Free edge-sealed film articles

United States Patent [19]

Miller et al.

[54] FREE EDGE-SEALED FILM ARTICLES

[75] Inventors: Burdette W. Miller, Freeland; John O. McCree, Bay City; William D. Price, Midland, all of Mich.

[73] Assignee: Dowbrands, Indianapolis, Ind.

[21] Appl. No.: 173,281

[22] Filed: Dec. 27, 1993

Related U.S. Application Data

[60] Division of Ser. No. 994,605, Dec. 21, 1992, Pat. No. 5,292,392, which is a continuation of Ser. No. 513,537, Apr. 23, 1990, abandoned.

[51] Int. CI.6 B32B 3/02; B32B 27/08;

B32B 27/32; B65D 30/08

[52] U.S. CI 428/192; 428/35.2;

428/35.7; 428/516; 383/107

[58] Field of Search 428/34.9, 35.2, 34.8,

428/515, 516, 192, 126, 35.7; 264/230, 171;

383/63, 107, 108

[56] References Cited

U.S. PATENT DOCUMENTS

2,979,113 4/1961 Stageberg 156/500 X

FREE EDGE-SEALED FILM ARTICLES

CROSS REFERENCE TO RELATED

APPLICATION 5

This is a divisional application of allowed application Ser. No. 07/994,605, filed Dec. 21, 1992 now U.S. Pat. No. 5,292,392. Application Ser. No. 07/994,605 is a continuation of abandoned application Ser. No. 07/513,537, filed Apr. 23, 1990. 10

FIELD OF THE INVENTION

The present invention relates to that class of film articles which will for present purposes be termed the "free edge-sealed" film articles and to methods for mak- 15 ing such articles, and more particularly, to such articles comprising film portions which consist essentially of a plurality of layers of diverse thermoplastic materials.

Many film articles are currently made by processes involving the application of heat, solvents or the like to 20 adjacent film portions to effect a seal therebetween, wherein at the point of application or at the location where a seal is effected, the adjacent film portions are fundamentally unsupported and thus possess some freedom of movement to respond to the application of such 25 heat. Manufacturing processes which can be characterized in this fashion are described, for example, in U.S. Pat. Nos. 3,508,378 to Fehr et al., 3,736,219 to McTaggart, 3,947,198 to Hutt, 4,055,452 to Carlisle, and 4,502,906 to Young et al. Each of these processes in- 30 volve the application of some film-sealing medium or means across a gap between two film plies, wherein the film plies are not pinched or pressed between a pair of heated surfaces in sealing the plies together but in a sense are sealed between two "free" edges or portions 35 of the plies.

The "free edge-sealed" articles to which the present invention relates will, then, be understood to encompass the broad spectrum of film articles made by the processes characterized according to the preceding para- 40 graph.

Among the many film articles which may be described as "free edge-sealed" are the majority of recusable plastic storage bags. In the context of such reclosable plastic storage bags, it has been appreciated that 45 bags having sides, bottoms and constituent film portions generally which consist essentially of a plurality of layers of diverse thermoplastic materials can have better structural and/or barrier properties than bags made from a blend of such materials or from a single material 50 only. These improved properties, for example, improved puncture and/or barrier resistance, are highly desirable in the consumer's eyes.

In previous constructions of free edge-sealed film articles such as these reclosable plastic bags wherein 55 diverse thermoplastic materials have been used, the materials have been used in a single blend layer or in a layer structure within a layered film portion which is balanced in terms of the moduli of the layers in the structure. These articles have been constructed in the 60 manner indicated at least in part because of concerns over the curling at room temperature of plural layer films of the various diverse materials.

Each of the film portions in the single blend layer and balanced layer constructions handles and seals essen- 65 tially in the fashion of a layer of a single material, with the seal strength of a seal between adjacent film portions being dependent generally on the same factors

2

known to be implicated in determining the seal strength of free edge-sealed film portions comprised of a single material. These factors include whether the film portions to be joined are properly clamped, the gauge of the film portions to be joined, and the tension placed on the film portions.

Manufacturers of free edge-sealed film articles have because of these factors experienced significant difficulties in the past in achieving consistent seals, and these poor or inconsistent seals can limit the improvement in barrier or structural properties which can be achieved by the use of diverse and perhaps more costly materials, in addition to reducing the appeal of the articles to consumers.

It would be desirable, then, if free edge-sealed articles could be made wherein an improvement in properties realized by a combination of diverse materials in the articles and the consumer appeal of such a combination were not limited or even overcome by the formation of weak or incomplete seals between film portions in a significant number of the articles.

SUMMARY OF THE INVENTION

The present invention fulfills this desire by providing a free edge-sealed film article which is comprised in general terms of a plurality of film portions and which contains a free edge-seal between two of the plurality of film portions. At least one of the two free edge-sealed film portions consists essentially of a plurality of layers of diverse thermoplastic materials and is curled toward the other of the two film portions along at least a portion of the free-edge seal in free-edge sealing the film portions together.

Thus, it may be that only one of a respective pair of free edge-sealed film portions is layered, with the other film portion being comprised of a single layer only and only the one layered film portion curling toward the single layer portion on sealing the two portions together. Or, both of the two free edge-sealed film portions may be layered, but with one of the two film portions having a balanced structure such that again only one of the two layered film portions is curled toward the other. Or, both of the two film portions may be layered, and the layers within each ordered so that on sealing the two film portions together both film portions are curled toward the other.

The curling of a given film portion toward a second film portion during the free edge-sealing of such film portions enables the formation of a superior seal between the two film portions on a more consistent basis, as particularly evidenced by a lesser likelihood of leaks in certain reclosable plastic containers constructed in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of apparatus for free edge-sealing two layered film portions together.

FIG. 2, taken along line 2—2 of FIG. 1, is an enlarged fragmentary cross-sectional view of the two layered film portions to be free edge-sealed together.

FIG. 3 is an enlarged fragmentary cross-sectional view of a typical bead formed by a single layer film portion of substantially uniform composition on contact with a hot sealing wire in one free edge sealing method.