US 3307773 A
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MAE-Mb 3957 J. c. KRATZER ETAL 3,30%??3 READILY CLOSABLE AND REOPENABLE PLASTIC BAG Filed March 26, 1963 INVENTORS JAMES C. KRATZER PETER WILTON 3 Specific gravityabout 0.96 at 25 C. Moisture contentnot more than 0.5% by weight Total monoglycerides (a and [3 forms) about 54 to about 59% by weight Free fatty acid (as oleic)-not more than 0.5% Remainder-principal1y, diglycerides and propylene glycol with less than 1 percent by weight preservatives The liquid 16 may be coated on the bag in an undiluted form, or may be first diluted in a volatile solvent, such as ethanol, methanol, water, and the like, and then coated on the bag. Preferred coating methods include spraying, roller or brush coating, and doctor blading, but any suitable technique, such as compounding the liquid 16 with the plastic material before making the plastic film or bag, may be employed. If the liquid 16 is compounded with the plastic material, it will migrate to the surface of the plastic to form a liquid film thereon. Undiluted liquid has been successfully used in the coating methods as well as 2, 2.5, 4, 5, l0, and 20 percent concentrations by volume in ethanol. In any event, a thin film of the liquid 16 must be present on the bag at the appropriate places. The thin film must be thick enough to achieve sufiicient cling but preferably not so thick as to appear unsightly or to feel undesirably sticky to one who handles the bag. Between about 50 and about 800 milligrams of the liquid 16 per square meter of plastic material has been found to be satisfactory.
Several bags made in accordance with the invention have been tested, with glycerol monooleate as the liquid cling agent in most cases. The bags were of a size suitable for sandwiches, and when the flap was folded over to close the bag, the closure was sufficiently positive and strong to permit liberal handling without causing the bag to open. In fact, the bag with its contents was vigorously shaken without a loosening of the flap from the bag wall. The bag can be opened, however, merely by pulling up a corner of the flap and continuing the action until the flap is loose. In addition, the bag may be closed and opened a number of times without harming the bag or the cling agent. Thus, the invention provides a readily closable and reopenable bag, and eliminates the need for separate closure means for plastic bags or inconvenient adhesives which permanently bond one material to another.
The term liquid as used herein means a material or mixture of materials which will by its inherent nature without the aid of solvents flow at 25 C. but which does not diffuse and fill any container virtually uniformly in which it is put, as a gas will do. The term substantially nonvolatile, high viscosity liquid as used herein means a liquid which evaporates very slowly at room temperatures and pressures, thus being relatively permanent when exposed under ordinary conditions, and which resists flow to a greater extent than materials such as water, ethylene glycol, and 98 percent sulfuric acid, which have viscosities less than about 25 centipoises at 25 C. In general, this term means a liquid having a vapor pressure at 25 C. below about 20 millimeters of mercury and 'a viscosity at 25 C. above about 25 centipoises.
The liquid cling agent in accordance with the invention is to be contrasted with adhesive materials which must be wet with water or other solvents before they can be used as 'an adhesive and which almost always produce a permanent bond after drying again, i.e., a bond which can be broken only with great difficulty and usually by harming the bonded materials or the adhesive.
What is claimed is:
1. A readily closable and reopenable bag made of a flexible plastic material; said bag having a first wall and opposite said first wall a second wall, an open end between said first and second walls, and a flap extending from said first wall for folding over said open end and against said second wall, thereby closing said open end; and said bag having a thin film thereon, on at least one surface which exists between said flap and said second wall when said flap is folded over, consisting essentially of from 54 to about 59% by weight of a monoglyceride selected from the group consisting of glycerol monostearate and glycerol monooleate, not more than 0.5% by weight oleic acid, and the remainder diglycerides and propylene glycol; said film causing said flap to cling to said second wall when said flap is folded over.
2. The bag as defined in claim 1 wherein said liquid has a vapor pressure at 25 C. between about 0.01 and about 10 millimeters of mercury and a viscosity at 25 C. between about and about 250 centipoises.
3. The bag as defined in claim 1 wherein the monoglyceride is glycerol monooleate.
References Cited by the Examiner UNITED STATES PATENTS 1,800,143 4/1931 Hughes 229-48 2,496,934 2/1950 Carson 117-122 XR 2,790,732 4/1957 McGarry et a1. 117-122 2,949,370 8/1960 Hughes 99173 2,970,920 2/1961 Forkner 99-172 XR 3,052,566 9/1962 Smith 117-122 XR 3,070,280 12/1962 Richmond 22962 ALEXANDER H. BRODMERKEL, Primary Examiner. S. H. BLECH, F. T. GARRETT, Examiners. D. M. BOCKENEK, J. EVANS, Assistant Examiners.