merely closely superimposed. Moreover, those individuals with visual impairments such as color blindness or reduced visual acuity may not correctly interpret the condition of the seal by vision alone.

Accordingly, it would be desirable to provide a closure which provides for a positive indication of when a complete closure has been achieved.

SUMMARY OF THE INVENTION The present invention provides a flexible storage bag having an opening and a closure system for the opening, wherein the closure system provides a high contrast color indication when complete closure of the closure system has been achieved. The closure system may be a mechanical interlocking seal or an adhesive-based closure system. The high contrast color indication may be a change from colorless to colored, from white to black, and/or from translucent to opaque.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: Figure 1 is an elevational view of a flexible storage bag employing a closure in accordance with the present invention; Figure 2 is an elevational view of another flexible storage bag in accordance with the present invention; Figure 3 is a perspective view of a further flexible storage bag in accordance with the present invention; and Figure 4 is an elevational view of yet another flexible storage bag in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 depicts a presently preferred embodiment of a flexible storage bag 10 according to the present invention. In the embodiment depicted in Figure 1, the flexible storage bag 10 includes a bag body 20 formed from a piece of flexible sheet material folded upon itself along fold line 22 and bonded to itself along side seams 24 and 26 to form a semi-enclosed container having an opening along edge 30. Flexible storage bag 10 also includes a mechanical closure system 40 located adjacent to edge 30 for sealing edge 30 to form a fully-enclosed container or vessel. Bags such as the flexible storage bag 10 of Figure 1 can be also constructed from a continuous tube of sheet material, thereby eliminating side seams 24 and 26 and substituting a bottom seam for fold line 22. The mechanical closure system 40 includes an interlocking mechanical seal of any suitable conventional design.

In accordance with the present invention the closure system 40 provides a high contrast color indication when complete closure of the closure system has been achieved. As utilized herein, the term"high contrast color indication"is used to refer to refer to a change in visual appearance that is categorical rather than a matter of degree. For example, the high contrast color indication may be a change from colorless to colored, from white to black, and/or from translucent to opaque, rather than a change from one color to another of the same degree. The high contrast color indication may be visible from one or both sides of the bag.

With continued reference to Figure 1, the closure system 40 provides a high contrast color indication in the form of a change from the initial clear/transparent/colorless appearance indicated by the numeral 60 to the purple color appearance indicated by the numeral 50 when the hand 70 of the consumer is translated along the closure system 40 to interlock the opposing elements of the mechanical interlocking seal.

Figure 2 illustrates a similar flexible storage bag 10 wherein the high contrast color indication is in the form of a change from the initial white appearance indicated by the numeral 60 to the black color appearance indicated by the numeral 50.

Figure 3 illustrates a flexible storage bag 10 which utilizes a pressure-activated adhesive- based closure system 45 which provides a high contrast color indication in the form of a change from the initial clear/transparent/colorless appearance indicated by the numeral 60 to the green color appearance indicated by the numeral 50. A suitable adhesive-based closure system comprises a selectively activatible adhesive-bearing structure protected from inadvertent contact by a plurality of compressible, collapsible protrusions surrounded by adhesive which provides a secure closure seal upon activation. Suitable representative three-dimensional materials of this variety which include a thin layer of pressure-sensitive adhesive protected from inadvertent contact, as well as methods and apparatus for manufacturing them, have been developed and are

described in detail in commonly-assigned U. S. Patent Nos. 5,662,758, issued September 2,1997 to Hamilton and McGuire, entitled"Composite Material Releasably Sealable to a Target Surface When Pressed Thereagainst and Method of Making", and 5,871,607, issued February 16,1999 to Hamilton and McGuire, entitled"Material Having A Substance Protected by Deformable Standoffs and Method of Making", and commonly-assigned, co-pending U. S. Patent Application Nos. 08/745,339 (allowed), filed November 8,1996 in the names of McGuire, Tweddell, and Hamilton, entitled"Three-Dimensional, Nesting-Resistant Sheet Materials and Method and Apparatus for Making Same", 08/745,340, filed November 8,1996 in the names of Hamilton and McGuire, entitled"Improved Storage Wrap Materials", all of which are hereby incorporated herein by reference.

Figure 4 is a flexible storage bag 10 similar to that of Figure 1, but employing a sliding mechanical closure (not numbered) as a mechanism for closing the interlocking mechanical closure 40. The sliding mechanical closure may be of suitable conventional design for the type of interlocking mechanical seal employed.

Any suitable means for generating the high contrast color indication consistent with the materials utilized for bag and closure system construction, the intended contents of the bag (i. e., food grade, sterile, etc.), and the environmental conditions foreseen may be utilized. Colors and indications can be selected depending upon the color of the bag components, bag contents, and chemical/structural approaches utilized.

For example, the high contrast color indication from translucent to opaque or black can be accomplished through opposing surfaces having coatings that when pressed together blocked enough light to appear much darker when together. Another more exotic approach would be to use coatings that polarized light so that when they were separate they appeared completely clear but when together would block sufficient light transmission to make them appear opaque.

Another suitable approach to generating a high contrast color indication would be to use a system of chemicals that when contacted created a color via chemical reaction. One such system would include a microencapsulated phenolthalene solution sprayed on one side of a seal and a microencapsulated basic solution sprayed on the other. When the two sides were pressed together under sufficient pressure to make a seal the capsules would break, the indicators would react, and a pink color would be apparent. Potentially this could be done without the microcapsules if adequate water could be entrained in an adhesive.

Another approach would be to use encapsulated ink similar to that utilized for carbonless forms. These could be printed within the texture of the adhesive closure sytem opposite the adhesive and covered with a varnish or other impervious coating, or potentially between the adhesive and the bag material. For mechanical closure systems, the encapsulated ink could be located within the mechanical interlocking seal.

Various compositions suitable for constructing the flexible storage bags of the present invention include substantially impermeable materials such as polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyethylene (PE), polypropylene (PP), aluminum foil, coated (waxed, etc.) and uncoated paper, coated nonwovens etc., and substantially permeable materials such as scrims, meshes, wovens, nonwovens, or perforated or porous films, whether predominantly two-dimensional in nature or formed into three-dimensional structures. Such materials may comprise a single composition or layer or may be a composite structure of multiple materials, including a substrate material utilized as a carrier for a substance.

Once the desired sheet materials are manufactured in any desirable and suitable manner, comprising all or part of the materials to be utilized for the bag body, the bag may be constructed in any known and suitable fashion such as those known in the art for making such bags in commercially available form. Heat or adhesive sealing technologies may be utilized to join various components or elements of the bag to themselves or to each other. In addition, the bag bodies may be thermoformed, blown, or otherwise molded rather than reliance upon folding and bonding techniques to construct the bag bodies from a web or sheet of material. Two recent U. S.

Patents which are illustrative of the state of the art with regard to flexible storage bags similar in overall structure to those depicted in Figures 1 and 2 but of the types currently available are Nos.

5,554,093, issued September 10,1996 to Porchia et al., and 5,575,747, issued November 19,1996 to Dais et al.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.